Organic Reactions Volume 4 - Sciencemadness Dot Org

258 ORGANIC REACTIONS
Blanc during the course of their studies x of the sodium reduction of
aliphatic esters in alcoholic solution to the corresponding primary
alcohols. Their isolation of the glycol C7H15CHOHCHOHC7H15 instead
of the expected primary alcohol from the sodium reduction of
methyl caprylate in ether solution led Bouveault and Locquin to a survey
of the reaction of sodium on aliphatic esters in inert solvents. 2 The
preparation of the diacyl derivatives of the acyloins by the action of
sodium on acid chlorides had been reported in the very early literature, 3
but the structures of the compounds were not established until much
later. 4
Mechanism of the Reaction. The formation of an acyloin from an
ester or acid chloride is a combination reduction-condensation reaction
x r x
RC=O RC-ONa I RC=O
+ 2Na -> I
RC=O RC-ONa | RC=O
x Lx
X = Cl or OR
+ 2NaX
that undoubtedly involves the initial formation of the diketone. The
further reduction of this diketone by the metal yields the sodium salt
of the enediol form of the acyloin. 6 The reaction is similar to the reduction
of a ketone to a pinacol. 6 The yellow diketone, which is usually
RC=O
RC=O
+ 2Na
RC-ONa
RC-ONa
present to color the acyloin, has been postulated as resulting from air
oxidation of the acyloin; 2 but later work with the acid chloride 7 and
the ester 5 of trimethylacetic acid has shown that this assumption is
questionable, since the intermediate diketone (R is £-butyl), which is
very resistant to further reduction, appears as a major product of the
reaction.
1 Bouveault and Blanc, Bull soc. chim. France, [3] 29, 787 (1903); [3] 31, 666, 672 (1904);
Compl rend., 136, 1676 (1903).
2 Bouveault and Locquin, Compt. rend., 140, 1593, 1669 (1905); Bull soc. chim. France,
[S] 35, 629, 633, 637 (1906).
3 Freund, Ann., 118, 35 (1861); Bruhl, Ber., 12, 315 (1879).
4 Klinger and Schmitz, Ber., 24, 1271 (1891); Basse and Klinger, Ber., 31, 1218 (1898).
5 Snell and McElvain, J. Am. Chem. Soc, 53, 750 (1931).
6 An interesting-—but nevertheless inaccurate-—description of the reaction is that the
ester may be considered as being reduced to an aldehyde, which then goes to the acyloin
through a condensation of the benzoin type. Houben-Weyl, 3rd ed., Vol. 2, p. 931 (1925),
7 Egorova, /. Russ. Phys. Chem. Soc, 60, 1199 (1928) [C. A., 23, 2935 (1929)].