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 to about 2000 atmos ester reactant employed. For example, from methyl meth pheres are satisfactory although preferred reaction pres acrylate is produced methyl hydroxypivalate and from sures vary from about 350 atmospheres to about 1000 decyl methacrylate is produced decyl hydroxypivalate. The atmospheres. The reactants and catalyst are contacted in hydroxypivalate ester products find utility as high boiling any convenient manner. In one process modification, the reaction solvents and are transesterified to produce poly ester reactant, Solvent and catalyst are charged to an ester polymers useful in synthetic fiber production. autoclave or similar reactor which is then pressurized To further illustrate the improved process of the in with the gaseous reactants. In an alternate modification, 30 vention, the following examples are provided. It should the reactants and catalyst are contacted in a continuous be understood that the details thereof are not to be operation as by effecting the contacting during passage regarded as limitations as they may be varied as will be through an elongated reactor. understood by one skilled in this art. At the conclusion of the hydroformylation reaction, the EXAMPLE I initial hydroformylation product comprises an o-formyl isobutyrate ester corresponding to the methacrylate ester To an autoclave was charged 500 g. of ethyl meth reactant. To produce the desired hydroxy-ester product, acrylate, 2500 g. of benzene, 0.2 g. of rhodium oxide the c-formylisobutyrate ester is hydrogenated. and 5 g. of tributylphosphine. The reactor was pres In one modification, the hydrogenation is conducted as surized with an equimolar mixture of carbon monoxide a separate operation after isolation of the hydroformyl and hydrogen to a pressure of 300 atmospheres while the ation product. At the conclusion of the hydroformylation reaction mixture was maintained at 120° C. After a re procedure the reactor is cooled and vented and the action time of 10 hours the autoclave was cooled to room rhodium catalyst is removed by conventional methods as temperature and vented. The catalyst decomposition prod by filtration, centrifugation or water washing. The initial lucts were removed by filtration and the solvent was re hydroformylation product is freed from solvent as by dis moved by distillation. The resulting mixture was dis tillation of the solvent therefrom at a reduced pressure tilled to afford ethyl a-formylisobutyrate, B.P. 60° C. at and is then hydrogenated by contact with molecular hy 12 mm. n20=1.4150, in a yield of 82% of theory. The drogen in a conventional manner. product had the following elemental analysis. Illustrative conventional hydrogenation catalysts include Analysis.-Calc'd. (percent wt.) : C, 58.3; H, 9.39. Group VIII transition metals such as platinum, palladium, Found: C, 58.4; H, 8.7. nickel and cobalt or metal oxide catalysts such as palla 50 A 300 g. sample of ethyl ox-formylisobutyrate, 900 ml. dium oxide, platinum oxide and copper chromite. Suitable of ethanol and 10 g. of Raney nickel were charge to an temperatures for the separate hydrogenation process are autoclave and contacted with molecular hydrogren at 65 from about 20° C. to about 250° C. when employed in C. and a hydrogen pressure of 80 atmospheres for a 2 conjunction with hydrogen pressures from about 1 atmos hour period. The resulting yield of ethyl hydroxypivalate, phere to about 400 atmospheres. In this modification B.P. 88° C. at 12 mm., n20=1.4235, was 88% of theory. where hydrogenation is conducted subsequent to separa The product had the following elemental analysis. tion of the initial hydroformylation product, conven Analysis.