Patent GB-760117-A (GB)
Title: Process for preparing unsaturated organic compounds
IPC: C07C1/26
Filed: 1953-07-13
Abstract: Organic compounds containing at least one allyl type radical <FORM:0760117/IV(b)/1> attached to a carbon atom through one of the valencies of the saturated carbon atom of the allyl radical are prepared by pyrolysing an allylic halide (as hereinafter defined) at a temperature between about 450 DEG  C. and about 750 DEG  C. for a period of between about 1 and 50 seconds in the presence of a stoichiometric excess of an organic compound which is stable in the presence of hydrogen halide at the pyrolysis temperature and contains at least one replaceable hydrogen atom which is attached to a carbon atom and is capable of being removed at the pyrolysis temperature by a halogen atom split off from the allylic halide. The expression "allylic halide" denotes an organic compound having a double bond between two aliphatic carbon atoms, one of which is joined to an aliphatic carbon atom bearing a labile halogen atom, the compound being incapable of losing hydrogen halide at the pyrolysis temperature to form conjugated double bonds and not possessing a system of conjugated double bonds. Specified allylic halides are allyl chloride or bromide, methallyl chloride or bromide, 1-chloro - 2,4,4 - trimethyl - 2 - pentene, 1 - chloro-3 - phenyl - 2 - propene, 1 - chloro - 1 - xylyl - 2 - propene, 1 - chloro - 3 - chlorophenyl - 2 - propene, 1,3 - dichloro - 2 - propene and 1,2,3 - trichloro-2-propene.  The organic compounds containing the replaceable hydrogen atoms may be saturated or unsaturated aliphatic, cycloaliphatic, aromatic or heterocyclic and may contain non-interfering substituents such as halogen atoms or ether, ester or carboxyl radicals; preferably, they have a carbon/hydrogen bond strength of less than 90 kgm. cals. per mol.  The compounds specified include alkanes and cycloalkanes, e.g. propane, dodecane, cyclohexane and 2,4-dimethyl cyclopentane; aliphatic and cycloaliphatic mono- and di-olefines, e.g. ethylene, hexene, decene and methylcyclopentene; aralkyl compounds containing 7 to 15 carbon atoms, e.g. ethyl benzene, cumene and butyl benzene; acids such as butyric or propionic acid and aliphatic ketones, e.g. diethyl ketone, dibutyl ketone and diamyl ketone.  The compounds containing the replaceable hydrogen are preferably used in a molar ratio of at least 3 : 1.  One or both the reactants may be added at a plurality of points throughout the reaction zone.  Reaction is generally effected under atmospheric pressure.  The reacted mixture is condensed and scrubbed or otherwise treated to remove hydrogen halide; the desired product is then recovered, e.g. by distillation or extraction from unchanged starting materials and by-products such as benzene, cyclohexadiene and naphthalene.  The reaction mixture to be subjected to the pyrolysis may be obtained by contacting a beta-gamma ethylenically-unsaturated organic compound containing a replaceable hydrogen atom attached to an alphacarbon atom thereof, which compound is stable in the presence of hydrogen halide at the subsequent pyrolysis temperature, with a halogen in a molar ratio of more than 4 : 1 and at a temperature at which substitution halogenation occurs to form a mixture containing an allylic halide (as above defined), which temperature is below that at which pyrolysis is subsequently effected.  This process may be carried out in the first stage of the reaction zone and the pyrolysis may then be effected at the higher temperature in the remainder of the zone.  The reactants are preferably preheated and may comprise inert diluents, e.g. nitrogen.  The total residence time should only be slightly longer, say 2 to 10 secs., than that needed for the direct pyrolysis and turbulent flow rates are preferred.  Examples employ a glass tube reactor externally heated electrically at three points wherein (1) allyl chloride and propylene are pyrolysed at 540 DEG  C. yielding diallyl and some benzene and cyclohexadiene; isobutylene reacted likewise yields 2-methyl-1,5-hexadiene; (2) methallyl chloride and propylene are pyrolysed similarly yielding dimethallyl; (3) allyl chloride and toluene are reacted at 560 DEG C. yielding 4-phenylbutene-1 and small amounts of dibenzyl, stilbene and naphthalene; (4) 1,3-dichloro propene and propylene are similarly reacted at 540 DEG  C., yielding initially 1-chloro-1,5-hexadiene which is then converted to cyclohexadiene at the temperature used; (5) allyl bromide is pyrolysed with propylene as in (1); (6) allyl chloride and propane are reacted at 560 DEG  C., yielding 1-hexene; (7) a preheated mixture of chlorine, nitrogen and propylene in a molar ratio of 1 : 3 : 9 is fed down the reaction tube, the top part of which is at 480 DEG  C. and the remainder at 560 DEG  C. and the products are distilled to recover diallyl and some allyl chloride; (8) a 12 : 3 : 1 feed mixture of isobutylene, nitrogen and chlorine is reacted substantially as in (7) to give dimethallyl and methallyl chloride.