EP0000880B1 - Process for the preparation of aromatic carbonic acid esters - Google Patents

Process for the preparation of aromatic carbonic acid esters Download PDF

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EP0000880B1
EP0000880B1 EP78100571A EP78100571A EP0000880B1 EP 0000880 B1 EP0000880 B1 EP 0000880B1 EP 78100571 A EP78100571 A EP 78100571A EP 78100571 A EP78100571 A EP 78100571A EP 0000880 B1 EP0000880 B1 EP 0000880B1
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Prior art keywords
methanol
dimethyl carbonate
transesterification
azeotrope
acid esters
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French (fr)
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EP0000880A1 (en
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Heinrich Dr. Krimm
Hans-Josef Dr. Buysch
Hans Dr. Rudolph
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Bayer AG
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    • CCHEMISTRY; METALLURGY
    • C07ORGANIC CHEMISTRY
    • C07CACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C68/00Preparation of esters of carbonic or haloformic acids
    • C07C68/06Preparation of esters of carbonic or haloformic acids from organic carbonates

Definitions

  • the invention relates to a process for the preparation of aromatic carbonic acid esters from dimethyl carbonate and phenols by transesterification.
  • 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, since considerable amounts of carbon dioxide are released in a side reaction.
  • DE-OS 2 528 412 describes a corresponding transesterification process for the preparation of aromatic carbonic acid esters in the presence of Lewis acids, i.e. Transition metal halides, or the corresponding acyloxy, alkoxy or aryloxy compounds described as catalysts.
  • Lewis acids i.e. Transition metal halides
  • acyloxy, alkoxy or aryloxy compounds described as catalysts.
  • a complex cleaning and separation operation must be carried out to obtain pure dimethyl carbonate (USP 3803201, DBP 2450856 and DE-OS 2 607 003), since in the known production processes of dimethyl carbonate (USP 2 642 858 and DE -OS 2 615 665) an approximately 30% by weight azeotrope with methanol is obtained.
  • dimethyl carbonate is thus transesterified with phenols to give the corresponding aromatic carbonates, transesterification catalysts being present.
  • Example 9 is carried out in the presence of n-hexane and an azeotrope of hexane, dimethyl carbonate and methyl alcohol is distilled off from the mixture of dimethyl carbonate, phenol, hexane and methyl alcohol. The consequence of this is that hexane and dimethyl carbonate have to be supplied continuously. In other words, with the methyl alcohol to be removed from the reaction, hexane and dimethyl carbonate are also separated, which is actually undesirable.
  • the task was therefore to find a transesterification process which allows the use of this azeotrope or another mixture of dimethyl carbonate and methanol.
  • concentration of dimethyl carbonate in methanol is in the range from 95 to 10% by weight.
  • the technically important 30% by weight azeotrope is preferred.
  • the invention therefore relates to a process for the preparation of aromatic carbonic acid esters by transesterification of dimethyl carbonate with phenols with the elimination of methanol in the presence of transesterification catalysts, which is characterized in that mixtures of dimethyl carbonate / methanol and methanol-immiscible azeotrope formers for methanol are used for the transesterification.
  • Azeotropic agents suitable according to the invention are preferably saturated aliphatic hydrocarbons with C 5 C 8 and with boiling points of 40-130 ° C, such as pentane, hexane, heptane, octane and isooctane, and also technical gasoline fractions which predominantly contain the hydrocarbons mentioned, such as petroleum ether, ligroin and Light petrol, as well as mixtures of the hydrocarbons mentioned.
