Handbook of Solvents - George Wypych - ChemTech - Ventech!

800 Maw-Ling Wang
[13.3.2]
Inverse phase-transfer catalysis (IPTC) can be applied to synthesize symmetric and
antisymmetric acid anhydride in organic synthesis. 26,54,69,102,148-150,153 Pyridine 1-oxide
(PNO), 4-dimethylaminopyridine (DMAP), 4-pyrrolidinopyridine (PPY) and
1-methyl-2(1H)-pyridothione are usually used as the inverse phase-transfer catalysts
(IPTC). 159
[13.3.3]
The characteristics of two-phase phase-transfer catalytic (PTC) systems are: the presence
of at least two phases and at least one interfacial region separating the
phases. 24,26,42,43,50,69,107,109,110,152 The reactions involve: (1) transfer of an ion or compound
from its normal phase into the reaction phase or interfacial region, (2) reaction of the transferred
ion or compound with the non transferred reactant located in the reaction phase or interfacial
region, and (3) transfer of the product from the reaction phase or interfacial region
into its normal phase. For example, a successful NPTC process involves (1) the maximization
of the rate of transfer of reactant anions from the aqueous or solid phase to the organic
phase, (2) the maximization of the rate of transfer of product anions from the organic phase
to the aqueous phase or solid phase, and (3) the related equilibrium partitioning of the reactant
and product anions between organic and aqueous or solid phases. The anion must not
only transfer to the organic phase, but once there the anion must be in a highly reactive form.
Some organic-phase reactions are so fast that the transferred anion requires little or no activation
beyond just being delivered to the organic phase. Other reactions require substantial
anion activation before useful and practical reaction rates can be achieved. It is obvious that
the polarity of the organic solvent affects the activation of the anion as well as the difference