DE2736062A1 - Process for the preparation of aromatic carbonic acid esters - Google Patents

Description

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5090 Leverkusen, Bayerwerk Str-kl

Process for the production of aromatic carbonic acid esters

The invention relates to a process for the production 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 alkali compounds is known from DBP 971 790, 1 020 184, 1 026 958 and 1 031 312. Such catalyzed transesterification processes have the disadvantage of being not very selective, so that considerable amounts of carbon dioxide are released in a side reaction will.

In DOS 2 528 412 and 2 552 9Ο7 transesterification processes for the production of aromatic carbonic acid esters are described, where Lewis acids are used as catalysts, i.e. transition metal halides or the corresponding acyloxy, Alkoxy or aryloxy compounds can be used. From 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. These

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However, titanium-based catalysts have the disadvantage that they give the end products a strong red-brown color. This coloring is especially unpleasant when the end products are not crystallized or distilled have it cleaned, as is the case with polycarbonates, for example.

It was therefore the task of finding catalysts that, in addition to at least one of the titanium catalysts Equivalent transesterification effectiveness and selectivity also have the advantage that the end products are not essential to discolor.

The inventive solution to the problem was achieved by Use of organotin compounds as transesterification catalysts. The invention is therefore a Process for the production of aromatic carbonic acid esters by transesterification of dialkyl carbonates with phenols with elimination of alcohols in the presence of catalysts, which is characterized in that as catalysts Organotin compounds are used.

The favorable catalytic action of the catalysts according to the invention is surprising, since it is difficult to find them can be referred to as Lewis acids. On the contrary, it can be stated that it is precisely the organotin halogen compounds such as dibutyltin dichloride or dioctyltin dichloride, which are most likely to have a formal relationship could be attributed to typical Lewis acids such as aluminum trichloride or titanium tetrachloride, completely ineffective are.

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The effectiveness of the catalysts of the invention, as measured by the rate at which alcohol is split off, differs practically do not differ from compounds of titanium such as tetrabutyl titanate Advantages can be seen in the fact that in the two process products alkyl aryl carbonate and diaryl carbonate Has a ratio has been shifted in favor of the latter and, under comparable conditions, is about half the amount Carbon dioxide elimination is observed.

Are particularly suitable for the method according to the invention Organotin compounds of the general formula (I)

(R ¹ J-Sn- (Y) (I),

4-x ^X

in the

Y is a radical OCR ² , OH or OR ² , where R ^{2 is} an alkyl radical with C ^ -C ₁₂ / an aryl radical with C, - or an alkylaryl radical with C ₇ -C ₁₃ , and

R has the meaning of R, and

χ denotes an integer from 1-3, or dialkyltin oxides each with 1-12 C atoms in the alkyl radical or organotin compounds of the general formula (II)

(ID, in the

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3 4
R and R, identical or different, have the meaning of

R have

5 2

and R has the meaning of R or for a radical

OR stands in which R has the meaning of R.

Very particularly suitable ones for the process according to the invention Organotin compounds are z. B .:

Trimethyltin acetate, triethyltin benzoate, tributyltin acetate, triphenyltin acetate, dibutyltin diacetate, dibutyltin dilaurate, Dioctyltin dilaurate, dibutyltin adipinate, methoxytributyltin, Methoxytriphenyltin, phenoxytriethyltin, dimethoxydibutyltin, Dimethyltin glycolate, diethoxydibutyltin, diphenoxydibutyltin, Dimethoxydiphenyltin, triethyltin hydroxide, triphenyltin hydroxide, hexaäthylstannoxane, hexabutylstannoxane, tetrabutyldiphenoxystannoxane, Dibutyl tin oxide and dioctyl tin oxide.

It is preferred to use compounds whose vapor pressure is also at the required reaction temperatures is low, i.e. those with organometallic alkyl radicals of at least four carbon atoms.

Preferred dialkyl carbonates are those of the general formula (III)

C- (OR ⁷ J ₂ (III)

used, in which R is an alkyl radical with C ₁ -C ₁ -. Dimethyl carbonate, diethyl carbonate, dipropyl carbonate, diisopropyl carbonate, dibutyl carbonate,
Dioctyl carbonate, diisooctyl carbonate and dicyclohexyl carbonate can be used.

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Suitable phenols are preferably those of the general formula (IV)

(IV)

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

Instead of the monohydric phenols, bisphenols such as dihydroxydiarylalkanes with C ₁ -C ₄ in the alkyl radical, for example bisphenol A, can also be used. They are not split under the process conditions and can thus be converted directly into polycarbonates. Assuming pure raw materials, these are almost colorless and do not require any additional purification steps.

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

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

The reaction temperatures are preferably in the range of 50 - 25O ° C, more preferably in the range of 200 1OO ⁰ C. Advantageously, abs at a pressure of 1 Torr to 20 atm, preferably 1-5 atm worked.

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

A preferred procedure is to bring the transesterification mixture on a longer column to the desired reaction temperature, during the
Alcohol overhead to the extent that it is in the reaction product
is released, optionally separated with the aid of an inert gas stream.

