Process for preparing organic carbonates

Organic carbonates: ##STR1## and cyclic organic carbonates: ##STR2## are prepared by reacting an alcohol (R--OH), or respectively a diol (HO--R'--OH), with carbon monoxide, in the presence of: PA0 a halogen, or PA0 a halogen and/or a halide ion and an oxidizing agent.

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, "Encyclopedia 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 (U.S. Pat. No. 4,361,519; Germany 3,212,535; GB 
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 (U.S. Pat. 
Nos. 3,846,468; 4,218,391; 4,318,862; 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. 
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 a process for 
preparing an organic carbonate: 
##STR3## 
or a cyclic organic carbonate: 
##STR4## 
by reacting an alcohol R--OH, or respectively a diol HO--R'--OH, with 
carbon monoxide (CO), where: 
R is a C.sub.1 -C.sub.10 linear or branched alkyl radical; or a C.sub.5 
-C.sub.8 cycloalkyl radical; and 
R' is a C.sub.2 -C.sub.5 linear or branched alkylene radical; the process 
being characterised by conducting the reaction in the liquid phase at a 
temperature of between 25.degree. and 200.degree. C. under a carbon 
monoxide pressure of between 1 and 100 kg/cm.sup.2, and: 
in the presence of a halogen chosen from chlorine, bromine or iodine; or 
in the presence of such a halogen and/or a corresponding halide ion and an 
oxidizing agent able to oxidize the halide ion to halogen. 
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-iso-propyl 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: 
##STR5## 
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: 
##STR6## 
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'".sub.4 N.sup.+ X.sup.- and R'".sub.4 P.sup.+ X.sup.- 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-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. 
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.sub.2, (N.sub.2 O.sub.4), N.sub.2 O.sub.3 and N.sub.2 O.sub.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.sub.2, (N.sub.2 O.sub.4), N.sub.2 
O.sub.3 and N.sub.2 O.sub.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: 
EQU 2X.sup.- +2H.sup.+ +1/2O.sub.2 .fwdarw.X.sub.2 +H.sub.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.degree. and 200.degree. C. under a carbon monoxide pressure generally 
between 1 and 100 kg/cm.sup.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.degree. and 
200.degree. C. under a carbon monoxide pressure of between 1 and 100 
kg/cm.sup.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.degree. and 150.degree. 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 co-product 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. According to a particular embodiment, a 
metal, compound or complex of an element of group VIII of the periodic 
table is added to the reaction mixture as catalyst. The use of such a 
catalyst, usable also in supported form on an inert solid support if a 
metal, enables the reaction to be conducted under milder temperature and 
pressure conditions. The preferred elements of group VIII are palladium, 
rhodium and platinum, such as lithium and palladium chloride and platinum 
chloride. The compound or complex is preferably added in a quantity of 
0.01-1 mol % on the halogen. 
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.sup.-3 
and 1 mole/liter and the oxidizing agent concentration between 10.sup.-1 
and 5 moles/liter of alcohol, their mole ratio generally being between 
1:100 and 1:1. The reaction is conducted at a temperature of between 
25.degree. and 200.degree. C. under a carbon monoxide pressure of between 
1 and 100 kg/cm.sup.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.sup.-2 to 0.5 moles/liter, the oxidizing agent concentration 
varies from 10.sup.-1 to 2 moles/liter 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.degree. to 120.degree. C. and the carbon 
monoxide pressure varies from 2 to 100 kg/cm.sup.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.sup.-3 
and 2 moles/liter of alcohol and the oxygenated nitrogen compound 
concentration between 10.sup.-3 and 2 moles/liter 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.degree. and 
200.degree. C. under a total carbon monoxide plus oxygen pressure of 
between 1 and 100 kg/cm.sup.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.sup.-2 
to 1 mole/liter of alcohol, the oxygenated nitrogen compound concentration 
varies from 10.sup.-2 to 1 mole/liter 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.degree. to 120.degree. C., the 
total oxygen plus carbon monoxide pressure varies from 2 to 100 
kg/cm.sup.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 a preferred 
embodiment a metal, compound or complex of an element of group VIII of the 
periodic table is added to the reaction mixture as catalyst to increase 
the reaction rate. The preferred elements of group VIII are palladium, 
rhodium and platinum, such as lithium and palladium chloride and platinum 
chloride. Such a catalyst is conveniently used in a quantity of 0.01-1 mol 
% on the halogen or halide ion. 
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.RTM. and fitted with a 
mechanical stirrer and heat transfer means. Carbon monoxide is fed into 
the pressure vessel to a pressure of 10 kg/cm.sup.2. It is heated to 
85.degree. 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.RTM. and fitted with a 
mechanical stirrer and heat transfer means. Carbon monoxide is fed into 
the pressure vessel to a pressure of 10 kg/cm.sup.2. It is heated to 
110.degree. 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 3 kg/cm.sup.2. It is heated to 50.degree. 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.RTM. 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. 
TABLE 1 
______________________________________ 
Example No. 3 4 5 
______________________________________ 
Temp. (.degree.C.) 
