CA1073463A - Process for the production of 2-aryl-2h-benzotriazoles - Google Patents
Process for the production of 2-aryl-2h-benzotriazolesInfo
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- CA1073463A CA1073463A CA251,140A CA251140A CA1073463A CA 1073463 A CA1073463 A CA 1073463A CA 251140 A CA251140 A CA 251140A CA 1073463 A CA1073463 A CA 1073463A
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Abstract
Abstract of the Disclosure A process for the production of 2-aryl-2H-benzotriazoles (I) comprising reducing and cyclizing the corresponding o-nitrozaobenzenes (II) with hydrogen at a temperature in the range of about 20°C to about 100°C
and at a pressure in the range of about 1 atomosphere to about 66 atmospheres in an organic solvent mixture containing an organic amine at a pH over 10 in the presence of noble metal hydrogenation catalyst, preferably palladium.
High yields of pure product are obtained with a concomitant reduction of undesired by-products and a reduction in effluent polution problems.
and at a pressure in the range of about 1 atomosphere to about 66 atmospheres in an organic solvent mixture containing an organic amine at a pH over 10 in the presence of noble metal hydrogenation catalyst, preferably palladium.
High yields of pure product are obtained with a concomitant reduction of undesired by-products and a reduction in effluent polution problems.
Description
10~4~3 This inven~ion pertains to a process for the preparation of 2-aryl-2H-benzotria~oles and derivatives thereof. More particularly, the invention rel~tes to a novel process for preparing 2-aryl-2H-benzotriazoles where-by high yields of the desired products are obtained and ef-fluent pollution problems occurring with present processes for making such products are essentially eliminated.
Heretofore, the conversion of an ortho-nitroazo-benzene to the corresponding 2-aryl-2H-benzotriazole has been accomplished by chemical and electrolytic reduction processes. For example, as seen in U.S. Patents 3,072,585 ~; and 3,230,194, o-nitroazobenzene derivatives have been chemically reduced utilizing zinc in alcoholic sodium hy-droxide 301utions to give good yields of the corresponding
Heretofore, the conversion of an ortho-nitroazo-benzene to the corresponding 2-aryl-2H-benzotriazole has been accomplished by chemical and electrolytic reduction processes. For example, as seen in U.S. Patents 3,072,585 ~; and 3,230,194, o-nitroazobenzene derivatives have been chemically reduced utilizing zinc in alcoholic sodium hy-droxide 301utions to give good yields of the corresponding
2-aryl-2H-benzotriazoles~ Ammonium sulfide, alkali sulfides, zinc with ammonia at 80-100C, sodium hydrosulfide and zinc with hydrochloric acid have also been used as the chemical reducing agents for this transformation as disclosed in U.S. Patent 2,362,988. The use of ammonium sulfide was also reported by S. N. Chakrabarty et al, J. Indian Chem. Soc., 5, 555 (1928); Chem. Abst., 23, ~36, (1929) with mixed results depending on the presence or absence of substituent groups on the 2-ar~l group. In some cases the desired 2-aryl-2H-.
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, ...... , . , . ,, . , . , .. , . . . ... , , .. ... , . .... . . ~ ...... ... . ... . .. .... .. ... . . . . .
. .
.. ; .: - .
, .. . , .. ... . ~ .
1073~63 benzotriazoles were not formed at all with the products of redllction being only the corresponding o-aminoazobenzenes.
Electrolytic reduction of o-nitroazobenzenes was reported by H. Itomi, Mem. Coll. Sci. Kyoto Imp. Univ., 12A, No. 6, 343 (1929); Chem. Abst., 24, 2060 (1930) with the use of a copper cathode in dilute sodium hydroxide solution.
Yields varied from 25 to 60% depending on specific embodi-ments and conditions with a major impurity being formed, namely the corresponding o-aminoazobenzene.
~he widely used zinc dust and soaium hydroxide chemical reducing system for transforming o-nitroazobenzenes into the corresponding 2-aryl-2H-benzotriazoles was reported by ~. Elbs, et al, J. Prakt. Chem., 108, 204 (1924); Chem.
Abst., 19, 514 (1925). The yields of the desired 2-aryl-2H-benzotriazoles varied from 30 to 85% depending on the spe-cific o-nitroazobenzene intermediate reduced.
~ The known chemical and electrolytic reduction processes for preparing 2-aryl-2H-~enzotriazoles are not practical or economically attractive in many cases. The widely used zinc dust and~sodium hydroxide system produces effluent pollution problems in respect to waste disposal of ~inc sludge which is of increasing environ~ental con-cern.
- . . . .
~ 07 ~ Ç~3 The preparation in good yield of the isomeric but chemically distinct lH-benzotriazoles by the catalytic reduction in alkaline medium of o-nitrophenylhydrazine and selected phenyl ring substituted alkyl and perfluoroalkyl derivatives thereof was reported in Japanese patent publication, Sho 48-26012, August 3, 1973. The isomeric 2H-benzotriazoles of this invention cannot be prepared from phenylhydrazines.
The present invention is therefore directed at providing a novel process for the preparation of 2-aryl-2H-benzotriazoles avoiding severe pollution and environmental problems.
By the present invention 2-aryl-2H-benzotriazoles are prepared by reducing and cyclizing the corresponding o-nitroazobenzene under certain conditions hereinafter set forth in greater detail whereby high yields of the ~oducts can be obtained in good purity.
According to the present invention, there is provided a process for the production of 2-aryl-2H-benzotriazoles of the formula I
~ N \ ~ tl) wheTein Rl is hydrogen or chlorine, R2 is hydrogen, chlorine, lower alkyl of 1 to 4 carbon atoms, lower alkoxy of 1 to 4 carbon atoms, carboalkoxy of 2 to 9 carbon atoms, carboxy or -S03H, R3 is alkyl of 1 to 12 carbon atoms, alkoxy of 1 to 4 carbon atoms, phenyl, phenyl substituted with alkyl groups, said alkyl groups having 1 to 8 carbon atoms, cycloalkyl of 5 to 6 carbon atoms, carboalkoxy of 2 to 9 carbon .. . .
.
atoms chlorine, carboxyethyl or arylalkyl of 7 to 9 carbon atoms, R4 is hydrogen, lower alkyl of 1 to 4 carbon atoms, lower alkoxy of 1 to 4 carbon atoms, chlorine or hydroxyl, and R5 is hydrogen, alkyl of 1 to 12 carbon atoms, chlorine, cycloalkyl of 5 to 6 carbon atoms or arylalkyl of 7 to 9 carbon atoms, which comprises reducing and cyclizing the corresponding o-nitroazo-benzene with hydrogen at a temperature in the range of from about 20C to about 100C and at a pressure in the range of from about 15 psig ~1.05 kg/cm2, 1 atmosphere) to about 1000 psig ~70 kg/cm2, 66 atmospheres) while mixed in an organic solvent mixture including an organic amine in a concentration of at least 0.1 mole of amine per mole of o-nitroazobenzene in the presence of hydrogenation catalyst selected from the group consisting of the noble metals of Group VIII of the Periodic Table, with the proviso that, when Rl, R2, R3, R4 or R5 is chlorine, the hydrogenation catalyst cannot be palladium, and recovering the desired 2-aryl-2H-benzotriazole.
A further embodiment of this invention is found in a process for the production of 2-~2-hydroxy-5-methyl-phenyl)-2H-benzotriazole which com-prises treating 2-nitro-2'-hydroxy-5'-methylazobenzene with hydrogen at a ~-temperature in the range of from about 20C to about 100 C and at a pressure in the range of about 1 atmosphere to about 66 atmospheres in an organic solvent mixture comprising toluene and methanol and including a water-soluble amine, such as diethylamine, in the presence of a hydrogenation catalyst comprising a noble metal of Group VIII of the Periodic Table, removing the noble metal catalyst by filtration, isolating a crude product by distillation, purifying the crude product by removing amine impurities by acid extraction, and recovering the desired 2-~2-hydroxy-5-methylphenyl)-2H-benzotriazole by conventional procedures.
The process of this invention is preferably carried out at a temperature in the range of from about 30C to about 80C, and most .....
. ., . - , ; -- ~ :
- . ...
iO~3463 pre~erably from about 40C to abou~ 70C.
A specific embodiment of the invention is exempli-fied in a process for the production of 2-(2-hydroxy-5-methylphenyl)-2H-benzotriazole, which comprises treating 2-nitro-2'-hydroxy-5'-methylazobenzene with hydrogen at a temperature in the range of from about 20C to about 100C
and at a pressure in the range of from about 1 to about 66 atmospheres in an organic solvent mixture comprising tolu-ene, methanol and diethylamine in the presence of hydrogen-ation catalyst comprising palladium composited on charcoal, .and recovering the desired 2-(2-hydroxy-5-methylphenyl)-2H-benzotriazvle.
- A preferred specific embodiment of this invention comprises the reductive cyclization of 2-nitro-2'-hydroxy-5'-methylazobenzene dissolved in a toluene/methanol solution .
and containing 0.925 equivalents of the water-miscible amine, diethylamine, per mole of the o-nitroazobenzene compound.
With the- more difficulty soluble and more hydro-carbon-like members of the 2-àryl-2H-benzotriazoles and the corresponding o-nitroazobenzene starting materials, it is beneficial to employ other organic solvents which can en-hance the solubility of said compcunds in the reaction mix-~- ~
. ~ , . , -lOq3463 ture. The use of other organic solvents such as isopropanol and additional amounts of organic amines is especially use~
ful with such compounds.
A further preferred specific embodiment of this invention is found in the production of 2-12-hydroxy-3,5-di-tert-amylphenyl)-2H-benzotriazole by the reductive cyclization of 2-nitro-2'-hydroxy-3',5'-di-tert-amylazo-benzene dissolved in isopropanol with 1.1 moles OI diethyl-amine or other organic amine per mole of o-nitroazobenzene starting material.
~ ith these more hydrocarbcn-like compounds, the absorption of hydrogen is often considerably above theory indicating that some further reduction of desired product may have occurred.
Other objects and embodiments will be found in the following, further detailed description of this invention.
The reduction of 2-nitro-2'-hydroxy-5'-methylazoben-zene was carried out in a mixture of toluene, methanol and diethylamine emplcying sufficient methanol to assure one liquid phase in the system as two moles of water/mol azoben-zene were generated in the system during reduction, and suffi-cient (about 0.9 moles per mole of azobenzene) diethylamine "
.. ~ .
. : , . :.............................. . . :
~ ' ' ' ' . -, ' ." ' , 10734~3 to provide a strongly alkaline milieu. A hydrogenation catalyst comprising palladium composited on ~arbon was used and the reduction and cyclization effected at a hydro-gen pressure of from about 1 to about 5.7 atmospheres at temperatures from about 20C to about 100C, with a recovery of pure product in yields in the order or up to 75%. How-ever, higher pressures up to about 66 atmospheres may also be used with equivalent results.
- In like manner, the reduction of 2-nitro-2'-hydroxy-3',5'-di-tert-amylazobenzene was effected in a solution in isopropanol containing at least 1.1 moles of diethylamine per mole of azobenzene to provide the strongly alkaline milieu. A preferred hydrogenation catalyst was palladium composited on alumina.
The catalysts which are employed in the process of this invention for effecting the reduction af o-nitroazo-benzenes to form 2-aryl-2H-benzotriazoles comprise metals selected from the noble metals of Group VIII of the Periodic Table, the preferred metal comprising palladium although it is contemplated within the scope of this invention that the other noble metals such às platinum, rhodium, ruthenium, osmium and iridium can also be used, although not necessarily with equivalent results. The metals may be used per se, as . - 8 -., , ~ . . . ... , : . .. . , . . . . ~ ~ .:: - :. - -: , . : : , . ..
. . - .. - : .
. .. .. . . . . . . .. ..
:: : . ................. : ~ .. . .. ..
1073~63 their oxides, or in a preferred embodiment of the invention, composited on a solid support such as carbon, silica or alumina. A particularly effective support comprises char-coal or alumina. Very small quantities of catalyst are re-quired to effect the reductive cyclization of this invention.
Amounts of noble ~.etal catalyst as low as about 0.001 to 0.005 mol/mol of o-nitroazobenzene to be reduced are effective.
More catalyst can be used, but using amounts over 0.01 mol/mol of the o-nitroazobenzene is generally neither needed nor economically attractive.
