SK284530B6 - Process for the preparation of cyclic carbonates - Google Patents

Abstract

Cyclic carbonates of the general formula (I), wherein R a R' are the same or different and are H, alkyl, alkenyl or haloalkyl with 1 to 20 carbon in the molecule, cycloalkyl and its halo derivative with 5 to 12 carbon, aryl, alkylaryl and their halo derivatives and nitro derivatives, are prepared by addition of carbon dioxide to at least one epoxycompound of the general formula (II), wherein R and R' have mentioned meaning, at the temperature 50 to 180 °C, by synergism of aprotic alkaline solvent and at least one catalyst or catalytic system, whereby partial pressure of carbon dioxide in reaction medium is 20 kPa to 3.5 MPa and total pressure of reaction medium is maximum 6 MPa. Reaction medium is water free or the content of the water is mostly 0.8 % by weight/epoxyreactants. Catalyst or catalytic system contains in the molecule on average 0.5 to 4 of halide anions or ligands and at least the part of catalyst is recycled.

Description

The present invention relates to a process for the preparation of cyclic carbonates under mild reaction conditions allowing to obtain high selectivity for cyclic carbonates, using technically available and readily regenerable catalysts, respectively. catalytic systems.

BACKGROUND OF THE INVENTION

Alkylene carbonates or cyclic esters of carbonic acid and alpha-, beta-diols, but also alkenyl carbonates and ether carbonates can be produced by reacting α-, β-unsaturated or α-, γ-diols with phosgene or with alkyl chloroformates [Nemirovskij J .: J prakt. Chem. 28, 439 (1883); Vorländer D .: Hun. 280, 186 (1894); Allpress CF, Maw V .: J. Chem. Soc. 125, 225g (1924)]. Also, by reaction of alkyl chloroformates with alkali metal glyconates, as well as by the action of concentrated sodium carbonate solutions with 1,2- and 1,3-dichlorohydrins [German Pat. 516,281 (1931); France. pat. 1,139,206 (1957)]. These processes are resource-intensive and, in particular, produce low-value or waste-by-products, burdening waste water, which need to be disposed of at considerable cost. In this regard, the transesterification of dialkyl carbonates with diols is more technically interesting [Morgan MS, Gretcher LH: J. Am. Chem. Soc. 68, 781 (1946)], but the process requires the availability of some dialkyl carbonate [Sarel S. et al: J. Org. Chem. 24 (12), 1873 (1959)]. In the case of addition of trichloroacetic acid to the oxirane, respectively. alkyloxirates [US 2,784,201 (1957)], in turn, the need for corrosive and technically demanding trichloroacetic acid. However, the addition of carbon dioxide epoxides [nem. pat. 740,366 (1943); U.S. Pat. No. 2,667,497 (1954), 1,758,946, 2,773,881 (1956) and 2,873,282 (1956), with alkali metal hydroxides on activated carbon, anhydrous calcium and magnesium halides known as catalysts. Further, pyridine, acridine and some aliphatic tertiary amines have proven to be effective catalysts, and at such catalysts at 180-200 ° C and 5-10 MPa the yield of alkylene carbonates reaches 97-98%. 2,733,070 (1956)] and the use of quaternary halides of ammonium, such as (C _e H ₅₎ NBR, and the. Since, however, also form undesirable by-polymeric products, for the suppression of the formation is suggested [US 2,773,881 (1956) and No. 2,873,282 (1959)] to apply a large excess of 50-500% by weight of carbon dioxide [Hechler G .: Chem., 43, 16903, (1971); Levin SZ et al: Neftechimija 11 (4), 573 (1962), Nomura R. et al .: J. Org. Chem., 45, 3735 (1980)]. However, the company substantial excess carbon dioxide can suppress production of only certain by-products. Thus, it is not surprising that other catalysts for the addition of carbon dioxide to oxirane, methyloxirane and other epoxy compounds are sought, such as alkylchloroantimone compounds [Gorski R., Kliniec J .: Przemysl Chemicz. 70/9, 392 (1991); CH 620434 (1976); Polish Pat. 138, 902 (1983); US 2,994704 (1961)], cerium nitrates [US 5,179,214 (1993)], chromium carbonylporphirins [US 4,663,467 (1987)], transition metal phthalocyanines [US 5,283,356 (1994)], and catalytic systems for based on quaternary transition metal complexes IV.b or Vb of the Lewis base periodic system group [EP 069 494 A1 (1982)] as well as transition metal halides, but also alkali metal, zinc and nickel halides in combination with an aprotic base - e.g. Ν, Ν-dimethylformamide [Bobylev LI et al .:

Nephtechimija 36/3, 209 (1996)]. The reaction temperature is most often 180 to 200 ° C and the pressure above 5 MPa, or the reaction temperatures are even below 70 ° C, but the reaction time is at least 24 h. In some known experimental results, although the high pressure did not correlate with the synthesis of cyclic carbonates in high yield, but as the catalyst has also generally changed, the anomaly is clearly attributed to the type of catalyst or catalyst system. Thus, the advantages of the known cyclic carbonate preparation processes take advantage of the problems and "anomalies" of the processes solved by the method of the present invention.

SUMMARY OF THE INVENTION

According to the present invention, a process for the preparation of cyclic carbonates of the formula wherein R and R 'are the same or different and are hydrogen, alkyl, alkenyl or haloalkyl of 1 to 20 carbon atoms, cycloalkyl and its halogen derivative with 5 to 5 carbon atoms 12, aryl or alkylaryl and their halogenated derivatives having a carbon number of 6 to 12, etheralkyl with a carbon number of 2 to 12 and their halogenated derivatives and nitro derivatives, by the addition of carbon dioxide to at least one epoxy compound of the general formula

ABOUT /\

HC - CH

R ^{x X} R 'at 50 to 180 ° C, in association with an aprotic basic medium and at least one catalyst and / or catalyst system selected from quaternary ammonium halides and bases, urea salts, alkaline earth, zinc, cadmium, aluminum halides , iron, cobalt, nickel, chromium, molybdenum, thallium, antimony, zirconium, hafiiium, cerium, niobium, organometallic compounds of transition metals such as metallphorphyrins, iron phthalocyanines, chromium, manganese, titanium, vanadium, zirconium, zirconium hydroxyaluminium phthalocyanine, chloraluminium phthalocyanine, organotetraalkylphosphonium tin halide complexes such that the partial pressure of carbon dioxide in the reaction medium is 20 kPa to 3.5 MPa and the total reaction medium pressure is maximum 6 MPa, the reaction medium being free of water or water content not more than 0.8% %, calculated on the weight of epoxy reactants or a mixture of epoxy reactants, and pro solvent-containing products, wherein the catalyst and / or catalyst system comprises on average 0.5 to 4 halide anions and / or ligands per molecule and at least a portion of the catalyst or catalyst system is recycled.

An advantage of the process of the present invention is the high selectivity of addition of carbon dioxide with epoxy compounds to cyclic carbonates, at a minimum partial pressure of carbon dioxide. Possibility to utilize unrefined carbon dioxide including inert natural gas or other gases containing carbon dioxide and also low sensitivity of catalysts,

Catalyst systems for conventional catalytic poisons. Then lower operating costs, in particular lower energy consumption, as well as substantially lower investment costs for equipment.

Known catalysts and catalyst systems are suitable for carrying out the process of the invention, with metal compounds containing halide anions or ligands in the molecule being most suitable.

As the carbon dioxide-containing gas, in addition to the pure carbon dioxide, not only conventional commercial technical carbon dioxide, but even inert natural gas containing at least 50% by volume of water can be used. carbon dioxide or exhaled carbon dioxide. It is possible to utilize the released carbon dioxide from fermentation processes, even from limestone, dolomite and magnesite burning. However, it is advisable to take care not only of "dedusting", minimizing the nitrogen and oxygen content, but especially of the water vapor, which would react with the epoxy compounds in a competitive reaction.

A sufficient carbon dioxide partial pressure of at least 20 kPa is required for sufficient propulsion and hence a sufficient reaction rate. However, at a substantially higher carbon dioxide partial pressure, a surprisingly negative effect on the selectivity of the cyclic carbonates is achieved. Thus, at a higher partial pressure of carbon dioxide, this increasingly even more preferably prior to its insertion into the oxirane ring, aids in particular in the polyaddition of the epoxy compounds, thereby clearly reducing the selectivity to the desired cyclic carbonates. When assessing the effect of the total pressure, the vapor pressure at the reaction temperature must be taken into account in particular for ethylene oxide and propylene oxide. A good aid for selecting a suitable partial pressure of carbon dioxide is the vapor pressure dependence of ethylene oxide, propylene oxide vapor and epichlorohydrin, shown in FIG. Obviously, in a continuous process of production, whether ethylene carbonate or propylene carbonate, or both, at a constant "shortage" of ethylene oxide or propylene oxide in the reaction medium, their vapor pressure is actually lower.

