Process for preparing organic disulfides

A process is described for preparing organic disulfides, useful as accelerators in vulcanization and as anti-oxidants for synthetic rubber latexes, which comprises reacting an organic sulfonyl halide with a mercaptan in a ratio of at least about 5 moles of mercaptan per mole of sulfonyl halide, wherein by-product sulfinic acid is not formed in the final product.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a new and improved process for preparing organic 
disulfides from organic sulfonyl halides and mercaptans. 
2. Brief Description of the Prior Art 
Disulfides are extensively used in the area of polymerization technology. 
They are used as accelerators in vulcanization, as anti-oxidants and 
stabilizers for synthetic rubber latexes, as softeners for reclaimed 
vulcanizates, as intermediates in the manufacture of pigments and 
insecticides, and as agents for improving the properties of fuel and 
lubricating oils. 
The conventional prior art method for producing organic disulfides involves 
the oxidation of mercaptans and possesses the disadvantage of requiring 
expensive and/or hazardous oxidizing agents, such as peroxides or iodine. 
Another methd used to prepare disulfides involves reacting a sodium or 
potassium disulfide with an alkyl halide which has the disadvantage of 
forming impurities which are difficult to remove. Still another method 
involves the reaction of highly toxic sulfenyl halides with mercaptans. 
Disulfides can also be produced by reduction of organic sulfur-oxygen 
containing compounds containing sulfur in a higher valence state, such as 
sulfonyl halide, or thiosulfonates. One such procedure involves th 
electrochemical reduction of sulfonyl halides, particularly sulfonyl 
chlorides, to disulfides utilizing a mercury cathode. However, the use of 
this procedure is not attractive since it tends to lead to mercury 
pollution of streams and waters and requires expensive equipment and is 
not well suited to a batch type of process in a plant operation. 
Mercaptans, also known as thiols, are known reducing agents in the art for 
organic sulfur-oxygen containing compounds, as exemplified in Field, JACS 
74, 394 (1952) in which aromatic sulfonic acid anhydrides reduced by 
mercaptans yielding mixtures of thiosulfonates and disulfides. 
It is also known in the art that when sulfonyl chlorides are reacted with 
mercaptans in a ratio of 2 moles of mercaptan per mole of sulfonyl 
chloride, a mixture of the corresponding sulfinic acid and disulfide is 
obtained, as exemplified in Gibson, Miller and Smiles, J. Chem. Soc. 127, 
1821 (1925). The above reference also discloses that when thiosulfonates 
(disulphoxides) are reacted with mercaptans in a ratio of 1 mole mercaptan 
per mole of thiosulfonate, a mixture of sulfinic acid and disulfide is 
formed. It would appear in light of the prior art that sulfinic acid is a 
stable by-product in reduction of organic sulfur-oxygen containing 
compounds using mercaptans. 
Thus, the prior art does not provide any process whereby sulfonyl chlorides 
may be reacted with mercaptans to produce disulfides in high yield and 
purity, free of by-product sulfinic acid. 
SUMMARY 
In accordance with the present invention, organic disulfides are produced 
in high yield and high purity free of by-product sulfinic acid by a 
process which comprises reacting an organic sulfonyl halide with a 
mercaptan in ratio of at least about 5 moles of mercaptan per mole of 
organic sulfonyl halide. 
Although we do not wish to be bound by any theory, the reaction is believed 
to proceed in accordance with the following equation: 
##STR1## 
where X is a halogen and R and R' can be the same or different and are 
organic radicals selected from the group consisting of: linear or branched 
alkyl radicals containing 1 to 18 carbon atoms; substituted benzyl 
radicals of the formula: 
##STR2## 
wherein substitutents A.sub.1, A.sub.2 and A.sub.3 are independently 
selected from hydrogen, halogen and alkoxy containing 1 to 4 carbon atoms; 
cycloaliphatic radicals containing 5 to 8 carbon atoms and 0 to 2 chlorine 
atoms; aromatic radicals of the formula: 
##STR3## 
wherein Y.sub.1, Y.sub.2 and Y.sub.3 are independently selected from 
hydrogen, halogen, alkyl containing 1 to 12 carbon atoms, alkoxy 
containing 1 to 4 carbon atoms, phenyl and a fused benzene ring formed 
from two adjacent Y substituents; and heterocyclic radicals of the 
formula: 
##STR4## 
wherein Z is either oxyen, nitrogen or sulfur, and B.sub.1 and B.sub.2 are 
independently selected from hydrogen, halogen and alkoxy containing 1 to 4 
carbon atoms. 
