CA1117536A - Process for the preparation of 2-mercaptobenzothiazole - Google Patents
Process for the preparation of 2-mercaptobenzothiazoleInfo
- Publication number
- CA1117536A CA1117536A CA000325642A CA325642A CA1117536A CA 1117536 A CA1117536 A CA 1117536A CA 000325642 A CA000325642 A CA 000325642A CA 325642 A CA325642 A CA 325642A CA 1117536 A CA1117536 A CA 1117536A
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- CA
- Canada
- Prior art keywords
- nitrobenzene
- reaction
- carbon disulfide
- hydrogen sulfide
- reacting
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07D—HETEROCYCLIC COMPOUNDS
- C07D277/00—Heterocyclic compounds containing 1,3-thiazole or hydrogenated 1,3-thiazole rings
- C07D277/60—Heterocyclic compounds containing 1,3-thiazole or hydrogenated 1,3-thiazole rings condensed with carbocyclic rings or ring systems
- C07D277/62—Benzothiazoles
- C07D277/68—Benzothiazoles with hetero atoms or with carbon atoms having three bonds to hetero atoms with at the most one bond to halogen, e.g. ester or nitrile radicals, directly attached in position 2
- C07D277/70—Sulfur atoms
- C07D277/72—2-Mercaptobenzothiazole
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
- Thiazole And Isothizaole Compounds (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A process for the preparation of 2-mercaptobenzothiazole is disclosed. In a first embodiment the process comprises heating a reaction mixture comprising nitrobenzene and hydrogen sulfide in a molar ratio of from about 1:3 to about 1:6, respectively, to a temperature from about 100 to about 170°C, for a time sufficient to substantially reduce the nitrobenzene. Subsequently, the resultant product mixture is reacted with from about 1 to about 3 mol equivalents of carbon disulfide, based on the weight of the originally present nitrobenzene, at a temperature from about 200 to about 300°C for a time sufficient to convert at least a portion of the reactants into 2-mercaptobenzothiazole. Preferably, the water of reaction formed by reacting the nitrobenzene and hydrogen sulfide is removed prior to reacting the resultant product mixture with carbon disulfide. In an alternative embodiment, the process comprises reacting a mixture comprising nitrobenzene, hydrogen sulfide, and carbon disulfide in a molar ratio of about 1:3 to 6:1 to 3, at gradually increasing incremental temperatures which are above about 100°C and below about 170°C until the nitrobenzene is substantially reduced. Subsequently, the temperature is increased to at least about 200°C for a period of time sufficient to convert at least a portion of the reactants into 2-mercaptobenzothiazole.
A process for the preparation of 2-mercaptobenzothiazole is disclosed. In a first embodiment the process comprises heating a reaction mixture comprising nitrobenzene and hydrogen sulfide in a molar ratio of from about 1:3 to about 1:6, respectively, to a temperature from about 100 to about 170°C, for a time sufficient to substantially reduce the nitrobenzene. Subsequently, the resultant product mixture is reacted with from about 1 to about 3 mol equivalents of carbon disulfide, based on the weight of the originally present nitrobenzene, at a temperature from about 200 to about 300°C for a time sufficient to convert at least a portion of the reactants into 2-mercaptobenzothiazole. Preferably, the water of reaction formed by reacting the nitrobenzene and hydrogen sulfide is removed prior to reacting the resultant product mixture with carbon disulfide. In an alternative embodiment, the process comprises reacting a mixture comprising nitrobenzene, hydrogen sulfide, and carbon disulfide in a molar ratio of about 1:3 to 6:1 to 3, at gradually increasing incremental temperatures which are above about 100°C and below about 170°C until the nitrobenzene is substantially reduced. Subsequently, the temperature is increased to at least about 200°C for a period of time sufficient to convert at least a portion of the reactants into 2-mercaptobenzothiazole.
Description
~753~;
BACKGROUND OF T~IE INVEI~IION
~; The present invent;on relates to a new process for the preparation of 2-~ercaptobenzothiazole.
BACKGROUND OF T~IE INVEI~IION
~; The present invent;on relates to a new process for the preparation of 2-~ercaptobenzothiazole.
2-mercaptohenzothiazole was described for the first time 5 by A. W. Hofmann in the year 1887. Today, the compound, as well as its derivatives, the so-called "mercaptos", is made in large quantities and is one of the most important vulcanization acceler-`ators. Numerous syntheses and modes of formation are known. Themost important preparation processes are based on o~nitrochloro-benzene, hydrogen sulfide and carbon disulfide, or on aniline, ~sulfur and carbon disulfide (Ullmann, Encyclopedia of IndustrialChemistry, 3rd edition (1960), Urban & Schwarzenberg, publishers, Munich ~ Berlin, vol. 12, p. 304).
