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SynopsisA linear polymer with a high melting point is obtained from the water-formaldehydehydrogen sulfide system in the presence of sulfuric acid. This polymer is substantially formed by a polythiomethylene chain with a few oxymethylene units. Its formation involves a topochemical reaction of the mercaptomethanol present in solution on the first separation solid of the system. On heating, the polymer loses oxymethylene units; in the same way, the first solid product separated from the system loses formaldehyde and undergoes a morphological and chemical transformation to polythiomethylene.

The cyclic symmetrical-formals, symmetrical-thioformals, and their polymers have been largely investigated in recent years. In contrast symmetrical-selenoformalsl and their p~l y m e r s z~~ have received comparatively little study. This paper, which will be a cmtribution to this field, deals with a new preparative method of 1,3,5triselenane and of hexagonal polyselenomethylene and the isolation of a new oligomer, the ryclic tetramer of selenoformaldehyde, 1,3,5,7-tetraselenorane I, previously unknown in the literature.

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