CH615165A5 - Process for the preparation of 2-aryl-2H-benzotriazoles - Google Patents

Description

The invention relates to a process for the preparation of 2-aryl-2H-benzotriazoles and derivatives thereof, in which high yields of the desired products are obtained and problems of environmental pollution, as they involve previously known processes, are avoided.

So far, the conversion of an ortho-nitroazobenzene into the corresponding 2-aryl-2H-benzotriazole has been carried out by chemical or electrolytic reduction. For example, US Pat. Nos. 3,072,585 and 3,230,194, such as o-nitro-azobenzene derivatives, can be converted chemically with zinc in alcoholic sodium hydroxide solution into the corresponding 2-aryl-2H-benzotriazoles in good yields. Ammonium sulfide, alkali sulfide, zinc with ammonia at 80 to 25 100 ° C, sodium hydrosulfide and zinc with hydrochloric acid have also been used as chemical reducing agents for the conversion, see US Patent 2,362,988. The use of ammonium sulfide has been also from SN Chakrabarty et al, J. Indian Chem., Soc., 5, 555 (1928), Chem. Abst., 23, 836 30 (1929) reported with different results, depending on the presence or absence of substituents on the 2-aryl- Group. In some cases, the desired 2-aryl-2H-benzotriazoles were not formed at all as reduction products, rather only the corresponding o-aminoazo-35 benzenes.

H. Itomi, Mem. Coli describes the electrolytic reduction of o-nitroazobenzenes. Be. Kyoto Imp. Univ., 12A, No. 6, 343 (1929), Chem. Abst., 24, 2060 (1930), using a copper cathode in dilute sodium hydroxide solution. The 40 yields vary from 25 to 60% depending on the particular circumstances, with one major by-product being the corresponding o-aminoazobenzene.

The widely used zinc dust and sodium hydroxide chemical reduction system for converting o-nitroazo-benzenes into the corresponding 2-aryl-2H-benzotriazoles is described by K. Elbs, et al, J. Prakt. Chem., 108, 204 (1924), Chem. Abst., 19, 514 (1925). The yields of desired 2-aryl-2H-benzotriazoles vary from 30 to 85%, depending on the o-nitroazobenzene intermediate that is reduced. 50 The known chemical and electrolytic reduction processes for the production of 2-aryl-2H-benzotriazoles are often not practical or economical. The widespread zinc dust and sodium hydroxide system brings with it pollution problems, particularly the waste disposal of zinc sludge, which is increasingly coming up against environmental concerns.

The production in good yields of isomeric but chemically different IH-benzotriazoles by catalytic reduction in an alkaline medium from o-nitrophenylhydrazine and certain alkyl and per-fluoroalkyl derivatives thereof substituted on the phenyl ring is described in Japanese ÖS Sho 48-26012 dated 3.8.1973 . The isomeric 2H-benzotriazoles of the present invention cannot be prepared from phenylhydrazines 65.

The object of the invention was therefore to create a new process for the preparation of 2-aryl-2H-benzotriazoles which avoids the waste problems.

3rd

615 165

The aim was to produce 2-aiyl-2H-benzotriazoles by reduction and cyclization of the corresponding o-nitroazobenzenes under certain conditions, as specified in more detail below, high yields being obtained in acceptable purity. 5

The process for the preparation of 2- (2-hydroxy-5-methylphenyl) -2H-benzotriazole is characterized in that 2-nitro-2'-hydroxy-5'-methylazobenzene with hydrogen under reducing conditions in aqueous-alkaline Medium in the presence of a noble metal hydrogenation catalyst of group VIII of the periodic table reduced and cyclized, and the desired 2- (2-hydroxy-5-methylphenyl) -2H-ben-zotriazole isolated.

The process is characterized in that 2-Ni-tro-2'-hydroxy-5'-methylazobenzene is used with hydrogen at about 15 20 to about 100 ° C. and about 1 atmosphere to about 66 atmospheres in an aqueous alkaline medium in the presence of a noble metal hydrogenation catalyst of group VIII of the periodic table, filter the noble metal catalyst, bring the pH of the aqueous system below 10 to precipitate the desired product, and the desired 2- (2 - hydroxy-5-methylphenyl) -2H- benzotriazole isolated in the usual way.

The process according to the invention is carried out at temperatures from about 20 to about 100 ° C., in particular from about 30 to about 25 ° C. to 80 ° C., especially at about 40 to about 70 ° C.

