Organic compounds -- part of the class 532-570 series – Organic compounds – Carbonate esters
Reexamination Certificate
2001-07-24
2002-10-22
McKane, Joseph K. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carbonate esters
Reexamination Certificate
active
06469192
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to the solventless preparation of ester-substituted diaryl carbonates and in particular to a solventless method of making bis-methyl salicyl carbonate. In addition the present invention relates to a methods of preparing ester-substituted diaryl carbonates which minimize the use of organic solvents.
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. Features of this process include the passage of phosgene gas into a reaction mixture comprising phenol and an organic solvent, and the removal of excess phosgene from the reaction mixture by passage of an inert gas such as nitrogen through the reaction mixture following completion of the phosgenation step. In both instances, solvent is entrained out of the reaction mixture by the flowing gases and must be trapped and recovered. Containment systems for preventing the escape of volatile organic compounds such as solvent emanating from reaction vessels frequently represents a significant cost of equipment used in chemical manufacturing.
Known methods for the preparation of diaryl carbonates such as diphenyl carbonate suffer in that their application to the preparation to ester-substituted diaryl carbonates results in only modest conversion of starting ester-substituted phenol to product ester-substituted diaryl carbonate and such known methods employ organic solvents during critical stages of the process where solvent containment is most difficult. The use of reaction systems which do not employ organic solvents to effect chemical transformations is desirable in that both environmental enhancements and reduction in manufacturing costs are made possible.
It would be desirable, therefore, to discover means for the efficient preparation of ester-substituted diaryl carbonates generally. In addition, it would be highly desirable to discover an efficient means of making ester-substituted diaryl carbonates from ester-substituted phenols and phosgene in a reaction system which avoids entirely or minimizes the use of organic solvents. Moreover, it would be desirable to use such a reaction system for the preparation of bis-methyl salicyl carbonate from methyl salicylate and phosgene.
BRIEF SUMMARY OF THE INVENTION
The present invention provides 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 catalyst and an aqueous phase in a mixture free of solvent, wherein the aqueous phase is maintained at a pH of at least about 8.3 throughout the contact time, said phosgene being used in an amount corresponding to between about 0.10 and about 1.20 moles of phosgene per mole of ester-substituted phenol.
The present invention further relates to a method of preparing bis-methyl salicyl carbonate, an ester substituted diaryl carbonate showing promise as a starting material for the synthesis of polycarbonates incorporating methyl salicyl endgroups.
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 “solvent free” is used interchangeably with the terms “free of solvent” and “solventless”.
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.
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 in a reaction system which is free of solvent. The present invention provides a method of converting an ester-substituted phenol to an ester-substituted diaryl carbonate, said method comprising contacting in a reaction mixture the ester-substituted phenol, a catalyst, an aqueous phase, and phosgene under conditions which promote the reaction of the ester-substituted phenol with the phosgene in the absence of a solvent other than water or the ester-substituted phenol itself.
The method of the present invention provides a means for the preparation of ester-substituted diaryl carbonates in a reaction system which is free of solvent. By “free of solvent” it is meant that no solvent other than water or starting ester-substituted phenol is present in the reaction mixture during the reaction of ester-substituted phenol with phosgene to afford intermediate ester substituted phenyl chloroformate and product ester-substituted diaryl carbonate. For example, in embodiments of the present invention wherein phosgene is contacted with a mixture comprising an aqueous phase, a catalyst and an ester-substituted phenol, no solvent other than water or the ester-substituted phenol itself is present during the conversion of the phosgene to intermediate ester-
Burnell Timothy Brydon
Cella James Anthony
Kailasam Ganesh
McCloskey Patrick Joseph
Caruso Andrew J.
General Electric Company
Johnson Noreen C.
McKane Joseph K.
Murray Joseph
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