EP0000879B1 - Process for the preparation of aromatic carbonic acid esters - Google Patents

Description

The invention relates to a process for the preparation of aromatic carbonic acid esters from aliphatic carbonic acid esters and phenols by transesterification in the presence of organotin compounds.

The transesterification of aliphatic carbonic acid esters with phenols in the presence of strong bases or of alkali compounds is known according to DBP 971 790, 1 020 184, 1 026 958 and 1 031 512. Transesterification processes catalyzed in this way have the disadvantage of not being very selective, so that considerable amounts of carbon dioxide are released in a side reaction.

DOS 2 528 412 and 2 552 907 describe transesterification processes for the preparation of aromatic carbonic acid esters in which Lewis acids, i.e. Transition metal halides or the corresponding acyloxy, alkoxy or aryloxy compounds can be used. Of the compounds of the elements Al, Ti, U, V, Zn, Fe and Sn, only those of titanium are of economic interest, since only these are sufficiently effective and selective. However, these titanium-based catalysts have the disadvantage that they color the end products strongly red-brown. This coloring is particularly unpleasant if the end products cannot be purified by recrystallization or distillation, such as e.g. is the case with polycarbonates.

U.S. Patent 3,714,234 now teaches to reesterify carboxylic acid esters in the presence of certain tin compounds. However, these tin compounds are reaction products of organic or inorganic tin compounds with alkali metal alkoxides or phenoxides. In any case, the products contain alkali in some form, are therefore basic and greatly favor the elimination of CO ₂ . It is clear that these catalysts are not suitable for the transesterification of carbonic acid esters.

It was therefore the task of finding catalysts which, in addition to a transesterification activity and selectivity at least equivalent to the titanium catalysts, also have the advantage of not significantly discoloring the end products.

in der

• Y für einen Rest
  
  OH oder OR² steht, wobei R² einen Alkylrest mit C_i-C₁₂, einen Arylrest mit C₆―C₁₂ oder einen Alkylarylrest mit C₇―C₁₃ bedeutet, und
• R' die Bedeutung von R² hat, und
• x eine ganze Zahl von 1-3 bedeutet, oder Dialkylzinnoxide mit jeweils 1-12 C-Atomen im Alkylrest oder zinnorganische Verbindungen der allgemeinen Formel (11)
  
  in der
• R³ und R⁴ gleich oder verschieden, die oben angegebene Bedeutung von R^l haben, und
• R⁵ die Bedeutung von A2 hat oder für einen Rest ^OR6 steht, in dem R⁶ die Bedeutung von R² hat,

werwendet werden.The object of the invention was achieved by using certain organotin compounds as transesterification catalysts. The invention therefore relates to processes for the preparation of aromatic carbonic acid esters by transesterification of dialkyl carbonates with phenols with the elimination of alcohols in the presence of catalysts, which are characterized in that organostannic compounds of the general formula (I)

in the

• Y for a rest
  
  Is OH or OR ² , where R ^{2 is} an alkyl radical with C _i -C ₁₂ , an aryl radical with C ₆ ―C ₁₂ or an alkylaryl radical with C ₇ ―C ₁₃ , and
• R 'has the meaning of R ² , and
• x denotes an integer from 1-3, or dialkyltin oxides each having 1-12 C atoms in the alkyl radical or organotin compounds of the general formula (11)
  
  in the
• R ³ and R ^{4 are the} same or different and have the meaning of R ¹ given above, and
• R ^{5 has} the meaning of A2 or represents a radical ^OR6 in which R ^{6 has} the meaning of R ² ,

be used.

The favorable catalytic action of the catalysts according to the invention is surprising since they cannot be called Lewis acids. On the contrary, it can be stated that the organotin halogen compounds such as dibutyltin dichloride or dioctyltin dichloride, in which a formal relationship to typical Lewis acids such as aluminum trichloride or titanium tetrachloride could most likely be assigned, are completely ineffective. The organotin compounds used according to the invention may therefore not contain any direct tin-halogen compound.

