CA2013689C - Process for producing diaryl carbonate - Google Patents

Abstract

The invention relates to a process for producing a diaryl carbonate which comprises diproportionating an alkylaryl carbonate to a diaryl carbonate and a dialkyl carbonate in the presence of a lead catalyst.

Description

PROCESS FOR PRODUCING DIARYL CARBONATE

BACKGROUND OF THE INVENTION

The present invention relates to a process for producing a diaryl carbonate. More particularly, the present invention relates to a process for producing a diaryl carbonate according to the disproportionation reaction of an alkylaryl carbonate.
It has been already known to obtain diphenyl carbonate by disproportionation of an alkylphenyl carbonate [Japanese Patent Publication No. 1~8537/1983 (USP 4,045,~164)]. However, in this method, a catalyst selected from among Lewis acids and transition metal compounds capable of forming Lewis acids is used, and specifically AlX3, TiX3, UX4, VOX3, VX5, ZnX2, FeX3, SnX4 are included, wherein X is a halogen, an acetoxy group, an alkoxy group, or an aryloxy group. Such Lewis acids are highly corrosive to the metallic materials of reaction vessels, pipelines and valves. Thus methods using these Lewis acids involve a problem when industrially practiced.
Further, it has been also praposed to conduct such a method using a catalyst consisting of a mixture of a Lewis acid and a protonic acid [Japanese Laid-open Patent Application No.
173016/1985 (USP 1l,609,501)~ lowever, in this method, because a protonio acLd is uaed in addition to a Lewis acid, not only the problem of corro.sion becomes more serious, but also separation and recovery of the catalyst are difficult.

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Also, some proposals have been made to use organic tin compounds or organic titanium compounds as a catalyst in such methods [Japanese Laid-open Patent Publications Nos . 169444/1985 (USP ~,554,110), 169l~45/l985 (USP 4,552,704), 265062/1989, 265063/1989), but these organic tin compounds or organic titanium compounds are difficult to separate completely from the products whereby it is very difficult to obtain the diaryl carbonate with high purity. One irnportant use of a diaryl carbonate is its use as a monorner ror prod~cing polycarbonate, and in this case, if an organic tin compound or an organic titanium compound is present, even in a small amount, in the diaryl carbonate, the physical properties of the polycarbonate thus produced will be lowered.
Therefore, the diaryl carbonate produced by the methods using such catalysts cannot be effectively used as the monomer for producing the polycarbonate.
Further, it has been also proposed to use in such a method a catalyst selected from a compound containing Sc, Cr, Mo, W, Mn, Au, Ga, In, Bi, Te, and lanthanoid (Japanese Laid-Open Patent Application No. 265064/1989). However the yield of the desired diaryl carbonate is low in this method.

SUMMARY OF TH~ INVENTION

The above-identified problems have been eliminated by the present invention which provides a process for produclng a diaryl carbonate, which comprises disproportionating an alkylaryl carbonate to a diaryl carbonate and a dialkyl carbonate in the presence of a lead catalyst.

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DETAILED DESCRIPTION OF THE INVENTIO~
The process o~ the present invention is represented by the reac~ion (I) as shown below:
O O
Il 11 2R - O - C - O - Ar = Ar - O - C - O - Ar ~
o ll ....................... (I) R - O - C - O - R
(wherein R represents an alkyl group such as an aliphatic group, an alicyclic group, an aralkyl group, and Ar represents an aryl eroUP which is an aromatic group).
The alkylaryl carbonate to be used as the starting material of the present invention is a compound shown on the left side of the above reaction (I). As R, for example, aliphatic groups including various isomers such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl and the like; alicylic groups such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, methylcyclobutyl, cyclohexylmethyl and the like; aralkyl groups such as benzyl, phenethyl and the like are preferred. As Ar, unsubstituted aromatic groups such as phenyl, naphthyl, pyridyl, etc.; substituted aromatic groups represented by the following f'ormulae are preferred:

