Process for preparing organic carbonates

Abstract: Organic carbonates: and cyclic organic carbonates: are prepared by reacting an alcohol (R-OH), or respectively a diol (HO-R′-OH), with carbon monoxide, in the presence of: a halogen, or a halogen and/or a halide ion and an oxidizing agent.

Description: This invention relates to a process for preparing organic carbonates. Organic carbonates are useful intermediates in the chemical sector, and of these dimethyl carbonate is widely used in the synthesis of other alkyl and aryl carbonates (used as plasticizers, synthetic lubricants, monomers for organic glasses etc.), in methylation and carbonylation reactions (for preparing urethanes, isocyanates, polycarbonates etc.), as a fuel additive and as an organic solvent. The classical method of preparing alkyl carbonates is to react an alcohol with phosgene, as described for example in Kirk-Othmer, "Encydopedia of Chemical Technology", 3rd edition, No. 4, page 758. This method involves numerous technical problems, as well as safety problems deriving from the use of phosgene. To overcome these problems, alternative synthesis methods have been proposed, such as oxidative carbonylation of methanol in the presence of palladium catalysts (US-A-4,361,519; DE-A-3,212,535; GB-A-2,148,881). The drawbacks of such a process are essentially the high catalyst cost, the co-production of oxalic acid esters [see Fenton, J. Org. Chem., 39, 701 (1974)] and the negative effect of the co-produced water, which even at low concentrations renders the catalyst ineffective. Copper-based carbonylation catalysts have also been proposed (US-A-3,846,468; US-A-4,218,391; US-A-4,318,862; US-A-4,360,477), which however present problems deriving from the heterogeneousness of the reaction system and a certain sensitivity to water, this reducing the selectivity of carbon monoxide towards the formation of dimethyl carbonate and the reaction rate. For example, EP-A-220863 discloses a process for the preparation of an ester of carbonic ester by reaction of an alcohol with CO in the presence of a dihydrocarbyl peroxide and a catalyst comprising a platinum group metal and a copper compound, which may be added as halides. Patent Abstract of Japan vol.9, no.237 (c-305, 1960) discloses a process where CO is reacted with nitrous acid ester in the presence of oxygen in a solution containing a salt such as PdCl2 and an alcohol. Patent Abstract of Japan vol.3, no.128 (c-62) discloses the preparation of a carbonic ester by reacting an alcohol with CO and oxygen in the presence of a copper salt such as copper chloride and bromide and a nitrous ester. Other processes proposed in the art, but which have little practical importance, are the transesterification of other carbonates, the reaction of urea or urethanes with alcohols in the presence of catalysts, the reaction of alkyl halides or sulphates with alkaline carbonates, the reaction of alcohols with carbon dioxide and electrochemical synthesis. It has now been found that dimethyl carbonate and other organic carbonates, including cyclic carbonates, can be prepared simply and conveniently, under mild conditions and with high yields, from an alcohol or diol and carbon monoxide, operating in the presence of a halogen or in the presence of a halogen and/or a halide ion and an oxidizing agent In accordance therewith the present invention provides for preparing an organic carbonate A process for preparing an organic carbonate having the general formula: or a cyclic organic carbonate having the general formula: wherein: R is a C 1 -C 10 linear or branched alkyl, or a C 5 -C 6 cycloalkyl, and R' is a C 2 -C 5 linear or branched alkylene, by reacting an alcohol R-OH, or a diol HO-R'-OH, respectively, with carbon monoxide in the liquid phase at a temperature of from 25°C to 200°C, the cabon monoxide pressure being of from 0.1 MPa to 10 MPa (1 kg/cm 2 to 100 kg/cm 2 ), characterized in that said reaction is carried out in the presence of a halogen selected from chlorine, bromine and iodine, or in the presence of said halogen and/or a halide ion selected from the chloride, the bromide and the iodide ion and an oxidizing agent capable of oxidizing said halide ion to its corresponding halogen, with the proviso that metals of the platinum group and copper in their metallic form or in the form of their salts are absent. In the preferred embodiment R-OH is chosen from methanol, ethanol, n-propanol, iso-propanol, n-butanol, iso-butanol, 2-ethylhexanol and cyclohexanol, so that R in formula (I) represents the methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, 2-ethylhexyl and cyclohexyl