50 70 70 
P(CO) (kg/cm.sup.2) 
3 10 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.RTM. and fitted with a mechanical stirrer and heat 
transfer means. Carbon monoxide is fed into the pressure vessel to a 
pressure of 10 kg/cm.sup.2. It is heated to 100.degree. 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.RTM. and fitted with a 
mechanical stirrer and heat transfer means. Carbon monoxide is fed into 
the pressure vessel to a pressure of 10 kg/cm.sup.2. It is heated to 
85.degree. 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 9 
60 g of methanol, 3.25 g (20 mmoles) of bromine, 13 mg (0.05 mmoles) of 
lithium palladium chloride (Li.sub.2 PdCl.sub.4) and 2.12 g (20 mmoles) of 
sodium carbonate 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 3 kg/cm.sup.2. It is heated to 
50.degree. 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 17.4 mmoles (1.57 g) is 
determined, equal to 87% on the moles of bromine introduced. 
EXAMPLE 10 
60 g of methanol, 5.04 g (20 mmoles) of iodine, 13 mg (0.05 mmoles) of 
lithium tetrachloropalladate (Li.sub.2 PdCl.sub.4) and 2.12 g (20 mmoles) 
of sodium carbonate are introduced into a 250 ml glass pressure vessel 
lined internally with Teflon.RTM. and fitted with a mechanical stirrer and 
heat transfer means. Carbon monoxide is fed into the pressure vessel to a 
pressure of 3 kg/cm.sup.2. It is heated to 50.degree. C. under stirring 
for 220 minutes. It is then cooled to ambient temperature, the gas vented 
and the liquid subjected to gaschromatography analysis. 
A dimethyl carbonate yield of 17.3 mmoles (1.56 g) is determined, equal to 
86% on the moles of iodine introduced. 
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.RTM. and 
fitted with a mechanical stirrer and heat transfer means. Carbon monoxide 
is fed into the pressure vessel to a pressure of 10 kg/cm.sup.2. It is 
heated to 85.degree. 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 12 
60 g of methanol, 1.0 g (6.25 mmoles) of bromine and 13 mg (0.05 mmoles) of 
lithium tetrachloropalladate (Li.sub.2 PdCl.sub.4) are introduced into a 
250 ml glass pressure vessel lined internally with Teflon.RTM. and fitted 
with a mechanical stirrer and heat transfer means. Carbon monoxide is fed 
into the pressure vessel to a pressure of 10 kg/cm.sup.2. It is heated to 
100.degree. C. under stirring for 20 minutes. It is then cooled to ambient 
temperature, the gas vented and the liquid subjected to gaschromatography 
analysis. A dimethyl carbonate yield of 5.74 mmoles (0.516 g) is 
determined, equal to 92% 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.RTM. and fitted with a mechanical stirrer and heat 
transfer means. Carbon monoxide is fed into the pressure vessel to a 
pressure of 30 kg/cm.sup.2. It is heated to 85.degree. 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 14 
60 g of methanol, 0.8 g (5 mmoles) of bromine and 31 mg (0.11 mmoles) of 
platinum chloride (PtCl.sub.2) are introduced into a 250 ml glass pressure 
vessel lined internally with Teflon.RTM. and fitted with a mechanical 
stirrer and heat transfer means. Carbon monoxide is fed into the pressure 
vessel to a pressure of 20 kg/cm.sup.2. It is heated to 100.degree. 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 4.7 mmoles (0.42 g) is determined, equal to 
94% 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.RTM. and fitted with a mechanical stirrer and heat 
transfer means. Carbon monoxide and oxygen are fed into the pressure 
vessel to partial pressures of 20 and 5 kg/cm.sup.2 respectively. It is 
heated to 110.degree. 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.RTM. and fitted with a mechanical stirrer and heat 
transfer means. Carbon monoxide and oxygen are fed into the pressure 
vessel to partial pressures of 20 and 5 kg/cm.sup.2 respectively. It is 
heated to 100.degree. 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.RTM. and fitted with a mechanical stirrer and heat 
transfer means. Carbon monoxide and oxygen are fed into the pressure 
vessel to partial pressures of 10 and 5 kg/cm.sup.2 respectively. It is 
heated to 100.degree. 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.RTM. and fitted with a mechanical stirrer and 
heat transfer means. Carbon monoxide and oxygen are fed into the pressure 
vessel to partial pressures of 20 and 5 kg/cm.sup.2 respectively. It is 
heated to 110.degree. 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.RTM. and fitted with a mechanical stirrer and heat 
transfer means. Carbon monoxide and oxygen are fed into the pressure 
vessel to partial pressures of 20 and 5 kg/cm.sup.2 respectively. It is 
heated to 100.degree. 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 g (33 mmoles) of fuming nitric acid and 0.837 g (3.3 
mmoles) of iodine are introduced into a 250 ml pressure vessel lined 
internally with Teflon.RTM. and fitted with a mechanical stirrer and heat 
transfer means. Carbon monoxide and oxygen are fed into the pressure 
vessel to partial pressures of 20 and 5 kg/cm.sup.2 respectively. It is 
heated to 100.degree. 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.RTM. and fitted with a mechanical stirrer and 
heat transfer means. Carbon monoxide and oxygen are fed into the pressure 
vessel to partial pressures of 20 and 5 kg/cm.sup.2 respectively. It is 
heated to 100.degree. 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.sub.4).sub.2 
Ce(NO.sub.3).sub.6 and 0.87 g (10 mmoles) of lithium bromide are 
introduced into a 250 ml pressure vessel lined internally with Teflon.RTM. 
