Concerning the Preparation of Some Diazo-Thio-Ethers of Thio-Beta-Napthol

Abstract

Although aromatic mercaptans closely resemble phenols in their general character, it has as yet been found impossible to couple them directly with diazonium salts, so as to form thio-azo-derivatives. Hantzsch and Freese (1), in 1896, working with thio phenol, found that it coupled to form diazo-thioethers of the general type, R-N =N-S-R, which more closely resembled the diazo-amino type than the azo. Their first preparation, obtained by diazotizing aniline and coupling with phenyl-mercaptan in a strongly alkaline solution, resulted in an extremely unstable, impure oil, which decomposed slowly with the evolution of nitrogen even at a temperature as low as -5? C. A very large excess of sodium hydroxide was necessary in order to keep decomposition at a minimum. It was impossible to obtain this compound in a state pure enough for analysis. Hantzsch and Freese assumed the diazo constitution since it was split by concentrated hydrochloric acid into benzene-diazonium chloride and thiophenol. Their next derivative, obtained by treating the diazonium salt of p-chloro aniline with sodium carbonate until alkaline and coupling with a strong alkaline solution of phenyl mercaptan, was obtained' as a yellow crystalline solid. During the coupling, which took place at 0? C., a small amount of nitrogen was evolved. The product obtained from this reaction was purified by evaporation from absolute ether and analyzed. The results from this analysis proved the diazo structure. Derivatives of 2-4-di-bromo aniline and p-iodo aniline were prepared in a similar manner and were found to be unstable oils, incapable of analysis. The derivative formed from 24-di-chloro aniline was found to be a solid, which was purified and analyzed. p.-Nitraniline yielded a derivative, stable at 0? C., but it decomposed at slightly higher temperatures. Perhaps their best example of a diazo-phenyl-ether was obtained from sulfanilic acid. Diazo-sulfanilic acid was dissolved in cold concentrated sodium hydroxide and added to the calculated amount of phenyl mercaptan. Coupling did not take place immediately and thus gave a chance to filter any possible impurities. Upon standing at 0? C., the crystals of the sodium salt of diazosulfanilic acid thiophenyl-ether settled out slowly. After filtering and washing with cold water, alcohol and ether, the compound was pure enough for analysis. The sodium salt of the thiophenyl-ether was apparently stable at ordinary temperatures in the dessicator. The aqueous solution was stable at 0? C., but decomposed at ordinary temperatures with the evolution of nitrogen and the development of the odor of thiophenol. Attempts to obtain the free acid, H-S03-C6H4-N = N-S-C6H5, were unsuccessful. The addition of hydrochloric acid immediately reformed phenyl mercaptan and diazo-sulfanilic acid. The work of Hantzsch and Freese (1) was more or less substantiated by Fox and Pope (2), who prepared mainly substituted thio-azo derivatives of ben-