  • the azeotroping agents are expediently used at least in an amount which is sufficient to distill over both the mixture introduced with the dimethyl carbonate / methano) mixture and the methanol formed during the transesterification.
  • the amount of azeotroping agent to be added can be found in the known tables (e.g. in Handbook of Chemistry and Physics, 51st Edit. (1970), the Rubber Comp., Cleveland / Ohio) with the information about the respective azeotrope compositions or can be determined by simple preliminary tests. An excess of azeotrope does not harm, it can only be kept as low as possible in the interest of an economic energy balance.
  • the process according to the invention succeeds in separating the azeotrope formed from the methanol formed during the transesterification reaction and one of the hydrocarbons mentioned, although these hydrocarbons are also known to form azeotropic-boiling mixtures with dimethyl carbonate.
  • the process of the invention achieves practically the same yields as in the known process without the dimethyl carbonate used having to be isolated before the transesterification reaction.
  • Suitable phenols are preferably compounds of the general formula (I) in which X is hydrogen, an alkyl radical with C, -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 are particularly preferred -Chlorphenol, o, m, p-ethylphenol, o, m, p-propylphenol, o, m, p-nitrophenol, 2e-dimethylphenol, 2,4-dimethylphenol or 3,4-dimethylphenol used.
  • X is hydrogen, an alkyl radical with C, -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 are particularly preferred -Chlorphenol, o, m, p-ethylphenol
  • bisphenols such as dihydroxydiarylalkanes with C 1 -C 4 in the alkyl radical, such as bisphenol A, can also be used.
  • the known transesterification catalysts can be used as catalysts. These are preferably alkali compounds such as lithium, sodium, potassium hydroxides, alcoholates, phenolates, carboxylates and carbonates. Preferably also be organotin compounds such as trimethyltin acetate, Triäthylzinnbenzoat, tributyltin acetate, triphenyltin acetate, dibutyltin acetate, dibutyltin dilaurate, dioctyltin dilaurate, Dibutylzinnadipinat, Methoxytributylzinn, Methoxytriphenylzinn, Phenoxytriäthylzinn, Dimethyldibutylzinn, Dimethylzinnglykolat, Diäthoxydibutylzinn, Diphenoxydibutylzinn, Dimethoxydiphenylzinn, Triäthylzinnhydroxid, triphenyltin hydroxide, Hexa
  • the catalysts are used in concentrations of about 0.001-20% by weight, based on the total reaction amount.
  • the weight ratio of dimethyl carbonate: phenol can vary within wide limits and can be between about 1:99 and 99: 1, preferably 1: 9 and 9: 1. It depends on this ratio whether arylphenyl carbonate or diaryl carbonate predominates in the final product.
  • the methylaryl carbonate formed in addition to diaryl carbonate can be separated off without difficulty by distillation and either reacted with fresh phenol or, after the diaryl carbonate has been separated off, recycled for further reaction.
  • the reaction temperatures are preferably in the range from 50 to 250 ° C., particularly preferably from 100 to 200 ° C. It is advantageous to work at a pressure of 1 Torr to 20 Atms., Preferably 1-5 Atms.
  • the preferred procedure is to bring the transesterification mixture to the desired reaction temperature in a longer column, to separate the methanol to the extent that it is released in the reaction mixture together with the azeotrope, if appropriate with the aid of an inert gas stream, and to dimethyl carbonate with the azeotrope in the Measurements of how poor the reaction material on both substances are to be fed to the lower part of the column.