Where R and R' are the same,three moles of the same disulfide are formed, 
and where R and R' are different, a mixture of disulfides is formed. 
This reaction can be carried out in the presence of a polar solvent in 
which the organic sulfonyl halide and mercaptan are soluble or can be 
conducted neat in a liquid state in the presence of basic catalyst, 
preferably an organic amine. 
DETAILED DESCRIPTION OF THE INVENTION AND THE PREFERRED EMBODIMENTS 
The advantages of the process of this invention over the prior art are the 
preparation of organic disulfides in high yield and purity in the absence 
of by-product sulfinic acid which does not require metal electrodes, or 
expensive and/or hazardous oxidizing reagents or highly toxic starting 
materials and which incorporates the reagents used in the reaction into 
the final product. The products of the invention are either symmetrical or 
unsymmetrical organic disulfides generally containing 2 to 40 carbon 
atoms. 
In general, mercaptans containing an R' group as defined above can be used, 
and the term mercaptan refers to an organic molecule containing the --SH 
group generally referred to as the mercapto, thiol or sulfhydryl group. 
Alkyl or aliphatic mercaptans useful in the present invention include those 
which contain 1 to 18 carbon atoms and are linear or branched, including 
secondary and tertiary types. 
Representative examples of linear aliphatic mercaptans are methyl-, ethyl-, 
propyl-, butyl-, decyl-, dodecyl-, an octadecylmetcaptan. Examples of 
branched mercaptans are isopropyl-, secondary butyl-, tertiary butyl- and 
tertiary dedeocylmercaptan. 
Representative examples of substituted benzyl mercaptans are benzyl-, 
p-bromobenzyl-, p-chlorobenzyl-, p-methoxybenzyl-, 2,4-dichlorobenzyl-, 
2,4,5-trichlorobenzyl-, 3,4,5-trimethoxybenzyl-, p-ethoxybenzyl- and 
p-butoxy-benzylmercaptan. 
Representative examples of cycloaliphatic mercaptans are cyclopentyl-, 
cyclohexyl-, methylcyclohexyl-, ethylcyclohexyl-, 2-chlorocyclohexyl- and 
2,4-dichlorocyclohexylmercaptan. Preferred among the general classes of 
aliphatic mercaptans discussed above are those containing 6 to 14 atoms. 
Aromatic mercaptans, usually referred to as aromatic thiols or thiophenols, 
are also applicable in the present invention. In general, they contain 6 
to 20 carbon atoms, and it is preferred to use those containing 6 to 10 
carbon atoms. 
Representative examples of aromatic mercaptans are benzene-, p-tolyl-, 
p-bromobenzene-, p-chlorobenzene-, p-methoxybenzene-, p-butoxybenzene-, 
2,4-dichlorobenzene-, 2,5-dichlorobenzene-, p-dodecylbenzene-, p-phenyl-, 
2,3,6-trichlorobenzene-, 2,4-dimethylbenzene-, 1-naphthalene-, and 
2-naphthalenethiol. Among the aromatic mercaptans or thiols, a 
particularly preferred embodiment is 2,5-dichlorobenzenethiol. 
Representative examples of heterocyclic mercaptans which are useful in the 
disclosed invention are 2-mercaptobenzimidazole, 2-mercaptobenzothiazole, 
2-mercaptobenzoxazole, 5-chloro-2-mercaptobenzothiazole, 
5-chloro-2-mercaptobenzoxazole, 5-chloro-2-mercaptobenzimidazole, and 
5-methoxy-benzoxazole. A preferred embodiment is 2-mercapto-benzothiazole. 
