Quaternary onium salts, liquid

Quaternary onium salts, liquid, 723 a general treatment, 527... 

The reaction was originally used by Starks ( ) in his early studies of ptc mechanism. The reaction was monitored by gas-liquid chromatography and decane served both as solvent and internal standard. The reaction was run using a quaternary onium salt, Aliquat 336, and 18-crown-6 for calibration. The rates are shown in Table II. Please note that the relative rate of 1.00 corresponds to an absolute rate at 105 of 1.34 X 10 M-lsec . ... 

Ue M, Ida K, Mori S. Electrochemical properties of organic liquid electrolytes based on quaternary onium salts for electrical double-layer capacitors. Journal of the Electrochemical Society 1994 141(ll) 2989-2995. 

Q" X = quaternary onium salt CE = crown ether CR cryptand LL = liquid-liquid PTC (aqueous-organic two-phase system) SL = solid-liquid PTC... 

A slow non-competing liquid/liquid reaction with no catalyst present gave only 78 % O-alkylation. Thus the active site of the lipophilic phosphonium ion catalysts appears to be aprotic, just as in analogous phase transfer catalyzed alkylations with soluble quaternary ammonium salts 60), Regen 78) argued that the onium ion sites of both the 17% and the 52% RS tri-n-butylphosphonium ion catalysts 1 are hydrated, on the basis of measurements of water contents of the resins in chloride form. Mon-tanari has reported measurements that showed only 3.0-3.8 mols of water per chloride ion in similar 25 % RS catalysts 74). He argued that such small hydration levels do not constitute an aqueous environment for the displacement reactions. No measurements of the water content of catalysts containing phenoxide or 2-naphthoxide ions have been reported. 

The main use of crown ethers in PTC is in solid-liquid phase-transfer. In particular, it has been emphasized that they should be the catalysts of choice under such conditions. Due to its particular structure, the crown ether can approach the crystalline lattice so that the extraction and subsequent complexation of the cation require very little cation displacement, while the anion is contemporaneously associated to the complex. In the case of quaternary salts, on the other hand, the steric hindrance around the cationic center makes its interaction with the surface of the crystal difficult and the solution mechanism more complicated in this case only the anion must be extracted to displace the one originally associated with the lipophilic cation. These conclusions met with some scepticism Indeed, onium salts, cryptands, polypodes, polyamines, etc. have been successfully employed as solid-liquid PTC catalysts (see Sects. 4, 5.2, 5.3, 5.4). Moreover, when the catalytic activity of quaternary salts, crown ethers and polyamines was compared with respect to the extraction of anions from the crystalline state into an organic solvent, crown ethers were found to be the best system for the transport of CN . The catalytic effectiveness is completely reversed in the case of other anions, such as F and CHjCOO , the quaternary salt being the most efficient in these cases... 

Solid-Liquid Phase Transfer.—Very few examples are known in onium ion chemistry where the anion to be phase transferred is part of a solid phase rather than in aqueous solution. This contrasts with the situation in crown ether chemistry, as will be discussed later in this review. A useful method, which is cheaper than alternatives, for the generation of dichlorocarbene in neutral conditions involves warming solid sodium trichloroacetate in chloroform, in the presence of quaternary salts. Formaldehyde acetals (25) can be synthesized in good yields by the action of solid KOH on alcohols or phenols dissolved in methylene dibromide containing a quaternary ammonium ion, and a phosphonium salt catalyses the alkylation of solid potassium phthalimide in toluene. Solid-liquid phase transfer mediated by polyamines has been reported. ... 

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