Trichloromethyl cations

A similar type of activated trichloromethyl cation has been generated from CCI4 in excess Lewis acids (SbFj or AICI3, vide infra). 

Another computational study examined the structures and energies of the trichloromethyl cation-AlCl3 complexes by semi-empirical and ab... 

Aromatic hydroxycarboxylic acids, especially salicylic acid, have a wide range of applications, for example, as valuable raw materials and intermediates in the production of pharmaceutical chemicals. Originally, salicylic acid was synthesized by the Kolbe-Schmitt reaction [57], which consists of two steps (1) the synthesis and purification of alkali metal phenoxides and (2) carboxylation (Scheme 4.4). Another possible synthetic method is via the attack of a trichloromethyl cation (generated by a copper catalyst from carbon tetrachloride) on the phenoxide anion, followed by hydrolysis of the C—Cl bonds with concentrated sodium hydroxide, because it is fairly difficult to replace an aromatic hydrogen with carboxyl functionality [58]. 

Styrene, a powerful quencher for the trichloromethy1 radical, showed no measurable effect on the selective carboxylation using B-CyD at the initial molar ratio 0.04 to carbon tetrachloride. Consequently, the selective carboxylation using 3-CyD as catalyst probably proceeds with trichloromethyl cations, formed in situ from carbon tetrachloride by the catalysis of copper powder, as the active species. 

Almost all the trichloromethyl cations should form inclusion complexes with 3-CyD prior to the attack at phenols, since the selective carboxylation is achieved at quite a small molar ratio of 3 CyD to phenol or carbon tetrachloride. Trichloromethyl cations can be trapped in the cavity of 3-CyD immediately after being formed on the surface of copper powder. Alternatively, the trichloromethyl cation can be formed predominantly from the carbon tetrachloride included in the cavity, also with catalysis by copper powder, and thus be trapped in the cavity. There, the electrostatic attraction between the positive charge of the cation and the negative charges of 3-CyD is cooperatively functioning with the apolar interaction between the cation and the 3-CyD. Then, the trichloromethyl cation should attack overwhelmingly at the para-carbon atom of phenols, which is located in close proximity. 4-Hydroxybenzoic acid is formed by the hydrolyses of the C-Cl bonds in the resulting intermediates. 

Formylations of phenol, resorcinol and indole, dichloromethylations of 4-methylphenol and 5,6,7,8-tetrahydro-2-naphthol, carboxylation of phenol, and allylation of 2,4,6-trimethylphenol proceed site-selec-tively in high yields by using 3-cyclodextrin as catalyst. The formation of ternary inclusion complex composed of cyclodextrin, substrate, and dichlorocarbene, trichloromethyl cation or allyl cation in the reaction mixture is an important factor of the site-selective reactions. The cyclodextrin is also effective by limiting the molecular size of the reaction intermediate. 

In contrast, the immobilized a-CyD catalyst IV exhibits minimal selective catalysis. The selectivity (59 %) with this immobilized catalyst is almost identical with the value (56 %) in its absence, although the yield is considerably larger. The cavity of a-CyD is too small to accommodate the electrophilic species trichloromethyl cation, produced in situ from carbon tetrachloride. 

The selective catalysis by the immobilized 3-CyD catalysts proceed in a similar manner to that by free 3 CyD catalyst (13). The 3-CyD residue forms a ternary molecular complex with phenol and trichloro-methyl cation, produced in situ from carbon tetrachloride with the catalysis by copper powder. As a result, the mutual conformation between phenol and trichloromethyl cation is regulated through the non-covalent interactions. The para-carbon atom of phenol is predominantly attacked by the cation, since the carbon atom is located in close proximity to the cation. 4-Hydroxybenzoic acids are selectively formed by the hydrolyses of the C-Cl bonds in the resulting intermediates. 

