Studies in the nitration of thioxanthene

Thioxanthene is a heterocyelie sulfur compound first synthesized by Graebe and Schultess in 1891. It was prepared by the pyrolysis of phenyl o-tolyl sulfide and in a second and better method, by the reduction of thioxanthone to thioxanthene. Thioxanthene was prepared in this laboratory from anthranilic acid, the synthesis progressing through the following stages. Anthranilic acid was converted, by diazotization to thiosalicylic acid. The thiosalicylic acid was then condensed with benzene to give thioxanthone. Thioxanthone was reduced by the action of hydrogen iodide and red phosphorous to thioxanthene. It was the purpose of the present study to investigate a substitution reaction of thioxanthene with a hope that a contribution to the knowledge of orientation in this nucleus might be made, nitration as one of the important types of aromatic substitution was chosen for the study. Most of the known methods of nitration were exhausted in an attempt to nitrate the thioxanthene nucleus. Nitration of thioxanthene was accomplished by the action of the "mixed acid", red fuming nitric acid and concentrated sulfuric acid. Other methods of nitration resulted mainly in oxidative decomposition. The use of high temperatxireE as well as earriers, incapable of repressing oxidation eliminated many accepted methods of nitration. No definite proof of structure was established, it is believed, however, that nitration occured in the 9-position of thioxanthene. It will be left to subsequent workers to provide absolute proof of the structure of the nitrated product.