GB2188625A - A process for the production of amides - Google Patents

Abstract

A process for the production of an amide, which process comprises reacting an alpha -olefin at a concentration in the range of from 0.01 to 0.05 mol 1<-1> with formamide under ultra-violet radiation in the presence of from 0.02 to 5% w/v of acetone as a photoinitiator.

Description

SPECIFICATION A process for the production of amides The present invention relates to a process for the production of amides and, in particular, to a process for the production of amides by the direct reaction of -olefins with formamide under ultra-violet radiation and in the presence of acetone as a photoinitiator.

This method is advantageous in that it provides a simple process for making amides with an odd number of carbon atoms from a-olefin feed stocks which, predominantly, have an even number of carbon atoms.

A process for the production of carboxylic acid amides from olefinic, araliphatic or aromatic compounds is disclosed in GB 1064728, and the formation of undecanoicamide from 1-decene and formamide is described.

The process disclosed in GB 1064728 is, however, inefficient in that much electricity is consumed to produce little amide, and the low efficiency of this method has prevented its commercial exploitation.

We have now developed an efficient process for the production of amides by careful selection and control of the reaction conditions, in particular having regard to the reagent concentration and ultra-violet radiation intensity.

Accordingly, the present invention provides a process for the production of an amide, which process comprises reacting an cx-olefin at a concentration in the range of from 0.01 to 0.05 mol 1-1 with formamide under ultra-violet radiation in the presence of from 0.02 to 5% w/v of acetone as a photoinitiator.

The photo-amidation is preferably carried out in a mixture of formamide and tertiary butanol, which homogenizes the mixture, in a ratio of 1:1 by volume, that is a formamide concentration of 60% w/v. The olefin concentration is in the range of from 0.01 to 0.05 mol 1-1 (for dodecene from 0.2 to 0.8% w/v), preferably from 0.02 to 0.04 mol 1-1. The acetone concentration is in the range of from 0.02 to 5% w/v, preferably from 0.1 to 1% w/v.

The low acetone and olefin concentrations used in the following Examples, up to 450 and 7.5 times respectively lower than those of the prior art lead to greater efficiency by reducing the quantity of side-products formed during the free radical chain reaction.

The ultra-violet radiation is preferably provided by a lamp with an efficiency greater than 1% and preferably greater than 10% for the conversion of electrical energy to ultra-violet radiation. The ultra-violet radiation preferably has wavelengths of from 250 nm to 350 nm and more preferably 260 nm to 330 nm. The ultra-violet lamp will generally be arranged in such a way that a high proportion of the radiation is incident on the reaction mixture and that the radiation which is absorbed over the average path length of the reactiom mixture has an average intensity of from 0.05 to 10 milliwatts cm-2 over the irradiated area, more preferably an average intensity of from 1.5 to 4 milliwatts cm-2.

The use of a low intensity ultra-violet lamp results in increased reaction efficiency with a reduction in side-product formation and a further advantage is that no complex cooling mechanism is required and indeed in a preferred embodiment of the invention, the lamp is operated in direct contact with the reaction mixture, to maximise absorbtion.

The process of the present invention may be carried out in a batchwise or continuous manner. For continuous operation the reactor contents are preferably maintained at a temperature of about 50"C and the reaction mixture is circulated through another vessel which is maintained at room temperature or below in which the product amide precipitates. The product is then periodically removed by filtration and the filtrate recycled to the reaction vessel.

The invention is further illustrated by means of the following Examples. Examples 1 to 3 illustrate the fundamental research; Examples 4 to 11 illustrate the application of the finding of that fundamental research, Examples 4 to 9 showing the use of an ultra-violet lamp sited externally of the reaction mixture and Examples 10 and 11 showing the use of a lamp immersed in the reaction mixture.

Example 1 A 1 cm path length quartz spectrophotometer cell containing 3 cm3 of reaction mixture was placed in the sample compartment of a Perkin Elmer MPF 44A Fluorescence Spectrophotometer, which was used to provide radiation with peak output at a wavelength of 33 nm and bandpass 20 nm from a 150 watt xenon lamp via a diffraction grating monochromator. The reaction mixture consisted of a solution of 2.75% w/v acetone and 0.46% w/v dodec-1 -ene in a 1:1 by volume mixture of formamide and tertiary butanol. The quartz spectrophotometer cell formed part of an evacuated vessel sealed with a grease-free tap in which, prior to irradiation, the reaction mixture had been degassed by freeze-pump-thaw cycles on a vacuum line ( < 5x10-5mmHg), in order to remove dissolved oxygen.

