Radical addition carbon tetrachloride

Radical addition. Carbon tetrachloride adds to alkenes in the presence of (Ph3P)2Ru(=CHPh)Cl2. 

The present method offers several advantages over earlier methods. The use of carbon tetrachloride instead of diethyl ether as solvent avoids the intrusion of certain radical-chain reactions with solvent which are observed with bromine and to a lesser degree with chlorine. In addition, the potassium bromide has a reduced solubility in carbon tetrachloride compared to diethyl ether, thus providing additional driving force for the reaction and ease of purification of product. The selection of bro-... 

One of the older preparative free-radical reactions is the addition of polyhalomethanes to alkenes. Examples of addition of carbon tetrabromide, carbon tetrachloride, and bromoform have been recorded. The reactions are chain processes that depend on facile abstraction of halogen or hydrogen from the halomethane ... 

Halocarbons including carbon tetrachloride, chloroform, bromotrichloroincthane6 (Scheme 6.7) and carbon tetrabromide have been widely used for the production of tclomcrs and transfer to these compounds has been the subject of a large number of investigations." Representative data are shown in Table 6.4. Telomerization involving halocarbons has also been developed as a means of studying the kinetics and mechanism of radical additions.66... 

On the other hand, microsomes may also directly oxidize or reduce various substrates. As already mentioned, microsomal oxidation of carbon tetrachloride results in the formation of trichloromethyl free radical and the initiation of lipid peroxidation. The effect of carbon tetrachloride on microsomes has been widely studied in connection with its cytotoxic activity in humans and animals. It has been shown that CCI4 is reduced by cytochrome P-450. For example, by the use of spin-trapping technique, Albani et al. [38] demonstrated the formation of the CCI3 radical in rat liver microsomal fractions and in vivo in rats. McCay et al. [39] found that carbon tetrachloride metabolism to CC13 by rat liver accompanied by the formation of lipid dienyl and lipid peroxydienyl radicals. The incubation of carbon tetrachloride with liver cells resulted in the formation of the C02 free radical (identified as the PBN-CO2 radical spin adduct) in addition to trichoromethyl radical [40]. It was found that glutathione rather than dioxygen is needed for the formation of this additional free radical. The formation of trichloromethyl radical caused the inactivation of hepatic microsomal calcium pump [41]. 

Allenylcobaloximes, e.g. 26, react with bromotrichloromethane, carbon tetrachloride, trichloroacetonitrile, methyl trichloroacetate and bromoform to afford functionalized terminal alkynes in synthetically useful yields (Scheme 11.10). The nature of the products formed in this transformation points to a y-specific attack of polyhaloethyl radicals to the allenyl group, with either a concerted or a stepwise formation of coba-loxime(II) 27 and the substituted alkyne [62, 63]. Cobalt(II) radical 27 abstracts a bromine atom (from BrCCl3) or a chlorine atom (e.g. from C13CCN), which leads to a regeneration of the chain-carrying radical. It is worth mentioning that the reverse reaction, i.e. the addition of alkyl radicals to stannylmethyl-substituted alkynes, has been applied in the synthesis of, e.g., allenyl-substituted thymidine derivatives [64],... 

As an alternative to radical chlorination, use has been made of carbon tetrachloride and hexachloroethane in the presence of a quaternary ammonium salt, as source of the chloronium ion for reaction with activated alkylbenzenes [38], Benzyl chlorides need the additional activation of a nitro group for their conversion into the corresponding nitrobenzotrichlorides, whereas benzal chlorides do not need the extra activation for a similar conversion. The same synthetic protocol, using hexachloroethane, has been used for the conversion of allylic sulphones into the 1,1-dichloro derivatives [39],... 

Irradiation of diazo 21d in carbon tetrachloride gave, in addition to 72 (R = Me) and 73, the 3-chloro-3-trichloromethyl-l-methyloxindole (76a) (64JOC3577). Since the photolysis in carbon tetrachloride under comparable conditions produces, in the primary step, CCI3 radicals and chlorine atoms (63JOC3442), in the formation of 76a and probably in the reaction with oxygen to give 74, the carbene 71 shows biradical properties in the... 