A specific embodiment is a process for the preparation of 2- (2-hydroxy-5-methylphenyl) -2H-benzotriazole, characterized in that 2-nitro-2'-hydroxy-5'-methylazobenzene with hydrogen at about Treated 20 to about 100 ° C and about 1 to about 66 atmospheres in an aqueous alkaline medium in the presence of a palladium on activated carbon hydrogenation catalyst, and isolated the desired 2- (2-hydroxy-5-methylphenyl) -2H-benzotriazole .

The following description shows further embodiments.

The use of organic solvents in the catalytic reduction of 2-nitroazobenzenes to 2-aryl-2H-ben-zotriazoles has inherent disadvantages. One is economical because of the cost and recovery of the solvent, another is the known risk of using low-boiling solvents in the hydrogenation of nitro compounds.

To avoid organic solvents, the reduction of 2-nitro-2'-hydroxy-5'-methylazobenzene was carried out in an aqueous alkaline solution with sufficient sodium hydroxide to convert the water-insoluble azobenzene intermediate into the corresponding water-soluble sodium phenolate salt. Palladium on carbon is used as the hydrogenation catalyst. The reduction and cyclization is carried out at a hydrogen pressure of about 1 to about 5.7 atmospheres and about 20 to about 100 ° C. The pure product is isolated in yields of up to 77%. Higher pressures up to about 66 atmospheres can be used with the same result.

Some of the 2-nitro-2'-hydroxyazobenzene intermediates have such a combination of chemical and physical properties that they can be converted into the corresponding water-soluble alkali phenolate salts in a strongly aqueous alkaline solution. Other 2-nitro-2'-hydroxyazobenzene intermediates remain practically insoluble in these strongly aqueous alkaline solutions because of their more hydrocarbon nature. In order to ensure the close contact of catalyst, hydrogen and o-nitroazobenzene intermediate in this heterogeneous reaction, the use of a wetting or dispersing agent is necessary.

In the process according to the invention, dispersions in water are used in the case of 2-nitro-2'-hydroxyazobenzenes which are insoluble in strongly aqueous alkali solution. The term dispersion is used here to describe any fine distribution of the 2-nitro-2'-hydroxyazobenzenes. Dispersions are prepared by adding dispersants to the aqueous alkaline system with the 2-nitro-2'-hydroxyazobenzene in a concentration of 0.1 to 5% (weight), especially 0.5 to 3% dispersant. At the same time, strong stirring may be necessary. The vigorous stirring should be maintained after the noble metal catalyst is added and during the hydrogenation to maximize contact between the various components of this heterogeneous system.

Examples of dispersants are those from the following list (Ullmann, Encyclopedia of Industrial Chemistry, 3rd edition, volume 16, 1965, pages 724-741).

In the case of anionic surfactants, the anion is given. The cation is generally an alkali metal ion. In the case of the cationic surfactants, the cation is given. The anion is generally a chloride or methosulfate ion.

'In the following list mean:

R is a long chain alkyl,

R 'is a short chain alkyl or hydrogen,

x alkylene, e.g. - (CH2) „-, with n = 1-3.

Aionic surfactants

30th

a) salts of carboxylic acids r — coo ""

35 r-comi; ~ x-coo ~

r

Soap

40

^ CII-SO ^ NH-X- /

coo r

45 r-o-x-coo "r-» s ~ x-coo "

Modified soaps with links

2nd

20th

615 165

b) sulfuric acid ester f

R-CII-X-C

i ~ \

oso:

r-cii-x-c '

\

or 'O

hhr1

0s03

r-oso7

Sulphated oils and e) surfactants with less

Fatty acids

Sulphated esters

R-

common anionic groups o

II / O-

Alkyl phosphates Q- (various types)

Salts of alkylbenzene phosphonic acids

Sulphated amides

Cationic surfactants 15 a) Amine salts

■ + r — nu

R-C00-CH ~ CH-CHo-0S0 2 1 ^

Oh

R ~ cc: 3ii- ~ x-ono "R-0-X - 0S03

- Sulphated fatty acid monoglycerides and others

3rd

R - nh2-R '

Sulphated fatty acid alkyl amides

Sulfated ether

25 R-NH-R '

1.

