Preparation of cyclic carbonate

Abstract: A process for preparing a cyclic carbonate, which comprises reacting at least one 1,3-diol or 1,2-diol with a dialkylcarbonate in the presence of a basic catalyst.

Description: This invention relates to a process for preparing cyclic carbonates from diols. It is well known to prepare cyclic carbonates from diols. For example, JP-A-58-49377 discloses a process for preparing 1-isopropyl-2,2-dimethyl-1,3-propylene carbonate by heating 2,2,4-trimethyl-1,3-pentanediol and a dialkylcarbonate in the presence of a conventional esterifying catalyst such as para-toluenesulfonic acid to effect ester exchange reaction. The typical dialkylcarbonate used in examples is diethylcarbonate. We carried out a similar reaction in the presence of para-toluenesulfonic acid catalyst by substituting dimethylcarbonate for the diethylcarbonate. There was obtained only a small amount of cyclic carbonate. It was found that the reaction does not proceed smoothly with every dialkylcarbonate when a cyclic carbonate is prepared by reaction of a diol with a dialkylcarbonate in the presence of an acid catalyst such as para-toluenesulfonic acid. JP-A-56-133246 discloses reacting a diallyl carbonate ester with a polyhydric alcohol such as diethylene glycol in the presence of a basic catalyst to form an allyl carbonate ester of a polyhydric alcohol. The carbonate obtained by this process is a chain carbonate such as ethylene glycol bisallyl carbonate. There are obtained no cyclic carbonates. Houben-Weyl, Methoden der organischen Chemie, volume E4, 1983, pages 88 to 92 describes the preparation of cyclic carbonates by reacting a 1,2-diol or 1,3-diol with a dialkylcarbonate in the presence of a basic catalyst. J. Am. Chem. Soc. 80, 1958, 4596-4599 discloses that reaction of a 1,3-propanediol with diethylcarbonate often results in the formation of a polymeric by-product which can be converted into the cyclic monomer by heating. The present invention seeks to provide a process for preparing a cyclic carbonate from a diol in a high yield with high selectivity. According to the present invention, there is provided a process for preparing a cyclic carbonate, which comprises (a) reacting at least one 1,3-diol or 1,2-diol with dimethylcarbonate in the presence of a basic catalyst at atmospheric pressure or above, (b) subjecting the reaction mixture thus obtained to heat aging at 150° to 200°C under a pressure of 13.3 to 53300 Pa (0.1 to 400 mmHg) in the presence of a basic catalyst, and (c) isolating the resulting cyclic carbonate from the mixture. In one preferred embodiment of the present invention, the basic catalyst used in step (a) and/or step (b) is a basic compound containing an alkali or alkaline earth metal. Most often, the basic catalyst used in heat aging step (b) is the same as used in reaction step (a). Heat aging step (b) is preferably carried out for a time of from 1/2 to 5 hours. More preferably heat aging step (b) is carried out while removing from the system the dialkyl carbonate generated during step (b). The presence of a basic catalyst in reaction step (a) is essential for the cyclization reaction to proceed. The basic catalysts used herein include basic compounds of alkali metals and alkaline earth metals, for example lithium hydroxide, sodium hydroxide, potassium hydroxide, cesium hydroxide, sodium hydrogen carbonate, potassium carbonate, sodium methoxide, sodium ethoxide, sodium phenoxide, sodium acetate, sodium hydride, metallic sodium, sodium amide, butyl lithium and calcium hydroxide; amines such as imidazole, ethylamine and 1,8-diazabicyclo[5.4.0]-undecene-7 (DBU); and basic ion-exchange resins. Higher yields of the end product, cyclic carbonate are expected with the use of strongly basic catalysts among others. Preferred basic catalysts are basic compounds of alkali metals and alkaline earth metals, for example sodium hydroxide, potassium hydroxide, sodium methoxide and potassium methoxide. Most preferred are sodium hydroxide and sodium methoxide. The basic catalyst is preferably added to the reaction mixture such that 0.0001 to 0.1 mol, more preferably 0.001 to 0.05 mol of basic catalyst is present per mol of diol. In the practice of the present invention, the reaction may generally be carried out without solvent. If necessary, any desired solvent may be used insofar as it does not adversely affect the reaction. The reaction between diol and dimethylcarbonate may be carried