Organic Reactions Volume 4 - Sciencemadness Dot Org

THE ACYLOINS 267
is thought that pyruvic acid is decarboxylated into nascent acetaldehyde,
which then is dimerized to acetoin. This method is believed 29 to have
preparative possibilities for acetoin. When the ultraviolet irradiation
of pyruvic acid is carried out in the presence of benzaldehyde a small
yield of phenylacetylcarbinol is obtained along with the acetoin. 30 The
irradiation of a-ketovaleric acid produces butyroin to the extent of
35-40% of the acid decomposed. 30
Fermentation processes for the production of acetoin and its oxidation
and reduction products, biacetyl and 2,3-butylene glycol, have been
studied extensively. They are not reviewed here because they are not
generally applicable to other acyloins. It may be mentioned, however,
that the yeast fermentation of pyruvic acid yields an optically active
acetoin. 31 The fermentation of sucrose to 2,3-butylene glycol in 90%
yield is reported, 32 and in this publication references are given to previous
work on the formation of this glycol and acetoin by fermentation processes.
EXPERIMENTAL PROCEDURES
Butyroin from Ethyl Butyrate. The preparation of this acyloin in
65-70% yield from ethyl butyrate is described in Organic Syntheses.
Propionoin, isobutyroin, and pivaloin (hexamethylacetoin) can be prepared
similarly in 50-55, 70-75, and 52-60% yields, respectively.
Lauroin from Methyl Laurate. 12 A mixture of 115 g. (5 atoms) of
sodium and 3 1. of xylene (c.p.) is charged into a 5-1., three-necked flask
immersed in an oil bath at 105°. The flask is fitted with a high-speed
stirrer (2000-2500 r.p.m.), and the air over the xylene is replaced by
nitrogen or other inert gas. When the temperature of the xylene reaches
105° and the sodium melts, the stirrer is started and the sodium dispersed
in a finely divided state in the xylene. From a separatory funnel 535 g.
(2.5 moles) of methyl laurate, or the equivalent quantity of another
ester, is then introduced into the reaction flask. The addition is at
such a rate that the temperature does not rise above 110°. The addition
of the ester requires about one hour. Stirring is continued for one-half
hour after the ester has been added.
Small particles of unchanged sodium are decomposed by the addition
of an excess of methanol (1-2 moles). Then, after cooling to about 80°,
water (0.5 to 11.) is added cautiously until the alkali has dissolved, and
the layers are separated by decantation. After one or two more washings
30 Dirscherl, Z. physiol. Chem., 219, 177 (1933).
81 Dirscherl and Schollig, Z. physiol. Chem., 252, 53 (1938).
32 Fulmer, Christensen, and Kendall, Ind. Eng. Chem., 25, 798 (1933).
88 Snell and McElvain, Org. Syntheses, Coll. Vol. 2, 114 (1943).