formaldehyde - Sciencemadness Dot Org

H3S
FORMALDEHYDE
The preparation and isolation of phenol alcohols was first accomplished
in 1S94 by two independent investigators, Manasse 36 and Lederer, 34 who
employed processes involving basic catalysis. Although acid catalysts, as
previously stated, usually accelerate the more complex condensations, it
has been definitely demonstrated that phenol alcohols are also produced in
the early stages of the normal acid reaction 26 . This fact supports the
theory that methylolphenols are the primary products of all phenol-formaldehyde
condensations.
The procedure of Lederer 34 involved the use of heat in the presence of a
small amount of base, whereas Manasse 36 favored the employment of an
approximately equiniolar amount of strong alkali and allowed the reaction
to take place at ordinary temperature. The latter method has been generally
adopted as the standard procedure for phenol alcohol preparation.
Saligenin and Polymethylol Phenols. Saligenin (ortho-hydroxybenzyl
alcohol, ortho-methylolphenol), the simplest phenol alcohol, was first
described in 1343 by Piria^j who isolated it from the natural glucoside,
salicin, long before the reactions of phenol and formaldehyde had been
explored. Saligenin is a crystalline compound melting at 82°C. On heating
alone or in the presence of an acid it is converted to resinous products.
Piria 45 obtained a resin of this sort by warming it with hydrochloric acid.
This resin was named saliretin by Piria, a name which has since been
applied generally to the primary condensation products of phenol alcohols.
Saligenin is synthesized by the method of Manasse. Phenol is dissolved
in somewhat more than an equivalent amount of dilute sodium hydroxide
and a molecular quantity of commercial 37 per cent formaldehyde is added.
The reaction mixture is then allowed to stand at room temperature for one
day or more until the odor of formaldehyde has disappeared. After this,
the solution is neutralized with acetic acid and extracted with ether, which
removes the phenol alcohols and unreacted phenol. The latter is distilled
with steam, leaving a mixture consisting principally of saligenin and the
isomeric para-methylolphenol. Saligenin may be isolated from an anhydrous
mixture of these two alcohols by extraction with benzene at 50°C.
Saligenin is readily crystallized from the benzene solution. The impure
p-methyiolphenolj which Is left behind when the phenol alcohol mixture is
treated with benzene, is a liquid in the crude state and has apparently
never been purified.
According to Granger 24 , only two-thirds of the phenol reacts in the
above preparation, although all the aldehyde is consumed. Polymethylolphenols
are formed as by-products, and remain in the reaction mixture
from which they are not extracted, since they are more soluble in water
than in ether. By working up this mixture, Granger isolated three phenol
alcohol fractions. This finding is in accordance with theory, since only