Preparation of alkyl alkanethiolsulfonates

Alkyl alkanethiolsulfonates are prepared by oxidation of the corresponding alkanethiol, dialkyl disulfide, or mixture thereof by aqueous hydrogen peroxide in the presence of a Group VIII transition metal catalyst.

FIELD OF THE INVENTION 
This invention relates to the manufacture of alkyl alkanethiolsulfonates by 
the oxidation of the corresponding alkanethiol or dialkyl disulfide. More 
specifically, it relates to the oxidation of such compounds by hydrogen 
peroxide in the presence of a Group VIII transition metal catalyst to form 
the corresponding alkyl alkanethiolsulfonate. 
BACKGROUND OF THE INVENTION 
Alkyl alkanethiolsulfonates have been prepared by electrochemical oxidation 
of the corresponding alkyl disulfide (CA 101:110070j (1984), abstract 
Machion et al., An. Simo. Bras. Electroquim. Electroanal., 4th, 289-292 
(1984)) and electrochemical reduction of the corresponding sulfonyl 
chloride and sodium salt of the sulfonic acid (CA 100:87666b (1984), 
abstracting Polish PL 117,553). 
Various oxidizing agents have been employed in the preparation of alkyl 
alkanethiolsulfonates from the corresponding disulfides. These include, 
m-chloroperbenzoic acid (Bhattacharya et al., J. Org. Chem. 43(13) 
2728-2730 (1978)); organic hydroperoxide in the presence of a 
Mo(VI)-containing catalyst (U.S. Pat. No. 3,670,002); air in the presence 
of various transition metal halides and oxyhalides (CA 76:3397q (1972), 
abstracting French Patent No. 2,044,265); and nitrogen dioxide (U.S. Pat. 
No. 3,153,078). 
U.S. Pat. No. 3,365,480 describes the preparation of various 
nitrogen-containing thiolsulfonates by the oxidation of the acid salts of 
the corresponding disulfide with hydrogen peroxide in a polar solvent such 
as an alcohol or an organic acid. Propyl propanethiolsulfonate has been 
identified by thin layer chromatography in the product mixture resulting 
from the oxidation of dipropyl disulfide by hydrogen peroxide in acetic 
acid solution (Nogami et al., Chem. Pharm. Bull. 19(12), 2472-77 (1971)). 
In cases where an organic solvent such as acetic acid is employed in 
conjunction with hydrogen peroxide, the de facto oxidizing agent is likely 
to be the corresponding peracid. In such instances, and, in general, when 
an organic solvent is employed, there is a need to recover and recycle the 
solvent to make the process economic. 
In other prior art processes, exotic and expensive oxidizing agents such as 
m-chloroperbenzoic acid, sodium metaperiodate, and the like are utilized. 
Commercial application of such processes is questionable. 
SUMMARY OF THE INVENTION 
The invention described herein is a process for preparing an alkyl 
alkanethiolsulfonate by contacting the corresponding alkanethiol, dialkyl 
disulfide or mixture thereof with aqueous hydrogen peroxide in the 
presence of one or more transition metal catalysts selected from the Group 
VIII elements of the Periodic Table of the Elements. 
DETAILED DESCRIPTION OF THE INVENTION 
Alkanethiols, dialkyl disulfides or mixture thereof are oxidized by aqueous 
hydrogen peroxide in the presence of a catalytic amount of one or more 
Group VIII transition metal catalysts. An advantage of the process of the 
present invention is that it uses a heterogeneous catalytic system. The 
process can be operated in a batchwise manner in which case the catalyst 
can be easily removed from the product mixture by filtration and recycled. 
If desired, the process can also be operated in a continuous manner by 
using a fixed bed of the heterogeneous catalyst. 
Without wishing to be bound by any theory, it is believed that the alkyl 
alkanethiolsulfonate corresponding to the starting alkanethiol or dialkyl 
disulfide is prepared according to the following proposed chemical 
equations: 
##STR1## 
The alkanethiols which may be converted to their corresponding alkyl 
alkanethiolsulfonates in the process of the invention typically may have 
1-18 carbon atoms, preferably 1-8 carbon atoms. Thus, there may be used, 
for example, methanethiol, ethanethiol, n-propanethiol, isopropanethiol, 
1-butanethiol, 2-butanethiol, 1-hexanethiol, 1-octanethiol or 
1-decanethiol. 
The dialkyl disulfides which may be converted to their corresponding alkyl 
alkanethiolsulfonates according to the present invention, typically may 
have 2-20 carbon atoms, preferably 2-16 carbon atoms. Thus, there may be 
used, for example, dimethyl disulfide, diethyl disulfide, dipropyl 
disulfide, diisopropyl disulfide, dibutyl disulfide, diamyl disulfide, 
dihexyl disulfide, dioctyl disulfide, or didecyl disulfide. 
The catalyst that can be employed in the process of the present invention 
is a transition metal chosen from among the metals of Group VIII of the 
Periodic Table of the Elements, preferably selected from the group of 
iridium, palladium, platinum, rhodium, and mixtures thereof. The catalyst 
can be employed either in the form of pure metal, i.e., pure powdered 
metal, or is alternatively loaded on an inert solid support. The solid 
support may comprise, for example, a metal oxide such as alumina, silica, 
titania, zirconia or a mixture thereof. The catalyst may be in the form of 
a powder, pellets, or any other convenient form. 
When the catalyst is in the form of a metal loaded onto a support, the 
loading may advantageously be in the range of from about 1 weight percent 
to about 20 weight percent metal, based upon the weight of the entire 
supported catalyst, including the support. Preferably the loading is from 
about 2 to about 10 weight percent. 
The amount of metal catalyst used in the process of the invention may 
advantageously range from about 0.1 to about 5.0 g of metal per mole of 
the alkanethiol or dialkyl disulfide. Preferably, the metal catalyst is 
present in the range of from about 0.2 to about 2.0 g of metal per mole of 
the alkanethiol or dialkyl disulfide. 
The concentration of hydrogen peroxide in the aqueous hydrogen peroxide 
solution can range from about 3 weight percent to about 90 weight percent. 
However, concentrations of from about 30 weight percent to about 70 weight 
percent hydrogen peroxide are preferred, because of the ready availability 
of solutions of this concentration. 
The amount of hydrogen peroxide contacted with the alkanethiol or dialkyl 
disulfide can range from about 1 to about 10 moles of hydrogen peroxide 
for each mole of alkanethiol or dialkyl disulfide. Preferably, the amount 
of hydrogen peroxide contacted is from about 2 to about 6 moles for each 
mole of dialkyl disulfide, or from about 3 to about 6 moles for each mole 
of alkanethiol. 
The temperature at which the process of the invention is carried out can 
vary over a broad range. Typically, the temperature may be from about 
25.degree. C. to about 100.degree. C. Preferably, the temperature is from 
about 40.degree. C. to about 60.degree. C. 
The reaction time, that is, the time during which the reactants and 
catalyst are in contact, is selected such as to obtain maximum conversion 
of the alkanethiol or dialkyl disulfide to the corresponding alkyl 
alkanethioltet-sulfonate. sulfonate. Although the reaction time selected 
depends of course, upon several factors such as the reaction temperature, 
the amount of catalyst used, and the efficiency of agitation of the 
reaction mixture, the reaction time is generally between about one hour 
and about four hours. 
The process of this invention can be carried out in a batchwise or a 
continuous manner. In the batchwise manner, the reaction vessel is charged 
with either the alkanethiol or the dialkyl disulfide, or a mixture 
thereof, and the catalyst and brought up to the desired temperature. 
Aqueous hydrogen peroxide is added over a selected time period, while 
maintaining the reaction mixture at the desired temperature. The contents 
are preferably vigorously agitated to give maximum mixing of the 
reactants. After the completion of the hydrogen peroxide addition, the 
reaction mixture is further agitated and maintained at the desired 
temperature for a period of time sufficient to achieve the maximum yield 
of the alkanethiolsulfonate. 
In the continuous mode of operation, the alkanethiol, dialkyl disulfide or 
mixture thereof, and the aqueous hydrogen peroxide are continuously fed to 
a reaction zone containing the catalyst, wherein the reactants are reacted 
at the desired temperature. The reaction mixture containing the desired 
alkyl alkanethiolsulfonate is continuously removed from the reaction zone 
at a rate so as to give a maximum yield of the corresponding alkyl 
alkanethiolsulfonate. The alkyl alkanethiolsulfonate is then separated 
from the unreacted alkanethiol or dialkyl disulfide and the catalyst in a 
manner known to those skilled in this art. The unreacted alkanethiol or 
dialkyl disulfide and catalyst may be recycled to the reactor. 
The process of this invention is demonstrated by, but not limited to, the 
following illustrative examples.