radical respectively. On this basis the organic carbonates (I) preferably prepared by the process of the present invention are dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, di-isopropyl carbonate, di-n-butyl carbonate, di-iso-butyl carbonate, di-2-ethylhexyl carbonate and dicyclohexyl carbonate. In the most preferred embodiment dimethyl carbonate is prepared. Again in the preferred embodiment the diol HO-R'-OH is ethylene glycol or propylene glycol, the cyclic carbonate (II) having the formula: where R" is hydrogen or methyl respectively. It is considered that the reactions involved in the formation of the organic carbonate (I) and of the cyclic organic carbonate (II) are respectively the following: where X represents the halogen fed into the reaction environment or formed in situ by reaction between the halide ion and the oxidizing agent The preferred halogens are bromide and iodine, of which bromine is the more preferred. The preferred halide ions are bromides and iodides, of which bromides are the more preferred. The halide ions can be the byproduct of the reaction between halogen, alcohol (or diol) and carbon monoxide, or can be supplied as such to the reaction environment. In particular the halide ions can be supplied in the form of hydrohalogen acids such as hydrobromic acid and hydroiodic acid, or in the form of metal halides, especially of alkaline or alkaline earth metals such as potassium halide or lithium bromide; or in the form of ammonium or phosphonium halides, such as those definable by the formulas R''' 4 N + X - and R''' 4 P + X - where R''' indicates a hydrogen atom or an alkyl group. The oxidizing agent able to oxidize the halide ion into halogen can be chosen from: (a) hydrogen peroxide, an organic percompound, N-bromo-succinimide, a nitrogen oxide, nitrous acid, nitric acid, a sulphur peracid, or a metal salt or an ester of said acids and peracids; or (b) an oxidizing system formed from oxygen and an oxygenated nitrogen compound chosen from nitrogen oxides, nitrous and nitric acids, and the salts or esters of said acids. Of the oxidizing agents (a), the hydrogen peroxide is conveniently used in the form of an aqueous solution of a concentration of the order of 35-60% by weight. The organic percompounds can be chosen from organic peroxides, hydroperoxides and peresters, such as tert-butyl hydroperoxide and di-tert-butyl peroxide. Nitrogen oxides usable for this purpose are NO 2 , (N 2 O 4 ), N 2 O 3 and N 2 O 5 . The nitric acid used is preferably nitric acid having a concentration of about 67% by weight or more, such as fuming nitric acid. The nitrate and nitrite salts usable for the purpose are preferably the salts of alkaline or alkaline earth metals or ammonium. The nitrous and nitric acid esters preferably used are the alkyl esters. An example of such esters is butyl nitrite. A sulphur peracid suitable for the purpose is peroxydisulphuric acid, preferably used in the form of an alkaline or alkaline earth metal salt. Finally, it has been found that N-bromosuccinimide acts as an oxidizing agent in the process of the present invention. When the oxidizing system (b) is used, the oxygenated nitrogen compounds are conveniently chosen from NO, NO 2 , (N 2 O 4 ), N 2 O 3 and N 2 O 5 . The nitric acid used is preferably nitric acid having a concentration of about 67% by weight or more, such as fuming nitric acid. The nitrate and nitrite salts usable for the purpose are preferably the salts of alkaline or alkaline earth metals or ammonium, or the salts of metals such as cerium and gallium, specific examples of which are sodium nitrite, cerium and ammonium nitrate and gallium nitrate. The nitrous and nitric acid esters preferably used are the alkyl esters. An example of such esters is butyl nitrite. When using the catalytic system (b), catalytic quantities of a halogen (or halide) and an oxygenated nitrogen compound are generally required. In this case the halide ion is oxidized to halogen by the oxygen in accordance with the equation: 2X - + 2H + + ½O 2 → X 2 + H 2 O The process for preparing organic carbonates according to the present invention is conducted by bringing the reactants into mutual contact operating in the liquid phase at a temperature generally between 25 and 200°C under a carbon monoxide pressure generally between 0.1 MPa and 10 MPa (1 and 100 kg/cm 2 ) for a time of between 1 and 240 minutes. In the embodiment in which a halogen is used without an oxidizing agent, the process is conducted at a temperature of between 25 and 200°C under a carbon monoxide pressure of between 0.1 MPa and 10 MPa (1 and 100 kg/cm 2 ). The upper pressure limit