In particular, care must be taken that aprotic compounds, such as water, alcohols, acids, amines, etc., do not get into the reaction medium or only to a minor extent, whether with reactants or with a catalyst. It is therefore appropriate to dry the epoxy compounds as best as possible, as well as the carbon dioxide-containing gas. In the case of catalysts, preference is given to non-hydrated forms. Although the process according to the invention can also be carried out at a content of over 0.8% by weight. water / epoxy compounds in the reaction medium, even a polar catalyst may have an even better effect on conversion

Table 1 epoxy compounds, but the selectivity to cyclic carbonates clearly decreases.

Catalysts, respectively. catalyst systems, on average per molecule, should contain 0.5 to 4 halide anions and / or ligands, most preferably 1 to 2 halide anions and / or ligands per molecule. Given the relatively good stability of the catalysts or catalyst system, it is appropriate to recirculate them. As a rule, technically demanding regeneration is not necessary and only the compensation of the losses with the fresh catalyst may be sufficient.

Further data on carrying out the process of the invention as well as other advantages are apparent from the examples.

DETAILED DESCRIPTION OF THE INVENTION

Example 1

Weigh 15.0 g of Ν, Ν-dimethylformamide containing 0.05% w / w into a 125 cm ³ stainless steel autoclave equipped with a propeller stirrer (1000 rpm). water, 15 g propylene oxide with 0.013 wt. water and various types and quantities of cobalt salts, taking care of their solubility in the prepared batch. After the autoclave was closed and the air was removed, carbon dioxide was passed to a pressure of 2.5 MPa. Thereafter, the contents of the autoclave are heated to 120 ° C with constant stirring and maintained at an accuracy of +2 ° C for 3 h. When the total pressure in the autoclave drops below 2 MPa, it is pressurized with carbon dioxide. The autoclave is then rapidly cooled, the product is removed, weighed and analyzed by GC.

In both experiments, instead of ethylene oxide with 0.013 wt. The water used is propylene oxide-free water, refined with zeolites. Its purity is 99.997 wt.

The results obtained with the different types and amounts of catalyst are summarized in Tab. First

Example 2

The procedure is analogous to Example 1, but comparing the halide activities of the different catalysts at 0.0195 mol / mol propylene oxide. The results are summarized in Tab. Second

catalyst Product quantity [g] PO conversion [%] Selectivity to propylene carbonate r% i kind of number [G] mol / mol PO ” CoCl ₂ · 6H ₂ O 0.1 0.0016 33.5 83.4 53.3 CoCl ₂ .6H ₂ O 0.6 0.0098 35.5 98.9 66.3 CoCl ₂ .6H ₂ O 1.2 0.0195 41.2 99.3 93.3 CoC1 ₂ 1.2 0.0195 41.4 99.9 97.2 CoCl ₂ 1.2 0.0195 41.4 99.9 ^b 98.8 ^b CoCl ₂ 1.2 0.0195 41.4 99.9 ^b 98.9 ^b CoCl ₂ · 6H ₂ O 2.4 0.0391 31.6 99.5 35.7 FeCl ₃ .6H ₂ O 1.44 0.0206 38.6 100 77.1 FeCl ₃ .6H ₂ O 2.88 —71 --------- 0.0413 36.5 100 59.9

'PO = propylene oxide ^b PO = water-free (anhydrous), purity 99,997% w / w

Table 2

catalyst Total product weight [G] Conversion PO% 1% Selectivity to propylene carbonate r% i NiCl ₂ .6H ₂ O 38,40 99.5 87.8 SnCl ₂ .2H ₂ O 39.20 94.9 71.2 CuC1 ₂ 2H ₂ O 26.80 38.9 20,05 CuC1 ₂ 28.2 41.9 23.3 CaCl ₂ 39.8 99.2 82.5 FeCl ₃ 37.2 99.6 71.3 ZnCl ₂ 38.8 99.98 90.6 NaCl 29.70 44,21 0.1 CoCO ₃ 27.1 30.9 0.1 (CH ₃ COO) ₂ Co 30.3 48.6 0.2 (HCOO) ₂ Ca 28.0 50.1 0.5

Example 3

The procedure is as in Example 1, except that 15.0 g of Ν, Ν-dimethylformamide containing 0.29% by weight of water, 15 g of propylene oxide with 0.013% by weight of water, 0.82 g of dry CaCl are used for each experiment. ₂ , the initial pressure at room temperature was 2.0 MPa and the effect of temperature was examined in isochronous (3 h) experiments. Thus at 70, 120 and 150 ° C the conversion of propylene oxide reaches 41.5; 99.2 and 93.6% and selectivity to propylene carbonate 0.2; 84.5 and 81% respectively.

