GB865478A - A process for the manufacture of unsaturated ketones - Google Patents

Abstract

Unsaturated ketones of the general formula: <FORM:0865478/IV (b)/1> where R1 represents hydrogen or a C1-6 alkyl or alkenyl radical and R2 represents a C1-6 alkyl radical or R1 and R2 together represent a polymethylene bridge, and R4 and R5 each represent an acyclic or cyclic hydrocarbon group, including alkyl, alkenyl, cycloaliphatic, aromatic and araliphatic groups, or together form a polymethylene bridge, R4 and R5 optionally bearing substituents, such as alkyl or alkoxy groups, which are inert under the hereinafter specified reaction conditions are prepared by reacting a ketal of the general formula: <FORM:0865478/IV (b)/2> or an enol ether of the general formula: <FORM:0865478/IV (b)/3> R3 representing a C1-6 alkyl group, with a 1, 1-disubstituted propargyl alcohol of the general formula: <FORM:0865478/IV (b)/4> in the presence of a catalytic amount of an acidic condensing agent which may be a strong mineral or organic acid, an acid-reacting salt or a Lewis acid, many examples being given. The reaction is suitably carried out in a solvent, for example a hydrocarbon solvent and a part of this solvent may be distilled off to remove alcohol formed in the reaction. Alternatively, the enol-ether reactant may be used in excess to bind the liberated alcohol. The resulting allene-type ketone may be isomerised to a ketone of the general formula: <FORM:0865478/IV (b)/5> by treatment with acidic or basic agents or by the influence of heat, for example by heating at about 100 DEG -180 DEG C. alone or with an acid such as acetic acid or by treatment with a dilute solution of alkali or alkaline earth metal hydroxide, preferably dilute methanolic NaOH at, for example, room temperature. If desired, the condensation step yielding the allene-type ketone may be so carried out that extensive isomerisation is also effected, namely by use of a lengthy heating period and larger amounts of the acidic condensing agent; the isomerisation is facititated by the addition of copper powder or a copper salt e.g. cupric acetate. The reactions are preferably carried out under an inert atmosphere and anti-oxidants such as hydroquinone or butoxy anisole may be present. The unsaturated ketones may be purified by partition between petroleum ether and aqueous methanol. The ketones may cyclise after the reaction or isomerisation steps to give a - and b -ionone type ketones (see Specification 865,479). Examples describe the preparation of (1) 4:7-dimethyl-octadien-4, 6-one-3, by the one step method; (2) 6:10-dimethyl-undecatrien-4, 5, 9-one-2 and its isomerisation to pseudo ionone; (3) 4:7:11-trimethyl-dodecatrien-5, 6, 10-one-3; (4) 3-allyl-6, 10-dimethyl undecatrien-4, 5, 9-one-2 and its isomerisation to 3-allyl-6, 10-dimethylundecatrien-3, 5, 9-one-2; (5) 6:9:10-trimethylundecatrien-4, 5, 9-one-2, acetone diethyl ketal being used to form isopropenyl ether in situ, and isomerisation of the allenic ketone to pseudo-irone;(6) (9) and (12) 3:6:10-trimethyl -undecatrien-4, 5, 9-one-2 and its isomerisation to iso methyl-pseudo-ionone; (7) 4-methyl-6-cyclohexylidene-hexene-5-one-3 and its isomerisation to 4-methyl-6-cyclohexylidene-hexene-4-one-3; (8) 1-[21-oxo-cyclohexylidene]-3, 6, 7-trimethyl-octadiene-2, 6 by the one step method; (10) iso ethyl-pseudo irone and (11) iso-methyl pseudoionone by the one step method; (13) a mixture of 4:7:10:11-tetramethyl-dodecatrien-5, 6, 10-one-3 and 4:7:10:11-tetramethyl-dodecatrien-4, 6, 10-one-3 by the one step method; (14) and (15) a mixture of 3:6:9:10-tetramethyl-undecatrien4, 5, 9-one-2 and iso methyl-pseudo irone, which mixture on further heating is converted wholly to iso methyl pseudo inone. Numerous other propargyl alcohols, ketals and enol-ethers are specified. Enol-ethers of the above type are prepared by acidic pyrolysis of the corresponding ketals in the presence of for example potassium bisulphate, or a mixture of acetic anhydride and pyridine. Hexene-5-one-2 diethyl ketal is prepared by reacting the ketone with ortho-formic ester and boron-trifluoride etherate.