-Calc'd (percent wt.): C, 57.5; H, 9.65. tional hydrogenation solvents are employed, e.g., alcohols, Found: C, 57.3; H, 9.4. esters and the like, particularly alkanols of up to 10 car EXAMPLE II bon atoms such as methanol, ethanol, isopropanol, n 60 hexanol, octanol and decanol. The procedure of Example I was employed to hydro In the preferred modification of the process, however, formylate 100 g. of cyclooctylmethyl methacrylate in 400 the hydrogenation is conducted without separating the g. of benzene in the presence of 0.1 g. of rhodium oxide initial hydroformylation product from the rhodium cata and 2.5 g. of tributylphosphine at a temperature of 120 lyst and solvent. In this modification, at the conclusion C. and a carbon monoxide-hydrogen (molar ratio of 1:1) of the initial hydroformylation the temperature is raised pressure of 300 atmospheres over a 5 hour period. The to at least 180° C. but no higher than about 250 C., pref yield of cyclooctylmethyl c-formylisobutyrate, B.P. 158 erably no higher than about 210 C., and the unreacted C. at 10 mm., n20=1.4693, was 79%. The product had hydrogen component of the initial product mixture serves the following elemental analysis. to effect the desired hydrogenation. It is seldom necessary Analysis.--Caic'd (percent wt.) : C, 69.69; H, 10.7. to altar the pressure of hydrogen in the system although Found: C, 70.4; H, 10.4. the hydrogen pressure at which hydrogenation is con The initial ester product was hydrogenated with Raney ducted should be at least 100 atmospheres, preferably at nickel in methanol at 100° C. and a hydrogen pressure of least 150 atmospheres, and additional hydrogen is added 80 atmospheres. A yield of 87% of theory of cyclooctyl if required. There is no critical limitation on the maximum methyl hydroxypivalate was obtained, B.P. 170-174° C. 3,446,839 5 6 at 10 mm., n20=1.4781. The product, believed to be a novel compound, had the following elemental analysis. EXAMPLE WII Analysis.--Calc'd (percent wt.): C, 69.38; M, 10.81. By the procedure of Example III, a 38% yield of cyclo Found: C, 71.2; H, 10.9. hexylmethyl hydroxypivalate, B.P. 143° C. at 10 mm., no?=1.4647, was obtained upon hydroformylation and EXAMPLE III Subsequent hydrogenation of cyclohexylmethyl methacry According to the procedure of Example II, a quantity late. This product, believed to be a novel compound, had of 300 g. of n-butyl methacrylate dissolved in 1200 g. of the following elemental analysis. benzene was hydroformylated in 4 hours in the presence Analysis.--Calcd (percent wt.): C, 67.35; H, 10.35. of 0.2 g. rhodium oxide and 5 g. tributylphosphine at 120 Found: C, 67.7; H, 10.4. C. and a carbon monoxide-hydrogen (1:1) pressure of 0 300 atmospheres. The yield of n-btuyl ox-formylisobutyr EXAMPLE VIII ate, B.P. 85 C. at 10 mm., was 91%. The product had the following elemental analysis. The procedure of Example I was followed to conduct Analysis.--Calc'd (percent wt.): C, 62.76; H, 9.36. a Series of runs wherein methyl methacrylate, dissolved in Found: C, 63.0; H, 9.7. 4 parts by weight of solvent per part of methyl methacry Hydrogenation of the ester product with a Raney nickel late, was contacted with carbon monoxide and hydrogen. catalyst yielded 88% of theory of n-butyl hydroxypivalate, The solvent was benzene in each run except for Run 6 B.P. 96° C. at 12 mm., n20=1.4288. The product, be wherein tetrahydrofuran was employed, The initial hydro lieved to be a novel compound, had the following ele formylation was conducted under the conditions identified mental analysis. 20 as a in each run. At the conclusion of the hydroformyla Analysis.--Calc'd (percent wt.): C, 62.04; H, 10.41. tion the temperature was raised and hydrogenation was Found: C, 61.8; H, 10.4. effected at the conditions identified as b without product EXAMPLE IV separation. The hydrogenation mixture was subsequently worked up in conventional manner by cooling, venting, By the procedure of Example III, n-hexyl methacrylate 2 5 filtering and distilling. The results of this series are shown was hydroformylated to afford n-hexyl co-formylisobutyr in Table I wherein the term "yield” refers to yield of ate, B.P.108° C. at 10 mm., in a yield of 83%. The prod methyl hydroxypivalate based on methyl methacrylate uct had the following elemental analysis. charged. TABLE I Methyl Molar methacry- ratio Temp., Pressure, Time, Run late, g. COH. Rh2O3, g. C. atml. hrs. Yield ------100 lil 0.1------a, 80------a, 1,000------a, 7------93.1 g. 2------100 111 0. 1-1-2, 5.g. of tributyl- a,b, 80-90------230------a,b, 1,000------1,000.---- a,b, 5------4------9471%. g. phosphine. b, 200------b, 1,000.---- b, 3------71.5% 5------300 111 0.2-5g. of l-phenyl- a, 80-130----- a, 200------a, 7------84 g. phospholine. b, 230-240---- b, 300------b, 20------32%. 