Ethyl chloride, pyrolysis

Chlorinated by-products of ethylene oxychlorination typically include 1,1,2-trichloroethane chloral [75-87-6] (trichloroacetaldehyde) trichloroethylene [7901-6]-, 1,1-dichloroethane cis- and /n j -l,2-dichloroethylenes [156-59-2 and 156-60-5]-, 1,1-dichloroethylene [75-35-4] (vinyhdene chloride) 2-chloroethanol [107-07-3]-, ethyl chloride vinyl chloride mono-, di-, tri-, and tetrachloromethanes (methyl chloride [74-87-3], methylene chloride [75-09-2], chloroform, and carbon tetrachloride [56-23-5])-, and higher boiling compounds. The production of these compounds should be minimized to lower raw material costs, lessen the task of EDC purification, prevent fouling in the pyrolysis reactor, and minimize by-product handling and disposal. Of particular concern is chloral, because it polymerizes in the presence of strong acids. Chloral must be removed to prevent the formation of soflds which can foul and clog operating lines and controls (78). 

By-products from EDC pyrolysis typically include acetjiene, ethylene, methyl chloride, ethyl chloride, 1,3-butadiene, vinylacetylene, benzene, chloroprene, vinyUdene chloride, 1,1-dichloroethane, chloroform, carbon tetrachloride, 1,1,1-trichloroethane [71-55-6] and other chlorinated hydrocarbons (78). Most of these impurities remain with the unconverted EDC, and are subsequendy removed in EDC purification as light and heavy ends. The lightest compounds, ethylene and acetylene, are taken off with the HCl and end up in the oxychlorination reactor feed. The acetylene can be selectively hydrogenated to ethylene. The compounds that have boiling points near that of vinyl chloride, ie, methyl chloride and 1,3-butadiene, will codistiU with the vinyl chloride product. Chlorine or carbon tetrachloride addition to the pyrolysis reactor feed has been used to suppress methyl chloride formation, whereas 1,3-butadiene, which interferes with PVC polymerization, can be removed by treatment with chlorine or HCl, or by selective hydrogenation. 

Since free-radical chlorination is a nonselective process, overchlorination may be a problem in the manufacture of ethyl chloride. Temperature-induced pyrolysis to yield ethylene and hydrogen chloride may occur, too. A fluidized-bed thermal chlorination reactor may be used to overcome these problems. The best selectivity achieved in the temperature range of 400-450°C is 95.5% with a chlorine to ethane ratio of 1 5. 

Electrophilic replacement constants crXr have been obtained for all the positions of benzo[6]thiophene from the solvolysis of isomeric l-(benzo[ >]thienyl)ethyl chlorides in 80% ethanol-water. These constants signify replacement of the entire benzene ring by another aromatic system (74JOC2828). The positional order of reactivity was determined to be 3>2>6>5>4>7, all positions being more reactive than benzene. The same order was also derived from the kinetic data for pyrolysis of the isomeric l-(benzo[6]thienyl)ethyl acetates (78JCS(P2)1053). A modified extended selectivity treatment has been developed to correlate electrophilic substitution data in benzo[Z> ]thiophene, which assumes a dual activation mechanism (79JOC724). 

This study on the kinetic chlorine isotope effect in ethyl chloride50 was extended to secondary and tertiary alkyl halides pyrolyses51. The isotope effects on isopropyl chloride and terf-butyl chloride pyrolysis were found to be primary and exhibited a definite dependence on temperature. They increased with increasing methyl substitution on the central carbon atom. The pyrolysis results and model calculations implied that all alkyl chlorides involve the same type of activated complex. The C—Cl bond is not completely broken in the activated complex, yet the chlorine participation involves a combination of bending and stretching modes. 

An additional example of neighboring group participation in the gas-phase pyrolysis of 2-substituted ethyl chlorides was the elimination kinetics of 2-dimethylaminoethyl chloride67. The magnitude of the effect of Me2N on the dehydrochlorination rate (Table 14) led to a similar consideration to that for CH3SCH2CH2C1 by assuming the transition state for the elimination as an intimate ion-pair as represented above. 

The rates of pyrolysis of o-, m- and z -methylphenylethyl chloride have been compared with that of ethyl chloride (Table 15). Even though the phenyl group participated in the HC1 elimination, electron release of the methyl group at the three isomeric position of the aromatic ring was found to be, within the experimental errors, ineffective on the rates when compared to the unsubstituted phenylethyl chloride. Consequently, the effect of the CH3 substituent was too small for the reinforcement of the phenyl assistance as reflected by the pyrolysis rate. 

In connection with the methoxy participation, the gas-phase pyrolytic elimination of 4-chloro-1 -butanol was investigated177. The products are tetrahydrofuran, propene, formaldehyde and HCl. It is implied that the OH group provides anchimeric assistance from the fact that, besides formation of the normal unstable dehydrochlorinated intermediate 3-buten-l-ol, a ring-closed product, tetrahydrofuran, was also obtained. The higher rate of chlorobutanol pyrolysis with respect to chlorethanol and ethyl chloride (Table 27) confirmed the participation of the OH group through a five-membered ring in the transition state. 

At low temperatures, PVC pyrolysis yields only traces of volatile chlorinated hydrocarbons. The main chlorine-containing hydrocarbons reported are methyl chloride, vinyl chloride, ethyl chloride and chlorobenzene. Heating PVC at 10°C/min up to 500°C in... 

