Organic Reactions Volume 4 - Sciencemadness Dot Org

364 ORGANIC REACTIONS
("quinoline-S," thioquinanthrene, phenylisothiocyanate, thiourea). In
many reductions, however, it is not necessary to use a regulator, and
in some the use of the poison appears to be definitely disadvantageous.
Moreover, it has been reported u that the decisive factor in the acid
chloride reduction is the temperature; if it is kept near the lowest point
at which hydrogen chloride is evolved, the aldehydes are obtained in
optimal yields.
If further reduction of the aldehyde to alcohol and hydrocarbon does
take place, both the alcohol and the water react with the acid chloride,
yielding the ester and the acid anhydride, respectively. The formation
RCOCl + RCH2OH -> RCO2CH2R + HCl
RCOCl + H2O -» RCO2H + HCl
RCOCl + RCO2H -» (RCO)2O + HCl
of the acid anhydride is said to be an important side reaction in the
reduction of certain heterocyclic acid chlorides when traces of oxygen
and water are present in the hydrogen used. 12 Other reductions which
may occur as side reactions involve the formation of the ether,
RCH2OCH2R; and the cleavage of the ester, RC(^CH2R, to the acid,
RCO2H, and the hydrocarbon, RCH3. 3 - 4 These appear to be of no
practical significance, however.
Some acid chlorides undergo reductive removal of the —COCl group
according to the following scheme:
RCOCl + H2 -> RH + CO + HCl
This cleavage occurs as a side reaction in the reduction of many heterocyclic
acid chlorides and has been observed in the preparation of aldehydes
from p-anisoyl, 3 3,4,5-trimethoxybenzoyl, 13 and 2-naphthoyl chloride.
14 Tripheny!acetyl chloride is converted quantitatively to triphenylmethane.
15
The Rosenmund method appears to be generally applicable to the
preparation of aliphatic and aromatic monoaldehydes when the corresponding
acid chlorides are available. There have been fewer occasions
to use it in the aliphatic series than in the aromatic and heterocyclic
groups; however, the preparation of chaulmoogryl aldehyde 16 from the
11 Boehm, Schumann, and Hansen, Arch. Pharm., 271, 490 (1933).
12 Rojahn and Fahr, Ann., 434, 252 (1923).
13 Spath, Monatsh., 40, 129 (1919).
14 Hershberg and Cason, Org. Syntheses, 21, 84 (1941).
15 Daniloff and Venus-Danilova, Ber., 59, 377 (1926).
16 Wagner-Jauregg and Voigt, Ber., 71, 1973 (1938).