out under approximately atmospheric pressure or above. Usually, the reaction is carried out under ambient or atmospheric pressure. The term approximately atmospheric pressure used herein is a pressure approximate to the atmospheric pressure and having no adverse affect on the reaction and generally encompasses pressures in the range of atmospheric pressure ± 1.33 kPa (± 10 mmHg). Pressure may be applied during the reaction. The level of the applied pressure is not critical although generally the upper limit is 1.01 MPa (10 atmospheres). In the practice of the present invention, it is preferred to heat the reaction mixture in step (a) to at least the temperature at which the alcohol formed from the reaction is distilled off. The reaction forms methanol which forms an azeotrope with unreacted dimethylcarbonate. It is desired to azeotropically distil the methanol out of the system during the reaction. The reaction temperature varies with the type of diol used, but generally is from 60° to 180°C. The reaction time generally ranges from 1/2 to 20 hours. When the reaction of diol with dimethylcarbonate is carried out under a pressure lower than approximately atmospheric pressure, one reactant, dimethylcarbonate will be distilled off at a low temperature. It may then be inconvenient to maintain the reaction temperature in the above-mentioned range. For this reason, the reaction preferably is carried out under approximately atmospheric pressure or under applied pressure. In the practice of the present invention, the reactor may be charged with an entire amount of dimethylcarbonate from the first. It is also possible to charge the reactor with incremental amounts of dimethylcarbonate. The reaction may be carried out under the above-mentioned conditions while maintaining the dimethylcarbonate under reflux. However, as described above, it is desired to distil the resulting alcohol such as methanol out of the system during the reaction. The diol used herein is a 1,3-diol or 1,2-diol. Examples of the 1,3-diols include hydrocarbon diols such as 2,2,4-trimethyl-1,3-pentanediol (abbreviated as TMPD), 1,3-propanediol, and 1,3-butanediol. Examples of the 1,2-diols include hydrocarbon diols such as ethylene glycol, propylene glycol, 2,3-butanediol, and 1,2-butanediol. Preferred diols are TMPD and 2,3-butanediol with TMPD being most preferred. In the practice of the present invention, the reaction mixture preferably contains the diol and the dimethylcarbonate in such a proportion that 0.1 to 10 mol, more preferably 1 to 2 mol, of dimethylcarbonate is present per mol of diol. The process of the present invention produces the cyclic carbonate 1-isopropyl-2,2-dimethyl-1,3-propylene carbonate (abbreviated as HCC). If the cyclic carbonate is recovered from the reaction mixture in which 1,3-diol or 1,2-diol has been reacted with dimethylcarbonate by distilling the cyclic carbonate followed by recrystallization the cyclic carbonate is recovered in a low yield because the reaction mixture contains a large amount of by-products. In accordance with the invention therefore it is necessary to carry out heat aging under reduced pressure on the reaction mixture before the cyclic carbonate is isolated therefrom. Then a cyclic carbonate of higher purity is obtained in higher yields. The heat aging step (b) may be carried out in a simple manner as described below. The reaction mixture is subjected to heat aging at 150° to 200°C under a pressure of 13.3 to 53300 Pa (0.1 to 400 mmHg) in the presence of the basic catalyst, that is, without removing the basic catalyst which has been used in the reaction between diol and dimethylcarbonate. If necessary, an additional amount of the same or different basic catalyst may be introduced. The heat aging may be carried out while removing dimethylcarbonate generated from by-products in the reaction mixture. While the reaction mixture contains by-products as impurities, heat aging of the reaction mixture converts the by-products into the intended cyclic carbonate. This conversion was discovered by the present inventors. The temperature can depend on the type of diol and should in general be below the boiling point of the desired cyclic carbonate at the pressure employed. The aging time generally is from 1/2 to 5 hours. By carrying out the heat aging step (b), by-products in the reaction mixture can be very efficiently converted into cyclic carbonate when the temperature and pressure are within the