Patent GB-605471-A (GB)
Title: Improvements in and relating to the condensation of ketene with keto esters or diketones
IPC: C07C69/145
Filed: 1945-10-02
Abstract: Unsaturated carboxylic esters are prepared by condensing ketene, in the presence of an acid catalyst, with a ketocarboxylic ester or diketone in which there are at least two hydrogen atoms and preferably at least three hydrogen atoms on a carbon atom or atoms adjacent to the keto-carbonyl group of the ketoester or to one of the keto groups of the diketone.  An inert reaction medium, e.g. an aliphatic or aromatic hydrocarbon may be employed. Typical keto esters which may be employed are the a -, b -, g  and d -keto carboxylic esters, e.g. ethyl pyruvate, ethyl-propionyl formate, ethyl n-butyryl formate and ethyl-isovaleryl formate; methyl-, ethyl- and benzyl - acetoacetates, methyl (or ethyl) a -acetyl-propionate, methyl (or ethyl) propionacetate, methyl n-butyroacetate, phenyl acetoacetate, ethyl decanoylacetate; methyl (or ethyl) levulinate; ethyl g  - (n-butyryl) - n - butyrate.  The 1 : 2-, 1 : 3-, 1 : 4- and the 1 : 5-diketones may be employed, e.g. biacetyl, acetyl propionyl, acetyl isobutyryl, bipropionyl, bi-n-butyryl and acetyl caproyl; acetyl acetone, 2,4-hexanedione, 2,4-heptanedione, 5-methyl-2,4-hexanedione, acetyl acetophenone, propionyl (and n- or iso-butyryl)-acetophenone, acetyl-methylbenzyl ketone and 3-methyl-2,4-pentanedione; 2,5-hexanedione; 6-methyl-2,5-heptanedione; 3,6-octanedione; 4-benzoyl-2-butanone; 2,6-heptanedione; and cyclic diketones, e.g. 1,3-cyclohexanedione. Especially suitable are ketocarboxylic esters of the general formula R.CH2.CO.(CH2)n-1.CO.OR1 and diketones of the formula R.CH2.CO.CH2)n-1.CO.R1, wherein R is hydrogen or an alkyl, aralkyl or aryl group, R1 is an alkyl, aryl or aralkyl group and n is 1, 2 or 4 or more.  When n is 3, cyclization of the esters formed is liable to take place.  With ketocarboxylic esters of the above formula in which n is 2 or more, the following different esters are formed with one molecular proportion of ketene: (1) R.CH : C(OOCCH3).(CH2)n-1.CO.OR1; (2) R.CH2.C(OOCCH3) : CH.(CH2)n-2.CO.OR1.  With diketones of the formula R.CH2.CO.(CH2)n-1CO.CH2.R1 in which R and R1 represent a hydrogen atom or an alkyl, aryl or aralkyl group and n is a positive integer, diunsaturated di-esters of the following formula may be formed with two molecular proportions of ketene: R.CH : C(OOCCH3).(CH2)n-1.C(OOCCH3) : CH.R1.  Any ketene of the type (Z)(Z1)C : C : O, wherein Z and Z1 represent a hydrogen atom an alkyl, aryl or aralkyl group may be used in the process.  The acid catalyst employed is preferably one which contains the -SO2OH group and is preferably of the type X.SO2.OH, where X is a hydroxyl group an organic group containing a non-metal in addition to carbon and hydrogen, X being linked to the S atom through the non-metallic atom, or an inorganic group of non-metallic atoms other than carbon. Sulphuric acid, chlorosulphonic and sulphamic acid are especially suitable.  The reaction temperature is preferably from about 60 DEG C. to about 90 DEG  C.  In examples, ketene is added to: (1) ethyl acetoacetate, the temperature raised to 70 DEG  C. and the mixture distilled under reduced pressure and the fraction obtained is rectified.  The product is a mixture of the unsaturated acetates CH2:C(OOCCH3).CH2.CO.OC2H5 and CH3.C(OOCCH3) : CH.CO.OC2H5; (2) ethyl levulinate, the product being a mixture of CH2:C(OOCCH3).CH2.CH2.CO.OC2H5 and CH3.C(OOCCH3) : CH.CH2.CO.OC2H5; (3) acetyl acetone, the product being a mixture of CH2 : C(OOCCH3).CH2.CO.CH3 and CH3.C(OOCCH3) : CH.CO.CH3; (4) biacetyl, the product being CH2:C(OOCCH3).CO.CH3; concentrated sulphuric acid is used as catalyst in each case.  The keto-carboxylic esters employed as starting materials may be prepared by heating the sodium salt of the corresponding acid with the appropriate organic iodide.