# Patent

## Title
Process of preparing organic acids

## Abstract

Alternatively, a ligand or coordination complex compound of the metal salt compound, and catalytic quantities of an alcohol may be employed.

## Background
The oxidative carbonylation of mono-olefins such as ethylene and propylene to prepare carboxylic acids and derivatives employing various catalyst systems, particularly noble metal catalysts is known; see for example, Fenton and Steinwand, Journal of Organic Chemistry, Vol. 37, 2034 (1972) as well as U.S. Pat. Nos. 3,397,226; 3,876,694; 3,907,882, 3,923,883; and 3,960,934.

In an article by Jiro Tsuji, Accounts of Chemical Research, Vol. 2, 144, (1969) and bibliographic references (36) and (37) noted therein, the carbonylation of butadiene-isoprene-palladium chloride complexes in alcohol to give 1,4-dichloro-2-butene and ethyl 3-pentenoate and ethyl 5-ethoxy-3-methyl-3-pentenoate and dimethylbutyrolactone, with other minor products is described. In a related article by S. Hosaka and J. Tsuji, Tetrahedron, Vol. 27, 3821-3829 (1971) the palladium catalyzed carbonylation in alcohol of various conjugated dienes and the reaction mechanism are shown.

A recent Japanese Kokai Pat. No. 75,130714, Oct. 16, 1975, describes the preparation of carboxylic acid esters by reacting conjugated dienes, carbon monoxide and at least stoichiometric amounts and generally an excess of an monohydric alcohol in the presence of molecular oxygen and a Group 8 noble metal catalyst. Dehydrating agents may be used if necessary to maintain non-aqueous conditions.

While oxidative carbonylation reactions are generally known, the prior art does not show or describe the process of the present invention for the oxidative carbonylation of a diolefin, such as butadiene, to selectively prepare an unsaturated monoester employing stoichiometric amounts of reactant dehydrating agent compound which monoester may be further processed by catalytic dimerization, catalytic hydrogenation and catalyzed hydrolysis reaction sequences to prepare pelargonic and sebacic acid and related derivatives including useful difunctional monomers. Catalytic dimerization of the monoester, methyl penta-2,4-dienoate, can provide fatty acid precursors. The diene monoesters of the instant invention are especially useful as difunctional monomers for the preparation of speciality block, graft, and other polymers.

The process of the present invention is directed to the preparation of a diene monoester by the catalytic oxidative carbonylation of a diolefin. More particularly, the instant process relates to the synthesis of monoesters by reacting carbon monoxide, oxygen and a diolefin such as 1,3-butadiene, isoprene, chloroprene, 2,3-dimethylbutadiene, 1,3-pentadiene and the like, under elevated temperature and pressure conditions in the presence of a catalytic amount of a ruthenium, rhodium, palladium, osmium, iridium or platinum metal salt compound or mixtures thereof, a copper (I), copper (II), iron (II) or iron (III) oxidant salt compound and a stoichiometric amount of a reactant dehydrating agent which may be, for example, an orthoester, ketal, acetal, or trialkyl orthoborate. Co-catalytic ligands or coordination complex compounds of the metal salt compounds and catalytic quantities of a primary, secondary or tertiary saturated alcohol while not required in the process of the invention, may also be employed.

The process of this invention provides an economic process for the selective preparation of a diene monoester, which may be a monobasic fatty acid or sebacic acid precursor, by the oxidative carbonylation of a conjugated diolefin such as butadiene. There is provided a good conversion of the diolefin employed, especially 1,3-butadiene, and excellent yield selectivity to the diene monoester. Carbonate esters, oxalate esters, carbon dioxide as well as other side reaction products associated with the oxidative carbonylation reaction are obtained in only trace amounts or eliminated by the reaction conditions employed in carrying out the process of the invention. The reaction is catalytic in both the platinum group metal salt compound and oxidant salt compound and employs at least stoichiometric quantities of reactant diolefins, carbon monoxide, oxygen and/or air, and dehydrating agent. The reaction can be safely and conveniently carried out under a non-explosive oxygen or air/carbon monoxide atmosphere.

According to the present invention diolefins are oxidatively carbonylated with carbon monoxide and oxygen or an oxygen-containing gas in the presence of a platinum group metal compound such as a palladium halide, a copper or iron oxidant salt compound such as a copper (I) iodide and a stoichiometric amount of a dehydrating agent such as dimethoxycyclohexane to produce a diene monoester. The process is carried out at suitable temperatures and pressures and alternatively contemplates the use of catalytic quantities of an aliphatic, alicyclic or aralkyl alcohol and the use of catalytic amounts of various ligands, which will not work in themselves, in conjunction with the platinum group metal salt compound and the oxidant salt.