Before and after exposure of the reaction mixture, the irradiation intensity was measured by the technique of ferrioxalate actinometry, employing the Kurien modification of the original Hatchard and Parker method [Kurien K.C.,J.Chem.Soc(B) 1971 2081; Hatchard C.C. and ParkerCA., Proc. Proc. Roy. Soc. (London)A235518 (1956)]. The two determinations were in good agreement with each other and it was calculated that 1 0.6x 1014 quanta s-2, (0.705 milliwatts) were incident on the reaction mixture.The area of the incident beam was 1.12 cm2, giving an average irradiation intensity of 9.46x 1014 quanta cm-2s- (0.629 milliwatts cm2). The actinometry method was also used to determine the proportion of incident radiation which was absorbed by the reaction mixture, and this was calculated to be 98%.

Irradiation of the reaction mixture was carried outfora period of 17 hours, afterwhich analysisofthe mixture by gas chromatography showed that 12.1 mg (7.2x 10-5 moles) of dodec-1 -ene had been consumed, and that 10.5 mg (4.9x10-5 moles) of tridecanamide had been produced, giving a chemical yield, based on dodec-1 -ene consumption, of 68% and a quantum yield for tridecanamide formation of 0.5 moles per einstein (1 einstein=6.023x1023 quanta).

Example 2 The procedure of Example 1 was followed with the exception that the radiation intensity was reduced by a factor of approximately 10, by placing a metal gauze filter in the beam. By the ferrioxalate actinometry method, it was calculated that 1.03x1014quantas- (0.0683 milliwatts) of the 300 nm centred band of radiation was incident on the reaction mixture, giving an average irradiation intensityoverthe 1.12cm2 beam area of 0.92x 1014 quanta cm-2s-' (0.0609 milliwatts cm-2).Irradiation of the vacuum degassed reaction mixture, of the same starting composition as given in Example 1, for a period of 17 hours, resulted in the consumption of 5.9 mg (3.5x 10-5 moles) of dodec-l-ene, and the formation of 4.1 mg (1.9x 10-5 moles) of tridecanamide, giving a chemical yield of 54% and a quantum yield for tridecanamide formation of 1.8 moles per einstein.

Example 3 The procedure of Example 2 was followed with the following exceptions: (i) the concentration of acetone in the reaction mixture was reduced by a factor of approximately 5 to 0.57% wiv; (ii) a 5 cm path length cylindrical quartz spectrophotometer cell was used to contain the reaction mixture (14 cm3), the cross-sectional area of the beam of radiation incident on one of the flat end-faces of the cell being 1.40 cm2.

By carrying out ferrioxalate actinometry it was calculated that 1.30:; 1014 quanta s-l (0.0861 milliwatts) of the 300 nm centred band of radiation were incident on the reaction mixture, corresponding to an average irradiation intensity of 0.93:; 1014 quanta cm-2s-l (0.0615 milliwatts cm-2).

Following vacuum degassing, the reaction mixture was irradiated for a period of 51.5 hours, during which 56.4 mg (3.36x10-4moles) of dodec-1-enewerefoundto have been consumed and 50.3 mg (2.36x 10-4 moles) of tridecanamide produced, giving a chemical yield of 70% and a quantum yield fortridecanamide formation of 5.9 moles per einstein.

A comparison of the results of Examples 1 to 3 shows how the alteration of a single variable, the light intensity or acetone concentration will alter the efficiency of the photoamidation process.

By comparing the results of Examples 1 and 2 we see that a reduction in light intensity by a factor of 10 results in an almost four-fold increase in the efficiency of the process, expressed as the yield of tridecanamide in moles per einstein.

A comparison of the results of Examples 2 and 3 shows that a fivefold reduction in acetone concentration results in a three-fold increased in the yield of tridecanamide in moles per einstein.