Methods for Reducing Toxic Effects. The usefulness of methods and treatments for reducing peak absorption and reducing the body burden of carbon tetrachloride are rather limited due to the chemical s rapid rates of absorption and tissue disposition. On the other hand, investigations of antidotal therapy based on the mechanism of action has been limited to a few studies involving the administration of compounds to reduce free radical injury. Additional studies would be useful to better establish the effectiveness of both acute and prolonged antidotal therapy, since carbon tetrachloride is persistent in the body. 

Another application of ruthenium indenylidene complexes was the atom transfer radical addition of carbon tetrachloride to vinyl monomers reported by Verpoort [61]. This Kharasch reaction afforded good yields for all substrates tested, especially with the catalyst VIII (Equation 8.11, Table 8.8). 

Radical addition, 312-323 carbon tetrachloride, 320 halogens, 313 hydrogen bromide, 316 sulphenyl halides, 320 vinyl polymerisation, 320 Radical anions, 218 Radical rearrangements, 335 Radicals, 20, 30,299-339 acyl, 306, 330, 335 addition to 0==C, 313-323 alkoxyl, 303... 

Homolytic cleavage of covalent bonds is an alternative means of generating free radicals. This may be assisted by the addition of an electron as in the case of carbon tetrachloride activation. The electron may be donated by cytochrome P-450, allowing the loss of chloride ion and the production of a trichloromethyl radical (Fig. 4.7). This can initiate other radical reactions by reacting with oxygen or unsaturated lipids. 

Styrene is a colorless liquid with an aromatic odor. Important physical properties of styrene are shown in Table 1. Styrene is infinitely soluble in acetone, carbon tetrachloride, benzene, ether, -heptane, and ethanol. Polymerization generally takes place by free-radical reactions initiated thermally or catalytically. Styrene undergoes many reactions of an nnsaturated compound, such as addition, and of an aromatic compound, such as substitution. 

Radical-mediated brominations of carbohydrate derivatives have usually been conducted in refluxing carbon tetrachloride, under a tungsten (150— 250 W) or heat (250-450 W) lamp, with either JV-bromosuccinimide (1.2— 5 molar equivalents) or bromine (2-5 equivalents) as the source of halogen. Addition of bromotrichloromethane to the carbon tetrachloride can be advantageous.25 Substrate concentrations have ranged from 0.02 to 0.2 mol.l-1 and have depended to some degree on solubility factors, and ordinary laboratory glassware has most often been used. 

The reactions of cyclic disilenes with haloalkanes proceed in a similar way. Cyclotrisilene 48 reacts with carbon tetrachloride without cleavage of endocyclic Si-Si bonds to give trans-1,2-dichlorocyclotrisilane 179 stereo specifically [Eq. (84)].24 The a h -stereochemistry is in good accord with the radical mechanism of the reactions as stated above. Similarly, cyclic disilenes 49 and 50 react with carbon tetrachloride and 1,2-dibromoethane giving the corresponding trau.v-1,2-dihalodi-silanes 180 [Eq. (85)].129 Methyl iodide adds to cyclic disilene 50 in an a tz-addition manner to give 181.104... 

Susuki and Tsuji reported the first Kharasch addition/carbonylation sequences to synthesize halogenated acid chlorides from olefins, carbon tetrachloride, and carbon monoxide catalyzed by [CpFe(CO)2]2 [101]. Its activity is comparable to or better than that of the corresponding molybdenum complex (see Part 1, Sect. 7). Davis and coworkers determined later that the reaction does not involve homolysis of the dimer to a metal-centered radical, which reduces the organic halide, but that radical generation occurs from the dimeric catalyst after initial dissociation of a CO ligand and subsequent SET [102]. The reaction proceeds otherwise as a typical metal-catalyzed atom transfer process (cf. Part 1, Fig. 37, Part 2, Fig. 7). 

Copper(I) salts have been found to be particularly good catalysts for radical addition of alkyl halides to alkenes689. These catalysts have been used in the reaction of carbon tetrachloride with ester-containing alkenes, the products being key intermediates in the synthesis of -lactams (equation 108). 

---