According to the older, discontinuous process; o-nitro chlorobenzene is first reacted with excess sodium hydrosulfide at ,about 100C to form 2-aminothiophenol. Subsequently, the reaction mixture is cooled, mixed with excess carbon disulfide, and again heated to about 80 - 90C. APter cooling, it is acidi~ied with l,sulfuric acid to precipitate the desired 2-mercaptobenzothiazole and the crude product is puri~ied via the calcium salt. In the foregoing process, the~yield is about 85% of theoretical.
. 11 jl According to the more recent, continuous process for the industrial preparation of 2 mercaptobenzothiazole, aniline is 'reacted wit~h a solution of sulfur in carbon disulfide at an ele-25lvated temperature (250 - 2850) and under a pressure of about 150 jbar~ In such a process, the cycliza~ion reaction is the step ,'de~ermining the velocity ancl it requires drastic conditions and ., .
, 7~i3~
. 1 the use of Cdtdlysis (e.t~. ptlosphorus or mercury and iodine com~
pounds). ~s a result of the reaction condi~ions, the resultiny crude mercaptobenzothiazo'le is contamindted ~lith tar-like by-prod-`ucts and must be purified through dissolution and subsequent precipitation with sulfuric acid. The yield of pure mercaptoben-zothiazole is only about ~0% of theoretical.
The concomitant use of a nitro or a nitroso compound, such as nitrobenzene, in the preparation of 2-mercaptobenzothia-`zole is also known. In the process described in U.S. Patent No.
2,001,587, aniline, carbon disulfide and nitrobenzene are heated for 6 hours at 220C in an autoclave. The carbon disulfide reacts with the aniline to form an addition product, and the nitrobenzene is needed instead of elemental su'lfur for the cyclization reac-tion, by which it is concurrently reduced to a nitrogen compound 15 ~with a lower valen~cy level. The reaction mixture is subsequently dissolved in sodium hydroxide, filtered, and mixed with hydrochlo-ric or sulfuric acid, which precipitates the 2-mercaptobenzothia-zole. Pursuant to the process of USSR Patent No. 179,306 (C.A.
,65, 22~ f (1966)), aniline, sulfur, nitrobenzene and carbon 20''disulfide are reacted with one another in a melt at elevated tem-perature and elevated pressure. In the synthesis, 2 mols of nitrobenzene are used per 5!mols of aniline but, in contrast to . .
the process pursuant to the present invention, the nitrobenzene is not utilized as the only initial aromatic compound and cyclization 25 ~component~ but as an oxid;z;ng a~ent. In the process~ the selec-tivity and yield are low and the reaction times are very long.
,~ A process for the preparation of 2-mercaptobenzothiazole 1.
has now been found, which is distinguished from prior art ~processes by milder reaction conditions, shorter reaction times and higher selectiv;ties and yield, . . .
' -2-~7~3~
~ SU~MARY OF TI~E II~VENTION
-There has now been discovered a process for the prepara~
tion of 2-mercaptobenzothiazole colllprising first heatiny a reac-tion mixture comprising nitrobenzene and hydrogen sulfide in a molar ratio of from about 1:3 to about 1:6, respectively, to a temperature from about 100 to about 170C, for a time sufficient to substantially reduce the nitrobenzene and subsequently reacting the resultant product mixture with from about 1 to about 3 mol equivalents of carbon disulfide~ based on the weight of the origi-nally present nitrobenzene, at a temperature from about 200 toabout 300C for a time sufficient to convert a-t least a portion of -the reactants into 2-mercaptobenzothiazole. Preferably the water of reaction formed by reacting the nitrobenzene and hydrogen sul-fide is removed prior to reacting the resulting product mixture with carbon disulfide.
In an alternative process for the preparation of 2-mer-captobenzothiazole, the process comprises reacting a mixture com-i~
- iprising nitrobenzene, hydrogen sulfide and carbon disulfide in a imolar ratio of about 1:3 to 6:1 to 3, at increasing temperatures which are above about 100C and below about 170C until the nitro-benzene is substantially reduced and subsequently increasing the temperature to at least about 200C for a period of time suffi-cient to convert at least a portion of the reactants into 2-mer-captobenzothiazole.