~ R~- ~ ( R~-~ - ~ - ( R~
(wherein R' represents a sub.stltuent such as lower alkyl group, all<oxy group, acyl group, halogen, aryloxy group, aromatic group, nitro group, cyano group, aralkyl group, etc., Q is an integer of 1 to 5, m is an integer of' 1 to 7, n is an integer of 1 to 4, and '3 ~
wl.~n Q, m and n are each an integer of 2 or more, and R' may be either the same or dif'ferent). Also, in R, those wherein one or more hydrogen is subst1tuted with a substituent such as halogen, alkoxy group having 1 ~o 10 carbon atoms, cyano group, etc. can be also used.
A particularly preferable alkylaryl carbonate is one where the alkyl group is a lower aliphatic group having 1 tG l~ carbon atoms such as rnethyl, ethyl, propyl, butyl, and where the aryl group i3 phenyl eroup or a sub,stituted phenyl group having 7 to 15 carbon atoms with a sub.stituent having 1 to 9 carbon atoms such as methyl, dirnethyl, ethyl, t-butyl., 2-phenyl-2-methylethyl, etc.
'rhe lead catalyst to be used in the present invention may be lead containing material or a compound containing lead, but particularly preferable are basic or neutral lead compounds.
Examples of such lead compounds preferably used may include lead oxides such as PbO, PbO2, Pb304; lead sulfides such as PbS, PbS2, PbS3; lead halides such as PbC12, PbBr2, PbI2, 3PbBr2-2PbO, PbC12-Pb(OH)2 etc.; lead hydroxides such as Pb(OH)2, Pb302(0H)2, Pb2~PbO2(0H)21, Pb20(0H)2, etc.; plumbites such as Na2PbO2, K2PbO2, NaMPbO2, KHPbO2, etc.; plumbates such as Na2PbO3, Na2H2PbOIl, K2PbO3, K2[Pb(OH)6], K~PbOIl, Ca2PbO4, CaPbO3, etc.;
carbonates of lead or lead compounds and basic salts thereof such as PbC03, 2PbC03 Pb(0~1)2' PbC03 PbC12~ 2pbco3-pbsol~-pb(oH) etc.; lead salts of' orgarlic acLds such as Pb(OCOCH3)2, Pb(OCOCH3)1l~ Pb(~C~CH3)2-PbO-3H20, etc.; organ:ic lead compounds such as BullPb, Phl~Pb, Bu3PbCl, Ph3PbBr, Ph3Pb (or Ph6Pb2), 2~ 3 ~_3PbOH, Ph2PbO, etc. (Bu and Ph represent a butyl group and a phenyl group, respectively); lead alkoxides or lead aryloxides Such as Pb(~CH3~2' Pb(~C2H5)2~ (CH30)pb(oph)~ Pb(OPh)2, etc.;
alloys of lead such as Pb-Na, Pb-Ca, Pb-Ba, Pb-Sn, Pb-Sb, etc.;
lead ores such as galena, boulagerite, etc., and hydrates o~
these coMpounds and so on. Of course, these lead compounds may be also those which are reacted with the organic compounds existing in the reaction systern such as alkylaryl carbonates, diaryl carbonates, dialkyl carbonates, or hydrolyzed products of these cornpounds (alcohols, aromatic hydroxy compounds, etc.), and may be also those subjected to heat treatment with the starting material, the products or alcohols or aromatic hydroxy compounds prior to the reaction.
Among these, particularly preferred catalysts are lead and lead compounds such as powdery lead, fine particulate or powdery lead-sodium alloys, various lead oxides, lead hydroxides, lead carbonates and basic lead carbonates, plumbites and plumbates, lead acetates and basic lead acetates, lead alkoxides and lead aryloxides. These lead and lead compounds can be also pretreated by being reacted with organic compounds which exist in the re~ction system, or by being subjscted to a heat treatrnent with the starting material, with the products or with a]cohols or aromatic hydroxy compounds and used as the catalyst system. In the present invention, when these particularly preferred catalysts are used, not only can a diaryl carbonate be obtained in high yield and high s~lectivity, but also the diaryl carbonate can be easily separated frorn the catalysts used. More Q~ ~' ~' s~ecifically, the diaryl carbonate thus produced is generally separated and purified by distillation under reduced pressure from the reaction mixture, and none of the lead components of these particularly preferred catalysts is distilled off together with the diaryl carbonate, because there is entirely no or very little vapor pressure of the lead components under such distillation conditions. Accordingly, a highly pure diaryl carbonate free from any lead components can be obtained. This is one of the excellent features of the present invention.
The catalyst of the present invention is excellent in producing a diaryl carbonate in a high yield with high selsctivity, and further it has also the specifio feature that there is no problem of corrosion of the metallic materials of the installation caused by the prior art use of a Lewis acid, because the lead and lead compounds constituting the catalyst are neither Lewis acids nor transition metal compounds which can form Lewis acids.
The catalyst comprising such lead materials or lead compounds can be used either singly or as a mixture of two or more kinds.
The amount of the lead catalyst to be used in the present invention is not particularly limited, but may be generally used in the range of from 0.00001 to 100 moles, preferably from 0.001 to 2 moles per mole of the alkylaryl carbonate used.
Since the reactlon of the present invention is an equilibrium reaction as shown by the reaction (I), by removing at least one of the diaryl carbonate or the dia:Lkyl carbonate which are the reaction products ~rom the reaction system, the reaction can f, ~ J ~ 3 better progress.
Since the reaction of the present invention is generally carried out in liquid phase or gas phase, it is preferable to progress the reaction while distilling off the component with the lower boiling point of the reaction products. The order of the boiling points of ~he starting materials and the products are generally diaryl carbonate > alkylaryl carbonate > diall<yl carbonate, or dialkyl carbonake > alkylaryl carbonate > diaryl carbonate, and thus it is easy to distill off one of the products. A dialkyl carbonate of which the alkyl group comprises a lower aliphatic group such as methyl, ethyl, propyl, butyl, etc. has a low boiling point, and therefore can be easily distilled off from the reaction system. In such meaning, an alkylaryl carbonate having a lower aliphatic group may be preferably used.
For effectively distilling off the lower boiling components, there may be preferably employed the method in which an inert gas such as nitrogen, helium, carbon dioxide, etc. or a lower hydrocarbon gas or mi~ture thereof is introduced into the reaction system, and the method is performed under reduced pressure. These methods may be also used in combination. In the case of a tank type reactor, it is also a preferable method to perform effective stirring to increase the interfacial area between the gas and llquid phases, or to promote the interfacial renewal, while in the case of a tower type reactor, it is also a preferable method to rnake an apparatus with a large interfacial area between the gas and llquid phases.