is not critical and is dictated mainly by practical considerations. It has been found that the organic carbonate yield is a function of temperature, with optimum results between 50 and 150°C, and carbon monoxide pressure, the yield increasing as the pressure increases. The process can be carried out in an inert organic solvent with a halogen quantity stoichiometrically equivalent to the chosen alcohol or diol. However in the preferred embodiment the alcohol or diol is used in excess over the stoichiometric, the excess serving as the reaction solvent In practice a solution of the chosen halogen in an excess of alcohol or diol is prepared and the solution is placed under carbon monoxide and stirred at the above temperature, until the halogen has been completely or substantially completely converted. Under these conditions the reaction time can generally vary from 1 to 240 minutes and is typically of the order of 5-120 minutes. The reaction can be conducted in the presence of a base able to block the hydrohalogen acid which forms as a coproduct of the reaction. The base can be a carbonate or bicarbonate of an alkaline or alkaline earth metal, such as sodium carbonate or bicarbonate, in stoichiometric or approximately stoichiometric quantity to the hydrohalogen acid developed. When the process of the present invention is conducted with a halogen and/or a halide ion, in the presence of the oxidizing agent (a), the halogen or halide ion concentration used is conveniently between 10 -3 and 1 mole/litre and the oxidizing agent concentration between 10 -1 and 5 moles/litre of alcohol, their mole ratio generally being between 1:100 and 1:1. The reaction is conducted at a temperature of between 25 and 200°C under a carbon monoxide pressure of between 0.1 MPa and 10 MPa (1 and 100 kg/cm 2 ) for a reaction time of between about 1 and about 240 minutes. In the preferred embodiment, the halogen or halide ion concentration varies from 10 -2 to 0.5 moles/litre. the oxidizing agent concentration varies from 10 -1 to 2 moles/litre of alcohol, the molar ratio of halogen or halide ion to oxidizing agent varies from 1:50 to 1:1, the temperature varies from 50 to 120°C and the carbon monoxide pressure varies from 0.2 MPa to 10 MPa (2 to 100 kg/cm 2 ). When the process of the present invention is conducted with a halogen and/or a halide ion, in the presence of the oxidizing system (b), the halogen or halide ion concentration used is conveniently between 10 -3 and 2 moles/litre of alcohol and the oxygenated nitrogen compound concentration between 10 -3 and 2 moles/litre of alcohol, their molar ratio not being critical but generally being between 500:1 and 0.002:1. The reaction is conducted at a temperature of between 25 and 200°C under a total carbon monoxide plus oxygen pressure of between 0.1 MPa and 10 MPa (1 and 100 kg/cm 2 ). The upper pressure limit is not critical and is dictated mainly by practical reasons. The ratio of oxygen partial pressure to carbon monoxide partial pressure in the gaseous mixture is not critical and can generally vary from 0.005:1 to 500:1. In the preferred embodiment, the halogen or halide ion concentration varies from 10 -2 to 1 mole/litre of alcohol, the oxygenated nitrogen compound concentration varies from 10 -2 to 1 mole/litre of alcohol, the molar ratio of halogen or halide ion to the oxygenated nitrogen compound varies from 50:1 to 0.02:1, the temperature varies from 50 to 120°C, the total oxygen plus carbon monoxide pressure varies from 0.2 MPa to 10 MPa (2 to 100 kg/cm 2 ) and the ratio of oxygen partial pressure to carbon monoxide partial pressure varies from 0.01:1 to 1:1. Under these conditions the reaction time varies from about 1 to about 240 minutes. In the preceding embodiments either pure carbon monoxide or mixtures containing carbon monoxide and other inert gases can be used. Likewise, when oxygen is required among the reactants, either pure oxygen or oxygen diluted with an inert gas such as nitrogen, for example air or oxygen-enriched air, can be used. In all cases, operating under the aforesaid conditions the organic carbonate is obtained with high yield and a high reaction rate. The organic carbonate produced in this manner can be separated from the reaction mixture by normal methods such as distillation or fractionation. The process of the present invention can be conducted discontinuously (batchwise), semicontinuously or continuously. The following experimental examples are given to better illustrate the invention. EXAMPLE 1 60 g of methanol and 3.25 g (20 mmoles) of bromine are introduced into a 250 ml pressure vessel lined internally with