Patent GB-764122-A (GB)
Title: The manufacture of ª ,ª  unsaturated aldehydes
IPC: C07C47/225
Filed: 1955-01-12
Abstract: The invention comprises the aldehydes [2,6,6 - trimethyl - cyclohexen - (2) - ylidine(1)] - acetaldehyde and [2,6,6 - trimethylcyclohexylidene - (1)] - acetaldehyde.  These, and known a ,b -unsaturated aldehydes may be prepared by a process comprising treating a b -halogeno-vinyl ether with an alkali-metal amide in liquid ammonia, reacting the resulting liquid ammonia solution containing an alkalimetal derivative of an ethinyl ether with an aldehyde or a ketone, hydrolysing and partially hydrogenating at the triple bond (in either sequence) the reaction product and treating the hydrolysis/partial hydrogenation product so obtained with an acidic agent.  Suitable vinyl ethers are for example, b -chloro-vinyl methyl ether, p-chloro-vinyl ethyl ether, b -bromovinyl ethyl ether and b -chloro-vinyl phenyl ether. Suitable aldehydes and ketones are for example propionaldehyde, butyraldehyde, methacrolein, b  - methyl - crotonaldehyde, citral, 4 - [21,61,61 - trimethyl - cyclohexen-(11 - yl - (1)] - 2 - methyl - buten - (2) - al - (1); benzaldehyde, cinnamaldehyde, acetone, methyl ethyl ketone, diethyl ketone, mesityl oxide, methyl-heptanone, dimethyl-heptanone, pseudoionone, cyclohexanone, 2,6,6-trimethylcyclohexanone - (1), cyclohexenone, 2,6,6-trimethyl - cyclohexen - (2) - one - (1), dihydrobetaionone, betaionone, 8 - [21,61,61 - trimethylcyclohexen - (1) - yl] - 6 - methyl - octatrien(3,5,7) - one - (2), acetophenone, acetonylacetone, octene - (4) - dione - (2,7), succinic dialdehyde, 2,7 - dimethyl - octatrien - (2,4,6)-dial - (1,8), 2,7 - dimethyl - octadien - (2,6) - in-(4) - dial - (1,8), methoxy - acetone, levulinic acid, p - dimethylamino - benzaldehyde, p-hydroxy - benzaldehyde, androsterone, and oestrone.  Preferably the b -halogeno-vinyl ether is a lower alkyl ether, i.e. the alkyl group contains from 1 to 4 carbon atoms, and the acidic agent is a dilute aqueous solution of a mineral acid. The partial hydrogenation of the triple bond may be carried out by adding sodium or lithium to the ammoniacal solution of the condensation product, or by treating the reaction product, after removal of the ammonia, with sodium in damp ether or with lithium aluminium hydride in dry ether, followed by hydrolysis.  It is preferred however to carry out the hydrolysis first by the addition of an ammonium salt and to subsequently carry out the partial hydrogenation, for example, by treatment with lithium aluminium hydride in dry ether or by catalytic hydrogenation using a palladium catalyst, advantageously a palladium/calcium - carbonate catalyst partially deactivated by means of lead and quinoline.  In the examples: (a) b -chloro-vinyl-ethyl ether is treated with lithium dissolved in liquid ammonia and 4-[21,61,61-trimethyl-cyclohexen-(11) - yl] - 2 - methyl - buten - (2) - al - (1) is added; the resulting mixture is then treated with ammonium chloride and then treated with hydrogen in the presence of a lead-poisoned palladium catalyst to give 6-[21,61,61-trimethyl cyclohexen - (11) - yl] - 4 - methyl - hexadien - (2,4) - al - (1); (b) 6 - methyl - hepten - (5) - one-(2) is added to a mixture of sodium in liquid ammonia and b -chloro-vinyl-ethyl ether and the reaction product is treated with ammonium chloride to give 1-ethoxy-3-hydroxy-3,7-dimethyl - octen - (6) - ine - (1) which is then treated with hydrogen in the presence of a lead-poisoned palladium catalyst to give citral; (c) b -chloro-vinyl ethyl ether is added to a solution of lithium in liquid ammonia and the product is treated with 2,6,6-trimethyl-cyclohexene-(2)-one-(1) (prepared from 2,6,6-trimethyl-cyclohexane by bromination followed by dehydrohalogenation with pyridine); the reaction mixture is then treated with ammonium chloride and the product subsequently treated with hydrogen in the presence of a leadpoisoned palladium catalyst to give [2,6,6-trimethyl - cyclohexen - (2) - ylidine - (1)] - acetaldehyde; (d) in a process similar to that of (c) except that 2,6,6-trimethyl-cyclohexanone is used as starting material the product is [2,6,6-trimethyl - cyclohexylidine - (1)] - acetaldehyde; (e) b -chlor-vinyl ethyl ether is added to a solution of lithium in liquid ammonia and 4 - [21,61, 61 - trimethyl - cyclohexene - (21)-ylidine - (1)1] - 2 - methyl - buten - (2) - al - (1) (prepared by bromination of 4-[21,61,61-trimethyl - cyclohexene - (11) - yl] - 2 - methylbutene - (2) - al - (1), followed by dehydrobromination) is added to the resulting mixture; the reaction mixture is then hydrolysed and partially reduced as in the previous examples to give 6-[21,61,61-trimethyl-cyclohexene-(21) -ylidine - (11)] - 4 - methyl - hexadien - (2,4)-al-(1); (f) in a process similar to that of (e) but using 4 - [21,61,61 - trimethyl - cyclohexadien-(11,31) - yl - (11)] - 2 - methyl - buten - (2) - al-(1) as starting material 6-[21,61,61-trimethylcyclohexadiene - (11,31) - yl - (11)] - 4 - methylhexadien-(2,4)-al-(1) is obtained; (g) in a pro cess similar to that of (e) but using 4-[21,61,61-trimethyl - cyclohexylidine - (11)] - 2 - methylbuten - (2) - al - (1) as starting material, 6 - [21,61,61 - trimethyl - cyclohexylidine - (11)]-4 - methyl - hexadien - (2,4) - al - (1) with a small amount of 6-[21,61,61-trimethyl-cyclohexene - (11) - yl - (11)] - 4 - methyl - hexadien-(2,4)-al-(1) is obtained.  The starting material in the last example is prepared by acetalizing (2,6,6 - trimethyl - cyclohexylidine) - acetaldehyde (prepared as in (d) above) with orthoformic acid triethyl ester in the presence of p-toluene sulphonic acid; the resulting (2,6,6:trimethylcyclohexylidine)-acetaldehyde diethyl acetal is condensed with ethyl propenyl ether in the presence of zinc chloride to form 4-[21,61,61-trimethylcyclohexylidine - (11) - 2 - methyl - 1,1,3 - triethoxy-butane which upon hydrolysis-dealcoholation by heating with acetic acid and sodium acetate gives the required 4-[21,61,61 trimethyl - cyclohexylidine - (11)] - 2 - methylbuten - (2) - al - (1).  This latter compound may be condensed with isopropenyl acetate to yield 4 - [21,61,61 - trimethyl - cyclohexenyl-(11)] - 2 - methyl - 1 - acetoxy - butadiene - (1,3) which on hydrolysis yields 4-[21,61,61-trimethyl cyclohexen - (11) - yl] - 2 - methyl - buten - (2)-al-(1).