The effectiveness of the catalysts according to the invention, measured by the rate of alcohol splitting, practically does not differ from that of compounds of titanium, such as of tetrabutyl titanate. However, there are advantages to be seen in the fact that the ratio in the two process products alkylaryl carbonate and diaryl carbonate is shifted in favor of the latter, and approximately half the reduction in carbon dioxide is observed under comparable conditions.

• Trimethylzinnacetat, Triethylzinnbenzoat, Tributylzinnacetat, Triphenylzinnacetat, Dibutylzinndiacetat, Dibutylzinndilaurat, Dioctylzinndilaurat, Methoxytribytylzinn, Methoxytriphenylzinn, Phenoxytriethylzinn, Dimethoxydibutylzinn, Diethoxydibutylzinn, Diphenoxydibutylzinn, Dimethoxydiphenylzinn, Triethylzinnhydroxid, Triphenylzinnhydroxid, Hexaethylstannoxan, Hexabutylstannoxan, Tetrabutyldiphenoxystannoxan, Dibutylzinnoxid und Dioctylzinnoxid.

Are for the method according to the invention very particularly suitable organic tin compounds, such as:

• Trimethyltin, triethyltin benzoate, tributyltin, triphenyltin, dibutyltin dilaurate, dioctyltin Methoxytribytylzinn, Methoxytriphenylzinn, Phenoxytriethylzinn, dimethoxydibutyltin, Diethoxydibutylzinn, Diphenoxydibutylzinn, Dimethoxydiphenylzinn, Triethylzinnhydroxid, triphenyltin, Hexaethylstannoxan, Hexabutylstannoxan, Tetrabutyldiphenoxystannoxan, dibutyltin and dioctyltin.

Preferably those compounds are used whose vapor pressure is low even at the required reaction temperatures, i.e. those with organometallically bonded alkyl radicals of at least four carbon atoms.

werwendet, in der R⁷ für einen Alkylrest mit C₁-C₁₀ steht. Bevorzugt können Dimethylcarbonat, Diethylcarbonat, Dipropylcarbonat, Diisopropylcarbonat, Dibutylcarbonat, Dioctylcarbonat, Diisooctylcarbonat und Dicyclohexylcarbonat eingesetzt werden.Preferred bialkyl carbonates are those of the general formula (III)

used, in which R ^{7 is} an alkyl radical having C ₁ -C ₁₀ . Dimethyl carbonate, diethyl carbonate, dipropyl carbonate, diisopropyl carbonate, dibutyl carbonate, dioctyl carbonate, diisooctyl carbonate and dicyclohexyl carbonate can preferably be used.

in der X für Wasserstoff, einen Alkylrest mit C_l-C₃, ein Halogenatom, vorzugsweise Chlor, oder eine Nitrogruppe und n für 1 oder 2 stehen. Besonders bevorzugt werden als Phenole für das erfindungsgemäße Verfahren Phenol, o,m,p-Kresol, o,m,p-Chlorphenol, o,m,p-Ethyl- phenol, o,m,p-Propylphenol, o,m,p-Nitrophenol, 2,6-Dimethylphenol, 2,4-Dimethylphenol und 3,4-Dimethylphenol verwendet.Suitable phenols are preferably those of the general formula (IV)

in which X is hydrogen, an alkyl radical with C ₁ -C ₃ , a halogen atom, preferably chlorine, or a nitro group and n is 1 or 2. Phenol, o, m, p-cresol, o, m, p-chlorophenol, o, m, p-ethylphenol, o, m, p-propylphenol, o, m, p are particularly preferred as phenols for the process according to the invention -Nitrophenol, 2,6-dimethylphenol, 2,4-dimethylphenol and 3,4-dimethylphenol are used.

Instead of the monohydric phenols it is also possible to use bisphenols such as dihydroxydiarylalkanes with C ₁ -C ₄ in the alkyl radical, for example bisphenol A. They are not split under the process conditions and can therefore be converted directly into polycarbonate. Based on pure raw materials, these are almost colorless and do not require any additional cleaning steps.

