formaldehyde - Sciencemadness Dot Org

34
FORMALDEHYDE
Skrabal and Leutner 17 disagree with Auerbach's conclusions on the basis
that reactions of the type which are believed to take place in formaldehyde
solutions normally proceed in the step-wise fashion indicated below:
2CH2(0H),^ HOCH2OCH£OH -f H20
HOCH2OCH2OH + CH3(OH)3^HOCH3OCH3OCH2OH + H-0
etc.
The absence of dioxymethylene glycol molecules would accordingly appear
to be highly irregular.
Chemical derivatives of polyoxymethylene glycols involving two, three,
and four formaldehyde units have been isolated from reactions involving
formaldehyde polymers and serve as indirect evidence for the existence of
the parent glycols. The diacetate (CH8OOCHaOCH2OOCCH3) and the
dimethyl ether (CH3OCH2OCH2OCH3) of dioxymethylene glycol are well
known. The production of triformals on reaction of an excess of 30 per
cent formaldehyde with amines (page 199) may be an indication of the
existence of trioxymetlrylene glycol in these solutions. Higher members
of the homologous polyoxymethylene diacetates and dimethyl ether** were
isolated and characterized by Staudinger and Luthy 19 (Chapter 7),
Kinetics of Changes in Solution Equilibrium
As previously pointed out, the state of equilibrium between mono- and
polymeric formaldehyde hydrates is determined by the temperature and
concentration of the formaldehyde solution. On dilution, the polymeric
hydrates de-polymerize and a new state of equilibrium is attained. This
fact, primarily demonstrated by cryoscopic data, is also supported by
thermochemical evidence. The work of Delepme 4 haw .shown that when a
formaldehyde solution is diluted with water there is a gradual absorption
of heat following the initial heat of dilution, which is instantaneously liberated.
The absorption of heat is due to the gradual dcpolyraerization of the
polymeric hydrates.
Xeitber cryoscopic nor thermochemical measurements afford an accurate
means for studying the depolymerization reaction. Fortunately, however,
the progress of this reaction can be followed by measuring small changes
in refractive index and density which follow dilution of formaldehyde
solutions. The changes in refractive index can be accurately measured
with a liquid interferometer 11 . The density changes can be measured with
a dilatometer 17 . These methods give consistent results which are in substantial
agreement with cryoscopic findings and afford an accurate basis
for the study of the kinetics of the reactions involved.
According to Wadano and co-workers 22 , who made an extended study of
formaldehyde solution kinetics based on interferometer measurements: the
rate constants for the depolymerization reaction on dilution to low con-