Tetraalkylammonium salts elimination from

Let us return to the finding that k 2 cjs > k 2 tmm in the E2 eliminations from the isomeric tetraalkylammonium salts in Figure 4.19. The transition state geometries of these reactions are derived from the chair conformers shown in Figure 4.19. The stereostructure is fixed in each... 

Finally, chemical or thermal-induced dealkylation (Hofmann elimination) from tetraalkylammonium salts can occur even in the absence of base as shown in Scheme 6.4. The formation of a palladium bis-imidazole complex from PdCl41 and [C4Ciim][BF4] has been reported to take place during the hydrodimerisation of butadiene1291 and an analogous product was obtained from a [PdBr4]2 imidazolium salt in the presence of the radical initiator 2, 2 -azabisisobutyronitrile.[30]... 

The tetraphenylarsonium cation is useful in coordination chemistry because of its large size. Tetraphenylarsonium cyanate dihydrate was prepared byNor-buryand Sinhain 1968. The preparation involved precipitation of the cyanate from an aqueous solution, but the method suffers from the disadvantage of low yields. Tetraphenylarsonium cyanide has been prepared from methanol solution with fairly good yields, but the product is isolated as the monohydrate. The ion-exchange method developed for the tetraalkylammonium salts can be readily applied to the preparation of anhydrous tetraphenylarsonium cyanate and cyanide, thus eliminating many of the problems initially involved in the synthesis of these componds. 

The most commonly used quaternary ammonium salts are tetrabutylammonium perchlorate (TBAP), tetrafluoroborate (TBAT), the halides (TBACl, TBAB, and TBAI), and the corresponding tetraethylammonium salts, such as the perchlorate (TEAP), but also the tetramethyl- or tetrapropylammonium salts have been employed the former cannot undergo a base-promoted Hofmann elimination. However, evidence has been found for the formation of trimethylammonium methylide [460]. In nonpolar solvents it may be necessary to employ tetrahexyl- or tetraoctylammonium salts. The tetraalkylammonium ions are soluble in many nonaqueous media, and they may be extracted from an aqueous solution by means of chloroform or methylene chloride [461,462], and tetraalkylammonium salts may thus be prepared by ion extraction [462]. Tetrakis(decyl)ammonium tetra-phenylborate is soluble even in hexane [442,443]. 

Aprotic solvents such as acetonitrile [15,16] or dimethylformamide [17-20] considerably improved the stability of the radical anions but normally had little effect on the reactions of the more basic dianions [19-21]. The increased irreversibility of the dianion formation is probably due to the ability of dianions to abstract protons even from the solvent, or, by Hofmann elimination, from the tetraalkylammonium salts that are common supporting electrolytes in aprotic solvents [2],... 

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