There is a long felt need for an economically viable process for the formation of vinyl carboxylates such as, for example, vinyl benzoate. Vinyl carboxylates, such as for example vinyl benzoate, find use in a variety of applications including, for example, paints, adhesives and various other coating formulations as well as cement mortar admixtures.
It is known in the art that vinyl esters can be formed from the reaction of corresponding carboxylic acid with acetylene. A variety of catalysts have been proposed including base metals such as zinc, cadmium and mercury as well as precious metal catalysts such as rhenium, ruthenium, palladium, etc. In fact, the zinc carboxylate catalyzed process has been commercialized by Hexion Specialty Chemicals for the production of VEOVA™ Monomer 10, which is a vinyl ester of VERSATIC™ Acid 10, a synthetic saturated monocarboxylic acid of highly branched structure containing ten carbon atoms. More particularly, see U.S Pat. No. 6,891,052 to Tanner et al., wherein is disclosed zinc carboxylate catalyst is used for the formation of vinyl ester from the reaction of carboxylic acid with acetylene.
Similarly, various other processes have been reported in the literature wherein a carboxylic acid is reacted with acetylene to form the corresponding vinyl ester. See U.S. Pat. No. 3,607,915 to Borsboom et al. and Transition-Metal-Catalyzed Addition of Heteroatom-Hydrogen Bonds to Alkynes, Alonso et al., Chem. Rev., 2004, 104 (6), 3079-3160. In particular, Borsboom et al. disclose generally another method involving zinc-catalyzed carboxylic acid reaction with acetylene, as already noted above. Whereas, Alonso et al. provide an analysis of the state of the art for catalytic addition chemistry of the reaction of acetylene with a carboxylic acid. See also, U.S. Pat. No. 2,066,075 to Reppe, German Patent No. DE 740678 to I.G. Farbenindustrie AG, U.S. Pat. Nos. 2,339,066 and 2,342,463 to Fischer et al., British Patent No. GB 641,438A to General Aniline and Film Corporation, U.S. Pat. No. 2,472,086 to Beller et al., Swiss Patent No. CH 324667 to Staeger Reinhard, U.S. Pat. No. 3,062,863 to Fernholz et al., U.S. Pat. No. 3,125,593 to Hargrave et al., U.S. Pat. No. 3,285,941 to Engel et al., German Patent No. DE 1237557 to Shell Internationale Research, U.S. Pat. No. 3,646,077 to Hübner et al., and U.S. Pat. No. 6,500,979 to Wiese et al.
It has also been reported in the literature that a variety of Group VIII metal complex catalysts are effective in the formation of vinyl esters by the reaction of carboxylic acids with acetylene. See, for example, U.S. Pat. No. 3,479,392 to Stern et al. and U.S. Pat. No. 5,395,960 to Heider et al. Both Stern et al. and Heider et al. disclose vinylation of aromatic carboxylic acids in the presence of a catalyst based on ruthenium, rhodium, palladium, osmium, iridium, or platinum. Stern et al. is specifically drawn to a process for producing substituted olefins from a reactant other than acetylene or acetylenic compounds, and Heider et al. only disclose branched aliphatic carboxylic acids suitable for the catalyzed vinylation reaction, providing examples including 2-ethylhexanoic acid, 4-tert-butylbenzoic acid, suberic acid, and monomethyl succinate. However, Heider et al. disclose use of only ruthenium metal as a catalyst by way of examples and employ a very low molar ratio of carboxylic acid to ruthenium of about 25 to 100. That is, Heider et al. conditions require a large amount of catalyst per mole of vinyl ester produced. Additionally, Heider et al. employ longer reaction times of 7 to 17 hours rendering these conditions unsuitable for an industrial operation.
Palladium used as a co-catalyst with a cadmium or zinc catalyst is also known in the vinylation art. See, for example, German Patent No. DE 1161878 to Farbwerke Hoechst Aktiengesellschaft and British Patent No. GB 1,130,245 to Shell Internationale Research. Both patents disclose vinylation of benzoic acid and acetylene in the presence of a zinc or cadmium catalyst and a palladium co-catalyst. The palladium compounds taught are, however, free palladium metal or palladium chloride, and the processes are typically operated at temperatures above 120° C.
U.S. Pat. No. 5,430,179 to Lincoln et al. describes a homogeneous process for vinyl ester synthesis, such as vinyl benzoate, by ruthenium-catalyzed addition of carboxylic acids, including benzoic acid, to alkynes, including acetylene. Lincoln et al. disclose reaction conditions that include an optional solvent, such as toluene or mineral oil, and a temperature range of from about 40 to about 200° C. Lincoln et al. further disclose use of a ruthenium catalyst selected from a group that includes ruthenium dodecacarbonyl in concentrations ranging from about 50,000 ppm to about 0.5 ppm ruthenium based on the weight of the liquid phase reaction medium optionally in combination with a ligand such as triphenyl phosphine, tris(methoxyphenyl)-phosphine, or tris(p-fluoromethylphenyl)phosphine. However, Lincoln et al., disclose only one example of forming vinyl pivalate from the reaction of pivalic acid with acetylene in the presence of ruthenium dicarbonyl acetate under the reaction conditions disclosed therein.
WO 2007/060176 A1 to BASF Aktiengesellschaft provides a process for preparing vinyl carboxylates by reacting a carboxylic acid with an alkyne compound in the presence of a catalyst selected from a group of metal compounds including rhenium-based compounds. BASF specifically discloses reacting benzoic acid and acetylene in the presence of dirheniumdecacarbonyl; see Example 1. The Example teaches a molar ratio of carboxyl group to rhenium atom of 388, wherein the reaction takes place in a toluene solvent at 140° C. over a reaction time of 6 hours. The reported yield is 99%.
However, it has now been found that none of the existing processes is suitable for the production of vinyl benzoate (VB) or vinyl 2-ethyl hexanoate (V2EH) via the vinylation reaction, particularly, the conventional zinc catalysts provided unacceptable reaction rates and yields for an industrial scale-up operation. The other methods as described hereinabove are equally not suitable for the production of vinyl esters such as VB or V2EH in an industrial scale. Thus it is desirable to develop economically viable catalytically active reactions to form vinyl esters, such as VB or V2EH from their respective carboxylic acids under mild reaction conditions.