Handbook of Solvents - George Wypych - ChemTech - Ventech!

832 Maw-Ling Wang
ied. 82,83,97,101 Much work has been done on
the preparation and testing of phase-transfer
catalysts supported on resins including
extensive work by Montanari and
co-workers 71,74 and by Ford and Tomoi 28
and their co-workers. Most published
works on resin-bound phase-transfer catalysts
use a styrene-divinylbenzene resin
(SDV) and related resins, taking advantage
of the huge amount of technology available on these resins due to their use as ion-exchange
resin supports (Figure 13.3.11).
Tomoi and co-workers 117 suggest that solvents may affect rates of triphase-catalyzed
reaction in three ways: intrinsic chemical reactivity; solvent effect on ion-exchange rate;
and overall activity, including diffusion effects due to swelling of polymer-supported
phosphonium salts under three-phase conditions. First, the intrinsic activity of the catalysts,
as well as of soluble phosphonium salts, depended slightly on organic solvents for cyanide
displacement reactions. Second, the exchange rate of chloride ion in the catalysts vs. that of
acetate depends on the solvents when the degree of ring substitution is less than 16%. With
30% ring-substituted catalysts, the rate increases and hardly depends on the solvents. Third,
the overall catalyst reactivity for the reaction of organic halides with NaCN depends on the
substrate and organic solvents. For 1-bromooctane, the catalysts were more reactive in good
solvents (e.g., chlorobenzene) than in poor solvent (e.g., octane). Shan and co-workers, 98
Wang and Wu 136,137 examined the effects of solvents and other resin-bound catalysts parameters
(macroporosity, microporosity, crosslink density and size of catalyst pellet). They all
show that the swelling in organic solvents is an important factor affecting the conversion of
the reactant, as shown in Table 13.3.26. 98
Figure 13.3.11. Crosslink to other polymer chains.
Table 13.3.26. Effect of the organic solvent on the yield of ester from benzyl bromide
and aqueous KOAc under standardized conditions
Catalyst a
Macro (6%)-400
Micro (6%)-400
Solvent (dielectric constant, ε) b
Cyclohexane (2.02)
Toluene (2.38)
Chlorobenzene (5.62)
Benzyl ethyl ketone (17.4)
Nitrobenzene
Cyclohexane (2.02)
Toluene (2.38)
Chlorobenzene (5.62)
Benzyl ethyl ketone (17.4)
Nitrobenzene
Yield of ester, %
13.2
16.5
23.3
94.5
100.0
9.2
13.5
18.2
86.0
100.0
Data obtained from Shan, Kang and Li; 98 a 6% crosslinking; b PEG-400 used for active sites on catalyst