formaldehyde - Sciencemadness Dot Org

STATE OF DISSOLVED FORMALDEHYDE 31
CHiCOOCHaOOCCH, + H20 > CH2(pH)2 + 2CH3COOH
Methylene acetate Water Methylene Acetic
glycol acid
CH3OCH2OCHs + H20 > CH2(OH)2 + 2CHS0H
Metkylal Water Methylene Methanol
glycol
By ether extraction of a SO per cent formaldehyde solution, Staudinger 13
succeeded in isolating a viscous liquid containing 58 per cent combined
formaldehyde. According to theory, pure methylene glycol should contain
62.5 per cent formaldehyde (CH20). Staudinger's oil was easily
soluble in water and ethyl acetate, but showed only a limited solubility
in ether and benzene. On standing, it polymerized quickly to a solid
mixture of polymeric formaldehyde hydrates. All attempts to isolate
methylene glycol in a pure state have been unsuccessful. It should be
noted, however, that the properties of the above-mentioned oil are similar
to those of ethylene glycol, which shows similar solubility relationships
and is extremely difficult to crystallize.
Polymeric Hydrates and Solution Equilibrium
Evidence of the presence of polymers in aqueous formaldehyde was first
obtained by Tollens and Mayer 20 in 1888 and Eschweiler and Grossmann 7
in 1890, who observed that molecular-weight values for formaldehyde
considerably above 30 were obtained on measuring the freezing point of
recently diluted formaldehyde solutions. The fact that these solutions
gave the normal value of 30 after standing for some time showed that the
polymers gradually dissociated after dilution. In 1905, Auerbach and
Barschall 1 made an extensive study of this phenomenon and determined
the average molecular weight of dissolved formaldehyde at room temperature
(approx. 20°C) in solutions of various concentrations up to approximately
38 per cent. All measurements were made in dilute solutions by
the cryoscopic method. The concentrated solutions studied were diluted
with ice-water for freezing-point measurement. The success of this
method lay in the fact that depolymerization on dilution was slow at
ice-water temperatures. Only in the case of the most concentrated solutions
was difficulty encountered. With such solutions a series of molecular
weight measurements were made at various time intervals after dilution.
By plotting these values against time and extrapolating to zero time, the
molecular weight value for the instant of dilution w r as estimated. These
data are shown in Table 3.
Auerbach found that these cryoscopic data were consistent with a chemi-