No abstract

A convenient synthesis of 2,3-dihydrobenzo-1,4-thiazine has been developed, and the preparation of a number of substituted diphenylamines, phenothiazines, and phenoselenazines is described.

A number of alkoxy- and chlorophenothiazines have been prepared. A simple synthesis of 1,4-thiazane is described, and improved methods of preparation of 1-benzyl- and 1-benzoylpiperazine have been developed and used in the preparation of some monosubstituted piperazines.

The reduction by sodium and ethanol, with or without liquid ammonia as solvent, of various amidines followed by acid hydrolysis, leads in many cases to a good yield of the corresponding aldehyde. Further reduction in liquid ammonia of several Z-arylimidazolines or imidazolidines followed by acid hydrolysis leads to the 2,5-dihydrobenzaldehyde derivative.The reduction of some acid amides by sodium and proton sources in liquid ammonia has been examined. Under the right conditions this process is of preparative value for aldehydes.

Arylthioureas, when heated in chlorobenzene at 150" for 5-10 hr., undergo fission to give good yields of aryl isothiocyanates containing 1, 2, 3, and 4 aromatic rings. The mechanism of the reaction has been investigated. METHODS of preparation of aryl isothiocyanates 1 include (a) the use of thiocarbonyl chloride or its precursor thiocarbonyl tetrachloride (the latter reaction fails with naplithj*l compounds 3), (b) acid-induced fission of an NN'-diarylthiourea, iiivolving the loss of 1 mol. of amine, and (c) decomposition of an ammonium aryldithi~carbamate,~ the last method giving low yields for naphthyl and other compound^.^It has now been found that arylthioureas, when heated in a suitable solvent at 150°, undergo fission into ammonia and the aryl isothiocyanate. No isothiocyanate was obtained on attempted vacuum-distillation of 4-diphenylyl-or a-naphthyl-thiourea without a solvent.the methods of de Clermont 8 and Bertram failed for the latter substance. N-4-Diphenylylthiourea was obtainable by either method, or from N-4-diphenylylammoniuni thiocyanate. The related N-4-diphenylyl-S-methylisothiourea, ammonium N-4-diphenylyldithiocarbamate, and N-Pdiphenylylguanidine were prepared, the last by heating N-4-diphen ylyldiguanide.When N-4-diphenylylthiourea was heated in solvents of various b. p.s, chlorobenzene gave optimum yields of N-4-diphenylyl isothiocyanate ; 1 : 2-dichlorobenzene also aff ordecl the desired product, though in smaller yield, while nitrobenzene or 1 : 2 : 4trichlorobenzene gave no isothiocyanate. N-4-Diphenylyl isothiocyanate had m. p. 63.5--64-5", though Desai, Hunter, and Kureishy lo claim m. p. 119-120".Brewster and Horner 11 claim preparation of this isothiocyanate by 3 hours' boiling of the "'-diary1 thiourea with acetic anhydride. This procedure in our hands gave NN-diacetyl-4-aminodipheny1, m. p. 118.5-11 9", and NN'-diacetyl-NN'-bis-4-diphenylylurea, hydrolysed by alkali to 4-acetamidodiphenyl. Reaction of acetic anhydride with the isothiocyanate afforded the same products. Werner l2 reported the action of acetic anhydride on NN'-diphenylthiourea to give phenyl isothiocyanate in 96,37,7, and 0% yield after 5,30,45, and 60 minutes' boiling respectively, but did not identify the product of decomposition. This isothiocyanate is known l3 to give the N-acylaniline and diphenylurea when treated with acetic or formic acid, while benzoic anhydride gives NN-diben~oylaniline.1~ The mechanism of isothiocyanate formation was investigated by using a-naphthylthiourea. The rate of evolution of ammonia a t 150°, measured during 6 hr., gave the results shown in the Figure . A plot of log,, CAo/(Cao -CNH,) (where CAo = initial concentration of thiourea and CNH, = concentration of ammonia at time t ) was linear only for 1.5 hr., although the " half-time " of the reaction (65 min.) was independent of the magnitude of Cbo. The possibility of the reaction's occurring in three successive steps (a), (b), and (c), with the intermediate formation of a dithiobiuret, could be dismissed in view of the failure of ...