Transfer catalysis

The benzoic acid derivative 457 is formed by the carbonylation of iodoben-zene in aqueous DMF (1 1) without using a phosphine ligand at room temperature and 1 atm[311]. As optimum conditions for the technical synthesis of the anthranilic acid derivative 458, it has been found that A-acetyl protection, which has a chelating effect, is important[312]. Phase-transfer catalysis is combined with the Pd-catalyzed carbonylation of halides[3l3]. Carbonylation of 1,1-dibromoalkenes in the presence of a phase-transfer catalyst gives the gem-inal dicarboxylic acid 459. Use of a polar solvent is important[314]. Interestingly, addition of trimethylsilyl chloride (2 equiv.) increased yield of the lactone 460 remarkabiy[3l5]. Formate esters as a CO source and NaOR are used for the carbonylation of aryl iodides under a nitrogen atmosphere without using CO[316]. Chlorobenzene coordinated by Cr(CO)j is carbonylated with ethyl formate[3l7]. 

Aryl sulfides are prepared by the reaction of aryl halides with thiols and thiophenol in DMSO[675,676] or by the use of phase-transfer catalysis[677]. The alkenyl sulfide 803 is obtained by the reaction of lithium phenyl sulfide (802) with an alkenyl bromide[678]. 

NaH must be used when the starting thiazolones are not easily enolized (453, 467). Phase-transfer catalysis could be helpful for this t pe of reactivity. 

More recently, the use of phase-transfer catalysis to promote the deproto-deuteration of thiazole and various alkylthiazoles enabled Spil-lane and Dou (435) to increase considerably the rate of H/D exchange and afforded the possibility of labeling alkylthiazoles in preparative quantities and at positions otherwise difficult to label. 

Sulfides (172) in which Rj = alkyl can be obtained also by direct alkylation of the 2-mercaptothiazoles either in alcaline medium (156, 597) or by phase-transfer catalysis in better yield (824). 

This property of quaternary ammonium salts is used to advantage m an experi mental technique known as phase transfer catalysis Imagine that you wish to carry out the reaction... 

Phase transfer catalysis is the subject of an article in the April 1978 issue of the Journal of Chemical Educa tion (pp 235-238) This arti cle includes examples of a variety of reactions carried out under phase transfer conditions... 

Phase transfer catalysis succeeds for two reasons First it provides a mechanism for introducing an anion into the medium that contains the reactive substrate More important the anion is introduced m a weakly solvated highly reactive state You ve already seen phase transfer catalysis m another form m Section 16 4 where the metal complexmg properties of crown ethers were described Crown ethers permit metal salts to dissolve m nonpolar solvents by surrounding the cation with a lipophilic cloak leav mg the anion free to react without the encumbrance of strong solvation forces... 

Quaternary ammonium salts compounds of the type R4N" X find application m a technique called phase transfer catalysis A small amount of a quaternary ammonium salt promotes the transfer of an anion from aqueous solution where it is highly solvated to an organic solvent where it is much less solvated and much more reactive... 

Phase separation Phase structure Phase-transfer agents Phase-transfer catalysis... 

Phase Transfer Catalysis in Industry, PTC Interface, Inc., Marietta, Ga. 

C. M. Starks and C. Liotta, Phase Transfer Catalysis, Academic Press, Inc., New York, 1978. 

A method for the polymerization of polysulfones in nondipolar aprotic solvents has been developed and reported (9,10). The method reUes on phase-transfer catalysis. Polysulfone is made in chlorobenzene as solvent with (2.2.2)cryptand as catalyst (9). Less reactive crown ethers require dichlorobenzene as solvent (10). High molecular weight polyphenylsulfone can also be made by this route in dichlorobenzene however, only low molecular weight PES is achievable by this method. Cross-linked polystyrene-bound (2.2.2)cryptand is found to be effective in these polymerizations which allow simple recovery and reuse of the catalyst. 

C. Starks, Ind. Appl. Surfactants IZ, 77, 165 (1990) C. Starks, ed., Phase-Transfer Catalysis Neir Chemisty, Catalysts and Applications American Chemical Society, Washington, D.C., 1987 E. Dehmlov, Phase-Transfer Catalysis Vedag Chemie, Deerfield Beach, Fla., 1983 M. Halpem, Phase-Transfer Catalysis in Climan s Tnyclopedia of Industrial Chemisty Vol. A19, VCH V6, New York, 1991 M. Halpem, Phase-Transfer Catalysis Commun. 1, 1 (1995). Specialty Sufactants Worldwide in Specialty Chemicals SRI International, Menlo Park, Calif., 1989, pp. 81—94. 

The reaction of thiophosgene with various bisphenols using phase-transfer catalysis gives polythiocarbonates (44) ... 

Industrial examples of phase-transfer catalysis are numerous and growing rapidly they include polymerisa tion, substitution, condensation, and oxidation reactions. The processing advantages, besides the acceleration of the reaction, include mild reaction conditions, relatively simple process flow diagrams, and flexibiHty in the choice of solvents. 

---