Example 1 
To a well-stirred mixture of dimethyl disulfide (9.47 g; 100 mmole) and 1.0 
g of a catalyst consistinq of alumina loaded with 5% rhodium, was added 
30% hydrogen peroxide (66.7 g; 588 moles) over the course of 35 minutes, 
while maintaining the temperature of the reaction mixture at 
50.degree.-60.degree. C. Upon completing the addition of the hydrogen 
peroxide, the reaction mixture was agitated for an additional one hour 
while maintaining the temperature at 50.degree. C. The reaction mixture 
was then cooled, filtered to remove the catalyst, and extracted with three 
25 ml portions of methylene chloride. Analysis of the methylene chloride 
extract by gas chromatography indicated the formation of 8.9 g (70.1% 
yield) of methyl methanethiolsulfonate. 
Example 2 
To a well-stirred mixture of dimethyl disulfide (9.36 g; 99.6 mmole) and 
0.1 g of powdered palladium black, was added 30% hydrogen peroxide (66.7 
g; 588 moles) over 40 minutes, while maintaining the temperature of the 
reaction mixture at 50.degree.-60.degree. C. Upon completing the addition 
of the hydrogen peroxide, the reaction mixture was agitated for an 
additional one and one half hour while maintaining the temperature at 
50.degree.-60.degree. C. The reaction mixture was then cooled, filtered 
and extracted with three 25 ml portions of methylene chloride. Analysis of 
the methylene chloride extract by gas chromatography indicated the 
formation of 8.3 g (66.5% yield) of methyl methanethiolsulfonate. 
Example 3 
To a well-stirred mixture of n-propanethiol (15.3 g; 200 mmole) and 1.0 g 
of a catalyst consisting of alumina loaded with 5% rhodium, was added 30% 
hydrogen peroxide (66.7 g; 588 moles) over 1 hour, while maintaining the 
temperature of the reaction mixture at 50.degree. C. After the completion 
of the addition the reaction mixture was agitated for an additional one 
hour while maintaining the temperature at 50.degree. C. The reaction 
mixture was then cooled, filtered, and extracted with three 25 ml portions 
of toluene. Analysis of the toluene extract by gas chromatography 
indicated the formation of 1.6 (9.0% yield) of propyl 
propanethiolsulfonate and 5.6 g (37.0% yield) of dipropyl disulfide. 
The present invention may be embodied in other specific forms without 
departing from the spirit or essential attributes thereof and, 
accordingly, reference should be made to the appended claims, rather than 
to the foregoing specification, as indicating the scope of the invention.