Primary, secondary and tertiary amine salts c) alkyl sulfonates

R-

rr so3

cil -COOR

I 2

"O S-CII-COOR

rc00-x-50

3rd

R-CON-X-SO

R '

R

O

R-COO-X-NJIR ^

Simple alkyl sulfonates j_

*

Sulfosuccinic acid 35 R ~ CONII "-X-NIIR ^ esters

Intermediate link alkyl sulfonates

■ o-x-so-

d) alkylarylsulfonates R '

Alkylnaphthalene sulfonates

40

Primary, secondary and tertiary amine salts with pontics

R-O-X-NIIR ^

b) Quaternary ammonium salts

R1

i

R-n'-r *

l.

c) Phosphonium salts r:

R-P * '~ R' and

IV

(Also with pontics, as in the case of amine salts)

d) sulfonium salts

R *

lo.

R-S

i

R '

Alkylbenzosulfonates 65

5

615 165

Amphoteric surfactants

R «

! +

R-N-X-COO betaines

1

r> «

R1

l + -

R-N-X-SO.

Sulfobetaines

R '

R '

■ l +

R-N-X-O ^ SO.

Sulfate betaine

R *

25th

v Nonionic surfactants a) Ethylene oxide adducts

R ~ (O-CHo-CII-,) _-OH alkyl polyethylene - ** 11, glycols

30th

R

- (0-CII0-CII9) oil

R-CO (0-ClI2-CIl2) n-OII

Alkylphenyl poly ethylene glycols

Alcyl polyethylene glycols

H ~ (0-CH2 "CIÏ2> n- (0-CI ': - CIl2) m- (0-ClI2-C! L2) n ~ OH

Oxethylated polypropylene glycols

CII

3rd

b) Other non-ionic surfactants

R-COO-C II2-CII-CII 2-011 'fatty acid monoglycerides

R-COO-

011

c6IÏ13. ° 4

R-CONII-X-OII

R-CON - X-OII

\

r-coo-

X-OIÎ

C12H21 °

10th

Anhydrous sorbitol mono-fatty acid esters

Fatty acid OH alkyl amides

Sucrose mono fatty acid ester

Effective dispersants are the cationic, anionic and non-ionic types of compounds.

Preferred dispersants are long-chain amines, amine salts of long-chain acids, alkyl-polyethylene-glycols, alkylphenyl-polyethylene glycols, polyhydroxyalkyl-monoesters of fatty acids and the like. Examples are sorbitan mono-oleate, sorbitol monooleate, lauryl polyethylene glycol, p-dode-55 cylphenyl-polyethylene glycol, octadecylamine salts, diethylamine salts of myristic acid and the like. Particularly effective wetting agents are polyhydroxyalkyl monoesters of fatty acids, such as sorbitan monooleate (Span 80).

The catalysts which are used according to the invention to reduce the o-nitroazobenzenes to 2-aryl-2H-benzotriazoles are noble metals from group VIII of the periodic table, especially palladium, although other noble metals such as platinum, rhodium, ruthenium, osmium or Iridium can be used, not necessarily with an equivalent result. The metals can be used as such, as their oxides, or in particular on a solid support such as carbon, silicon oxide or aluminum oxide. Activated carbon is preferred as the carrier. Very small amounts of catalyst

615165

6

tor are required to perform the reductive cyclization, about 0.001 to 0.0015 mol / mol o-nitroazobenzene to be reduced. More catalyst can be used. Amounts above 0.005 mol / mol o-nitroazobenzene are generally neither necessary nor economically sensible.

The noble metal catalysts used according to the invention can generally be interchanged. However, there are some differences between the individual metals. If the o-nitroazobenzene starting material is substituted with chlorine, the use of a palladium catalyst in the reductive cyclization to give the 2-aryl-2H-benzotriazole also results in the chlorine being split off. However, if palladium is replaced by rhodium, a milder, more selective catalyst, a 2-aryl-2H-benzotriazole is obtained which still contains the chlorine. If the production of a 2-aryl-2H-benzotriazole, which contains chlorine in one or both aromatic rings, is intended, a rhodium catalyst should be used, a palladium catalyst should be avoided, rhodium on activated carbon is preferred.

As said, the reduction is carried out at about 20 to about 100 ° C and a pressure of about 1 to 66 atmospheres, and with sufficient aqueous alkaline solution to convert the hydroxy-substituted o-nitroazobenzenes into their corresponding water-soluble or water-dispersed alkaline To convert phenolate salts. The water-soluble alkaline phenolate salts are prepared by adding the respective hydroxy-substituted o-nitroazobenzene to an aqueous alkaline solution of sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium carbonate, potassium carbonate, ammonia, barium hydroxide, calcium hydroxide or the like. The alkaline solution preferably contains about 5 to 15% (weight) of sodium hydroxide in water. If this aqueous-alkaline solution is used, at the end of the reduction and cyclization reaction the catalyst can be filtered off and re-cyclized, if desired, while the desired 2-aiyl-2H-benzotriazole product in the aqueous solution as alkaline Salt remains in the case of the water-soluble salts.

