US 5,344,954 AGranted

Process for the preparation of diaryl carbonates

AssigneeBayer Aktiengesellschaft

InventorsNorbert Schon, Hans-Josef Buysch, Paul Wagner, Reinhard Langer

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Abstract

Diaryl carbonates are prepared from dialkyl carbonates and phenolic compounds by transesterification in the presence of a transesterification catalyst at 60.degree.-320.degree. C. in an apparatus composed of two columns in a continuous procedure. In the first column, the starting materials form essentially the associated alkyl aryl carbonate, from which, in the second column, the diaryl carbonate is produced by further transesterification and disproportionation.

Claims20

Dependent claims

A process for the preparation of a diaryl carbonate of the formula

Ar.sup.1 --O--CO--O--Ar.sup.1
in which
Ar.sup.1 denotes unsubstituted phenyl or naphthyl or mono-substituted to trisubstituted phenyl, the substituents being identical or different and belonging to the group comprising C.sub.1 -C.sub.4 -alkyl, C.sub.1 -C.sub.4 -alkoxy and halogen,
by transesterification of 1 mol of an aromatic hydroxyl compound of the formula
Ar.sup.1 --OH
in which Ar.sup.1 has the meaning mentioned, with 0.1 to 10 mol of a dialkyl carbonate of the formula
R.sup.1 --O--CO--O--R.sup.1
in which
R.sup.1 denotes straight-chain or branched C.sub.1 -C.sub.6 -alkyl, cyclopentyl or cyclohexyl,
in the presence of a transesterification catalyst known per se in column apparatuses known from transesterifications, wherein the transesterification reaction is carried out in two columns connected one after the other in such a way that
a) in the first column, the aromatic hydroxyl compound is conducted in the liquid state from head to bottom and the dialkyl carbonate is conducted in the gaseous state against this liquid stream, the temperature being kept in the range from 100.degree. to 300.degree. C. and the pressure being kept in the range from 0.5 to 20 bar, and the dialkyl carbonate containing a portion from 0 to 5% by weight of the underlying alcohol, based on the overall weight of dialkyl carbonate and alcohol, that
b) at the head of the first column, the alcohol underlying the dialkyl carbonate and liberated in the transesterification is withdrawn in the gaseous state and at the bottom of the first column, a partly reacted transesterification product essentially composed of alkyl aryl carbonate is withdrawn in the liquid state, that
c) the bottom stream of the first column is fed into the central part of a second column, the temperature of which is kept in the range from 60.degree. to 320.degree. C. and the pressure of which is kept in the range from 0.05 to 10 bar, depending on the boiling point of the bottom stream fed in from the first column, a temperature gradient being applied to this second column in such a way that the alkyl aryl carbonate contained in the bottom stream fed in can escape from the central part of the second column essentially neither to the head nor to the bottom and that
d) at the head of the second column, a mixture of dialkyl carbonate, the underlying alcohol and excess aromatic hydroxyl compound and at the bottom of the second column, diaryl carbonate, which can contain alkyl aryl carbonate and aromatic hydroxyl compound, are withdrawn.

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Dependencies are inferred from the claim text.

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Abstract

A process for the preparation of a diaryl carbonate of the formula

Ar.sup.1 --O--CO--O--Ar.sup.1
in which
Ar.sup.1 denotes unsubstituted phenyl or naphthyl or mono-substituted to trisubstituted phenyl, the substituents being identical or different and belonging to the group comprising C.sub.1 -C.sub.4 -alkyl, C.sub.1 -C.sub.4 -alkoxy and halogen,
by transesterification of 1 mol of an aromatic hydroxyl compound of the formula
Ar.sup.1 --OH
in which Ar.sup.1 has the meaning mentioned, with 0.1 to 10 mol of a dialkyl carbonate of the formula
R.sup.1 --O--CO--O--R.sup.1
in which
R.sup.1 denotes straight-chain or branched C.sub.1 -C.sub.6 -alkyl, cyclopentyl or cyclohexyl,
in the presence of a transesterification catalyst known per se in column apparatuses known from transesterifications, wherein the transesterification reaction is carried out in two columns connected one after the other in such a way that
a) in the first column, the aromatic hydroxyl compound is conducted in the liquid state from head to bottom and the dialkyl carbonate is conducted in the gaseous state against this liquid stream, the temperature being kept in the range from 100.degree. to 300.degree. C. and the pressure being kept in the range from 0.5 to 20 bar, and the dialkyl carbonate containing a portion from 0 to 5% by weight of the underlying alcohol, based on the overall weight of dialkyl carbonate and alcohol, that
b) at the head of the first column, the alcohol underlying the dialkyl carbonate and liberated in the transesterification is withdrawn in the gaseous state and at the bottom of the first column, a partly reacted transesterification product essentially composed of alkyl aryl carbonate is withdrawn in the liquid state, that
c) the bottom stream of the first column is fed into the central part of a second column, the temperature of which is kept in the range from 60.degree. to 320.degree. C. and the pressure of which is kept in the range from 0.05 to 10 bar, depending on the boiling point of the bottom stream fed in from the first column, a temperature gradient being applied to this second column in such a way that the alkyl aryl carbonate contained in the bottom stream fed in can escape from the central part of the second column essentially neither to the head nor to the bottom and that
d) at the head of the second column, a mixture of dialkyl carbonate, the underlying alcohol and excess aromatic hydroxyl compound and at the bottom of the second column, diaryl carbonate, which can contain alkyl aryl carbonate and aromatic hydroxyl compound, are withdrawn.

11 more elements