Ammonium and sulfonium salts

Sulfones and sulfoxides containing at least one b-hydrogen atom undergo a bimolecular elimination reaction (E2) an treatment with alkoxides, leading preferentially to the formation of the least substituted alkene (Hofmann s rule) (Scheme 37). The reaction resembles the analogous eliminations of quaternary ammonium and sulfonium salts (see Chapter 6, p. 83). 

Another example of asymmetric induction in the transfer of chirality from tricoordinate sulfur to the nitrogen atom was reported by Kobayashi (157), who found that methylation of benzylethylani-line with (+)-methoxymethyl-p-tolylsulfonium salt 113 yields (-)-benzylethylmethylphenylammoniumtetrafluoroborate 268. A similar asymmetric methylation reaction was observed with benzyl ethyl sulfide. Chiral ammonium 268 and sulfonium salts 112 were formed... 

Substances that can potentially be taken up across the skin include gases and vapors, liquids and particulates. Liquids and substances in solution are taken up more readily than dry particulates. Dry particulates will have to dissolve into the surface moisture of the skin before uptake can begin. Absorption of volatile liquids across the skin may be limited by the rate at which the liquid evaporates off the skin surface. As a result of binding to skin components, the uptake of chemicals with the following groups can be slowed certain metal ions, acrylates, quaternary ammonium ions, heterocyclic ammonium ions, and sulfonium salts. 

Another type of ylidic rearrangement, the Sommelet-Hauser rearrangement, was discovered later, in 1937, by Sommelet and studied extensively by Sommelet and by Hauser. This transposition involves the base-promoted rearrangement of non stabilized ammonium and sulfonium ylides. Thus, the ammonium salt (11), when heated with alkali, gave cleanly the substituted diphenylmethane derivative (12 Scheme 5). Wittig found that the dibenzyl ammonium salt (13) reacted with phenyllithium giving two... 

The leaving groups in the bimolecular elimination mechanism (E2) are essentially the same as those in substitution reactions (that is, halides and tosylate). Alcohols do not usually react by the E2 mechanism, but quaternary ammonium salts, such as RN(CH3)3X and sulfonium salts, such as RS(CH3)2X- do. 

The transformation of quaternary ammonium salts 1 and sulfonium salts 3 to the corresponding amines 2 and sulfides 4 in the presence of a strong base is known as Stevens rearrangement. The salts are usually obtained by the alkylation of the corresponding amines and sulfides. The competing reaction is the Sommelet-Hauser rearrangement. 

In the field of surface-active cations, ion-pair chromatography is predominantly applied to the analysis of quaternary ammonium compounds, pyridine-, pyrrohdine-, and piperidine quatemisates, and for sulfonium-, phos-photiium-, ammonium- and hydrazinium salts. 

Examples of cationic antistatic agents include the long chain quaternary ammonium and sulfonium alkyl salts such as chlorides, nitrates and methosulfates. They are used in high concentrations in polar polymers such as PVC, and also in various styrene based polymers. Anionic antistats are usually alkali salts of alkyl phosphonic, sulfonic or dithiocarba-mic acids. Examples of their application are the styrene polymers, and the saturated (thermoplastic) polyesters. 

Phase transfer catalysis, which proved extremely useful in classical ylid reactions with both phosphonium and sulfonium salts (Ref, 8, 42-45), was first used with a polymer by Farrall, Durst and Frechet in 1978 (Ref, 15) according to scheme 4. In this reaction, the polymeric sulfonium salt (IX), which is suspended in a dichloromethane solution of the carbonyl compound, is treated with aqueous sodium hydroxide in the presence of tetrabutyl ammonium hydroxide to give over 95% yield of the desired epoxide together with a polymeric by-product (X) which can be recycled and reused repeatedly without any loss of activity. In contrast, the same polymeric reagent (IX) used under classical conditions affords lower yields of epoxides and loses its activity rapidly on repeated recycling. This last observation shows clearly that phase transfer catalysis may contribute significantly to the prevention of side reactions in some modifications of polymers. 

Allylic amine is a less reactive leaving group[7], but the allylic ammonium salts 214 (quaternary ammonium salts) can be used for allylalion(l30,131]. Allylic sulfonium salts are also used for the allylation[130]. The allylic nitrile in the cyclic aminonitrile 215 can be displaced probably via x-allylic complex formation. The possibility of the formation of the dihydropyridinium salts 216 and subsequent conjugate addition are less likelyfl 32],... 

The benzylation of a wide variety of aHphatic, aromatic, and heterocycHc amines has been reported. Benzyl chloride is converted into mono-, di-, and tribenzyl amines by reaction with ammonia. Benzylaniline [103-32-2] results from the reaction of benzyl chloride with aniline. Reaction with tertiary amines yields quaternary ammonium salts with trialkylpbospbines, quaternary phosphonium salts and with sulfides, sulfonium salts are formed. 

Hofmann Rule Elimination from quaternary ammonium and tertiary sulfonium salts generally provides the lesser-substituted alkene as major product. 

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