Organic Reactions Volume 4 - Sciencemadness Dot Org

270 ORGANIC REACTIONS
THE REACTION OF MANDELAMIDES AND MANDELONITRILES WITH THE GRIGNARD
PAGE
REAGENT 289
Experimental Procedure 290
4'~Dimethylaminobenzoin 290
THE REDUCTION OF BENZILS 291
Experimental Procedures 293
Catalytic Reduction (General Procedure) 293
Reduction of 4,4'-ToIiI with Magnesium-Magnesium Bromide 293
THE REDUCTION OF AROMATIC ACIDS AND THEIR DERIVATIVES 293
Experimental Procedures 294
Benzoin from Benzoic Acid 294
Mesitoin from 2,4,6-Trimethylbenzoyl Chloride 294
THE CONVERSION OF DESOXYBENZOINS INTO BENZOINS 295
Scope and Limitations 296
Experimental Procedure 296
General Procedure 296
MISCELLANEOUS SYNTHESES OF BENZOINS 296
TABLE II. BENZOINS PREPARED BY VARIOUS METHODS 299
INTRODUCTION
Benzoins are aromatic a-hydroxy ketones of the general formula
Ar'CHOHCOAr. Similar compounds containing aromatic heterocyclic
nuclei also are classed as benzoins. If the two nuclei in a molecule are
alike, the benzoin is said to be symmetrical; if different, unsymmetrical
or "mixed." The reactions for the preparation of benzoins are (1) the
condensation of two molecules of an aromatic aldehyde in the presence
of cyanide ion (benzoin condensation), (2) the conversion of an unsymmetrical
benzoin into its isomer, (3) the condensation of an aryl glyoxal
with an aromatic hydrocarbon, (4) the reaction of an aryl Grignard
reagent with a mandelamide or a mandelonitrile, (5) the reduction of a
benzil, (6) the reduction of an aromatic acid or its derivative, (7) the
introduction of a hydroxyl group into a desoxybenzoin, (8) miscellaneous
methods of limited application. Through these many methods the
variety of benzoins that can be prepared is large.
The benzoins constitute convenient intermediates for the preparation
of many related compounds, such as desoxybenzoins, ArCH2COAr 7 J
benzils, ArCOCOAr'; hydrobenzoins, ArCHOHCHOHAr'; enediols,
ArC(OH)=C(OH)Ar'; stilbenes, ArCH=CHAr'; diphenylethylamines,
hydroxy amines, isoquinolines, etc.
The term "benzoin" is used to represent the molecule containing two
unsubstituted phenyl groups, C6H6CHOHCOC6H5, and substituents