Tetrabutylphosphonium halide

The alkylation of sodium 2-naphthoxide with benzyl bromide in tetrabutylam-monium and tetrabutylphosphonium halide salts was investigated by Brunet and Badri [50] (Scheme 5.1-21). The yields in this reaction were quantitative, and alkylation occurred predominantly on the oxygen atom of the naphthoxide ion (typically 93-97 %). The rate of the reaction was slower in the chloride salts, due to the benzyl bromide reacting with chloride ion to give the less reactive benzyl chloride. 

Because of the wide range of alkyl substituents and anions, phosphonium salts can be very hydrophilic or hydrophobic this in turn determines the miscibility of various solvents as outlined in Table 2. At the one extreme are salts such as the tetrabutylphosphonium halides which are hygroscopic solids which will form 80-85% aqueous solutions and which are very insoluble in nonpolar solvents such as hexane. At the other end of the scale are such salts as trihexyl(tetradecyl)phospho-nium bistriflamide and hexafluorophosphate which are very hydrophobic and are totally miscible with nonpolar solvents. 

Data in Table I illustrate the production of acetic acid from 1/1 syngas catalyzed by ruthenium-cobalt halide bimetallic combinations dispersed in tetrabutylphosphonium bromide (m.p. 100°C). 

Reactions conducted in molten quaternary phosphonium salts require no other solvent (199). This material serves as both promoter and reaction medium. Care must be exercised in choosing the salt in such a reaction, since any decomposition could lead to products such as trialkylphosphines and alkyl halides which are expected to be deleterious to catalyst performance. Tetrabutylphosphonium bromide is reported to provide a stable catalyst medium which can be recycled (199, 200), but other related salts show evidence of thermal decomposition during catalytic reactions. Experiments in tetrabutylphosphonium acetate, for example, are found to produce large amounts of methyl and ethylene glycol acetate esters (199). 

Data in Table V illustrate the production of acetic acid from 1/1 syngas. A variety of ruthenium-containing precursors - coupled with cobalt halide, carbonate and carbonyl compounds - at different initial Co/Ru atomic ratios, have been found to yield the desired carboxylic acid when dispersed in tetrabutylphosphonium bromide. In a more detailed examination of the ruthenium-cobalt-iodide melt catalyst system, we have followed the generation of acetic acid and its acetate esters as a function of catalyst composition and certain operating parameters, and examined the spectral properties of these reaction products, particularly with regard to the presence of identifiable metal carbonyl species. 

Many catalysts can be used tetrabutylammonium halides, tetrabutylammonium hydroxide, tetrabutylammonium hydrogen sulfate, tetrabutylphosphonium bromide, 18-crown-6 ether, and cryptand[2.2.2]. There have been few studies on the influence of the catalyst on the reactions. However, Nishibuko et al carried out an excellent study on the influence of experimental conditions on phase transfer catalyzed polymer modification they showed that the nature of the catalyst and the type of phase transfer reaction (solid-liquid, liquid-liquid), as well as the polarity of the solvent are very important parameters. The purity of the system must be carefully controlled thus, the presence of traces of water may have a great influence on the conversion and the occurrence of side reactions. 

---