GB1560186A - Manufacture of 2-chloroacetoacetic acid esters - Google Patents

Description

(54) MANUFACTURE OF 2-CHLOROACETOACETIC ACID ESTERS (71) We, CONSORTIUM FCJR ELEKTROCHEMISCHE INDUSTRIE GMBH., a body corporate organised according to the laws of the Federal Republic of Germany, of Zielstattstrasse 20, 8000 Miinchen 70, Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a process for the manufacture of 2-chloroacetoacetic acid esters, (that is esters of 2-chloro-3-oxo-butanoic acid).

2-Chloroacetoacetic acid esters may be manufactured by the chlorination of acetoacetates (cf. Liebig's Annalen, Vol. 245, page 59). This may be achieved by means of a discontinuous process in which a stream of gaseous chlorine is passed through the acetoacetate for a period of a few hours until the acetoacetate has been reacted to the desired degree. This method has the disadvantage, however, that the chlorination has to be terminated at a relatively low degree of reaction since, at higher degrees of reaction, the selectivity with regard to the desired 2-chloroacetoacetic acid ester decreases considerably. The unreacted acetoacetate then has to be recovered by distillation.

Alternatively, chlorination may be effected using sulphuryl chloride instead of chlorine (cf.

Organic Syntheses, Vol. 33, page 45), in which case much higher degrees of reaction can be achieved with a good yield of the 2-chloroacetoacetic acid ester. A disadvantage of this method, however, is that sulphuryl chloride is more expensive than chlorine and that the sulphur dioxide formed during the reaction has to be reconverted into sulphuryl chloride in a separate process.

The present invention provides a process for the manufacture of a 2-chloroacetoacetic acid ester, which comprises introducing chlorine and an acetoacetic acid ester (hereinafter referred to as "an acetoacetate") separately into a reaction chamber in a continuous manner at a temperature within the range of from -20 to + 300C and in a respective molar ratio within the range of from 0.5 : 1 to 1.3 : 1 and causing them to pass through the reaction chamber in co-current flow while reacting.

It was surprising to discover that, by means of the continuous process according to the invention, the selectivity of the reaction with regard to the desired 2-chloroacetoacetic acid ester could be considerably improved at higher degrees of reaction, and consequently that improved yields could be obtained. It would have been expected that a poorer result might be obtained because the total heat of reaction is produced over a very short period in a continuous process in which the total amount of both reactants is brought together rapidly.

In the present process, the chlorine and the acetoacetate are used in a respective molar ratio within the range of from 0.5 1 to 1.3 1, preferably from 0.8 1 to 1.2: 1. It has been found that the use of molar ratios of this order ensures, on the one hand, that a relatively high degree of reaction of the acetoacetate is achieved and consequently that only a small amount of the acetoacetate has to be recycled and, on the other hand, that the formation of by-products, more of which would be formed using higher chlorine: acetoacetate molar ratios, is kept acceptably low.

In the present process, the two reactants are introduced separately into a reaction chamber in a continuous manner at a temperature within the range of from -20 to + 30"C, preferably from + 10 to + 20"C. Although the use of temperatures below + 100C can result in improved selectivity and yield with regard to the desired 2-chloroacetoacetic acid ester, it has the disadvantage that it is necessary to use brine, instead of water, as a coolant around the pipes used to supply the reactants to the reaction chamber.

The chlorine is preferably used in liquid form and the reaction is preferably carried out at a pressure within the range of from 1 to 10 atmospheres, preferably from 3 to 5 atmospheres, above the vapour pressure of liquid chlorine at the temperature at which the reactants enter the reaction chamber. It has been found that the use of liquid chlorine means that the chlorine dissolves more rapidly in the acetoacetate and that, consequently, the heat of reaction is decreased, because the heat of condensation of the chlorine has been removed prior to mixing of the reactants, with the result that an improved selectivity and yield with regard to 2-chloroacetoacetic acid ester is achieved.

The two reactants flow through the reaction chamber in co-current flow and the rate of flow is advantageously so adjusted that the dwell time of the reactants within the reaction chamber is within the range of from 0.5 to 5 minutes.

