SUBJECTS 198 tetrachloride

As chlorination proceeds from methyl chloride to carbon tetrachloride, the length of the C—Cl bond is decreased from 0.1786 nm in the former to 0.1755 nm in the latter (3). At ca 400°C, thermal decomposition of carbon tetrachloride occurs very slowly, whereas at 900—1300°C dissociation is extensive, forming perchloroethylene and hexachloroethane and Hberating some chlorine. Subjecting the vapor to an electric arc also forms perchloroethylene and hexachloroethane, as well as hexachlorobenzene, elementary carbon, and chlorine. 

Carbon tetrachloride is the oldest and was the most extensively used chlorinated solvent in degreasing and dry-cleaning operations for many years. Consequently, its narcotic and toxic properties have been the subject of much investigation. Carefiil investigations have repeatedly shown carbon tetrachloride to be one of the most harm fill of the common solvents (37). 

A systematic investigation of compounds of these types by Mason has recently placed this subject on a firm basis. The infrared spectra of chloroform and carbon tetrachloride solutions of... 

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... 

The rapid autocatalytic dissolution of aluminium, magnesium or zinc in 9 1 methanol-carbon tetrachloride mixtures is sufficiently vigorous to be rated as potentially hazardous. Dissolution of zinc powder is subject to an induction period of 2 h, which is eliminated by traces of copper(II) chloride, mercury(II) chloride or chromium(III) bromide. 

Mixtures of the tetraoxide with dichloromethane, chloroform, carbon tetrachloride, 1,2-dichloroethane, trichloroethylene and tetrachloroethylene are explosive when subjected to shock of 25 g TNT equivalent or less [1], Mixtures with trichloroethylene react violently on heating to 150°C [2], Partially fluorinated chloroalkanes were more stable to shock. Theoretical aspects are discussed in the later reference [2,3], The effect of pressure on flammability limits has been studied [4],... 

More interesting is the use of nonpolar solvents (e. g. xylene, toluene, carbon tetrachloride, hydrocarbons), because these are transparent to MW and absorb them only weakly. They therefore enable specific absorption by the reactants. If these reactants are polar, energy transfer occurs from the reactants to the solvent and the results might be different under the action of MW and A. This effect seems to be clearly dependent on the reaction and is, therefore, the subject of controversy. In xylene under reflux, for example, no MW-specific effects were observed for the Diels-Alder reaction [5] whereas important specific effects were described for aryldiazepinone synthesis [33]. 

More traditional carbon nucleophiles can also be used for an alkylative ring-opening strategy, as exemplified by the titanium tetrachloride promoted reaction of trimethylsilyl enol ethers (82) with ethylene oxide, a protocol which provides aldol products (84) in moderate to good yields <00TL763>. While typical lithium enolates of esters and ketones do not react directly with epoxides, aluminum ester enolates (e.g., 86) can be used quite effectively. This methodology is the subject of a recent review <00T1149>. 

The first case was reported by Lehnhoff and Ugi <1995H(40)801> the starting compound was phthalazin-l(2//)one 97 (Y = 0) which was first subjected to transformation with Lawesson s reagent to the corresponding thione 97 (Y = S), and this compound was treated with trimethylsilylazide and stannous tetrachloride to yield tetrazolo[5,l- ]phthalazine 98 in 95% yield. 

Kinetic studies on the polymerisation of isobutene at low temperatures by titanium tetrachloride in various solvents form the subject of a series of papers by Plesch and his co-workers [9, 10, 13, 28, 32, 33, 71, 77, 80, 81]. The reactions were followed in an apparatus approximating to an adiabatic calorimeter by means of the temperature rise accompanying the polymerisation. In the early studies moisture was not rigorously excluded from the systems, but later [81] an elaborate vacuum technique was evolved and all reagents were carefully purified and dried. Titanium tetrachloride was also used as catalyst by Okamura and his collaborators [79] in a series of studies concerning the effects of solvent, catalyst, and co-catalyst on the DP of polyisobutene. 