The organic sulfonyl halides that are useful in the present invention are 
the sulfonyl iodides, bromides or chlorides, but it is preferred to use 
the sulfonyl chlorides. 
The organic sulfonyl halides useful in the disclosed invention have the 
same organic radicals as defined for the mercaptans, and generally contain 
1 to 20 carbon atoms. 
Representative examples of aliphatic sulfonyl halides are methane-, 
decane-, dodecane- and octadecanesulfonyl chloride. Representative 
examples of cycloaliphatic sulfonyl halides are cyclohexanesulfonyl 
chloride, cyclopentanesulfonyl chloride, 2-methylcyclopentanesulfonyl 
chloride and 2-chlorocyclopentanesulfonyl chloride. 
Representative examples of substituted benzyl mercaptans, also named 
-toluenesulfonyl chlorides, are -toluenesulfonyl chloride, 4-chloro-, 
4-bromo, 4-methoxy-, 4-butoxy, 2,4-dichloro-, 2,4-dimethoxy- and 
3,4,5-trimethoxy- -toluenesulfonyl chloride. 
Representative examples or aromatic sulfonyl halides are those containing a 
benzene or naphthalene nucleus, such as benzene-, para-toluene-, 
para-methoxy-benzene-, para-chlorobenzene-, para-butoxybenzene-, 
para-phenylbenzene-, p-dodecylbenzene 2,5-dichlorobenzene-, 
2,4,5-trichlorobenzene-, xylene-, 1-naphthalene- and 2-naphthalenesulfonyl 
chloride. Preferred among the aromatic sulfonyl halides are the 
benzenesulfonyl chlorides containing 6 to 10 carbon atoms and in 
particular 2,5-dichlorobenzenesulfonyl chloride. 
Representative examples of heterocyclic sulfonyl chlorides are 
benzimidazole-2-sulfonyl chloride, benzoxazole-2-sulfonyl chloride, 
benzothiazole-2-sulfonylchloride, 5-chlorobenzothiazole-2-sulfonyl 
chloride and 5-methoxybenzothiazole-2-sulfonyl chloride. 
Symmetrical or unsymmetrical organic disulfides can be prepared by the 
process of this invention. It is preferred however, to produce symmetrical 
disulfides since a mixture of disulfides requires additional processing 
for their separation. Such methods of separation, however, should be 
obvious to one skilled in the art and include fractional distillation and 
fractional crystallization techniques. 
The molar of mercaptan to sulfonyl halide employed in the process of this 
invention must be at least about 5 to 1. By use of such molar ratio, no 
detectable sulfinic acid will be present in the final reaction mixture, 
which is in marked contrast to the prior art processes where sulfinic acid 
is invariably formed. It is preferred that only about a 1 to 4 percent 
excess (over 5 moles) of mercaptan be employed in order to insure high 
conversion of the sulfonyl halide to disulfide. A larger excess of 
mercaptan can be used but is not necessary since it does not increase the 
efficiency or yield of the reaction. 
