Liquid-solid-liquid triphase catalysis. Consideration of the rate-limiting step, role of stirring, and catalyst efficiency for simple nucleophilic displacement

Abstract

Results and DiscussionSuch a phase shift makes it difficult to measure J from the coupled spectrum. We report here a simple means for removing this phase shift, so that all lines in the multiplet have identical phase. The modification, called by the palindrome PCJCP (phase corrected J-cross polarization), consists of the conventional JCP sequence1'5 6 in which either the I or S spin locking rf field remains on an additional time Í90 given by 7s5|st9o = 7i-S| [Í90 = tt/2. As usual, 713 is the magnetogyric ratio and Bn.s is the rf field strength for the nuclear species 1,S. To the extent that it is instantaneous, the S extension pulse flips the transverse S magnetization into the direction of the static field, where it is unobservable. An I extension pulse, either in phase or in quadrature with the cross-polarization rf, can also be used; the explanation in this case is more involved and will appear elsewhere.4 The operation of this sequence is shown in Figure 1. During cross polarization the multiplet lines grow at different rates4 and the conventional multiplet intensity ratios are not preserved either in JCP or PCJCP.The ease of operation suggests that, for a weak resonance of unknown J, one should use a reasonable guess for the cross-polarization time to produce a coupled cross-polarization spectrum by PCJCP. The value of J determined is then 4059 used to select an optimal r for maximum cross-polarization signal.The PCJCP sequence is best used near resonance (| -7¿?oI « 761). Operating significantly off resonance introduces amplitude asymmetries in the S multiplet which the tt/2 extension pulse will convert back into phase shifts. In a reciprocal manner, any phase shifts initially present will, under off-resonance operation, be converted by the pulse extension into an asymmetry in the multiplet. References and Notes(1) P.

Catalytic Potential of a New Polymer-Anchored Multisite Phase Transfer Catalyst in the Dichlorocarbene Addition to Indene

“…Quaternary onium salts, crown ethers and cryptands have all been immobilized on various kinds of supports, including polymers (most commonly (methylstyrene-costyrene) resin crosslinked with divinylbenzene), alumina, silica gel, clays, and zeolites [10][11][12][13][14][15][16][17][18][19][20][21]. We previously [22] demonstrated the feasibility of triphase catalysis for the alkylation of phenylacteonitrile.…”

Role of Mass Transfer in Phase Transfer Catalytic Heterogeneous Reaction Systems

“…crown ethers and cryptands have all been immobilized on various kinds of supports, including polymers (most commonly (methylstyrene-costyrene) resin crosslinked with divinylbenzene), alumina, silica gel, clays, and zeolites [40][41][42][43][44][45][46][47][48][49][50][51]. Kinetics of triphase phasetransfer-catalyzed reactions [52] are influenced by (i) mass transfer of reactant from bulk liquid to catalyst surface; (ii) diffusion of reactant through polymer matrix to active site; (iii) intrinsic reaction rate at active site; (iv) diffusion of product through polymer matrix and mass transfer of product to external solution; (v) rate of ion exchange at active site.…”

Kinetic study of reaction of hexachlorocyclophosphazene with phenol by triphase catalysis

“…Thus, the insoluble polymer-supported phase-transfer catalyst can be easily separated from the reaction mixtures simply by filtration or centrifugation. The most common method used for triphase catalysis was studied by Regen (1975Regen ( , 1976Regen ( , 1977Regen ( , 1979, Regen and Besse (1979), Tomoi and Ford (1981a, b) and Tomoi et al (1982Tomoi et al ( ,1983Tomoi et al ( ,1985.In the past, the characteristics of a reaction subjected to the mass transfer limitation of the reactants and ion exchange rate in the aqueous phase have been discussed (Tomoi et al, 1983;Marconi and Ford, 1983; Telford et al, 1986;Cha, 1987;Wang and Wu, 1992b). The ion exchange rate in the aqueous phase affects the reactivity of the triphase 'Author to whom correspondence may be addressed.…”

“…Thus, the insoluble polymer-supported phase-transfer catalyst can be easily separated from the reaction mixtures simply by filtration or centrifugation. The most common method used for triphase catalysis was studied by Regen (1975Regen ( , 1976Regen ( , 1977Regen ( , 1979, Regen and Besse (1979), Tomoi and Ford (1981a, b) and Tomoi et al (1982Tomoi et al ( ,1983Tomoi et al ( ,1985.…”