Description

Die Erfindung betrifft ein Verfahren zur Herstellung aromatischer Kohlensäureester aus Dimethylcarbonat und Phenolen durch Umesterung.The invention relates to a process for the preparation of aromatic carbonic acid esters from dimethyl carbonate and phenols by transesterification.

Die Umesterung aliphatischer Kohlensäureester mit Phenolen in Anwesenheit starker Basen bzw. von Alkaliverbindungen ist nach DBP 971 790, 1 020 184, 1 026 958 und 1 031 512 bekannt. Derart katalysierte Umesterungsverfahren haben den Nachteil, wenig selektiv zu sein, da in einer Nebenreaktion erhebliche Mengen an Kohlendioxid freigesetzt werden.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, since considerable amounts of carbon dioxide are released in a side reaction.

In der DE-OS 2 528 412 ist ein entsprechendes Umesterungsverfahren zur Herstellung aromatischer Kohlensäureester in Gegenwart von Lewissäuren, d.h. Übergangsmetallhalogeniden, oder den entsprechenden Acyloxy-, Alkoxy- oder Aryloxyverbindungen als Katalysatoren beschrieben. Wird hierbei als Ausgangsmaterial Dimethylcarbonat verwendet, dann muß eine aufwendige Reinigungs- und Trennoperation zur Gewinnung reinen Dimethylcarbonats vorgenommen werden (USP 3803201, DBP 2450856 und DE-OS 2 607 003), da bei den bekannten Herstellungsverfahren von Dimethylcarbonat (USP 2 642 858 und DE-OS 2 615 665) ein etwa 30 Gew.-% Azeotrop mit Methanol anfällt. Gemäß DE-OS 2 528 412 wird somit Dimethylcarbonat mit Phenolen zu den entsprechenden aromatischen Carbonaten umgeestert, wobei Umesterungskatalysatoren vorhanden sind. Insbesondere wird im Beispiel 9 in Anwesenheit von n-Hexan gearbeitet und aus dem Gemisch von Dimethylcarbonat, Phenol, Hexan und Methylalkohol ein Azeotrop aus Hexan, Dimethylcarbonat und Methylalkohol abdestilliert. Dies hat zur Folge, daß ständig Hexan und Dimethylcarbonat nachgeliefert werden muß. Anders gesagt, mit dem Methylalkohol, der aus der Reaktion entfernt werden soll, wird auch Hexan und Dimethylcarbonat abgetrennt, was eigentlich unerwünscht ist.DE-OS 2 528 412 describes a corresponding transesterification process for the preparation of aromatic carbonic acid esters in the presence of Lewis acids, i.e. Transition metal halides, or the corresponding acyloxy, alkoxy or aryloxy compounds described as catalysts. If dimethyl carbonate is used as the starting material, then a complex cleaning and separation operation must be carried out to obtain pure dimethyl carbonate (USP 3803201, DBP 2450856 and DE-OS 2 607 003), since in the known production processes of dimethyl carbonate (USP 2 642 858 and DE -OS 2 615 665) an approximately 30% by weight azeotrope with methanol is obtained. According to DE-OS 2 528 412, dimethyl carbonate is thus transesterified with phenols to give the corresponding aromatic carbonates, transesterification catalysts being present. In particular, Example 9 is carried out in the presence of n-hexane and an azeotrope of hexane, dimethyl carbonate and methyl alcohol is distilled off from the mixture of dimethyl carbonate, phenol, hexane and methyl alcohol. The consequence of this is that hexane and dimethyl carbonate have to be supplied continuously. In other words, with the methyl alcohol to be removed from the reaction, hexane and dimethyl carbonate are also separated, which is actually undesirable.

Es stellte sich deshalb die Aufgabe, ein Umesterungsverfahren zu finden, das die Verwendung dieses Azeotrops bzw. eines sonstigen Gemisches aus Dimethylcarbonat und Methanol gestattet. Die Konzentration von Dimethylcarbonat in Methanol liegt im Bereich von 95 bis 10 Gew.-%. Bevorzugt wird das technisch wichtige 30 Gew.-% Azeotrop.The task was therefore to find a transesterification process which allows the use of this azeotrope or another mixture of dimethyl carbonate and methanol. The concentration of dimethyl carbonate in methanol is in the range from 95 to 10% by weight. The technically important 30% by weight azeotrope is preferred.

Die Lösung dieser Aufgabe gelang durch die Mitverwendung von mit Methanol nicht mischbaren Azeotropbildnern für Methanol.This problem was solved by using methanol-immiscible azeotroping agents for methanol.

Gegenstand der Erfindung ist daher ein Verfahren zur Herstellung aromatischer Kohlensäureester durch Umesterung von Dimethylcarbonat mit Phenolen unter Abspaltung von Methanol in Gegenwart von Umesterungskatalysatoren, das dadurch gekennzeichnet ist, daß man zur Umesterung Gemische aus Dimethylcarbonat/Methanol und mit Methanol nicht mischbare Azeotropbildner für Methanol verwendet.The invention therefore relates to a process for the preparation of aromatic carbonic acid esters by transesterification of dimethyl carbonate with phenols with the elimination of methanol in the presence of transesterification catalysts, which is characterized in that mixtures of dimethyl carbonate / methanol and methanol-immiscible azeotrope formers for methanol are used for the transesterification.

Erfindungsgemaß geeignete Azeotropbildner sind vorzugsweise gesättigte aliphatische Kohlenwasserstoffe mit C5 C8 und mit Siedepunkten von 40 - 130°C, wie Pentan, Hexan, Heptan, Octan und Isooctan, ferner technische Benzinfraktionen, die vorwiegend die genannten Kohlenwasserstoffe enthalten, wie Petrolether, Ligroin und Leichtbenzin, sowie Gemische der genannten Kohlenwasserstoffe.Azeotropic agents suitable according to the invention are preferably saturated aliphatic hydrocarbons with C 5 C 8 and with boiling points of 40-130 ° C, such as pentane, hexane, heptane, octane and isooctane, and also technical gasoline fractions which predominantly contain the hydrocarbons mentioned, such as petroleum ether, ligroin and Light petrol, as well as mixtures of the hydrocarbons mentioned.

