Patent GB-814205-A (GB)
Title: Production of alkoxy-esters and of polyolefinic acids and their salts
IPC: C07C51/377
Filed: 1956-06-11
Abstract: Alkoxy esters are prepared by the action of a ketene on an alkoxyacetal preferably in the presence of an acid catalyst and at a temperature between - 100 DEG  and + 150 DEG  C., optimum results being obtained between 0 DEG  and + 25 DEG  C.  The ketenes employed have the general formula <FORM:0814205/IV (b)/1> where R and R1 are alkyl, e.g. methyl, ethyl, or propyl, or aryl, e.g. phenyl, tolyl or xylyl, or hydrogen, and R and R1 may be the same or different. Preferably ketene itself is used. The alkoxy acetals preferably have alkoxy groups containing 1-4 carbon atoms although higher alkoxy groups, e.g. lauroxyl, may be present.  Suitable examples are 1,13-trimethoxyhexane, 1,1,3,5 - tetramethoxyhexane, 1,1,3,5,7 - pentamethoxyoctane, 1,3-dimethoxy-1-ethoxybutane or 1,3,5-triethoxy-1-methoxyhexane. Thus when ketene is reacted with 1,1,3-trimethoxybutane, the reaction mixture contains methyl 3,5 - dimethoxyhexanoate and methyl 5 - methoxy-2-hexenoate, both of which are novel compounds.  The catalyst used may be a Friedel-Crafts catalyst, e.g. boron trifluoride or one of its complexes such as an etherate, ferric chloride or aluminium chloride, but other acid catalysts including sulphuric acid, phosphoric acid and p-toluene sulphonic acid may be used.  The amount of catalyst used depends on the particular catalyst and the temperature.  Thus at 0 DEG  to 25 DEG  C. about 0.5 to 2 parts of BF3 per 100 parts by weight of alkoxyacetal are effective.  A solvent may also be present, e.g. an excess of the alkoxyacetal, or diethyl ether, carbon tetrachloride or hexane.  The ketene may be bubbled or diffused into a body of the reaction medium, the reaction being effected in a continuous manner, with counter-current or co-current mixing. In a preferred method, a stream of ketene vapour, which may contain an inert diluent such as nitrogen, is fed continuously into a cooled stream of the alkoxyacetal and catalyst, and the resulting gas-liquid mixture is passed continuously through an appropriate reactor which may comprise a packed column. Unreacted ketene vapour is separated from the mixture leaving the reactor and is passed in a counter-current manner through the stream of alkoxyacetal and catalyst entering the reactor. The liquid mixture leaving the reactor is neutralized and the product separated, as by distillation.  The product comprises an ester of an alkoxy acid and may also contain an ester of an unsaturated alkoxy acid.  The alkoxyester may then be dealcoholated, preferably with accompanying hydrolysis of the ester linkage to give a corresponding polyolefinic acid or salt thereof.  The dealcoholation and hydrolysis is preferably effected in alkaline medium, e.g. by heating with an excess of caustic soda solution (up to a 5-molar excess) either in an autoclave at temperatures below 150 DEG  C. or under reflux at atmospheric pressure and a temperature below 110 DEG  C.  The product may be separated as a solid salt by cooling and adding methanol or the acid may be isolated by acidifying the dealcoholation mixture. Thus when the reaction products of ketene and 1,1,3-trimethoxybutane are heated with aqueous caustic soda there is obtained an aqueous solution of sodium sorbate, from which sorbic acid is precipitated by acidification.  In a similar manner, 2,4-octadienoic acid and 2,4,6-octatrienoic acid are obtained from 1,1,3-trimethoxy hexane and 1,1,3,5-tetramethoxyhexane respectively.  In examples: (1) ketene diluted with nitrogen is mixed with 1,1,3-trimethoxybutane containing BF3 etherate and the mixture is maintained at 9-10 DEG  C. while passing through a spiral condenser and packed column, the unreacted gaseous part of the mixture is drawn off continuously and recycled in counter-current with the fresh alkoxyacetal, and the remaining liquid is neutralized with sodium methoxide in methanol, flash distilled, and fractionated to yield methyl 5-methoxy-2-hexenoate, and methyl 3,5-dimethoxyhexanoate; (2) a mixture of methyl 3,5-dimethoxyhexanoate obtained in (1) sodium hydroxide and water is heated in an autoclave for 4.1 hours at 147-149 DEG  and after distilling off methanol the residue is acidified with sulphuric acid and cooled to precipitate sorbic acid; (3) methyl 5-methoxy-2-hexenoate is treated by the procedure of (2) to yield sorbic acid; (4) Example (1) is repeated except that the total residue after flash distillation is heated with sodium hydroxide and worked up to yield sorbic acid; (5) Example (2) is repeated using more sodium hydroxide at 90-96 DEG  C. for 16.1 hours; (6) methyl 3,5-dimethoxyhexanoate obtained in (1) is heated under reflux with sodium hydroxide and worked up to yield sorbic acid.