P-Bromophenyl isothiocyanate

Phenyl isothiocyanate may be prepared in quantity (Expt 6.98, Method 2) by allowing aniline to react with carbon disulphide to form phenyldithiocarbamic acid (cf. 1), which is isolated as the ammonium salt. Treatment of the latter with lead nitrate removes the elements of hydrogen sulphide to produce phenyl isothiocyanate. As indicated in the preparation of p-bromophenyl isothiocyanate which is given as a further example, a slightly modified procedure which requires the use of rectified spirit as a reaction solvent is necessary in order to obtain good yields of isothiocyanates from substituted anilines. 

A soln. of p-bromophenyl isothiocyanate in alcohol allowed to react gradually with an equimolar amount of aq. NaHS, 3 moles 37%-formalin soln. and aq. benzylamine sulfate added, stirred 0.5 hr. at room temp. 5-benzyl-3-p-bromophenyltetrahydro-l,3,5-thiadiazine-2-thione. Y 85%. P. Kristidn and J. Bernat, Tetrah. Let. 1968, 679. 

Other isothiocyanates obtained by this method are phenyl isothiocyanate (65%), -phenylene diisothiocyanate (71%), p-acetylaminophenyl isothiocyanate (73%), />-ethoxyphenyl isothiocyanate (64%), and -bromophenyl isothiocyanate (55%). 

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