formaldehyde - Sciencemadness Dot Org

FORMALDEHYDE POLYMERS 69
Octo-oxymethylene glycol crystallises in large, well-formed needles that
uniformly extinguish the rays of polarized light. It differs from crude
mixtures of polyoxymethylene glycols which, even under the microscope,
show no apparent crystalline form. It also differs from such products in
having comparatively little formaldehyde odor. Staudinger is of the
opinion that this is because it contains no formic acid, traces of which are
present in crude polymers and catalyze decomposition.
The x-ray diagram of Staudinger's octo-oxymethylene dihydrate showed
the characteristic lines of the higher polyoxymethylenes, but did not show
interference rings from which the length of the molecule could be calculated
58 . It was concluded that this result might have been due either to
the presence of small quantities of other polyoxymethylene glycols or to
the possibility that the reflection planes containing the hydroxyl end groups
did not occupy a regular position in a zone band. The ends of the molecules
probably approach one another so closely that a chain of linear
molecules has the net effect of a single molecule permeating the whole
ciystaL
Paraformaldehyde
Paraformaldehyde is denned as a mixture of polyoxymethylene glycols
containing from 93 to 99 per cent formaldehyde. Commercial paraformaldehyde,
which is often erroneously designated as i£ triox3Tnethy3ene J, ?
contains 95 per cent or more formaldehyde, usually analyzing in the range
95-96 per cent.
Early History. Paraformaldelryde was first prepared by Butlerov 12 who
obtained it hy the vacuum distillation of formaldehyde solution. However,
due to an erroneous determination of its vapor density, he concluded that
it was dioxymethylene, (CH30)^ This mistake was corrected by Hofmann
26 in 1869. Hofmaim found that the polymer gave monomelic formaldehyde
on vaporization, but made the incorrect assumption that it was
a trimer and gave it the name, ''trioxymethylene*'. The assumption was
based on the apparent analogy of formaldehyde with thioformaldehyde,
CH2S3 which was known to give a trimeric polymer. As a result of Hofmann's
error, the term "trioxymefchylene" has been applied in numerous
instances to paraformaldehyde and the polyoxymethylenes and is often
accompanied by the formula, (CH20)3, when thus misused. Around the
turn of the century, investigators such as Delepine 16 reserved "trioxymethylene"
as a designation for polymers which were believed to be substantially
free of combined water. However, in recent years, it has been
employed chiefly as a synonym for paraformaldehyde.
The name paraformaldehyde was first employed in 1888 by Tollens and
Mayer 89 who applied it to the polymeric residue which is left behind when