In the case of alkaline phenolate salts dispersed in water, a suitable dispersant must be present in the system. In these cases, recovery of the catalyst requires precipitation of the crude 2-aryl-2H-benzotri-azole product, filtering off the crude product contaminated with the noble metal catalyst, dissolving the crude product in an organic solvent such as toluene, xylene, Pe- trol ether, cyclohexane, hexane, chlorobenzene, ethylene dichloride, and the like, and isolating the noble metal catalyst by filtration. The crude product in the organic solution is extracted with warm mineral acid, such as 70% sulfuric acid, and then recrystallized in the usual way.

Isolation of the product in good yields and acceptable purity is another feature of the invention. The aqueous alkali solution of the desired hydroxy-substituted 2-aryl-2H-benzotriazole salt, especially the sodium salt, is acidified with aqueous mineral acid, especially with sulfuric or hydrochloric acid, to a pH of 10 or below to give the desired hydroxy-substituted Precipitate 2-aryl-2H-benzotriazole as a crude product in yields of 75 to 90%. The crude product can be further purified to high purity and a yield of 70 to 80%. Various by-products are formed in traces during the reduction of o-nitroazobenzene, e.g. the corresponding o-aminoazobenzenes, o-aminohydrazobenzenes, o-phenylenediamine, anilines, aminophenols and 1,2,3-benzotriazoles. Most of these by-product impurities are removed with acid, especially with sulfuric acid, followed by an alcohol wash, especially with isopropanol, and finally a water wash of the crude 2H-ben-

zotriazole product. Alternatively, the crude product can be formed in an organic solvent, such as toluene, and the impurities are extracted with an aqueous acid solution, and the product is then isolated from the organic solution in a conventional manner.

The process according to the invention can be carried out in any suitable manner, either batchwise or continuously. E.g. using a batch process, an amount of the hydroxy-substituted o-nitroazo. io benzene, water, sufficient alkali such as sodium hydroxide to form the water-soluble or water-miscible alkaline phenolate salt, with the palladium on activated carbon catalyst, and dispersant, if necessary, placed in a suitable apparatus, such as in a chute 1- or Stirred autoclave. i5 Hydrogen is pressed in until the desired initial pressure is reached. The contents of the autoclave are then heated, if necessary, kept at the desired reaction temperature and with stirring / shaking until a little more than the theoretical amount of hydrogen has been absorbed. The excess pressure is then released and the aqueous alkaline solution, usually still warm, in the case of water-soluble alkaline phenolate salts, is filtered, in particular under an inert gas atmosphere, such as under nitrogen or argon, in order to remove catalyst. The solution is then cooled to room temperature and acidified with mineral acid solution to precipitate the desired crude hydroxy-substituted 2-aryl-2H-benzotriazole product, which may optionally be further purified by treating with aqueous acid and from a recrystallized organic solvent.

30 In the case of water-dispersed alkaline phenolate salts, the mixture is brought to room temperature and acidified with a mineral acid solution. The insoluble, hydroxy-substituted 2-aryl-2H-benzotriazole crude product containing the noble metal catalyst residue is then dissolved in a solvent such as toluene. The crude product solution is filtered to remove the catalyst residue. The raw product is further cleaned as above.

According to the invention, the 2-aryl-2H-benzotriazoles can also be prepared by continuous reduction and cyclization of o-nitroazobenzenes, although not necessarily with the same result. With continuous operation, e.g. the hydroxy-substituted o-nitroazobenzene starting material is premixed and dissolved or dispersed in aqueous alkaline solution. This solution or dispersion is continuously introduced into a reaction zone which is kept at the correct reaction temperature and pressure and which contains the hydrogenation catalyst.

Hydrogen is forced into the reaction zone through another such device. After the desired dwell time, the reactor effluent is continuously removed and acidified to isolate the desired product. Because of the type of catalyst used, a particularly effective way of carrying it out continuously is with a fixed catalyst bed with either a descending or ascending reaction solution. If it is desired to perform the reduction as a two-step process with different working temperatures for each step, two reaction zones can be used in series, each operating at the preferred temperature for the specific reduction step.