The solvents which are useful in the present invention are polar organic 
and inorganic solvents which generally contain nitrogen and/or sulfur 
and/or oxygen, are effective solvents for the organic sulfonyl halide and 
mercaptans, and are inert under the conditions of the reaction. Examples 
of solvents that may be used are halogenated aliphatic hydrocarbons 
containing 1 to 4 carbon atoms such as carbon tetrachloride, 
tetrachloroethane and dichlorobutane; halogenated olefinic hydrocarbons 
containing 2 to 4 carbon atoms such as chlorobutadiene an 
perchloroethylene; halogenated aromatic hydrocarbons containing 6 to 10 
carbon atoms such as chlorobenzene, an chloronaphthalene; ketones 
containing 3 to 6 carbon atoms such as acetone, butanone and 
methylisobutyl ketone; aromatic hydrocarbons containing 6 to 10 carbon 
atoms such as toluene, benzene and naphthalene; linear and cyclic 
aliphatic ethers containing 2 to 8 carbon atoms such as butyl ether and 
tetrahydrofuran; carboxylic acids containing 1 to 4 carbon atoms such as 
acetic, butyric and trichloroacetic acids; mineral aqueous acids such as 
85 percent phosphoric acid; lower alkyl glycols containing 2 to 4 carbon 
atoms such as ethylene glycol and butylene glycol; polyethylene glycol; 
trialkylphosphites containing 3 to 15 carbon atoms such as 
tributylphosphite and tripentylphosphite; monohydric aliphatic alcohols 
containing 1 to 8 carbons such as methanol, ethanol, isopropanol and 
octanol; monoalkoxyethanols containing 3 to 6 carbon atoms such as 
methoxyethanol, ethoxyethanol and butoxyethanol; linear and cyclic 
alkylene sulfones containing 1 to 8 carbons such as tetramethylene sulfone 
and dibutylsulfone; lower aliphatic amides containing 1 to 4 carbon atoms 
such as formamide and butyramide; N,N-dialkylalkanoylmides containing 1 to 
4 carbon atoms such as dimethylformamide and dimethylacetamide, and 
N-alkyl cyclic lactams containing 1 to 6 carbon atoms such as N-methyl- 
and N-ethylpyrrolidone. 
The amount of solvent used is based on the molar ratio of solvent to 
sulfonyl halide and is generally in the range of 5 to 1 moles solvent per 
mole of sulfonyl halide with a preferred range being of about 3 to 1 moles 
solvent per mole of sulfonyl halide. The yields of disulfide are to some 
extent dependent upon the polarity of the solvent employed in addition to 
the molar ratio of solvent to sulfonyl halide. In general, the more 
strongly polar solvents such as ethanol, sulfolane and 
N,N-dimethylformamide give higher yields than less polar solvents such as 
benzene, toluene or chlorobenzene. A molar ratio of solvent to sulfonyl 
halide of at least about two is preferred for obtaining higher yields with 
a particular solvent used. 
When the organic sulfonyl halide and mercaptan reactants are either liquids 
or low melting solids, the reaction can be conducted neat in the absence 
of a solvent. When the reaction is conducted neat, the reaction should be 
carried out in the liquid phase in the presence of a basic catalyst in 
order to obtain high disulfide yields. 
Basic catalysts which are suitable for the process of this invention are 
inorganic bases or organic amines. Examples of inorganic bases are ammonia 
and sodium carbonate. Examples of organic amines are those containing 1 to 
10 carbon atoms, preferably tertiary amines, such as ethanolamine, 
N,N-dimethylethanolamine, triethylamine, pyridine or guinoline. The basic 
catalyst is usually used in the ratio of about 0.01 to 5 percent by weight 
of the organic sulfonyl halide, a preferred amount being about 3 weight 
percent. 
the temperature of the reaction is generally in the range of about 
50.degree. to 200.degree. C., preferably about 95.degree. to 135.degree. 
C. Usually, the solvents chosen have a boiling point of about 95.degree. 
to 135.degree. C so that the reaction is conducted within the temperature 
range of about 95.degree. to 135.degree. C. In the absence of a solvent, 
wherein the reaction is carried out neat with a basic catalyst, the 
reaction is conducted normally at about 125.degree. to 200.degree. C., at 
a temperature chosen slightly above the melting points of either the 
organic sulfonyl halide or mercaptan such that the reaction mass is in the 
liquid state. 
The time of reaction depends mainly upon the temperature employed and is 
generally about 5 minutes to 24 hours for a temperature range of about 
50.degree. to 200.degree. C. 
Yields of disulfides produced in reaction are generally about 50 to 100 
percent of theoretical, wherein the theoretical yield is based on 
theoretical amount of disulfides produced from the reaction of 1 mole of 
sulfonyl chloride with 5 moles of mercaptan. 
Methods of product recovery will of course be obvious to one skilled in the 
art and will depend on the physical nature of the obtained disulfide. If 
it is a solid, precipitation from the reaction mixture can be utilized, if 
it is a liquid, then the reaction mixture can be distilled to yield the 
desired disulfide.

