I\BSTR~\CT T h e products obtained wher a-(0-~~itrophen~lthio) acids are reduced b y means o f sodi~~lll borohydride and palladi~lm-charcoal depend on ( a ) the reaction temperature, ( b ) the solvent, ( G ) the length o f time in which the a-(0-nitrophenylthio) acid is in contact with the reducing agent, and (d) the nature o f the substituents on the a-(0-nitrophenylthio) acid. B y varying theseconditions, benzothiazine hydroxamic acids (i.e. s~~bstituted 3,4-dihydro-4-hydroxy-3-0x0-Z-1,4-benzothiazines), the corresponding lactallls (3,4-dihydr0-3-ox0-2H-1,4-benzothiazines, and derivatives of 2-carboxymethyIthioazobenze~:e can be prepared.
In t\vo cases, additional products were obtained. W h e n (o-r~itrophe~~ylthio)acetic acid was catalytically reduced for 30 min in dioxane, 3,4-dihydro-3-0x0-2H-1,4-benzothiazine-l,1-dioxide (VIG) was an ~~ilexpected product, and when a-(4-trifl~1oromethyl-2-nitrophe11ylthio)-isob~~tyric acid was left for a prolonged time in contact with sodi~lirl borohydride and palladi~im-charcoal, a derivative o f hydrazobenzene, namely, 2-carboxy(a,a-dimethyl)methylthio-5-trifl~~orornethylhydrazobe~ize~~e (V), was one o f the three identified products.When reduced by means of sodium borohydride and palladiu~n-charcoal, certain aromatic nitro compounds which possess an ester group in a position suitably orientated with respect to the o-nitrophenyl group are converted into cyclic hydroxamic acids (1-3) ; the nitro group is reduced to a hydroxylanlino group which then cyclizes with the ester function. When t\vo nitro acids were reduced by siiuilar means, hoxvever, complete reduction to the corresponding amines occurred, and in both cases, lactamisation resulted on acidification (1).We have recently reported (3) that 2H-1,4-benzothiazine liydroxamic acids (I) are readily obtained by reducing suitably substituted (0-nitropl~enylt1~io)acetates bjr means of sodium borohydride and palladium-cliarcoal. On the suppositioil that reductioil of the corresponding acids would yield the related lactains (111), n-hich could be expected to possess anthelinintic properties (4, 5), substituted (0-nitropheny1thio)acetic acids were reduced sodiuin borohydride and palladium-charcoal. The resulting products depended on (a) time, (b) solvent, (c) nature of the substituents, and (d) temperature.When a-(4-trifluoroi~~etl~yl-2-nitrophenylthio)propionic acid (IIJ) was reduced in dioxane or illethanol over a period of 30 min n-ith excess sodium borohydride in the presence of palladium-charcoal, the corresponding anlino compound n-as not formed (6). The isolatioil of 6-trifluorometl~yl-3,4-dihydro-4-11ydroxy-2-~11et11yl-3-oxo-2H-l,4-benzothiazine (If) in good yield, on acidification of the filtrate, indicated that reductioil had proceeded only as far as the hydroxylamino stage. This reaction is a general one. For personal use only.