Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2000-02-24
2001-04-24
Stockton, Laura L. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
active
06222041
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an improved method for the production of 2-mercaptobenzothiazole.
More particularly, the invention relates to an improvement in a method for the production of 2-mercaptobenzothiazole from aniline, nitrobenzene, and carbon disulfide.
2. Description of Related Art
It is well known that 2-mercaptobenzothiazole is useful as a vulcanization accelerator for natural and synthetic rubbers and as a starting material in the synthesis of other thiazole compounds that are also useful as vulcanization accelerators.
One commercial means for the synthesis of 2-mercaptobenzothiazole involves the reaction of aniline, carbon disulfide, and sulfur. The overall chemistry of this reaction can be represented by the following equation.
Although this chemistry is straightforward, it is an oversimplification of the actual chemistry, which occurs through a variety of intermediates.
U.S. Pat. No. 1,712,968 discloses a process wherein an aromatic thiourea, e.g., thiocarbanilide, is reacted with carbon disulfide and sulfur according to the equation:
The reaction is run in an autoclave, which is slowly heated so that the temperature of the contents of the autoclave increases at a rate of approximately one degree per minute. This rate of heating is continued until the temperature reaches 225° C., whereupon the heat is moderated so that the temperature rise is about one degree every two minutes, and this rate is continued until the contents of the autoclave has reached a temperature of about 275° C. The time required for attaining the temperature mentioned under the conditions specified is approximately from five to six hours.
U.S. Pat. No. 2,001,587 discloses a method for preparing mercapto arylene thiazoles consisting of reacting a mixture of carbon disulfide, and arylamine and an organic oxidizing agent, such as an aromatic nitro compound, according to the equation:
wherein R represents an aromatic nucleus. The reactants are heated in an autoclave at 220° C. for six hours.
U.S. Pat. No. 3,818,025 discloses a process for the production of 2-mercaptobenzothiazole by the reaction of aniline, carbon disulfide and sulfur at a high temperature under elevated pressure, characterized in that the reaction is carried out first at 250° to 300° C. and then at 200° to 240° C.
U.S. Pat. No. 4,316,031 discloses a process for the preparation of 2-mercaptobenzothiazole comprising heating a reaction mixture comprising nitrosobenzene, hydrogen sulfide and carbon disulfide in a molar ratio of about 1: 1.5 to 4:1 to 3, respectively, to 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. In an alternative process, there is first reacted nitrosobenzene with hydrogen sulfide in a molar ratio of about 1:1.5 to 4, at a temperature from about 20 to about 100° C. for a period of time sufficient to substantially reduce the nitrosobenzene, and subsequently reacting the resulting product mixture with from about 1 to about 3 mole equivalents of carbon disulfide per mole of originally charged nitrosobenzene, at a temperature from about 200° C. to about 300° C.
U.K. Patent Application GB 2 018 774 A discloses a process for the preparation of 2-mercaptobenzothiazole which comprises reacting nitrobenzene or nitrosobenzene, hydrogen sulphide and carbon disulphide, the molar ratio of nitrobenzene or nitrosobenzene:hydrogen sulphide being from 1:3 to 1:6 or from 1:1.5 to 1:4, the molar ratio of nitrobenzene or nitrosobenzene:carbon disulphide being from 1:1 to 1:3 and the final reaction temperature being from 200 to 300° C.
Embodiments are disclosed wherein (a) nitrobenzene and H
2
S are reacted in a specified molar ratio under elevated temperature and pressure and the resulting reaction mixture is reacted with CS
2
in a specified molar ratio at 200 to 300° C.; (b) nitrosobenzene, H
2
S and CS
2
are reacted in a specified molar ratio at 200 to 300° C.; and (c) nitrosobenzene and H
2
S are reacted in a specified molar ratio at 20 to 100° C. and the resulting reaction mixture is reacted with CS
2
in a specified molar ratio at 200 to 300° C.
The disclosures of the foregoing are incorporated herein by reference in their entirety.
SUMMARY OF THE INVENTION
The present invention is directed to an improvement in the process for making 2-mercaptobenzothiazole that is represented by the overall equation:
wherein the improvement is directed to the control of the temperatures at the several stages of the reaction.
More particularly, the present invention is directed to an improved process for the preparation of 2-mercaptobenzothiazole by reacting aniline, nitrobenzene, and carbon disulfide wherein the improvement comprises employing a reaction temperature profile comprising the steps of
(A) heating the reactants to at least one temperature less than or equal to about 150° C.;
(B) then heating the reactants to a temperature in the range of from about 150° C. to about 170° C.; and
(C) then heating the reactants to a temperature in the range of from about 220° C. to about 275° C.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As disclosed above, the present invention is directed to an improved process for the preparation of 2-mercaptobenzothiazole by reacting aniline, nitrobenzene, and carbon disulfide according to the overall equation:
It should be understood that the above is an “overall” reaction equation, which is currently believed to be an integration of at least three individual reactions that may be represented by the following:
Equation I above represents the formation of thiocarbanilide from aniline and carbon disulfide. Above 160° C., thiocarbanilide decomposes to form aniline and carbon disulfide. See V. A. Ivanov et al.,
Zhur. Priklad Khim
. 30:447 (1957) (
Chemical Abstracts
51:14688 (1957)) Additionally, at 140° C., thiocarbanilide will react with hydrogen sulfide to produce aniline and carbon disulfide. Thus, the formation of the thiocarbanilide in the first stage of the reaction of the present invention requires the balancing of a delicate equilibrium, with the best temperature being at or below 150° C., preferably in a range of from about 140° C. to about 150° C.
Equation II above represents the reduction of nitrobenzene using hydrogen sulfide as the reducing agent. In the absence of catalyst, hydrogen sulfide only reduces nitrobenzene to any significant extent at 150° C. or above, but at temperatures above 170° C., e.g., 200° C., viscous polymers are formed. See U.K. Patent Application GB 2 018 774 A. Thus, the temperature must be kept at or above about 150° C., but no higher than about 170° C. during the second stage of the reaction of the present invention.
Equation III above represents the third stage of the reaction of the present invention and comprises the reaction of thiocarbanilide with carbon disulfide and sulfur to form 2-mercaptobenzothiazole and hydrogen sulfide. It is known from U.S. Pat. No. 1,712,968 that this reaction can be carried out at a temperature in the range of from 220° C. to 275° C.
Those skilled in the art will recognize that both the first step of the reaction and the second can be run at 150° C. If this is done, the first two reactions are, in substance, run at the same time and the process then has a two-step profile, rather than a three-step profile. It should also be noted that the only by-product of the overall reaction of the present invention is water, the hydrogen sulfide that is formed being consumed in the reaction to produce the 2-mercaptobenzothiazole.
The advantages and the important features of the present invention will be more apparent from the following examples.
REFERENCES:
patent: 1631871 (1927-06-01), Kelly
patent: 1712968 (1929-05-01), Roberts et al.
patent: 2001587 (1935-05-01), Semon et al.
patent: 3818025 (1974-06-01), Sugahara et al.
patent: 4316031 (1982-02-01), Bergfeld et al.
patent: 2 018 774 (1978-04-01), None
Ivanova et al., Journal of Applied Chemistry of the USSR, vol. 30, No. 3, (Mar., 1957), pp. 473
Malz, Jr. Russell E.
Reynolds Michael P.
Grandinetti Paul
Stockton Laura L.
Thompson Raymond D.
Uniroyal Chemical Company, Inc.
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