Direct chlorination

Figure 10.5 The direct chlorination step of the vinyl chloride process using a liquid phase reactor. (From McNaughton, Chem. Engg., December 12, 1983, pp. 54-58 reproduced by permission.)...

The azo-compounds are usually very stable, and can be directly chlorinated, nitrated and sulphonated. On vigorous reduction the molecule splits at the azo group to give two molecules of primary amines, e.g. bcnzene-azophenol gives PhNH2 and p-HOC H NHa. 

It is prepared by the direct chlorination of toluene in the presence of PClj. It is purified by fractionation from the unchanged toluene and the higher chlorinated products. It is used for benzylating amines and for preparing benzyl alcohol. 

The o- and p-isomers are manufactured by the direct chlorination of benzene in the presence of iron as a catalyst, the resulting mixture being separated by fractional distillation. The w-isomer may be obtained by isomerization of the 0- or p-compound in the presence of a catalyst. 

CH2CI2. A colourless liquid with a chloroform-like odour b.p. 4I°C. Prepared by heating chloroform with zinc, alcohol and hydrochloric acid manufactured by the direct chlorination of methane. Decomposed by water at 200°C to give methanoic and hydrochloric acids. Largely used as a solvent for polar and non-polar substances, particularly for paint removal (30%), dissolving cellulose acetate and degreasing (10%). It is more stable than carbon tetrachloride or chloroform especially towards moisture or alkali. It is somewhat toxic. U.S. production 1981 280000 tonnes. 

M.p. 255-257 C. Prepared by the direct chlorination of phlhalic anhydride in 50-60% oleum in the presence of iodine, the temperature being raised from 50-200 C as the reaction proceeds. 

Category includes only direct chlorine consumption the majority of consumption is included in Epichlorohydrin, propylene oxide. 

The direct chlorination of hydrofluorocarbons and fluoroolefins has also been used commercially, eg, in the preparations of CH2CCIF2 from CH2CHF2 and CCIF2CCIF2 from tetrafluoroethylene. 

Niobium Pent chloride. Niobium pentachloride can be prepared in a variety of ways but most easily by direct chlorination of niobium metal. The reaction takes place at 300—350°C. Chlorination of a niobium pentoxide—carbon mixture also yields the pentachloride however, generally the latter is contaminated with niobium oxide trichloride. The pentachloride is a lemon-yeUow crystalline soHd that melts to a red-orange Hquid and hydrolyzes readily to hydrochloric acid and niobic acid. It is soluble in concentrated hydrochloric and sulfuric acids, sulfur monochloride, and many organic solvents. 

Properties ndReactions. Phosphoms trichloride can be prepared either by direct chlorination of elemental phosphoms. 

Of the halogens, only fluorine attacks siUca readily, forming SiF and O2. A number of halogen compounds of the nonmetals and metalloids react more or less readily with siUca, forming volatile siUcon halogen compounds (Table 1). The formation of SiCl by direct chlorination of mixtures of siUca and carbon is of some technical importance. 

Ma.nufa.cture. Sulfur monochloride is made commercially by direct chlorination of sulfur, usually in a heel of sulfur chloride from a previous batch. The chlorination appears to proceed stepwise through higher sulfur chlorides (S Cl2, where x > 2). If conducted too quickly, the chlorination may yield products containing SCI2 and S Cl2 as well as S2CI2. A catalyst, eg, iron, iodine, or a trace of ferric chloride, faciUtates the reaction. The manufacture in the absence of Fe and Fe salts at 32—100°C has also been reported (149—151). 

Stannic chloride is made by the direct chlorination of tin at 110—115°C. Any stannous chloride formed in the process is separated from the stannic chloride by volatilization and subsequently chlorinated to stannic chloride. The latter is inert to steel in the absence of moisture and is shipped in plain steel dmms of special design. Because prolonged contact with the skin causes bums, goggles and protective clothing should be used in the handling of stannic chloride. Stannic chloride, like stannous chloride, also forms many complexes (3). 

In a typical balanced plant producing vinyl chloride from EDC, all the HCl produced in EDC pyrolysis is used as the feed for oxychlorination. On this basis, EDC production is about evenly spHt between direct chlorination and oxychlorination, and there is no net production or consumption of HCl. The three principal operating steps used in the balanced process for ethylene-based vinyl chloride production are shown in the block flow diagram in Eigure 1, and a schematic of the overall process for a conventional plant is shown in Eigure 2 (76). A typical material balance for this process is given in Table 2. 

Direct Chlorination of Ethylene. Direct chlorination of ethylene is generally conducted in Hquid EDC in a bubble column reactor. Ethylene and chlorine dissolve in the Hquid phase and combine in a homogeneous catalytic reaction to form EDC. Under typical process conditions, the reaction rate is controlled by mass transfer, with absorption of ethylene as the limiting factor (77). Ferric chloride is a highly selective and efficient catalyst for this reaction, and is widely used commercially (78). Ferric chloride and sodium chloride [7647-14-5] mixtures have also been utilized for the catalyst (79), as have tetrachloroferrate compounds, eg, ammonium tetrachloroferrate [24411-12-9] NH FeCl (80). The reaction most likely proceeds through an electrophilic addition mechanism, in which the catalyst first polarizes chlorine, as shown in equation 5. The polarized chlorine molecule then acts as an electrophilic reagent to attack the double bond of ethylene, thereby faciHtating chlorine addition (eq. 6) ... 

