[1]3 @ 6 5 1 2 1 3 0 Utlited States Patent Office Patented Mar. 21, 1972 PROCE 3,651,130 SS FOR THE PRODUCTION OF ACETOACETIC ACID ESTERS Othmar Marti and Willi Zimmerli, Visp, Valais, Swit. zerland, assignors to Lonza, Ltd., Basel, Switzerland 5 No Drawing. Ffled July 25, 1968, Ser. No. 747,467 Int. Cl. C07c 69172 U.S. C]. 260-483 6 Claims 10 ABSTRACT OF THE DISCLOSURE An improved yield of an acetoacetic acid ester is obtained from a reaction between diketene and an alcohol in the presence of an acid catalyst, by converting the palkoxycrotonic acid ester, which is formed as secondary 15 product in the reaction, into the corresponding acetoacetic acid ester by heating it with water. This invention relates to a process for the production 20 of acetoacetic acid esters. It is known that acetoacetic acid esters can be prepared by reacting diketene with alcohols, lower aliphatic alcohols in particular, in the presence of acid catalysts. It is also known that diketene, an alcohol and a cata- 25 lyst may be introduced into the product of reaction of these same materials, heated to the reaction temperature, which comprises acetoacetic acid ester and palkoxycrotonic acid ester and which acts both as reaction medium and as diluent. The esterification reaction takes place at 30 temperatures between 90' C. and the boiling point of the acetoacetic acid ester formed in the presence of acid esterification catalysts, for example sulphuric acid, phosphoric acid and/or sulphonic acids, which are advantageously used in a ratio of 1 mol per 300-600 mols of dike- 35 tene. The secondary products formed, boiling at temperatures below the reaction temperature, and unused alcohol are separated off from the reaction product formed by distiflation during the reaction. 40 One major disadvantage of this process is thate-alkoxycrotonic acid ester is formed in appreciable quantities as secondary product. The present invention relates to a process for the production of acetoacetic acid esters in high yields in which a large proportion at least of the 6-alkoxycrotonic acid 45 ester formed during the reaction is converted into the corresponding acetoacetic acid ester. The present invention, therefore, provides a process for the production of acetoacetic acid esters which com- 50 prises reacting diketene with an alcohol in the presence of an acid catalyst and a reaction medium, and a,6- alko:@ycrotonic acid ester which is formed as secondary product in the reaction product is converted with water into the correspondin- acetoacetic acid ester. 55 The invention also relates to a process for the production of acetoacetic acid esters in high yields in which the unconverted residue of the 0-alkoxycrotonic acid ester is recycled into the reaction medium. According to the invention, an acetoacetic acid ester is 60 prepared by reacting diketene with an alcohol in the presence of an acid catalyst and a reaction medium by a process in which at least sorae of the palkoxycrotonic acid ester formed as secondary product in the reaction product is converted with water in the corresponding 65 acetoacetic acid ester, and all the acetoacetic acid eslter is recovered by distillation. The molar ratio of water required to convert the alkoxycrotonic acid ester is at most 3:1, preferably 1:1, related to the 6-alkoxycrotonic acid ester in the rourse of 70 formation or already formed. The starting materials are introduced, either separately 2 or in admixture, into a reaction medium which is preferably the reaction products of diketene and an alcohol. if the starting materials are mixed before introduction into the reaction medium, the mixing is with advantage carried out at temperatures low enough for no reaction to take place, for example at a temperature from 10 to 40' C. Aliphatic alcohols, for example methanol, ethanol and isopropyl alcohol, are the alcohols reacted with the diketene. Diketene and alcohol are preferably reacted in such a ratio that, on the one hand, the acetoacetic acid ester is formed whilst, on the other hand, the p-alkoxycrotonic acid and acetic acid formed as secondary products are esterified. The most -suitable excess of alcohol to diketene is less than 15 mol percent. Suitable catalysts include, for example, sulphuric acid, phosphoric acid, and sulphonic acids such as p-toluene sulphonic acid' They are used with advantage in quantities of 1 mol to 300-600 mols of diketene. Esteri,fication takes place at a temperature between 90' C. and the boiling point of the reaction mixture. Depending on circumstances, it may be carried out at reduced pressure, at atmospheric pressure or at elevated pressure. The heat required to maintain, and optionally to reach the reaction temperature and to separate the readily volatile secondary products from the reaction product, is supplied by the exothermic reaction between diketene and alcohol. The optimal reaction conditions are maintained by accurately dispensing suitable amounts of the as yet unreacted starting mixture into the warm reaction product. The process according to the invention is preferably carried out by introducing I liter/hour of the alcohol/ diketene starting mixture and optionahy 0.002 to 0.005 liter of water into 0.3 to 0.7 liter of reaction medium. The process may be carried out either continuously or in batches. The invention may be put into practice as described below for the purposes of a befter understanding. A starting mixture is formed continuously at room temperature by mixffig diketene, an alcohol and an acid catalyst and is introduced continuously into a still which is provided with a rectification column, is kept at the reaction temperature and contains the reaction product as reaction medium. On the one hand, acetoacetic acid ester and p-alkoxycrotonic acid ester are formed whilst, on the other hand, the readily volatile secondary products accumulating during the reaction, for example acetic acid ester, acetone and the water formed during the formation