Example 4

The procedure is as in Example 3 was used instead of N, N-dimethylformamide was used 15 g of triethylamine with the addition of 0.04% by weight of water, and the place of 0.8 g of CaCl ₂ was used as 0.3 grams, but the addition of 0.6 g of chromium tetraporphyrin chloride. At an initial pressure of 2 MPa of carbon dioxide and not exceeding 3 MPa, while decreasing to 1.2 to 2 MPa, the carbon dioxide was pressurized to 3 MPa. At a temperature of 120 ± 2 ° C for 3 h the conversion of propylene oxide reaches 100% and the selectivity to propylene carbonate is 94.5%. However, at a total pressure of 6-9 MPa, the conversion of propylene oxide also reaches practically 100%, but the selectivity to propylene carbonate is only 74 to 76%, the remainder being mainly propylene glycol and oligomers.

Table 3

Epoxy (epoxy compound) Maintained total pressure [MPa] Conversion of an epoxy compound Γ 1% Selectivity of converted epoxy compound to cyclic carbonate [%] propylene oxide 6-8 100 62 propylene oxide 2-3 100 92 epichlorohydrin 6-8 100 57 epichlorohydrin 1-2 100 89 butadiénmonoxid 6-8 100 60 3,4-epoxy-l-butene 1-1,8 100 94 glycidylvinyléter 6-8 97 59 epoxycyklopentén 1-1.4 96 95 glycidylvinyléter 0.8 - 1.2 96 91 cyclohexene 1.8-2.2 94 93 oktadecénoxid (1,2-Epoxyoctadecane) 6-8 98 58 oktadecénoxid (1,2-Epoxyoctadecane) 0.3 - 0.7 94 95 glycidylalkohol 7-9 100 29 glycidylalkohol 1.5-2.5 100 72 butylene 7-9 100 58 butylene 1-2 100 92 Ethylene oxide 7-9 100 54 Ethylene oxide 2-3 100 96

Example 5

15 g of Ν, Ν-dimethylformamide, 5 g of triisobutylamine, 1 g of triphenylantiminodibromide, 0.1 g of cobalt bromide and 15 g of epoxide are weighed into the autoclave specified in Example 1. After removal of air, carbon dioxide is passed. The reaction temperature is maintained at 120 ± 2 ° C for 180 min. In each experiment, the total pressure and the type of epoxide vary.

The content of cyclic carbonates formed is determined in the product by GC or HPLC. The dependence of the conversion and selectivity of the individual epoxides on the corresponding cyclic carbonates on the total pressure during the reaction of carbon dioxide with the epoxy compound is evident from the results in Tab. Third

Example 6

10 g of Ν, Ν-dimethylformamide are added to the autoclave specified in Example 1 with a water admixture of 0.28% by weight. 5 g of formamide with 0.11 wt. water, various amounts of catalyst, respectively. 15 g of ethylene oxide with an admixture of 0.06 wt. % water or a mixture of ethylene oxide with propylene oxide with an admixture of 0.013 wt. water. Further, "natural" carbon dioxide (inert natural gas) of the following composition (in% vol.) Is introduced: CO ₂ = 91.82, N ₂ = 4.96, CH ₄ = 3.07, ethane = 0.11, propane = 0.03, n-butane = 0.01 and admixtures of hydrogen sulfide and carbonyl sulfide. The reaction is carried out at different total pressures which are maintained by the introduction of fresh inert natural gas. The reaction temperature is 110 ± 3 ° C and time 180 min. Further reaction conditions and the achieved results of the conversion of alkylene oxides as well as the selectivity to ethylene carbonate and / or propylene carbonate are summarized in Tab. 4. The temperature dependence of the vapor pressure of ethylene oxide, propylene oxide and epichlorohydrin is shown graphically in FIG. First