Oxychlorination of Ethylene. When compared with direct chlorination, the oxychlorination process is characterized by higher capital investment, higher operating costs, and slightly less pure EDC product. However, use of the oxychlorination process is dictated by the need to consume the HCl generated in EDC pyrolysis. 

Direct chlorination usually produces EDC with a purity greater than 99.5 wt %, so that, except for removal of the FeCl, Httle further purification is necessary. Ferric chloride can be removed by adsorption of a sofld, or the EDC can be distilled from the FeCl in a boiling reactor, as noted above. Alternatively, the FeCl can be removed by washing with water, usually in conjunction with EDC from the oxychlorination process. 

EDC from the oxychlorination process is less pure than EDC from direct chlorination and requires purification by distillation. It is usually first washed with water and then with caustic solution to remove chloral and other water-extractable impurities (103). Subsequently, water and low boiling impurities are taken overhead in a first (light ends or heads) distillation column, and finally, pure, dry EDC is taken overhead in a second (heavy ends or product) column (see Fig. 2). 

The resistance of graphite to thermal shock, its stabiUty at high temperatures, and its resistance to corrosion permit its use as self-supporting vessels to contain reactions at elevated temperatures (800—1700°C), eg, self-supporting reaction vessels for the direct chlorination of metal and alkaline-earth oxides. The vulnerabiUty of cemented joints in these appHcations requires close tolerance ( 0.10 mm) machining, a feat easily accompHshed on graphite with conventional metal machining equipment. 

The principal U.S. producers of 1,1,1-trichloroethane include The Dow Chemical Company, PPG Industries Inc., and Vulcan Materials Co. Several European and Japanese companies also produce large amounts aimually. Over 70% of the production is based on the vinyl chloride-1,1-dichloroethane process, 20% on the 1,1-dichloroethylene process, and about 10% on the direct chlorination of ethane. 

Tetrachloroethane is produced by direct chlorination or oxychlorination utilizing ethylene as a feedstock. In most cases, 1,1,2,2-tetrachloroethane is not isolated, but immediately thermally cracked at 454°C to give the desired trichloroethylene and tetrachloroethylene products (122). A two-stage chlorination of 1,2-dichloroethane to give 1,1,2,2-tetrachloroethane has been patented (126). High purity 1,1,2,2-tetrachloroethane is made by chlorinating acetylene. 

Dichloroethylene can be produced by direct chlorination of acetylene at 40°C. It is often produced as a by-product ia the chlorination of chloriaated compounds (2) and recycled as an iatermediate for the synthesis of more useful chloriaated ethylenes (3). 1,2-Dichloroethylene can be formed by contiauous oxychloriaation of ethylene by use of a cupric chloride—potassium chloride catalyst, as the first step ia the manufacture of vinyl chloride [75-01-4] (4). 

Chlorobenzenes were first synthesized around the middle of the nineteenth century the first direct chlorination of benzene was reported in 1905 (1). Commercial production was begun in 1909 by the former United Alkali Co. in England (2). In 1915, the Hooker Electrochemical Co. at Niagara EaUs, New York, brought on stream its first chlorobenzenes plant in the United States with a capacity of about 8200 metric tons per year. 

The ring-chlorinated derivatives of toluene form a group of stable, industrially important compounds. Many chlorotoluene isomers can be prepared by direct chlorination. Other chlorotoluenes are prepared by indirect routes involving the replacement of amino, hydroxyl, chlorosulfonyl, and nitro groups by chlorine and the use of substituents, such as nitro, amino, and sulfonic acid, to orient substitution followed by their removal from the ring. 

Side-Chain Chlorinated Xylene Derivatives Only a few of the nine side-chaia chlotinated derivatives of each of the xylenes are available from direct chlorination. All three of the monochlotinated compounds, a-chloro-o-xylene (l-(chloromethyl)-2-meth5lbenzene [552-45-4] a-chloro-y -xylene (1-(ch1oromethy1)-3-methylhenzene [620-19-9] a-chloro-/)-xylene (1-(ch1oromethy1)-4-methylhenzene [104-82-5]) are obtained ia high yield from partial chlorination of the xyleaes. 1,3-Bis(ch1oromethy1)henzene [626-16-4] can be isolated ia moderate yield from chlorination mixtures (78,79). 

The piincipal by-pioducts aie the result of direct chlorine addition to give 1,2-dichlotoptopane [78-87-5] and ether formation. The ether product is dichloropropyl ether [108-60-1] or 2,2 -oxybis(l-chloropropane). 

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