Phase transfer catalysis polyethylene glycol

The synthetic applications of the palladium-catalyzed oxidation of alkenes to ketones have recently been reviewed. Improvements in the Wacker palladium-catalyzed ketonization of terminal alkenes have been obtained using phase-transfer catalysis, " polyethylene glycol or phosphomolybdovanadic acids. ... 

With the discovery of the crowns and related species, it was inevitable that a search would begin for simpler and simpler relatives which might be useful in similar applications. Perhaps these compounds would be easier and more economical to prepare and ultimately, of course, better in one respect or another than the molecules which inspired the research. In particular, the collateral developments of crown ether chemistry and phase transfer catalysis fostered an interest in utilizing the readily available polyethylene glycol mono- or dimethyl ethers as catalysts for such reactions. Although there is considerable literature in this area, much of it relates to the use of simple polyethylene glycols in phase transfer processes. Since our main concern in this monograph is with novel structures, we will discuss these simple examples further only briefly, below. 

It was a result of demand from industry in the mid-1960s for an alternative to be found for the expensive traditional synthetic procedures that led to the evolution of phase-transfer catalysis in which hydrophilic anions could be transferred into an organic medium. Several phase-transfer catalysts are available quaternary ammonium, phosphonium and arsonium salts, crown ethers, cryptands and polyethylene glycols. Of these, the quaternary ammonium salts are the most versatile and, compared with the crown ethers, which have many applications, they have the advantage of being relatively cheap, stable and non-toxic [1, 2]. Additionally, comparisons of the efficiencies of the various catalysts have shown that the ammonium salts are superior to the crown ethers and polyethylene glycols and comparable with the cryptands [e.g. 3, 4], which have fewer proven applications and require higher... 

In the case of acrylates mono- or disubstituted at C3, the adducts of dichlorocarbene, formed under phase-transfer catalysis conditions, react further to give the esters of 1,1,2,2-tetrachloro-spiro[2.2]pentanecarboxylic acid as the major products (Houben-Weyl, Vol. E19b, pp 1548-1549). Therefore, the catalyst(s) used for the selective cyclopropanation by phase-transfer catalysis of various acrylates vide supra) were examined. Dichlorocyclopropane 1 was formed from tert-butyl 3-methylbut-2-enoate and chloroform in the presence of 55% aqueous potassium hydroxide and a mixed catalyst polyethylene glycol ( Triton-N-lOl ) and tricapryl-methylammonium chloride ( Aliquat 336 ). The same reaction carried out in the presence of 18-crown-6 as a catalyst afforded three products, the cyclopropane as a minor product. 

Neumann, R., and Y. Sasson, An Evaluation of Polyethylene Glycol as a Catalyst in Liquid-(3as Phase Transfer Catalysis The Base Catalyzed Isomerization of Allylbenzene, /. Mo/. Cato/., 55,20/ (1985a). 

Neumann, R., and Y. Sasson, The Autooxidation ofAlkylnitroaro-matic Compounds in Base-Catalyzed Phase Transfer Catalysis by Polyethylene Glycol under Ultrasonic Condition, /. Chem. Soc., Chem. Common., 616 (1985b). 

CS Chu. Kinetics for Synthesizing Benzyl Phenyl Ether via Solid-Liquid Phase-Transfer Catalysis over Polyethylene Glycol and Quaternary Ammonium Salts. MS thesis. National Chung Hsing University, Taichung, Taiwan, 2001. 

A -Aroyl-A -substituted thiourea derivatives have been prepared from reaction of aroyl isothiocyanate with amines under solid-liquid phase transfer catalysis condition using polyethylene glycol-400 (PEG-400) as catalyst. Reaction of isothiocyanates with lithiated chiral secondary amines has provided chiral thioureas (Scheme 40). °... 

Chan, L. L., and Smid, J., Effect of the polyethylene glycol derivatives upon the reaction rate in phase-transfer processes,/. Am. Chem. Soc., 89, 4547, 1967. Panayotov, 1. M., and Tsvetanov, C. B., The role of polyfethylene glycol) in phase transfer catalysis, Makromol. Chem., 134, 313, 1970. 

MacKenzie, W, M., and Sherington, D. C., Supported polyethylene glycol and phase transfer catalysis of dehydration reactions, Polymer, 22, 431, 1981. 

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