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The reaction of the present invention is generally carried out at about 50 to about 400 ~C, preferably in the range of from about oO to about 300 ~C. The reaction time which may vary depending on the reaction system employed and o~her reaction condition.s chosen is typically about one minute to about 50 hours. The reaction pressure may be either reduced pressure, normal pressure or in the range of ~rom about 0.01 I<g/cm~ to about 50 kg/cm2.
The procet~s of the present invention can also be practiced wlth or without the use of solvent. When a solvent is used, it is also a preferable method to distill off the lower boiling products together with a part of the solvent. Examples of such solvent may include aliphatic hydrocarbons such as pentane, hexane, heptane, octane, nonane, decane, undecane, tridecane, etc.; aromatic hydrocarbons such as benzene, toluene, xylene, ethylbenzene, styrene, etc.; alicyclic hydrocarbon~ such as cyclohexane, methylcyclohexane, etc.; halogenated hydrocarbons sucn as methyl chloride, methylene chloride, chloroform, carbon tetrachloride, dichloroethane, chlorobenzene, dichlorobenzene, etc.; nitrilies such as acetonitrile, propionitrile, benzonitrile, etc.; ketones such as acetone, methyl ethyl ketone, acetophenone, etc.; ethers such as diethyl ether, tetrahydro~uran, dioxane, diphenyl ether. etc.
The process of the present invention can be practlced by either a batch systetn or a continuous system.

DRTAILED DESCRIPT:L~N OF TllE P~EEERRED EMBODIMENTS

The preserlt invention is described in more detail by re~erring to tl1e ~ollowin~ examples, which shoulcl not be .Isidered as limiting in any way the sense of the present invention.

Example 1 Pre-treatment of the catalyst is performed by heating 2 g Or PbO and 10 g of rnethylphenyl carbonate under a small amount of nil;rogen streaM at about 180~C for one hour. Subsequently, by distilling off unreacted methylphenyl carbonate and most o~ the diphenyl carbonate formed at about 150~C under a reduced pressure of about 0.5 mm Hg, 2.5 g of a pale yellow solid is obtained. To thi.s is added 76 g (0.5 mole) of rnethylphenyl carbonate, and the whole amount is transferred into a 200 ml four-necked flask equipped with a stirring device, a reflux condenser, a gas introducing inlet reaching lower level than the liquid surface, and a thermometer. The reaction is carried out by dipping the flas~ in an oil bath of 190 - 195~C under stirring, while introducing dry nitrogen at a rate of 80 N ml/min. Through the jacket of the reflux condenser is conveyed water at a temperature of about 90~C, and the reaction is carried out while distilling off dimethyl carbonate by-produced, and refluxing methylphenyl carbonate and the diphenyl carbonate formed to return them into the reactor. The results are shown in Table 1. Selectivity of anisole which is the by-product is 1 ~ or less even after 3 hours.