The noble metal catalysts of this invention can be generally used interchangeably with one another in the instant process. However, as intimated above there are some differences between the individual metals. If the o-nitro-azobenzene starting material is substituted with a chlorine atom, the use of palladium catalysts results in the reductive cyclization to the 2-aryl-2H-benzotriazole, but the chlorine atom is also concomitantly cleaved o~f. However, substitu-tion of palladium by rhodium the latter which appears to be a milder, more selective catalyst results in the pre-paration of the 2-aryl-2H-benzotriazole still containing the chlorine atom Accordingly, when the preparation of a 2-aryl-2H-benzotriazole containing cnlorine or either or _ g _ - ~.~ . . - --:, .
- ,: . - . - -. . . . . . ,. .. , - :
107~63 both aromatic rings is involved, a rhodium catalyst should be used and the use o palladium catalysts should be avoided. A preferred catalyst for the reductive cyclization of a 2-nitroazobenzene intermediate substituted with chlorine S to the corresponding chlorine substituted 2-aryl-2H-benzo-triazole is rhodium composited on charcoal.
A particularly important feature of this inven- -tion is the ability of the noble metal catalyst to be used repeatedly to effect the reductive cycliza~ion without ap-preciable loss in reactivity. As many as 10 batches have been run consecutively with excellent results.
As hereinbefore stated, the reduction is effected at reducing conditions including a temperature within the range of from about 20C to about 100C, a pressure ranging from about 1 to about 66 atmospheres and with sufficient organic solvent, such as toluene, to keep the starting materiaL and product in solution, water-miscible orgsnic medium, such as methanol, to assure that the water liberated during the reduction is kept in one liquid phase in the system and organic amine, such as diethylamine, to provide a strongly alkaline milieu to permit the desired reaction to occur with minimum of by-product impurities. In the absence of the amine, the desired reaction does not occur.
, -- 10 --. .
10~3~63 The organic solvents which may be used in this process to dissolve the o-nitroazobenzene intermediates and corresponding 2-aryl-2H-benzotriazoles can be non-polar hydrocarbon solvents such as benzene, toluene, xylene, cyclohexane, aliphatic hydrocarbons, such as hexane, heptane, pet-.oleum mineral spirits, and other hydrocarbon materials and mixtures thereof. For reasons of economy, ease of operation and availability, toluene is particularly useful in the process o~ this invention.
Since water is liberated during the reductive cyclization reaction, it is necessary that a water-miscible solvent or cosolvent be used in the process of this inven-tion in order to keep everything except the dispersed cata-lyst in one liquid phase. This is particularly needed when the non-polar solvents described above are employed. Water-miscible solvents or cosolvents useful in this invention include the water-miscible alcohols such as methanol, ethanol, isopropanol, n-propanol, n-butanol and methyl cellosolve (2-methoxye han~ articularly useful are me'hanol when used with non-polar cosolvents or isopropanol when used alone. - -Other water-miscible solvents or cosolvents use-ful in this process include ethers such as tetrahydrofuran, ., _ 11 --.. . : - -: .. ~ : -.
. . .
, . . - . . ,,, , , . , ~ .
: ~ , ' , - , ~ , :
:. : . : . , . -l~q3~163 1,4-dioxane, 1,2-dimethoxyethsne, 1,2-diethoxyethane and the like.
Other solvents found useful in this process include the trialkyl phosphates such as triethyl phos-phate, tributyl phosphate, trioctyl phosphate and the like.
The reductive cyclization of o-nitroazobenzenes to the corresponding 2-aryl-2H-benzotriazoles in the~ process of this inven~ion requires the presence of a strongly alka~
line milieu. In the absence of an organic amine or ~mnonia, - the desired reaction does not take place. Organic amines ~seful in the process of this invention are preferably water-miscible for the reasons given above although other amines may also be used provided sufficient water-miscible sol-vent ox cosolvent is present. Organic amines useful in this process include the primary, secondary or tertiary aliphatic amines with alkyl groups of preferably 1 to 4 car bon atoms, e.g. ammonia, methylamine, dimethylamine, tri-methylamine, athylamine, propylamine, i-propylamine, di-i-propylamine, butylamine, octylamine, cyclohexylamine, ethanolamine, diethanolamine, triethynolamine and further piperidine, hydroxypiperidine, piperazine, morpholine, pyrrolidine, guanidine and the like. For reasons of economy, :
- : : ~ : . ::: . -- . . :. ,,:: -10~3463 ease of operation and availability, morpholine, piperidine, and the lower dialkylamines such as diethylamine, dimethyl-amine, di-n-propylamine and the like are preferred. Parti-cularly preferred is diethylamine.
The reductive cyclization reaction may be carried out under a variety of concentrations of solvents, cosolvents and organic amines.
While the reductive cyclization reaction does not occur in the absence of a strong alkaline milieu such as is provided by one or more of the organic amines described above, it is often expedient to run the instant process where the organic solvent consists essentially entirely of one of the organic amines alone. In such a case, an excess molar quantity of amine relevant to the o-nitroazobenzene is always present. This solvent system has the advantage of simplified solvent recovery at the end of the reaction since mixtures of solvents are not involved. Amines providin~
a particularly goo~ balance of base strength, solvent character, physical properties, ease of handling, avail-ability and operability in the instant process include n-propylamine, diethylamine, triethylamine, isopropylamine, n-butylamine, dibutylamine, tert-butylamine, amylamine, morpholine and the like.
.. : . : . : : .
The amount of organic amine which must be used in the process of this invention is at least 0.1 moles of amine per mole of o-nitroazobenzene intermediate and preferably at least 0.9 moles per mole of o-nitroazobenzene inter-mediate. Additional quantities o~ organic amine may be used, but employing amounts over l.S moles/mole of o-nitroa-zobenzene is neither necessary nor economically attractive.
The concentrations by weight of o-nitroazobenzene intermediate in the organic solvent system can range from dilute solutions in the range of S-10% to concentrated solutions in the range of 20-30%. For reasons of economy, ~he more concentrated solutions are preferred.
The organic solvent system useful in this process can comprise 100% of a water-miscible organic alcohol or ether without the presence of any non-polar cosolvent.
These systems can also comprise a mixture of a non-polar organic solvent with a water-miscible organic cosolvent, especially trialkyl phosphates where the maximum amount of non-polar solvent by weight in the total solvent system is in the range of 65 to 75%. Examples of non-polar solvents are hydrocarbons as benzene7 toluene, xylene, mesitylene.
~ ` , - ': : ~" -: ` ` :
With many of the 2-aryl-2H-benzotriazoles of this invention, a tolu~ne/methanol/diethylamine mixture is preferred partially because of fortuitous combination of boiling points allow their convenient recovery by distillation for recycling after removing of the reaction water in the subsequent reaction runs. When using this organic solvent mixture, it is possible at the end of the reduction and cyclization reaction to remove the catalyst by filtrati~n for further recycling which is a special fea-ture of this process while leaving the desired 2-aryl-2H-benzotriazole product in organic solution.
Isolation of a product in good yield and acceptable purity is another feature of this invention. The organic so-lution of the desired 2-aryl-2H-benzotriazole after removal of the noble metal catalyst by filtration is subjected to distillation to remove the organic solvents and small amount of water formed during the reduction to give a crude product in the range of 75 to 85~ yield, but which contains some amine by-product impurities. The crude product may conven-iently be purified by redissolving in toluene, extracting the amine impurities by aqueous mineral acid, preferably 70 sulfuric acid, and isolating by conventional procedures to give purified products o high purity in yields in the range .
~, . ,,; , . . :.- - . :
. , ,. . -. -. , .: . .: : , . .
o$ 70 to 8~. A variety of trace ~y-products are formed during the reduction of o-nitroazobenzenes. These include the corresponding o-aminoazobenzenes, o-aminohydrazobenzenes, o-phenylenediamine, anilines, aminophenols and 1,2,3-benzo-triazoles. Most of these by-product impurities are removed by the acid, preferably sulfuric acid, wash.
With 2-aryl-2H-benzotriazoles such as 2-(2-hydroxy-
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. .
.. ; .: - .
, .. . , .. ... . ~ .
1073~63 benzotriazoles were not formed at all with the products of redllction being only the corresponding o-aminoazobenzenes.
Electrolytic reduction of o-nitroazobenzenes was reported by H. Itomi, Mem. Coll. Sci. Kyoto Imp. Univ., 12A, No. 6, 343 (1929); Chem. Abst., 24, 2060 (1930) with the use of a copper cathode in dilute sodium hydroxide solution.
Yields varied from 25 to 60% depending on specific embodi-ments and conditions with a major impurity being formed, namely the corresponding o-aminoazobenzene.
~he widely used zinc dust and soaium hydroxide chemical reducing system for transforming o-nitroazobenzenes into the corresponding 2-aryl-2H-benzotriazoles was reported by ~. Elbs, et al, J. Prakt. Chem., 108, 204 (1924); Chem.
Abst., 19, 514 (1925). The yields of the desired 2-aryl-2H-benzotriazoles varied from 30 to 85% depending on the spe-cific o-nitroazobenzene intermediate reduced.
~ The known chemical and electrolytic reduction processes for preparing 2-aryl-2H-~enzotriazoles are not practical or economically attractive in many cases. The widely used zinc dust and~sodium hydroxide system produces effluent pollution problems in respect to waste disposal of ~inc sludge which is of increasing environ~ental con-cern.
- . . . .
~ 07 ~ Ç~3 The preparation in good yield of the isomeric but chemically distinct lH-benzotriazoles by the catalytic reduction in alkaline medium of o-nitrophenylhydrazine and selected phenyl ring substituted alkyl and perfluoroalkyl derivatives thereof was reported in Japanese patent publication, Sho 48-26012, August 3, 1973. The isomeric 2H-benzotriazoles of this invention cannot be prepared from phenylhydrazines.
The present invention is therefore directed at providing a novel process for the preparation of 2-aryl-2H-benzotriazoles avoiding severe pollution and environmental problems.
By the present invention 2-aryl-2H-benzotriazoles are prepared by reducing and cyclizing the corresponding o-nitroazobenzene under certain conditions hereinafter set forth in greater detail whereby high yields of the ~oducts can be obtained in good purity.
According to the present invention, there is provided a process for the production of 2-aryl-2H-benzotriazoles of the formula I
~ N \ ~ tl) wheTein Rl is hydrogen or chlorine, R2 is hydrogen, chlorine, lower alkyl of 1 to 4 carbon atoms, lower alkoxy of 1 to 4 carbon atoms, carboalkoxy of 2 to 9 carbon atoms, carboxy or -S03H, R3 is alkyl of 1 to 12 carbon atoms, alkoxy of 1 to 4 carbon atoms, phenyl, phenyl substituted with alkyl groups, said alkyl groups having 1 to 8 carbon atoms, cycloalkyl of 5 to 6 carbon atoms, carboalkoxy of 2 to 9 carbon .. . .
.
atoms chlorine, carboxyethyl or arylalkyl of 7 to 9 carbon atoms, R4 is hydrogen, lower alkyl of 1 to 4 carbon atoms, lower alkoxy of 1 to 4 carbon atoms, chlorine or hydroxyl, and R5 is hydrogen, alkyl of 1 to 12 carbon atoms, chlorine, cycloalkyl of 5 to 6 carbon atoms or arylalkyl of 7 to 9 carbon atoms, which comprises reducing and cyclizing the corresponding o-nitroazo-benzene with hydrogen at a temperature in the range of from about 20C to about 100C and at a pressure in the range of from about 15 psig ~1.05 kg/cm2, 1 atmosphere) to about 1000 psig ~70 kg/cm2, 66 atmospheres) while mixed in an organic solvent mixture including an organic amine in a concentration of at least 0.1 mole of amine per mole of o-nitroazobenzene in the presence of hydrogenation catalyst selected from the group consisting of the noble metals of Group VIII of the Periodic Table, with the proviso that, when Rl, R2, R3, R4 or R5 is chlorine, the hydrogenation catalyst cannot be palladium, and recovering the desired 2-aryl-2H-benzotriazole.
A further embodiment of this invention is found in a process for the production of 2-~2-hydroxy-5-methyl-phenyl)-2H-benzotriazole which com-prises treating 2-nitro-2'-hydroxy-5'-methylazobenzene with hydrogen at a ~-temperature in the range of from about 20C to about 100 C and at a pressure in the range of about 1 atmosphere to about 66 atmospheres in an organic solvent mixture comprising toluene and methanol and including a water-soluble amine, such as diethylamine, in the presence of a hydrogenation catalyst comprising a noble metal of Group VIII of the Periodic Table, removing the noble metal catalyst by filtration, isolating a crude product by distillation, purifying the crude product by removing amine impurities by acid extraction, and recovering the desired 2-~2-hydroxy-5-methylphenyl)-2H-benzotriazole by conventional procedures.