Teflon (R) and fitted with a mechanical stirrer and heat transfer means. Carbon monoxide is fed into the pressure vessel to a pressure of 1 MPa (10 kg/cm 2 ). It is heated to 85°C under stirring for 10 minutes. It is then cooled to ambient temperature, the gas vented and the liquid subjected to gaschromatography analysis. A dimethyl carbonate yield of 17 mmoles (1.53 g) is determined, equal to 85% on the moles of bromine introduced. Methyl formate (11 mmoles) is formed as by-product. EXAMPLE 2 60 g of methanol and 5.07 g (20 mmoles) of iodine are introduced into a 250 ml pressure vessel lined internally with Teflon (R) and fitted with a mechanical stirrer and heat transfer means. Carbon monoxide is fed into the pressure vessel to a pressure of MPa (10 kg/cm 2 ). It is heated to 110°C under stirring for 1.5 hours. It is then cooled to ambient temperature, the gas vented and the liquid subjected to gaschromatography analysis. A dimethyl carbonate yield of 1 mmole (0.09 g) is determined, equal to 5% on the moles of iodine introduced. Dimethoxymethane (1.5 mmoles) is formed as by-product. EXAMPLE 3 60 g of methanol and 3.25 g (20 mmoles) of bromine are introduced into a 150 ml glass pressure vessel fitted with a mechanical stirrer and heat transfer means. Carbon monoxide is fed into the pressure vessel to a pressure of 0.3 MPa (3 kg/cm 2 ). It is heated to 50°C under stirring for 60 minutes. It is then cooled to ambient temperature, the gas vented and the liquid subjected to gaschromatography analysis. A dimethyl carbonate yield of 3.6 mmoles (0.32 g) is determined, equal to 18% on the moles of bromine introduced. Methyl formate (9 mmoles) is formed as by-product. Table 1 shows the results obtained in this example. EXAMPLES 4 and 5 60 g of methanol, 3.25 g (20 mmoles) of bromine and 2.12 g (20 mmoles) of sodium carbonate are introduced into a 250 ml pressure vessel lined internally with Teflon (R) and fitted with a mechanical stirrer and heat transfer means. Carbon monoxide is fed into the pressure vessel under the conditions shown in Table 1, which also shows the results obtained. Example No. 3 4 5 Temp. (°C) 50 70 70 P(CO) (kg/cm 2 ) MPa 0.3 (3) 1(10) 4 (40) Time (min) 60 30 25 DMC (mmoles) 3.6 14.6 15.6 (grams) 0.32 1.32 1.40 (yield %) 18 73 78 HCOOMe (mmoles) 9 traces traces DMC = dimethyl carbonate HCOOme = methyl formate the DMC yield being evaluated on the moles of bromide introduced. EXAMPLE 6 The procedure of example 4 is repeated, but replacing the sodium carbonate with 3.36 g (40 mmoles) of sodium bicarbonate. 6 mmoles (0.54 g) of dimethyl carbonate are obtained with a molar yield of 30% on the bromine. EXAMPLE 7 60 g of methanol, 5.07 g (20 mmoles) of iodine and 2.12 g (20 mmoles) of sodium carbonate are introduced into a 250 ml pressure vessel lined internally with Teflon (R) and fitted with a mechanical stirrer and heat transfer means. Carbon monoxide is fed into the pressure vessel to a pressure of 1 MPa (10 kg/cm 2 ). It is heated to 100°C under stirring for 60 minutes. It is then cooled to ambient temperature, the gas vented and the liquid subjected to gaschromatography analysis. A dimethyl carbonate yield of 11 mmoles (0.99 g) is determined, equal to 55% on the moles of iodine introduced. EXAMPLE 8 60 g of ethanol and 3.25 g (20 mmoles) of bromine are introduced into a 250 ml pressure vessel lined internally with Teflon (R) and fitted with a mechanical stirrer and heat transfer means. Carbon monoxide is fed into the pressure vessel to a pressure of 1 MPa (10 kg/cm 2 ). It is heated to 85°C under stirring for 15 minutes. It is then cooled to ambient temperature, the gas vented and the liquid subjected to gaschromatography analysis. A diethyl carbonate yield of 9 mmoles (1.06 g) is determined, equal to 45% on the moles of bromine introduced. Ethyl formate (4 mmoles) is formed as by-product. EXAMPLE 11 91.7 g of ethylene glycol and 3.25 g (20 mmoles) of bromine are introduced into a 250 ml glass pressure vessel lined internally with Teflon (R) and fitted with a mechanical stirrer and heat transfer means. Carbon monoxide is fed into the pressure vessel to a pressure of 1 MPa (10 kg/cm 2 ). It is heated to 85°C under stirring for 15 minutes. It is then cooled to ambient temperature, the gas vented and the liquid subjected to gaschromatography analysis. An ethylene carbonate yield of 7 mmoles (0.62 g) is determined, equal to 35% on the moles of bromine introduced. EXAMPLE 13 60 g of methanol, 16 g (100 mmoles) of bromine and 10.6 g (100 mmoles) of sodium carbonate are introduced into a 250 ml glass pressure vessel lined internally with Teflon (R) and fitted with a