Carbon tetrachloride (CCI4), once a very widely used solvent, has perhaps been the subject of more experimental study than any other organic chemical. Since the early 1920s experimentalists have been investigating its various effects on the liver and have come to understand in great detail how this molecule performs its deeds. 

A project at the University of Arizona (FEDRIP 1996) will study microbial dehalogenation of several compounds, including chloroform. A major part of the study will focus on the facultative anaerobic bacteria Shewanella putrefaciens sp., which is known to catalyze the transformation of carbon tetrachloride to chloroform and other as yet unidentified products. The organic substrates will also contain metals. It is hoped that the end-products from the biochemical treatment can be subjected to a photolytic finishing process that will completely mineralize any remaining halogenated compounds. 

Cobalt(II) R-dtp complexes have been the subject of several studies js3,34i) Co(ethyl-dtp)2 occurs in a tetrahedral non-solvated form in carbon tetrachloride but undergoes solvation in other non-aqueous solvents 3 9. The spectrochemical series for tetrahedral Co(S2PX2)2 (where X = F,... 

The relative importance of hepatic microsomal lipid peroxidation versus covalent binding of carbon tetrachloride-derived radicals has been the subject of considerable debate. Since cytochrome P-450 loss has been shown to be related to lipid peroxidation and to covalent binding, each in the absence of the other, both of these early consequences of carbon tetrachloride metabolism may contribute to P-450 destruction. Nevertheless, it is still not clear how these initial events are related to subsequent triglyceride accumulation, polyribosomal disaggregation, depression of protein synthesis, cell membrane breakdown and eventual death of the hepatocytes. Carbon tetrachloride... 

Ethanol. Alcohol (ethanol) ingestion has repeatedly been associated with potentiation of carbon tetrachloride-induced hepatic and renal injury in humans. In two cases in which men cleaned furniture and draperies with carbon tetrachloride, one man, a heavy drinker, became ill and died (Smetana 1939). His coworker, a nondrinker, suffered a headache and nausea but recovered quickly after breathing fresh air. Both men were subjected to the same carbon tetrachloride exposure, as they had been working in the same room for the same amount of time. In 19 cases of acute renal failure due to carbon tetrachloride inhalation or ingestion, 17 of 19 patients had been drinking alcoholic beverages at about the time of their carbon tetrachloride exposure (New et al. 

Comparative Toxicokinetics. Metabolic pathways and mechanisms of hepatotoxicity of carbon tetrachloride have been the subject of many studies in intact animals and in vitro, and are therefore better understood than for many other chemicals. However, there are apparently no data on metabolism of carbon tetrachloride in humans. It would be valuable to conduct in vitro experiments with human liver samples and hepatocytes to determine whether metabolic pathways and toxic metabolites are similar to those found in animals. It would also be beneficial to identify an animal model in which MFO systems develop in uteroas they do in the human fetus. 

Interest in the total synthesis of the Aspergillus terreus derived quadrone fi06), an antitumor agent has been very intense. Success was first realized in Danishefsky s laboratory Once 601 was reached, its sidechain was elaborated and ring closure effected (Scheme LII). Condensation of 602 with 1-tert-butoxy-l-tcrt-butyl-dimethylsiloxyethylene in the presence of titanium tetrachloride and subsequent desilylation resulted in introduction of an angular acetic acid moiety. The two sidechains were next connected by intramolecular alkylation and the resulting keto add was subjected to selenenylation in order to produce 603. The a, P-unsaturated double bond was used to force enolization to the a position. Indeed, 604 was... 

The reaction of nitrosyl chloride with cyclopentene, cyclohexene, and cyclo-heptene in carbon tetrachloride solution at 5°C afforded the corresponding adducts in good yield, although during the cyclohexene reaction considerable hydrolysis to 2-chlorocyclohexanone took place and, in the case of cyclohep-tene, the crude product was not identified but rather was immediately subjected to levulinic acid hydrolysis to 2-chlorocycloheptene. From the products isolated, it may be inferred that cyclopentadiene adds nitrosyl chloride in a 1,4-manner in moderate yields [55]. 

---