The process of this invention is preferably carried out at a temperature in the range of from about 30C to about 80C, and most .....
. ., . - , ; -- ~ :
- . ...
iO~3463 pre~erably from about 40C to abou~ 70C.
A specific embodiment of the invention is exempli-fied in a process for the production of 2-(2-hydroxy-5-methylphenyl)-2H-benzotriazole, which comprises treating 2-nitro-2'-hydroxy-5'-methylazobenzene with hydrogen at a temperature in the range of from about 20C to about 100C
and at a pressure in the range of from about 1 to about 66 atmospheres in an organic solvent mixture comprising tolu-ene, methanol and diethylamine in the presence of hydrogen-ation catalyst comprising palladium composited on charcoal, .and recovering the desired 2-(2-hydroxy-5-methylphenyl)-2H-benzotriazvle.
- A preferred specific embodiment of this invention comprises the reductive cyclization of 2-nitro-2'-hydroxy-5'-methylazobenzene dissolved in a toluene/methanol solution .
and containing 0.925 equivalents of the water-miscible amine, diethylamine, per mole of the o-nitroazobenzene compound.
With the- more difficulty soluble and more hydro-carbon-like members of the 2-àryl-2H-benzotriazoles and the corresponding o-nitroazobenzene starting materials, it is beneficial to employ other organic solvents which can en-hance the solubility of said compcunds in the reaction mix-~- ~
. ~ , . , -lOq3463 ture. The use of other organic solvents such as isopropanol and additional amounts of organic amines is especially use~
ful with such compounds.
A further preferred specific embodiment of this invention is found in the production of 2-12-hydroxy-3,5-di-tert-amylphenyl)-2H-benzotriazole by the reductive cyclization of 2-nitro-2'-hydroxy-3',5'-di-tert-amylazo-benzene dissolved in isopropanol with 1.1 moles OI diethyl-amine or other organic amine per mole of o-nitroazobenzene starting material.
~ ith these more hydrocarbcn-like compounds, the absorption of hydrogen is often considerably above theory indicating that some further reduction of desired product may have occurred.
Other objects and embodiments will be found in the following, further detailed description of this invention.
The reduction of 2-nitro-2'-hydroxy-5'-methylazoben-zene was carried out in a mixture of toluene, methanol and diethylamine emplcying sufficient methanol to assure one liquid phase in the system as two moles of water/mol azoben-zene were generated in the system during reduction, and suffi-cient (about 0.9 moles per mole of azobenzene) diethylamine "
.. ~ .
. : , . :.............................. . . :
~ ' ' ' ' . -, ' ." ' , 10734~3 to provide a strongly alkaline milieu. A hydrogenation catalyst comprising palladium composited on ~arbon was used and the reduction and cyclization effected at a hydro-gen pressure of from about 1 to about 5.7 atmospheres at temperatures from about 20C to about 100C, with a recovery of pure product in yields in the order or up to 75%. How-ever, higher pressures up to about 66 atmospheres may also be used with equivalent results.
- In like manner, the reduction of 2-nitro-2'-hydroxy-3',5'-di-tert-amylazobenzene was effected in a solution in isopropanol containing at least 1.1 moles of diethylamine per mole of azobenzene to provide the strongly alkaline milieu. A preferred hydrogenation catalyst was palladium composited on alumina.
The catalysts which are employed in the process of this invention for effecting the reduction af o-nitroazo-benzenes to form 2-aryl-2H-benzotriazoles comprise metals selected from the noble metals of Group VIII of the Periodic Table, the preferred metal comprising palladium although it is contemplated within the scope of this invention that the other noble metals such às platinum, rhodium, ruthenium, osmium and iridium can also be used, although not necessarily with equivalent results. The metals may be used per se, as . - 8 -., , ~ . . . ... , : . .. . , . . . . ~ ~ .:: - :. - -: , . : : , . ..
. . - .. - : .
. .. .. . . . . . . .. ..
:: : . ................. : ~ .. . .. ..
1073~63 their oxides, or in a preferred embodiment of the invention, composited on a solid support such as carbon, silica or alumina. A particularly effective support comprises char-coal or alumina. Very small quantities of catalyst are re-quired to effect the reductive cyclization of this invention.
Amounts of noble ~.etal catalyst as low as about 0.001 to 0.005 mol/mol of o-nitroazobenzene to be reduced are effective.
More catalyst can be used, but using amounts over 0.01 mol/mol of the o-nitroazobenzene is generally neither needed nor economically attractive.
The noble metal catalysts of this invention can be generally used interchangeably with one another in the instant process. However, as intimated above there are some differences between the individual metals. If the o-nitro-azobenzene starting material is substituted with a chlorine atom, the use of palladium catalysts results in the reductive cyclization to the 2-aryl-2H-benzotriazole, but the chlorine atom is also concomitantly cleaved o~f. However, substitu-tion of palladium by rhodium the latter which appears to be a milder, more selective catalyst results in the pre-paration of the 2-aryl-2H-benzotriazole still containing the chlorine atom Accordingly, when the preparation of a 2-aryl-2H-benzotriazole containing cnlorine or either or _ g _ - ~.~ . . - --:, .
- ,: . - . - -. . . . . . ,. .. , - :
107~63 both aromatic rings is involved, a rhodium catalyst should be used and the use o palladium catalysts should be avoided. A preferred catalyst for the reductive cyclization of a 2-nitroazobenzene intermediate substituted with chlorine S to the corresponding chlorine substituted 2-aryl-2H-benzo-triazole is rhodium composited on charcoal.
A particularly important feature of this inven- -tion is the ability of the noble metal catalyst to be used repeatedly to effect the reductive cycliza~ion without ap-preciable loss in reactivity. As many as 10 batches have been run consecutively with excellent results.
As hereinbefore stated, the reduction is effected at reducing conditions including a temperature within the range of from about 20C to about 100C, a pressure ranging from about 1 to about 66 atmospheres and with sufficient organic solvent, such as toluene, to keep the starting materiaL and product in solution, water-miscible orgsnic medium, such as methanol, to assure that the water liberated during the reduction is kept in one liquid phase in the system and organic amine, such as diethylamine, to provide a strongly alkaline milieu to permit the desired reaction to occur with minimum of by-product impurities. In the absence of the amine, the desired reaction does not occur.
, -- 10 --. .
10~3~63 The organic solvents which may be used in this process to dissolve the o-nitroazobenzene intermediates and corresponding 2-aryl-2H-benzotriazoles can be non-polar hydrocarbon solvents such as benzene, toluene, xylene, cyclohexane, aliphatic hydrocarbons, such as hexane, heptane, pet-.oleum mineral spirits, and other hydrocarbon materials and mixtures thereof. For reasons of economy, ease of operation and availability, toluene is particularly useful in the process o~ this invention.
Since water is liberated during the reductive cyclization reaction, it is necessary that a water-miscible solvent or cosolvent be used in the process of this inven-tion in order to keep everything except the dispersed cata-lyst in one liquid phase. This is particularly needed when the non-polar solvents described above are employed. Water-miscible solvents or cosolvents useful in this invention include the water-miscible alcohols such as methanol, ethanol, isopropanol, n-propanol, n-butanol and methyl cellosolve (2-methoxye han~ articularly useful are me'hanol when used with non-polar cosolvents or isopropanol when used alone. - -Other water-miscible solvents or cosolvents use-ful in this process include ethers such as tetrahydrofuran, ., _ 11 --.. . : - -: .. ~ : -.
. . .
, . . - . . ,,, , , . , ~ .
: ~ , ' , - , ~ , :
:. : . : . , . -l~q3~163 1,4-dioxane, 1,2-dimethoxyethsne, 1,2-diethoxyethane and the like.
Other solvents found useful in this process include the trialkyl phosphates such as triethyl phos-phate, tributyl phosphate, trioctyl phosphate and the like.
The reductive cyclization of o-nitroazobenzenes to the corresponding 2-aryl-2H-benzotriazoles in the~ process of this inven~ion requires the presence of a strongly alka~
line milieu. In the absence of an organic amine or ~mnonia, - the desired reaction does not take place. Organic amines ~seful in the process of this invention are preferably water-miscible for the reasons given above although other amines may also be used provided sufficient water-miscible sol-vent ox cosolvent is present. Organic amines useful in this process include the primary, secondary or tertiary aliphatic amines with alkyl groups of preferably 1 to 4 car bon atoms, e.g. ammonia, methylamine, dimethylamine, tri-methylamine, athylamine, propylamine, i-propylamine, di-i-propylamine, butylamine, octylamine, cyclohexylamine, ethanolamine, diethanolamine, triethynolamine and further piperidine, hydroxypiperidine, piperazine, morpholine, pyrrolidine, guanidine and the like. For reasons of economy, :
- : : ~ : . ::: . -- . . :. ,,:: -10~3463 ease of operation and availability, morpholine, piperidine, and the lower dialkylamines such as diethylamine, dimethyl-amine, di-n-propylamine and the like are preferred. Parti-cularly preferred is diethylamine.
The reductive cyclization reaction may be carried out under a variety of concentrations of solvents, cosolvents and organic amines.
While the reductive cyclization reaction does not occur in the absence of a strong alkaline milieu such as is provided by one or more of the organic amines described above, it is often expedient to run the instant process where the organic solvent consists essentially entirely of one of the organic amines alone. In such a case, an excess molar quantity of amine relevant to the o-nitroazobenzene is always present. This solvent system has the advantage of simplified solvent recovery at the end of the reaction since mixtures of solvents are not involved. Amines providin~
a particularly goo~ balance of base strength, solvent character, physical properties, ease of handling, avail-ability and operability in the instant process include n-propylamine, diethylamine, triethylamine, isopropylamine, n-butylamine, dibutylamine, tert-butylamine, amylamine, morpholine and the like.
.. : . : . : : .
The amount of organic amine which must be used in the process of this invention is at least 0.1 moles of amine per mole of o-nitroazobenzene intermediate and preferably at least 0.9 moles per mole of o-nitroazobenzene inter-mediate. Additional quantities o~ organic amine may be used, but employing amounts over l.S moles/mole of o-nitroa-zobenzene is neither necessary nor economically attractive.
The concentrations by weight of o-nitroazobenzene intermediate in the organic solvent system can range from dilute solutions in the range of S-10% to concentrated solutions in the range of 20-30%. For reasons of economy, ~he more concentrated solutions are preferred.
The organic solvent system useful in this process can comprise 100% of a water-miscible organic alcohol or ether without the presence of any non-polar cosolvent.
These systems can also comprise a mixture of a non-polar organic solvent with a water-miscible organic cosolvent, especially trialkyl phosphates where the maximum amount of non-polar solvent by weight in the total solvent system is in the range of 65 to 75%. Examples of non-polar solvents are hydrocarbons as benzene7 toluene, xylene, mesitylene.
~ ` , - ': : ~" -: ` ` :
With many of the 2-aryl-2H-benzotriazoles of this invention, a tolu~ne/methanol/diethylamine mixture is preferred partially because of fortuitous combination of boiling points allow their convenient recovery by distillation for recycling after removing of the reaction water in the subsequent reaction runs. When using this organic solvent mixture, it is possible at the end of the reduction and cyclization reaction to remove the catalyst by filtrati~n for further recycling which is a special fea-ture of this process while leaving the desired 2-aryl-2H-benzotriazole product in organic solution.
Isolation of a product in good yield and acceptable purity is another feature of this invention. The organic so-lution of the desired 2-aryl-2H-benzotriazole after removal of the noble metal catalyst by filtration is subjected to distillation to remove the organic solvents and small amount of water formed during the reduction to give a crude product in the range of 75 to 85~ yield, but which contains some amine by-product impurities. The crude product may conven-iently be purified by redissolving in toluene, extracting the amine impurities by aqueous mineral acid, preferably 70 sulfuric acid, and isolating by conventional procedures to give purified products o high purity in yields in the range .
~, . ,,; , . . :.- - . :
. , ,. . -. -. , .: . .: : , . .
o$ 70 to 8~. A variety of trace ~y-products are formed during the reduction of o-nitroazobenzenes. These include the corresponding o-aminoazobenzenes, o-aminohydrazobenzenes, o-phenylenediamine, anilines, aminophenols and 1,2,3-benzo-triazoles. Most of these by-product impurities are removed by the acid, preferably sulfuric acid, wash.
