Organic Reactions Volume 4 - Sciencemadness Dot Org

260 ORGANIC REACTIONS
which one of the reactants and the final reaction product are insoluble.
It also may be significant that ethyl benzoate is the only one of the
esters studied that gives evidence (color) for a free radical.
Application of the Reaction. The original procedure of Bouveault and
Locquin 2 consisted in treatment of the ester with sodium in ether at 0°.
The reaction was allowed to proceed for several days, and yields approximating
80% were obtained from the esters of propionic, butyric, caproic,
isobutyric, and trimethylacetic acids. Acetoin was produced in a much
lower yield, and no experiments with formic esters were reported. A
substantial improvement in the conditions for carrying out this reaction
has been described. 5 With the same esters and ether, benzene, xylene,
or in some cases an excess of ester as the reaction medium, the low
temperature previously employed is avoided and the reaction time reduced
from several days to a few hours merely by allowing the reaction
to proceed at the temperature of the refluxing solvent.
Small amounts of 1,2-diketone (RCOCOR) and some higher-boiling
materials generally accompany the acyloins. The presence of the di~
ketone is a result of incomplete reduction to the sodium derivative of the
acyloin; the higher-boiling materials are formed possibly from the
acyloins during distillation or by polymerization or rearrangement of
the diketones under the influence of alkali produced in the reaction. 5
Ether is the preferred solvent for esters of low molecular weight,
though benzene also is fairly satisfactory. Table I summarizes the
yields of the acyloins and the corresponding diketones from a number of
such esters.
TABLE I
ACYLOINS AND DIKETONES FROM LOW-MOLECULAR-WEIGHT ALIPHATIC ESTERS
(Two gram-atoms of sodium with one mole equivalent of ester)
Ethyl Ester
Acetate
Propionate
Butyrate
Isobutyrate
Trimethylacetate
Solvent
Ether
Ether
Benzene
Ether
Benzene
Ether
Benzene
Ether
Benzene
Yield of Acyloin
%
23
52
30
72
61
75
68
62
63
Yield of Diketone
%
7
9
7
7
7
4
8
32
15