25i DET~ILED DESCRIPTION OF THE PREFERRED EM~ODIMENTS
¦' lt must be con:sidered surprising, that nitrobenzene can be transformed substantially quantitdtively to 2-nlercaptobenzo--- 'i . -3-S~6 thiazole with hydrogen sulficle and carbon disulfide. The reaction may be rel~resented by a summation fornlula, as follo~s:
~ ~2H2S + CS 2 ~ Sl-l t 2~20 ~ S~
However, the reaction is in fact much more complicated and is composed of a great number of individual reactions partly taking place concurrently and partly taking place sequentially. At any rate, it can be stated with certainty that an initial quantitative reduction of the nitrobenzene by hydrogen sulfide to aniline, which then reacts with carbon disulfide to 2-mercaptobenzothiazole in the known manner, is not possible. ~Jithout a catalyst, hydro-gen sulfide will noticeably reduce nitrobenzene only at tempera-tures above 150C. The main reaction product of nitrobenzene and hydrogen sulfide is indeed aniline, which is formed with a yield of about 75%, but at least ten more reaction products with aromat-ic nitrogen groupings are also formed thereby. When this mixture of products is subsequently reacted with carbon disulfide, one ~nevertheless obtains an almost quantitative ~ based on the charged nitrobenzene - yield of 2-mercaptobenzothiazole, thus a much higher yield than would correspond to the aniline content of the reaction mixture. It follows therefore, that, surprisingly~
~the other reaction products are also transformed into 2-mercapto-/benzothiazole. If the reduction of nitrobenzene with hydrogen sulfide is performed above about 170C, such as at about 200C, ~viscous, polymeric compounds are chiefly formed, the majority ofwhich would subsequently no longer be converted to 2-mercaptoben-zothiazole with carbon disulfide.
1 ~s already stated above, the stoichiometric ratio of the reactants, nitrobenzene, carbon clisulfide and hydrogen sulfide, is ,~ ~
.
~1~7536 1:2:1, respectively. EY~cesses of hydrogen sulfide and carbon ~disulfide exert a favorable influence on the selectivity of the reaction to 2-mercaptobenzoth;azole ancl on the purity of the latter. Therefore, 3 to 6 mols of hydrogen sulfide and 1 to 3 mols of carbon disulfide are charged per mo1 of nitrobenzene.
Preference is given to a molar ratio of nitrobenzene : hydrogen sulfide : carbon disulfide of about 1:3.2 to ~:1.2 to 2.2. Large excesses of hydrogen sulfide and carbon disulfide do not have an adverse effect on the reaction, but are not advisable for economic reasons.
The reactior, pressure is not critical and is determined by the partial pressures of the participants in the reaction at the selected conversion temperatures. As in all reactions deter-mined by mass transfer, the reaction time in the present case as well is pressure-dependent and, for example, by increasing the hydrogen sulfide pressure, it is possible to attain shorter reac-tion times. In general, however, reaction pressures which are too high will result in difficulties with the equipment and require `greater investments, so that part of the obtained advantage is lost again. It is possible to work withln a wide range of pres sures, beginning with about 1 bar, up to about 150 bar, typically from about 5 to about 100 bar, in particular from about 8 to about 15 bar. Preferably, the reactions are performed under the intrin-~sic partial pressures of the reactants.
25, In contrast to the reaction pressure, the reaction tem-l¦perature in the process pursuant to the present invention is ~.
~significant. Whereas at about 100C there is practically no ,reàction, above about 100C reduction of the nitrobenzene starts, '~at first slowly, and from 150C on progresses with adequate velo-30 "city, forming various nitrogen coMpounds with a lower oxidation l,number for the nitrogell atonl. If car~on disulfide is present:, a ., .
,~F~_ , 75~6 slight cyclization o~ thcse reductiorl products ~Jith the carbon ~disulfide ~lill simultaneously occur as ~lell. It is essential for the invention~ that the reaction temperature does not rise above about 170C before the nitrobenzene has been substantially reduced. Otherwise, tarry by-products ~lill occur, which are of course detrimental to the yield and purity of 2-mercaptobenzothia-zole. Above about 170C, in particular from about 200C on, cyclization of the reaction products to 2~mercaptobenzothiazole will take place in a relatively fast reaction. Preferably, use is at first, as during reaction of the nitrobenzene with hydrogen sulfide, made of temperatures from about 150 to about 170C, and subsequently, as during reaction of the resulting reaction mixture with carbon disulfide, of temperatures from about 200 to about 250C. Higher temperatures, up to about 350C, can also be used durins cyclization, but are not economically or otherwise advise-able because at such high temperatures there will be losses in ,yield due to continuing reaction of the 2-mercaptobenzothiazole.
¦I No general statement may be made concerning the reaction ,time, since it depends upon a number of factors, such as the 20lstoichiometric ratio of the reaction components, the reaction ,pressure, reaction temperature and~ in particular, the stirring ,velocity. The end of the reaction can easily be determined from the fact that the reaction pressure remains constant. This is so, Ilbecause first the pressure drops because of the consumption of 25 lhydrogen sulfide, and then rises again, from 200C on, due to the l~starting of the cyclization reaction and the re-formation of hydrogen sulfide connected therewith. After complete conversion of the nitrobenzene to 2-mercaptobenzothiazole9 or after complete ~conversion o;F the reaction products of nitrobenzene and hydrogen ~ .
~1 , ~753~
sulfide with carbon ~isulfi(le, Tthe prt~ssure ~inally remains constant and is only ~ Function of the temperatlJre.