With 2-aryl-2H-benzotriazoles such as 2-(2-hydroxy-
3,5-di-tert-amlyphenyl)-2H-benzotriazoles, the crude products are obtained in yields in the range of 52-67%, and these materials may contain somewhat larger amounts of amine by-products than those such as 2-(2-hydroxy-5-methylphenyl)-2H-benzotriazole. However, these amine by-products are also removed as hereinbefore stated by dissolving the crude product in an organic solvent such as petroleum mineral spirits, extracting with aqueous mineral acid, and isolating the desired products of high purity by conventional procedures in good yields.
The process of this invention may be effected in any suitable manner and may comprise either a batch or continuous type of operation. For example, when a batch-type operation is used, a quantity of the hydroxy-substi.uted o-nitroazobenzene, toluene, methanol, diethylami~e along with -. .. .. .. :. . - .
~O73A/~63 the catalyst such as palladi~m composited on charcoal, is placed in an appropriate apparatus such as a shaking or stirred autoclave. Hydrogen is pressurized in until the de-sired initial pressure is reached. The autoclave and the contents thereof are then heated, if needed, to the desired reaction temperature and maintained thereat with agitation until the theoretical amount of hydrogen is absorbed wher~-upon no further hydrogen is taken up and the reductio~ re-action is c~mplete. At the end of this time the excess pres-sure is vented, the solution, usually warm, is subjected to -~
filtration, preferably under an inert atomsphere such as nitrogen or argon, to remove the catalyst. The solution is then subjected to distillation to yield the crude product which may be further purified by dissolving in toluene, ex-traction ~ith aqueous acid and recrystallization rom an organic solvent.
It is also contemplated wi.hin the scope of this invention that the preparation of the 2-aryl-2H-benzotriazoles by the reduction and cyclization o~ o-nitroazobenzenes may also be effected in a continuous manner, although not neces-æarily with equivalent results. For example, when a con-tinous type operation is used, the hydroxy-substituted o-nitroazobenzene starting material is premixed with, and ~issolved in an organic solvent mixture containing a water . ~ .- - . . .~ . .............. :. . .
.- -: - . :- . . .
. -,: . -:
- , ~ .
1073 a~;3 ~oluble amine, said mixture fed continuously to a reaction zone which is maintained at the proper operating conditi,ons of temperaiure and pressure and which contains the hydrogena-tion catalyst. Hydrogen is pressurized into the reacticn zone by a separate means. After a desired residence time, the reactor effluent is continuously discharged and the effluent solution is distilled to isol~te the desired product. Due to the nature of the catalyst employed r a particularly effective continuous ~-ype of operation comprises a fixed bed of cata-lyst subjected to either an upward or downward flow of the reaction solution. If it is desirable to carry out the reduction as a two-step process with a different operating temperature for each step, two reaction zones in series each operating at the preferred temperature range for the specific reduction step involved may be used.
The reduction of o-nitroazobenzenes to the cor-responding 2-aryl-2H-benzotria201es is a two-step process as outlined below.
, ~
: ::. . ,, - . : .... :-; ; . ., ,, .. , :
- : , - : : ... :: , :
10~34~3 OH
Rl ~ N=N ~ R5 Step l R2 NO2 ~ ~_ ` ~, -.
. .
OH
~ ~X ~SR4 . Step 2 ,~ ~ ' ,'.
OH
Rl~N\ _~5, Step l - The reduction of the o-nitroazobenzene to the N-oxybenzotriazole derivative proceeds rapidly and exot~er-mically even at low temperature under the process cor.ditions of this invention.
. -- 19 --,-: .. ': , :. ., . , ' ' : , ;: ', `.. `' ~ - : .
~0~3~63 Step 2 - The reduction of the N-o~ybenzotriazole intermediate to the corresponding 2-aryl-2H-benzotriazole product goes more slowly. This reduction can be greatly expedited by adding more catalyst, raising the temperature, increasing the hydrogen pressure or by combination of these factors.
Generally, the reaction ceases when the N-oxy in-termediate is completely reduced to the corresponding 2-aryl-2H-benzotriazole making for facile control of this catalytic hydrogenation process. However, with some highly substituted benzotriazoles, reduction snouid be stopped when the appropri-ate amount of hydrogen has been absorbed and.reacted to prevent further reductive cleavage of the desired 2-aryl-2H-benzotria-zoles prepared.
Specifically, the instant invention provides an improved process for production of compounds having the formula I
~ N ~ R4 .. R3 ,.
~- . . . . .. . . ~, ", ,. , ~ ~ "
I -, :: . - -10~ ~ ~3 wherein Rl is hydrogen or chlorine, . .
R2 is hydrogen, chlorine, lower alkyl of l to 4 carbon atoms, lower alkoxy of l to 4 carbon atoms, carbo-alkoxy of 2 to 9 carbon atoms, carboxy or -S03H, R3 is alkyl of l to 12 carbon atoms, alkoxy of 1 to 4 carbon atoms, phenyl, phenyl substituted with alkyl groups, said alkyl groups having l to 8 carbon atoms, cyclo-alkyl of 5 to 6 carbon atoms, carboalkoxy of 2 to 9 carbon atoms, chlorine, carboxyethyl or arylalkyl of 7 to 9 carbon atoms, R4 is hydrogen, lower alkyl of 1 to 4 carbon atons, lower alkoxy of l to 4 carbon atoms, chlorine or Xydroxyl, and . . -R5 is hydrogen, alkyl of 1 to 12 carbon atoms, . chlorine, cycloalkyl of 5 to 6 carbcn atoms or aryla~kyl of 7 to 9 carbon atoms.
R2 can be lower alkyl of 1 to 4 carbon atoms such as methyl, ethyl or n-butyl. R2 can also be lower alkoxy of 1 to 4 carbon atoms such as methoxy, e~hoxy or n-butoxy. R2 --: - , , . j- .... , ~ , . .
- : : ., :- .: : - - ~
~0734~3 can also be carboalkoxy of 2 to 9 carbon atoms such as carbo-methoxy, carboethoxy, or carbo-n-octoxy.
R3 can be alkyl of 1 to 12 carbon atoms such as mPthyl, ethyl, sec-butyl, tert-butyl, amyl, tert-octyl or n-dodecyl. R3 can also be alkoxy of 1 to 4 carbon atoms such as methoxy, ethoxy or n-butoxy. R3 is also phenyl substituted with alkyl groups, said alkyl groups having 1 to ~ carbon atoms such as methyl, tert-butyl, tert-amyl or tert-octyl. R3 can also be cycloalkyl of 5 to 6 carbon atoms such as cyclopentyl or cyclohexyl. R3 is also carboalkoxy of 2 to 9 carbon atoms such as carbomethoxy, carboethoxy, carbo-n-butoxy or carbo-n-octoxy. R3 is also arylalkyl of 7 to 9 carbon atoms such as benzyl, ~-methylbenzyl or ~,a-dimethylbenzyl.
R4 can be lower alkyl of 1 to 4 carbon atoms such as methyl, ethyl or n-butyl.
R4 can also be lower alkoxy of 1 to 4 carbon atoms such as methoxy, ethoxy or n-butyloxy.
R5 can be lower alkyl of 1 to 8 carbon atoms such as methyl, sec-butyl, tert-butyl, tert-amyl or tert-octyl.
-: . ... , : . . : .. . . ...
: . . .:~ . -, , . -~-:.
- ~ , , .,., : . : .
R5 can also be cycloalkyl of 5 to 6 carbon atoms such as cyclopentyl or cyclohexyl. R5 is also arylalkyl of 7 to 9 carbon atoms such as benzyl, ~-methylbenzyl or ,~-dimethylbenzyl.
Preferably Rl is hydrogen.
. .
Preferably R2 is hydrogen, chlorir.e, lower alkyl of 1 to 2 carbon atoms, methoxy or carboxy.
Preferably R3 is alkyl of 1 to 12 carbon atoms cyclohexyl, phenyl, chlorine, ~-methylbenzyl or carboxyethyl.
lG Preferably R4 is hydrogen, hydroxyl or methyl.
Preferably R5 is hydrogen, chlorine, alkyl of 1 tol2 carbon atoms, cyclohexyl, benzyl or a-methylbenzyl.
Most preferably R2 is hydrogen or chlorine.
- Most preferably R3 is methyl, tert-butyl, ~ert-amyl, tert-octyl, sec-butyl, cyclohexyl, chlorine or carboxyethyl.
Most preferably R4 is hydrogen.
Most preferably R5 is hydrogen, chlorine, methyl, _ 23 --:: - ~ :. , ... ' , ~ ' sec-butyl, tert-butyl, tert-amyl, tert-octyl or ~-methylbenzyl.
The process involved the reduction of an o-nitroazo-benzene intermediate of the formula II
OH
R2 ~ 3 II
wherein Rl, R2, R3, R4 and ~5.are as described previously.
The starting o-nitroazobenzene intermediates are prepared by coupling the appropriate c-nitrobenzenediazonium compounds of formula III
~Q
Rl ~ =N X III
wherein Rl and R2 are as described previously and X is chlo-ride, sulfate, or other anionic species, but preferably chloride, with phenols of formula IV
:.- :::
.... :
073463.
OH
~nS
. . R3 ~:
which couple in the ortho position to the hydroxy group.
The o-nitrobenzenediazonium compounds are in turn prepared by standard diazotization procedures using sodium nitrite in acid solution with the corresponding o-nitro-anilines of formula V
.
~NQ2 ' V
For illustration purposes some specific examples of compounds of formulas rv and V are listed. These items are generally available as items of commerce.
Compounds of Formula rv p-cresol 2,4-di-tert-butylphenol 2,4-di-tert-amylphenol 2,4-di-tert-octylphenol 2-tert-butyl-4-methylphenol
The process of this invention may be effected in any suitable manner and may comprise either a batch or continuous type of operation. For example, when a batch-type operation is used, a quantity of the hydroxy-substi.uted o-nitroazobenzene, toluene, methanol, diethylami~e along with -. .. .. .. :. . - .
~O73A/~63 the catalyst such as palladi~m composited on charcoal, is placed in an appropriate apparatus such as a shaking or stirred autoclave. Hydrogen is pressurized in until the de-sired initial pressure is reached. The autoclave and the contents thereof are then heated, if needed, to the desired reaction temperature and maintained thereat with agitation until the theoretical amount of hydrogen is absorbed wher~-upon no further hydrogen is taken up and the reductio~ re-action is c~mplete. At the end of this time the excess pres-sure is vented, the solution, usually warm, is subjected to -~
filtration, preferably under an inert atomsphere such as nitrogen or argon, to remove the catalyst. The solution is then subjected to distillation to yield the crude product which may be further purified by dissolving in toluene, ex-traction ~ith aqueous acid and recrystallization rom an organic solvent.
It is also contemplated wi.hin the scope of this invention that the preparation of the 2-aryl-2H-benzotriazoles by the reduction and cyclization o~ o-nitroazobenzenes may also be effected in a continuous manner, although not neces-æarily with equivalent results. For example, when a con-tinous type operation is used, the hydroxy-substituted o-nitroazobenzene starting material is premixed with, and ~issolved in an organic solvent mixture containing a water . ~ .- - . . .~ . .............. :. . .
.- -: - . :- . . .
. -,: . -:
- , ~ .
1073 a~;3 ~oluble amine, said mixture fed continuously to a reaction zone which is maintained at the proper operating conditi,ons of temperaiure and pressure and which contains the hydrogena-tion catalyst. Hydrogen is pressurized into the reacticn zone by a separate means. After a desired residence time, the reactor effluent is continuously discharged and the effluent solution is distilled to isol~te the desired product. Due to the nature of the catalyst employed r a particularly effective continuous ~-ype of operation comprises a fixed bed of cata-lyst subjected to either an upward or downward flow of the reaction solution. If it is desirable to carry out the reduction as a two-step process with a different operating temperature for each step, two reaction zones in series each operating at the preferred temperature range for the specific reduction step involved may be used.
The reduction of o-nitroazobenzenes to the cor-responding 2-aryl-2H-benzotria201es is a two-step process as outlined below.
, ~
: ::. . ,, - . : .... :-; ; . ., ,, .. , :
- : , - : : ... :: , :
10~34~3 OH
Rl ~ N=N ~ R5 Step l R2 NO2 ~ ~_ ` ~, -.
. .
OH
~ ~X ~SR4 . Step 2 ,~ ~ ' ,'.
OH
Rl~N\ _~5, Step l - The reduction of the o-nitroazobenzene to the N-oxybenzotriazole derivative proceeds rapidly and exot~er-mically even at low temperature under the process cor.ditions of this invention.
. -- 19 --,-: .. ': , :. ., . , ' ' : , ;: ', `.. `' ~ - : .