6------00 114 0.1-2.5g of l-phenyl- a, 130-140---- a, 200------23------40 g. phospholane. b, 230------b, 300------ll------30.5% 5------100 112 0. i-t-2.5g. of tributyl- a, 120------phosphine. b, 210-- 6------100 111 0. --5g. of tributyl- a, 130--- phosphine. b, 210------b, 300------b, 20 Analysis.--Calc'd (percent wt.) : C, 65.97; H, 10.7. Found: C, 66.0; H, 10.0. Methyl hydroxypivalate, believed to be a novel com Hydrogenation of this product with Raney nickel in pound has a boiling point of 65° C. at 10 mm. and a re methanol yielded 97% of n-hexyl hydroxypivalate, B.P. fractive index, n20 of 1.4281. 130° C. at 10 mm. The product, believed to be novel, had EXAMPLE IX the following elemental analysis. A series of runs was made wherein 100 g. of methyl Analysis.-Calc'd (percent wt.): C, 65.31; H, 10.96. methacrylate in 400 g. of benzene was hydroformylated Found: C, 65.3; H, 11.1. by contact with an equimolar mixture of carbon monox ide and hydrogen at various pressures. In Runs 1-4 the EXAMPLE V hydroformylation was conducted at 80° C. in the presence By the procedure of Example III, n-octyl methacrylate of 0.1 g. of rhodium oxide and in Ruins 5-9 the hydro was hydroformylated to afford n-octyl c-formylisobutyr 55 formylation was conducted at 120-130° C. in the presence ate, B.P. 142° C. at 12 mm., n0=1.4320, in a yield of of 0.1 g. of rhodium oxide and 2.5 g. of tributylphosphine. 91%. The product had the following elemental analysis. The results of this series are shown in Table II wherein Analysis.--Calc'd (percent wt.) : C, 68.38; H, 10.5. the percentages represent the yield of methyl ox-formyliso Found: C, 68.3; H, 10.6. butyrate obtained under the indicated conditions. Hydrogenation of this product with Raney nickel in 60 n-octanol yielded 88% of theory of n-octyl hydroxy TABLE I pivalate, B.P. 146° C. at 10 mm., n20=1.4392. This prod Pressure, atm------200 250 300 400 500 1,000 uct, believed to be a novel compound, had the following Runs l-4, percent------48 52 72 elemental analysis. Runs 5-9, percent------65 74 80 9 ------92 Analysis.-Calc'd (percent wt.): C, 67.78; H, 11.38. 65 We claim as our invention: Found: C, 68.0; H, 11.7. 1. The process of producing an alkyl hydroxypivalate EXAMPLE VI which comprises initially intimately contacting (a) alkyl methacrylate wherein the alkyl is alkyl of up to 20 carbon By the procedure of Example III, a 91% of n-lauryl atoms, (b) carbon monoxide, and (c) from about 0.25 hydroxypivalate, B.P. 148 C. at 0.4 mm., was obtained 70 mole to about 4 moles of hydrogen per mole of carbon upon hydroformylation and subsequent hydrogenation of monoxide in liquid-phase solution in inert solvent in the n-lauryl methacrylate. This product, believed to be a novel presence of from about 0.0001 gram-atom to about 0.01 compound, had the following elemental analysis. gram-atom of rhodium catalyst per mole of methacrylate Analysis.-Calc'd (percent wt.): C, 71.28; H, 11.96. ester and up to about 20% by weight based on the meth Found: C, 71.3; H, 11.6. acrylate ester of a tertiary phosphine, at a temperature 3,446,839 7 8 from about 80° C. to about 120° C. and a pressure from References Cited about 100 atmospheres to about 2000 atmospheres; and UNITED STATES PATENTS subsequently maintaining the resulting mixture at a tem 2,880,241 3/1959 Hughes ------260-604 perature of from about 180° C. to about 250 C. thereby 2,983,734 5/1961 Sargent ------260-484 XR hydrogenating the c-formylisobutyrate ester product re 5 3,176,038 3/1965 Zachry et al. -- 260-484 XR sulting from said initial intimate contacting. 3,239,566 3/1966 Slaugh et al. ------. 260-604 2. The process of claim 1 wherein the amount of said tertiary phosphine is at least 0.1% by weight based on the 3,253,018 5/1966 Zachry et al. ---- 260-484 XR methacrylate ester. OTHER REFERENCES 3. The process of claim 2 wherein the tertiary phos 0. Tsuji: The Journal of the Society of Organic Synthetic phine is trialkylphosphine wherein each alkyl is alkyl of Chemistry, Japan, vol. 22, pp. 892-893, November 1964. up to 8 carbon atoms. 4. The process of claim 3 wherein the trialkylphosphine LORRAINE A. WEENBERGER, Primary Examiner, is tributylphosphine. 5. The process of claim 2 wherein the temperature of A. G. HALLUIN, Assistant Examiner. said initial contacting is from about 80° C. to about U.S. C. X.R. 135° C. 6. The process of claim wherein the rhodium is pro 260-343.6, 483 vided as rhodium oxide.