mechanical stirrer and heat transfer means. Carbon monoxide is fed into the pressure vessel to a pressure of 3 MPa (30 kg/cm 2 ). It is heated to 85°C under stirring for 35 minutes. It is then cooled to ambient temperature, the gas vented and the liquid subjected to gaschromatography analysis. A dimethyl carbonate yield of 64 mmoles (5.76 g) is determined, equal to 64% on the moles of bromine introduced. EXAMPLE 15 40 g of methanol, 2.07 g (33 mmoles) of fuming nitric acid and 0.54 g (3.3 mmoles) of bromine are introduced into a 250 ml pressure vessel lined internally with Teflon (R ) and fitted with a mechanical stirrer and heat transfer means. Carbon monoxide and oxygen are fed into the pressure vessel to partial pressures of 2 MPa and 0.5 MPa (20 and 5 kg/cm 2 ) respectively. It is heated to 110°C under stirring for 30 minutes. It is then cooled to ambient temperature, the gas vented and the liquid subjected to gaschromatography analysis. A dimethyl carbonate yield of 6.0 g (67 mmoles) is determined. EXAMPLE 16 40 g of methanol, 2.07 g (33 mmoles) of fuming nitric acid and 0.13 g (0.8 mmoles) of bromine are introduced into a 250 ml pressure vessel lined internally with Teflon (R) and fitted with a mechanical stirrer and heat transfer means. Carbon monoxide and oxygen are fed into the pressure vessel to partial pressures of 2 MPa and 0.5 MPa (20 and 5 kg/cm 2 ) respectively. It is heated to 100°C under stirring for 180 minutes. It is then cooled to ambient temperature, the gas vented and the liquid subjected to gaschromatography analysis. A dimethyl carbonate yield of 4.85 g (54 mmoles) is determined. EXAMPLE 17 60 g of methanol, 5.25 g (50 mmoles) of lithium nitrate dihydrate and 0.80 g (5 mmoles) of bromine are introduced into a 250 ml pressure vessel lined internally with Teflon (R) and fitted with a mechanical stirrer and heat transfer means. Carbon monoxide and oxygen are fed into the pressure vessel to partial pressures of 1 MPa and 0.5 MPa (10 and 5 kg/cm 2 ) respectively. It is heated to 100°C under stirring for 180 minutes. It is then cooled to ambient temperature, the gas vented and the liquid subjected to gaschromatography analysis. A dimethyl carbonate yield of 1.29 g (14.3 mmoles) is determined. EXAMPLE 18 40.8 g of methanol, 2.07 g (33 mmoles) of fuming nitric acid and 0.87 g (10 mmoles) of lithium bromide are introduced into a 250 ml pressure vessel lined internally with Teflon (R) and fitted with a mechanical stirrer and heat transfer means. Carbon monoxide and oxygen are fed into the pressure vessel to partial pressures of 2 MPa and 0.5 MPa (20 and 5 kg/cm 2 ) respectively. It is heated to 110°C under stirring for 120 minutes. It is then cooled to ambient temperature, the gas vented and the liquid subjected to gaschromatography analysis. A dimethyl carbonate yield of 3.87 g (43 mmoles) is determined. EXAMPLE 19 40 g of methanol, 3.07 g (5.6 mmoles) of ammonium cerium nitrate and 0.53 g (3.3 mmoles) of bromine are introduced into a 250 ml pressure vessel lined internally with Teflon (R) and fitted with a mechanical stirrer and heat transfer means. Carbon monoxide and oxygen are fed into the pressure vessel to partial pressures of 2 MPa and 0.5 MPa (20 and 5 kg/cm 2 ) respectively. It is heated to 100°C under stirring for 210 minutes. It is then cooled to ambient temperature, the gas vented and the liquid subjected to gaschromatography analysis. A dimethyl carbonate yield of 2.97 g (33 mmoles) is determined. EXAMPLE 20 40 g of methanol, 2.07 (33 mmoles) offuming nitric acid and 0.837 g (3.3 mmoles) of iodine are introduced into a 250 ml pressure vessel lined internally with Teflon (R) and fitted with a mechanical stirrer and heat transfer means. Carbon monoxide and oxygen are fed into the pressure vessel to partial pressures of 2 MPa and 0.5 MPa (20 and 5 kg/cm 2 ) respectively. It is heated to 100°C under stirring for 100 minutes. It is then cooled to ambient temperature, the gas vented and the liquid subjected to gaschromatography analysis. A dimethyl carbonate yield of 2.80 g (31 mmoles) is determined. EXAMPLE 21 40 g of methanol, 2.07 g (33 mmoles) of fuming nitric acid and 1.66 g (10 mmoles) of potassium iodide are introduced into a 250 ml pressure vessel lined internally with Teflon (R) and fitted with a mechanical stirrer and heat transfer means. Carbon monoxide and oxygen are fed into the pressure vessel to partial pressures of 2 MPa and 0.5 MPa (20 and 5 kg/cm 2 ) respectively. It is heated to 100°C under stirring for 75 minutes. It is then cooled to ambient temperature, the gas vented and the liquid subjected to gaschromatography analysis. A dimethyl