These fundamental Examples show that a decreased light intensity and acetone concentration will lead to a more efficient photoamidation process, and these principles are applied and further illustrated in Examples 4 to below.

Example 4 A photochemical reactor was constructed using a low pressure mercury lamp coated internally with a phosphor as the source of ultra-violet radiation. The lamp was obtained from the GTE Sylvania company and was designated type G6T5. The tubular bulb of the lamp was 19 cm in length and had an outside diameter of 1.5 cm. The nominal power rating of the lamp was 6 watts when operated using standard circuitry specified by the above company. The phosphor was designated type 2061 (strontium hexaborate:Pb). On operating the lamp, the phosphor emitted radiation over the wavelength range 275 nm to just beyond 350 nm, with the peak emission at 302 nm. The lamp also emitted spectral lines characteristic of mercury, for example at 254 nm, 313 nm and 365 nm.The total radiation output from the lamp between 275 nm and 350 nm was measured as being 0.0603 watts, and between 250 nm and 260 nm as being 0.111 watts. There was no detectable emission from the lamp in the wavelength regions 260 nm to 275 nm and 200 nm to 250 nm.

In the construction of the photochemical reactor, the lamp was housed in a polished aluminium reflector having parabolic cross-section, the central axis of the lamp being coincident with the focal line of the reflector, which lay 1.25 cm from the rear of the reflector. The distance between the two front edges of the reflector was 12 cm. The lamp and reflector were positioned directly above a cylindrical, double-walled glass vessel of internal diameter 22.5 cm and depth 60 cm, the top of which was covered with an optically polished circular quartz plate, of thickness 0.5cm, which was highly transparent to all ultra-violet radiation having wavelengths longer than 200 nm. The contents of the vessel could be maintained at a specified temperature by circulating thermostatically controlled water between the inner and outer walls of the vessel.

The vessel was charged with 20 litres of a mixture consisting of 0.026% w/v acetone and 0.413% w/v dodec-1 -ene in a 1:1 by volume mixture of formamide and tertiary butanol. Nitrogen was bubbled though the mixture at a rate of 1 litre minute-l via a sintered glass tipped tube sealed into the bottom of the vessel. After allowing 24 hours to deplete the mixture of dissolved oxygen, the mixture was heated to 50"C and the lamp was switched on. The UV/visible absorption spectrum of the reaction mixture indicated that, over the 60 cm depth of the reactor, the mixture would absorb the majority of radiation emitted by the lamp in the region 250 nm to 350 nm, and that it would not absorb ultra-violet and visible radiation having wavelengths longer than 350 nm to any significant degree.The rate of absorption of ultra-violet energy by the reaction mixture therefore lay within the range 0.357 to 0.714 milliwatts. Distributed over the area of the base of the parabolic reflector, this represents an average intensity of absorbable ultra-violet radiation incident on the reaction mixture of between 1.57 and 3.13 milliwatts cm-2.

Irradiation of the reaction mixture was continued for a period of 24 hours, after which analysis of the mixture by gas chromatography showed that 23.6 g (0.140 moles) of dodec-1-ene had been consumed and that 19.1 g (0.090 moles) of tridecanamide had been produced, giving a chemical yield of 64%. Based on the nominal lamp power rating of 6 watts, the electrical energy efficiency for the formation of tridecanamide corresponded to 133 g per kWh.

Examples 5 to 9 The procedure of Example 4 was followed using reaction mixtures differing in their starting compositions with respect to the acetone and dodec-1-ene concentrations. All of the mixtures exhibited negligible absorption of ultra-violet and visible radiation having wavelengths longer than 350 nm. The temperature at which the reaction mixture was maintained was also varied. The results obtained are given in Table 1, together with the results for Example 4.