It was particularly surprising to find that a high selectivity and yield could be achieved using co-current flow at relatively low flow rates, since it would normally be expected that, in order to achieve thorough mixing and to avoid localised over-heating (localised over-heating may be expected to cause a reduction in the selectivity), the rate of flow would need to be sufficiently high that the turbulent flow range is reached. On the other hand, it was however found that, a much improved selectivity and yield is achieved with the continuous process according to the invention as compared with a discontinuous process carried out to the same degree of reaction of the acetoacetate, as may be seen from the figures in the Table discussed below.

The process according to the invention may be carried out in any reactor in which two reactants may be introduced separately and simultaneously and may flow through the reaction chamber in co-current flow. Advantageously, however, the reactor should be such that the heat of reaction may be removed rapidly from the reaction chamber, since this causes an improvement in the selectivity and yield with regard to the desired 2-chloroacetoacetic acid ester, and, to this end, the walls of the reaction chamber are advantageously of silver or of a silver-plated material. Cooling of the reaction chamber may be effected by conventional means, for example by surrounding it by a cooling jacket through which a coolant flows. The coolant may suitably be water at a temperature within a range of from 11 to 25"C.

The reaction chamber may merely consist of a simple tube surrounded by a cooling jacket into which tube the two reactants may be separately introduced and may be mixed and reacted, or may consist of an assembly of tubes or a coiled tube. Alternatively, a thin-layer reactor, for example a falling-film reactor, may be used.

The acetoacetate used in the present process may be an ester of acetoacetic acid with an aliphatic alcohol, preferably an alkanol, advantageously having not more than 10 carbon atoms, preferably not more than 4 carbon atoms. Suitable acetoacetates are, for example, methyl acetoacetate, ethyl acetoacetate, n-butyl acetoacetate and isobutyl acetoacetate.

2-Chloroacetoacetic acid esters manufactured by the process of the invention may be used as plant protective agents, or may be used in the manufacture of coumarilic acid derivatives, which are used as intermediates in the manufacture of other plant protective agents.

As will be apparent from the above discussion, the process of the invention has the advantages over the prior-art processes discussed above, first, that chlorine, and not sulphuryl chloride, is used as the chlorinating agent, and, secondly, that an improved selectivity and yield with regard to the desired 2-chloroacetoacetic acid ester is achieved at high degrees of reaction of the acetoacetate.

An apparatus suitable for use in carrying out the process of the invention and a method of carrying out the process of the invention will now be described, by way of example only, with reference to the accompanying drawing which is a diagrammatic representation of such an apparatus.

The apparatus includes a falling-film reaction 1 which consists of an outer tube 2 provided with a cooling jacket 3 having an inlet 4 and an outlet 5 and containing a concentrically located ribbed inner tube 6 provided with an inlet 7 and an outlet 8 for coolant and on top of which is located a dish 9.

In carrying out the process according to the invention, an acetoacetic acid ester is continuously fed through pipe 10 into the dish 9 such that it overflows from the dish 9 and continuously and uniformly flows down the outside of the ribbed tube 6. Simultaneously, chlorine is continuously fed through pipe 11, to which a manometer 12 is attached, into the outer tube 2, where it reacts with the acetoacetate flowing down the outside of the ribbed tube 6 while the two reactants flow through the reaction chamber in co-current flow. Both reactants are introduced into the reaction 1 at a temperature within the range of from -20 to + 30"C and in such amounts that the molar ratio of the chlorine to the acetoacetate is within the range of from 0.5:1 to 1.3:1. The reaction products, namely hydrogen chloride and the 2-chloroacetoacetic acid ester, together with unreacted reactants, leave the reaction 2 through pipe 13 from which they pass into a separator 14. The gaseous products leave the separator 14 through pipe 15 and the liquid products leave the separator 14 through pipe 16 and pass into a collecting vessel 17, from which any remaining hydrogen chloride may be removed through pipe 18 connected, together with pipe 15, to exhaust gas line 19.The liquid reaction product may be removed from the collecting vessel 17 through pipe 20 and may be worked up in a conventional manner.

The following examples illustrate the process of the invention and compare the results achieved with those achieved in a discontinuous process carried out according to the prior art.

