11. Interfacial Mechanism and Kinetics of Phase-Transfer Catalysis
11. Interfacial Mechanism and Kinetics of Phase-Transfer Catalysis
11. Interfacial Mechanism and Kinetics of Phase-Transfer Catalysis
You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
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 Er<strong>of</strong>eev equation described the observed kinetics much betterthan other simple kinetic equations. Yufit <strong>and</strong> Zinovyev [212] compared the kinetic study <strong>of</strong>nucleophilic substitution under PTC conditions in liquid–liquid <strong>and</strong> solid–liquid systems.They observed the effect <strong>of</strong> initial exponential burst (IB) on the kinetic curve in the reactionwith solid salts for the S N 2 reaction <strong>of</strong> 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 <strong>of</strong> complexes <strong>of</strong> salts, catalysts, <strong>and</strong>substrate [212–215]. They also concluded that the phenomenon <strong>of</strong> IB was characterized bythe first-order dependence on the initial stage <strong>of</strong> conversion <strong>and</strong> by zero-order dependenceup to high conversion. Therefore, the kinetic equation for the reaction becomes a sum <strong>of</strong>linear <strong>and</strong> exponential terms with correlated parameters A <strong>and</strong> B½PŠ ¼At þ½XŠð1 exp BtÞ ð107Þwhere P represents the key product, [X] is the concentration <strong>of</strong> product formed by the firstorderlaw, <strong>and</strong> 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 <strong>of</strong> topochemical reaction, which meansthat the reaction rate is dependent on the characteristics or properties <strong>of</strong> the interface, hasbeen proposed by Yang <strong>and</strong> Wu [216] in investigating the esterification <strong>of</strong> 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 <strong>of</strong> SeK 2 from the solid surface to the organic film.SeK 2 ðsolidÞ !SeK 2 ðorgÞð116ÞCopyright © 2003 by Taylor & Francis Group, LLC