Table 4

alkylene [G] catalyst type (g) % wt. alkylene oxides Max. total pressure [MPa] Conversion of alkylene oxides r%] Selectivity to cyclic carbonates [1% propylene oxide (15) CaCl ₂ (0.82) 5.47 1.4 100 95 propylene oxide (15) CaCl ₂ (0.82) 5.47 2.2 100 84 propylene oxide (15) propylene oxide (10) CaCl ₂ (0.82) 5.47 4.3 100 75 + ethylene oxide (5) CaCl ₂ (0.82) 5.47 1.4 100 96 + ethylene oxide (5) CaCl ₂ (0.82) 5.47 6 100 68 ethylene oxide (15) ethylene oxide (10) CaCl ₂ (0.82) 5.47 3 100 94 + propylene oxide (5) CaCl ₂ (0.82) 5.47 8 100 63 propylene oxide (15) FeCl ₃ (0.82) 5.47 1 100 82 propylene oxide (15) FeCl ₃ (0.82) 5.47 3 100 72 propylene oxide (15) FeCl ₃ .3H ₂ O (1,44) 9.6 1 100 79 propylene oxide (15) FeCl ₃ .3H ₂ O (1,44) 9.6 4 100 62 propylene oxide (15) FeCl ₃ .3H ₂ O (1,44) 9.6 5 100 51 ethylene oxide (15) FeCl ₃ .3H ₂ O (1,44) 9.6 2.5 100 92 ethylene oxide (15) FeCl ₃ .3H ₂ O (1,44) 9.6 8 100 54 ethylene oxide (15) Bu ₃ SnJ (0.5) 3.3 2.5 98 95 ethylene oxide (15) Bu ₃ SnJ (0.5) 3.3 7.8 98 57 ethylene oxide (15) Bu ₃ PJ (0.6) 4.0 2.5 96 98 ethylene oxide (15) Bu ₃ PJ (0.8) 4.0 7.5 99 58 ethylene oxide (15) Bu ₃ SnCl (0.9) 6.0 2.5 65 94 ethylene oxide (15) Bu ₃ SnCl (0.9) 6.0 7.5 69 74 ethylene oxide (15) CoBr ₂ (0.4) 2.7 2.5 99 96 ethylene oxide (15) CoBr ₂ (0.4) 2.7 6.8 100 62 propylene oxide (15) (CH ₃ ) ₃ SbBr ₂ (0.8) 5.3 2.0 100 88 propylene oxide (15) (CH ₃ ) ₃ SbBr ₂ (0.8) 5.3 6.0 100 64 ethylene oxide (15) chloro (5,10,15,20-tetra-p-lylporfyrinát chromium (0,8) 5.3 2.5 85 89 ethylene oxide (15) Chromium (5,10,15,20-tetra-p-to-lylporphyrinate) (0,8) 5.3 6.0 89 59

Example 7

Using dry calcium chloride in an amount of 0.82 g for each experiment, 15 g of Ν, Ν-dimethylformamide and 15 g of propylene oxide, as specified in Example 6, in the same manner, at a reaction time of 180 min. and max. 3.5 MPa investigates the effect of temperature on propylene oxide conversion and selectivity to propylene carbonate, at temperatures of 70 + 2 ° C, 120 + 2 ° C and 150 + 2 ° C.

The conversion of propylene oxide is 42%, 100% and 94%. The selectivity to propylene carbonate is 19.6%, 84% and 82%, respectively.

At a temperature of 120 + 2 ° C, with the same amount of dry calcium chloride of 0.82 g in each experiment and max.

The pressure of 3.5 MPa was monitored for the effect of the amount of Ν, Ν-dimethylformamide at a reaction time of 3 h, using 4.4 g, 15 g and 30 g of Ν, Ν-dimethylformamide. The conversion of propylene oxide reached 84.5%, 99.8% and 93.9%. Selectivity to propylene carbonate 64.5%, 84% and 62%. The remainder to 100% are mainly propylene glycol and oligomers of propylene oxide, respectively. polypropylene.

