Process for preparing organo-sulfonium halides

Disclosed is a process for preparing organo-sulfonium halide of the formula ##STR1## wherein X is an halide, R.sub.1, R.sub.2 and R.sub.3 are the same or different and are selected from the group consisting of: alkyl having 1 to 24 carbon atoms, inclusive; allyl having 2 to 24 carbon atoms, inclusive; alkenyl having 2 to 24 carbon atoms, inclusive; alkynyl having 2 to 24 carbon atoms, inclusive; aryl having 6 to 24 carbon atoms, inclusive; and wherein said alkyl, allyl, alkenyl, alkynyl and aryl are optionally substituted with a group that is inert to organo-sulfides comprising: reacting an alcohol, e.g. methanol, with an halide derivative which when reacted with an organo-sulfide forms an organo-sulfonium halide, e.g., thionyl halide, sulfuryl halide and carbonyl halide; and then adding an organo-sulfide, e.g., dimethyl sulfide, to the above reaction mixture with agitation while allowing the gas formed to be eliminated so that the organo-sulfonium halide, e.g., trimethyl sulfonium halide, is formed. This process can take place in the presence of an insert solvent, e.g., methylene chloride.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a process for preparing organo-sulfonium halides. 
More particularly, it relates to a process for preparing trialkylsulfonium 
halides. 
2. Related Art 
Organo-sulfonium halides are useful in the preparation of pesticides and 
herbicides. Specifically, the sulfonium salts of N-phosphonomethylglycine 
have been found to be particularly effective herbicides against various 
types of grasses and other unwanted weeds. 
In the preparation of the trialkylsulfonium salts of 
N-phosphonomethylglycine, the starting material is trialkylsulfonium 
hydroxide which is derived from the salt, trialkylsulfonium halide, in a 
number of different ways including electrolysis. 
Sulfonium salts are, in part, known compounds, and methods for preparing 
all of these salts are shown in the art. U.S. Pat. No. 3,101,265 (Smutny 
et al., Aug. 20, 1963) discloses plant growth-modifying compositions 
comprising trialkylsulfonium salts and describes therein a method for 
preparing these salts. This method involves the reaction of a thioether, 
RSR' with a suitable aliphatic derivative of the anion of an inorganic 
acid i.e., an aliphatic halide, R"X or an aliphatic sulfate, 
R'"R""SO.sub.4. 
The Encyclopedia of Chemical Technology, Kirk-Othmer, Volume 13, pages 
440-441 describes the conventional synthesis of sulfonium compounds by the 
reaction of alkyl halides with sulfides, disulfides, thioaldehydes or 
thioketones. 
However, novel ways of preparing these salts are sought because of their 
importance. It is an object of the present invention to provide an 
alternative method of producing organo-sulfonium salts and, in particular, 
trialkylsulfonium halides. 
Other objects and advantages of the present invention are shown throughout 
the specification. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, it has now been discovered that 
an organo-sulfonium halide can be prepared by reacting an alkylhaloformate 
with an organo-sulfide preferably with agitation while allowing the gas 
formed to be eliminated so that the organo-sulfonium halide is formed. 
This invention further comprises a process for preparing an 
organo-sulfonium halide in which an alcohol is first reacted with an 
halide derivative which when reacted with an organo-sulfide forms an 
organo-sulfonium halide and then reacting the product of this first step 
with an organo-sulfide preferably accompanied by agitation while allowing 
the gas formed to be eliminated so that the organo-sulfonium halide is 
formed. 
DETAILED DESCRIPTION OF THE INVENTION 
The present invention comprises a process for preparing an organo-sulfonium 
halide. This process comprises the step of reacting an alkylhaloformate 
with an organo-sulfide preferably with agitation while allowing the gas 
formed to be eliminated so that the organo-sulfonium halide is formed. 
This invention further comprises a process for preparing an 
organo-sulfonium halide in which an alcohol is first reacted with an 
halide derivative which when reacted with an organo-sulfide forms an 
organo-sulfonium halide and then reacting the product of the first step 
with an organo-sulfide. This second step is preferably accompanied by 
agitation while allowing the gas formed to be eliminated so that the 
organo-sulfonium halide is formed and remains in the reactor. 