Die Azeotropbildner werden zweckmäßig zumindest in einer solchen Menge eingesetzt, die ausreicht, sowohl das mit dem Dimethyl- carbonat/Methano)-Gemisch eingebrachte als auch das während der Umesterung gebildete Methanol überzudestillieren. Die zuzusetzende Menge an Azeotropbildner kann den bekannten Tabellen (z.B. in Handbook of Chemistry and Physics, 51. Edit. (1970), the Rubber Comp., Cleveland/Ohio) mit den Angaben über die jeweiligen Azeotropzusammensetzungen entnommen oder durch einfache Vorversuche ermittelt werden. Ein Überschuß an Azeotropbildner schadet nicht, er ist nur im Interesse einer ökonomischen Energiebilanz möglichst niedrig zu halten.The azeotroping agents are expediently used at least in an amount which is sufficient to distill over both the mixture introduced with the dimethyl carbonate / methano) mixture and the methanol formed during the transesterification. The amount of azeotroping agent to be added can be found in the known tables (e.g. in Handbook of Chemistry and Physics, 51st Edit. (1970), the Rubber Comp., Cleveland / Ohio) with the information about the respective azeotrope compositions or can be determined by simple preliminary tests. An excess of azeotrope does not harm, it can only be kept as low as possible in the interest of an economic energy balance.

Überraschenderweise gelingt es mit dem erfindungsgemäßen Verfahren, das aus dem während der Ümesterungsreaktion gebildeten Methanol und einem der genannten Kohlenwasserstoffe bestehende Azeotrop abzutrennen, obwohl diese Kohlenwasserstoffe bekanntlich auch mit Dimethylcarbonat azeotropsiedende Gemische bilden. Nach dem Verfahren der Erfindung werden praktisch die gleichen Ausbeuten wie nach dem bekannten Verfahren erzielt, ohne daß das eingesetzte Dimethylcarbonat vor der Umesterungsreaktion isoliert werden muß.Surprisingly, the process according to the invention succeeds in separating the azeotrope formed from the methanol formed during the transesterification reaction and one of the hydrocarbons mentioned, although these hydrocarbons are also known to form azeotropic-boiling mixtures with dimethyl carbonate. The process of the invention achieves practically the same yields as in the known process without the dimethyl carbonate used having to be isolated before the transesterification reaction.

Als Phenole eignen sich vorzugsweise Verbindungen der allgemeinen Formel (I)

Figure imgb0001
in der X für Wasserstoff, einen Alkylrest mit C,-C3, ein Halogenatom, vorzugsweise Chlor, oder eine Nitrogruppe und n für 1 oder 2 stehen, besonders bevorzugt werden Phenol, o,m,p-Kresol, o,m,p-Chlorphenol, o,m,p-Äthyl- phenol, o,m,p-Propylphenol, o,m,p-Nitrophenol, 2e-Dimethylphenol, 2,4-Dimethylphenol oder 3,4-Dimethylphenol verwendet.Suitable phenols are preferably compounds of the general formula (I)
Figure imgb0001
in which X is hydrogen, an alkyl radical with C, -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 are particularly preferred -Chlorphenol, o, m, p-ethylphenol, o, m, p-propylphenol, o, m, p-nitrophenol, 2e-dimethylphenol, 2,4-dimethylphenol or 3,4-dimethylphenol used.

Anstelle der einwertigen Phenole können auch Bisphenole wie Dihydroxydiarylalkane mit Cl-C4 im Alkylrest wie z.B. Bisphenol A, eingesetzt werden.Instead of the monohydric phenols, bisphenols such as dihydroxydiarylalkanes with C 1 -C 4 in the alkyl radical, such as bisphenol A, can also be used.

Als Katalysatoren können die bekannten Umesterungskatalysatoren verwendet werden. Vorzugsweise sind dies Alkaliverbindungen wie Lithium-, Natrium-, Kaliumhydroxide, -alkoholate, -phenolate, -carboxylate und -carbonate. Vorzugsweise werden auch zinnorganische Verbindungen wie Trimethylzinnacetat, Triäthylzinnbenzoat, Tributylzinnacetat, Triphenylzinnacetat, Dibutylzinnacetat, Dibutylzinndilaurat, Dioctylzinndilaurat, Dibutylzinnadipinat, Methoxytributylzinn, Methoxytriphenylzinn, Phenoxytriäthylzinn, Dimethyldibutylzinn, Dimethylzinnglykolat, Diäthoxydibutylzinn, Diphenoxydibutylzinn, Dimethoxydiphenylzinn, Triäthylzinnhydroxid, Triphenylzinnhydroxid, Hexaäthylstannoxan, Hexabutylstannoxan, Tetrabutyldiphenoxystannoxan, Dibutylzinnoxid und Dioctylzinnoxid und Titanverbindungen vom Typ des Tetrabutyl- oder Tetraphenyltitanats eingesetzt.The known transesterification catalysts can be used as catalysts. These are preferably alkali compounds such as lithium, sodium, potassium hydroxides, alcoholates, phenolates, carboxylates and carbonates. Preferably also be organotin compounds such as trimethyltin acetate, Triäthylzinnbenzoat, tributyltin acetate, triphenyltin acetate, dibutyltin acetate, dibutyltin dilaurate, dioctyltin dilaurate, Dibutylzinnadipinat, Methoxytributylzinn, Methoxytriphenylzinn, Phenoxytriäthylzinn, Dimethyldibutylzinn, Dimethylzinnglykolat, Diäthoxydibutylzinn, Diphenoxydibutylzinn, Dimethoxydiphenylzinn, Triäthylzinnhydroxid, triphenyltin hydroxide, Hexaäthylstannoxan, Hexabutylstannoxan, Tetrabutyldiphenoxystannoxan, dibutyl tin oxide and Dioctyltin oxide and titanium compounds of the tetrabutyl or tetraphenyl titanate type are used.

