Diacylamidobiphenylenedioxydialkyl carboxylic acids of the formula FORM:0607762/IV(b)/1 where R is an alkylene radical such as -CH2-, -CH2.CH2- or -CH2.CH2.CH2- and Ac is a carboxylic acid radical such as acetyl, benzoyl or propionyl; are prepared by de-alkylating a dialkoxy benzidine by known methods, preferably by the action of aluminium chloride; acylating the amino groups; and reacting with a halogenoalkyl carboxylic acid in an aqueous alkaline medium. When de-alkylation takes place by reaction with aluminium chloride a diluent may advantageously be added, such as an inert organic solvent, e.g. benzene, nitrobenzene toluene or xylene; or an inorganic salt, e.g. sodium or potassium chloride. Suitable acylating agents are the anhydrides and chlorides of acetic, propionic, butyric or benzoic acids. Reaction with the halogenocarboxylic acid takes place in an alkaline medium specifically aqueous caustic soda solution. Specified halogenocarboxylic acids are chloropropionic, chlorobutyric, chlorophenylacetic and chloroacetic acids, but bromoacetic acid may also be used. In an example, bianisidine dihydrochloride is de-alkylated by the action of aluminium chloride either in toluene solution or in admixture with sodium chloride; the resultant 3,31-dihydroxy benzidine is acylated with acetic anhydride to give 3,31-dihydroxy-4,41-biacetanilide which reacts with chloro-acetic acid to give 4,41-acetamido-3,31-biphenylene-dioxyacetic acid. By using m-anisidine in the process of the above example 4 : 41-diacetamido - 2 : 21 - biphenylenedioxyacetic acid is obtained.
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