carbonate yield of 1.42 g (15.8 mmoles) is determined. EXAMPLE 22 40 g of methanol, 3.07 g (5.6 mmoles) of (NH 4 ) 2 Ce(NO 3 ) 6 and 0.87 g (10 mmoles) of lithium bromide are introduced into a 250 ml pressure vessel lined internally with Teflon (R) and fitted with a mechanical stirrer and heat transfer means. Carbon monoxide and oxygen are fed into the pressure vessel to partial pressures of 2 MPa and 0.5 MPa (20 and 5 kg/cm 2 ) respectively. It is heated to 100°C under stirring for 150 minutes. It is then cooled to ambient temperature, the gas vented and the liquid subjected to gaschromatography analysis. A dimethyl carbonate yield of 0.23 g (2.5 mmoles) is determined. EXAMPLE 23 50 g of ethanol, 2.07 g (33 mmoles) of fuming nitric acid and 0.54 g (3.3 mmoles) of bromine are introduced into a 250 ml pressure vessel lined internally with Teflon (R) and fitted with a mechanical stirrer and heat transfer means. Carbon monoxide and oxygen are fed into the pressure vessel to partial pressures of 2 MPa and 0.5 MPa (20 and 5 kg/cm 2 ) respectively. It is heated to 100°C under stirring for 45 minutes. It is then cooled to ambient temperature, the gas vented and the liquid subjected to gaschromatography analysis. A diethyl carbonate yield of 1.21 g (15 mmoles) is determined. EXAMPLE 24 50 g of methanol, 0.15 g (2.1 mmoles) of sodium nitrite and 4.95 g (29 mmoles) of hydrobromic acid in 48 wt% aqueous solution are introduced into a 250 ml pressure vessel lined internally with Teflon (R) and fitted with a mechanical stirrer and heat transfer means. Carbon monoxide and oxygen are fed into the pressure vessel to partial pressures of 2 MPa and 0.7 MPa (20 and 7 kg/cm 2 ) respectively. It is heated to 71°C under stirring for 135 minutes. It is then cooled to ambient temperature, the gas vented and the liquid subjected to gaschromatography analysis. A dimethyl carbonate yield of 4.95 g (55 mmoles) is determined. Three successive additions each of 0.15 g (2.1 mmoles) of sodium nitrite are made, after each addition pressurizing with carbon monoxide and oxygen to partial pressures of 2 MPa and 0.8 MPa (20 and 8 kg/cm 2 ) respectively, and heating to 70°C for the time indicated in the following table, which also shows the results obtained in the three successive additions. Addition 1st 2nd 3rd Time (min) 130 170 165 DMC (mmoles) 56 56 45 (grams) 5.04 5.4 4.05 DMC total (mmoles) 111 167 212 (grams) 9.99 15.03 19.02 DMC = dimethyl carbonate EXAMPLE 25 55 g of methanol, 0.9 g (8.7 mmoles) of butyl nitrite and 4.95 g (29 mmoles) of hydrobromic acid in 48 wt% aqueous solution are introduced into a 250 ml pressure vessel lined internally with Teflon (R) and fitted with a mechanical stirrer and heat transfer means. Carbon monoxide and oxygen are fed into the pressure vessel to partial pressures of 2 MPa and 0.7 MPa (20 and 7 kg/cm 2 ) respectively. It is heated to 90°C under stirring for 120 minutes. It is then cooled to ambient temperature, the gas vented and the liquid subjected to gaschromatography analysis. A dimethyl carbonate yield of 8.91 g (99 mmoles) is determined. EXAMPLE 26 55 g of methanol, 0.43 g (1.1 mmoles) of gallium trinitrate and 4.95 g (29 mmoles) of hydrobromic acid in 48 wt% aqueous solution are introduced into a 250 ml pressure vessel lined internally with Teflon (R) and fitted with a mechanical stirrer and heat transfer means. Carbon monoxide and oxygen are fed into the pressure vessel to partial pressures of 2 MPa and 0.7 MPa (20 and 7 kg/cm 2 ) respectively. It is heated to 80°C under stirring for 140 minutes. It is then cooled to ambient temperature, the gas vented and the liquid subjected to gaschromatography analysis. A dimethyl carbonate yield of 5.49 g (61 mmoles) is determined. EXAMPLE 27 55.2 g of methanol, 0.15 g (2.1 mmoles) of sodium nitrite, 2.08 g (24 mmoles) of lithium bromide and 1.32 g (7.8 mmoles) of hydrobromic acid in 48 wt% aqueous solution are introduced into a 250 ml pressure vessel lined internally with Teflon (R) and fitted with a mechanical stirrer and heat transfer means. Carbon monoxide and oxygen are fed into the pressure vessel to partial pressures of 2 MPa and 0.7 MPa (20 and 7 kg/cm 2 ) respectively. It is heated to 80°C under stirring for 140 minutes. It is then cooled to ambient temperature, the gas vented and the liquid subjected to gaschromatography analysis. A dimethyl carbonate yield of 5.58 g (62 mmoles) is determined. EXAMPLE 28 61.29 g of methanol, 5.68 g (75 mmoles) of N 2 O 3 and 4.95 g (29 mmoles) of hydrobromic acid in 48 wt% aqueous solution are introduced into a 250 ml pressure vessel lined internally with Teflon (R) and fitted