Chlorination, of hydrocarbons

For many years chlorination of carbon disulfide was the only process used to manufacture carbon tetrachloride. In the 1950s, chlorination of hydrocarbons, particularly methane, became more popular ia the United States. Many hydrocarbons and chloriaated hydrocarbons are now used to feed chlorination reactors to make carbon tetrachloride. 

Chlorination of Hydrocarbons or Chlorinated Hydrocarbons. Chlorination at pyrolytic temperatures is often referred to as chlorinolysis because it involves a simultaneous breakdown of the organics and chlorination of the molecular fragments. A number of processes have been described for the production of carbon tetrachloride by the chlorinolysis of various hydrocarbon or chlorinated hydrocarbon waste streams (22—24), but most hterature reports the use of methane as the primary feed. The quantity of carbon tetrachloride produced depends somewhat on the nature of the hydrocarbon starting material but more on the conditions of chlorination. The principal by-product is perchloroethylene with small amounts of hexachloroethane, hexachlorobutadiene, and hexachloroben2ene. In the Hbls process, a 5 1 mixture by volume of chlorine and methane reacts at 650°C the temperature is maintained by control of the gas flow rate. A heat exchanger cools the exit gas to 450°C, and more methane is added to the gas stream in a second reactor. The use of a fluidi2ed-bed-type reactor is known (25,26). Carbon can be chlorinated to carbon tetrachloride in a fluidi2ed bed (27). 

Homogeneous reactions. Homogeneous noncatalytic reactions are normally carried out in a fluidized bed to achieve mixing of the gases and temperature control. The sohds of the bed act as a heat sink or source and facihtate heat transfer from or to the gas or from or to heat-exchange surfaces. Reaclious of this type include chlorination of hydrocarbons or oxidation of gaseous fuels. 

Dining chlorination of hydrocarbons with Lewis acid catalysis, the catalyst must be premixed with the hydrocarbon before admission of chlorine. Addition of catalyst to the chlorine-hydrocarbon mixture is very hazardous, causing instantaneous release of large volumes of hydrogen chloride. 

Chlorination reactions. Chlorination of hydrocarbons has been carried out in Japan, chlorination of toluene in the United States, chlorination of tetrachloropentane in the former U.S.S.R. to give octachlorocy-clopentane, and chlorination of propanoic acid in France to give chloro-propanoic acid. Chlorination of methane by irradiation to give lower halomethanes was found to be cost-effective. Chlorination of various amorphous polymers such as polypropylene, polybutadiene, and PVC, has also been carried out. 

On an industrial scale, HCl is also obtained in the chlorination of hydrocarbons. 

The chlorination of hydrocarbons proceeds via the chain mechanism [195]. Chlorine atoms are generated photochemically or by the introduction of the initiator. However, liquid-phase chlorination occurs slowly in the dark in the absence of an initiator. The most probable reaction of thermal initiation in RH chlorination is the bimolecular reaction... 

Therefore, the chain chlorination of hydrocarbons with alkyl hypochlorite results in the formation of chlorine-containing alcohols because of the faster bimolecular reaction compared to isomerization [37],... 

The results of gas phase chlorination of hydrocarbons suggest that, due to differences in activation energy, tertiary radicals are more readily formed than secondary radicals which in turn are more readily formed than primary radicals. 

As noted IN the preceding chapter, almost all elemental chlorine is made as a by-product of caustic soda production, although the obsolete Deacon process of 1868 has been revived (with improvements) for recycling CI2 onsite in plants where chlorination of hydrocarbons forms gaseous HC1, an objectionable waste product ... 

The free-radical-induced reaction of alkanes with sulfuryl chloride characteristically results in the chlorination of hydrocarbons. However, when pyridine is added to the irradiated reactants, sulfochlorination occurs in quite satisfactory yield. For example, the irradiated reaction of cyclohexane and sulfuryl chloride in the presence of pyridine resulted in a 54.8% yield of cyclohexanesulfonyl chloride and only 9.4% of chlorocyclohexane.161... 

In general, the stable thermodynamic products of ordinary flames have little worth, but many of the uncommon flames have products of value. The chlorination of hydrocarbons may be carried out in a flame process which was recently announced (A4). A most fascinating example is the formation of boron nitride from the flame reaction between diborane and hydrazine, two compounds which are ordinarily thought of as fuels (B2, VI). The stabilization of this flame depends upon the proper preparation of the premixed gases, since a solid adduct between the reactants prevents flame stabilization if the preflame residence time is too great. 

