Carbon tetrachloride radical cation

Mehnert, R., Brede, O., Bos, J., and Naumann, W., Charge transfer from the carbon tetrachloride radical cation to alkyl chlorides, alkanes, alkenes and aromatics, Ber. Bunsenges. Phys. Chem., 83, 992,1979. 

According to the results of Ben Taarit and co-workers (76) and Neikam (77) Ce(III) Y zeolites will not form anthracene cation radicals but upon oxidation to Ce(IV) the radicals are readily formed. This experiment suggests that one role of oxygen during calcination may be to oxidize certain cations. The surface may be oxidized by molecules other than oxygen since the chlorination of 7-alumina by carbon tetrachloride considerably increases the sites responsible for the acceptor character. These sites, which oxidize perylene into the paramagnetic radical ion, have been attributed to biocoordinated positive aluminum atoms (78). 

Aromatic cation-radicals can also react with NOj", giving nitro compounds. Such reactions proceed either with a preliminary prepared cation-radical or starting from nncharged componnd if iodine and silver nitrite are added. As for mechanisms, two of them seem feasible—first, single electron transfer from the nitrite ion to a cation-radical and second, nitration of ArH with the NOj radical. This radical is quantitatively formed when iodine oxidizes silver nitrite in carbon tetrachloride (Neelmeyer 1904). 

To elevate p-selectivity in nitration of toluene is another important task. Commercial production of p-nitrotoluene up to now leads with twofold amount to the unwanted o-isomer. This stems from the statistical percentage of o m p nitration (63 3 34). Delaude et al. (1993) enumerate such a relative distribution of the unpaired electron densities in the toluene cation-radical—ipso 1/3, ortho 1/12, meta 1/12, and para 1/3. As seen, the para position is the one favored for nitration by the attack of NO (or NO2 ) radical. A procednre was described (Delande et al. 1993) that used montmorillonite clay supported copper (cupric) nitrate (claycop) in the presence of acetic anhydride (to remove excess humidity) and with carbon tetrachloride as a medinm, at room temperature. Nitrotoluene was isolated almost quantitatively with 23 1 76 ratio of ortho/meta/para mononitrotoluene. 

Carbon-centred free radicals or radical cations R. Ar CH 2 Carbon tetrachloride 7,12-dimethylbenz(a)anthracene... 

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). 

Mehnert et al. studied the formation of cationic intermediates in alkane solutions containing a small amount of electron scavengers such as carbon tetrachloride [29.30]. The radical cations of styrene are formed by the following mechanism ... 

In cyclohexane geminate recombination occurs very efficiently and the observation of polymer ions is rather difficult [57, 58]. However, when the electron scavenger such as chloroform and carbon tetrachloride was added to the solution of polystyrene in cyclohexane, a weak, broad absorption band with a maximum at lOOOnm due to dimer cation of benzene was observed. The dimer cation radical might be produced by the hole migration, along the polymer chain, from a radical cation to a site suitable for the dimer-cation formation [59]. 

The pulse radiolysis studies of liquid alkanes have relevance to the radiolysis of polyethylene and related polymers. In liquid alkanes at ambient temperature, the reaction intermediates such as alkane radical-cations, olefin radical-cations, olefine dimer-cations, excited states, and alkyl radicals have been observed after the electron-pulse irradiation [90-93]. According to the nanosecond and subnanosecond studies by Tagawa et al., the observed species were alkane radical cations, excited states, and alkyl radicals in n-dodecane excited states and cyclohexyl radical were observed in cyclohexane, and only radicals in neopentane [91, 93]. Olefin radical-cations were also detected in cyclohexane containing carbon tetrachloride [92],... 

The concept of intra-intermolecular or cydopolymerization was first described in 1957 for free radical systems (102) and shortly thereafter extended to cationic initiators. Jones (103) polymerized alloocimene with boron trifluoride etherate in ethyl chloride at 0° C. The product was a low melting (85—87° C.) soluble (benzene, carbon tetrachloride, etc.) material. The iodine number of the polymer indicated one residual double bond per monomer unit. The following polymerization mechanism was proposed ... 

The reactions of thiiranes with alcohols, water, or acetic acid, in the presence of equimolar amounts of cerium(iv) trifluoromethanesulfonate, led to corresponding disulfides in 75-90% yield. When the reaction was carried out without nucleophiles in carbon tetrachloride, only the cyclic disulfide was formed (Equation (37) Table 7) <1998SC347>. A radical cation from thiirane and Ce(iv) is formed first. It attacks a molecule of solvent and the resultant radical dimerizes to form the disulfide. 