In another variant of the process, excess
Dialkyl carbonate through a melt of the to be reacted
Phenol passed, while a mixture consisting of the alcohol and dialkyl carbonate is continuously distilled off. The separation of the components can be done in a separate
Step according to usual methods.

The results of both approaches differ
not essential.

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

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example 1

a) In a 2.9 m high mirrored one filled with glass rings Full body column are 470 g (5 mol) of phenol, 90 g (1 mol) of dimethyl carbonate, 50 g of n-heptane and 5.7 g of diphenoxydibutyltin heated to the boil. By dropping in heptane, the internal temperature is at Maintained 155 ° C. A mixture of methanol and heptane is distilled overhead at 59.5-60 ° C. In this scale, as the reaction progresses, more dimethyl carbonate is added dropwise in the lower third of the column. All in all 315 g = 3.5 mol of dimethyl carbonate are used within 30 h. For example during the reaction The carbon dioxide that is split off is filled with η sodium hydroxide solution by means of a weak stream of nitrogen Wash bottle absorbed. The reaction material is fractionated over a 1.1 m high column. After one out Methanol, dimethyl carbonate and heptane existing first runnings go at 80-87 ° C / 15 Torr 313 g (3.33 mol) unreacted Phenol, at 95 - 97 ° C / 13 Torr 118 g (0.78 mol) Methylphenyl carbonate (n 1.4970) and after removing the column at 165-172 ° C / 13 Torr 90 g (0.44 mol) of crystalline Diphenyl carbonate over. The yield, based on converted phenol, is thus 98.5% of theory. Th. According to the analytical C0_ determination, 0.011 mol of carbon dioxide is absorbed in the washing 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 prepared according to a)

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provided diphenyl carbonate and 0.008 g sodium methylate is slowly heated up to 210 ° below 20 Torr, with most of the phenol held off by distillation. Then the pressure is decreased to 0.2 torr and

the temperature is increased to 250 ° C. over the course of one hour and to 280 ° C. over a further two hours until the melt has become so tough that it can hardly be stirred. When cooling down you get a clear, colorless, elastic plastic, molded from its melt with excellent strength properties can be produced.

Example 2

470 g (5 moles) of phenol, 118 g (1 mol) of diethyl carbonate, 200 g of xylene and 4 g dimethoxydibutyltin are heated to boiling in a 2.3 m high mirrored packed column overhead is at 78-80 ⁰ C over ethanol. So much diethyl carbonate is added dropwise to the lower part of the column that the internal temperature is kept at 157-158 ° C. A total of 2.5 mol of diethyl carbonate are introduced over the course of 28 hours, while 1.8 mol of ethanol are distilled off. A weak stream of nitrogen leads the exhaust gas through a washing bottle filled with η-sodium hydroxide solution. The reaction mixture is fractionated over a 1 m column. 302 g phenol 80 ⁰ C / 13 Torr over - after distilling off xylene and unreacted diethyl go at 76th The residue has a pale gray color. Ethyl phenyl carbonate (113 g = 0.68 mol; n _ß 1.4871) distills at 102-1107 ° C./12 Torr and 110 g after removal of the column at 165-170 ° C./13 Torr

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(O, S4 moles) diphenyl carbonate. The yield based on converted phenol, is over 99% of theory. Th. During the reaction, 0.005 mol of CO- are split off, which corresponds to a loss of 0.41% carbonate.

Example 3 (comparative example)

In the same way as described in Example 2, 5 moles of phenol with 2.5 moles of diethyl carbonate are included Use of 4 g of titanium tetrabutoxide as a catalyst within 28 hours at an internal temperature of 157-158 ° C implemented.

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

The yield, based on converted phenol, is therefore 96% of theory. Th. 0.014 mol of CO _{2 are} split off during the reaction. This corresponds to a carbonate loss of 1.05%.

The reaction product: Before the distillation, it is deeply red-brown in color. Even after the distillation, the diphenyl carbonate has another red-brown cast.

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 under transfer

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heated to boiling by nitrogen, until ethanol distilled off overhead at 78-79.5 ° C. In the lower part of the column, diethyl carbonate is added in such a way that the bottom temperature is kept at 176.degree. C.-178.degree. In the course of 25 hours, a total of 644 g (8 mol) of diethyl carbonate are used. 253 g (5.5 mol) of ethanol are distilled off. After the unreacted diethyl carbonate has been distilled off, 1339 g of phenol pass over at 82-88 ° C./20 Torr, and 291 g (1.75 mol) of ethylphenyl carbonate and 391 g (1.825 mol) of diphenyl carbonate at 114-118 ° C./20 Torr. The yield, based on 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.

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Claims (1)

Claim * 1. Process for the production of aromatic carbonic acid esters by transesterification of dialkyl carbonates with phenols with elimination of / alcohols in the presence of transesterification catalysts, characterized in that the transesterification catalysts used are organotin compounds used. Le A 18 288-1Γ. - 909808/021