Melting point, paraformaldehyde

The rise in stability is remarkable. Polyformaldehyde is insoluble in the reaction mixture and is removed as a slurry while capped polyformaldehyde is about 75 % crystalline and has a definite melting point. The reason is that both are held by acetal-type bonds, except that polyformaldehyde reacts with base (unlike acetals) to reverse the polymerization. Capped paraformaldehyde lacks a terminal hydroxyl hydrogen and cannot react so easily with base. The reactions can be summarized as ... 

Polymerization of formaldehyde takes place with great readiness. The liquid aldehyde slowly polymerizes at its boiling point ( — 21 ). When an aqueous solution is evaporated over concentrated sulphuric acid, or by heat, only a part of the aldehyde escapes as a gas- the rest is left as a white crystalline mass which melts at 63 . The molecular weight of the substance which is called paraformaldehyde, is not known. It is sold in... 

---