Sam and Sutherlandin a continuation of their studies on the cyclization of germacratriene (222) have shown that both radical- and cation-induced cycliza-tions follow similar directional and stereoselective pathways. Thus irradiation of germacratriene in the presence of carbon tetrachloride or benzenethiol leads to (236 = CCI3, = Cl) and (236 R = SPh, R = H) respectively. 

A study of the reaction of benzoquinone with alkenes has sought to identify the nature of the transients involved. In the case of reaction with tetraphenylallene irradiation in carbon tetrachloride at 355 or 532 nm yields the indene (376) as the sole product. When methanol is added to the reaction mixture the same indene (376) is accompanied by the methoxy derivative (377), The suggested mechanism for the formation of the indene (376) involves electron transfer to yield the radical cation / radical anion pair (378). Protonation followed by combination yields the cation (379) which is the key intermediate to the final product.Benzoquinone adds photochemically to the enol lactones (380) and (381) to give the oxetans (382) and (383)... 

It was noted above that laser flash photolysis of carotene in chloroform as solvent, led to carotenoid cation radical production and a corresponding transient absorption in the infrared. However, Mortensen and Skibsted (1996b) have also shown that, in carbon tetrachloride as solvent, whilst the parent carotenoid was bleached, no infrared absorbing species arose. Possibly the neutral carotene radical (CAR ) was produced via hydrogen atom transfer ... 

In another radiation technique, pulse radiolysis, high-energy electrons formed in a Van de Graaff generator lead to cation radical reactions in solution with very short periods of irradiation. Solvent ions or radicals are formed which may next remove an electron from the solute. For example, TMPD and some triarylaminc cation radicals have been made in carbon tetrachloride solution [(66) and (67)] by... 

Ordinarily, the catalyst is activated by heating in a current of air or oxygen for several hours and next heated under continuous pumping for several hours. We shall discuss the active sites on catalysts later, but note now that activation is necessary for cation-radical formation. The substrate is usually added to the catalyst as a solution, say in benzene, carbon disulfide, and carbon tetrachloride, and the solvent is removed by pumping. Occasionally the substrate is added neat, either as a liquid or in the vapor phase. One-electron oxidation is usually immediate. 

J. Grodkowski, J.H. Chambers, Jr., and P. Neta, Kinetics of Electron Transfer from Cobalt(II) Porphyrins to Various Metalloporphyrin x-Radical Cations in Irradiated Carbon Tetrachloride Solutions, J. Phys. Chem., 88 (1984) 5332. 

Most oxy or halo free radicals readily oxidize phenjienediamines to radical cations called Wurster salts (12), which are stable in water-ethanol solutions at pH 3. On the other hand, carbon and sulfur radicals generally do not produce Wurster salts. The intense color of Wurster salts can be used as a quick spot test for variously substituted phenylenediamines when oxidized with bromine in carbon tetrachloride solution. For example, Al,AT-diaIkyl substitution gives red, N,N,N N gives blue, and N-alkyl-TST-aryl gives light blue or green. 

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. 

Earlier polarographic studies indicated that the bis-compound (72) is reversibly oxidized to the radical cation (75) and the dication (76). It has now been shown that the simpler bis-dithiole (77), obtained by deprotonation of 1,3-dithiolium hydrogen sulphate, reacts with chlorine in carbon tetrachloride to give a deep purple crystalline salt (78) further... 

Benzophenone was used as photosensitizer in a study of the photo-decomposition of benzene solutions of polystyrene and poly(a-methyl styrene). Laser photolysis (A 265 nm) of poIy(a-methyl styrene) in chlorofonn and carbon tetrachloride proceeded by attack of solvent radicals in the polymer molecules resulting in main chain cleavage. " A series of papers have been devoted to the study of the photo-induced decomposition of poly(a-methyl styrene) in benzene solutions, using a,a -bisisobutyronitrile, benzophenone, and triphenyl-methyl cations as sensitizers. Spin-trapping techniques were used to detect transient radicals formed during benzophenone-sensitized degradation of poly-(a-methyl styrene). The rate constant for intramolecular reaction of the macroradical was estimated. 

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