The process pursuant to the present invention is excep-tionally well suited for the industrial preparation of 2-mercapto-benzothiazole dnd may be per~ormed discontinuolJsly, as well ascontinuously. Compared with the known industrial processes, the process has several advantages. It is distinguished by the Fact that no catalysts are needed, but shorter reaction times are nevertheless attained. Beyond that, one obtains quantitative conversions and substantially higher yields than with the known processes. In an economic and processing-technological respect, it is especially aclvantageous that no additional auxiliary chemi-cals and no undesirable and unusable waste or by products result, and that the process may be carried out at relatively low pres-sures. The sulfur accumulating as a by-product in the process can be utilized in the production of carbon disulfide, while the ~required hydrogen sulfide is again obtained as a by-product in in carbon disulfide production. And finally it must also be pointed out that, in the process pursuant to the present inven-tion, 2-mercaptobenzothia~ole is obtained with high purity, so that its purification is unnecessary. Thus, the auxiliary chemicals requirecl in the known process are not needed and the flows of waste resulting therefrom do not occur.
Examples 1 to ~
., Af~er the air contained in a reaction vessel is dis-;placed by hydrogen sulFide, the vessel (1 - 2 1it. Glass autoclave with bottom discharge valve and manometer, or 100 ml No. 316 stainless steel autoclave with gas supply tube, flo~ breaker, manolTIeter and magnetic stirrer, as well as gas discharge valve) is cha~ged with the appropriate quantity of carbon disulfide and 7~36 nitrobenzene ancl the vegsel carefully closed. Subseyuently, the desired quantity of hydro~en sulfide is forced into the reaction veqsel and the solution heated to 160 - 170C. When no further hydrogen sulfide consumption can be determined tdrop in pressure), the reaction mixture is heated to 240 -250C with vigorous gtirring. ~fter the reaction comes to an end (constant H2S pressure), the reaction vessel pressure is released and the discharged gas investigated gas-chromato-graphically. The reactor is now emptied, either by removing the reaction mixture at 150 - 180C through the bottom discharge valve in the form of a melt, or by suspending the reaction mix-ture in methanol after it has been cooled to room temperature and separating the formed sulfur from the 2-mercaptobenzo-thiazole by filtration. After removal of the methanol, the purity of the formed MBT is determined titrimetrically and chromatographically (HPLC). Additional purification of the 2-mercaptobenæothiazole (as by reprecipitation via its alkali salt) is not necessary. Polymeric products, such as are formed when aniline or o-chloronitrobenzene are used, does not occur.
me processing conditions, as well as the obtained yields are compiled in Table 1. The yields refer to pure 2-mercaptobenzothiazole, and are determined by means of acidi-metric and argentometric titration~
Examples 6 to 8 show the significant influence of the reaction temperature in the process pursuant to the inven-tion.
Example 9 12031 g (100 mmol) of nitrobenzene are reacted with 12.6 g (369 mmol) of hydrogen sulfide, in the equipment des-cribed for Examples 1 to 8, at 165C and 16 ba~ in the course of 3 hours. The reaction rate is 100%. Among other things, the mixture contain.s 77% of the theoretical amount of aniline and 86.5% of the th00retical amount of sulfur. Subsequently, 13.3 g of (174 mmol) carbon disulfide are added to the mixture, which is heated to 245C at 20 bar for 30 minutes. Ihe conver-sion rate is lC0%. ~e yield is 96.2% of the khéoretical amount of 2-mercaptobenzothiazole 99.5% of the theoretical amount of sulfur, 1.0% of the theoretical amount of benzothiazole and 1.2% of the theoretical amount of 2-anilinobenzothiazole.
Example 10 For one hour, 14.7 g (119 mmol3 of nitrobenzene and 12.6 g (369 mmol) of hydrogen sulfide are reacted with one another at 165C and 15 bar in the equipment described for Ex-amples 1 to 8. A~Tong other things, the mixture contains 74%
of the theoretical amount of aniline and 92% of the theoretical amount of sulfur. It is subsequently heated for 30 minutes with 13.3 ml (16.7 g = 220 mmol) of carbon disulfide at 250~C
and 19 bar. me conversion rate is 100% theoretical. The yield is 98% of the theoretical amount of 2-mercaptobenzo-thiazole, 100% of the theoretical amount of sulfur, 0.5% of the theoretical amount of benzothiazole and 0.5% of the theoretical amount of analinobenzothiazole.