~0~3~63 Step 2 - The reduction of the N-o~ybenzotriazole intermediate to the corresponding 2-aryl-2H-benzotriazole product goes more slowly. This reduction can be greatly expedited by adding more catalyst, raising the temperature, increasing the hydrogen pressure or by combination of these factors.
Generally, the reaction ceases when the N-oxy in-termediate is completely reduced to the corresponding 2-aryl-2H-benzotriazole making for facile control of this catalytic hydrogenation process. However, with some highly substituted benzotriazoles, reduction snouid be stopped when the appropri-ate amount of hydrogen has been absorbed and.reacted to prevent further reductive cleavage of the desired 2-aryl-2H-benzotria-zoles prepared.
Specifically, the instant invention provides an improved process for production of compounds having the formula I
~ N ~ R4 .. R3 ,.
~- . . . . .. . . ~, ", ,. , ~ ~ "
I -, :: . - -10~ ~ ~3 wherein Rl is hydrogen or chlorine, . .
R2 is hydrogen, chlorine, lower alkyl of l to 4 carbon atoms, lower alkoxy of l to 4 carbon atoms, carbo-alkoxy of 2 to 9 carbon atoms, carboxy or -S03H, R3 is alkyl of l to 12 carbon atoms, alkoxy of 1 to 4 carbon atoms, phenyl, phenyl substituted with alkyl groups, said alkyl groups having l to 8 carbon atoms, cyclo-alkyl of 5 to 6 carbon atoms, carboalkoxy of 2 to 9 carbon atoms, chlorine, carboxyethyl or arylalkyl of 7 to 9 carbon atoms, R4 is hydrogen, lower alkyl of 1 to 4 carbon atons, lower alkoxy of l to 4 carbon atoms, chlorine or Xydroxyl, and . . -R5 is hydrogen, alkyl of 1 to 12 carbon atoms, . chlorine, cycloalkyl of 5 to 6 carbcn atoms or aryla~kyl of 7 to 9 carbon atoms.
R2 can be lower alkyl of 1 to 4 carbon atoms such as methyl, ethyl or n-butyl. R2 can also be lower alkoxy of 1 to 4 carbon atoms such as methoxy, e~hoxy or n-butoxy. R2 --: - , , . j- .... , ~ , . .
- : : ., :- .: : - - ~
~0734~3 can also be carboalkoxy of 2 to 9 carbon atoms such as carbo-methoxy, carboethoxy, or carbo-n-octoxy.
R3 can be alkyl of 1 to 12 carbon atoms such as mPthyl, ethyl, sec-butyl, tert-butyl, amyl, tert-octyl or n-dodecyl. R3 can also be alkoxy of 1 to 4 carbon atoms such as methoxy, ethoxy or n-butoxy. R3 is also phenyl substituted with alkyl groups, said alkyl groups having 1 to ~ carbon atoms such as methyl, tert-butyl, tert-amyl or tert-octyl. R3 can also be cycloalkyl of 5 to 6 carbon atoms such as cyclopentyl or cyclohexyl. R3 is also carboalkoxy of 2 to 9 carbon atoms such as carbomethoxy, carboethoxy, carbo-n-butoxy or carbo-n-octoxy. R3 is also arylalkyl of 7 to 9 carbon atoms such as benzyl, ~-methylbenzyl or ~,a-dimethylbenzyl.
R4 can be lower alkyl of 1 to 4 carbon atoms such as methyl, ethyl or n-butyl.
R4 can also be lower alkoxy of 1 to 4 carbon atoms such as methoxy, ethoxy or n-butyloxy.
R5 can be lower alkyl of 1 to 8 carbon atoms such as methyl, sec-butyl, tert-butyl, tert-amyl or tert-octyl.
-: . ... , : . . : .. . . ...
: . . .:~ . -, , . -~-:.
- ~ , , .,., : . : .
R5 can also be cycloalkyl of 5 to 6 carbon atoms such as cyclopentyl or cyclohexyl. R5 is also arylalkyl of 7 to 9 carbon atoms such as benzyl, ~-methylbenzyl or ,~-dimethylbenzyl.
Preferably Rl is hydrogen.
. .
Preferably R2 is hydrogen, chlorir.e, lower alkyl of 1 to 2 carbon atoms, methoxy or carboxy.
Preferably R3 is alkyl of 1 to 12 carbon atoms cyclohexyl, phenyl, chlorine, ~-methylbenzyl or carboxyethyl.
lG Preferably R4 is hydrogen, hydroxyl or methyl.
Preferably R5 is hydrogen, chlorine, alkyl of 1 tol2 carbon atoms, cyclohexyl, benzyl or a-methylbenzyl.
Most preferably R2 is hydrogen or chlorine.
- Most preferably R3 is methyl, tert-butyl, ~ert-amyl, tert-octyl, sec-butyl, cyclohexyl, chlorine or carboxyethyl.
Most preferably R4 is hydrogen.
Most preferably R5 is hydrogen, chlorine, methyl, _ 23 --:: - ~ :. , ... ' , ~ ' sec-butyl, tert-butyl, tert-amyl, tert-octyl or ~-methylbenzyl.
The process involved the reduction of an o-nitroazo-benzene intermediate of the formula II
OH
R2 ~ 3 II
wherein Rl, R2, R3, R4 and ~5.are as described previously.
The starting o-nitroazobenzene intermediates are prepared by coupling the appropriate c-nitrobenzenediazonium compounds of formula III
~Q
Rl ~ =N X III
wherein Rl and R2 are as described previously and X is chlo-ride, sulfate, or other anionic species, but preferably chloride, with phenols of formula IV
:.- :::
.... :
073463.
OH
~nS
. . R3 ~:
which couple in the ortho position to the hydroxy group.
The o-nitrobenzenediazonium compounds are in turn prepared by standard diazotization procedures using sodium nitrite in acid solution with the corresponding o-nitro-anilines of formula V
.
~NQ2 ' V
For illustration purposes some specific examples of compounds of formulas rv and V are listed. These items are generally available as items of commerce.
Compounds of Formula rv p-cresol 2,4-di-tert-butylphenol 2,4-di-tert-amylphenol 2,4-di-tert-octylphenol 2-tert-butyl-4-methylphenol
4-cyclohexylphenol 4-tert-butylphenol 4-tert-amylphenol 4-tert-octylphenol 2,4-dimethylphenol 3,4-dimethylphenol 4-chlorophenol 2,4-dichlorophenol . 3,4-dichlorophenol 4-phenylphenol 4-phenoxyphenol 4-o-tolylphenol . 4-(4'-tert-octyl)phenylphenol ethyl 4-hydroxybenzoate n-octyl 4-hydroxybenzoate 4-methoxyphenol -4-n-octylphenol _ 26 -.. . . .. . " ;, : . . - . ,- . , . - - , , . :. - . .
. , . , . ~ ~ . . . . . . ... . . . . ...
10~34~3 4-n-dodecylphenol resorcinol 4-(~-methylben2yl)phenol ~ - 2-(a-methylbenzyl)-4-methylphenol 2-cyclohexyl-4-methylphenol 4-sec-butylphenol 2-sec-butyl-4-tert-butylphenol 2-tert-butyl-4-sec-butylphenol 4-carboxyethylphenol 2-methyl-4-carboxyethylphenol Preferably compounds of formula IV useful in this invention are p-cresol . 2,4-di-tert-butylphenol 2,4-di-tert-amylphenol 2,4-di-tert-octylphenol - 2-tert-butyl-4-methylphenol 4-tert-octylphenol , ~-n-octylphenol `
4-n-dodecylphenol resorcinol 2-sec-butyl-4-tert-butylphenol - ~- .. , .. . -, ,. . . . - .
,. . . - . - :. ., . : :,: ~ , :
.
.:
10734~
2~ methylbenzyl)-4-methylphenol Compounds of Formula V
o-nitroaniline 4-chloro-2-nitroaniline 4,5-dichloro-2^nitroaniline 4-methoxy-2-nitroaniline -4-methyl-2-nitroaniline 4-ethyl-2-nitroaniline n-butyl 3-nitro-4-aminobenzoate n-octyl 3-nitro-4-aminobenzoate 4-n-butoxy-2-nitroaniline 3-nitro-4-aminobenzoic acid 3-nitro-4-aminobenzenesulfonic acid ...*
- Preferably compounds of formula V useful in this invention are - o-nitroaniline 4-chloro-2-nitroaniline The 2-aryl-2H-benzotriazoles have found wide use as dyestuff intermediates, optical brightner blue fluorescent agents and selective ultraviolet light absorbing stabilizers affording valuable protection for fibers, films and a variety ; ~ .
.. . . .. . .. . . ..... .. . . . .. .. .
- ~ . . . . . . . . . .
.~, . - -, ~ , , , - ~: , ... i . ..
.
, - ' . ,: . -10734~3 of polymeric structures subject to deterioration by ultra-~iolet radiation. These materials have become important items of commerce.
The 2-aryl-2H-benzotriazoles are complex organic molecules which require careful synthetic procedures for their production in good yield and acceptable purity.
The present invention is concerned with an improved process to prepare ultra~iolet stabilizers which are substi-tu~ed 2-aryl-2H-benzotriazoles. ~hese are distinguished by a very slight absorption in visible light and very high fast-ness to light in various substrates. Particularly valuable members of these stabilizers are compounds having a free hy-droxyl group in the 2-position of the aryl group linked to the 2-nitrogen of the benzotriazole and which are further substituted in the 3- and 5- or in the 4- and 5-positions by lower alkyl groups and may be substituted by a chlorine in the 5-position of the benzotriazole nucleus.
The description, preparation and uses of these valuable substituted 2-aryl-2H-benzotriazoles are further taught in the U.S. Patent Numbers 3,004,896, 3,055,896, 3,072,585, 3,074,910, 3,189,615 and 3,230,194.
., ,, .
.. . . ... . .. . .
- . - . :.. . .. .. .:
~ .
- - . .
Particular advantages of the process according to the present invention are the high purity of the desired triazoles, the high yields, the possibility to recycle the reaction medium preferably after removing of S the reaction water and optionally after a distillation step and the maintainance of the catalysts activity which is only lowered in small amounts. Therefore the catalyst can also be recycled, optionally together with the addi-tion of small amounts, e.g. about 10% by weight of fresh catalyst. Also the reaction times are lowered as compared to a process in aqueous reaction medium.
The following examples are given to illustrate the process to the present invention, but are not intended to limit the scope of the present invention in any manner whatsoever.
.
' .~ ~ ' .
, 0~3~63 Example 1 _ _ 2-(2-Hydroxy-5_methylphenyl)-2H-benzotriazole To a l-liter, low pressure hydrogenation reactor were charged under nitrogen at room temperature 20 grams of 2-nitro-2'-hydroxy-5'-methylazobenzene (95% pure) dissolved in 55 grams of toluene, 25 grams of methanol and 5 grams of diethylamine and 1.5 grams of 5% palladium on charcoal hydro-genation catalyst slurried in the aforementioned organic solvents. The amount of catalyst is 7.5~ based on the azo-benzene intermediate and the molar ratio of diethylamine to azobenzene intermedia~e is 0.925. The reactor was flushed several times with hydrogen and then pressurized to 1 atmosphere with hydrogen. External cooling was pro- -vided to prevent the temperature of the reactor contents from exceeding 35C during the exothermic first step of the reduction. The first step was complete in 15 minutes when fresh catalyst was used or in 30 minutes when the catalyst 4 times recycled was used.
The second step of the reduction of the N-oxy benzotria~ole to the deslred 2-aryl-2H-benzotriazole was carried out at a temperature of 50C. This step is not extremely exothermic and some external heating was required -,., I . . ..
, . . .. . . .
- . . , .. ,....... . . :
1073~3 in the latter stages of the reduction. The second step was complete in another 30 minuies when fresh catalyst was used or in another 60 minutes when catalyst 4 times recycled was employed.
~hen hydrogen absorption ceased and the reaction - was complete, the hydrogen remaining in the reactor was now vented and a nitrogen atmosphere ~as reimposed on the reactor ?
contents.
The reactor contents were then filtered under nitrogen to remove the palladium on charcoal catalyst di-spersed therein. The recovered catalyst was washed on the filter with toluene. This washed catalyst was then ready for recycling in the hydrogenation process where it could be used for many additional cycles with minimum loss in catalyst activity.
The combined alkaline organic solution of the de-sired product was then concentrated by distillation under vacuum to gi~e as distillates toluene-methanol, toluene-diethylamine and finally toluene-water. Form the latter, water can be separated. The recovered solvents can then be recycled to another hydrogenation reaction. The still pot residue comprises the crude product in a yield of , - , .
