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Chapter 9
Reactions of Formaldehyde with Inorganic Agents
Formaldehyde reacts chemically with a wide 'variety of inorganic agents.
Representative reactions are summarized in this chapter beginning with
those involving the strongly electropositive elements and compounds
(viz., alkalies, ammonia, and metals) and ending with those involving the
electronegative mineral acids and halogens. This order has been followed
because it emphasizes the fact that the chemical behavior of formaldehyde
is determined to a very great extent by the polarity of the reactant or hy
the acidity or alkalinity of the reaction medium. As a result, related
reaction types are grouped together and maybe the more readily interpreted
and compared.
Reactions of formaldehyde with simple carbon compounds which are
often treated in inorganic texts will be found in this chapter. These compounds
include carbon monoxide, cyanides, and ammonium thiocyanate.
Alkali Metals. Alkali metals apparently show little tendency to react
with anhydrous formaldehyde. Elemental sodium does not act upon
liquid formaldehyde at its boiling point 115 . However, according to Foelsing
33 hydrogen is liberated when sodium is heated with gaseous formaldehyde
and a sodium derivative, possibly NaCHO, is produced.
Alkali and Alkaline-earth Hydroxides. In the field of formaldehyde
chemistry, alkalies are chiefly of importance as reaction catalysts. Since
the utility of alkalies in this connection has already been pointed out, the
subject need only be reviewed briefly in this place. When pure formaldehyde,
paraformaldehyde 7 alpha-polyoxymethylene, or any of the poryoxymethylene
glycols are treated with alkalies in aqueous systems the following
reactions are catalyzed:
(1) Hydrolytie polymerizations or depolymerizations.
(2) Canmzzaro reactions.
(3) Aldol-type condensations.
With respect to hydrolytie polymerizations and depolymerizations, it
is apparent that addition of small quantities of alkalies to aqueous systems
containing dissolved formaldehyde or suspended polymers of the polyoxymethylene
glycol type accelerates reactions leading to a state of equilibrium
between solution and polymer. Alpha-polyoxymethylene is precipitated
from solutions containing more than about 30 per cent formaldehyde
at room temperature and paraformaldehyde or alpha-polyoxymethylene
dissolve rapidly in approximately 3 times their weight of water under similar
circumstances.
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