The reduction of o-nitroazobenzenes to the corresponding 2-aryl-2H-benzotriazoIen in a two-stage process is explained below.

7

615 165

N-N

Step 1

vi /

Very i f. t.

yf

Step 1 - The reduction of the o-nitrobenzene to the N-oxy-benzotriazole derivative is rapid and exothermic even at low temperature under the conditions according to the invention.

Step 2 - The reduction of the N-oxybenzotriazole intermediate to the corresponding 2-aryl-2H-benzotriazole product is slower. This reduction can be accelerated considerably by adding more catalyst, as well as by increasing the temperature, hydrogen pressure, or both.

In general, the reaction stops when the N-oxy intermediate is completely reduced to the corresponding 2-aryl-2H-benzotriazole. This makes it easy to control this catalytic hydrogenation. For some highly substituted benzotriazoles, the reduction should be stopped as soon as the appropriate amount of hydrogen has been absorbed and reacted to avoid further reductive cleavage of the 2-aryl-2H-benzotriazole produced.

55

In some cases, the reduction with Raney nickel at room temperature leads further than the desired benzotriazole product to the corresponding 4-, 5-, 6-, 7-tetrahy-drobenzotriazoles as undesired by-products.

The invention relates to a process for the preparation of compounds of the formula I.

615 165

8th

wherein

R! Is hydrogen or chlorine,

R2 hydrogen, chlorine, Ci-C4-alkyl, C1-C4-alkoxy, C2-C9-

Is carboalkoxy, carboxy or -SOsH,

R3 is Cj-C12-alkyl, CrC4-alkoxy, phenyl, phenyl-substituted with CrC8-alkyl, C5-C6-cycloalkyl, C2-C9-carboalkoxy, chlorine, carboxyethyl or C7-C9-arylalkyl, R.5 is hydrogen, C1 Is -C4 alkyl, Cj-C4 alkoxy, chlorine or hydroxy, and

R5 is hydrogen, C1-C12-alkyl, chlorine, C5-C6-cycloalkyl or Cy-Cg-arylalkyl.

R2 can be used as CrC4 alkyl e.g. be: methyl, ethyl or n-butyl. R2 can be used as CrC4 alkoxy e.g. be: methoxy, ethoxy or n-butoxy. R2 can be used as C2-C9 carboalkoxy e.g. be: carboni ethoxy, carboethoxy or carbo-n-octoxy.

R3 can be CrC12 alkyl, such as methyl, ethyl, sec-butyl, tert-butyl, amyl, tert-octyl or n-dodecyl. R3 can also be CrC4 alkoxy, such as methoxy, ethoxy or n-butoxy. R3 can also be phenyl substituted with CrC8 alkyl, such as methyl, tert-butyl, tert-amyl or tert-octyl. R3 can also be Cf) -C6 cycloalkyl, such as cyclopentyl or cyclohexyl. R3 can also be C2-C9 carboalkoxy, such as carbomethoxy, carboethoxy, carbo-n-butoxy or carbo-n-octoxy. R3 can also be C7-C9 arylalkyl, such as benzyl, a-methylbenzyl or a, a-dimethylbenzyl.

R4 can be CrC4 alkyl, such as methyl, ethyl or n-butyl. R4 can also be C1-C4 alkoxy, such as methoxy, ethoxy or n-butyloxy.

R5 can be C1-C12 alkyl, such as methyl, sec-butyl, tert-butyl, tert-amyl or tert-octyl. R5 can also be C5-C6 cycloalkyl, such as cyclopentyl or cyclohexyl. R5 can also be C7-C9 arylalkyl, such as benzyl, a-methylbenzyl or a, a-dimethylbenzyl.

Rx is preferably hydrogen.

R2 is preferably hydrogen, chlorine, C1-C2-alkyl, methoxy or carboxy.

R3 is preferably CrC12-alkyl, cyclohexyl, phenyl, chlorine, a-methylbenzyl or carboxyethyl.

R4 is preferably hydrogen, hydroxy or methyl. R5 is preferably hydrogen, chlorine, CrC8-alkyl, cyclohexyl, benzyl or a-methylbenzyl.

R2 is particularly preferably hydrogen or chlorine. R3 is particularly preferably methyl, tert-butyl, tert-amyl, tert-octyl, sec-butyl, cyclohexyl, chlorine or carboxyethyl. R4 is particularly preferably hydrogen.

R5 is particularly preferably hydrogen, chlorine, methyl, sec-butyl, tert-butyl, tert-amyl, tert-octyl or a-methylbenzyl.