- " -~'. .
iO~34G:~
grams ~80~ of theory). The crude product contains some amine by-product wnich can be removed by acid extraction.
The crude product WaS purified by dissolving 8.0 grams of the crude product in 11.0 grams of toluene. This solution was extracted with 8.0 grams of 70% aqueous sulfuric acid. The toluene solution was then stirred with 0.8 grams of Prolit Rapid, an acidic clay, which was removed then by ~iltration. The clay was washed wi.h 3.0 grams of toluene.
The combined toluene filtrate was then concentrated by vacuum distillation. After 9.0 grams of toluene was isolated, 6.5 grams ol isopropanol was added dropwise to the still-pot resi~ue. The resulting solution was then cooled to 0-5C
and the resulting crystals were isolated by filtration, wash2d wi~ 4.0 grams of cold isopropanol and vacuum dried at 70-80C.
The yield of pure product was 7.6 grams (75% of theory based on the original azobenzene intermediate).
Example 2 - ~--2-(2-Hydroxy-5-methYl~henyl)-2H-benzotriazole When using the procedure of Example 1, the hydrogen pressure employed was in the range of 3.3-2 atmospheres in-stead of 1 atmosphere, the reaction temperature was held at 58-60C rather than 35C for the first step and SOC for .- : . . .: : . . . --. ,: . - . :: ~ . -.
. - .. .... ... .
~, . ~ . . . .
fO~3~63 the second step and only 3% by weight of 5% p~lladium on eharcoal catalyst was used instead of 7.5~/0 by weight based on azobenzene intermediate, the reaction time for total absorption of hydrogen was 125 minutes. The yield of crude .
product was nearly the same, namely 75% of theory.
- When in Example 2, the hydrogen pressure employedwas 1 atmosphere, the reaction time was extended to 250 minutes, but the yield of crude product was the same (75%
of theory).
10 . If in Example 2, the diethylamine component of the organic solvent system was left out, complete absorption of hydrogen occurred in 60 minutes, but none of the desired product was obtained. The presence of the organic base, such as diethylamine, is essential for the process to yield the desired 2-aryl-2H-benzotriazoles upon reduction of tne cor- -responding o-nitroazobenzenes.
. Example 3 - -2-(2-Hydroxy-5-methylphenyl)-2H-benzotriazole If in Example 2, the 5~ palladium on charcoal catalyst was replaced by an equivalent amount of 5% platinum on charcoal catalyst and the reaction carried out at a tem-~, .
. : . ' . -. .
- . . ~ , ,-.
107 ~ 63 perature in the ~ange of 58-78~C, the reaction time for complete absorption of hydrogen was 50 minutes, and the yield of crude desired product was 55%.
Platinum is an operative catalyst for this hydro-genation, but is less selective than palladium giving rise to more und~sired by-products.
If in Example 3, the diethylamine component of the organic solvent system was left out, complete absorption of hydrogen occurred in 60 minutes, but no desired product was obtained. Thus, it is essential for the organic solvent system to contain a base such as an organic amine for the process to be operable to produce 2-aryl-2~-benzotriazoles.
Example 4 - 2-(2-Hydroxy-5-methylphenyl)-2H-benzotriazole If in Example 2, the S~ palladium on charcoal cata-lyst is xeplaced by an equivalent amount of 5% rhodium on charcoal catalyst, the crude desired product is obtained.
If Example 4, the diethylamine component of the organic solvent system was left out, complete absorption of hydrogen occurred in 90 minutes, but no desired product was obtained.
;' . .
.,, ~,. ,. , - ,;. .. ..
,. . .. . . .
As with both the palladium and platinum catalysts, ~' no product was obtained with the rhodium on charcoal catalyst with the organic solvent system in the absence of a base such as diethylamine.
S Example 5 2-(2-Hydroxy-3,5-di-tert-amylphenyl)-2H-benzotriazole When using the general procedure of Example 1, an equivalent amount of 2-nitro-2'-hydroxy-3',5'-di-tert-arnyl-azobenzene was substituted for 2-nitro-2'-hydroxy-5'-methylazobenzene, the above noted product was obtained in yields ranging from 52 to 67% based on the original azoben-zene intermedia~e used. The reaction was carried out in a 23.3~ by weight solution of the azobenzene in isopropanol with l to 3% by ~eight of catalyst and with 1.1 to 2.0 moles of diethylamine per mole of azobenzene intermediate.
~, .
The effect of the quantity of water-miscible organic amine on the yield of 2-aryl-2H-benzotriazole is seen from Table A. At least l.l moles of organic amine per mole of o-nitroazobenzene is required to give good yields of the desired product. Using more than 1.5 moles organic amine per mole of o-nitroazobenzene intermediate did not further enhance product yields.
.. .. . . .
,: : : , . . :,:. .. ., : , -107 ~ 6 Table A
Effect of Quantity of Diethylamine on Yield of 2-(2-Hydroxy-3,5-di-tert-_ amylphenyl)-2H-benzotria7.ole*
Hydrogen Equivalents .~ Yield of Absorbed Amine to 2-Aryl-2H-% of Theory o-Nitroazobenzene benzotriazole 143 0.1 24.7 155 1.1 55.0 15~ 1.5 49.5 156 2.0 -50.0 * Reaction conditions: .
- 23.3% by weight solution of corresponding ` o-nitroazobenzene intermediate in isopropanol.
- atmospheric pressure - temperature range 55-60C
- catalyst 5% palladium-on-charcoal used at 3% by weight of o-nitroazobenzene intermediate In Table B are shown the effect of other variables on the yields of 2-(2-hydroxy-3,5-di-tert-amylphenyl)-2H-benzotriazole prepared by the reductive cyclization of 23.3%
by weigh' solution of the corresponding o-nitroazobenzene intermediate in isopropanol using 5~ palladium catalysts . - 37 -~. . ' , ~ " ' ,` , .
' ''' '' " ' ' ' ' ""~ ~ ' ' ' `
10~6~
composited on various substrates, using various concentra-tions of said catalysts and various temperatures in the presence of 2 moles of diethylamine per mole of o-nitro-azobenzene intermediate run at atmospheric pressure.
- . - . - : ..................... .
. .
10'~;~4~;3 o Z;
N ~rl ~ C~
~ O O
S-~
0 ~1 N N ~ N
O
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I H
.bV O
O C~ N
~ ~ ¢
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O C~
. , . , . ~ ~ . . . . . . ... . . . . ...
10~34~3 4-n-dodecylphenol resorcinol 4-(~-methylben2yl)phenol ~ - 2-(a-methylbenzyl)-4-methylphenol 2-cyclohexyl-4-methylphenol 4-sec-butylphenol 2-sec-butyl-4-tert-butylphenol 2-tert-butyl-4-sec-butylphenol 4-carboxyethylphenol 2-methyl-4-carboxyethylphenol Preferably compounds of formula IV useful in this invention are p-cresol . 2,4-di-tert-butylphenol 2,4-di-tert-amylphenol 2,4-di-tert-octylphenol - 2-tert-butyl-4-methylphenol 4-tert-octylphenol , ~-n-octylphenol `
4-n-dodecylphenol resorcinol 2-sec-butyl-4-tert-butylphenol - ~- .. , .. . -, ,. . . . - .
,. . . - . - :. ., . : :,: ~ , :
.
.:
10734~
2~ methylbenzyl)-4-methylphenol Compounds of Formula V
o-nitroaniline 4-chloro-2-nitroaniline 4,5-dichloro-2^nitroaniline 4-methoxy-2-nitroaniline -4-methyl-2-nitroaniline 4-ethyl-2-nitroaniline n-butyl 3-nitro-4-aminobenzoate n-octyl 3-nitro-4-aminobenzoate 4-n-butoxy-2-nitroaniline 3-nitro-4-aminobenzoic acid 3-nitro-4-aminobenzenesulfonic acid ...*
- Preferably compounds of formula V useful in this invention are - o-nitroaniline 4-chloro-2-nitroaniline The 2-aryl-2H-benzotriazoles have found wide use as dyestuff intermediates, optical brightner blue fluorescent agents and selective ultraviolet light absorbing stabilizers affording valuable protection for fibers, films and a variety ; ~ .
.. . . .. . .. . . ..... .. . . . .. .. .
- ~ . . . . . . . . . .
.~, . - -, ~ , , , - ~: , ... i . ..
.
, - ' . ,: . -10734~3 of polymeric structures subject to deterioration by ultra-~iolet radiation. These materials have become important items of commerce.
The 2-aryl-2H-benzotriazoles are complex organic molecules which require careful synthetic procedures for their production in good yield and acceptable purity.
The present invention is concerned with an improved process to prepare ultra~iolet stabilizers which are substi-tu~ed 2-aryl-2H-benzotriazoles. ~hese are distinguished by a very slight absorption in visible light and very high fast-ness to light in various substrates. Particularly valuable members of these stabilizers are compounds having a free hy-droxyl group in the 2-position of the aryl group linked to the 2-nitrogen of the benzotriazole and which are further substituted in the 3- and 5- or in the 4- and 5-positions by lower alkyl groups and may be substituted by a chlorine in the 5-position of the benzotriazole nucleus.
The description, preparation and uses of these valuable substituted 2-aryl-2H-benzotriazoles are further taught in the U.S. Patent Numbers 3,004,896, 3,055,896, 3,072,585, 3,074,910, 3,189,615 and 3,230,194.
., ,, .
.. . . ... . .. . .
- . - . :.. . .. .. .:
~ .
- - . .
Particular advantages of the process according to the present invention are the high purity of the desired triazoles, the high yields, the possibility to recycle the reaction medium preferably after removing of S the reaction water and optionally after a distillation step and the maintainance of the catalysts activity which is only lowered in small amounts. Therefore the catalyst can also be recycled, optionally together with the addi-tion of small amounts, e.g. about 10% by weight of fresh catalyst. Also the reaction times are lowered as compared to a process in aqueous reaction medium.
The following examples are given to illustrate the process to the present invention, but are not intended to limit the scope of the present invention in any manner whatsoever.
.
' .~ ~ ' .
, 0~3~63 Example 1 _ _ 2-(2-Hydroxy-5_methylphenyl)-2H-benzotriazole To a l-liter, low pressure hydrogenation reactor were charged under nitrogen at room temperature 20 grams of 2-nitro-2'-hydroxy-5'-methylazobenzene (95% pure) dissolved in 55 grams of toluene, 25 grams of methanol and 5 grams of diethylamine and 1.5 grams of 5% palladium on charcoal hydro-genation catalyst slurried in the aforementioned organic solvents. The amount of catalyst is 7.5~ based on the azo-benzene intermediate and the molar ratio of diethylamine to azobenzene intermedia~e is 0.925. The reactor was flushed several times with hydrogen and then pressurized to 1 atmosphere with hydrogen. External cooling was pro- -vided to prevent the temperature of the reactor contents from exceeding 35C during the exothermic first step of the reduction. The first step was complete in 15 minutes when fresh catalyst was used or in 30 minutes when the catalyst 4 times recycled was used.
The second step of the reduction of the N-oxy benzotria~ole to the deslred 2-aryl-2H-benzotriazole was carried out at a temperature of 50C. This step is not extremely exothermic and some external heating was required -,., I . . ..
, . . .. . . .
- . . , .. ,....... . . :
1073~3 in the latter stages of the reduction. The second step was complete in another 30 minuies when fresh catalyst was used or in another 60 minutes when catalyst 4 times recycled was employed.
~hen hydrogen absorption ceased and the reaction - was complete, the hydrogen remaining in the reactor was now vented and a nitrogen atmosphere ~as reimposed on the reactor ?
contents.
The reactor contents were then filtered under nitrogen to remove the palladium on charcoal catalyst di-spersed therein. The recovered catalyst was washed on the filter with toluene. This washed catalyst was then ready for recycling in the hydrogenation process where it could be used for many additional cycles with minimum loss in catalyst activity.
The combined alkaline organic solution of the de-sired product was then concentrated by distillation under vacuum to gi~e as distillates toluene-methanol, toluene-diethylamine and finally toluene-water. Form the latter, water can be separated. The recovered solvents can then be recycled to another hydrogenation reaction. The still pot residue comprises the crude product in a yield of , - , .
- " -~'. .
iO~34G:~
grams ~80~ of theory). The crude product contains some amine by-product wnich can be removed by acid extraction.
The crude product WaS purified by dissolving 8.0 grams of the crude product in 11.0 grams of toluene. This solution was extracted with 8.0 grams of 70% aqueous sulfuric acid. The toluene solution was then stirred with 0.8 grams of Prolit Rapid, an acidic clay, which was removed then by ~iltration. The clay was washed wi.h 3.0 grams of toluene.
