The invention relates to a process for the preparation of benzothiazepinone derivatives from optionally substituted benzothiazoles which are first hydrolyzed to give o-amino-thiophenols and then reacted further with optionally substituted acrylic acids.
Benzothiazepinone derivatives are outstandingly suitable co-catalysts for controlling isomer ratios in nuclear chlorinations of alkylbenzenes in the presence of Friedel-Crafts catalysts.
It has been disclosed in U.S. Pat. No. 2,791,612 that the preparation of o-amino-thiophenol by alkaline hydrolysis of benzothiazole and subsequent acidification with mineral acid leads to by-products which in some cases enter into the reverse reaction to give benzothiazole; only unsatisfactory yields are therefore obtained even with careful maintenance of the reaction parameters. It is therefore proposed to work with acetic acid instead of with a mineral acid.
The reaction of optionally substituted o-amino-thiophenols with optionally substituted acrylic acids is disclosed in U.S. Pat. No. 3,075,967. For example, phenylcrotonic acid and o-amino-thiophenol are fused together at 160.degree.-175.degree. C. It is disadvantageous in this connection that these reactions in the melt lead to low yields (J. Chem. Soc. 130 (1927), 2738) and that in this connection not only benzothiazepinone derivatives but also isomeric benzothiazine derivatives are formed (Chem. Ber. 119 (1986), 3109).
The reaction of some substituted acrylic acids with o-amino-thiophenol in high-boiling, water-miscible solvents is furthermore known (Tetrahedron 42 (1986), 2731); in this connection, the benzothiazepinone derivatives can only be isolated by aqueous work-up.