The process involves the reduction of an o-nitroazo-benzene intermediate of formula II

Oh

\ R

NO

II

wherein Rj, R2, R3, R4 and R5 have the above meaning.

The o-nitroazobenzene intermediates are prepared by the corresponding o-nitroazobenzene diazonium compound of the formula III

wherein R 1 and R 2 have the above meaning and X is chloride, sulfate or another anion, in particular chloride, with a phenol of the formula IV

oh converts, which couples in the ortho position to hydroxy.

The o-nitrobenzene diazonium compounds are in turn obtained by customary diazotization with sodium nitrite in acid solution with the corresponding o-nitro-anilines of the formula V.

nh

NO

produced.

Some specific examples of compounds of the formulas IV and V are given for illustration. These are generally commercially available.

Compounds of formula IV

p-cresol

2,4-di-tert-butylphenol

2,4-di-tert-amylphenol

2,4-di-tert-octylphenol

2-tert-butyl-4-m ethylphenol

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-M ethoxyphenol

4-n-octylphenol

4-n-dodecylphenol

Resorcinol

5

10th

15

20th

25th

30th

35

40

45

50

55

60

65

9

615165

4- (oi-methylbenzyl) 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.

Preferred suitable compounds of formula IV 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 4-n-octylphenol 4-n-dodecylphenol resorcinol

2-sec-butyl-4-tert-butylphenol

2- (a-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-nitro aniline 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.

Preferred suitable compounds of formula V are: o-nitroaniline

4-chloro-2-nitroaniline.

The o-nitroazobenzene intermediates of formula II, wherein Rx is chlorine, R2 is chlorine, C1-C4-alkyl, C ^ C ^ alkoxy, C2-C9-carboalkoxy, R3 phenyl, phenyl substituted with CrCs-alkyl, CrC9-carboalkoxy , C7-C9 arylalkyl, C9-C12-alkyl, R4 is C1-C4-alkyl, CrC4-alkoxy or chlorine, and R5 C1-C12-alkyl, chlorine, C5-C6-cycloalkyl or C7-C9-aryl -alkyl is generally poor in solubility in aqueous alkaline solution. In the case of such intermediates, the use of a dispersing or wetting agent, as described above, is generally necessary in the process according to the invention.

The 2-aiyl-2H-benzotriazoles are widely used as dye intermediates, optical brighteners, blue fluorescent agents and selective UV light-absorbing stabilizers for the effective protection of fibers, films and various polymeric structures that are subject to destruction by UV radiation. These substances are important commercial products.

The 2-aryl-2H-benzotriazoles are complex organic molecules that require careful synthetic processes for their preparation in good yields and acceptable purity.

The invention relates to a process for the preparation of 2-aryl-2H-benzotriazoles. These are characterized by very low absorption in visible light and great light protection in various substrates. Particularly valuable stabilizers of this type are compounds with free hydroxy in the 2-position of the aryl, which is bonded to the 2-N atom of benzotriazole, and those in the 3- and 5- or 4- and 5-position Lower alkyl are substituted, and may be substituted by chlorine in the 5-position of the benzotriazole nucleus.

The description, preparation and use of these valuable substituted 2-aryl-2H-benzotriazoles is further described in US Patents 3,004,896,3,055,896, 3,072,585, 3,074,910, 3,189,615 and 3,230,194.

The following examples illustrate the process according to the invention without restricting the scope of the invention.

example 1

2- (2-Hydroxy-5-methylphenyl) -2H-benzotriazole In a 1 liter low-pressure stirred hydrogenation reactor, 85 g of 2-nitro-2'-hydroxy-5'-methylazobenzene ( contain 45% water) dissolved in 37.2 g 50% sodium hydroxide solution and 200 g water and 1.4 g 5% palladium on an activated carbon hydrogenation catalyst, suspended in 18. g water. The amount of catalyst is 3% based on the azobenzene intermediate. The reactor is purged several times with hydrogen and then depressurized with 5.7 atmospheres of hydrogen. The reactor is then heated to 38 to 40 ° C and the contents are stirred vigorously. Reduction begins and the first, very exothermic reduction stage of the azobenzene to the N-oxybenzo-triazole intermediate takes place. The temperature slowly rises to 56 to 58 ° C. It is kept at 58 to 60 ° C for the remaining reaction. Hydrogen uptake is monitored until no more hydrogen is absorbed. The hydrogen pressure in the reactor is maintained at 5.3 to 4.7 atmospheres during the reduction. A little more than the theoretical amount of hydrogen is absorbed. When the reduction of the azo-benzene intermediate to the desired 2-aryl-2H-benzotriazole is complete, the hydrogen absorption ceases. The duration of the reduction reaction is 2.5 hours. Then the remaining hydrogen is released from the reactor. A nitrogen atmosphere is placed over the reactor contents.

