GB768172A - Dialkoxy derivatives of bis-acetals of an unsaturated dial and their preparation and conversion into a trienic dial - Google Patents

Abstract

The invention comprises 2,7-dimethyl-1,1,3,6, 8,8-hexa-alkoxy-octene-(4)s. These C10-dietherdiacetals may be prepared by condensing a butene-2-dial-(1,4) di(dialkyl)-acetal with at least 2 mols. of a propenyl-(1) alkyl ether in the presence of an acidic condensing agent, preferably boron trifluoride etherate, zinc chloride, titanium tetrachloride, aluminium chloride or tin tetrachloride. Generally, a temperature below 50 DEG C. is used. Preferably, the alkyl groups in the reactants contain 1 to 4 carbon atoms. The products are mixtures of stereoisomers, which as such or separated into their components may be hydrolysed in an acidic medium to the C10-dialdehyde 2,7-dimethylocta-trien-(2,4,6)-dial-(1,8). Suitably, the hydrolysis is effected in the presence of water-soluble organic or inorganic non-volatile acids or watersoluble acidic salts, many examples being given, if desired in conjunction with a water-miscible solvent and an antioxidant; the alcohol liberated is continuously removed. Alternatively, hydrolysis may be effected by heating with aqueous acetic acid for several hours and then diluting with water. The C10-dialdehyde may be subjected to a Reformatsky reaction with 2 mols. of g -bromo tiglic acid ester and water split-off from the resulting product to give a crocetin ester. Also, the dialdehyde may be acetalized, the resulting acetal condensed with two mols. of a vinyl ether and the condensation product treated with an acid to produce 4.9-dimethyl - dodecapentaene - (2,4,6,8,10) - dial - (1,12) which is of value in the synthesis of crocetin, bixin and lycopene. In the example: propenyl-1 ethyl ether is reacted with butene-2-dial-(1,4-di(diethyl acetal) using zinc chloride as catalyst yielding a crude mixture of isomers of 2,7-dimethyl-1,1,3,6,8,8-hexaethoxy-octene-(4) from which one isomer, melting-point 70 DEG C., crystallizes out on cooling. The crude mixture or isolated isomer is hydrolysed in a mixture of water and dioxane containing phosphoric acid at 100 DEG C., the water-alcohol-dioxane distilling off being replaced by water-dioxane mixture, and thereafter water is added to precipitate the resulting C10 dialdehyde. The crude diether diacetal may be purified by distillation and then hydrolysed to the C10 dialdehyde by heating with an aqueous mixture of acetic acid and ethyl acetate at 100 DEG C. and thereafter distilling off the ethyl acetate formed and present initially in vacuo. Butene - 2 - dial - (1,4) diacetals used as starting materials may be prepared by catalytic partial reduction of acetylene-dialdehyde diacetals derived, for example, from methanol, ethanol, propanol and butanol. Propenyl-(1)-methyl, ethyl and butyl ethers specified as reagents may be prepared by pyrolysis of propionaldehyde dialkyl-acetals.