of palkoxycrotonic acid ester are distilled off from the head of the column with unreacted alcohol at a temperature from 50 to 80' C. According to one embodiment of the invention, water may be added during esterification. In this instance, the alkoxy crotonic acid ester formed by the elimination of water from acetoacetic acid ester is hydrolysed and the equilibrium is displaced in favour of the acetoacetic acid ester. The product left behind in the still, comprising acetoacetic acid ester, almost involatfle materials and the catalyst is continuously run off and then, if desired, subjected to a subsequent reaction, for example by heating at 90 to 140' C. for I to 20 minutes, so that any unreacted diketene is able to react completely. In a preferred embodiment of the process according to the invention, diketene, an alcohol and a catalyst are mtroduced into the reaction product of a reaction between the same materials as reaction medium, which is kept at a temperature between 90' C. and the boiling point and which comprises acetoacetic acid ester and 6alkoxycrotonic acid, and at the same time the secondary products formed boiling below the reaction temper-
[2]3 ature and the unreacted alcohol are separated by distillation. After the catalyst and resinification residues have been distilled off, the reaction product is subjected to rectification in the presence of water, the p-alkoxycrotonic acid ester being hydrolysed into acetoacetic acid ester and all the acetoacetic acid ester being recovered. The -first and last runnings from rectification, which may still contain 6-alkoxycrotonic acid ester, may with advantage be recycled into the starting mixture. It is possible in this way not only to operate at such temperatures that high reaction velocities are obtained, making the use of fairly smah apparatus possible, but also to keep the residence time in the reaction zone at elevated temperature so short that there are no appreciable losses in yield through polymerisation or decomposition reactions involving the heat-sensitive starting materials or end products, nor is the acetoacetic acid ester hydrolysed into acetoacetic acid or dissociated. The process is particularly suitable for fully continuous operation, although it. may readfly be carried out in batches. EXAMPLE I A mixture of 1690 g. of diketene (97 to 99.5% pure), 675 g. of methanol and 3.4 g. of concentrated sulphuric acid is continuously introduced hourly into 1000 cc- Of reaction product preheated to 125' C. (crude acetoacetic acid methyl ester, 92 to 95%) in a reaction still equipped with a fractionating column, corresponding to a feed rate of about 40 cc./min. The temperature is kept constant at 125' C., without external heating, by means of the heat generated by the reaction. At the same time, 68 g. per hour of a readily boiling mixture comprising about 40% of acetone, 40% of methyl acetate, 20% of methanol and a little water, are run off from the head of the fractionating column at 50 to 60' C. The heat required to heat the starting mixture to the reaction temperature and to distih the readily volatile secondary products is supplied externally at the outset. Extemal heating is stopped when the reaction between the alcohol and diketene has supplied sufficient heat for heating the starting mixture and for distillation. The reaction mixture running off passes through a post-reaction system where the components react completely at a temperature of about 100' C. and for an average residence time of some 10 minutes. 2305 g./hour of crude ester containing 95% of acetoacetic acid methyl ester are obtained. A 99.9% pure ester free of acid can be obtained from this crude ester in a single fract ionation following the addition of 12 g. of water in vacuo. EXAMPLE 2 As described in Example 1, 1690 g. of diketene are reacted with 675 g. of methanol in 1000 cc. of reaction product to form acetoacetic acid methyl ester. 2305 g.1 hour of crude ester are obtained, 95% of which is acetoacetic acid ester and 4% is cemethoxycrotonic acid methyl ester. If the crude ester is then rectified, acetoacetic acid methyl ester is obtained in a purity of 99.5% in a total yield of 87%. If the crude ester is rectified, and 13 g. of water added to the sump product enriched to about 20% with Pmethoxycrotonic acid methyl ester, the acetoacetic acid methyl ester is obtained in a yield of 89% and a purity of 99.5%. EXAMPLE 3 Diketene, ethanol and sulphuric acid are mixed in a ratio by weight of 72:39:0.3 at a temperature of 20' C. and the resulting mixture, having been combined with 100 I./h. of first and last runnings from the pure-ester rectification column, fed at a rate of 325 kg./h. into a reaction vessel comprising a stih with a rectification column having 7,theoretical plates. 'fhe stifl contains 200 liters of reaction mixture which is kept at 130' C. by 3)651)130 4 heating. Approximately 18 kg./h. of first runnings, comprising 40% of acetone, 40% of ethyl acetate, 15% of ethanol and a little water, are run off from the head of the column. The crude ester formed is transferred from the sump of the reaction column to a separation column which has a head temperature of 100' C. and a still temperature of I 10' C. and in whose sump the catalyst and any resins formed are retained whilst the ester is run off from the head. The head fraction, of which 92% is ace10 toacetic acid ethyl ester and 6% is 6-ethoxyci-otonic acid ethyl ester, is fed to a continuous rectification column for purification, 2.9 I./h. of water being simultaneously introduced at a lower end of the rectification column with 5 theoretical plates. The last runnings separated off at 15 about 80 I./h. comprise 88% of acetoacetic acid ethyl ester and the first runnings comprise 90% of acetoacetic acid ethyl ester. 290 kg./h. of highly pure acetoacetic acid ethyl ester (99.5% ) are obtained at the third plate from the head of the column, corresponding to a yield 20 of 89%, based on diketene. We
