11. Interfacial Mechanism and Kinetics of Phase-Transfer Catalysis

More documents

Recommendations

Info

FIG. 7 Effect of solvent on formation of PhOQ in SLPTC: benzyl bromide 0.005 mol, sodiumphenoxide 0.005 mol, TBAB 0.001 mol, solvent 50 mL, agitation 350 rpm, temperature 70 C; (*)C 6 H 5 Cl, (~) C 6 H 4 Cl 2 ,(&) n-C 7 H 16 .the TCs. From the kinetic analysis of different reaction mechanisms, the observed reactionrate constant k obs was determined by the equation:k obs ¼k½MYŠ 0 ½QXŠ 01 þ K½RXŠ 0 ½MYŠ 0 þ½QXŠ 0 ð99ÞIn Eq. (99), k is the combined rate constant and K is the equilibrium constant for thereversible reaction of TC formation.Generally, many experimental results can be described by applying pseudo-firstorderor pseudo-second-order kinetics successfully. Sometimes, however, using confinedkinetic data to elucidate exactly the reaction mechanism is indeed difficult. Hence, severalsimplified reaction mechanisms are usually employed to describe the kinetic behaviors ofthe reaction systems successfully. The technique of topochemistry is an effective methodfor achieving an approximate and quite precise interpretation of the kinetic data. Sirovskiet al. [209] discussed the applicability of the models developed for the topochemical reactionsin SLPTC. They considered that the simplest kinetic equation, called the Erofeevequation [210,211]:x ¼ 1 exp k n ð Þ ð100Þwith the rate constant k, the conversion degree x, and the parameter n depending on thegeometry of the nuclei, is more appropriate for a description of SLPTC than more complicatedones recommended in the literature. Such a kinetic equation is widely used for thedescription of topochemical processes. Sirovski et al. [209] investigated an S N 2 reaction ofbenzyl chloride with sodium acetate under SLPTC conditions:PhCH 2 Cl þ AcON Aliquat !336 PhCH 2 OAcð101ÞThey observed that the reaction rate did not follow simple kinetic laws under their operatingconditions. A possible reaction scheme was thus proposed [209]:Copyright © 2003 by Taylor & Francis Group, LLC
QCl þ AcONa ðsÞ ÐQCl:AcONa ðsÞQCl:AcONa ðsÞþPhCH 2 Cl Ð QCl:AcONa:PhCH 2 ClQCl:AcONa:PhCH 2 Cl ! QCl:NaCl:PhCH 2 OAcQCl:NaCl:PhCH 2 OAc Ð QCl:NaCl ðsÞþPhCH 2 OAcQCl:NaCl ðsÞ ÐQCl þ NaCl ðsÞð102Þð103Þð104Þð105Þð106ÞThey also found that the Erofeev equation described the observed kinetics much betterthan other simple kinetic equations. Yufit and Zinovyev [212] compared the kinetic study ofnucleophilic substitution under PTC conditions in liquid–liquid and solid–liquid systems.They observed the effect of initial exponential burst (IB) on the kinetic curve in the reactionwith solid salts for the S N 2 reaction of 2-octylmesylate with potassium halides under PTCconditions. In their study, they assumed that the active sites on which the reaction occuredwere present on the solid surface through the formation of complexes of salts, catalysts, andsubstrate [212–215]. They also concluded that the phenomenon of IB was characterized bythe first-order dependence on the initial stage of conversion and by zero-order dependenceup to high conversion. Therefore, the kinetic equation for the reaction becomes a sum oflinear and exponential terms with correlated parameters A and B½PŠ ¼At þ½XŠð1 exp BtÞ ð107Þwhere P represents the key product, [X] is the concentration of product formed by the firstorderlaw, and t is the reaction time. They also proposed a reaction mechanism includingthe adsorption on the solid surface for the solid–liquid system [212]:KBr ðsÞþQCl ð1Þ !KCl ðsÞþQBr ð1Þð108ÞQBr ð1ÞþROMs ð1Þ !QOMs ð1ÞþRBr ð1ÞQOMs ð1ÞþKBr ðsÞ ÐQOMs:KBr ðadsÞQOMs:KBr ðadsÞþROMs ð1Þ ÐQOMs:KBr:ROMs ðadsÞQOMs:KBr:ROMs ðadsÞ !RBr ð1ÞþQOMs:KOMs ðadsÞQOMs:KOMs ðadsÞþKBr ðsÞ ÐQOMs ð1ÞþKOMs:KBr ðadsÞð109Þð110Þð111Þð112Þð113ÞKOMs:KBr ðadsÞ !KOMs ðsÞþKBr ðsÞð114ÞAnother mechanism based on the concept of topochemical reaction, which meansthat the reaction rate is dependent on the characteristics or properties of the interface, hasbeen proposed by Yang and Wu [216] in investigating the esterification of linear dicarboxylateusing SLPTC for solid dipotassium sebacate (SeK 2 ) reacted with benzyl bromide(RBr). The overall reaction isKOOCC 8 H 16 COOK ðsÞþ2C 6 H 5 CH 2 Br ðorgÞ QBr!C 6 H 5 CH 2 OOCC 8 H 16 COOC H 2 C 6 H 5 ðorgÞþ2KBrðsÞð115ÞThe reaction steps involves [216]:1. Dissolution of SeK 2 from the solid surface to the organic film.SeK 2 ðsolidÞ !SeK 2 ðorgÞð116ÞCopyright © 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: solubility in the organic phase, th
Page 47 and 48: curve of the product SeK 2 . The pa
Page 49 and 50: Taking the mass balance for the cat
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

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?