Process for the production of aryl carbonates

Details Process for the production of aryl carbonates Process for the production of aryl carbonates

1993-08-18

2001-01-16

Rotman, Alan L. (Department: 1625)

Organic compounds -- part of the class 532-570 series

Organic compounds

Heterocyclic carbon compounds containing a hetero ring...

C558S280000, C558S281000, C558S282000, C549S478000

Reexamination Certificate

active

06175017

ABSTRACT:

This invention relates to a process for the production of carbonates containing aromatic ester groups by reaction of aromatic monohydroxy compounds with phosgene or chlorocarbonic acid esters of aromatic monohydroxy compounds with elimination of hydrogen chloride in the presence of active carbon.
Carbonates containing aromatic ester groups are suitable for the production of polycarbonates by the melt transesterification process and for the production of phenyl urethanes or are intermediates for the production of active substances in the pharmaceutical and plant protection fields.
It is known that aryl carbonates can be obtained by interfacial phosgenation (Schotten-Baumann reaction) of aromatic hydroxy compounds. The use of solvents and sodium hydroxide in this reaction is a disadvantage because partial saponification of phosgene or chlorocarbonic acid ester can occur under the effect of the sodium hydroxide. In either case, the large quantities of sodium chloride accumulating are a source of wastewater pollution. In addition, care has to be taken in recovery of the solvent to ensure effective protection of the environment.
Accordingly, it has been proposed to carry out a condensation reaction without using solvents in the presence of tetramethyl ammonium halides as catalysts (U.S. Pat. No. 2,837,555). However, the quantities of catalyst required for this purpose are relatively large. Quantities of 5 to 7% by weight catalyst, based on the quantity of phenol used, generally have to be used to obtain economic reaction rates. The reaction temperatures of 180 to 215° C. involve the danger of decomposition of the thermolabile tetramethyl ammonium halides. In addition, the catalyst has to be subsequently removed by washing with water which seriously complicates its recovery. In addition, far more than the stoichiometrically necessary quantity of phosgene is used. The yields of diphenyl carbonate amount to little more than 80% of the theoretical.
In another process (U.S. Pat. No. 3,234,263), diphenyl carbonates are obtained by heating phenyl chlorocarbonic acid esters in the presence of large quantities of alkali (alkaline earth) metal compounds and tertiary nitrogen bases as catalysts. However, this process has the disadvantage that high temperatures have to be applied to obtain even remotely economical reaction times. In this process, half the phosgene originally used is lost in the form of CO
2
. In addition, the chlorocarbonic acid esters have to be synthesized in a separate preliminary process step.
DE-OS 2,447,348 relates to a process for the production of aryl carbonates in which phenols are phosgenated in the presence of heterocyclic nitrogen bases. Although this process is simpler than the processes mentioned above and gives better yields, the difficulties of clean removal of the catalyst remain. Accordingly, there is still a need for a simple continuous process.
It has now been found that carbonates containing aryl groups can be obtained very simply by reaction of phenols with phosgene or chlorocarbonic acid esters at elevated temperature in the presence of active carbon as catalyst.
Accordingly, the present invention relates to a process for the production of aryl carbonates by reaction of aromatic monohydroxy compounds with phosgene or chlorocarbonic acid esters of aromatic monohydroxy compounds, characterized in that the reaction is carried out at a temperature of 50 to 350° C. in the presence of active carbon as catalyst.
The process according to the invention has the major advantage that the catalyst can be removed very easily and no impurities are left in the crude reaction product. Working up is thus made considerably easier.
Aromatic monohydroxy compounds for the process according to the invention are those corresponding to the following formula
Ar
1
—OH  (I)
in which
Ar
1
represents phenyl, naphthyl, anthryl, phenanthryl, indanyl, tetrahydronaphthyl or the residue of a 5- or 6-membered aromatic heterocycle containing 1 or 2 hetero atoms from the group consisting of N, O and S; these isocyclic or heterocyclic residues may be substituted by 1 or 2 substituents from the group consisting of linear or branched C
1-4
alkyl, linear or branched C
1-4
alkoxy, phenyl, cyano and halogen and the heterocyclic residues may be attached to a fused benzene ring.
The linear or branched C
1-4
alkyl or C
1-4
alkoxy may be methyl, ethyl, propyl, isopropyl, butyl, isobutyl or methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, preferably methyl or methoxy. The halogen is, for example, fluorine, chlorine or bromine, preferably chlorine.
Preferred aromatic hydroxy compounds for the process according to the invention are those corresponding to the following formula
Ar
2
—OH  (II)
in which
Ar
2
represents phenyl or pyridyl which may be substituted by 1 or 2 substituents from the group consisting of linear or branched C
1-4
alkyl, linear or branched C
1-4
alkoxy, phenyl, cyano and halogen; in addition, the pyridyl may be attached to a fused benzene ring.
Particularly preferred aromatic hydroxy compounds for the process according to the invention are those corresponding to the following formula
Ar
3
—OH  (III)
in which
Ar
3
represents phenyl which may be substituted by 1 or 2 substituents from the group consisting of linear or branched C
1-4
alkyl, linear or branched C
1-4
alkoxy, phenyl, cyano and halogen and is preferably mono- or disubstituted by methyl, ethyl, propyl, isopropyl, methoxy, ethoxy, cyano, fluorine, chlorine and/or bromine. Examples of aromatic monohydroxy compounds are phenol, o-, m- and p-cresol, o-, m- and p-isopropylphenol, the corresponding halophenols or alkoxyphenols, such as p-chlorophenol or p-methoxyphenol; also monohydroxy compounds of naphthalene, anthracene and phenanthrene; and 4-hydroxypyridine and hydroxyquinoline.
The process according to the invention may be carried out both with phosgene and with chlorocarbonic acid esters of aromatic monohydroxy compounds. Where the process according to the invention is carried out with phosgene, the chlorocarbonic acid ester of the aromatic monohydroxy compound is initially formed and is reacted with more of the aromatic monohydroxy compound present in the reaction mixture to form the symmetrical diaryl carbonate of this aromatic monohydroxy compound. Where chlorocarbonic acid esters and an aromatic monohydroxy compound are used as starting materials, symmetrical or asymmetrical carbonates may be obtained, depending on the ester group in the chlorocarbonic acid ester. Symmetrical carbonates are obtained when the ester group present in the chlorocarbonic acid ester and the aromatic monohydroxy compound are the same. However, since symmetrical diaryl carbonates such as these can also be directly prepared from the aromatic monohydroxy compound by reaction with phosgene in the described manner, a procedure such as this has only minimal significance. However, the production of asymmetrical carbonates from an aromatic monohydroxy compound and a chlorocarbonic acid ester is of considerable significance. In this case, the ester group in the chlorocarbonic acid ester may also be an aromatic monohydroxy compound which falls within the scope of the disclosure for Ar
1
—OH (I) or AR
2
—OH (II) or AR
3
—OH (III), but—in the context of the formation of asymmetrical diaryl carbonates—has a different substitution pattern from the monohydroxy compound used.
Accordingly, suitable chlorocarbonic acid esters for the process according to the invention are those corresponding to the following formula
R
1
—OCOCl  (IV)
in which R
1
represents Ar
1
.
Particularly suitable chlorocarbonic acid esters for the process according to the invention are those corresponding to the following formula
R
2
—OCOCl  (V)
in which R
2
represents Ar
2
.
Particularly preferred chlorocarbonic acid esters for the process according to the invention correspond to the following formula
R
3
—OCOCl  (VI)
in which R
3
represents Ar
3
. Where Ar
1
or Ar
2
or Ar
3
is disubstituted, the two subs

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