3,446,839 United States Patent Office Patented May 27, 1969 2 3,446,839 of the process is not dependent upon the alkyl moiety of PRODUCTION OF ALKYL HYDROXY-PVALATES the methacrylate ester, best results are obtained when a Jurgen F. Falbe, Bonn, Germany, and Nicolaas Huppes, lower acyclic alkyl methacrylate is employed, that is, an Amsterdam, Netherlands, assignors to Shell Oil Com ester of the above formula wherein R is acyclic alkyl of up pany, New York, N.Y., a corporation of Delaware to 6 carbon atoms. Particularly preferred as the ester No Drawing. Filed Feb. 18, 1966, Ser. No. 528,397 reactant is methyl methacrylate. Claims priority, application Germany, Sept. 22, 1965, To effect hydroformylation, the ester reactant is con S 99,581. C. C07. 69/66 tacted with carbon monoxide and hydrogen. No special U.S. C. 260-484 6 Claims precautions are required with regard to these materials 10 and commercially available grades are satisfactory. The molar ratio of carbon monoxide to hydrogen is not critical and molar ratios from about 4:1 to about 1:4 are satis ABSTRACT OF THE DISCLOSURE factorily employed. Generally preferred, however, are Process of initially reacting an alkyl methacrylate, car molar ratios from about 2:1 to about 1:2. The hydrogen bon monoxide, and hydrogen in the presence of a rhodi 15 and carbon monoxide are suitably charged to the reac um-containing catalyst and a tertiary phosphine to pro tion system as such although it is also useful to employ duce a-formylisobutyrates and then raising the tempera commercial mixtures of these gaseous reactants, e.g., syn ture to produce alkyl hydroxypivalates, thereby hydro thesis gas. formylating and hydrogenating sequentially in one opera The catalyst is a rhodium carbonyl catalyst optionally tion without a change of catalyst or gas. modified by the presence of tertiary phosphine. In one modification, the rhodium-containing catalyst is employed in the substantial absence of complexing ligands other This invention relates to an improved method for the than carbonyl. The rhodium carbonyl is suitably intro production of hydroxypivalic acid esters. duced as a preformed material or is formed in situ by A method for the production of the ethyl ester of hy reaction of some other form of rhodium with the other droxypivalic acid, i.e., the ethyl ester of 2,2-dimethyl-3- reaction mixture components. Thus, the rhodium is pro hydroxypropionic acid, is known in the art. Rothstein et vided as the metal, or as the salt of an organic or inor al., J. Chem. Soc., 1948 (1949), describe the production ganic acid, e.g., rhodium chloride, rhodium nitrate, rho of ethyl hydroxypivalate by a cumbersome and uneco dium napthenate or rhodium octanoate. In yet another nomic methed which comprises reacting the cy-bromoiso 30 and frequently preferred modification, the rhodium is in butyric acid ester with a form of formaldehyde and zinc. troduced in the form of the oxide, Rh2O3. Although the It is an object of the present invention to provide an precise catalytically active species is not known with cer improved method for the production of esters of hydroxy tainty, it is considered that regardless of the form in pivalic acid esters. More particularly it is an object to which the rhodium is provided, reaction with the carbon provide an improved process for the production of alkyl 3 5 monoxide and/or the hydrogen present in the reaction hydroxypivalates. system results in the formation of a rhodium carbonyl It has now been found that these objects are accom catalyst. plished by the process of initially contacting an ester of In the preferred modification of the invention, the methacrylic acid with carbon monoxide and hydrogen rhodium carbonyl catalyst is modified by the presence of in the presence of certain rhodium-containing catalysts 40 tertiary phosphine. Phosphines that are suitably employed under controlled reaction conditions and subsequently as catalyst modifiers are preferably hydrocarbon mono hydrogenating the product resulting therefrom. phosphines of up to 20 carbon atoms which are free from The hydroformylation of methacrylate esters under acetylenic unsaturation. Illustrative of such tertiary phos other conditions is known in the art. For example, Falbe phines are trialkyl phosphines including triethylphos et al., Chem. Ber., 97, 877 (1964) report that hydro phine, tributylphosphine, dimethyllaurylphosphine, propyl formylation of methyl methacrylate in the presence of a 45 butyloctylphosphine and dibutyldecylphosphine; aromatic cobalt catalyst affords a 51% yield of cy-methyl-y-butyro phosphines such as triphenylphosphine, phenyldiethyl lactone as well as a 42% yield of methyl isobutyrate, the phosphine, propyldi(tolyl)phosphine, dibutylnaphthylphos product resulting from