ORGANIC SULFUR COMPOUNDS: PART I. BENZOTHIAZINE HYDROXAMIC ACIDS AND RELATED COMPOUNDS

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Abstract
2H-1,4-Benzothiazine hydroxamic acids of type V (see Table I) are readily prepared by reducing suitably substituted (o-nitrophenylthio)acetates (II, R″ = Me or Et) by means of sodium borohydride and palladium–charcoal. The ester precursors can be prepared by the interaction of o-nitrothiophenols and α-bromoesters, but such a method is limited in scope. Diethyl bromomalonate, for example, reacts atypically with o-nitrothiophenol. The ester precursors are better prepared by Fischer–Speier esterification of the corresponding acids (II, R″ = H) which, in turn, are the products of nucleophilic attack by α-mercaptoacids on suitable o-chloro- (or bromo-) nitrobenzenes. This general preparative method failed in two instances. When o-chloronitrobenzene or 4-chloro-3-nitrotoluene was reacted with α-mercaptoisobutyric acid, the only acidic product obtained was α.,α′-dithiodiisobutyric acid.Reduction of methyl 2-(o-nitrophenylthio)benzoate (VI) with sodium borohydride and palladium–charcoal gave an azoxy compound, namely 2,2'-bis((o-methoxycarbonyl)phenylthio)azoxybenzene (VII).

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