It is a primary object of this invention to provide a process for the preparation of diene monoesters in high yield and good conversion of reactants which esters may be further processed to pelargonic, other fatty acids and sebacic acid derivatives.

It is another object of the invention to provide a novel reaction system for the conversion of carbon monoxide, oxygen and diolefins to diene monoesters.

It is a further object of this invention to provide a specific catalytic mechanism for the employment of platinum group metal compounds, oxidant salt compounds and dehydrating agents in an oxidative carbonylation process employing a diolefin.

These and other objects and advantages of this invention will become apparent from the description of the invention which follows and from the claims.

In accordance with this invention, a diene monoester having the formula ##STR3## wherein R and R' are as hereinafter described, is produced by reacting, under liquid phase conditions, a mixture of carbon monoxide and oxygen or an oxygen-containing gas with a diolefin, at elevated temperatures and pressures in the presence of a catalyst system comprising (1) a platinum group metal or platinum group metal compound or mixtures thereof, with or without a ligand or coordination complex compound such as lithium iodide and (2) a catalytic amount of a copper (I), copper (II), iron (II) or iron (III) metal oxidant salt compound. In addition, a stoichiometric quantity of a suitable dehydrating agent, based on the diolefin being reacted, is employed in the reaction in order to essentially avoid the problems associated with the presence of water in the system which is produced therein by the oxidant-reoxidation reaction. While not essential to the oxidative carbonylation of the diolefin as set forth herein, a catalytic amount of an alcohol especially an aliphate alcohol, is preferably employed in the reaction to aid in initiating the oxidative carbonylation reaction. The reactants are initially charged in an essentially anhydrous condition.

A general postulated equation for the reaction of the present invention may for example be represented as follows: ##STR4## wherein R is an alkyl group of from 1 to 4 carbon atoms or an aralkyl group containing 6 carbon atoms in the ring and from 1 to 4 carbon atoms in the alkyl substituent, and R' is hydrogen, a halogen, an alkyl group of from 1 to 4 carbon atoms or an alkyl group containing 6 carbon atoms in the ring.

The reaction between the diolefin, carbon monoxide, oxygen, and dehydrating agent may be carried out in an autoclave or any other appropriate reactor. Although the order of addition of reactants and catalyst components may vary, a general procedure is to charge the diolefins, dehydrating agent, platinum group metal compound, oxidant salt compound into the reaction vessel, and if desired a ligand or coordination complex compound and a catalytic quantity of an alcohol, then introduce the proper amount of carbon monoxide and oxygen to the desired reaction pressure and then heat the mixture to the desired temperature for the appropriate period. The reaction can be carried out batchwise or as a continuous process and the order of addition of reactants and catalyst may be varied to suit the particular apparatus employed. The addition of the oxygen or oxygencontaining gas, such as air, can be a pulsed or continuous addition to the reaction system. The reaction products are recovered and treated by any conventional method such as distillation and/or filtration, etc. to effect separation of the monoesters from unreacted materials, platinum group metal salt compound, oxidant salt compound, by products, including for example, when reacting 1,3-butadiene, dimethyl hex-3-endioate, dimethyl hex-2,4-diendioate, methylpent-3-enoate, methyl 3-methoxypent-4-enoate, methyl 5-methoxypent-3-enoate, methyl nonadilnoates, dimethl decadiendioates, dimethyl oxalate, and CO.sub.2, etc. Catalysts, including solvents which may have been employed, may be recycled to the system.

The diolefins which may be employed in concentrations of from about 10 to 80 weight percent, preferably 20 60 weight percent, or on a stoichiometric molar basis with the dehydrating agent employed, and suitable for use in the process of the present invention conform to the general formula ##STR5## wherein R' which may be the same or different, is hydrogen, a halogen, an alkyl group of from 1 to 4 carbon atoms or an aryl group containing 6 carbon atoms in the ring. Representative diolefins within the above noted formula include for example, butadiene, isoprene, chloroprene, 2,3-dimethyl-, 2,3-diethyl-, 2,3-dipropyl, and 2,3-dibutylbutadiene, 1,3- and 2,4-heptadienes, 1,3-pentadiene, piperylene, 2-ethyl-1,3-butadiene, 1-phenylbutadiene, 1,4-diphenylbutadiene, 2,-chloro-3-methylbutadiene, 1-chlorobutadiene, 2,5-dimethyl-2,4-hexadiene, 2-bromobutadiene, 2-iodobutadiene, 2-chloro-1-phenylbutadiene, etc. Butadiene and isoprene are the preferred diolefins and butadiene is most preferred.

Suitable dehydrating agents which may be employed and in at least stoichiometric amounts in the process of the invention include, for example, acetals, ketals, carboxylic orthoesters, trialkylorthoborates and dialkoxycycloalkanes.