Example 11 12.31 g (100 mmol) of nitrobenzene are reacted with 11.4 g (334 mmol) of hydrogen sulfide for one hour at 168 to 170C in the equipment described for Examples 1 to 8. A
maximum pressure of 17 bar comes about thereby. Subsequently, the reaction vessel pressure is released while the reactor is hot, and the water of reaction (3.6 g = 200 mmol) is removed by fractionation. The gas discharge valve is closed again and 8~37 g (6.65 ml = 110 mmol) Oe carbon disulfide are metered into the reaction vessel, followed by heating to 250C for 45 _9_ 53~;
minutes with vigorous stirring. Processing of the reaction mix-ture is carried out in the manner described for Exarnples 1 to 8. The conversion rate is 100% of theoretical, the yield of sulfur 99.8% of theoretical and that of 2-mercaptobenzothiazole 97.9% of theoretical. In addition, 0.2% of the theoretical amount of benzothiazole and 1.6% of the theoretical amount of anilinobenzothiazole is formed.
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According to the older, discontinuous process; o-nitro chlorobenzene is first reacted with excess sodium hydrosulfide at ,about 100C to form 2-aminothiophenol. Subsequently, the reaction mixture is cooled, mixed with excess carbon disulfide, and again heated to about 80 - 90C. APter cooling, it is acidi~ied with l,sulfuric acid to precipitate the desired 2-mercaptobenzothiazole and the crude product is puri~ied via the calcium salt. In the foregoing process, the~yield is about 85% of theoretical.
. 11 jl According to the more recent, continuous process for the industrial preparation of 2 mercaptobenzothiazole, aniline is 'reacted wit~h a solution of sulfur in carbon disulfide at an ele-25lvated temperature (250 - 2850) and under a pressure of about 150 jbar~ In such a process, the cycliza~ion reaction is the step ,'de~ermining the velocity ancl it requires drastic conditions and ., .
, 7~i3~
. 1 the use of Cdtdlysis (e.t~. ptlosphorus or mercury and iodine com~
pounds). ~s a result of the reaction condi~ions, the resultiny crude mercaptobenzothiazo'le is contamindted ~lith tar-like by-prod-`ucts and must be purified through dissolution and subsequent precipitation with sulfuric acid. The yield of pure mercaptoben-zothiazole is only about ~0% of theoretical.
The concomitant use of a nitro or a nitroso compound, such as nitrobenzene, in the preparation of 2-mercaptobenzothia-`zole is also known. In the process described in U.S. Patent No.
2,001,587, aniline, carbon disulfide and nitrobenzene are heated for 6 hours at 220C in an autoclave. The carbon disulfide reacts with the aniline to form an addition product, and the nitrobenzene is needed instead of elemental su'lfur for the cyclization reac-tion, by which it is concurrently reduced to a nitrogen compound 15 ~with a lower valen~cy level. The reaction mixture is subsequently dissolved in sodium hydroxide, filtered, and mixed with hydrochlo-ric or sulfuric acid, which precipitates the 2-mercaptobenzothia-zole. Pursuant to the process of USSR Patent No. 179,306 (C.A.
,65, 22~ f (1966)), aniline, sulfur, nitrobenzene and carbon 20''disulfide are reacted with one another in a melt at elevated tem-perature and elevated pressure. In the synthesis, 2 mols of nitrobenzene are used per 5!mols of aniline but, in contrast to . .
the process pursuant to the present invention, the nitrobenzene is not utilized as the only initial aromatic compound and cyclization 25 ~component~ but as an oxid;z;ng a~ent. In the process~ the selec-tivity and yield are low and the reaction times are very long.
,~ A process for the preparation of 2-mercaptobenzothiazole 1.
has now been found, which is distinguished from prior art ~processes by milder reaction conditions, shorter reaction times and higher selectiv;ties and yield, . . .
' -2-~7~3~
~ SU~MARY OF TI~E II~VENTION
-There has now been discovered a process for the prepara~
tion of 2-mercaptobenzothiazole colllprising first heatiny a reac-tion mixture comprising nitrobenzene and hydrogen sulfide in a molar ratio of from about 1:3 to about 1:6, respectively, to a temperature from about 100 to about 170C, for a time sufficient to substantially reduce the nitrobenzene and subsequently reacting the resultant product mixture with from about 1 to about 3 mol equivalents of carbon disulfide~ based on the weight of the origi-nally present nitrobenzene, at a temperature from about 200 toabout 300C for a time sufficient to convert a-t least a portion of -the reactants into 2-mercaptobenzothiazole. Preferably the water of reaction formed by reacting the nitrobenzene and hydrogen sul-fide is removed prior to reacting the resulting product mixture with carbon disulfide.
In an alternative process for the preparation of 2-mer-captobenzothiazole, the process comprises reacting a mixture com-i~
- iprising nitrobenzene, hydrogen sulfide and carbon disulfide in a imolar ratio of about 1:3 to 6:1 to 3, at increasing temperatures which are above about 100C and below about 170C until the nitro-benzene is substantially reduced and subsequently increasing the temperature to at least about 200C for a period of time suffi-cient to convert at least a portion of the reactants into 2-mer-captobenzothiazole.
