Use of Alkylphosphonium Salts

SCHEME 6.13 Example of the Fiirst-Plattner product from a pyranose epoxide. 

SCHEME 6.15 Furanose epoxides are substrates for nucleophilic ring opening. 

SCHEME 6.16 Mechanism for phosphine mediated conversion of alcohols to halides. 

SCHEME 6.17 Phosphine mediated conversion of a primary hydroxyl group to a bromide. 

SCHEME 6.18 Phosphine mediated conversion of a secondary alcohol to an iodide. 

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The use of tetra-alkylphosphonium salts to catalyse heterogeneous reactions involving anion transfer has been described. ... 

K. Okamoto and M. Okamoto also investigated the biodegradability of neat PBS before and after nanocomposite preparation with three different types of OMLF. They used alkylammonium or alkylphosphonium salts for the modification of pristine layered silicates, and these surfactants are toxic for microorganisms [56]. 

Two standard routes to y-functional phosphonium salts with electron-withdrawing groups consist in using the corresponding Michael alkenes to achieve either halide substitution in the -position to the functional group, in order to obtain y-functional vinylphosphonium salts, or Michael addition in the presence of acid to produce the y-functional alkylphosphonium salt (reaction 85). 

Formulations by National Starch also include antioxidant species, including phosphorus-based [123], hindered phenols [124] or aromatic amines [125]. Allied Chemical use ethylene carbonate along with an alkali metal iodide, whereas Rhodia enhance the reactivity of the ethylene carbonate by including an alkylphosphonium salt as... 

The early work mainly used alkylammonium and alkylphosphonium salts dispersed on commercially available packing materials such as chromosorb [25-27]. These packed SILP columns had two major drawbacks, namely, low thermal stability (Tjjjjx < 200 °C) and poor separation efficiency. One of the first examples of an IL overcoming these limitations was 1-ethylpyridinium bromide ([EPy]Br)... 

Room temperature ionic liquids arc currently receiving considerable attention as environmentally friendly alternatives to conventional organic solvents in a variety of contexts.144 The ionic liquids have this reputation because of their high stability, inertness and, most importantly, extremely low vapor pressures. Because they are ionic and non-conducting they also possess other unique properties that can influence the yield and outcome of organic transformations. Polymerization in ionic liquids has been reviewed by Kubisa.145 Commonly used ionic liquids are tetra-alkylammonium, tetra-alkylphosphonium, 3-alkyl-l-methylimidazolium (16) or alkyl pyridinium salts (17). Counter-ions are typically PF6 and BF4 though many others are known. 

A number of methods used for preparing phosphonium compounds has already been indicated on p. 7. Some tetra-alkylphosphonium hydroxides may be produced by heating white phosphorus and the corresponding alcohol above 250° C. for a long period. The compound PgHgg reacts with alkyl iodides to form quaternary compounds, and the latter also occur when trialkylphosphines react with alkyl halides. There are also special methods of preparation applying only to individual derivatives. The iodides are converted into the hydroxides by treatment with moist silver oxide, and bromides, cyanides, carbonates, acetates, oxalates and sulphates are similarly obtained when the appropriate silver salt is used. Such salts also result when the hydroxides are treated with the corresponding acids. 

Thermotropic liquid crystallinity is also presented by alkylphosphonium halides. The influence of covalently attaching hydroxymethylene to the methyl groups of methyl-tri-n-alkylphosphonium halides (the alkyl chains are decyl, tetradecyl, or octadecyl and the halide is chloride or bromide) or adding methanol as a solute to the salts on their liquid crystalline phase (smectic A2) has been studied by various experimental techniques, including NMR for determination of dipolar splittings. These systems can be used as hosts to determine solute structure from NMR spectroscopic measurements. ... 

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