Sodium 4'-Hydroxyazobenzene-4-sulfonate as a Teaching Material

Abstract

Azo dyes comprise over a half of all synthetic dyes. Some of them, eg. P-hydroxyazobenzene, Orange II, etc., are also important as teaching materials of chemical experiments in upper secondary high school or in university. The object of this paper is to describe the use of sodium 4'-hydroxyazobenzene-4-sulfonate(HAS) for the same purpose. This compound has a simple skeleton of p-hydroxyazobenzene with an additional sulfoxyl group, and can easily be accessed by the method well established for Orange II. Merits of this compound in using chemical experiments are as follows. i) HAS, which exists in azo form in a neutral aqueous solution, can easily be explained as to its structure and spectrum, while those of Orange II is rather complexive due to azo-quinoid tautomerism. ii) As an acidic azo dyes, HAS can be chromatographed by the same conditions as in food dyes, so that the com pound is just adequate in making azo dyes to be familiar for students, as well as in illustrating them effectiveness of thin layer chromatography (TLC). These characteristics show that HAS is usuful as a teaching material of dprogressive study after p-hydroxy azobenzene in upper secondary high school or that of foundamental organic synthesis in university. This compound is also usuful to study "separation of substances" of lower secondary school, since the experiments include essential techniques of recrystallization and chromatography. Thus the subject is thought to be appropri ate for a teaching material in faculty of education.