Die Katalysatoren werden in Konzentrationen von etwa 0,001-20 Gew.%, bezogen auf die gesamte Reaktionsmenge, eingesetzt. Das Gewichtsverhältnis von Dimethylcarbonat: Phenol kann in weiten Grenzen schwanken und zwischen etwa 1:99 und 99:1, vorzugsweise 1:9 und 9:1 liegen. Von diesem Verhältnis hängt es ab, ob im Endproduckt Arylphenylcarbonat oder Diarylcarbonat überwiegt.The catalysts are used in concentrations of about 0.001-20% by weight, based on the total reaction amount. The weight ratio of dimethyl carbonate: phenol can vary within wide limits and can be between about 1:99 and 99: 1, preferably 1: 9 and 9: 1. It depends on this ratio whether arylphenyl carbonate or diaryl carbonate predominates in the final product.

Ohne Schwierigkeit kann des neben Diarylcarbonat gebildete Methylarylcarbonat durch Destillation abgetrennt und entweder mit frischem Phenol umgesetzt oder nach Abtrennung des Diarylcarbonats zur weiteren Umsetzung zurückgeführt werden.The methylaryl carbonate formed in addition to diaryl carbonate can be separated off without difficulty by distillation and either reacted with fresh phenol or, after the diaryl carbonate has been separated off, recycled for further reaction.

Die Reaktionstemperaturen liegen bevorzugt im Bereich von 50 - 250°C, besonders bevorzugt von 100 - 200°C. Vorteilhafterweise wird bei einem Druck von 1 Torr bis 20 Atms., vorzugsweise bei 1-5 Atms gearbeitet.The reaction temperatures are preferably in the range from 50 to 250 ° C., particularly preferably from 100 to 200 ° C. It is advantageous to work at a pressure of 1 Torr to 20 Atms., Preferably 1-5 Atms.

Die bevorzugte Verfahrensweise besteht darin, das Umesterungsgemisch an einer längeren Kolonne auf die gewünschte Reaktionstemperatur zu bringen, das Methanol in dem Maße, wie es im Reaktionsgut freigesetzt wird, zusammen mit dem Azeotropbildner gegebenenfalls mit Hilfe eines inerten Gasstromes abzutrennen und Dimethylcarbonat mit dem Azeotropbildner in dem Maße wie das Reaktionsgut an beiden Stoffen verarmt, dem unteren Teil der Kolonne zuzuführen.The preferred procedure is to bring the transesterification mixture to the desired reaction temperature in a longer column, to separate the methanol to the extent that it is released in the reaction mixture together with the azeotrope, if appropriate with the aid of an inert gas stream, and to dimethyl carbonate with the azeotrope in the Measurements of how poor the reaction material on both substances are to be fed to the lower part of the column.

Die Verfahrensproduckte können in bekannter Weise zu Polycarbonaten umgesetzt werden oder dienen als Ausgangsstoffe für Pflanzenschutzmittel.
Beispiel

