11. Interfacial Mechanism and Kinetics of Phase-Transfer Catalysis

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quaternary cation solvates the solid reactant anion much more easily, and leads to a fasterinitial reaction rate. The order of reactivity for different PT catalysts is determined asTBPB > TBAB > TBAI TBAHS Aliquat 336 for the reaction.Yang et al. [219] investigated the kinetics of the etherification of ethyl 2-bromoisobutyrate(RX) with potassium 4-benzyloxyphenoxide in the presence of potassium iodidein SLPTC. In that work, we found that for various molar ratios of TBAB to RX (denotedas f ) the yield of product ArOR increased with increasing catalyst amounts up to f ¼ 0:60.Too much catalyst employed in the presence of KI results in the reduction of catalyticefficiency. This effect is due to two major reasons: first, the solubility of the catalyticintermediate in the organic solvent is limited; second, the formation of the catalytic intermediatein chlorobenzene is retarded because use of a higher amount of catalyst inducedrapid deposition of the generated potassium salts on the solid surface. Adding the extrasalt KI enhances the reactivity of PT catalyst, but the active intermediate in the organicphase is diminished when much KI is present. Small amounts of KI promote the conversionof RX into RI, which is more reactive in the organic reaction. The reaction stepsconcerning the deactivation of the catalyst are shown below [219].The overall reaction isKI;QXArOK ðsÞþRX ðorgÞ ! ArOR ðorgÞþKX ðsÞ ð124ÞThe reaction mechanism for the overall reaction is as the following steps:ArOKðsÞ ! ArOK ðorgÞKI ðsÞ ! KI ðorgÞð125Þð126ÞK 1!KI ðorgÞþQX ðorgÞ KX ðorgÞþQI ðorgÞð127ÞK 2!KI ðorgÞþRX ðorgÞ KX ðorgÞþRI ðorgÞð128ÞKXðorgÞ ! KX ðsÞð129ÞK 3!ArOK ðorgÞþQX ðorgÞ ArOQ ðorgÞþKX ðorgÞð130ÞK 4ArOK ðorgÞþQI ðorgÞ! ArOQ ðorgÞþKI ðorgÞð131ÞRX ðorgÞþArOQ ðorgÞk b! ArOR ðorgÞþQX ðorgÞð132ÞRI ðorgÞþArOQ ðorgÞk b! ArOR ðorgÞþQI ðorgÞð133ÞThe rate of change of ArOR is then expressed asdC orgArOR¼ kdt a C orgRX þ k bC org RI CorgArOQð134ÞCopyright © 2003 by Taylor & Francis Group, LLC
Taking the mass balance for the cation Q of the PT catalyst in the system givesC orgQX;0 ¼ Corg QX þ Corg QI þ Corg QrOQThe expression for the active intermediate isC orgArOQ ¼1 þ 1C org ArOKC orgQX;0C orgKXþ Corg KIK 3 K 4ð135Þ ð136ÞThe concentration of ArOQ depends on the amounts of ArOK, KX, and KI, and theinitial usage of the catalyst QX. Combining the mass balance equation for initial RX in theorganic phase with Eq. (134), a deactivation function can be introduced in the situationunder decline of catalytic efficiency, leading to the following equations:withdC orgArORdt¼ k app;0C orgRX;0C orgArORk app;0 ¼ðk a þ k b K 2 C orgKI =Corg KX ÞCorg QX;0ð137Þand1 ¼ 1 þ K 2C org ð138ÞKIC org 1 þ 1 C orgKXC org KXþ Corg KIArOK K 3 K 4In Eq. (137), k app;0 is the initial apparent reaction rate constant and is dependent on theamounts of KI, KX, and QX in the organic phase. If the rate of change of ArOR follows apseudo-first-order reaction, then would be approximately a constant. In such cases, nodeactivation effect appears. If the reaction rate behaves as a diminished first order, then decreases with the progress of the overall reaction.To evaluate the exact variation of with time is to measure the rate of deposition ofKX and the other parameters directly or to apply an empirical correlation relating to theeffect of the decrease in C orgArOKon the overall reaction. The expression of the deactivationfunction and the kinetic data would determine the form of , such as1 ¼ð1 þ k d tÞ 2 or ¼ 1ð139Þ1 þ k d tLepertit and Che [220] discussed the definitions of interfacial co-ordination chemistry(ICC) and surface organometallic chemistry (SOMC) and compared their maincharacteristics and applications. The concepts of ICC applied to catalyst preparation,adsorption, and relations with catalysis are also useful in the development of interfacialmechanisms.C. Mass Transfer EffectsSufficient kinetic information should be collected to proceed the process design for aspecific reaction system. The factors affecting the performance of SLPTC includes agitationrate, particle size of solid salt, reaction temperature, the amount of solid reactant, thekinds and amount of PT catalyst, the solubility and the dissolution rate of solid reactant inthe organic solvent, extra addition of other metal salts, the polarity, surface tension, andCopyright © 2003 by Taylor & Francis Group, LLC
Page 1 and 2: 11Interfacial Mechanism and Kinetic
Page 3 and 4: Other factors in selecting asuitabl
Page 5 and 6: 1. Applications in BiologyOrsini et
Page 7 and 8: Tundo et al. [15] reported an effic
Page 9 and 10: transfer of catalyst from the react
Page 11 and 12: A summary of characteristic kinetic
Page 13 and 14: dy 1ady o¼ QYy ody 2ody o¼ QXy
Page 15 and 16: (a) Pseudo-Steady-State LLPTC model
Page 17 and 18: The order of magnitude of D Q for q
Page 19 and 20: E T Q þ ;H 2 O ¼ ½Qþ Š½X :jH
Page 21 and 22: Gustavii [101] and Bockries and Red
Page 23 and 24: The mass transfer resistances stron
Page 25 and 26: The extractive effectiveness factor
Page 27 and 28: Quaternary onium salts, crown ether
Page 29 and 30: 26 > Dowex 1 2 > A-27 IRA-410 > I
Page 31 and 32: C 6 H 6 > C 6 H 5 CH 3 and the tren
Page 33 and 34: Many experimental studies on three-
Page 35 and 36: FIG. 4 Yields of products and conve
Page 37 and 38: transfer of organic or aqueous reac
Page 39 and 40: [187-196]. Several reactions that c
Page 41 and 42: the solid salt directly reacts with
Page 43 and 44: solubility in the organic phase, th
Page 45 and 46: QCl þ AcONa ðsÞ ÐQCl:AcONa ðs
Page 47: curve of the product SeK 2 . The pa
Page 51 and 52: The ion-exchange reaction occurs at
Page 53 and 54: in both aqueous and organic phases
Page 55 and 56: Type I.The catalyst resides in the
Page 57 and 58: V orgk obs ¼V org þD A V thirdk o
Page 59 and 60: @C orgRX@t@C catQY@t@C catQX@t¼ D
Page 61 and 62: tively. When the amount of the thir
Page 63 and 64: V org volume of organic phase (L)Xa
Page 65 and 66: 44. Halpern, HA Zahalka, Y Sasson,
Page 67 and 68: 140. SL Regen. Angew Chem, Int Ed E
Page 69: 223. SD Naik, LK Doraiswamy. AIChE

11. Interfacial Mechanism and Kinetics of Phase-Transfer Catalysis

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