25i DET~ILED DESCRIPTION OF THE PREFERRED EM~ODIMENTS
¦' lt must be con:sidered surprising, that nitrobenzene can be transformed substantially quantitdtively to 2-nlercaptobenzo--- 'i . -3-S~6 thiazole with hydrogen sulficle and carbon disulfide. The reaction may be rel~resented by a summation fornlula, as follo~s:
~ ~2H2S + CS 2 ~ Sl-l t 2~20 ~ S~
However, the reaction is in fact much more complicated and is composed of a great number of individual reactions partly taking place concurrently and partly taking place sequentially. At any rate, it can be stated with certainty that an initial quantitative reduction of the nitrobenzene by hydrogen sulfide to aniline, which then reacts with carbon disulfide to 2-mercaptobenzothiazole in the known manner, is not possible. ~Jithout a catalyst, hydro-gen sulfide will noticeably reduce nitrobenzene only at tempera-tures above 150C. The main reaction product of nitrobenzene and hydrogen sulfide is indeed aniline, which is formed with a yield of about 75%, but at least ten more reaction products with aromat-ic nitrogen groupings are also formed thereby. When this mixture of products is subsequently reacted with carbon disulfide, one ~nevertheless obtains an almost quantitative ~ based on the charged nitrobenzene - yield of 2-mercaptobenzothiazole, thus a much higher yield than would correspond to the aniline content of the reaction mixture. It follows therefore, that, surprisingly~
~the other reaction products are also transformed into 2-mercapto-/benzothiazole. If the reduction of nitrobenzene with hydrogen sulfide is performed above about 170C, such as at about 200C, ~viscous, polymeric compounds are chiefly formed, the majority ofwhich would subsequently no longer be converted to 2-mercaptoben-zothiazole with carbon disulfide.
1 ~s already stated above, the stoichiometric ratio of the reactants, nitrobenzene, carbon clisulfide and hydrogen sulfide, is ,~ ~
.
~1~7536 1:2:1, respectively. EY~cesses of hydrogen sulfide and carbon ~disulfide exert a favorable influence on the selectivity of the reaction to 2-mercaptobenzoth;azole ancl on the purity of the latter. Therefore, 3 to 6 mols of hydrogen sulfide and 1 to 3 mols of carbon disulfide are charged per mo1 of nitrobenzene.
Preference is given to a molar ratio of nitrobenzene : hydrogen sulfide : carbon disulfide of about 1:3.2 to ~:1.2 to 2.2. Large excesses of hydrogen sulfide and carbon disulfide do not have an adverse effect on the reaction, but are not advisable for economic reasons.
The reactior, pressure is not critical and is determined by the partial pressures of the participants in the reaction at the selected conversion temperatures. As in all reactions deter-mined by mass transfer, the reaction time in the present case as well is pressure-dependent and, for example, by increasing the hydrogen sulfide pressure, it is possible to attain shorter reac-tion times. In general, however, reaction pressures which are too high will result in difficulties with the equipment and require `greater investments, so that part of the obtained advantage is lost again. It is possible to work withln a wide range of pres sures, beginning with about 1 bar, up to about 150 bar, typically from about 5 to about 100 bar, in particular from about 8 to about 15 bar. Preferably, the reactions are performed under the intrin-~sic partial pressures of the reactants.
25, In contrast to the reaction pressure, the reaction tem-l¦perature in the process pursuant to the present invention is ~.
~significant. Whereas at about 100C there is practically no ,reàction, above about 100C reduction of the nitrobenzene starts, '~at first slowly, and from 150C on progresses with adequate velo-30 "city, forming various nitrogen coMpounds with a lower oxidation l,number for the nitrogell atonl. If car~on disulfide is present:, a ., .
,~F~_ , 75~6 slight cyclization o~ thcse reductiorl products ~Jith the carbon ~disulfide ~lill simultaneously occur as ~lell. It is essential for the invention~ that the reaction temperature does not rise above about 170C before the nitrobenzene has been substantially reduced. Otherwise, tarry by-products ~lill occur, which are of course detrimental to the yield and purity of 2-mercaptobenzothia-zole. Above about 170C, in particular from about 200C on, cyclization of the reaction products to 2~mercaptobenzothiazole will take place in a relatively fast reaction. Preferably, use is at first, as during reaction of the nitrobenzene with hydrogen sulfide, made of temperatures from about 150 to about 170C, and subsequently, as during reaction of the resulting reaction mixture with carbon disulfide, of temperatures from about 200 to about 250C. Higher temperatures, up to about 350C, can also be used durins cyclization, but are not economically or otherwise advise-able because at such high temperatures there will be losses in ,yield due to continuing reaction of the 2-mercaptobenzothiazole.
