Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acid esters
Reexamination Certificate
1998-10-09
2001-01-16
Wilson, James O. (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acid esters
C560S205000, C560S220000, C560S221000, C204S157870, C422S186290, C522S004000, C522S006000, C522S135000
Reexamination Certificate
active
06175037
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for preparing acrylate esters, methacrylate esters, polyester acrylates or polyester methacrylates by reacting acrylic or methacrylic acid with a monohydroxy containing compound or a polyhydroxy containing compound in a reaction vessel in the presence of a catalyst and polymerization inhibitor.
2. Description of Related Art
Conventionally, methacrylate esters and acrylate esters have been prepared via a direct esterification reaction by reacting methacrylic acid or acrylic acid, usually in excess, with an alcohol or a polyol in the presence of an azeotroping solvent for water removal, typically a hydrocarbon solvent, an esterification catalyst and a polymerization inhibitor. Limited examples are also known where synthesis can also occur in the absence of a hydrocarbon solvent, for example, European Patent Application 0 202 610 by BASF Corporation and European Patent Application 0 376 090 by Henkel Corporation. In addition, (meth)acrylate esters have been prepared using transesterification reaction conditions as described in U.S. Pat. Nos. 5,498,751 and 5,554,785.
In all of the above mentioned patents and published applications, the source of heating is conventional thermal methods, such as placing a heating unit into the reaction mixture or jacketing the reaction vessel and reaction mixture with an external heating source. In conventional thermal methods, the reactants are placed in a vessel, the vessel is heated by conventional thermal methods, and the heat is transferred to the reaction mixture conductively, usually in the presence of a solvent.
Microwaves have been used as an energy source in various esterification reactions where reactants are not prone to undergo further reaction via free radical initiated propagation. For example, U.S. Pat. No. 5,239,017 to Pelesko et al. discloses that anhydride groups of a polymer can be esterified in a cross-linking reaction with a polyol using microwave heating.
A working example in U.S. Pat. No. 5,387,397 to Strauss uses microwave heating to react certain unsaturated acids with an alcohol. This patent also couples the reactor directly to refrigeration for cooling in order to prevent by-product formation or product degradation. Further, water produced by the esterification reaction in the example is not separated from the reaction mixture. The rapid heating and cooling is to prevent decomposition or polymerization of the product, and is disclosed as an advantage. The Strauss patent does not disclose that methacrylic acid or acrylic acid can be esterified using microwaves as the energy source, but only discloses that acids with internal hydrocarbon chain unsaturation, such as crotonic acid, can be esterified. It is well known in the art that internal unsaturation is generally more stable to thermal or free radical induced reactions than terminal unsaturation in unsaturated compounds, such as those terminated with (meth)acrylic functionality.
Raner et al.,
J. Org. Chem
., 57, 6231-6234 (1992), compares the properties and parameters of the esterification reaction of 2,4,6-Trimethylbenzoic Acid with 2-propanol using as a heat source, microwaves, verses a conventional heat source. Raner et al.,
J. Org. Chem
., 58, 950-953 (1993), continues the investigations of the preceding article. These articles do not disclose the esterification of (meth)acrylic acid.
Strauss et al.,
Aust. J. Chem
., 48, 1665-1692 (1995), reviews microwave assisted organic synthesis. On pages 1677-78 of this article, a discussion of the further reaction of a terminally unsaturated acrylate compound using microwaves is presented. This article does not disclose that the particular (meth)acrylic acid or acrylic acid material can be prepared by using a microwave, only that it can be further reacted with additional reactants via microwave energy. Additionally, like the patent to Strauss discussed previously, this article indicates a need to rapidly cool the reaction mixture in order to limit hydrolysis, dimerization and polymerization of the resulting product containing the unsaturation.
BRIEF SUMMARY OF THE INVENTION
Surprisingly, it has been discovered that microwaves can be used in the synthesis of highly reactive compounds which are prepared from acrylic acid or methacrylic acid reactants. These highly reactive compounds are further capable of free radical polymerization via thermal, photochemical or other means of initiation. Synthesis of these reactive products using microwaves as the heating source, can be accomplished without any significant polymerization of the products or of the acrylic acid or methacrylic acid reactants used to prepare the highly reactive compounds. It has thus been discovered that microwaves can be effectively used to synthesize methacrylate esters, acrylate esters, polyester methacrylates and polyester acrylates with certain advantages over conventional synthetic methods.
In a conventional inductive thermal heating process, the reactants are gradually heated as heat penetrates from the outside of the reactor to the reactants inside. In alternative processes, this heating may be supplied from the inside of the reactor, using a heating coil or other conductive heating devices. The heat is gradually absorbed by the reactants and any solvent, solid, or other component in the reactor, which in turn gets warmer and results in the reaction eventually taking place. In contrast, microwave energy is “cold”, producing heat only when the energy is absorbed directly by the reaction mixture components that are responsive to microwaves. The reactants which absorb the energy are rapidly heated when exposed to the microwave energy and the energy (as heat) is further distributed directly to the surrounding reaction medium. Because microwaves directly interact with the microwave-responsive molecules of the reactants, thereby generating heat, there is little need for an additional inert liquid or solid medium or additional solvent to convey heat from the heating means to the reactants. Using microwave heating for chemical reactions in place of conventional thermal heating has many advantages including: achieving higher reaction mixture temperatures more rapidly, shorter residence times, reduced production costs, increased capacity utilization of reaction vessels, and lower “waste” in energy utilization. Lower excesses of non-limiting reactants and solventless processing, which are environmentally friendly, are additional important advantages. The process of this invention has an important commercial significance as well as providing technical advantages for synthesis of the highly reactive acrylates and methacrylates over the prior art methods.
DETAILED DESCRIPTION OF THE INVENTION
The invention concerns a process for preparing an acrylate ester, a methacrylic ester, a polyester acrylate, or a polyester methacrylate, comprising reacting acrylic or methacrylic acid with a monohydroxy containing compound or polyhydroxy containing compound in a reaction vessel in the presence of a catalyst under microwave heating.
In the present invention, the term “(meth)acrylic acid” encompasses both acrylic acid and methacrylic acid. Likewise, the term (meth)acrylate encompasses both acrylates and methacrylates and “polyester (meth)acrylate” encompasses both polyester acrylates and polyester methacrylates.
The term “polyester (meth)acrylate” is defined as a (meth)acrylate derived from a polyol, and may have one or more (meth)acrylate functional groups present in the final product.
Microwaves can be generated by any of a variety of methods known in microwave technology. Typically these methods depend upon klystrons or magnetrons to serve as the microwave generation source. Typically, the frequency of generation is in the approximate range of 300 MHz to 30 GHz and the corresponding wavelength of about 1 m to 1 mm. Although any frequency in this range can theoretically be used, more or less effectively, it is preferable to use a frequency within the commercially accessible ranges wh
Deemie Robert W.
UCB S.A.
Wenderoth , Lind & Ponack, L.L.P.
Wilson James O.
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