Acetylenic acids. II. The reaction of sulfur chlorides with phenylpropiolic acid and its methyl ester

Abstract

The reactions of phenylpropiolic acid and methyl phenylpropiolate with thionyl chloride, sulfur monochloride, sulfur dichloride and sulfuryl chloride have been investigated. With thionyl chloride the presence of pyridine is necessary for a reaction to occur with the ester or for the reaction to proceed beyond the acid chloride stage in the case of the acid. In all cases the Z and E isomers of 2,3-dichlorocinnamic acid or its methyl ester are among the main products that have been identified. With all but sulfuryl chloride a 3-chloro-1-benzothiophen system is also formed. Sulfuryl chloride and phenylpropiolic acid form 4-chloro-1-phenylnaphthalene-2,3-dicarboxylic anhydride in low yield. The structures of other minor products and the pathways leading to all these products are discussed.