Example 8

At the bottom of the column, respectively. of a stainless steel absorber, filled to a height of 800 cm with a mixture of Ν, Ν-dimethylformamide and propylene carbonate in a weight ratio of 1 to 1% by weight. cobalt bromide, calculated on propylene carbonate, at a total pressure of 1100 ± 20 kPa and a temperature of 120 ± 3 ° C and at the bottom (reactor), propylene oxide is metered in at a rate of 0.40 dm ³ / dm ³ reaction volume per hour while feeding dry technical oxide % of carbon dioxide, purity 99.1 wt. maintains a pressure of 1100 ± 20 kPa. At the top of the absorber, in which propylene oxide is mainly reacted with carbon dioxide, the crude reaction product is removed, from which unconverted propylene oxide, Ν, Ν-dimethylformamide and propylene carbonate are separated by rectification. The remainder of the rectification column containing practically cobalt compounds, in particular cobalt bromide, propyl carbonate, propylene glycol to polypropylene glycol, as well as the addition of Ν, Ν-dimethylformamide, after addition of further Ν, Ν-dimethylformamide, obtained mainly by rectification together with the rectification at the bottom of the absorber. The conversion of propylene oxide is 88 to 92% and the selectivity to propylene carbonate is 90 to 93%.

Example 9

The procedure is similar to Example 8, but the working pressure is maintained at 2400 + 50 kPa. The conversion of propylene oxide is 90 to 93% and the selectivity to propylene carbonate is 82 to 87%.

Example 10

The procedure is similar to that of Example 8, except that 3,4-epoxy-1-butene is injected into the absorber instead of propylene oxide, the first absorber filling being only Ν, Ν-dimethylformamide containing 1 wt. In addition to the regenerated catalyst and part of the Ν, dim-dimethylformamide, a heavy organic residue from the reboiling column of the rectification column is returned to the regenerated catalyst in the next run of the unsaturated cyclic carbonate production process. The conversion of 3,4-epoxy-1-butene reaches 82 to 86% and the selectivity to the corresponding unsaturated cyclic carbonate is 88 to 88%.

Industrial usability

The process according to the invention is particularly useful in the chemical industry and, in the future, in other sectors, not only for the production of valuable organic intermediates, solvents, comonomers, but also for the utilization of increasingly problematic carbon dioxide.

Claims (5)

CLAIMS 1. A process for the preparation of cyclic carbonates of general formula 1 to 20, cycloalkyl and their halogen derivatives having a carbon number of 5 to 12, aryl, alkylaryl and their halogen derivatives having a carbon number of 6 to 12, etheralkyls having a carbon number of 2 to 12 adding carbon dioxide to at least one epoxy compound of the formula O / HC-CH ^x A; wherein R and R 'are as defined at 50 to 180 ° C, in association with an aprotic basic medium and at least one catalyst and / or catalyst system selected from quaternary ammonium halides and bases, urea salts, alkaline earth halides, zinc , cadmium, aluminum, iron, cobalt, nickel, chromium, molybdenum, thallium, antimony, zirconium, hafnium, niobium, cerium, organometallic compounds of transition metals such as metalporphyrins, iron phthalocyanines, chromium, manganese, zirconium, titanium, nickel, cadmium, zinc, hydroxyalunonium phthalocyanine, chloralumminumalocyanine, organotetraalkylphosphonium tin halide complexes, characterized in that the partial pressure of carbon dioxide in the reaction medium is 20 kPa to 3.5 MPa and the total pressure of the reaction medium is not more than 6 MPa wherein the reaction medium is free of water or the water content is at most 0.8 wt The catalyst and / or catalyst system comprises on average 0.5 to 4 halide anions and / or ligands per molecule and at least a portion of the catalyst or catalyst system is recycled. The process according to claim 1, characterized in that the partial pressure of carbon dioxide in the reaction medium is 0.1 to 3 MPa and the total pressure of the reaction medium is 0.15 to 4 MPa. Process according to Claim 1 and 2, characterized in that the catalyst in the reaction medium expressed in% by mass, cation and / or central atom per epoxy-reactant or epoxy-reactants is 0.01 to 3% by weight. Process according to claims 1 to 4, characterized in that the catalyst and / or the catalyst system is at least 1/3 homogeneous in one phase with the liquid reaction medium. A process according to claims 1 to 6, wherein the carbon dioxide donor is a gas selected from pure carbon dioxide, an inert natural gas predominantly carbon dioxide and an exhaled gas predominantly carbon dioxide. 1 drawing of the formula, About II \ / CH-HC / \ R r; in which R and R 'are the same or different and represent hydrogen, alkyl, alkenyl or haloalkyl having carbon numbers in the