The combined toluene filtrate was then concentrated by vacuum distillation. After 9.0 grams of toluene was isolated, 6.5 grams ol isopropanol was added dropwise to the still-pot resi~ue. The resulting solution was then cooled to 0-5C
and the resulting crystals were isolated by filtration, wash2d wi~ 4.0 grams of cold isopropanol and vacuum dried at 70-80C.
The yield of pure product was 7.6 grams (75% of theory based on the original azobenzene intermediate).
Example 2 - ~--2-(2-Hydroxy-5-methYl~henyl)-2H-benzotriazole When using the procedure of Example 1, the hydrogen pressure employed was in the range of 3.3-2 atmospheres in-stead of 1 atmosphere, the reaction temperature was held at 58-60C rather than 35C for the first step and SOC for .- : . . .: : . . . --. ,: . - . :: ~ . -.
. - .. .... ... .
~, . ~ . . . .
fO~3~63 the second step and only 3% by weight of 5% p~lladium on eharcoal catalyst was used instead of 7.5~/0 by weight based on azobenzene intermediate, the reaction time for total absorption of hydrogen was 125 minutes. The yield of crude .
product was nearly the same, namely 75% of theory.
- When in Example 2, the hydrogen pressure employedwas 1 atmosphere, the reaction time was extended to 250 minutes, but the yield of crude product was the same (75%
of theory).
10 . If in Example 2, the diethylamine component of the organic solvent system was left out, complete absorption of hydrogen occurred in 60 minutes, but none of the desired product was obtained. The presence of the organic base, such as diethylamine, is essential for the process to yield the desired 2-aryl-2H-benzotriazoles upon reduction of tne cor- -responding o-nitroazobenzenes.
. Example 3 - -2-(2-Hydroxy-5-methylphenyl)-2H-benzotriazole If in Example 2, the 5~ palladium on charcoal catalyst was replaced by an equivalent amount of 5% platinum on charcoal catalyst and the reaction carried out at a tem-~, .
. : . ' . -. .
- . . ~ , ,-.
107 ~ 63 perature in the ~ange of 58-78~C, the reaction time for complete absorption of hydrogen was 50 minutes, and the yield of crude desired product was 55%.
Platinum is an operative catalyst for this hydro-genation, but is less selective than palladium giving rise to more und~sired by-products.
If in Example 3, the diethylamine component of the organic solvent system was left out, complete absorption of hydrogen occurred in 60 minutes, but no desired product was obtained. Thus, it is essential for the organic solvent system to contain a base such as an organic amine for the process to be operable to produce 2-aryl-2~-benzotriazoles.
Example 4 - 2-(2-Hydroxy-5-methylphenyl)-2H-benzotriazole If in Example 2, the S~ palladium on charcoal cata-lyst is xeplaced by an equivalent amount of 5% rhodium on charcoal catalyst, the crude desired product is obtained.
If Example 4, the diethylamine component of the organic solvent system was left out, complete absorption of hydrogen occurred in 90 minutes, but no desired product was obtained.
;' . .
.,, ~,. ,. , - ,;. .. ..
,. . .. . . .
As with both the palladium and platinum catalysts, ~' no product was obtained with the rhodium on charcoal catalyst with the organic solvent system in the absence of a base such as diethylamine.
S Example 5 2-(2-Hydroxy-3,5-di-tert-amylphenyl)-2H-benzotriazole When using the general procedure of Example 1, an equivalent amount of 2-nitro-2'-hydroxy-3',5'-di-tert-arnyl-azobenzene was substituted for 2-nitro-2'-hydroxy-5'-methylazobenzene, the above noted product was obtained in yields ranging from 52 to 67% based on the original azoben-zene intermedia~e used. The reaction was carried out in a 23.3~ by weight solution of the azobenzene in isopropanol with l to 3% by ~eight of catalyst and with 1.1 to 2.0 moles of diethylamine per mole of azobenzene intermediate.
~, .
The effect of the quantity of water-miscible organic amine on the yield of 2-aryl-2H-benzotriazole is seen from Table A. At least l.l moles of organic amine per mole of o-nitroazobenzene is required to give good yields of the desired product. Using more than 1.5 moles organic amine per mole of o-nitroazobenzene intermediate did not further enhance product yields.
.. .. . . .
,: : : , . . :,:. .. ., : , -107 ~ 6 Table A
Effect of Quantity of Diethylamine on Yield of 2-(2-Hydroxy-3,5-di-tert-_ amylphenyl)-2H-benzotria7.ole*
Hydrogen Equivalents .~ Yield of Absorbed Amine to 2-Aryl-2H-% of Theory o-Nitroazobenzene benzotriazole 143 0.1 24.7 155 1.1 55.0 15~ 1.5 49.5 156 2.0 -50.0 * Reaction conditions: .
- 23.3% by weight solution of corresponding ` o-nitroazobenzene intermediate in isopropanol.
- atmospheric pressure - temperature range 55-60C
- catalyst 5% palladium-on-charcoal used at 3% by weight of o-nitroazobenzene intermediate In Table B are shown the effect of other variables on the yields of 2-(2-hydroxy-3,5-di-tert-amylphenyl)-2H-benzotriazole prepared by the reductive cyclization of 23.3%
by weigh' solution of the corresponding o-nitroazobenzene intermediate in isopropanol using 5~ palladium catalysts . - 37 -~. . ' , ~ " ' ,` , .
' ''' '' " ' ' ' ' ""~ ~ ' ' ' `
10~6~
composited on various substrates, using various concentra-tions of said catalysts and various temperatures in the presence of 2 moles of diethylamine per mole of o-nitro-azobenzene intermediate run at atmospheric pressure.
- . - . - : ..................... .
. .
10'~;~4~;3 o Z;
N ~rl ~ C~
~ O O
S-~
0 ~1 N N ~ N
O
~¢~
QJ
I N N
I H
.bV O
O C~ N
~ ~ ¢
E~
O C~
5 e O O ~ ~ ~ ~
The yields of the 2-aryl-2H-benzotriazole varied from 52 to 67%. A lower temperature (45C versus 60C), higher concentration of catalyst (2% versus 1~), and the use of alumina rather than carbon as the carrier for the palladium catalyst appeared to be marginally beneficlal. ln all of these runs, the products contained some 2-amino-2'-hydroxy-3',5'-di-tert-amylhydrazobenzene as an undesired by-product accounting for some lower yields (52-67~) with this particular 2-aryl-2H-benzotriazole compared to the yields of - 75-85% obtained with 2-(2-hydroxy-5-methylphenyl)-2H-benzo-triazole.
.
- Examp]e 6 ?- (2-Hydroxy-5-tert-octylphenyl)-2H-benzotriazole Wllen using the proce~ure of Example 1 an equiva-lent amount of 2-nitro-2'-hydroxy-5'-tert-octylazobenzene is substituted for 2-nitro-2'-hydroxy-5'-methylazobenzene, the above noted product is obtained.
Example 7 5-Chloro-2-(2-hydroxy-3,5-di-tert-burylphenyl)-2H-benzo-triazole When in Example 5, the 2-nitro-2'-hydroxy-3', 5'-di-tert-amylazobenzene was replaced by an equivalent ~ . ..
, : . .. ,:
- : " ,,,, -,: ,-.. ', .. .. ~
" ' . , ',~.,' ,''`' . ' , '' :
107 ~ 63 amount of 2-nitro-5-chloro-2'-hydroxy-3',5'-di-tert-butyl-azobenzene and the 5% palladium on charcoal catalyst was replaced by an equivalent amount of 5% rhodium on charcoal catalyst, the above noted product was obtained.
If the 5% palladium on charcoal catalyst was used, the resulting product was the dischloro compound 2-(2-hydroxy-3,5-di-tert-butylphenyl)-2H-benzotriazole.
Example 8 5-Chloro-2-(2-hydroxy-3-tert-butyl-5-methylphenyl)-2H-benzotriazole When in Example 5, the 2-nitro-2'-hydroxy-3',5'-di-tert-amylazobenzene was replaced by an equivalent amount of 2-nitro-5-chloro-2'-hydroxy-3'-tert-butyl-5'-methylazo-benzene and the 5% palladium on charcoal catalyst by a like amount of 5% rhodium on charcoal catalyst, the above noted product is obtained.
Example 9 2-(2-Hydroxy-3,5-di-tert-butylphenyl)-2H-benzotriazol2 When using the general procedure of ~xample 5, a 23% by weight suspension of 2-nitro-2'-hydroxy-3',5'-di-tert-butylazobenzene in isopropanol/triethylamine (1/0.18) was hydrogenated at 45C at 1 atmosphere for 3 hours in the , . ~ , .. .: . ., . : . .
. ." . - - - ~-. ::
., : . .. .. ::- . ~ .
107346:3 presence of 3/O of a 5% palladium on charcoal catalyst the above noted product was obtained in a yield of 77%.
Example 10 2-(2-Hydroxy-5-methylphenyl)-2H-benzotriazole When using the general procedure of Example 1, the organic solvent toluene was replaced by a trialkyl phosphate, the above noted product was obtained in good yield.
~ A suspension of 23.3 grams of 2-nitro-2'-hydroxy-5'-methylazobenzene in 80 grams of tributyl phosphate, 20 grams of methanol and 8 grams of diethylamine with 1.5 grams o~ 5~/0 palladium on charcoal catalyst was hydro-genated at 1 atmosphere for 55 minutes at a maximum tem-perature of 55C. The above noted product with a melting point of 129-130C was obtained in a yield of 80%.
When using the procedure listed above the tri-butyl phosphate was replaced by a like amount of triethyl phosphate and with no methanol being present, the above noted product (melting point 128-130C) was obtained in a yield of 76%.
- .. .~. . .- --; ,.. . ~, . :
: . . :",.. - . - . ~ .
10~ ~ 6 Example 11 2-(2-Hydroxy-5-methyl~-2H-benzotriazole When using the general procedure of Example 1 the toluene, methanol and diethylamine organic solvent mixture is replaced by a comparable weight of n-propyl-amine, the above noted product is obtained.
Example 12 2-(2-Hydroxy-3,5-di-tert-amylphenyl)-2H-benzotriazole When using the general procedure OL Example 5 the isopropanol and diethylamine organic solvent mixture is replaced by a comparable weight of morpholine, the above noted. -~: . :.
. : : . , : - , . : -
The yields of the 2-aryl-2H-benzotriazole varied from 52 to 67%. A lower temperature (45C versus 60C), higher concentration of catalyst (2% versus 1~), and the use of alumina rather than carbon as the carrier for the palladium catalyst appeared to be marginally beneficlal. ln all of these runs, the products contained some 2-amino-2'-hydroxy-3',5'-di-tert-amylhydrazobenzene as an undesired by-product accounting for some lower yields (52-67~) with this particular 2-aryl-2H-benzotriazole compared to the yields of - 75-85% obtained with 2-(2-hydroxy-5-methylphenyl)-2H-benzo-triazole.
.
- Examp]e 6 ?- (2-Hydroxy-5-tert-octylphenyl)-2H-benzotriazole Wllen using the proce~ure of Example 1 an equiva-lent amount of 2-nitro-2'-hydroxy-5'-tert-octylazobenzene is substituted for 2-nitro-2'-hydroxy-5'-methylazobenzene, the above noted product is obtained.
Example 7 5-Chloro-2-(2-hydroxy-3,5-di-tert-burylphenyl)-2H-benzo-triazole When in Example 5, the 2-nitro-2'-hydroxy-3', 5'-di-tert-amylazobenzene was replaced by an equivalent ~ . ..
, : . .. ,:
- : " ,,,, -,: ,-.. ', .. .. ~
" ' . , ',~.,' ,''`' . ' , '' :
107 ~ 63 amount of 2-nitro-5-chloro-2'-hydroxy-3',5'-di-tert-butyl-azobenzene and the 5% palladium on charcoal catalyst was replaced by an equivalent amount of 5% rhodium on charcoal catalyst, the above noted product was obtained.
If the 5% palladium on charcoal catalyst was used, the resulting product was the dischloro compound 2-(2-hydroxy-3,5-di-tert-butylphenyl)-2H-benzotriazole.
Example 8 5-Chloro-2-(2-hydroxy-3-tert-butyl-5-methylphenyl)-2H-benzotriazole When in Example 5, the 2-nitro-2'-hydroxy-3',5'-di-tert-amylazobenzene was replaced by an equivalent amount of 2-nitro-5-chloro-2'-hydroxy-3'-tert-butyl-5'-methylazo-benzene and the 5% palladium on charcoal catalyst by a like amount of 5% rhodium on charcoal catalyst, the above noted product is obtained.