  • a) An einer mit Glasringen beschickten 2,9 m hohen verspiegelten Füllkörperkolonne werden 940 g (10 Mol) Phenol, 150 g 30 proz. Dimethylcarbonat/Methanol-Azeotrop (0,5 Mol), 100 g n-Heptan und 2 g Tetrabutyltitanat erhitzt, so daß bei 58-59°C ein im wesentlichen aus Heptan und Methanol bestehendes zweiphasiges Azeotrop abgenommen werden kann. Im Laufe der 45 stdg. Reaktionszeit wird die dem abdestillierten Methanoi/Heptan-Gemisch entsprechende Menge Dimethylcarbonat und Heptan in der Mitte der Kolonne so zugesetzt, daß die Sumpftemperatur 160°C beträgt. Insgesamt werden auf diese Weise 340 g Dimethylcarbonat/Methanol-Azeotrop mit 400 g Heptan entsprechend 1,13 Mol Dimethylcarbonat eingesetzt. Das Reakationsgut wird über eine 1 m hohe Kolonne fraktioniert. Nach einem aus Methanol, Dimethylcarbonat und Heptan bestehenden Vorlauf gehen bei 69 - 74°C/8 Torr 887 g nicht umgesetztes Phenol, bei 83 - 93°C/8 Torr 30,6 g Methylphenylcarbonat und bei 146 - 160°C/8 Torr 32.5 g Diphenylcarbonat über. Somit beträgt die Ausbeute an aromatischen Carbonaten, bezogen auf umgesetztes Phenol 94 % d. Th.
  • b) Ein Gemisch von 45,6 g (0,2 Mol) 2,2-Bis-(4-hydroxyphenyl)-propan, 47.1 g (0,22 Mol) des nach a) hergestellten Diphenylcarbonats und 0,008 g Natriummethylat wird langsam bis auf 210° unter 20 Torr erhitzt, wobei die Hauptmenge des abgespaltenen Phenols abdestilliert. Dann wird der Druck auf 0,2 Torr errnäßigt und die Temperatur während einer Stunde auf 250°C und während zweier weiterer Stunden auf 280°C erhöht, bis die Schmelze so zäh geworden ist, daß sie sich kaum mehr rühren läßt. Beim Abkühlen erhält man einen klaren, farblosen, elastischen Kunstoff, aus dessen Schmelze Formkörper mit hervorragenden Festigkeitseigenschaften hergestellt werden können.
The process products can be converted to polycarbonates in a known manner or serve as starting materials for crop protection agents.
example
  • a) 940 g (10 mol) of phenol, 150 g of 30 percent are on a 2.9 m high mirrored packed column loaded with glass rings. Dimethyl carbonate / methanol azeotrope (0.5 mol), 100 g of n-heptane and 2 g of tetrabutyl titanate are heated so that a two-phase azeotrope consisting essentially of heptane and methanol can be removed at 58-59 ° C. In the course of the 45 hour reaction time, the amount of dimethyl carbonate and heptane corresponding to the distilled-off methanoi / heptane mixture is added in the middle of the column in such a way that the bottom temperature is 160.degree. A total of 340 g of dimethyl carbonate / methanol azeotrope with 400 g of heptane corresponding to 1.13 mol of dimethyl carbonate are used in this way. The reaction material is fractionated over a 1 m high column. After a preliminary run consisting of methanol, dimethyl carbonate and heptane, 887 g of unreacted phenol go at 69-74 ° C./8 torr, 30.6 g of methylphenyl carbonate at 83-93 ° C./8 torr and at 146-160 ° C./8 torr 32.5 g of diphenyl carbonate. The yield of aromatic carbonates, based on the converted phenol, is therefore 94% of theory. Th.
  • 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 is slowly to heated to 210 ° under 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.

Claims (4)

1. A process for the production of aromatic carbonic acid esters by transesterifying dimethyl carbonate with phenols under the elimination of methanol in the presence of transesterification catalysts, characterised in that for the transesterification mixtures of dimethyl car- bonate/methanol and methanol-immiscible azeotrope formers for methanol are used and the mixture of methanol and azeotrope former is distilled off during the reaction.
2. A process according to claim 1, characterised in that the azeotrope formers used are saturated aliphatic Cs-Ca hydrocarbons or commercial gasoline fractions which predominantly contain the above-mentioned hydrocarbons.
3.. A process according to claims 1 and 2, characterised in that the concentration of the dimethyl carbonate in methanol is within the range of 10 to 95% by weight.
4. A process according to claims 1 to 3, characterised in that the transesterification is carried out at temperatures from 50 to 250°C.
EP78100571A 1977-08-10 1978-08-02 Process for the preparation of aromatic carbonic acid esters Expired EP0000880B1 (en)

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DE19772736063 DE2736063A1 (en) 1977-08-10 1977-08-10 Process for the preparation of aromatic carbonic acid esters

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DE2860326D1 (en) 1981-03-12
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IT7850655A0 (en) 1978-08-08
US4252737A (en) 1981-02-24

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