Chemistry Reference
In-Depth Information
NHMe
NHMe
Cl
CH
2
CN
CN
Cl
NO
2
CH
Cl
NO
2
NaOH, PTC
NHMe
O
DMA, TEBA
Cl
C
NO
2
air
PTC=phase-transfer catalyst
DMA=dimethyl acetamide
Scheme 10.16
Cl
Cl
Me
Cl
O
N
Me
25% NaOH
TBAB, 65
°
C, 4 h
+
Me
N
OH
O
2
N
O
2
N
Me
CH
3
CH
3
71% yield
Scheme 10.17
LiAlH
4
, NaH and dimethyl sulfate was circumvented
and replaced with environmentally benign alterna-
tives, chiefly under PTC conditions. In this process
diaryl acetonitrile was formed via PTC arylation of
arylacetonitrile. Direct air oxidation yielded the
desired diaryl ketone (Scheme 10.16).
its hydration in the organic phase. Sawant
et al
. pub-
lished a comprehensive study explicating the process
development aspects of the reaction of benzyl chlo-
ride to yield benzyl ether [100].
Oxime ethers were prepared via basic PTC alkyla-
tion of oximes with dialkylcarbonates [101] or
dialkyl sulfates [102]. Acetone oxime was etherified
(Scheme 10.17) with substituted nitrochlorobenzene
in the presence of TBAB [103].
Aromatic difluoromethyl ethers were prepared
from substituted phenols and CHClF
2
. Typical sub-
strates (Scheme 10.18) were hydroxybenzaldehydes
[104] and dihydroxypyrimidines [105].
The solid/liquid PTC reaction of dipotassium
phthalate with benzyl bromide to yield dibenzyl
phthalate was analysed by Yang & Wu [106]. These
researchers resolved a kinetic model based on the
solid/liquid equilibration of the substrate in the pres-
ence of the onium catalyst. The rate data under
different conditions of concentration, agitation, tem-
perature, solvent and catalyst was interpreted using
pseudo-second-order kinetics. The model and some
of the conclusions of Yang & Wu were challenged by
Pilipauskas [107], who rejected the possibility of het-
erogeneous anion exchange and solubilisation in the
above reaction.
Hydrolysis of benzyl and alkyl chlorides to the cor-
responding alcohols via ester intermediates is a well-
established PTC technique [108]. This methodology
Phase-transfer catalysis in etherification, esterification
and hydrolysis reactions
These reactions are traditional PTC domains. Only a
few recent reports communicate genuine new devel-
opments and some are summarised below.
A comprehensive study on the synthetic scope
and mechanism of the etherification of halo esters
was carried out by Yang
et al
. [96]. The kinetics and
mechanism of the solid/liquid allylation of sodium
phenoxide was elucidated by the same group [97].
Wang analysed the PTC mechanism of the reaction
of 2,4,6-tribromophenol with dibromomethane [98]
and with a-bromo-
o
-xylene [99]. An exceptional
phenomenon in which the reaction rate in these
reactions did not change monotonously with the
concentration of the base (KOH) was observed. The
rate increased, decreased, increased again and then
remained constant with increasing amount of KOH.
This peculiar finding was attributed to the non-linear
change in the distribution of the intermediate ArOQ
(Q-quaternary ammonium) between the phases and