above-mentioned range. The heat aging under vacuum of the reaction mixture converts by-products into the intended cyclic carbonate, and dimethylcarbonate is released from the by-products. Thus the heat aging step (b) of the reaction mixture is preferably carried out while removing dimethylcarbonate from the system. The cyclic carbonate is isolated in step (c) in significantly increased yield and purity, after the reaction mixture has been subjected to the heat aging step (b). These improvements are illustrated by referring to an example of reaction using TMPD as a diol. Analysis of the reaction mixture by gas chromatography before it is heat aged gives the results shown in Fig 1. At least two peaks indicative of by-products (which are designated as unk-1 and unk-2 in Table 1 and Fig 1.) appear in addition to the peak indicative of the intended cyclic carbonate. Considering the results of NMR and gas mass analysis together, we suppose that these by-products have the structures: for unk-2. The reaction mixture contains a considerably amount of by-products. So as to obtain the cyclic carbonate in a high yield with high purity when it is isolated from the as-reacted mixture, the reaction mixture was subjected to heat aging at a reduced pressure as mentioned above. It was observed that the peaks of unk-1 and unk-2 were decreased and the peak of the intended cyclic carbonate was increased upon heat aging under reduced pressure. It was also found that dimethylcarbonate, used as the reactant, was generated from the by-products upon heat aging. These results suggest that heat aging of the reaction mixture is effective in converting by-products therein into the intended cyclic carbonate. The present invention is based on this finding. We have also found that effective conversion is not accomplished unless the heat aging is conducted in the presence of a basic catalyst. This means that the basic catalyst which is used in the reaction step prior to heat aging need not be removed by filtration (in the case of a solid basic catalyst), neutralization, or washing. The cyclic carbonate preparation process of the present invention is thus a very simple process. Subsequent to the heat aging, the cyclic carbonate may be isolated from the aged reaction mixture by an ordinary recovery technique such as distillation and recrystallization. The process of the present invention is successful in producing a cyclic carbonate of high purity in a high yield in a simple manner. The cyclic carbonates are useful in a variety of applications including organic electrolytes, ink medium, particularly as additives for special ink such as high-speed jet recording ink, reaction medium, and dispersing medium. The gas chromatogram of the reaction mixture of Example 4 is shown in FIG. 1. EXAMPLES Examples of the present invention are given below by way of illustration and not by way of limitation. Preparation Examples 1-4 A glass rotary evaporator having an interior volume of 50 liters and equippped with a reflux condenser was charged with 10.7 kg (73.3 mol) of 2,2,4-trimethyl-1,3-pentanediol (TMPD), 14.5 kg (161.1 mol) of dimethylcarbonate (DMC), and 0.03 kg (0.75 mol) of sodium hydroxide (NaOH). Reaction was carried out under atmospheric pressure at the temperature (bath temperature) and time shown in Table 1. During the reaction, methanol and DMC were evaporated off from the reactor. In Preparation Examples 1 and 2, evaporated methanol and DMC were cooled and condensed in the reflux condenser and returned to the reactor. In Preparation Examples 3 and 4, after reflux operation was carried out for 6 hours, the reaction was continued without reflux operation while the condensate which consisted of unreacted DMC and methanol was distilled out of the reaction system. After reaction was continued for a predetermined time, the reaction mixture was analyzed by gas chromatography (GC) using 2% Silion OV-225/Uniport HP column. The areas of the peaks indicative of TMPD, HCC, unk-1 and unk-2 excluding low-boiling substances such as methanol and DMC are calculated in % and reported in Table 1. An exemplary gas chromatogram is shown in FIG. 1. It is to be noted that unk-1 and unk-2 in Table 1 and FIG. 1 are as previously defined. Preparation Example 5 A glass flask having an internal volume of 500 ml was charged with 146 grams (1.0 mol) of TMPD, 135 grams (1.5 mol) of DMC, and 0.41 grams (0.01 mol) of NaOH. With stirring by a magnetic stirrer, reaction was carried