The catalysts are used in concentrations of about 0.001-20% by weight, based on the total amount of the reaction mixture. The weight ratio of dialkyl carbonate: phenol can vary within wide limits and is between about 1:99 and 99: 1, preferably 1: 9 and 9: 1. It depends on this ratio whether alkylphenyl carbonate or diaryl carbonate predominates in the end product.

The alkylaryl carbonate formed in addition to diaryl carbonate can be separated off by distillation without difficulty and either reacted with fresh phenol or, after the diaryl carbonate has been separated off, can react further with the phenol still present.

The reaction temperatures are preferably in the range of 50-250 ° C, particularly preferably in the range of 100-200 ° C. It is advantageous to work at a pressure of 1 torr to 20 atm abs, preferably 1-5 atm.

Solvents such as aliphatic or aromatic hydrocarbons can also be used.

A preferred procedure is to bring the transesterification mixture to the desired reaction temperature in a longer column, while the alcohol is released overhead, to the extent that it is released in the reaction mixture, and is optionally separated off using an inert gas stream.

In another process variant, excess dialkyl carbonate is passed through a melt of the phenol to be reacted, while a mixture consisting of the alcohol and dialkyl carbonate is continuously distilled off. The components can be separated in a separate step using customary methods.

The results of both procedures do not differ significantly.

The process products can be used as starting materials for the production of polycarbonates by known processes or of crop protection agents.

example 1

• a) 470 g (5 mol) of phenol, 90 g (1 mol) of dimethyl carbonate, 50 g of n-heptane and 5.7 g of diphenoxydibutyltin are heated to boiling in a 2.9 m high, mirrored packed column loaded with glass rings. The internal temperature is kept at 155 ° C. by dropping heptane. A mixture of methanol and heptane is distilled overhead at 59.5-60 ° C. As the reaction progresses, further dimethyl carbonate is added dropwise in the lower third of the column. In total, 315 g = 3.5 mol of dimethyl carbonates are thus used within 30 h. Carbon dioxide that is released during the reaction is absorbed by a weak stream of nitrogen in a wash bottle filled with n-sodium hydroxide solution. The reaction mixture is fractionated over a 1.1 m high column. After a preliminary run consisting of methanol, dimethyl carbonate and heptane, 313 g (3.33 mol) of unreacted phenol go at 80-87 ° C./15 Torr, and 118 g (0.78 mol) of methylphenyl carbonate at 95-97 ° C./13 Torr. nzo 1.4970) and after removing the column at 165-172 ° C / 13 Torr 90 g (0.44 mol) of crystalline diphenyl carbonate. Thus, the yield, based on the phenol converted, is 98.5% of theory. Th. According to the analytical CO _z determination, 0.011 mol of carbon dioxide is absorbed in the wash bottle, which corresponds to a loss of 0.9% of the carbonate used.
• b) A mixture of 45.6 g (0.2 mol) of 2,2-bis - (4-hydroxyphenyl) propane, 47.1 g (0.22 mol) of the diphenyl carbonate prepared according to a) and 0.008 g of sodium methylate slowly heated to 210 ° below 20 torr, the majority of the phenol cleaved off. The pressure is then reduced to 0.2 torr and the temperature is raised to 250 ° C. for one hour and to 280 ° C. for another two hours until the melt has become so tough that it can hardly be stirred. When cooling, a clear, colorless, elastic plastic is obtained, from the melt of which molded articles with excellent strength properties can be produced.

Example 2

470 g (5 mol) of phenol, 118 g (1 mol) of diethyl carbonate, 200 g of xylene and 4 g of dimethoxydibutyltin are heated to boiling on a 2.3 m high mirrored packed column. Ethanol passes overhead at 78-80 ° C. So much diethyl carbonate is dropped into the lower part of the column that the internal temperature is kept at 157-158 ° C. A total of 2.5 moles of diethyl carbonate are introduced over the course of 28 hours, while 1.8 moles of ethanol are distilled off. A weak stream of nitrogen leads the exhaust gas through a wash bottle loaded with n sodium hydroxide solution. The reaction mixture is fractionated over a 1 m column. After distilling off xylene and unreacted diethyl carbonate, 302 g of phenol pass over at 76-80 ° C./13 torr. The residue has a pale gray color. Ethylphenyl carbonate (113 g = 0.68 mol; n ²⁰ _D 1.4871) distill at 102-107 ° C / 12 torr and after removal of the column at 165-170 ° C / 13 torr 110 g (0.54 mol) diphenyl carbonate . The yield, based on the phenol converted, is over 99% of theory. Th. During the reaction, 0.005 mol of CO _{2 are} split off, which corresponds to a loss of 0.4196 carbonate.

