[¦sim trī′äk‚sān]
(organic chemistry)
(CH2O)3 White, flammable, explosive crystals; soluble in water, alcohol, and ether; melts at 62°C; used as a chemical intermediate, disinfectant, and fuel. Also known as metaformaldehyde; triformol; trioxin.



(or metaformaldehyde), [—CH2O—]3, a trimer of formaldehyde that forms colorless crystals having a characteristic odor. Melting point, 61°–62°C; boiling point, 114°–115°C; density 1.17 g/cm3 at 63°C. It is readily soluble in many organic solvents. With water it forms an azeotropic mixture that contains 70 percent sym-trioxane and boils at 91°C.

Sym-trioxane is obtained by heating a 50–55 percent aqueous solution of formaldehyde with 2 percent sulfuric acid. It decomposes completely into formaldehyde at 150°–180°C. This property permits its use for the production of pure formaldehyde.

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