All percentages and ratios are molar.

The yields and selectivity achieved in each example were determined by means of gas chromatography using a previously determined equilibration curve with nitrobenzene as the internal standard.

Example 1 This example illustrates a discontinuous process carried out according to the prior art for the purposes of comparison.

A stream of chlorine was fed at a rate of 15 1/h (0.67 moles/h) and at a temperature of 20"C, for a period of 4 hours, into a 1 litre round-bottomed flask containing 600 g (5.16 moles) of methyl acetoacetate and provided with a thermostat by means of which the internal temperature was maintained at 200C. The molar ratio of chlorine to methyl acetoacetate was 0.52 1. The product was then analysed and the results obtained showed that the yield of methyl 2-chloroacetoacetate was 37 mole %, based on the methyl acetoacetate used, and that the selectivity with respect to the methyl 2-chloroacetoacetate was 83.15 mole %.

The process was repeated using 27.7 l/h of chlorine (1.23 moles/h), instead of 15 1/h. In this case, the molar ratio of chlorine to methyl acetoacetate was 0.958: 1, the yield of methyl 2-chloroacetoacetate was 50.18 mole % and the selectivity with respect to this compound was 68.74 mole %.

Example 2 This example was carried out according to the process of the invention using, as the reaction chamber, a coiled silver tube having an inner diameter of 6 mm and a length of 1.4 m coiled in 5 windings. This coiled tube was contained within a glass tube through which water at 11"C continuously flowed as a coolant.

Methyl acetoacetate was continuously fed into the tube at a rate of 300 ml/h (2.78 moles/h) and chlorine was continuously fed into the tube, through a polyethylene tube the end of which narrowed to a diameter of 3 mm and which extended into the silver tube for a distance of 150 mm, in co-current flowwith the methyl acetoacetate, atarateof 32 1/h (1.42 moles/h). Both reactants entered the tube at a temperature of 20"C. The molar ratio of chlorine to methyl acetoacetate was 0.51 : 1. The product obtained was analysed and the results showed the yield of methyl 2-chloroacetoacetate to be 40.28 mole % and the selectivity with respect to this compound to be 87.91 mole %.

The process was repeated with the chlorine being fed in at a rate of 60 1/h (2.67 moles/h), instead of 32 l/h. In this case the molar ratio of chlorine to methyl acetoacetate was 0.967:1, the yield of methyl 2-chloroacetoacetate was 69.1 mole % and the selectivity was 83.19 mole %.

Example 3 This example also illustrates the process of the invention and was carried out using an apparatus identical to that used in Example 2 except that the coiled tube was of glass instead of silver.

The procedure was also identical to that used in Example 2 with the chlorine being fed in at a rate of 60 l/h and the methyl acetoacetate being fed in at a rate of 300 ml/h. The molar ratio of chlorine to methyl acetoacetate was 0.967:1, the yield obtained was 64.36 mole % of the selectivity was 79.9 mole %.

A comparison of the results obtained in this example with those obtained in Example 2 shows that better yields and selectivities are obtained when using a silver reactor because the heat of reaction can be removed more quickly.

Example 4 This example was carried out according to the process of the invention using the apparatus shown in the accompanying drawing and using the procedure described above with reference to the drawing.

5.5 kg/h (42.26 moles/h of ethyl acetoacetate were fed through pipe 10 into the reactor 1 and 900 l/h (40.18 moles/h) of chlorine were fed through pipe 11 into the reactor 1, while passing cooling water having a temperature of 11"C through the jacket 3 and through the ribbed tube 6. Both reactants entered the reactor 1 at a temperature of 20"C. The molar ratio of chlorine to ethyl acetoacetate was 0.95:1, the product collecting in the collecting vessel 17 still contained approximately 7% of hydrogen chloride (which was removed through pipe 18), the yield of ethyl 2-chloroacetoacetate was 86.59 mole % (based on the ethyl acetoace tate used), and the selectivity with respect to this compound was 83.5 mole %.

