formaldehyde - Sciencemadness Dot Org

FORMALDEHYDE PRODUCTION
Formaldehyde ^vas first prepared by Butlerov 11 ' 44 in 1859 as the product
of an attempted synthesis of methylene glycol [CH^OHJa]. The preparation
was carried out by hydrolyzing methylene acetate previously obtained
by the reaction of methylene iodide with silver acetate. Butlerov noticed
the characteristic odor of the formaldehyde solution thus produced, but
was unable to isolate the unstable glycol which decomposes to give formaldehyde
and water. Butlerov also prepared a solid polymer of formaldehyde
by reacting methylene iodide and silver oxalate. He showed that
this compound was a polymer of oxymethylene, (CH^O), but failed to
realize that it depolymerized on vaporisation. He also obtained the new
polymer by the reaction of methylene iodide and silver oxide, which gave
additional evidence of its structure. He showed that it formed a crystalline
product with ammonia (hexamethylenetetraniine) and even stated
that its reactions were such as one might expect from the unknown "formyl
aldehvde".
In 1868, A. W. Hofmann 13 prepared formaldehyde by passing a mixture
of methanol vapors and air over a heated platinum spiral, and definitely
identified it. This procedure was the direct forbear of modefn methods of
formaldehyde manufacture. To Hofmann, the teacher, it seemed bad
pedagogy that the first member of the aldehyde family should remain
unknownf and he accordingly supplied the missing information.
Present Methods of Manufacture
Today, formaldehyde is manufactured principally from methanol;
limited amounts are also produced by the oxidation of natural gas and the
lower petroleum hydrocarbons. Although other methods of preparation
involving the hyclrogenation of carbon oxides, the pyrofytic decomposition
of formates, etc., have been patented, they do not appear to have achieved
commercial importance. In connection with the reduction of carbon
oxides, Xewton and Dodge- 9 determined the equilibrium constant for the
reaction,
According to their findings:
CO+ H2^±CH20
PCH20 . -! T374 "I
KV PCO*PH; = ** \_~¥ ~* MX J
Yield values calculated from this constant indicate that the reaction would
appear to be hopelessly unfavorable as a means of formaldehyde synthesis*.
* Thus, even if a high reaction rate could be attained at a temperature as low as
300°Cj and if a pressure of 1000 atmospheres were used, the equilibrium conversion
to formaldehyde would be only about 0.8 per cent, while at high temperatures or
lower pressures the yields would be Still lower. Moreover, unless the hydrogeuation
catalyst used were highly selective, any formaldehyde formed would tend to be completely
hydrogenated to methanol,