with a mechanical stirrer and heat transfer means. Carbon monoxide and oxygen are fed Into the pressure vessel to partial pressures of 2 MPa and 0.7 MPa (20 and 7 kg/cm 2 ) respectively. It is heated to 85°C under stirring for 240 minutes. It is then cooled to ambient temperature, the gas vented and the liquid subjected to gaschromatography analysis. A dimethyl carbonate yield of 45.25 g (503 mmoles) is determined. EXAMPLE 29 48.5 g of methanol, 1.43 g (19 mmoles) of N 2 O 3 and 1.68 g (10 mmoles) of hydrobromic acid in 48 wt% aqueous solution are introduced into a 250 ml pressure vessel lined internally with Teflon (R) and fitted with a mechanical stirrer and heat transfer means. Carbon monoxide and oxygen are fed into the pressure vessel to partial pressures of 2 MPa and 0.7 MPa (20 and 7 kg/cm 2 ) respectively. It is heated to 80°C under stirring for 75 minutes. It is then cooled to ambient temperature, the gas vented and the liquid subjected to gaschromatography analysis. A dimethyl carbonate yield of 6.03 g (67 mmoles) is determined. EXAMPLE 31 40 g of methanol, 2.07 g (33 mmoles) of fuming nitric acid and 0.54 g (3.3 mmoles) of bromine are introduced into a 250 ml pressure vessel lined internally with Teflon (R) and fated with a mechanical stirrer and heat transfer means. Carbon monoxide is fed into the pressure vessel to a pressure of 2.5 MPa (25 kg/cm 2 ). It is heated to 100°C under stirring for 120 minutes. It is then cooled to ambient temperature, the gas vented and the liquid subjected to gaschromatography analysis. A dimethyl carbonate yield of 2.88 g (32 mmoles) is determined. EXAMPLE 32 60 g of methanol, 5.25 g (50 mmoles) of lithium nitrate dihydrate and 0.809 g (5.5 mmoles) of bromine are introduced into a 250 ml pressure vessel lined internally with Teflon (R) and fitted with a mechanical stirrer and heat transfer means. Carbon monoxide is fed into the pressure vessel to a pressure of 1 MPa (10 kg/cm 2 ). It is heated to 100°C under stirring for 180 minutes. It is then cooled to ambient temperature, the gas vented and the liquid subjected to gaschromatography analysis. A dimethyl carbonate yield of 1.29 g (14.3 mmoles) is determined. EXAMPLE 33 60 g of methanol, 9.71 g (100 moles) of hydrogen peroxide in a 35 wt% aqueous solution and 1.61 g (9.58mmoles) of hydrobromic acid in 48 wt% aqueous solution are introduced into a 250 ml pressure vessel lined internally with Teflon (R) and fitted with a mechanical stirrer and heat transfer means. Carbon monoxide is fed into the pressure vessel to a pressure of 3 MPa (30 kg/cm 2 ). It is heated to 80°C under stirring for 75 minutes. It is then cooled to ambient temperature, the gas vented and the liquid subjected to gaschromatography analysis. A dimethyl carbonate yield of 3.15 g (35 mmoles) is determined. EXAMPLE 34 60 g of methanol, 9.00 g (80 mmoles) of tert-butyl hydroperoxide in an 80 wt% soiution in di-tert-butyl peroxide and 1.76 g (10.5 mmoles) of hydrobromic acid in 48 wt% aqueous solution are introduced into a 250 ml pressure vessel lined internally with Teflon (R) and fitted with a mechanical stirrer and heat transfer means. Carbon monoxide is fed into the pressure vessel to a pressure of 3 MPa (30 kg/cm 2 ). It is heated to 65°C under stirring for 120 minutes. It is then cooled to ambient temperature, the gas vented and the liquid subjected to gaschromatography analysis. A dimethyl carbonate yield of 2.88 g (32 mmoles) is determined. EXAMPLE 35 60 g of methanol, 12.2 g (51 moles) of sodium peroxydisulphate and 1.68 g (10 mmoles) of hydrobromic acid in 48 wt% aqueous solution are introduced into a 250 ml pressure vessel lined internally with Teflon (R) and fitted with a mechanical stirrer and heat transfer means. Carbon monoxide is fed into the pressure vessel to a pressure of 3 MPa (30 kg/cm 2 ). It is heated to 110°C under stirring for 105 minutes. It is then cooled to ambient temperature, the gas vented and the liquid subjected to gaschromatography analysis. A dimethyl carbonate yield of 1.35 g (15 mmoles) is determined. EXAMPLE 36 70 g of methanol, 8.9 g (50 moles) of N-bromosuccinimide and 1.68 g (10 mmoles) of hydrobromic acid in 48 wt% aqueous solution are introduced into a 250 ml pressure vessel lined internally with Teflon (R) and fitted with a mechanical stirrer and heat transfer means. Carbon monoxide is fed into the pressure vessel to a pressure of 3 MPa (30 kg/cm 2 ). It is heated to 70°C under stirring for 120 minutes. It is then cooled to ambient temperature, the gas vented and the liquid subjected to gaschromatography analysis. A dimethyl carbonate yield of 4.23 g (47 mmoles) is determined.

