formaldehyde - Sciencemadness Dot Org

REACTIONS WITH HYDROXY COMPOUNDS 139
under acidic conditions the reaction proceeds further: water is liberated
and formaldehyde acetals or formals are formed:
CEsOCHfcOH + CH3OH > CHa0CH30CH, + H20
Methyl Methanol Methylal Water
Formaldehyde
Hemiacetal
In most cases, formal production takes place readily in the presence of
acidic catalysts such as sulfuric acid, hydrochloric acid, ferric chloride, zinc
chloride, and the like. ; As indicated above, the reaction is reversible and
proceeds to a state of equilibrium. It is closely analogous to esterincation.
Since a minimum concentration of Avater in the reaction mixture is most
favorable to a high conversion yield, paraformaldehyde is an excellent raw
material for formal preparation.
According to Fischer and Giebe 23 , methylal can be obtained in 75 per
cent theoretical yield by mixing commercial formaldehyde solution with
1| parts methanol containing 2 per cent hydrogen chloride, followed by
the addition of calcium chloride equivalent to the weight of formaldehyde
solution. Under these conditions methylal separates as an upper phase
which can be removed and purified by distillation. Still better yields can
be obtained by reacting methanol containing 1 per cent hydrogen chloride
with paraformaldehyde. Adams and Adkins 1 report excellent yields of
formals by heating alcohols with paraformaldehyde at 100°C in the presence
of ferric chloride. These investigators claim that ferric chloride-is
the most efficient catalyst for formal production.
In general, formals are ether-like compounds. They possess ;a .high
degree of chemical stability under neutral or alkaline conditions, but
hydrolyze to formaldehyde and alcohol in the presence of acids. Formals.
of the lower alcohols are miscible with water, whereas the higher members
of the group are insoluble or only partially soluble,
The formals of tertiary alcohols are not readily produced. Conant,
Webb, and Mendum 13 obtained tertiary butyl formal as a by-product in
the formation of tertiary butyl carbinol when tertiary butyl magnesium
chloride was reacted with anhydrous formaldehyde. This formal is recovered
unchanged by steam distillation from 80 per cent sulfuric acid, but
is hydrolyzed by heating with an equal weight of 95 per cent ethanol containing
2 cc of concentrated hydrochloric acid.
The boiling points of some of the formals which have been isolated and
studied are listed in Table 21.
Formals of the higher alcohols are wax-like materials which may be
obtained by heating the alcohol with paraformaldehyde in the presence of