Patent GB-707990-A (GB)
Title: Process for the manufacture of halogenated organic compounds
Inventor: PICKHOLZ SIEGFRIED
IPC: C07C45/63
Filed: 1951-01-15
Abstract: Compounds containing the grouping <FORM:0707990/IV (b)/1> the double bond being part of an aliphatic, cycloaliphatic, aromatic or heterocyclic group and the carbon atom carrying the hydrogen atom being part of an aliphatic or cycloaliphatic group (which may be substituted) are halogenated by heating with an N-halogeno carboxylic acid amide or imide, the N-halogen atom of which has an atomic number of at least 17, in the presence of an azo compound which undergoes thermal decomposition at a temperature at which the substance to be halogenated is in the liquid phase.  Usually 0.1-5, preferably 0.1-1 mol. per cent of azo compound based upon the halogenation reagent is used. Preferred azo compounds are those which decompose at an appreciable rate at 50-150 DEG  C. with activation energies of about 30 kilocalories.  Azo compounds specified are 2,21-azo-bismethanes obtainable by condensing aromatic ketones with hydrazine to form an azine, reducing the azine to the hydrazine and oxidizing the latter, and are of formula. <FORM:0707990/IV (b)/2> where R is a substituted or unsubstituted phenyl group and R1 is H or a straight or branched chain alkyl group, and 2,21-azo-bisnitriles obtainable by the condensation of aliphatic or cycloaliphatic ketones with hydrazine and hydrocyanic acid and oxidation of the resulting hydrazo compound to the corresponding azo-nitrile and are of formula <FORM:0707990/IV (b)/3> where R2, R3, R4 and R5 are alkyl or aralkyl groups or R2 and R3 together and/or R4 and R5 together are cycloalkyl.  Representative of specified compounds to be halogenated are amylene, methyl crotonate, cyclohexene, camphene, 1,3-cyclohexadiene, ethyl sorbate, crotylidene acetone, lycopene, toluene, para-nitrotoluene, 2-methyl-naphthalene, dibenzyl, triphenylmethane, dihydropyran, 3-methylthiophen, carbazol and 3-methylcoumarin.  Hydroxyl, mercapto, carboxylic or sulphonic groups present in compounds to be halogenated should be protected by conversion to another functional group such as ester, ether or acid chloride.  Thus a 3-ester of cholesterol or sitosterol may be used and the product subsequently hydrolysed; or an ester of a carboxylic or sulphonic acid such as methyl crotonate, b -,b -dimethylacrylate, sorbate or p-toluene sulphonate may be used; or the acid may be converted to the corresponding acid halide such as a fluoride or chloride, e.g. p-toluene sulphonyl chloride or fluoride.  N-halo-amides mentioned are N-bromo-acetamide and propionamide, N-chloro, N-bromo- and N-iodo-succinimide, N-chloro- and N-bromo-phthalmide, N-halogen methanes, N-mono- and N,N1-dichloro- and bromo-hydantoins and nuclear halogenated N-halogeno acetanilides.  An inert solvent is preferably used, e.g. pet. ether, carbon tetrachloride, chloroform, benzene, chlorobenzene or cyclohexane, or excess reactant may be present, e.g. in the bromination of cyclohexene, aromatic hydrocarbons or heterocyclic compounds.  Reactants are preferably taken in equimolar quantities. Temperatures specified are 50-150 DEG  C.  Products may be dehydrohalogenated after or during formation, e.g. by heating optionally in the presence of a dehydrohalogenating agent many of which are specified.  