Quarternary ammonium salts catalysts

A method for the depolymerisation of PETP fibres using quarternary ammonium salt phase transfer catalysts in saponification processes at atmospheric pressure and temperatures as low as room temperature is reported. Terephthalic acid was produced in yields as high as 93%. Also reported are similar processes for the depolymerisation of nylon 66 and nylon 46 fibres. Nylon 46 oligomers produced were repolymerised using solid-state polymerisation to produce high molecular weight nylon 46. Nylon 66 was depolymerised to produce oligomers and adipic acid in reasonable yields. 11 refs. USA... 

In the following example, although the synthesis of the azoniaspirocycle does not involve an acyclic compound, the reaction itself is very similar to those described in this section, hence its inclusion here (Equation 34). Maruoka and co-workers have designed a C2-symmetric chiral quarternary ammonium salt, which is then employed as a phase-transfer catalyst in an enantioselective alkylation <1999JA6519, 2001JFC(112)95, 2004TA1243>. 

Synthesis and Characterization of Lignin-like Model Epoxide. A series of epoxidation reactions were performed with hydroxypropyl guaiacol (HPG) as model compound and ECH. Molar ratios of ECH HPG varied from 1 to 10. Pelletized KOH and a quarternary ammonium salt (QAS) served as catalyst and reagent. Toluene was the solvent. Catalyst concentration and method of addition were varied. Experimental details are given elsewhere (11). 

Alkynes.10 Alkynes can be prepared by double dehydrobromination of pic-dibromides in petroleum ether by use of powdered KOH and catalytic amounts of a phase-transfer catalyst. Tetraoctylammonium bromide, 18-crown-6, or even Aliquat 336 are much more effective than more hydrophilic quarternary ammonium salts, such as tetrabutylammonium hydrogen sulfate, previously used (7, 354-355)." Isolated yields are 80-98%. Yields are generally lower when mc-dichlorides are used as the starting material. 

The catalytic activity of quarternary ammonium salt usually depends on the corresponding catalyst cation and counter anion[2]. For a series of tetraalkylammonium chlorides, the activity increased in the order of TP AC < TBAC < TOAC. Bulky quaternary salts, having longer distance between cation and anion, are generally known to exhibit higher activity in activating anions[3]. This explains why they are more effective in nucleophilic attack of the anion to oxirane ring of GVE. Table 1 also shows that the rate constant with different halide anions of the quaternary ammonium salts decreases in the order of Cf > Bf > T. This is consistent with the nucleophilicity of the halide anions. 

Catalyst benzyl dimethylamine. Catalyst Arquad quarternary ammonium salt. ... 

The reaction of a glycine Schiff base (159) with aldehydes can be catalyzed by cinchona-derived salts, though the stereoselectivity is rather low [171]. Maruoka reported that this reaction proceeded well with a C2-symmetric chiral quarternary ammonium salt (160) as a phase-transfer catalyst [172]. The reaction generated tz fi -(3-hydroxy-a-aminoacids with reasonable yields and stereoselectivities (Scheme 3.28). Further modifications of the catalyst structure led to a salt which provided predominantly jy -aldols [173]. 

By using phase transfer catalysts such as quarternary ammonium salts, quarternary phosphonium salts or crown ethers, a reaction, which could be done otherwise only in anhydrous organic media, can be carried out in organic solvent-water mixtures. 

The s-Triazine Compounds can be advantageously prepared in industrial scale using quarternary ammonium salts as phase transfer catalysts in water-chlorinated organic solvent. 

Okawara (5) reported that the degree of chlorine substitution on PVC suspended in water was 20% using thiophenoxide as nucleophile, and quarternary ammonium salt as phase transfer catalyst. 

The present situation with regard to non-supported catalysts has been admirably reviewed recently, with Wynberg s excellent articlebeing particularly informative. To date virtually all the work has employed quarternary ammonium salts based either on ephedrine [l] and its relatives or the cinchona alkaloids, notably quinine [II], as the active chiral catalyst. Some confusion still remains in the literature concerning the effectiveness of these catalystsi. However, the results of a number of Michael additions seem to be genuine and have been reproduced in more than one laboratory. For example, a chemical yield of100% in the addition of the cyclohexanone derivative, [III], to methyl... 

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