. 9 Table 1 Reaction time Methylphenyl carbonate Diphenyl carbonate (min.)conversion (~) ~ield (%) Selectivity (%) 56.6 56.2 99.3 7ll.5 73.9 99.2 120 85.5 84.7 99.1 180 90.~ 89.9 99.0 Three hours later, the system i9 gradually brought under reduced pressure to distill off unreacted methylphenyl earbonate.
Subsequently, in place of the reflux condenser, a packe-l column ith an inner diarneter of 2 em and a height of 30 cm (paeked with 6 mm~ Diekson paekings made of stainless steel) is rnounted, and distillation is performed under redueed pressure to give 45 g of diphenyl carbonate (purity 99.99 %) which is distilled out at 1B4 - 185 ~C/17 mm Hg. When metal analysis in the diphenyl earbonate is eondueted by ICP (Induetively eoupled diseharge speetrometry) method, no lead is detee'ced at all.

Comparative example 1 The disproportionation reae'cion of methylphenyl earbonate (76 g, 0.5 mole) is carried out in the same manner as in Example 1, by using of 3.8 g of Ti(OC6H5)4 as the catalyst proposed in USP 4,045,46ll. As a result, the conversion of methylphenyl earbonate after 3 hours is :found to be 60.3 %, and the yield of diphenyl carbonate 56.1 % and .lts selec~ivity 93.0 %. Anisole whieh is the by-produet is found to be forrned ac a seleetivity o:f 6.2 %. Subsequently, sirnilarly as in Example 1, unreaeted nl_~hylph~nyl carbonate is distilled off, and 23 g of diphenyl carbonate (purity 99.0 %) is obtained by reduced pressure distillation. When metal analysis in the diphenyl carbonate is conducted by the ICP method, 150 ppm of Ti is detected.

Example 2 - 11 According to the same procedure as in Example 1 except for using various lead cornpounds or lead in place of PbO, the reactions from methylphenyl carbonate (76 g) to diphenyl carbonate are carried out. The results of the reactions after 2 hours are listed in Table 2. In these Examples, the catalyst is used in an amount of 5 mmol or 5 mg-atom as lead. The Pb-Na alloy used in Example 3 contained 90 % by weight of Pb. In Examples 2, 3, 7, 8 and 9, the reaction is carried out directly without pre-treatment of the catalyst.

Table 2 Methylphenyl Diphenyl carbonate Example Catalyst carbonate Yield (%) Selectivity(%) conversion (%) 2 Powdery Pb 52.3 51.8 99.0 3 Fine particulate Pb-Na alloy 88.2 81.1 92.0 4 PbO2 86 5 85.7 99.1 Pb304 82.3 81.ll 98.9 6 Pb(OH)2 87.8 87.1 99.2 7 2PbC03-Pb~OH)2 85.6 83.3 97.3 8 Pb(OAc)2 Pb(OH)2 8Ll~5 82.0 97.0 9 Pb(OAc)2~3~l20 85.0 82.0 96.5 Na2PbO3 80.2 79.4 99 0 11 PbC03 83.0 82.0 98.8 ~ 3~
Examples 12 - 17 The reactions are carried out in the same manner as in Example 1 except for using various alkylaryl carbonates in place of methylphenyl carbonate, and the results of the reactions after 2 hours are shown in Table 3.

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Table 3 Example R - OCO - Ar Diaryl carbonate R Ar Yield (,~) Selectivity (,~) 12C2H5 ~> 76.5 9~.5 13 3 7 ~ CH3 70.2 97.0 1 4 3 <~ C - CH3 8 6 . 0 99 . O

CH
15CH3 ~ C ~> 88.5 98 .8 1 63 ~ CQ 8 4 . 0 97 . O

17CH3 ~ OC~13 85.8 97 .5 2 ~ ' $ ~, ~

However, in Examples 12 and 13, ~he reaction temperature is 205 - 210 ~C, and an oil of about 130 ~C is circulated through the reflux condenser.

Example 18 Into a flask equipped with a stirrer and a gas outlet is charged 578 g of phenol, and the flask is dipped in an oil bath.
The oil bath is heated to ;~bout 110 ~C, and 100 g o~ PbO is added little by little under stirring. The oil bath is heated to reach 190~C in 3 hours. Water and phenol are distilled off. When the amount of dlstilled liquid becomes 406 g, distillation is stopped, and after cooled to about 110 ~C, 300 ml of toluene is added and the mixture is cooled to room temperature. As a result, pale yellow crystals are precipitated. By recrystallization of the crystals by use of 350 ml of toluene, 120 g of crystals are obtained. The Pb content in the crystals is found to be 52.7 ~ by ICP analysis. Tne crystals are identified to be Pb(OC6H5)2.
The reaction is carried out in the same manner in Example 1 except for using 2 g of Pb(OC6H5)2, 100 g of n-butylphenyl carbonate, making the reaction temperature 205 - 210 ~C, the reaction pressure 80 mm Hg, and passing oil at a temperature of about 140 ~C through the jacket of the reflux condenser. One hour later, the conversion of n-butylphenyl carbonate i9 found to be 80.a %, and the yield of diphenyl carbonate i9 ~~0.0 ~, with its selectivity being 99.1 %.
According to the present invention, by use of a lead d $ '~ ~