The following examples are given for illustrative purposes only and are not 
to be construed as limitations upon the scope and spirit of the instant 
invention. In the examples, parts are by weight except where otherwise 
indicated. 
EXAMPLE 1 
A mixture of 150 parts (0.6 mol) of 2,5-dichlorobenzenesulfonyl chloride, 
550 parts (3.0 mols) of 2,5-dichlorobenzenethiol and 310 parts (2.6 mols) 
of sulfolane were mixed together and heated for 3 hours at 95.degree. C. 
.+-. 5.degree. C. while stirring. Two liquid layers separated at the end 
of the reaction. The upper layer consisted of water, hydrochloric acid 
(reaction by-products) and sulfolane. The lower layer contained product 
plus some solvent. The layers were separated and the lower layer was 
diluted with an equal amount of acetone. After cooling to about 15.degree. 
to 25.degree. C, the mixture was filtered, and resulting solid washed with 
acetone to recover 575 parts (1.6 mols) of 2,5-dichlorobenzene disulfide 
(90 percent of theory). The remaining 10 percent of product disulfide was 
recovered from the acetone - sulfolane layer by additional workup. The 
purity of the product as determined by gas chromatography versus a 
standard sample was 99 percent. No detectable sulfinic acid was observed. 
EXAMPLE 2 
A mixture of 30 parts (0.122 mol) of 2,5-dichlorobenzenesulfonyl chloride, 
110 parts (0.62 mol) of 2,5-dichlorobenzenethiol and 31 parts (0.245 mol) 
of sulfolane were heated for 2 hours at 95.degree. C. .+-. 5.degree. C. 
The product 2,5-dichlorobenzene disulfide was recovered by the method of 
Example 1 and corresponded to 96 percent of theory. The product purity was 
97 percent as determined by gas chromatography, with no detectable 
sulfinic acid being present. 
EXAMPLE 3 
A mixture of 30 parts (0.122 mol) of 2,5-dichlorobenzenesulfonyl chloride, 
110 parts (0.62 mol) of 2,5-dichlorobenzenethiol and 14.7 parts (0.319 
mol) of ethanol were mixed together and heated for 3 hours at 80.degree. 
to 85.degree. C. A 76.5 percent theoretical yield of 2,5-dichlorobenzene 
disulfide of 99 percent purity was recovered using the procedure of 
Example 1. 
EXAMPLE 4 
A mixture of 30 parts of 2,5-dichlorobenzenesulfonyl chloride, 110 parts of 
2,5-dichlorobenzenethiol and 23 parts of dimethylformamide was heated for 
3 hours at 95.degree. .+-. 5.degree. C. A 97 percent theoretical yield of 
the corresponding 2,5-dichlorobenzene disulfide was recovered using the 
procedure of Example 1. 
EXAMPLE 5 
A mixture of 30 parts (0.122 mol) of 2,5-dichlorobenzenesulfonyl chloride, 
110 parts (0.62 mol) of 2,5-dichlorobenzenethiol and 1 ml. triethylamine 
was heated for 3 hours at 95.degree. to 100.degree. C. Using the procedure 
of Example 1, 102 parts of pure 2,5-dichlorobenzene disulfide were 
recovered representing a yield of 78 percent of theory. 
EXAMPLE 6 
The same materials and quantities were used as in Example 5 but the 
reaction mixture as heated for 1/2 hour at 120.degree. to 125.degree. C. A 
quantitative yield (100%) of 2,5-dichlorobenzene disulfide as recovered by 
using the procedure of Example 1. 
EXAMPLE 7 
A mixture of 60 parts (0.245 mol) of 2,5-dichlorobenzenesulfonyl chloride, 
260 parts (1,23 mol) of 2,5-dichlorobenzenethiol and 100 ml. (0.64 mol) of 
octanol was reacted for 3 hours at 95.degree. .+-. 5.degree. C. A yield of 
78 percent of theory of 2,5-dichlorobenzene disulfide was recovered by the 
procedure of Example 1. The product purity as determined by gas 
chromatography was 99 percent, with no detachable sulfinic acid being 
present.