Patent GB-784628-A (GB)
Title: Improvements in the production of conjugated-unsaturated aldehydo carboxylic acid esters
IPC: C07C69/73
Filed: 1956-01-17
Abstract: Conjugated unsaturated aldehydo carboxylic acid esters are produced by reacting, while excluding water, an aldehydo carboxylic acid ester of the general formula: <FORM:0784628/IV (a)/1> in which m and n are 0, 1 or 2 and the sum of m and n is 1, 2 or 3, R represents hydrogen or a lower alkyl group and R1 represents a lower alkyl group, or a lower dialkyl acetal of said aldehydo carboxylic acid ester, the terms "lower alkyl" meaning alkyls of from 1 to 4 carbon atoms, in the presence of an acid condensing agent, with a vinyl ether of the general formula R-CH = CH-OR1 in which R and R1 have the same meaning as above, R and R1 of the said general formul  being individually or cojointly either the same or different radicals of the aforesaid kind, and heating the resultant alkoxy aldehydo carboxylic acid ester or its dialkyl acetal in the presence of at least 1 mol. of water per mol. of alkoxy aldehydo carboxylic acid ester with an acid until no more alcohol is split off.  In the final step, more than 1 mol. of water per mol. of ester may be present and an excess, e.g. 10 mols., is advantageous.  The water is preferably added in small portions during the heating, advantageously in the presence of benzene or toluene.  Suitable initial aldehydo esters are 2- or 4-methylbutene-2-al-1-oic acid-(4) methyl, ethyl or butyl esters or their dimethyl or diethyl acetals, 1,1,3-trimethoxy - or triethoxy - 4 - methylhexene - 4-oic acid-(6) methyl or ethyl esters, or 1,1,3-triethoxyhexene - 4 - oic acid - (6) ethyl ester.  Suitable vinyl ethers are vinyl or propenyl methyl, ethyl or propyl ethers. As acid condensing agents there may be used hydrogen fluoride, chloride and bromide, boron trifluoride, benzene sulphonic acid, p-toluene sulphonic acid, or zinc chloride, an amounts from 0.05 to 10 per cent with reference to the reactants.  The same acid agents may be used in the step of splitting off of alcohol.  In examples: (1) 2-methyl-butene - 2 - al - 1 - oic acid - (4) - ethyl ester (obtainable by oxidation of o -hydroxy-b -methyl-crotonic acid ethyl ester or by condensation of propionaldehyde with glyoxylic acid ethyl ester) is acetalized by stirring with absolute alcohol, ammonium nitrate and orthoformic acid ethyl ester, the 1,1-diethoxy-2-methylbutane - 2 - oic acid - (4) ethyl ester so obtained is reacted with vinyl ethyl ether and boron trifluoride etherate to give 1,1,3-triethoxy - 4 - methylhexene - 4 - oic acid - (6) ethyl ester, and this ester is heated with benzene, water and p-toluene sulphonic acid until no more alcohol is split off giving 4-methylhexadiene - 2.4 - al - 1 - oic acid - 6 - ethyl ester; (2) 1,1,3-triethoxy-4-methylhexene-4-oic acid-6 ethyl ester, obtained as in (1), is reacted with propenyl ethyl ether and boron trifluoride etherate yielding 1,1,3,5 - tetraethoxy - 2,6-dimethyloctene - 6 - oic acid - 8 ethyl ester, which is then heated with benzene, water and p-toluene sulphonic acid to give 2,6-dimethyloctatriene - 2,4,6 - al - 1 - oic acid - 8 ethyl ester; (3) 4 - methyl - hexadiene - 2,4 - ol - 1 oic acid-6 ethyl ester, obtained as in (1) is acetalized with orthoformic acid ethyl ester, ammonium nitrate and absolute ethanol giving 1,1 - diethoxy - 4 - methylhexadiene - 2,4 - oic acid-6 ethyl ester which is reacted with propenyl ethyl ether and boron trifluoride etherate giving the 1,1,3-triethoxy-2,6-dimethyl-octadiene - 4,6 - oic acid - 8 ethyl ester, and the latter is heated in toluene solution with water and p-toluene sulphonic acid to yield 2,6-dimethyl - octatriene - 2,4,6 - al - 1 - oic acid - 8 ethyl ester; (4) 2-methylbutene-2-al-1-oic acid-4 ethyl ester is reacted with vinyl ethyl ether and boron trifluoride etherate and the neutralized reaction product is heated in toluene with water and p-toluene sulphonic acid to yield 4-methylhexadiene - 2,4 - al - 1 - oic acid - 6 ethyl ester.