The organo-sulfonium halides prepared by this invention can be of various 
configurations. A preferred organo-sulfonium halide is of the formula: 
##STR2## 
wherein X is an halide, R.sub.1, R.sub.2 and R.sub.3 are the same or 
different and are selected from the group consisting of: alkyl having 1 to 
24 carbon atoms, inclusive; allyl having 2 to 24 carbon atoms, inclusive; 
alkenyl having 2 to 24 carbon atoms, inclusive; alkynyl having 2 to 24 
carbon atoms, inclusive; aryl having 6 to 24 carbon atoms, inclusive; and 
wherein said alkyl, allyl, alkenyl, alkynyl and aryl are optionally 
substituted with a group that is inert to the organo-sulfide used in this 
process. The halide X can be chloride, bromide, iodide or fluoride. 
Chloride is particularly preferred. 
A particularly preferred organo-sulfonium halide prepared according to this 
invention is a trialkylsulfonium halide, e.g., trimethylsulfonium 
chloride, which results when R.sub.1, R.sub.2 and R.sub.3 are methyl 
groups and X is a chloride group. 
The alkylhaloformate used in the present invention can be prepared by 
reacting an alcohol with a carbonyl halide as represented by the following 
equation: 
##STR3## 
A preferred alkylhaloformate is methylchloroformate which is prepared by 
reacting methanol with phosgene. 
The organo-sulfide used in the present invention can be of various 
configurations. A preferred organo-sulfide is of the formula: 
##STR4## 
wherein R.sub.2 and R.sub.3 are defined as stated above in the formula for 
the preferred organo-sulfonium halide. A particularly preferred 
organo-sulfide is a dialkyl sulfide, e.g., dimethyl sulfide, which results 
when R.sub.2 and R.sub.3 are methyl groups. 
The following equation illustrates the reaction of the alkylhaloformate 
with the organo-sulfide to form the organo-sulfonium halide. 
##STR5## 
As can be seen from this equation, the choice of the R groups of the 
reactants will determine the particular organo-sulfonium halide formed. 
In the process of this invention an alcohol is first reacted with an halide 
derivative which halide derivative when reacted with an organo-sulfide 
forms the organo-sulfonium salt. This halide derivative can be of various 
configurations, however a preferred specie can be selected from the group 
consisting of thionyl halide, sulfuryl halide and carbonyl halide. The 
chloride is particularly preferred. 
The process of this invention can be carried out in the presence of an 
inert solvent. This inert solvent is preferably one that does not contain 
an hydroxy group. Methylene chloride is a preferred solvent. 
The following generalized equation illustrates the process of this 
invention: 
##STR6## 
X, R.sub.1, R.sub.2 and R.sub.3 are defined as stated above in the formula 
for the preferred organo-sulfonium halide. Y can be either carbon or 
sulfur and n is either the integer 1 or 2. 
The reaction between the alkylhaloformate and the organo-sulfide can be 
carried out with agitation. This agitation aids the reaction and aids in 
the elimination of the gaseous reaction product from the reactor. However, 
agitation is only preferred and is not essential to the process. 
The temperature condition for the process of this invention as illustrated 
by the generalized equation above is not critical. The reaction between 
the alcohol, R.sub.1 OH, and the halide derivative, YO.sub.n X.sub.2, is 
exothermic, therefore heating is not preferred. This process has been 
carried out at temperatures from about 0.degree. C. up to about 30.degree. 
C., however there is nothing to prevent this process from being carried 
out at temperatures outside this range. 
The concentration of the various compounds used in the processes of this 
invention are generally not critical except that the alcohol concentration 
should be equal to or less than the concentration of the halide 
derivative. Preferred concentrations of alcohol to halide derivative are 
1:1 and 1:1.1, however any concentration of alcohol equal to or less than 
that of the halide derivative can be used. The preferred concentration of 
the organo-sulfide is one mole equivalent. Lower concentrations of 
organo-sulfide can affect the yield of the end product negatively and 
higher concentrations may not be economical, however other concentrations 
can be used. In general, the concentrations chosen will depend upon the 
amount of organo-sulfonium halide desired to be prepared with a minimum of 
operational difficulties.

The following Example illustrates certain embodiments of the present 
invention but should not be construed in a limiting sense. The scope of 
protection sought is set forth in the claims which follow the Example. 
EXAMPLE 
To a solution of methanol (10.1 ml, 0.25 moles) in methylene chloride (100 
ml), thionyl chloride (20.05 ml, 0.275 moles) was added at 0.degree. C., 
followed by the addition of a solution of dimethyl sulfide (20.2 ml, 0.275 
moles) in methylene chloride (50 ml). 
The temperature was allowed to rise to room temperature and the mixture was 
stirred over 72 hours. An oily layer was formed in the reactor. This layer 
was separated and then evaporated to obtain 19.5 g (70% yield) of the 
desired trimethylsulfonium chloride. 
The product was identified by analysis including NMR and mas spectroscopy.