Claims: An oxidative carbonylation process for preparing an organic carbonate having the general formula: or a cyclic organic carbonate having the general formula: wherein: R is a C 1 -C 10 linear or branched alkyl, or a C 5 -C 6 cycloalkyl, and R' is a C 2 -C 5 linear or branched alkylene, by reacting an alcohol R-OH, or a diol HO-R'-OH, respectively, with carbon monoxide in the liquid phase at a temperature of from 25°C to 200°C, the carbon monoxide pressure being of from 0.1 MPa to 10 MPa (1 kg/cm 2 to 100 kg/cm 2 ), characterized in that said reaction is carried out in the presence of a halogen selected from chlorine, bromine and iodine, or in the presence of said halogen and/or a halide ion selected from the chloride, the bromide and the iodide ion and an oxidizing agent capable of oxidizing said halide ion to its corresponding halogen, with the proviso that metals of the platinum group and copper in their metallic form or in the form of their salts are absent. A process as claimed in claim 1, characterised in that R-OH is chosen from methanol, ethanol, n-propanol, isopropanol, n-butanol, iso-butanol, 2-ethylhexanol and cyclohexanol, and is preferably methanol; and HO-R'-OH is chosen from ethylene glycol and propylene glycol. A process as claimed in claim 1, characterised in that the halogen is chosen from bromine and iodine and is preferably bromine. A process as claimed in claim 1, characterised in that the halide is chosen from bromide and iodide and is preferably bromide. A process as claimed in claim 1, characterised in that the oxidizing agent is chosen from: a) hydrogen peroxide, an organic percompound, N-bromosuccinimide, a nitrogen oxide, nitrous acid, nitric acid, a sulphur peracid, or a metal salt or an ester of said acids and peracids; or b) an oxidizing system formed from oxygen and an oxygenated nitrogen compound chosen from nitrogen oxides, nitrous and nitric acids, and the salts or esters of said acids. A process as claimed in claim 5, characterised in that the oxidizing agent (a) is chosen from hydrogen peroxide with a concentration of the order of 35-60% by weight; organic peroxides, hydroperoxides and peresters, and preferably tert-butyl hydroperoxide and di-tert-butyl peroxide; NO 2 , (N 2 O 4 ), N 2 O 3 and N 2 O 5 ; nitric acid having a concentration of about 67% by weight or more; suitable nitrate and nitrite salts of alkaline or alkaline earth metals or ammonium; alkyl esters of nitrous and nitric acids; and peroxydisulphuric acid salts of alkaline or alkaline earth metals. A process as claimed in claim 5, characterised in that in the oxidizing system (b) the oxygenated nitrogen compound is chosen from NO, NO 2 , (N 2 O 4 ), N 2 O 3 and N 2 O 5 ; nitric acid having a concentration of about 67% by weight; nitrate and nitrite salts of alkaline or alkaline earth metals, ammonium, cerium and gallium. A process as claimed in claim 1, characterised by using a halogen in the absence of an oxidizing agent, and operating at a temperature of between 25 and 200°C, and preferably between 50 and 150°C, under a carbon monoxide pressure of between 0.1 MPa and 10 MPa (1 and 100 kg/cm 2 ) for a reaction time of between 1 and 240 minutes, and preferably of the order of 5-120 minutes. A process as claimed in claim 8, characterised by operating in the presence of a base able to block the hydrohalogen acid which forms as reaction co-product. A process as claimed in claim 1, characterised by using a halogen and/or a halide ion, in the presence of the oxidizing agent (a), operating at a halogen or halide ion concentration of between 10 -3 and 1 mole/litre and an oxidizing agent (a) concentration of between 10 -1 and 5 moles/litre of alcohol, with a mole ratio generally of between 1:100 and 1:1, at a temperature of between 25 and 200°C under a carbon monoxide pressure of between 0.1 MPa and 10 Mpa (1 and 100 kg/cm 2 ) for a reaction time of between about 1 and about 240 minutes. A process as claimed in claim 10, characterised in that the halogen or halide ion concentration varies from 10 -2 to 0.5 moles/litre, the oxidizing agent concentration varies from 10 -1 to 2 moles/litre of alcohol, the molar ratio of halogen or halide ion to oxidizing agent varies from 1:50 to 1:1, the temperature varies from 50 to 120°C and the carbon monoxide pressure varies from 2 to 100 kg/cm 2 . A process as claimed in claim 1, characterised by using a halogen and/or a halide ion, in the presence of the oxidizing system (b), operating at a halogen or halide ion concentration of between 10 -3 and 2 moles/litre of alcohol and an oxygenated nitrogen compound concentration of between 10 -3 and 2 molesllitre of alcohol, their molar ratio being between 500:1 and 0.002:1, at a temperature of between 25 and 200°C under a total carbon monoxide plus oxygen pressure of between 0.1 MPa and 10 MPa (1 and 100 kg/cm 2 ) and with ratio of oxygen partial pressure to carbon monoxide partial pressure of between 0.005:1 and 500:1. A process as claimed in claim 12, characterised in that the halogen or halide ion concentration varies from 10 -2 to 1 mole/litre of alcohol, the oxygenated nitrogen compound concentration varies from 10 -2 to 1 mole/litre of alcohol, the molar ratio of halogen or halide ion to the oxygenated nitrogen compound varies from 50:1 to 0.02:1, the temperature varies from 50 to 120°C, the total oxygen plus carbon monoxide pressure varies from 0.2 MPa and 10 MPa (2 to 100 kg/cm 2 ), the ratio of oxygen partial pressure to carbon monoxide partial pressure varies from 0.01:1 to 1:1, and the reaction time varies from about 1 to about

Inventors: DELLEDONNE DANIELE, RIVETTI FRANCO, ROMANO UGO, DELLEDONNE, DANIELE, RIVETTI, FRANCO, ROMANO, UGO
Applicants: ENICHEM SPA, ENICHEM S.P.A.
Application year: 1991
Main classification: C07C69
IPC codes: C07C69, C07C68, B01J23, B01J31, C07B61, C07D317