The reactor contents are filtered under nitrogen to remove the dispersed palladium on activated carbon catalyst. The separated catalyst is washed on the filter with a solution of 4 g of 50% sodium hydroxide solution and 16 g of water. This catalyst is then suitable for use in another hydrogenation reaction after further washing.

The combined highly alkaline filtrates containing the desired product are cooled to 50 ° C under nitrogen. 25 g of 70% sulfuric acid solution are slowly added to bring the pH of the system to below 10. The slurry of a yellow precipitate that forms is held at 65-70 ° C for 15 minutes. The yellow precipitate is then filtered off and washed successively with water at 65 to 70 ° C, with water at room temperature, with isopropanol and finally again with water. A yellow crude product is thus obtained in a yield after drying of 34.4 g (84% of theory).

The crude product can be further purified by washing a toluene solution of the crude product with warm sulfuric acid solution, followed by recrystallization from toluene and isopropanol to 31.5 g (77% of theory) of pure material.

Example 2

2- (2-Hydroxy-5-methylphenyl) -2H-benzotriazole If the substances according to Example 1 are reacted as there, but if 1 atmosphere of hydrogen is added to the reactor instead of 5.7 atmospheres, the yield of product is 2- (2 -Hydroxy - 5-methylphenyl) -2H-benzotriazole, comparable to that according to Example 1. The reduction time is 5 instead of 2.5 hours.

Example 3

2- (2-Hydroxy-5-methylphenyl) -2H-benzotriazole According to Example 1, but with the replacement of 5% palladium on activated carbon by an equivalent amount of 5% platinum

5

IQ

15

20th

25th

30th

35

40

45

50

55

60

65

615 165

10th

Activated carbon and 3.3 to 2 atmospheres of hydrogen pressure during the reaction, the yield of the desired product is 40% with a reduction time of 6 hours.

All of the azobenzene intermediate is consumed in this reduction. The yield of the desired product with platinum is only half that of the preferred noble metal catalyst palladium.

Example 4

2- (2-hydroxy-5-methylphenyl) -2H-benzotriazole

According to Example 4, replacing the 5% palladium on activated carbon with an equivalent amount of 5% rhodium on activated carbon, the yield of the desired product is 46% of theory with a reduction time of 5.7 hours and a reactor hydrogen pressure of 3.3 to 2 atmospheres throughout the reaction and at a reaction temperature of 50 to 80 ° C.

All of the azobenzene intermediate is consumed in this reduction. However, the yield of the desired product was considerably lower with rhodium than with the preferred palladium. The effectiveness of rhodium appears to be between palladium and platinum, somewhat closer to platinum for this specific product.

Example 5

2- (2-hydroxy-3,5-di-tert-amylphenyl) -2H-benzotriazole

According to Example 1 with an equivalent amount of 2-nitro-2'-hydroxy-3 ', 5'-di-tert-amylazobenzene instead of 2-nitro-2'-hy-dioxy-5'-methylazobenzene, are added in 2 parts 4% by weight 5% palladium on activated carbon catalyst based on the azobenzene intermediate, and 0.5% (weight) as wetting agent sorbitan monooleate (Span 80) to facilitate the dispersion and wetting of the insoluble azobenzene intermediate. The above product is obtained in 31.7% yield.

Example 6

2- (2-Hydroxy-5-tert-octylphenyl) -2H-benzotriazole According to Example 1, an equivalent amount of 2-nitro - 2'-hydroxy-5'-tert-octylazobenzoI instead of 2-nitro-2'-hydroxy- 5 -5'-methyl azobenzene used. The above product is obtained.

Example 7

5-chloro-2- (2-hydroxy-3,5-di-tert-butylphenyl) -10 -2H-benzotriazole

According to Example 1, 2-nitro-2'-hydroxy-5'-methylzo-benzene is replaced by an equivalent amount of 2-nitro-5-chloro-2'-hydroxy-3'.5'-di-tert-butylazobenzene and the 5% palladium on activated carbon catalyst is replaced by an equivalent amount of 5% 15 rhodium on activated carbon. It works in the presence of 0.5% dispersant sorbitan monooleate and the above product is obtained.

