In the preparation of benzobisthiazoles from m-and p-phenylenediamines by thiocyanation or by ring closure of derived thioureas the linear tricyclic compound is usually the major or the only product. 3, 6-Diamino-1, 2-phenylene di (hydrogen thiosulphate)(the so-called p- phenylenediamino-2, 5-bisthiosulphuric acid) is the 2, 3-isomer and correction is required to structures assigned to its derivatives, eg, the diaminophenylenedithiol, the ...