TABLE 1 Dodec-1-ene Tridecanamide Starting composition consumption(2) formation(2) g/kWh(3) for % w/v(1) % w/v(1) Temp. Chemical tridecanamide Example acetone dodec-1-ene C g moles g moles yield formation 4 0.026 0.413 50 23.6 0.140 19.1 0.090 64% 133 5 0.193 0.395 50 30.6 0.182 27.0 0.127 70% 188 6 0.172 0.773 50 25.4 0.151 18.2 0.085 56% 126 7 0.246 0.232 50 18.6 0.111 15.0 0.070 63% 104 8 0.195 0.365 70 21.0 0.125 24.8 0.116 93% 172 9 0.229 0.389 30 20.6 0.123 16.4 0.077 63% 114 (1) in 1:1 by volume mixture of formamide and tertiary butanol (2) After 24h irradiation of the nitrogen-purged mixture (3) Based on the nominal lamp power rating of 6 watts Example 10 Another photochemical reactor was constructed using a lamp obtained from the Philips company.The lamp was designated type TL12 (UVB) and was again a low pressure mercury lamp coated internally with a phosphor. The tubular bulb of the lamp was 117.5 cm in length and had an outside diameter of 3.8 cm. The nominal power rating of the lamp was 40 watts. On operating the lamp, the phosphor emitted radiation over the wavelength range 270 nm to just beyond 350 nm, the peak of the phosphor emission being at 308 nm. The lamp also emitted spectral lines characteristic of mercury, for example at 313 nm and 365 nm. However no emission corresponding to the mercury 254 nm line, nor any other emission in the region 200 nm to 270 nm, was detected. Afterthe lamp had been run in for a period of 210 hour, the total output radiated between 270 nm and 350 nm was measured as being 4.95 watts.

In the construction of the photochemical reactor, the lamp was sealed into a double-walled glass vessel of overall length 127cm. Over 107 cm of its length, the vessel was cylindrical with internal diameter 15 cm. The reactor was operated in a vertical position, the longitudinal axes of the lamp and vessel being coincident. The bottom part of the vessel consisted of a flat buttress end reducer (Corning Process Systems, QVF catalogue number PR 6/2, type A) of overall length 20 cm. One end of the reducer was of internal diameter 15 cm, and was butted on to the cylindrical part of the vessel using standard fittings. The other end of the reducer comprised a short length of tubing of internal diameter 5 cm, into which one end of the lamp was fitted, using a piece of white silicone rubber tubing of internal diameter 3.8 cm and wall thickness 0.32 cm.A leak-proof seal was formed by doubling over the silicone tubing for part of its length. The doubled over region fitted snugly over the end of the lamp, and was then force-fitted into the 5 cm i.d. region of the reducer. The top of the vessel was covered with a flat glass disc containing a central socket of internal diameter 5 cm through which another piece of silicone rubber tubing passed, by means of which the top end of the lamp was positioned and sealed. The glass disc also contained four smaller sockets to facilitate operation of the reactor, for example introduction of a tube for nitrogen purging, and venting.

The vessel was charged with 19.2 litres of a mixture consisting of 0.945% w/v acetone and 0.405% w/v dodec-1 -ene in a 1:1 by volume mixture of formamide and tertiary butanol. Nitrogen was bubbled through the mixture at a rate of 0.1 litre minute- via a sintered glass tipped tube dipping down to near the bottom of the vessel. After a period of 24 hours, the nitrogen flow was increased to 1 litre minute-1 and the mixture was heated to 50"C by circulating water at a thermostatically controlled temperature between the inner and outer walls of the vesel. After a further 2 hour period, the lamp was switched on. The electrical energy consumed by the lamp circuit, which was the standard circuit specified by the lamp manufacturer, was monitored by a kWh meter through which the electrical supply was connected.The UV/visible absorption spectrum of the reaction mixture indicated that, over the 5.6 cm path length between the surface of the lamp and the inner wall of the reaction vessel, the mixture would absorb the majority of radiation emitted by the lamp having wavelengths shorter than 350 nm, and that it would not absorb ultra-violet and visible radiation having wavelengths longer than 350 nm to any significance degree. The rate of absorption of ultra-violet energy by the reaction mixture therefore lay with the range 2.48 to 4.95 watts. Distributed over the surface area of the lamp tube, this represents an average intensity of absorbable ultra-violet radiation incident on the reaction mixture, which was in direct contact with the lamp tube, of between 1.76 and 3.52 milliwatts cm-2.