If the 5% palladium on activated carbon catalyst is used, the product is the deschloro compound 2- (2-hydro-2oxy-3,5-di-tert-butylphenyl) -2H-benzotriazole.

Example 8

5-chloro-2- (2-hydroxy-3-tert-butyl-5-methylphenyl) - 2H-benzotriazole 25 According to Example 1, the 2-nitro-2'-hydroxy-5'-methyl-azobenzene is replaced by an equivalent Amount of 2-nitro-5-chloro-2 '- hydroxy-3'-tert-butyl-5-methylazobenzene and the 5% palladium on activated carbon catalyst replaced by an equal amount of 5% rhodium on activated carbon. The above product is obtained when the reaction is carried out in the presence of 0.5% dispersant sorbitan monooleate.

v

Claims (8)

615 165 2. The method according to claim 1, characterized in that the o-nitroazobenzene forms a water-soluble alkaline phenolate salt in the aqueous alkaline medium, that the noble metal catalyst is filtered off after the reaction, the pH of the aqueous alkaline medium is reduced to below 10 to precipitate the desired product and isolated the 2-aryl-2H-benzotriazole. 2nd PATENT CLAIMS 1. Process for the preparation of 2-aryl-2H-benzotriazo-len of the formula I Oh Rt R4 is hydrogen and Rg is hydrogen, methyl, tert-butyl, sec-butyl, tert-amyl, tert-octyl or a-methylbenzyl. 9. The method according to claim 5, characterized in that 2- (2-hydroxy-2-methylphenyl) -2H-benzotriazole is prepared. 10. The method according to claim 5, characterized in that 2- (2-hydroxy-5-tert-octylphenyl) -2H-benzotriazole is prepared. wherein R is hydrogen or chlorine, R2 hydrogen, chlorine, CrC4-AlkyI, CrC4-alkoxy, C2-C9- Is carboalkoxy, carboxy or S03H, R; i is CrC12-alkyl, C1-C4-alkoxy, phenyl, phenyl substituted with CrC8-alkyl, C5-C6-cycloalkyl, C2-C9-carboalkoxy, chlorine, carboxyethyl or C7-C9-arylalkyl, R4 is hydrogen, Cj- Is C4-alkyl, CrC4-alkoxy, chlorine or hydroxy and Rr, hydrogen, Cj-C12-alkyl, chlorine, C5-C6-cycloalkyl or Is C7-C9 arylalkyl, characterized in that a corresponding o-Ni-tro-azobenzene with hydrogen at 20 to 100 ° C and 1 to 66 atmospheres in a mixture with an aqueous alkaline medium with a pH above 10 in the presence of a noble metal hydrogenation catalyst of Group VIII of the periodic table or an oxide thereof and cyclized, wherein at R1; R.>. R: î. R4 or R5 is chlorine, the hydrogenation catalyst is not palladium, and the 2-aryl-2H-benzotriazole is isolated. 3. The method according to claim 1, characterized in that the o-nitroazobenzene forms a water-dispersed alkaline phenolate salt in the aqueous-alkaline medium, which additionally contains a dispersant or a mixture of dispersants, and in that the pH of the aqueous-alkaline medium to below 10 after the reaction has ended, the crude product mixed with the noble metal catalyst is filtered off, the crude product is dissolved in an organic solvent, the noble metal catalyst is filtered off and the 2-aryl-2H-benzotriazole is isolated. 4. The method according to claim 1, characterized in that the hydrogenation catalyst is palladium, platinum or rhodium. 5. The method according to claim 1, characterized in that the hydrogenation catalyst is palladium. 6. The method according to claim 5, characterized in that the palladium sits on activated carbon. 7. The method according to claim 5, characterized in that one produces a compound of formula I, wherein Rj is hydrogen, R2 is hydrogen, CrC2-alkyl, methoxy or carboxy, R3 is Cj-Cg-alkyl, cyclohexyl, phenyl, a-methylbenzyl or Is carboxyethyl, R4 is hydrogen, hydroxy or methyl, and R5 is hydrogen, CrC8-alkyl, cyclohexyl, benzyl or a-methylbenzyl. 8. The method according to claim 5, characterized in that one produces a compound of formula I, wherein Rj is hydrogen, R2 is hydrogen, R3 methyl, sec-butyl, tert-butyl, tert-amyl, tert-octyl, cyclohexyl or carboxyethyl is