catalyst, a diaryl carbonate can be produced in a high yield with high selectivity, and the problems of corrosion, etc. of the apparatus caused by the use of a catalyst such as Lewis acid has been solved. Furthermore, according to the present inventLon, a highly pure diaryl carbonate required for the production of polycarbonate with high qualitles can be easily obtained.

Claims (10)

1. A process for producing a diaryl carbonate which comprises disproportionating an alkylaryl carbonate at a temperature of about 50 to about 400° C in the presence of a lead catalyst to produce a diaryl carbonate and a dialkyl carbonate, and recovering the diaryl carbonate from the reaction products, wherein the alkyl group in said alkylaryl carbonate and in said dialkyl carbonate is an aliphatic group having 1 to 9 carbon atoms, an alicyclic group having 3 to 7 carbon atoms, an aralkyl group having 7 to 8 carbon atoms, or a group wherein one or more hydrogen in said alkyl group is substituted with a substituent selected from the group consisting of a halogen, an alkoxy group having 1 to 10 carbon atoms, and a cyano group, and wherein the aryl group is said diaryl carbonate and in said alkylaryl carbonate is an unsubstituted aromatic group having 5 to 10 carbon atoms, or a substituted aromatic group with one or more substituent selected from the group consisting of a lower alkyl group, an alkoxy group, an acyl group, a halogen, an aryloxy group, an aromatic group, a cyano group, and an aralkyl group.

2. The process according to claim 1, wherein lead and a neutral or basic lead compound are used as the lead catalyst.

3. The process according to claim 1, wherein at least one lead compound selected from lead oxides is used as the lead catalyst.

4. The process according to claim 3, wherein lead oxide subjected to a heat treatment with at least one organic compound selected from the group consisting of alkylaryl carbonates, diaryl carbonates, dialkyl carbonates, alcohols and aromatic hydroxyl compounds, is used as the catalyst, wherein the alkyl group in said alkylaryl carbonates and in said dialkyl carbonates and in said alcohols is an aliphatic group having 1 to 9 carbon atoms, an alicyclic group having 3 to 7 carbon atoms, an aralkyl group having 7 to 8 carbon atoms, or a group wherein one or more hydrogen in said alkyl group is substituted with a substituent selected from the group consisting of a halogen, an alkoxy group having 1 to 10 carbon atoms, and a cyano group, and wherein the aryl group is said diaryl carbonates, in said alkylaryl carbonates, and in said aromatic hydroxyl compounds is an unsubstituted aromatic group having 5 to 10 carbon atoms, or a substituted aromatic group with one or more substituent selected from the group consisting of a lower alkyl group, an alkoxy group, an acyl group, a halogen, an aryloxy group, an aromatic group, a cyano group, and an aralkyl group.

5. The process according to claim 1, wherein the lead catalyst is at least one lead compound selected from the group consisting of lead alkoxides and lead aryloxides, wherein the alkyl group in said alkoxides is an aliphatic group having 1 to 9 carbon atoms, an alicyclic group having 3 to 7 carbon atoms, an aralkyl group having 7 to 8 carbon atoms, or a group wherein one or more hydrogen in said alkyl group is substituted with a substituent selected from the group consisting of a halogen, an alkoxy group having 1 to 10 carbon atoms, and a cyano group, and wherein the aryl group in said aryloxides is an unsubstituted aromatic group having 5 to 10 carbon atoms, or a substituted aromatic group with one or more substituent selected from the group consisting of a lower alkyl group, an alkoxy group, a halogen, an aryloxy group, an aromatic group, a cyano group, and an aralkyl group.

6. The process according to claim 5, wherein the lead aryloxide is lead diphenoxide.

7. The process according to claim 1, wherein the alkyl group is a lower aliphatic group having 1 to 4 carbon atoms.

8. The process according to claim 1, wherein the aryl group is a phenyl group or a substituted phenyl group having 7 to 15 carbon atoms.

9. The process according to claim 3, wherein the alkyl group is a lower aliphatic group having 1 to 4 carbon atoms.

10. The process according to claim 3, wherein the aryl group is a phenyl group or a substituted phenyl group having 7 to 15 carbon atoms.