Exercise 28-7 The quantum yield in photochemical chlorination of hydrocarbons such as methane is quite sensitive to the experimental conditions. How would you expect to vary with (a) the intensity of the incident light, (b) the wavelength of the incident light from 250 nm to 450 nm, (c) the presence of oxygen, and (d) the presence of alkenes Explain. 

Alkyl chlorides have been obtained by the direct chlorination of hydrocarbons 1 and by the addition of hydrogen chloride to olefines.2 However, they have usually been prepared from the corresponding alcohol by the action of a number of reagents, such as dry hydrogen chloride,3 dry hydrogen chloride in the presence of zinc chloride,4 phosphorus trichloride,3 phosphorus oxychloride,6 phosphorus pentachloride,7 phosphorus trichloride... 

Hydrocarbons and Lewis Acids. In the chlorination of hydrocarbons in the presence of Lewis acid catalysts, large volumes of hydrochloric acid are released if the catalyst is added to the chlorine hydrocarbon mixture. The catalyst should always be mixed with the hydrocarbon before addition of chlorine.16... 

Chlorination of hydrocarbons, such as propane, and acetylene with chlorine also produces perchloroethylene via trichloroethylene. 

Solvent effects in the reactions of free radicals and atoms. III. Effects of solvents in the competitive photo-chlorination of hydrocarbons and their derivatives. J. Amer. chem. Soc. 80, 4997 (1958). 

Organolead compounds have been recently widely used. They are used in agriculture (as pesticides), in medicine, as well as in various chemical processes as catalysts for the polymerisation of vinyl monomers, chlorination of hydrocarbons, etc. Lead tetraalkyl derivatives are used as additives for engine fuels due to their antiknock properties. 

Activated carbon is an active catalyst for the free radical chlorinations of hydrocarbons. Methane108, in the gas phase, and acetic acid109, in the liquid phase, are both chlorinated in its presence. Surface free radicals are claimed to play a major role in the mechanism of this reaction. A similar mechanism has been established for the active carbon catalyzed chlorination of indane in aqueous solution by quenching methods110. Trimm111 has reviewed the activity of carbon in chlorination of carbon monoxide, ethylene and toluene. 

In the field of halogenation, the practical aspects of the work were stressed by a number of Russian workers. Thus, in 1940 and later Mamedaliev reported (215) on the chlorination of methane over cupric chloride, pumice, iron, or aluminum shavings. Yields of 75 to 80% of products ranging from methyl chloride to carbon tetrachloride with small amounts of hexachloroethane were obtained. Similar work on the continuous chlorination of hydrocarbons such as isopentane, unsaturated compounds, oxygenated compounds, and on the mechanism of chlorination has been reported by Russian researchers from time to time (180,248,366,367,389). 

In the case of HC1, large quantities are produced industrially by the chlorination of hydrocarbons. 

Another example of a solvent-dependent atom-transfer reaction is hydrogen abstraction by chlorine atoms during the photochemical chlorination of hydrocarbons with molecular chlorine for an excellent review, see reference [571]. Russel reported that in the photochlorination of 2,3-dimethylbutane, according to reaction scheme (5-68), certain solvents do not have any effect on the selectivity of the reaction as measured by the rate ratio whereas other solvents increase this ratio significantly (c/. 

Hydrogen chloride is produced industrially on a huge scale and is used as the anhydrous gas as well as a hydrochloric acid in aqueous solution. Several industrial routes to synthesize HCl are in use (1) direct burning of hydrogen in chlorine, which results in a very pure product (equation 85) (2) reaction of an inorganic metal halide with a less volatile protic acid, such as sulfuric acid, to form the more volatile hydrogen halide (equation 86) and (3) as a by-product of the chlorination of hydrocarbons (equation 87). 

PCTs are produced by a controlled chlorination of hydrocarbons [12]. The fully chlorinated perchloro-p-terphenyl is obtained from p-terphenyl by means... 

Radicals can undergo other reactions as well as monomer addition. Atom abstraction reactions usually involve transferof a hydrogen or halogen atom. An example from micromolecular chemistry involves the chlorination of hydrocarbons at about 200°C or during irradiation with light of wavelength less than 4875 x 10 m ... 

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