Example 3 (comparative example)

In the same way as described in Example 2, 5 mol of phenol are reacted with 2.5 mol of diethyl carbonate using 4 g of titanium tetrabutylate as catalyst within 28 hours at an internal temperature of 157-158 ° C.

298 g of phenol are recovered. 149 g (0.9 mol) of ethylphenyl carbonate and 92 g (0.43 mol) of diphenyl carbonate are obtained.

The yield, based on the converted phenol, is thus 96% of theory. Th. During the reaction, 0.014 mol of CO _{z are} eliminated. This corresponds to a loss of carbonate of 1.05%.

The reaction product is colored deep red-brown before distillation. Even after the distillation, the diphenyl carbonate still shows a red-brown tinge.

Example 4

In an apparatus as described in Example 2, 1880 g (20 mol) of phenol, 300 g (2.54 mol) of diethyl carbonate and 20 g of tetrabutyldiphenoxystannoxane are heated to boiling while passing nitrogen over them until ethanol is overhead at 78-79.5 ° C distilled off. Diethyl carbonate is added in the lower part of the column in such a way that the bottom temperature is kept at 176 ° C.-178 ° C. A total of 644 g (8 mol) of diethyl carbonate are used in the course of 25 hours. 253 g (5.5 mol) of ethanol are distilled off. After distilling off the unreacted diethyl carbonate at 82-88 ° C / 20 Torr 1339 g of phenol, at 114-118 ° C / 20 Torr 291 g (1.75 mol) of ethylphenyl carbonate and 391 g (1.825 mol) of diphenyl carbonate. The yield, based on the converted phenol, is thus 98.5% of theory. Th. 1.35 g (0.035 mol) of carbon dioxide are detected in the exhaust gas, which corresponds to a loss of 1% carbonate.

Claims (4)

1. A process for the production of aromatic carbonic acid esters by transesterifying dialkyl carbonates witn'phenols under the elimination of alcohols and in the presence of transesterification catalysts, wherein organo tin compounds of the general formula I

in which

Y represents an

_OH or _OR ² radical, R² denoting a C₁―C₁₂ alkyl radical, a C₆―C₁₂ aryl radical or a C₇―C₁₃ alkylaryl radical, and

R¹ has the meaning of R² and

x denotes an integer from 1 to 3,

or dialkyl tin oxides each with 1-12 C-Atoms in the alkyl radical or organo tin compounds of the general formula II

in which

R' and R⁴ are the same or different and have the above-indicated meaning of R², and

R⁵ has the meaning of R² or represents a radical OR⁶ in which R⁶ has the meaning of R²

are used as reesterification catalysts, in quantities of from 0.001 to 20% by weight, based on the total amount of the reaction mixture.

2. A process according to claim 1, wherein as organo tin compounds trimethyl tin acetate, triethyl tin benzoate, tributyl tin acetate, triphenyl tin acetate, dibutyl tin diacetate, dibutyl tin dilaurate, dioctyl tin dilaurate, methoxy tributyl tin, methoxy triphenyl tin, phenoxy triethyl tin, dimethoxy dibutyl tin, diethoxy dibutyl tin, diphenoxy dibutyl tin, dimethoxy diphenyl tin, triethyl tin hydroxide, hexa-ethyl stannoxane, tetrabutyl diphenoxy stannoxane, dibutyl tin oxide or dioctyl tin oxide are used.

3. A process according to claims 1 and 2, wherein the reesterification takes place at temperatures of from 50 to 250°C.