Chloronium compounds

The formation of chloronium compounds or ionization of acceptor chlorides is hardly expected in a solvent of low donor properties. The only exception appears to be phosphorus(V) chloride, because it gives unsolvated [PC1J+ units and thus does not require any stabilization by solvent coordination. 

No chloronium compounds are found in the FeC -POCU system although their existence has been postulated . Although aluminium chloride and iron(III) chloride have similar chloride ion affinities, the former has a much stronger affinity towards O-coordination than the latter. 

While no chloronium compounds of vanadium(III) were detected, chromium(III) gives a dichloronium ion which is probably tetrasolvated [Cl2Cr(NCCH3)4]+. The following compounds were isolated in these systems ... 

Solvolysis of butadiene monoxide (10.102) in saline solution is a rather unexpected reaction that further documents this compound s reactivity [168]. In aqueous NaCl solution at physiological pH and temperature, butadiene monoxide disappeared rapidly to form 1,2-dichloro-3,4-epoxybutane (10.111, Fig. 10.25). There was a linear dependence of the rate of reaction on the Cl concentration (in the range investigated (34-135 mM)). The reaction pathway was described as slow solvolytic formation of the bu-tenylchloronium ion, followed by Cl attack to yield Cl2 and butadiene. Cl2 is then rapidly trapped by a second molecule of butadiene monoxide to form a different chloronium ion that also reacts with Cl to yield the final, stable dichloro product (10.111). The formation of 1,2-dichloro-3,4-epoxy-butane under physiological conditions is believed to be toxicologically significant. 

Anodic regioselective acetamidosulfeny-lation of alkenes is similarly achieved by oxidation of diphenyldisulfide in acetonitrile [81]. Cyclic enamines, which are intermediates in the oxidation of cyclic N-methoxycarbonyl amines, react in aqueous acetonitrile that contains chloride ions to a-hydroxy- 8-chloro compounds via intermediate chloronium ions [82]. Enolethers undergo a regioselective azidomethoxyla-tion to yield acetals of a-azido carbonyl compounds upon electrolysis in methanol containing sodium azide [83]. The reaction proceeds possibly via addition of an anodicaUy generated azide radical. 

An interesting observation of the chlorination of allenes is that besides the addition products, monochlorinated compounds are also formed.252-254 Thus allene gave propargyl chloride, and tetramethylallenes gave 3-chloro-2,4-dimethyl-1,3-pentadiene. Since the reactions were carried out in the presence of oxygen, that is, under ionic conditions, proton loss from the intermediate chloronium ion or 2-chlorocarbocation explains these results. 

Frohn and coworkers have obtained the unique chloronium cation 374,1120 which is the first unambiguously characterized xenon(II) chlorine compound [Eq. (4.261)]. There is no strong contact between cation 374 and the anion in the solid state. The two C—Xe—Cl contacts are linear (bond angles = 176.0 and 178.8°) with shorter C—Xe (2.111 and 2.116 A) and longer Xe—Cl (2.784 and 2.847 A) bond lengths. The Xe—Cl—Xe bond angle is 116.96°. 

On the contrary, chlorine iodine is mainly added to compound 320 with the participation of the reagent (k ), because the iodonium ion is more stable than the chloronium one ... 

In addition to iodonium, sulfonium and selenonium compounds, onium salts of bromine, chlorine, arsenic, and phosphoras are also stable and can act as sources of cation radicals as well as Bronsted acids, when irradiated with light. Performance of diaryl chloronium and diaryl bromonium salts was studied by Nickers and Abu. Also, aryl ammonium and aryl phosphonium, and an alkyl aryl sulfonium salt were investigated. It appears that the general behavior of these materials is similar to diphenyl iodonium and triphenyl sulfonium salts. These are formations of singlet and triplet states followed by cleavages of the carbon-onium atom bonds and in-cage and out of cage-escape reactivity. The anions of choice appear to be boron tetrafluoride, phosphorus hexafluoride, arsenic hexafluoride, and antimony hexafluoride. 

Diaryliodoninm, bromonium, and chloronium salts (I) belong to the general class of organic polyvalent halogen compounds. By convention, the central... 

---