and fitted with a mechanical stirrer and heat transfer means. Carbon 
monoxide and oxygen are fed into the pressure vessel to partial pressures 
of 20 and 5 kg/cm.sup.2 respectively. It is heated to 100.degree. 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.RTM. and fitted with a mechanical stirrer and heat 
transfer means. Carbon monoxide and oxygen are fed into the pressure 
vessel to partial pressures of 20 and 5 kg/cm.sup.2 respectively. It is 
heated to 100.degree. 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.RTM. and fitted 
with a mechanical stirrer and heat transfer means. Carbon monoxide and 
oxygen are fed into the pressure vessel to partial pressures of 20 and 7 
kg/cm.sup.2 respectively. It is heated to 71.degree. 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 20 and 8 kg/cm.sup.2 respectively, and heating to 
70.degree. 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.RTM. and fitted 
with a mechanical stirrer and heat transfer means. Carbon monoxide and 
oxygen are fed into the pressure vessel to partial pressures of 20 and 7 
kg/cm.sup.2 respectively. It is heated to 90.degree. 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.RTM. and fitted 
with a mechanical stirrer and heat transfer means. Carbon monoxide and 
oxygen are fed into the pressure vessel to partial pressures of 20 and 7 
kg/cm.sup.2 respectively. It is heated to 80.degree. 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.RTM. and fitted with a mechanical stirrer and 
heat transfer means. Carbon monoxide and oxygen are fed into the pressure 
vessel to partial pressures of 20 and 7 kg/cm.sup.2 respectively. It is 
heated to 80.degree. 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.sub.2 O.sub.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.RTM. and fitted 
with a mechanical stirrer and heat transfer means. Carbon monoxide and 
oxygen are fed into the pressure vessel to partial pressures of 20 and 7 
kg/cm.sup.2 respectively. It is heated to 85.degree. 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.sub.2 O.sub.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.RTM. and fitted 
with a mechanical stirrer and heat transfer means. Carbon monoxide and 
oxygen are fed into the pressure vessel to partial pressures of 20 and 7 
kg/cm.sup.2 respectively. It is heated to 80.degree. 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 30 
50 g of methanol, 1.37 g (18 mmoles) of N.sub.2 O.sub.3, 1.68 g (10 mmoles) 
of hydrobromic acid in 48 wt % aqueous solution and 26.2 mg (0.1 mmoles) 
of lithium tetrachloropalladate (Li.sub.2 PdCl.sub.4) are introduced into 
a 250 ml pressure vessel lined internally with Teflon.RTM. and fitted with 
a mechanical stirrer and heat transfer means. Carbon monoxide and oxygen 
are fed into the pressure vessel to partial pressures of 20 and 7 
kg/cm.sup.2 respectively. It is heated to 80.degree. C. under stirring for 
20 minutes. It is then cooled to ambient temperature, the gas vented and 
the liquid subjected to gaschromatography analysis. 
A dimethyl carbonate yield of 5.13 g (57 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.RTM. and fitted with a mechanical stirrer and heat 
transfer means. Carbon monoxide is fed into the pressure vessel to a 
pressure of 25 kg/cm.sup.2. It is heated to 100.degree. 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.RTM. and fitted with a mechanical stirrer and 
heat transfer means. Carbon monoxide is fed into the pressure vessel to a 
pressure of 10 kg/cm.sup.2. 
It is heated to 100.degree. 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 (9.58 mmoles) of hydrobromic acid in 48 wt % 
aqueous solution are introduced into a 250 ml pressure vessel lined 
internally with Teflon.RTM. and fitted with a mechanical stirrer and heat 
transfer means. Carbon monoxide is fed into the pressure vessel to a 
pressure of 30 kg/cm.sup.2. It is heated to 80.degree. 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 % solution 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.RTM. and fitted with a 
mechanical stirrer and heat transfer means. Carbon monoxide is fed into 
the pressure vessel to a pressure of 30 kg/cm.sup.2. It is heated to 
65.degree. 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.RTM. and fitted 
with a mechanical stirrer and heat transfer means. Carbon monoxide is fed 
into the pressure vessel to a pressure of 30 kg/cm.sup.2. It is heated to 
110.degree. 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.RTM. and fitted 
with a mechanical stirrer and heat transfer means. Carbon monoxide is fed 
into the pressure vessel to a pressure of 30 kg/cm.sup.2. It is heated to 
70.degree. 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.