Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acid esters
Reexamination Certificate
2000-08-24
2003-10-28
Killos, Paul J. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acid esters
Reexamination Certificate
active
06639099
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to processes for the synthesis of di(meth)acrylic acid esters by transesterification, which permit the recovery of esters that are free of high levels of undesirable contaminants such as zirconium. Preferred processes involve the transesterification of (meth)acrylic acid esters of C
1
to C
4
alcohols with 1,n-diols (where n≧3) in the presence of chelates of metal compounds as catalysts. Most preferably, chelates of zirconium with 1,3-dicarbonyl compounds are employed as the catalytic metal compounds.
2. Description of the Related Art
Di(meth)acrylic acid esters are generally obtained by the catalyzed transesterification of (meth)acrylic acid esters. Conventional metal catalysts for this transesterification are widely known among those skilled in the art. For instance, alkali metal catalysts such as lithium and calcium hydroxide are used, as described, for example, in German Unexamined Applications DE-OS 3423441 and 3423443. However, the use of these basic catalysts may lead to undesireable side reactions such as the Michael addition, which diminish both the purity and yield of the desired di-esters.
Zirconium complexes may also be used for catalysis of reactions between the esters and alcohols. Since these catalysts are neutral these complexes provide extremely high conversions and high purity of the products. A further advantage of such catalysts is that the alcohols do not have to be dried prior to transesterification. Such catalysts are described in German Unexamined Application DE-OS 2805702 and European Patent EP 0236994 B1. Zirconium catalysts may also be formed in situ. For example, FR A 2747675 describes a process for transesterification of (meth)acrylates in which zirconium catalysts are formed in situ.
Whether formed in situ or merely added to a reaction mixture, it is desireable to remove such catalysts as completely as possible after transesterification to provide a non-turbid product free of highly reactive zirconium catalysts. Di-ester products free of highly reactive zirconium catalysts are more conveniently used in subsequent reactions because they do not risk introducing undesireable effects associated with presence of these highly reactive catalysts. Accordingly, it is desireable to separate zirconium-containing catalysts from the di(meth)acrylic acid esters produced by transesterification prior to sale.
Prior methods for removing these catalysts required complex, expensive and inconvenient separation steps. For instance, separating the catalyst required hydrolysis and centrifugation, or in many cases distillation to obtain non-turbid products which had the purity required for numerous applications.
BRIEF DESCRIPTION OF THE INVENTION
An object of the present invention is to provide an inexpensive and convenient process of obtaining di(meth)acrylic acid esters in highly pure form. The present invention thus provides processes for synthesis of di(meth)acrylic acid esters by transesterification of (meth)acrylic acid esters of C
1
to C
4
alcohols with 1,n-diols (where n≧3) in the presence of metal compounds as catalysts. Preferably, chelates of zirconium with 1,3-dicarbonyl compounds are used as the metal compound. These processes produce di(meth)acrylic acid esters inexpensively and in highly pure form.
Another object of the invention is to provide a process in which the catalyst can be separated from the transesterification reaction product without energy-intensive distillation. The inventors have found that this may be achieved by precipitating the metal catalyst with phosphoric acid after transesterification. The resulting precipitate can be conveniently separated from the ester-containing reaction mixture without distillation. Accordingly, a process is provided for the synthesis of di(meth)acrylic acid esters by transesterification of (meth)acrylic acid esters of C
1
to C
4
alcohols with 1,n-diols, where n≧3, in the presence of metal compounds as catalysts, wherein chelates of zirconium with 1,3-dicarbonyl compounds are used as the metal compound. This process provides the desired di(meth)acrylic acid esters inexpensively in highly pure form without significant amounts of contaminating zirconium compounds which can interfere with subsequent chemical reactions.
Other advantages of the claimed invention include:
The inventive processes lead to extremely high conversions and high purity of the products.
The 1,n-diols used, where n≧3, do not have to be dried before they are used.
Inexpensive zirconium compounds can be used in the process, since the catalyst can be synthesized in situ by addition of 1,3-dicarbonyl compounds.
After the zirconium compounds precipitated by phosphoric acid have been separated, it is no longer necessary to purify the end product by distillation.
Products free of turbidity are obtained by the inventive process.
The notation di(meth)acrylic acid esters includes diesters of methacrylic acid, acrylic acid and mixtures of the two acids.
Di(meth)acrylic acid esters that can be synthesized in the scope of the present invention may be generally represented by the formula:
where
R
1
and R
2
can be the same or different and denote a hydrogen or a methyl group,
Y denotes a divalent link group, wherein the two (meth)acrylic acid groups are separated by at least 3 carbon atoms. These link groups are derived from the 1,n-diols used for transesterification.
Examples of particularly preferred link group “Y” are straight-chain, branched or cyclic alkyl groups, which can be saturated or unsaturated, such as propyl, butyl, pentyl, hexyl, cyclopentyl, cyclohexyl, pentenyl as well as polyether glycols. Link groups can contain reactive groups, examples of which include halogen-containing groups, epoxy groups, aromatic and heteroaromatic groups as well as thiol groups.
Usable (meth)acrylic acid esters of C
1
to C
4
alcohols within the scope of the invention may be represented by the formula
where
R
1
is hydrogen or a methyl group and R
3
is an alkyl group with 1 to 4 carbon atoms.
Examples of alkyl groups with 1 to 4 carbon atoms are methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl and tert-butyl. These groups can be unsubstituted or substituted. Either acrylic acid esters or methacrylic acid esters, or mixtures of both can be used in the transesterification.
Commercially available (meth)acrylic acid esters can be used in the inventive process with methyl acrylate and methyl methacrylate being preferred, as these substances are particularly inexpensive. Furthermore, the methanol liberated during the transesterification of these compounds can be easily removed from the reaction mixture by distillation, allowing very high conversions to be achieved.
1,n-Diols (where n≧3), include in particular compounds of the formula:
HO—Y—OH (III)
where Y has the same meaning as in formula I.
The preferred 1,n-diols include among others alkoxyalkanediols, alkenoxyalkanediols, alkenediols, glycols, polyether glycols, phenoxyalkanediols, alkylphenoxyalkanediols, phenylalkanediols, alkylphenylalkanediols, alkylmorpholinoalkanediols, alkylpiperidinoalkanediols, pyridylalkanediols, and haloalkanediols.
Preferred 1,n-diols include 1,3-propanediol, n-butane-1,3-diol, 2-methyl-1,3-propanediol, neopentyl glycol (2,2-dimethyl-1,3-propanediol), 1,4-butanediol, triethylene glycol and polyethylene glycol 400. Most preferrably the 1,n-diol is characterized in that n=3,4or 6.
The 1,n-diols can be used alone or in the form of mixtures. In general they are commercially available, and their synthesis is widely known among those skilled in the art.
The chelate complex compounds of zirconium with 1,3-dicarbonyl compounds used as catalysts in the transesterification are well known to the person skilled in the art.
The 1,3-dicarbonyl compounds that can be used with particular success in the scope of the invention include among others acetoacetic esters, acetylacetonate, 2,4-hexanedionate, 3,5-heptanedionate, 3-methylacetylacetonate, 3-phenylacetylacetonate,
Carl Joachim
Graeff Guenter
Knebel Joachim
Wittkowski Andrea
Killos Paul J.
Roehm GmbH & Co. KG
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