¦I No general statement may be made concerning the reaction ,time, since it depends upon a number of factors, such as the 20lstoichiometric ratio of the reaction components, the reaction ,pressure, reaction temperature and~ in particular, the stirring ,velocity. The end of the reaction can easily be determined from the fact that the reaction pressure remains constant. This is so, Ilbecause first the pressure drops because of the consumption of 25 lhydrogen sulfide, and then rises again, from 200C on, due to the l~starting of the cyclization reaction and the re-formation of hydrogen sulfide connected therewith. After complete conversion of the nitrobenzene to 2-mercaptobenzothiazole9 or after complete ~conversion o;F the reaction products of nitrobenzene and hydrogen ~ .
~1 , ~753~
sulfide with carbon ~isulfi(le, Tthe prt~ssure ~inally remains constant and is only ~ Function of the temperatlJre.
The process pursuant to the present invention is excep-tionally well suited for the industrial preparation of 2-mercapto-benzothiazole dnd may be per~ormed discontinuolJsly, as well ascontinuously. Compared with the known industrial processes, the process has several advantages. It is distinguished by the Fact that no catalysts are needed, but shorter reaction times are nevertheless attained. Beyond that, one obtains quantitative conversions and substantially higher yields than with the known processes. In an economic and processing-technological respect, it is especially aclvantageous that no additional auxiliary chemi-cals and no undesirable and unusable waste or by products result, and that the process may be carried out at relatively low pres-sures. The sulfur accumulating as a by-product in the process can be utilized in the production of carbon disulfide, while the ~required hydrogen sulfide is again obtained as a by-product in in carbon disulfide production. And finally it must also be pointed out that, in the process pursuant to the present inven-tion, 2-mercaptobenzothia~ole is obtained with high purity, so that its purification is unnecessary. Thus, the auxiliary chemicals requirecl in the known process are not needed and the flows of waste resulting therefrom do not occur.
Examples 1 to ~
., Af~er the air contained in a reaction vessel is dis-;placed by hydrogen sulFide, the vessel (1 - 2 1it. Glass autoclave with bottom discharge valve and manometer, or 100 ml No. 316 stainless steel autoclave with gas supply tube, flo~ breaker, manolTIeter and magnetic stirrer, as well as gas discharge valve) is cha~ged with the appropriate quantity of carbon disulfide and 7~36 nitrobenzene ancl the vegsel carefully closed. Subseyuently, the desired quantity of hydro~en sulfide is forced into the reaction veqsel and the solution heated to 160 - 170C. When no further hydrogen sulfide consumption can be determined tdrop in pressure), the reaction mixture is heated to 240 -250C with vigorous gtirring. ~fter the reaction comes to an end (constant H2S pressure), the reaction vessel pressure is released and the discharged gas investigated gas-chromato-graphically. The reactor is now emptied, either by removing the reaction mixture at 150 - 180C through the bottom discharge valve in the form of a melt, or by suspending the reaction mix-ture in methanol after it has been cooled to room temperature and separating the formed sulfur from the 2-mercaptobenzo-thiazole by filtration. After removal of the methanol, the purity of the formed MBT is determined titrimetrically and chromatographically (HPLC). Additional purification of the 2-mercaptobenæothiazole (as by reprecipitation via its alkali salt) is not necessary. Polymeric products, such as are formed when aniline or o-chloronitrobenzene are used, does not occur.
me processing conditions, as well as the obtained yields are compiled in Table 1. The yields refer to pure 2-mercaptobenzothiazole, and are determined by means of acidi-metric and argentometric titration~
Examples 6 to 8 show the significant influence of the reaction temperature in the process pursuant to the inven-tion.
Example 9 12031 g (100 mmol) of nitrobenzene are reacted with 12.6 g (369 mmol) of hydrogen sulfide, in the equipment des-cribed for Examples 1 to 8, at 165C and 16 ba~ in the course of 3 hours. The reaction rate is 100%. Among other things, the mixture contain.s 77% of the theoretical amount of aniline and 86.5% of the th00retical amount of sulfur. Subsequently, 13.3 g of (174 mmol) carbon disulfide are added to the mixture, which is heated to 245C at 20 bar for 30 minutes. Ihe conver-sion rate is lC0%. ~e yield is 96.2% of the khéoretical amount of 2-mercaptobenzothiazole 99.5% of the theoretical amount of sulfur, 1.0% of the theoretical amount of benzothiazole and 1.2% of the theoretical amount of 2-anilinobenzothiazole.
Example 10 For one hour, 14.7 g (119 mmol3 of nitrobenzene and 12.6 g (369 mmol) of hydrogen sulfide are reacted with one another at 165C and 15 bar in the equipment described for Ex-amples 1 to 8. A~Tong other things, the mixture contains 74%
of the theoretical amount of aniline and 92% of the theoretical amount of sulfur. It is subsequently heated for 30 minutes with 13.3 ml (16.7 g = 220 mmol) of carbon disulfide at 250~C
and 19 bar. me conversion rate is 100% theoretical. The yield is 98% of the theoretical amount of 2-mercaptobenzo-thiazole, 100% of the theoretical amount of sulfur, 0.5% of the theoretical amount of benzothiazole and 0.5% of the theoretical amount of analinobenzothiazole.
