Chlorobutanes, dehydrochlorination

Oxidative catalysis over metal oxides yields mainly HC1 and C02. Catalysts such as V203 and Cr203 have been used with some success.49 50 In recent years, nanoscale MgO and CaO prepared by a modified aerogel/hypercritical drying procedure (abbreviated as AP-CaO) and AP-MgO, were found to be superior to conventionally prepared (henceforth denoted as CP) CP-CaO, CP-MgO, and commercial CaO/MgO catalysts for the dehydrochlorination of several toxic chlorinated substances.51 52 The interaction of 1-chlorobutane with nanocrystalline MgO at 200 to 350°C results in both stoichiometric and catalytic dehydrochlorination of 1-chlorobutane to isomers of butene and simultaneous topochemical conversion of MgO to MgCl2.53-55 The crystallite sizes in these nanoscale materials are of the order of nanometers ( 4 nm). These oxides are efficient due to the presence of high concentration of low coordinated sites, structural defects on their surface, and high-specific-surface area. 

Devulcanization in the Presence of Benzyl Chloride and Methyl Chloride. The above results suggest that catalyst efficiency might be improved when devulcanization is carried out with added alkylating agent. We find that this is, indeed, the case. Added benzyl chloride or methyl chloride further decreases the crosslink density for a given concentration of catalyst (Table 11). However, 1- and 2-chlorobutanes appear to be ineffective, possibly because of dehydrochlorination. 

Problem 7.54 How is conformational analysis used to explain the 6 1 ratio of trans- to ci5-2-butene formed on dehydrochlorination of 2-chlorobutane M... 

Comparison of the activity of different catalysts for the dehydrochlorination of 1-chlorobutane [174]... 

The influence of temperature on the ratio of the products of the dehydrochlorination of 2-chlorobutane is seen from Fig. 6 [190], Other examples may be found in the literature [190,194,195]. Some ratios are almost temperature-independent while some show large changes. Moreover, the data from various sources differ sometimes appreciably (cf. refs. 190 and 914 for 2-chlorobutane and refs. 66 and 195 for 1,1,2-trichloroethane). This might be caused by secondary isomerisation on strongly acidic catalysts of the olefins first formed such a reaction was proved at... 

Thermal elimination reactions of molecules in the gas phase and in solution usually occur by 1,2-processes by a variety of mechanisms (Banthorpe, 1963) some 1,4-elimination processes have also been suggested (Harding et al., 1967). In mass spectrometry, isotopic labelling shows that elimination of water from primary aliphatic alcohols occurred mainly by 1,4-processes, the remainder being 1,3- and 1,5-reactions, provided the aliphatic chain was sufficiently long (Benz and Biemann, 1964 S. Meyerson and Leitch, 1964). Similar studies showed that dehydrochlorination of 1-chloropentane and 1-chlorobutane luider electron impact proceeded preferentially by 1,3-elimination processes (Duffield et at., 1966). 

The unimolecular gas-phase elimination kinetics of 2-methoxy-l-chloroethane, 3-methoxy-l-chloropropane, and 4-methoxy-l-chlorobutane has been studied using density functional theory (DFT) methods. Results calculated for 2-methoxy-l-chloroethane and 3-methoxy-l-chloropropane suggest that the corresponding olefin forms by dehydrochlorination through a concerted nonsynchronous four-centered cyclic transition state. In the case of 4-methoxy-l-chlorobutane, in addition to the 1,2-elimination mechanism, anchimeric assistance by the methoxy group, through a polar five-centered cyclic transition state, provides 4-methoxybutene, tetrahydrofuran, and chloromethane. Polarization of the C-Cl bond is rate limiting in these elimination reactions. 

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