formaldehyde - Sciencemadness Dot Org

CHEMICAL PROPERTIES OF FORMALDEHYDE 103
together, separated only by commas. No designations will be employed
in reactions which are more or less generally applicable to all forms of
formaldehyde.
Chemical Stability and Decomposition
Aside from its tendency to form reversible polymers, formaldehyde
possesses a surprising degree of chemical stability. Measurable decomposition
of gaseous formaldehyde is practically negligible at temperatures
below 300°C, although at higher temperatures it decomposes almost
exclusively to carbon monoxide and hydrogen with no separation of
carbon 7 , as indicated by the equation:
CH20(g)^CO + H2
Although the studies of Newton and Dodge (page 3) have shown that the
equilibrium involved in this reaction favors the decomposition to such an
extent that it may be regarded as almost irreversible under ordinary circumstances,
reaction rates are almost infinitely slow below 3O0°C. Some
idea of the rates at higher temperatures may be gained by the data of
Medvedev and Hobinson 45 . These investigators report that when a
gaseous mixture containing 40 per cent formaldehyde and 60 per cent
carbon dioxide is passed through a refractory glass tube (30 cm long)
heated to various temperatures and under conditions such that the exposure
time is 29 seconds in each case, the per cent decomposition is as follows:
10.2 at 450°, 38.6 at 500°, 44.7 at 550°, 87.5 at 600°, 94.9 at 650°, and 97.6%
at 700°.
According to Fletcher 2 -, who studied formaldehyde decomposition between
510 and 607°C in a pressure range of 30 to 400 mm, the splitting of
formaldehyde to carbon monoxide and hydrogen, although unquestionably
the principal reaction, is also accompanied by condensation reactions which
exert a disturbing influence on the rate of decomposition even though
they eventually lead in part to carbon monoxide formation. An immediate
pressure rise due to simple splitting is followed by a subsidiary rise which
extends over several hours, Metcher 22 also reports that the molecular
heat of activation for the decomposition to carbon monoxide and hydrogen
is 44.5 kcal. Patat and Sachsse 54 claim that free radicals are not produced
when formaldehyde is decomposed.
Catalysts have considerable influence on both the rate and nature of
formaldehyde decomposition. In the presence of finely divided platinum,
decomposition is stated to occur at 150°O 7 , whereas copper shavings are
reported to have no effect below 500°C 37 , Various inorganic compounds,
such as sodium carbonate, chromium oxide, alumina, etc., are stated to