The proposed transition states have been supported by deuterium isotope studies Evidence such as the decomposition behaviour in solution and the nature of the increases in the rates of decomposition along the series of chloro-formates methyl, ethyl, isopropyl, 2-butyl, /-butyl suggests that the transition states are somewhat polar °> . Lewis and Herndon found 2-methylbut-1-ene and 2-methylbut-2-ene as the olefinic products of the elimination reaction of neopentyl chloroformate, and the kinetic evidence supports a Wagner-Meerwein rearrangement in the gas-phase as in the case of neopentyl chloride pyrolysis (refs. 407, 408, 566). 

Further studies on the pyrolysis of chlorinated and brominated hydrocarbons have been reported by Maccoll et al. for 3-bromopentane , menthyl and neo-menthyl chlorides , r-alkyl chlorides , dimethylallyl chlorides , a-chloro-o-xylene , and substituted 1-phenylethyl chlorides . Other workers have reported on the thermal reactions of ethyl chloride , monochloropentanes , 1-... 

The pyrolysis of ethyl chloride probably occurs by a concerted reaction at four centres ... 

Another complication with gas phase pyrolyses is that many possible nonconcerted reaction pathways are possible. Alkyl halides xmdergo elimination in the gas phase, and some compounds, such as ethyl chloride, appear to undergo unimolecular elimination. Their unimolecular decompositions may involve transition structures with significant carbocation character. For example, p5u-olysis of (-l- )-2-chlorooctane in the gas phase at 325-385°C was found to produce racemization of the starting material as well as elimination of HCl. Some compounds appear to react by radical chain mechanisms, and heterogeneous radical reactions often complicate studies that are not carried out in "well-seasoned" (i.e., coated with a layer of organic material) vessels. Furthermore, there appears to be a significant radical (but not radical chain) component to the pyrolysis of sulfoxides. These complications mean that many control studies are necessary to clarify the mechanism of gas phase elimination reactions. 

In a typical Knof procedure, 3jS-hydroxyandrost-5-en-17-one acetate is epoxidized with perbenzoic acid (or m-chloroperbenzoic acid ) to a mixture of 5a,6a- and 5)5,6)5-epoxides (75) in 99 % yield. Subsequent oxidation with aqueous chromium trioxide in methyl ethyl ketone affords the 5a-hydroxy-6-ketone (76) in 89% yield. Baeyer-Villiger oxidation of the hydroxy ketone (76) with perbenzoic acid (or w-chloroperbenzoic acid ) gives keto acid (77) in 96% yield as a complex with benzoic acid. The benzoic acid can be removed by sublimation or, more conveniently, by treating the complex with benzoyl chloride and pyridine to give the easily isolated )5-lactone (70) in 40% yield. As described in section III-A, pyrolysis of j5-lactone (70) affords A -B-norsteroid (71). Knof used this reaction sequence to prepare 3)5-hydroxy-B-norandrost-5-en-17-one acetate, B-noran-... 

The next three procedures provide useful synthetic intermediates. A stereospecific synthesis of ETHYL (Z)-3-BROMO-2-PROPENOATE affords an alternative vinyl bromide partner for the coupling chemistry in the preceding procedure. A very simple but elegant illustration of the flash vacuum pyrolysis technique is used to prepare BENZOCYCLOBUTENONE from o-toluoyl chloride. Another member of the functionalized indole family of synthetic intermediates is presented in a four-step procedure for 5-METHOXYINDOLE-2-ACETIC ACID METHYL ESTER. 

The bc portion (267) was synthesized (Scheme 19) by treatment of the ethyl ester of i3, 3-dimethyllevulinic acid with hot ethanolic ammonia, followed by pyrolysis to give (275). Meanwhile, treatment of /8, 8-dimethyllevulinic acid with thionyl chloride gave the butyrolac-tone (276), and the sodium salt of this was treated with (275) to give (277). Photochemically induced acyl migration gave (278), which was treated with methanolic ammonia subsequent dehydration afforded (279), which was then activated by O- ethylation with Meerwein s salt to give (267). 

Sebaconitrile has been obtained by heating sebacic acid in a stream of ammonia,1 and from sebacamide by pyrolysis 2 3 or by dehydration with phosphorus pentachloride 4 or phosphorus oxychloride.6 Sebacamide has been prepared from ethyl seba-cate6 or sebacyl chloride and ammonia,7 and by heating sebacic acid with urea2i3-8 or ammonium thiocyanate.9... 

Ethane occurs in natural gas, from which it is isolated. Ethane is among the chemically less reactive organic substances. However, ethane reacts with chlorine and bromine to form substitution compounds. Ethyl iodide, bromide, or chlorides are preferably made by reaction with ethyl alcohol and the appropriate phosphorus halide. Important ethane derivatives, by successive oxidation, are ethyl alcohol, acetaldehyde, and acetic acid. Ethane can also be used for the production of aromatics by pyrolysis (Fig. 1). 

In the preparation of l-ethyl-3-piperideine (8), the starting material l-ethyl-4-piperidone (6) was hydrogenated to give 1-ethyl-4-piperi-dinol. Treatment of the latter with thionyl chloride afforded 1-ethyl-4-chloropiperidine, the dehydrohalogenation of which (NaOMe/ MeOH) led to a low yield of l-ethyl-3-piperideine. A somewhat higher yield (37%) was obtained by pyrolysis (500°C) of l-ethyl-4-acetoxypiperidine (7).3... 

The pyrolysis of r-butyl peroxy esters in suitable hydrogen donor solvents has been reviewed by Rtichardt. Ihe method involves the reaction of an acyl chloride widi r-butyl hydroperoxide followed by thermolysis of die resulting pooxy ester in cumene or p-cymene. Yields are moderate, but the pyrolysis step tolerates a certain degree of functionality as Ulustrated in equation (8). More recendy, the use of ethyl phenylacetate as die pyrolysis solvent and hydrogen donor has been advocated. 

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