Organic Reactions Volume 4 - Sciencemadness Dot Org

LESS STABLE
V C6H5COCHOHC6H4OCH3^
VI C6H5COCHOHC6H4N(CH3)2-4
VII 4-CIC6H4COCHOHC6H4N(CH3M
THE SYNTHESIS OF BENZOINS 283
MORE STABLE
C6H5CHOHCOC6H4OCH3-4 VIII
C6H5CHOHCOC6H4N(CH3)2~4 IX
4~ClC6H4CHOHCOC6H4N(CH3)2-4 X
4-Methoxy- or 4'-methoxy-benzoin or the a-bromo derivative of
4-methoxybenzoin upon treatment with potassium acetate and acetic
anhydride gives a mixture of the benzoin monoacetate and enediol diacetate,
each of which on hydrolysis forms the stable isomer. 14 - 86
C6H5CHOHCOC6H4OCHH:]
C6H5COCHOHC6H4OCH3-4' K0Ac " Ac2 °
C6H6CHBrCOC6H4OCH3^
C6H5-C=
OAc OAc
H2SO4
C6H5-C=CC6H4OCH3~4
OH OH
C—C6H4OCHr4 + C6H5CHCOC6H4OCH3^
OAc
H2SO4
> C6H5CHQHCOC6H4OCH3-4
Most unsymmetrical benzoins undergo reduction to desoxybenzoins
in which the carbinol group of the benzoin has been replaced by methylene.
However, the isomeric desoxybenzoin or a mixture of both of the
two desoxy compounds may be obtained. 17,80 ' 90,91 In this latter class
may be cited 4-methoxy-, 4-dimethylamino-, 4'~chloro-4-dimethylamino~?
3'-chloro-4-methoxy-, and 2,4,64rimethyl-benzoin.
The reduction of either 2,4,64rimethylbenzoin (XI) or 2',4',6'-trimethylbenzoin
(XII) results in the same desoxybenzoin, 2,4,6-trimethylbenzyl
phenyl ketone (XIII). 88,89 If either 2,4,6-trimethylbenzoin (XI)
C6H5CHOHCOC6H2(CH3) r2,4,6
XI
CH3CO2Na
C6H5COCHOHC6H2(CH3) 3-2,4,6
XII
C6H5COCH2C6H2(CH3) s-2,4,6
XIII
or 2 / ,4',6 / -trimethylbenzoin (XII) is warmed with ethanolic sodium
acetate, an equilibrium mixture is formed; therefore the stabilities of the
two isomers are similar. It is obvious that one of the benzoins is reduced
much more readily, since a single desoxy Compound entirely free from
90 Jenkins, /. Am. Chem. Soc, 54, 1155 (1932).
91 Jenkins and Richardson, J. Am. Chem. Soc, 55, 3874 (1933).