Example 9 2-(2-Hydroxy-3,5-di-tert-butylphenyl)-2H-benzotriazol2 When using the general procedure of ~xample 5, a 23% by weight suspension of 2-nitro-2'-hydroxy-3',5'-di-tert-butylazobenzene in isopropanol/triethylamine (1/0.18) was hydrogenated at 45C at 1 atmosphere for 3 hours in the , . ~ , .. .: . ., . : . .
. ." . - - - ~-. ::
., : . .. .. ::- . ~ .
107346:3 presence of 3/O of a 5% palladium on charcoal catalyst the above noted product was obtained in a yield of 77%.
Example 10 2-(2-Hydroxy-5-methylphenyl)-2H-benzotriazole When using the general procedure of Example 1, the organic solvent toluene was replaced by a trialkyl phosphate, the above noted product was obtained in good yield.
~ A suspension of 23.3 grams of 2-nitro-2'-hydroxy-5'-methylazobenzene in 80 grams of tributyl phosphate, 20 grams of methanol and 8 grams of diethylamine with 1.5 grams o~ 5~/0 palladium on charcoal catalyst was hydro-genated at 1 atmosphere for 55 minutes at a maximum tem-perature of 55C. The above noted product with a melting point of 129-130C was obtained in a yield of 80%.
When using the procedure listed above the tri-butyl phosphate was replaced by a like amount of triethyl phosphate and with no methanol being present, the above noted product (melting point 128-130C) was obtained in a yield of 76%.
- .. .~. . .- --; ,.. . ~, . :
: . . :",.. - . - . ~ .
10~ ~ 6 Example 11 2-(2-Hydroxy-5-methyl~-2H-benzotriazole When using the general procedure of Example 1 the toluene, methanol and diethylamine organic solvent mixture is replaced by a comparable weight of n-propyl-amine, the above noted product is obtained.
Example 12 2-(2-Hydroxy-3,5-di-tert-amylphenyl)-2H-benzotriazole When using the general procedure OL Example 5 the isopropanol and diethylamine organic solvent mixture is replaced by a comparable weight of morpholine, the above noted. -~: . :.
. : : . , : - , . : -
Claims (20)
1. A process for the production of 2-aryl-2H-benzotriazoles of the formula I
(I) wherein R1 is hydrogen or chlorine, R2 is hydrogen, chlorine, lower alkyl of 1 to 4 carbon atoms, lower alkoxy of 1 to 4 carbon atoms, carboal-koxy of 2 to 9 carbon atoms, carboxy or -SO3H, R3 is alkyl of 1 to 12 carbon atoms, alkoxy or 1 to 4 carbon atoms, phenyl, phenyl substituted with alkyl groups, said alkyl groups having 1 to 8 carbon atoms, cyclo-alkyl of 5 to 6 carbon atoms, carboalkoxy of 2 to 9 carbon atoms chlorine, carboxyethyl or arylalkyl of 7 to 9 carbon atoms, R4 is hydrogen, lower alkyl of 1 to 4 carbon atoms, lower alkoxy of 1 to 4 carbon atoms, chlorine or hydroxyl, and R5 is hydrogen, alkyl of 1 to 12 carbon atoms, chlorine, cycloalkyl of 5 to 6 carbon atoms or arylalkyl of 7 to 9 carbon atoms, which comprises reducing and cyclizing the corresponding o-nitro-azobenzene with hydrogen at a temperature in the range of from about 20°C to about 100°C and at a pressure in the range of from about 15 psig (1.05 kg/cm2, 1 atmosphere) to about 1000 psig (70 kg/cm2, 66 atmospheres) while mixed in an organic solvent mixture including an organic amine in a concentration of at least 0.1 mole of amine per mole of o-nitro-azobenzene in the presence of hydrogenation catalyst selected from the group consisting of the noble metals of Group VIII
of the Periodic Table, with the proviso that, when R1, R2, R3, R4 or R5 is chlorine, the hydrogenation catalyst cannot be palladium, and recovering the desired 2-aryl-2H-benzo-triazole.
(I) wherein R1 is hydrogen or chlorine, R2 is hydrogen, chlorine, lower alkyl of 1 to 4 carbon atoms, lower alkoxy of 1 to 4 carbon atoms, carboal-koxy of 2 to 9 carbon atoms, carboxy or -SO3H, R3 is alkyl of 1 to 12 carbon atoms, alkoxy or 1 to 4 carbon atoms, phenyl, phenyl substituted with alkyl groups, said alkyl groups having 1 to 8 carbon atoms, cyclo-alkyl of 5 to 6 carbon atoms, carboalkoxy of 2 to 9 carbon atoms chlorine, carboxyethyl or arylalkyl of 7 to 9 carbon atoms, R4 is hydrogen, lower alkyl of 1 to 4 carbon atoms, lower alkoxy of 1 to 4 carbon atoms, chlorine or hydroxyl, and R5 is hydrogen, alkyl of 1 to 12 carbon atoms, chlorine, cycloalkyl of 5 to 6 carbon atoms or arylalkyl of 7 to 9 carbon atoms, which comprises reducing and cyclizing the corresponding o-nitro-azobenzene with hydrogen at a temperature in the range of from about 20°C to about 100°C and at a pressure in the range of from about 15 psig (1.05 kg/cm2, 1 atmosphere) to about 1000 psig (70 kg/cm2, 66 atmospheres) while mixed in an organic solvent mixture including an organic amine in a concentration of at least 0.1 mole of amine per mole of o-nitro-azobenzene in the presence of hydrogenation catalyst selected from the group consisting of the noble metals of Group VIII
of the Periodic Table, with the proviso that, when R1, R2, R3, R4 or R5 is chlorine, the hydrogenation catalyst cannot be palladium, and recovering the desired 2-aryl-2H-benzo-triazole.
2. A process according to Claim 1 which further comprises removing the noble metal catalyst by filtration, distilling the organic solvents to recover the crude product, any purifying the crude product by removing amine impurities by acid extraction.
3. A process according to Claim 1 wherein the hydrogenation catalyst is selected from the group consist-ing of palladium, platinum and rhodium, and the organic solvent mixture consists of a water-miscible organic alco-hol or ether, optionally containing non-polar hydrocarbon solvent, with at least 0.1 mole of organic amine per mole of o-nitroazobenzene being reduced and cyclized.
4. A process according to Claim 1 wherein the hydro-genation catalyst is palladium.
5. A process according to Claim 4 characterized in that said palladium is composited on charcoal or alumina.
6. A process according to Claim 3 wherein the or-ganic solvent mixture comprises toluene and methanol and the water-soluble amine is diethylamine.
7. A process according to Claim 3 wherein the organic solvent comprises isopropanol and the water-soluble amine is diethylamine.
8. A process according to Claim 3 wherein at least 0.9 moles of organic amine per mole of o-nitroazobenzene intermediate is used.
9. A process according to Claim 4, for the pro-duction of a compound of formula I wherein R1 is hydrogen, R2 is hydrogen, lower alkyl of 1 to 2 carbon atoms, methoxy or carboxy, R3 is alkyl of 1 to 12 carbon atoms, cyclohexyl, phenyl, .alpha.-methylbenzyl or carboxyethyl, R4 is hydrogen, hydroxyl or methyl, and R5 is hydrogen, alkyl of 1 to 12 carbon atoms, cyclohexyl, benzyl or .alpha.-methylbenzyl.
10. A process according to Claim 4 for production of a compound of formula I wherein R1 is hydrogen, R2 is hydrogen, R3 is methyl, sec-butyl, tert-butyl, tert-amyl, tert-octyl, cyclohexyl or carboxyethyl, R4 is hydrogen, and R5 is hydrogen, methyl, tert-butyl, sec-butyl, tert-amyl, tert-octyl or .alpha.-methylbenzyl.
11. A process according to claim 4 for the production of 2-(2-hydroxy-5-methylphenyl)-2H-benzotriazole which comprises reducing and cyclizing 2-nitro-2'-hydroxy-5'-methylazobenzene.
12. A process according to claim 4 for the production of 2-(2-hydroxy-5-tert-octylphenyl)-2H-benzotriazole which comprises reducing and cyclizing 2-nitro-2'-hydroxy-5'-tert-octylazobenzene.
13. A process according to claim 4 for the production of 2-(2-hydroxy-3,5-di-tert-amylphenyl)-2H-benzotriazole which comprises reducing and cyclizing 2-nitro-2'-hydroxy-3',5'-di-tert-amylazobenzene.
14. A process according to claim 1 wherein the hydro-genation catalyst is rhodium.
15. A process according to claim 14 characterized in that said rhodium is composited on charcoal.
16. A process according to Claim 14 for the produc-tion of a compound of formula I wherein R1 is hydrogen, R2 is hydrogen, chlorine, lower alkyl of 1 to 2 carbon atoms, methoxy or carboxy, R3 is alkyl of 1 to 12 carbon atoms, cyclohexyl, phenyl, chlorine, .alpha.-methylbenzyl or carboxyethyl, R4 is hydrogen, hydroxyl or methyl and R5 is hydrogen, alkyl of 1 to 12 carbon atoms, chlorine, cyclohexyl, benzyl or .alpha.-methylbenzyl.
17. A process according to Claim 14 for the production of a compound of formula I wherein R1 is hydrogen, R2 is hydrogen or chlorine, R3 is methyl, sec-butyl, tert-butyl, tert-amyl, tert-octyl, methoxy, cyclohexyl, chlorine or carboxyethyl, R4 is hydrogen, and R5 is hydrogen, chlorine, methyl, tert-butyl, sec-butyl, tert-amyl, tert-octyl or .alpha.-methylbenzyl.
18. A process according to claim 3 for the production of 5-chloro-2-(2-hydroxy-3,5-di-tert-butylphenyl)-2H-benzotriazole which comprises reducing and cyclizing 2-nitro-5-chloro-2'-hydroxy-3'-5'-di-tert-butylazobenzene.
19. A process according to claim 3 for the production of 5-chloro-2-(2-hydroxy-3-tert-butyl-5-methylphenyl)-2H-benzotriazole which comprises reducing and cyclizing 2-nitro-5-chloro-2'-hydroxy-3'-tert-butyl-5'-methylazobenzene.
20. A process according to claim 1 wherein the hydrogenation catalyst is selected from the group consisting of palladium, platinum and rhodium, and the organic solvent consists essentially entirely of an organic aliphatic or alicyclic amine selected from the group consisting of n-propylamine, diethylamine, triethylamine, isopropyl-amine, n-butylamine, dibutylamine, tert-butylamine, amylamine and morpholine.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US57738575A | 1975-05-14 | 1975-05-14 | |
| US66834476A | 1976-03-19 | 1976-03-19 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1073463A true CA1073463A (en) | 1980-03-11 |
Family
ID=27077228
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA251,140A Expired CA1073463A (en) | 1975-05-14 | 1976-04-27 | Process for the production of 2-aryl-2h-benzotriazoles |
Country Status (2)
| Country | Link |
|---|---|
| CA (1) | CA1073463A (en) |
| IT (1) | IT1071653B (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4642350A (en) * | 1983-06-01 | 1987-02-10 | Ciba-Geigy Corporation | Novel process for preparation of benzotriazoles using aryldiols and quinones |
| US5104992A (en) * | 1989-01-31 | 1992-04-14 | Chemipro Kasei Kaisha, Ltd. | Method of preparing 2-phenyl benezothriazoles |
| US5187289A (en) * | 1989-01-31 | 1993-02-16 | Chemipro Kasei Kaisha, Ltd. | Method of preparing 2-phenyl benzotriazoles |
-
1976
- 1976-04-27 CA CA251,140A patent/CA1073463A/en not_active Expired
- 1976-05-13 IT IT2324276A patent/IT1071653B/en active
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4642350A (en) * | 1983-06-01 | 1987-02-10 | Ciba-Geigy Corporation | Novel process for preparation of benzotriazoles using aryldiols and quinones |
| US5104992A (en) * | 1989-01-31 | 1992-04-14 | Chemipro Kasei Kaisha, Ltd. | Method of preparing 2-phenyl benezothriazoles |
| US5187289A (en) * | 1989-01-31 | 1993-02-16 | Chemipro Kasei Kaisha, Ltd. | Method of preparing 2-phenyl benzotriazoles |
Also Published As
| Publication number | Publication date |
|---|---|
| IT1071653B (en) | 1985-04-10 |
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