Phase transfer catalyst 2885779 221522284 2008-06-24T21:41:19Z 134.71.217.122 A '''phase transfer catalyst''' or '''PTC''' in [[chemistry]] is a [[catalyst]] which facilitates the migration of a reactant in a [[heterogeneous]] system from one phase into another phase where reaction can take place. Ionic reactants are often [[soluble]] in an [[aqueous]] phase but insoluble in an organic phase unless the phase transfer catalyst is present. '''Phase transfer catalysis''' (also PTC) refers to the acceleration of the reaction by the phase transfer catalyst. Phase transfer catalysts for anion reactants are often [[quaternary ammonium salt]]s. The corresponding catalysts for cations are often [[crown ether]]s. A PTC works by encapsulating the ion. The PTC-ion system has a [[hydrophilic]] interior containing the ion and a [[hydrophobic]] exterior. For example, the [[nucleophilic aliphatic substitution]] reaction of an [[aqueous]] [[sodium cyanide]] solution with the [[alkyl halide]] [[1-bromooctane]] does not ordinarily take place because 1-bromooctane does not readily dissolve in the aqueous solution. By the addition of small amounts of a [[phosphonium salt]] such as hexadecyltributylphosphonium bromide, [[cyanide]] ions can be ferried from the water phase into an organic phase (e.g., bromooctane + some hydrocarbon). With the phase transfer catalyst, [[nonanenitrile]] (1-cyanooctane) forms quantitatively in 90 minutes at reflux.<ref name=Starks1971>{{cite journal | author = Starks, C.M. | year = 1971 | title = Phase-transfer catalysis. I. Heterogeneous reactions involving anion transfer by quaternary ammonium and phosphonium salts | journal = [[J. Am. Chem. Soc.]] | volume = 93 | issue = 1 | pages = 195–199 | doi = 10.1021/ja00730a033}}</ref> :C<sub>8</sub>H<sub>17</sub>Br(org) + [[Sodium cyanide|NaCN]](aq) &rarr; C<sub>8</sub>H<sub>17</sub>CN(org) + [[Sodium bromide|NaBr]](aq) (catalyzed by a R<sub>4</sub>P<sup>+</sup>Cl<sup>&minus;</sup> PTC) Subsequent work by Herriott and Picker<ref name=Herriott1975>{{cite journal | author = Herriott, A.W. | coauthors = Picker, D. | year = 1975 | title = Phase transfer catalysis. Evaluation of catalysis | journal = [[J. Am. Chem. Soc.]] | volume = 97 | issue = 9 | pages = 2345–2349 | doi = 10.1021/ja00842a006}}</ref> demonstrated that many such reactions can be performed rapidly at around room temperature by using catalysts such as [[tetra-n-butylammonium bromide]] or [[methyltrioctylammonium chloride]] in benzene/water systems. By using a PTC process, one can achieve faster reactions, obtain higher conversions or yields, make fewer byproducts, eliminate the need for expensive or dangerous solvents which dissolve all the reactants in one phase, eliminate the need for expensive raw materials and/or minimize waste problems. Phase transfer catalysts are especially useful in [[green chemistry]] &mdash; by allowing the use of water, the need for [[organic solvent]]s is reduced.<ref>{{cite journal | author = J. O. Metzger | title = Solvent-Free Organic Syntheses | year = 1998 | journal = [[Angewandte Chemie International Edition]] | volume = 37 | issue = 21 | pages = 2975–2978 | doi = 10.1002/(SICI)1521-3773(19981116)37:21<2975::AID-ANIE2975>3.0.CO;2-A}}</ref><ref>{{cite journal | journal = [[Pure Appl. Chem.]] | volume = 72 | issue = 7 | pages = 1399–1403 | year = 2000 | title = Phase-transfer catalysis. A general green methodology in organic synthesis | author = Mieczyslaw Makosza | doi = 10.1351/pac200072071399}}</ref> Contrary to common perception, PTC is not limited to systems with aqueous and organic soluble reactants. PTC is sometimes employed in liquid/solid and liquid/gas reactions. As the name implies, one or more of the reactants are transported into a second phase, which contains the other reactants. ==References== {{reflist}} [[Category:Catalysts]] [[fr:Catalyseur de transfert de phase]] [[it:Catalisi per trasferimento di fase]] [[ja:相間移動触媒]] [[pl:Katalizatory przeniesienia fazowego]]