In examples N-bromo-succinimide is treated with (1) cyclohexene and 2,21-azo-bis-isobutyronitrile in carbon tetrachloride to yield 3-bromo-cyclohexene; (2) toluene and 2,21-azo-bis-isobutyronitrile in carbon tetrachloride to yield benzyl bromide; (3) and (4) are repeats of (2) using 2,21-azo-biscyclohexanonitrile and 2,21-azo-bis-2-benzylpropionitrile respectively instead of the nitrile of (2); (6) p-nitrotoluene and 2,21-azo-bis-isobutyronitrile in carbon tetrachloride to yield p-nitrobenzyl bromide; (8) 2-methylnaphthalene; (9) ethyl crotonate; (10) ethyl benzene; (11) p-cresyl methyl ether; (12) camphene; (13) p-chlorotoluene; (14, (15) and (16) dibenzyl; (17) diphenyl methane; (20) o-nitrotoluene; (21) m-nitrotoluene; (22) cholesterol benzoate; (23) p-toluene sulphonyl chloride; (25) p-toluene sulphonyl fluoride and (28) crotonylidene acetone with 2,21-azo-bis-iso butyronitrile in carbon tetrachloride (except (10), (13), (14) and (22) when pet. ether and (16) chloroform are used) to yield respectively 2 - bromo - methylnaphthalene, ethyl - g  bromo - crotonate, a  - bromo - ethylbenzene, p-methoxybenzyl bromide, monobromocamphene, p - chlorobenzyl bromide; (14)-(16) a product which treated with potassium acetate in glacial acetic acid yields stilbene, diphenyl methyl bromide, o-nitrobenzyl bromide, m-nitrobenzyl bromide, p 7-bromo-cholesterol benzoate, o -bromo-p-toluene sulphonyl chloride, o -bromo-p-toluene sulphonyl fluoride and e -bromo-crotnylidene acetone; N,N1-dibromo-5,5-dimethylhydantoin is treated with (7) p-nitrotoluene, (18) and (19) ethyl sorbate, (24) p-toluene sulphonyl chloride and (26) p-toluene sulphonyl fluoride with 2,21-azo-bis-isobutyonitrile in carbon tetrachloride (except (19) where pet. ether is used) to yield respectively p-nitrobenzyl bromide, (18) and (19) e -bromo-ethyl sorbate, o -bromo-p-toluene sulphonyl chloride and o -bromo-p-toluene sulphonyl fluoride, in (5) N,N1 - dichloro - 5,5 - dimethyl - hydantoin with 2,21 - azo - bis - isobutyronitrile in carbon tetrachloride yields benzyl chloride and (27) N-bromo-succinimide with methyl p-toluene sulphonate and 2,21 - azo - bis - (a  - methylbutyronitrile) in carbon tetrachloride yields o -bromo-methyl-p-toluene sulphonate.  For comparative purposes examples (6) and (8) are repeated using benzoyl peroxide as catalyst instead of the azo compound and a number of control experiments, in which no catalysts are used, are described in the examples. Specifications 589,282, 624,047 and 649,934 are referred to.ALSO:Rubber is halogenated by heating with an N-halogeno-carboxylic acid amide or imide, the N-halogen atom of which has an atomic number of at least 17, in the presence of an azo compound which undergoes thermal decomposition at a temperature at which the rubber is in the liquid phase.  Usually 0.1-5.0 preferably 0.1-1.0, mol. per cent. of azo compound based on halogenation reagent is used.  Preferred azo compounds are those which decompose at appreciable rates at 50-150 DEG C. with activation-energies of about 30 kilocalories.  Azo compounds specified are 2, 21-azo-bis-methanes and 2, 21-azo-bis-nitriles of Group IV (b).  Halo-amides mentioned are N-bromo-acetamide and -propionamide, N-chloro- N-bromo- and N-iodosuccinimide, N-chloro- and N-bromo phthalamide, N-halogen methanes, N-mono-and N, N1-dichloro- and bromo-hydantoins and nuclear halogenated N-halogeno-acetanilides.  An inert solvent is preferably present, e.g. pet. ether, carbon tetrachloride, chloroform, benzene, chlorobenzene or cyclohexane and reactants taken in equimolar quantities.  Temperatures indicated for reaction are 50-150 DEG C. Products may be dehydrogenated after or during formation. Specifications 589,282, [Group IV], 624,047 and 649,934, [both in Group IV (b)], are referred to.