Irradiation of the reaction mixture was carried out for a period of 20 hours, during which further amounts of acetone, dodec-1 -ene and tertiary butanol were added. Analyses of the reaction mixture showed that the acetone concentration was maintained between 0.72% wlv and 1.14% wlv and that the dodec-1-ene concentration was maintained between 0.27% w/v and 0.41 % w/v. Analysis of the reaction mixture at the end of the 20h irradiation period showed that 255 g (1.20 moles) of the tridecanamide had been formed, and that 66 g of dodec-1 -ene remained in solution. The total amount of dodec-1 -ene added had been 396 g.The amount of dodec-1 -ene consumed by reaction was therefore 330 g (1.96 moles) giving a chemical yield for tridecanamide formation of 61 %. From readings of the kWh meter, the total electrical energy consumption by the lamp circuit over the 20h irradiation period was 0.957 kWh. The electrical energy efficiency for the formation of tridecanamide was therefore 266 g per kWh.

The reaction mixture was removed from the reactor and allowed to stand for 2 days at a temperature of 0 C, during which a white precipitate formed. The mixture was then filtered under suction. Analysis of the filtrate showed that 98 g of tridecanamide had remained in solution. The solid product was re-dissolved in 400 cm3 of boiling acetone, and the mixture allowed to cool to room temperature. The white, crystalline product which formed was filtered off and dried in an oven at 60"C for 20 hours. Analysis of the acetone filtrate showed that 7.4 9 of tridecanamide had remained in solution. The weight of the dried, recrystallised product was 178 9.

Analysis showed the tridecanamide content to be 81% (144 g).

Example 11 The procedure of Example 10 was followed with the exception that a lower acetone concentration was used.

The starting concentration of acetone was 0.20% w/v, and the highest concentration reached on adding further amounts during the irradiation was 0.23% w/v. The starting concentration of dodec-1-ene was 0.39% w/v, and the highest concentration reached was 0.45% w/v. The mixture was irradiated for a total of 24 hours.

Analysis of the mixture at the end of this period showed that 441.69 (2.07 moles) of tridecanamide had been formed. The amount of dodec-1-ene consumed by the reaction was calculated to have been 514.89 (3.06 miles) giving a chemcial yield for tridecanamide formation of 68%. The total electrical energy consumption by the lamp circuit over the 24 hr. irradiation period had been 1.166 kWh. The electrical efficiency for the formation of tridecanamide was therefore 379 g per kWh.

Claims (13)

1. A process for the production of an amide, which process comprises reacting an &alpha;-olefin at a concentration in the range of from 0.01 to 0.05 mol 1- with formamide under ultra-violet radiation in the presence of from 0.02 to 5% w/v of acetone as a photoinitiator.

2. A process as claimed in claim 1 wherein the acetone concentration is in the range of from 0.1 to 1% w/v.

3. A process as claimed in claim 1 or claim 2 wherein the concentration of the cu-olefin is in the range of from 0.02 to 0.04 mol 1-1.

4. A process as claimed in any one of the preceding claims wherein the concentration of formamide is higher than 5 mol 1-1 and preferably higher than 10 mol 1-1 and wherein tertiary butanol is used as co-solvent to homogenise the mixture.

5. A process as claimed in any one of the preceding claims wherein the ultra-violet radiation is in the range of from 250 to 350 nm.

6. A process as claimed in claim 5 wherein the ultra-violet radiation is in the range of from 260 to 330 nm.

7. A process as claimed in any one of the preceding claims wherein the olefin is dodecene.

8. A process as claimed in any one of the preceding claims wherein the ultra-violet radiation has an average intensity in the range of from 0.05 to 10 milliwatts cm-2 over the irradiated area.

9. A process as claimed in claim 8 wherein the ultra-violet radiation has an average intensity in the range of from 1.5 to 4 milliwatts cm-2 over the irradiated area.

10. A process as claimed in any one of the preceding claims which is carried out in a continuous manner, with the amide product being removed periodically from the reaction mixture.

11. A process as claimed in any one of the preceding claims wherein the source of ultra-violet radiation is in direct contact with the reaction mixture.

12. A process as claimed in claim 1 substantially as hereinbefore described with reference to any one of the Examples.

13. An amide whenever produced by a process as claimed in any one of the preceding claims.