Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acid esters
Reexamination Certificate
2002-04-05
2004-03-09
Nazario-Gonzalez, Porfirio (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acid esters
C560S226000, C568S687000
Reexamination Certificate
active
06703520
ABSTRACT:
CLAIM OF PRIORITY
This application claims priority from European Patent Application No. 01201473.4 filed Apr. 24, 2001.
1. Field of the Invention
The present invention relates to a process for making halogenated esters such as for example methyl-3-methoxytetrafluoropropanoate. In particular, the present invention relates to a process of making such halogenated esters wherein the process can be run under more environmental friendly conditions and in an economically feasible way.
2. Background of the Invention
Halogenated esters such as for example methyl-3-methoxytetrafluoropropanoate are typically used in the preparation of halogenated vinyl ethers, in particular in the preparation of certain perfluorinated or partially fluorinated vinyl ethers. Such fluorinated vinyl ethers may be used in the manufacture of fluoropolymers, in particular in the manufacture of fluoropolymers including fluorinated ion exchange resins, fluoroelastomers and fluorothermoplasts that have desirable properties. Some of the benefits of employing vinyl ethers in fluoropolymers are described in various review articles. See for example, Modern Fluoropolymers, John Scheirs, Wiley Series in Polymer Science, 1997. See also Emel 'yanov et al, Zh. Org. Khim (1994), 30(8), 1266-70.
There are a number of routes to prepare fluorinated vinyl ethers. Generally these routes start with (per)fluorinated acid fluorides. See for example Modern Fluoropolymers, J. Scheirs, Wiley Series in Polymer Science, 1997 and the literature cited therein. These (per)fluorinated acid fluorides may for example be prepared from the fluorination of halogenated esters.
Processes for producing halogenated esters are already known. One such process is described in U.S. Pat. No. 2,988,537. However, the yields of the halogenated ester produced according to the process disclosed in this US-patent appear to be low and further the amounts of halogenated ketone byproduct are high. Although it is taught in this patent to generally conduct the first step in the reaction sequence in an organic solvent, there is also an example disclosing a process in which no organic solvent is used in the initial step. In this particular example, tetrafluoroethylene is added to a mixture of sodium methoxide and dimethyl carbonate at a temperature of 40° C. Subsequent thereto, the resulting mixture is taken up in ether as an organic solvent and acidified with sulfuric acid. According to the results disclosed, only 17% yield of the halogenated ester is obtained together with about 75% yield of the halogenated ketone. It thus appears that under the conditions of this example, the formation of halogenated ketone is preferred over that of the halogenated ester.
U.S. Pat. No. 5,235,094 describes a process designed to maximize the yield of halogenated ester while keeping the amount of the halogenated ketone as a byproduct as low as possible. According to U.S. Pat. No. 5,235,094, the halogenated esters are produced by contacting a mixture of an alkanolate and a diester in an organic solvent with a halogenated, ethylenically unsaturated olefin at a temperature of not more than 15° C. Further, it is taught that the mole ratio of the olefin to the alkanolate should be between 0.89 mole and 0.99 mole. Although the process disclosed in this US-patent can yield the desired halogenated ester in high amounts with a low amount of contamination with undesired halogenated ketone byproduct, the process has some disadvantages. For example, it appears that the process needs to be run under fairly strict conditions in order to achieve the high yields and to minimize the amount of byproduct. In particular, it appears that the temperature needs to be controlled carefully well below room temperature. Another important factor to control is the mole ratio of olefin to alkanolate. As can be seen from the examples, it is critical in the prior art process that the mole ratio of olefin to alkanolate is controlled carefully to just below the stoichiometric amount. This implies that the amount and purity of the reactants used need to be carefully controlled. Additionally, it is taught that the process should be run in very dry conditions to achieve a high yield of desired product. Finally, the use of organic solvent in the process presents environmental problems and may make the recycling of excess diester and solvent used in the reaction difficult. Recycling of excess diester and the solvent is complicated by the formation of equimolar amounts of alcohol in the acidification step.
Accordingly, it is now a desire to find an alternative process for making a halogenated ester in high yield and with a minimal amount of byproduct while avoiding some disadvantages of the prior art. For example, it would be desirable to find a process which is more convenient and flexible for use on an industrial scale. In particular, it would be desirable to develop a process which is less dependent on the purity levels of the reactants used. Additionally, it would be desirable to find a process in which recycling of unused diester can be practiced more efficiently and which process is more friendly from an environmental point of view.
SUMMARY OF THE INVENTION
The present invention provides a process for preparing a desired halogenated ester, which process comprises the steps of:
(a) contacting (A) a substantially organic solvent free liquid mixture of (i) an alkanolate of the formula M—O—Z, wherein M is an alkali or alkaline earth metal, and Z is a linear, branched or cyclic alkyl group of 1 to 10 carbon atoms and (ii) a diester with (B) a halogenated ethylenically unsaturated olefin at a temperature of not more than 40° C. and with a mol ratio of halogenated ethylenically unsaturated olefin to alkanolate of not more than 1.1;
(b) contacting an acid with a thus obtained reaction mixture thereby obtaining a mixture comprising the desired halogenated ester; and
(c) recovering the halogenated ester from said reaction mixture.
In step (a) of the process, the mixture of the alkanolate and diester is contacted with the halogenated ethylenically unsaturated olefin under conditions of agitation sufficient such that the weight ratio of halogenated ester to halogenated ketone as a byproduct obtained after step (b) is at least 10:1.
By the term “substantially organic solvent free” is meant that no organic solvent is added to carry out the reaction. However, the term should not be interpreted to mean that all organic solvents are excluded from the reaction. In particular, organic solvents may be present as part of a minor contamination (e.g. upto 1% by weight) of one or more reactants.
By the term “liquid mixture” is meant that the mixture should generally be liquid under the conditions at which the reaction is being carried out such that the mixture can be stirred. “Liquid mixture” in particular covers any stirrable mixture including solids free liquid, slurry in which some solid may be present, up to pasty like mixtures with high viscosity.
The process of the invention has the advantage that the reaction can be carried out without the need for the addition of organic solvents. In particular, steps (a) through (c) of the process can be conducted without using organic solvent. This makes recycling of reactants more easy. For example, the diester which is generally used in an excess amount in the reaction can be more easily recovered after the reaction. Also, the recovered diester can be reused in a subsequent run of the process. Furthermore, because no organic solvent is used, the process is also more environmentally friendly.
Further, despite the fact that no organic solvent is used, the process of the present invention can yield the desired halogenated ester in high amounts with minimal amounts of halogenated ketone byproduct. Also, in achieving these results, the process of the invention is less critical and less dependent on such factors as the exact reaction conditions and purity levels of the reactants used. For example, the process is generally less temperature dependent, a slight amount of olefinic reactant in excess
Hintzer Klaus
Obermaier Egon
Schwertfeger Werner
3M Innovative Properties Company
Lilly James V.
Nazario-Gonzalez Porfirio
Puttlitz Karl J.
Szymanski Brian E.
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