out under atmospheric pressure at the temperature (contents temperature) for the time both shown in Table 1. Methanol which generated with the progress of reaction was distilled out along with DMC. The results are shown in Table 1. Preparation Example 6 The procedure of Preparation Example 5 was repeated except that the catalyst NaOH was replaced by NaOCH₃ and the reaction temperature (contents temperature) was set to 85°C. The results are shown in Table 1. Comparative Example 1 The procedure of Preparation Example 5 was repeated except that the catalyst NaOH was replaced by p-toluenesulfonic acid and the reaction temperature (contents temperature) was set to 102°C. The results are shown in Table 1. Examples 1-3 The reaction mixture obtained in Preparation Example 4 was subjected to heat aging under reduced pressure without removing the basic catalyst NaOH therefrom. The temperature, pressure, and time used in the heat aging under vacuum are reported in Table 2. During aging, DMC released was distilled out of the system. The results are shown in Table 2. In all the examples, the compounds identified as unk-1 and unk-2 disappeared and the amount of the end product, 1-isopropyl-2,2-dimethyl-1,3-propylene carbonate (HCC) was increased at the end of heat aging of the reaction mixture in the presence of the catalyst NaOH. Comparative Example 2 In the reaction mixture composed of the composition reported in Table 2, the catalyst NaOH used in the reaction was neutralized with 1N NH₄Cl before the reaction mixture was subjected to heat aging at 150°C and 2kPa (15 mmHg) for 2 hours. The results are shown in Table 2. Comparative Example 3 A reaction mixture of the composition reported in Table 2 having a high concentration of unk-1 was prepared without adding a basic catalyst. It was subjected to heat aging at 150°C and 2kPa (15 mmHg) for 2 hours, with the results shown in Table 2. Example 4 To the same reaction mixture as used in Comparative Example 3 was added 0.1% by weight of NaOH. The mixture was subjected to heat aging at 150°C and 2kPa (15 mmHg) for 2 hours, with the results shown in Table 2. Example 5 The reaction mixture obtained in Preparation Example 5 was subjected to heat aging at 150°C and 2 kPa (15 mmHg) for 2 hours. The end product HCC was recovered by simple batch distillation under a pressure 0.7 kPa (5 mmHg) at a column top temperature of 123°C. The conversion of TMPD was 100%. The isolation yield was 95.4% as expressed in % by the amount (grams) of HCC isolated by distillation divided by the theoretical (grams). The resulting HCC was 99.6% pure. It is seen that by-products unk-1 and unk-2 in the reaction mixture resulting from reaction of TMPD and dimethylcarbonate reactants to synthesize HCC can be converted into the end product HCC by subjecting the reaction mixture to heat aging at a reduced pressure in the presence of a basic catalyst. The same applies to any other combination of basic catalyst and diol with dimethylcarbonate.

Claims: A process for preparing a cyclic carbonate, which comprises (a) reacting at least one 1,3-diol or 1,2-diol with dimethylcarbonate in the presence of a basic catalyst at atmospheric pressure or above, (b) subjecting the reaction mixture thus obtained to heat aging at 150° to 200°C under a pressure of 13.3 to 53300Pa (0.1 to 400 mmHg) in the presence of a basic catalyst, and (c) isolating the resulting cyclic carbonate from the mixture. A process according to claim 1 wherein the basic catalyst used in step (a) and/or step (b) is a basic compound containing an alkali or alkaline earth metal. A process according to claim 1 or 2 wherein the basic catalyst used in step (a) is not removed from the reaction mixture and is used in step (b). A process according to any one of the preceding claims wherein step (b) is carried out for from 1/2 to 5 hours. A process according to any one of the preceding claims wherein step (b) is carried out while removing from the reaction mixture dimethylcarbonate generated during said step (b).

Inventors: IMAGAWA MASAO MITSUI PETROCHEM, KISO YOSHIHISA MITSUI PETROCHE, MATSUNAGA YUUICHI MITSUI PETRO, IMAGAWA, MASAO, MITSUI PETROCHEMICAL IND.LTD., KISO, YOSHIHISA, MITSUI PETROCHEMICAL IND.LTD., MATSUNAGA, YUUICHI, MITSUI PETROCHEMICAL IND.LTD.
Applicants: MITSUI PETROCHEMICAL IND, MITSUI PETROCHEMICAL INDUSTRIES, LTD.
Application year: 1988
Main classification: C07D319
IPC codes: B01J27, C07D325, C07D317, C07B61, B01J31, B01J23, C07D319