The larger selectivity (100 %) for the immobilized 3 CyD catalysts than that (95-98 %) for free 3-CyD catalyst is ascribed to effective trapping of the trichloromethyl cation by the negatively charged reaction field of the immobilized catalyst, prior to the reaction between the cation and phenol. The reaction field is produced by many alkoxide ions of 3-CyD residues in the immobilized catalysts the pK of the secondary hydroxyl groups of CyD is around 12 (1). Thus, the less selective reaction involving free trichloromethyl cation is definitely inhibited here, and the predominance of the selective... 

Trichloroacetic acid behaves somewhat similarly in that protonation of the enamine occurs l7J7d). Subsequent decarboxylation of the trichloro-acetate gives trichloromethyl anion, which adds to the iminium cation to give the trichloromethyl amine derivative. Thus the enamine (113) undergoes reaction with trichloroacetic acid to give N-[l-(trichloromethyl)cyclo-hexyl]-morpholine (8). The latter compound undergoes rearrangement on... 

As indicated in Chapter 1, the hydroxide ion is not readily transported into the organic phase, particularly when the benzyltriethylammonium ion is employed as the catalytic cation. Hence, the reaction of chloroform with the hydroxide ion must occur by an interfacial mechanism. The interfacial reaction initially produces the trichloromethyl anion, which immediately forms an effective ion-pair with the benzyltriethylammonium cation. Diffusion of the ion-pair into the bulk of the organic phase occurs, followed by a slow decomposition of the trichloromethyl anion... 

Diphenyl-4//-pyran (151a R = Ph) undergoes a free-radical chain process with trichloromethyl radicals generated from carbon tetrachloride, affording pyrylium radical cation 378a353 (see Eq. 19). 

In the cationic polymerization of P-trichloromethyl-P-propiolactone retention (lie) dominates 21). 

Crivello and J.FI.W. Lam,. Polym. Set Polym. Lett. Ed. 17, 759 (1979) J.V. Crivello and J.L. Lee, Photosensitized cationic polymerizations using dialkylphenacylsulfonium and dialkyl(4 hydro xyphenyl)sulfonium salt photoinitiators, Macromolecules, 14, 1141 (1981) S.P. Pappas, Photo generation of acid Part 6 A review of basic principles for resist imaging applications, J. Imaging Technol. 11, 146 (1985) J.L. Dektar and N.P. Hacker, Triphenylsulfonium salt photochemistry. New evidence for triplet excited state reactions, J. Org. Chem., 53, (1988) J.L. Dektar and N.P. Hacker, Photochemistry of triarylsulfonium salts, J. Am. Chem. Soc. 112, 6004 (1990) G. Pohlers, J.C. Sciano, R.F. Sinta, R. Brainard, and D. Pai, Mechanistic studies of photoacid gen eration from substituted 4,6 bis(trichloromethyl) 1,3,5 triazines, Chem. Mater. 9, 1353 (1997). 

Method using Base and a Substituted Halogenomethane. The influence of catalyst anions (as their tetrabutylammonium salts) and cations (as chlorides or bromides) on the generation of dichlorocarbene from chloroform-sodium hydroxide has been studied under standard conditions by determining the yield of dichloronorcarane produced from the addition of the carbene to cyclohexene. The presence of olefin appears to be necessary since in its absence only very slow decomposition of the trichloromethyl anion occurs. Dehmlow has also devised a new procedure for phase-transfer-catalysed cyclopropanation. Treatment of an alkene (or cycloalkene) with sodium trichloroacetate and a tetra-alkylammonium salt in chloroform without... 

Arylmercaptans. Chlorine bubbled at room temp, into a soln. of phenyl methyl sulfide in CCI4 until g.l.c. shows completion of the reaction trichloromethyl phenyl sulfide (Y ca. 100%), methanol and Amberlyst 15 cation exdianger added, then the solvent distilled off through a column until the head temp, readies 64° thiophenol (Y ca. 100%). F. e. s. J. M. Lavanish, Tetrah. Let. 1973, 3847. 

---