Example 11 12.31 g (100 mmol) of nitrobenzene are reacted with 11.4 g (334 mmol) of hydrogen sulfide for one hour at 168 to 170C in the equipment described for Examples 1 to 8. A
maximum pressure of 17 bar comes about thereby. Subsequently, the reaction vessel pressure is released while the reactor is hot, and the water of reaction (3.6 g = 200 mmol) is removed by fractionation. The gas discharge valve is closed again and 8~37 g (6.65 ml = 110 mmol) Oe carbon disulfide are metered into the reaction vessel, followed by heating to 250C for 45 _9_ 53~;
minutes with vigorous stirring. Processing of the reaction mix-ture is carried out in the manner described for Exarnples 1 to 8. The conversion rate is 100% of theoretical, the yield of sulfur 99.8% of theoretical and that of 2-mercaptobenzothiazole 97.9% of theoretical. In addition, 0.2% of the theoretical amount of benzothiazole and 1.6% of the theoretical amount of anilinobenzothiazole is formed.
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Claims (9)
1. A process for the preparation of 2-mercaptobenzo-thiazole comprising heating a reaction mixture comprising nitro-benzene and hydrogen sulfide in a molar ratio of from about 1:3 to about 1:6, respectively, to a temperature from about 100 to about 170°C, for a time sufficient to substantially reduce the nitrobenzene, and subsequently reacting the resultant product mixture with from about 1 to about 3 mol equivalents of carbon disulfide, based on the weight of the originally present nitrobenzene, at a temperature from about 200 to about 300°C for a time sufficient to convert at least a portion of the reac-tants into 2-mercaptobenzothiazole.
2. The process of claim 1 wherein the water of reaction formed by reacting the nitrobenzene and hydrogen sulfide is removed prior to reacting the resulting product mixture with carbon disulfide.
3. The process of claim 1 or 2 wherein the reaction is performed at a pressure from about 5 to about 100 bar.
4. The process of claim 1 or 2 wherein the reaction is performed at a pressure from about 8 to 15 bar.
5. The process of claim 1 or 2 wherein the molar ratio of nitrobenzene:hydrogen sulfide:carbon disulfide is about 1:3.2 to 1:1.2 to 2.2.
6. A process for the preparation of 2-mercaptobenzo-thiazole comprising reacting a mixture comprising nitrobenzene, hydrogen sulfide, and carbon disulfide in a molar ratio of about 1:3 to 6:1 to 3, at increasing temperatures which are above about 100°C and below about 170°C until the nitrobenzene is substantially reduced and subsequently increasing the temper-ature to at least about 200°C for a period of time sufficient to convert at least a portion of the reactants into 2-mercapto-benzothiazole.
7. The process of claim 6 wherein the molar ratio of nitrobenzene:hydrogensulfide:carbon disulfide is about 1:3.2 to 4:1.2 to 2.2.
8. The process of claim 6 or 7 wherein the reaction is performed under the intrinsic partial pressure of the reactants.
9. The process of claim 6 or 7 wherein the reaction is initially performed at temperatures from about 150 to about 170°C until the nitrobenzene is substantially reduced and is subsequently performed at temperatures from about 200 to about 250°C.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP2816503.9 | 1978-04-15 | ||
| DE19782816503 DE2816503C3 (en) | 1978-04-15 | 1978-04-15 | Process for the preparation of 2-mercaptobenzothiazole |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1117536A true CA1117536A (en) | 1982-02-02 |
Family
ID=6037124
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000325642A Expired CA1117536A (en) | 1978-04-15 | 1979-04-12 | Process for the preparation of 2-mercaptobenzothiazole |
Country Status (2)
| Country | Link |
|---|---|
| CA (1) | CA1117536A (en) |
| DE (1) | DE2816503C3 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5367082A (en) * | 1990-09-07 | 1994-11-22 | Akzo N.V. | Process for the preparation of 2-mercaptobenzothiazole |
| DE4028473A1 (en) * | 1990-09-07 | 1992-03-12 | Akzo Gmbh | METHOD FOR PRODUCING 2-MERCAPTO-BENZOTHIAZOL |
-
1978
- 1978-04-15 DE DE19782816503 patent/DE2816503C3/en not_active Expired
-
1979
- 1979-04-12 CA CA000325642A patent/CA1117536A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| DE2816503C3 (en) | 1981-09-17 |
| DE2816503B2 (en) | 1980-10-16 |
| DE2816503A1 (en) | 1979-10-18 |
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