hydrogenation of the ester re phine and diphenylhexylphosphine; and heterocyclic phos actant. This reference, as well as others, illustrates a high phines such as 1-hexylphospholine, 1-phenylphospholane, selectively to 6-hydroformylated products in accord with 50 1 - ethylphospholidine, 1 - phenylphosphorinane, 44 - di the rule of Keulemans et al., Receuil, 67,298 (1948) that methyl-1-phenylphosphorinane, 3,6-dimethyl-1-phenyl quaternary carbon atoms are not formed during hydro phosphepane, 9-butyl-9-phosphabicyclo(4.2.1) nonane and formylation processes. However, in contrast, the hydro 9-phenyl-9-phosphabicyclo(3.3.1) nonane. Preferred ter formylation process of the invention is characterized by tiary phosphine catalyst modifiers are trialkylphosphines the formation of an a-hydroformylated product wherein wherein each alkyl is alkyl of up to 8 carbon atoms. Par a quaternary carbon atom has been formed, in direct con ticularly preferred as the tertiary phosphine catalyst modi tradiction of the rule of Keulemans et al. fier is tributylphosphine. When present, amounts of ter The methacrylate ester reactant employed in the process tiary phosphine up to about 20% by weight based on the of the invention is an ester of the formula methacrylic acid ester are satisfactory. As previously 60 stated, no tertiary phosphine is required, but best results are obtained when at least 0.1% by weight of tertiary phosphine based on the methacrylate ester is present. (H, The rhodium is employed in catalytic quantities, pref erably in amounts from about 0.0001 gram-atom to about wherein R is alkyl of up to 20 carbon atoms. Illustrative 65 0.01 gram-atom per mole of methacrylate ester and par alkyl R groups include acyclic alkyl groups such as methyl, ticularly in amounts from about 0.0004 gram-atom to ethyl, isopropyl, sec-butyl, amyl, hexyl, octyl, lauryl and about 0.004 gram-atom per mole of methacrylate ester. stearyl as well as cycloalkyl groups, preferably of from The hydroformylation process is conducted in an inert 5 to 13 carbon atoms, such as cyclopenty, cyclohexyl, 2, solvent and solvents which are liquid at reaction tem 3,5-trimethylcyclopentyl, cyclooctyl, cyclododecyl, cyclo perature and pressure and are inert to the reactants as hexylmethyl, and cyclooctylmethyl. Although the success well as the lactone product are suitably employed. Illus 3,446,839 3. 4. trative solvents include ethers such as dibutyl ether, di pressure used, and the hydrogen pressure may be as high octyl ether, anisole and diphenyl ether; and esters such as 2000 atmospheres or higher. The presence in the re as methylbenzoate, diethylphthalate and hexylbutyrate. action system of unreacted carbon monoxide does not Preferred inert solvents are hydrocarbons free from ali appear to be detrimental, the carbon monoxide serving phatic unsaturation such as benzene, toluene, cyclohexane, only as an inert diluent. decahydronaphthalene, dodecane and heptane. The 5 The preferred method of operation, i.e., conducting the amount of solvent is not critical but typically weight hydrogenation without separation of the initial product ratios of solvent to methacrylate ester from about 1:1 mixture, offers a substantial advantage with regard to to about 6:1 are employed. catalyst separation and recovery. At the conclusion of The process of cy-methyl-y-lactone production comprises reaction the pressure is released and the mixture is cooled, initially contacting the methacrylate ester reactant with O whereupon the rhodium catalyst decomposes and is de hydrogen and carbon monoxide in the presence of the posited as a powder in substantially quantitative yield. rhodium catalyst and subsequently hydrogenating the The rhodium is easily recoverable, as by filtration, and initial hydroformylation product. The temperature at may be recycled without further treatment. Under similar which the initial hydroformylation is conducted is some conditions, cobalt catalysts form cobalt mirrors and en what critical and temperatures from about 80° C. to crustations and considerable difficulty is obtained in re about 120° C. provide generally satisfactory results. In using such cobalt residues. The hydroxypivalate ester prod the modification of the process wherein tertiary phosphine uct is separated from the product mixture by conventional catalyst modifiers are employed, somewhat higher re procedures as by fractional distillation, selective extrac action temperatures may be utilized, e.g., up to about 20 tion, fractional crystallization and the like. 135° C. The initial hydroformylation process is con The product of the process of the invention is an ester of ducted at superatmospheric pressure and reaction pres hydroxypivalic acid corresponding to the methacrylate sures from about 100 atmospheres