Examples 5.1 to 5.4 In each of Examples 5.1 to 5.4, the procedures of Examples 1 to 4 respectively were repeated while varying the amount of chlorine used such that the molar ratio of chlorine to the acetoacetate was as listed in the Table below in order to achieve degrees of reaction of the acetoacetate as given in the first column of the Table. The selectivities and yields achieved are also shown in the Table. It can be seen from these results that, especially at high degrees of reaction of the acetoacetate, considerably better selectivities and yields are achieved by means of the continuous process according to the invention (Examples 5.2 to 5.4) as compared with the discontinuous prior-art process (Example 5.1).

TABLE Example 5.1 - Example 5.2 - Example 5.3 - Example 5.4 Discontinuous Continuous Continuous continouus Degree of proces - process using process using process using reaction of coiled glass silver tube - falling-film acetoacetate tube - reactor (%) Methyl acetoacetate Methyl acetoactate Methyl acetoacetate Ethyl acetoactate Selec- Cl2:Ac Yield Selec- Cl2:Ac Yield Selec- Cl2:Ac Yield Selec- Cl2: :Ac Yield tivity Ratio (%) tivityl Ratio (%) tivity Ratio (%) tivity Ratio (%) (%) (%) (%) (%) 40.00 85.00 0.46 34.00 87.00 0.45 34.80 88.50 0.44 35.40 - - 50.00 81.00 0.59 40.50 85.00 0.57 42.50 87.50 0.56 43.75 - - 60.00 76.00 0.74 45.60 83.50 0.69 51.10 87.00 0.67 52.20 - - 70.00 71.00 0.90 49.70 82.00 0.82 57.40 85.00 0.80 59.50 86.40 0.79 60.48 80.00 64.00 1.08 51.20 80.00 0.96 64.00 83.50 0.93 66.80 84.20 0.92 67.36 90.00 55.00 1.30 49.50 78.50 1.09 70.65 82.50 1.05 74.25 81.20 1.06 73.08 95.00 47.50 1.44 45.12 77.50 1.16 73.62 82.00 1.12 77.90 80.20 1.13 76.19

Claims (14)

WHAT WE CLAIM IS:

1. A process for the manufacture of a 2-chloroacetoacetic acid ester, which comprises introducing chlorine and an acetoacetic acid ester separately into a reaction chamber in a continuous manner at a temperature within the range of from -20 to +30"C and in a respective molar ratio within the range of from 0.5 : 1 to 1.3: 1 and causing them to pass through the reaction chamber in co-current flow while reacting.

2. A process as claimed in claim 1, wherein the said temperature is within the range of from +10 to +200C.

3. A process as claimed in claim 1 or claim 2, wherein the said molar ratio is within the range of from 0.8:1 to 1.2:1.

4. A process as claimed in any one of claims 1 to 3, wherein the chlorine is used in liquid form.

5. A process as claimed in claim 4, wherein the pressure within the reaction chamber is within the range of from 1 to 10 atmospheres above the vapour pressure of liquid chlorine at the temperature at which the reactants enter the reaction chamber.

6. A process as claimed in claim 5, wherein the pressure within the reaction chamber is within the range of from 3 to 5 atmospheres above the vapour pressure of liquid chlorine at the temperature at which the reactants enter the reaction chamber.

7. A process as claimed in any one of claims 1 to 6, wherein the reaction chamber has walls of silver or of a silver-plated material.

8. A process as claimed in any one of claims 1 to 7, wherein the acetoacetic acid ester is an ester of an aliphatic alcohol.

9. A process as claimed in claim 8, wherein the alcohol is an alkanol.

10. A process as claimed in claim 8 or claim 9, wherein the alcohol has not more than 10 carbon atoms.

11. A process as claimed in claim 10, wherein the alcohol has not more than 4 carbon atoms.

12. A process as claimed in any one of claims 1 to 6, wherein the acetoacetic acid ester is methyl acetoacetate, ethyl acetoacetate, n-butyl acetoacetate or isobutyl acetoacetate.

13. A process as claimed in claim 1, carried out substantially as described in any one of Examples 2, 3, 4, 5.2, 5.3 and 5.4 herein.

14. A 2-chloroacetoacetic acid ester that has been manufactured by a process as claimed in any one of claims 1 to 13.