Interfacial method of preparing ester-substituted diaryl...

Details Interfacial method of preparing ester-substituted diaryl... Interfacial method of preparing ester-substituted diaryl...

2001-07-24

2002-07-16

Lambkin, Deborah C. (Department: 1626)

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

Organic compounds

Carbonate esters

Reexamination Certificate

active

06420588

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to a method of making ester-substituted diaryl carbonates and in particular to a method of making bis methyl salicyl carbonate.
Ester-substituted diaryl carbonates such as bis-methyl salicyl carbonate have proven to be useful starting materials in the preparation of polycarbonates via the melt reaction of a diaryl carbonate with aromatic dihydroxy compounds. See for example, U.S. Pat. No. 4,323,668 in which rates of polymerization of bis-methyl salicyl carbonate with bisphenol A were shown to be higher than the corresponding rates of polymerization of bisphenol A with an unsubstituted diaryl carbonate, diphenyl carbonate. Notwithstanding the simplicity of its structure there are few reported preparations of ester-substituted diaryl carbonates.
A classical preparation of diaryl carbonates involves the reaction of a hydroxy aromatic compound such as phenol with phosgene gas in a two phase reaction system comprising water, an acid acceptor such as sodium hydroxide and a solvent such as methylene chloride or chloroform. Typical interfacial conditions used to prepare diphenyl carbonate (DPC) utilize water and methylene chloride phases, sodium hydroxide as a pH control measure and triethylamine as a catalyst. Under such conditions it is possible to convert phenol to DPC in essentially quantitative yield. However, application of these same conditions to methyl salicylate results in only modest conversion of this ester-substituted phenol to the corresponding diaryl carbonate. Even the use of as much as 20 percent excess phosgene does not result in conversion of more than 70 to 75% of methyl salicylate to the bis methyl salicyl carbonate.
It would be desirable, therefore, to discover means for the efficient preparation of ester-substituted diaryl carbonates generally, and in particular it would be desirable to discover a highly efficient means of preparing bis-methyl salicyl carbonate from methyl salicylate and phosgene.
BRIEF SUMMARY OF THE INVENTION
The present invention relates to a method of preparing ester-substituted diaryl carbonates, said method having a contact time, said method comprising contacting an ester-substituted phenol with phosgene and a phase transfer catalyst in the presence of an organic solvent and an aqueous phase wherein the aqueous phase is maintained at a pH of at least about 9.3 throughout the contact time, said phosgene being used in an amount corresponding to between about 0.95 and about 1.20 molar equivalents based on said ester-substituted phenol. In one embodiment of the present invention, there is provided a means whereby at least 90% of the ester-substituted phenol is converted into product ester-substituted diaryl carbonate.
The present invention further relates to a high yield method of preparing bis-methyl salicyl carbonate, a valuable starting material for use in the melt polymerization of bisphenols to afford polycarbonates.
DETAILED DESCRIPTION OF THE INVENTION
The present invention may be understood more readily by reference to the following detailed description of preferred embodiments of the invention and the examples included therein. In the following specification and the claims which follow, reference will be made to a number of terms which shall be defined to have the following meanings:
The singular forms “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise.
“Optional” or “optionally” means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event occurs and instances where it does not.
As used herein the term “polycarbonate” refers to polycarbonates incorporating structural units derived from one or more dihydroxy aromatic compounds and includes copolycarbonates and polyester carbonates.
As used herein, the term “melt polycarbonate” refers to a polycarbonate made by a process comprising the transesterification of a diaryl carbonate with a bisphenol.
“Catalytically effective amount” refers to the amount of the catalyst at which catalytic performance is exhibited.
As used herein the term “contact time” is used interchangeably with reaction time.
As used herein the term “alkyl radical” refers to a radical having a valence of at least one comprising a linear or branched array of atoms which is not cyclic. The array may include heteroatoms such as nitrogen, sulfur and oxygen or may be composed exclusively of carbon and hydrogen. Examples of alkyl radicals include methyl, methylene, ethyl, ethylene, hexyl, hexamethylene and the like.
As used herein the term “aromatic radical” refers to a radical having a valence of at least one comprising at least one aromatic group. Examples of aromatic radicals include phenyl, pyridyl, furanyl, thienyl, naphthyl, phenylene, and biphenyl. The term includes groups containing both aromatic and aliphatic components, for example a benzyl group.
As used herein the term “cycloalkyl radical” refers to a radical having a valance of at least one comprising an array of atoms which is cyclic but which is not aromatic. The array may include heteroatoms such as nitrogen, sulfur and oxygen or may be composed exclusively of carbon and hydrogen. Examples of cycloalkyl radicals include cyclcopropyl, cyclopentyl cyclohexyl, tetrahydrofuranyl and the like.
In the present invention it has been discovered that ester-substituted phenols such as methyl salicylate are efficiently converted to ester-substituted diaryl carbonates such as bis-methyl salicyl carbonate under mild reaction conditions while minimizing the use of excess phosgene.
In one aspect the present invention provides a method for the efficient preparation of an ester-substituted diaryl carbonate having structure I
wherein R
1
is independently at each occurrence C
1
-C
20
alkyl radical, C
4
-C
20
cycloalkyl radical or C
4
-C
20
aromatic radical, R
2
is independently at each occurrence a hydrogen atom, halogen atom, cyano group, nitro group, C
1
-C
20
alkyl radical, C
4
-C
20
cycloalkyl radical, C
4
-C
20
aromatic radical, C
1
-C
20
alkoxy radical, C
4
-C
20
cycloalkoxy radical, C
4
-C
20
aryloxy radical, C
1
-C
20
alkylthio radical, C
4
-C
20
cycloalkylthio radical, C
4
-C
20
arylthio radical, C
1
-C
20
alkylsulfinyl radical, C
4
-C
20
cycloalkylsulfinyl radical, C
4
-C
20
arylsulfinyl radical, C
1
-C
20
alkylsulfonyl radical C
4
-C
20
cycloalkylsulfonyl radical, C
4
-C
20
arylsulfonyl radical, C
1
-C
20
alkoxycarbonyl radical, C
4
-C
20
cycloalkoxycarbonyl radical, C
4
-C
20
aryloxycarbonyl radical, C
2
-C
60
alkylamino radical, C
6
-C
60
cycloalkylamino radical, C
5
-C
60
arylamino radical, C
1
-C
40
alkylaminocarbonyl radical, C
4
-C
40
cycloalkylaminocarbonyl radical, C
4
-C
40
arylaminocarbonyl radical, and C
1
-C
20
acylamino radical; and b is independently at each occurrence an integer 0-4.
Examples of ester-substituted diaryl carbonates which may be prepared using the method of the present invention include bis-methyl salicyl carbonate (CAS Registry No. 82091-12-1), bis-ethyl salicyl carbonate, bis-propyl salicyl carbonate, bis-butyl salicyl carbonate, bis-benzyl salicyl carbonate, bis-methyl 4-chlorosalicyl carbonate and the like. Typically bis-methyl salicyl carbonate is preferred for use in melt polycarbonate synthesis due to its lower molecular weight and higher vapor pressure.
According to the method of the present invention an ester-substituted phenol is contacted with phosgene in an amount equivalent to from about 0.95 to about 1.20, preferably about 1.0 to about 1.1 and even more preferably about 1.01 to about 1.05 moles of phosgene per mole of ester-substituted phenol, said contact taking place in a in a two phase system comprising water and a water-immiscible solvent, an acid acceptor, a phase transfer catalyst, and optionally a tertiary amine catalyst, the ester-substituted phenol being contacted with said phosgene for a contact time of sufficient length to allow the conversion of at least 90% of the ester-substituted phenol into the product ester-subst

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