The acetals and ketals suitable for use in the process of the present invention conform to the general formulae: ##STR6## respectively. R may be a substituted or unsubstituted alkyl group containing from 1 to 20 carbon atoms preferably 1 to 10 carbon atoms. R may also be a substituted or unsubstituted alicyclic, or an aryl group containing one or more benzenoid rings preferably not more than 3 rings which may be fused or joined by single valency bonds. R' and R" which may be the same of different may be a substituted or unsubstituted alkyl group containing from 1 to 8 carbon atoms preferably 1 to 4 carbons in the alkyl chain or an aralkyl group containing 6 carbon atoms in the ring and from 1 to 4 carbon atoms in the alkyl substituent. R, R' and R" may contain substituents such as amido, alkoxy, amino, carboxy, cyano, etc. radicals. Representative acetals suitable for use in this invention include, for example, the 1,1-dialkoxyalkanes such as dimethoxymethane, dibutoxymethane, 1,1-dimethoxyethane, 1,1-dimethoxypropane, ethyl diethoxyacetate, 1,1,2-trimethoxyethane, 1,1-dimethoxy-2-propene, and dimethoxy- and diethoxyphenylmethane, etc. In a like manner for example the acetals 1-methoxy-, 1-ethoxy- and 1-propoxytetrahydrofuran, 2,5-diethoxytetrahydrofuran, and 2-ethoxy-4-methyl-3,4-dihydro-2H-pyran etc. may be employed. Representative ketals suitable for use in this invention include for example, 2,2-dimethoxy-, 2,2-diethoxy- and 2,2-dipropoxypropane, butane, pentane, etc. 3,3-dimethoxy- and 3,3-diethoxy-1-pentene, 1-butene, etc., 1,1-dimethoxycyclohexane, 1,1-diethoxycyclohexane, 1,1-dibutoxycyclohexane, etc., 1,1-dibutoxy-4-methylcyclohexane, 1,1-dimethoxy-1,2,3,4-tetrahydronaphthalene, etc. and 1,1-bis(2-propenoxy)cyclohexane.

The carboxylic ortho esters suitable for use in the process of the invention conform to the general formula ##STR7## wherein R may be hydrogen or a substituted or unsubstituted alkyl group containing from 1 to 20 carbon atoms preferably 1 to 10 carbon atoms. R may also be an alicyclic, or an aryl group containing one or more benzenoid rings preferably not more than 3 rings which may be fused or joined by single valency bonds. R', R" and R'" which may be the same or different may be substituted or unsubstituted alkyl groups containing from 1 to 8 carbon atoms preferably 1 to 4 carbon atoms in the alkyl chain or an aralkyl group containing 6 carbon atoms in the ring and from 1 to 4 carbon atoms in the alkyl substituent. R, R', R", and R'" may contain substituents such as amido, alkoxy, amino, carboxy, cyano, etc. Representative carboxylic ortho esters suitable for use in this invention include, for example, trimethyl orthoformate, triethyl orthoformate, triphenyl orthoformate, tri-n-propyl orthoformate, etc., triethyl tripropyl, tributyl, trimethyl orthoacetate, etc., trimethyl, triethyl, tripropyl, tributylorthopropionate, etc., trimethyl, triethyl, tripropyl, tributyl orthobutyrate, etc., trimethyl, triethyl, tripropyl, tributyl, orthoisobutyrate, etc., trimethyl, triethyl, tripropyl, tributyl orthocyanoacetate, etc., trimethyl triethyl, tripropyl, tributyl orthophenylacetate, etc., trimethyl, triethyl, tripropyl, tributyl ortho-.alpha.-chloroacetate, etc., trimethyl, triethyl, tripropyl, tributyl ortho-.alpha.-bromoacetate, etc., trimethyl, triethyl, tripropyl, tributyl orthobenzoate, etc., trimethyl, triethyl, tripropyl, tributyl ortho-p-chlorobenzoate, etc., hexamethyl-p-diorthophthalate, etc., ethyl triethoxyacetate, hexaethyl orthooxalate, triethyl ortho-3-butynoate, etc. In a like manner the esters trimethyl, triethyl, tripropyl orthocarbonate, 2-isopropyl-2-methoxy-1,3-dioxolane, 2-methyl-2-ethoxy-1,3-dioxolane, 2,2-diethoxytetrahydrofuran, 2,2-diethoxychroman, 1,4,5-trioxaspiro[4,4]nonane, 2,6,7-trioxabicyclo[2,2,2]octanes, 2,4,10-trioxaadamantane-2,4,10-trioxatricyclo[3,3,1,13,7]decane may be employed.

The orthoborate esters employed in at least stoichiometric quantities and suitable for use in the process of the present invention are preferably symmetrical and conform to the general formula ##STR8## wherein R is a substituted or unsubstituted alkyl group containing from 1 to 8 carbon atoms in the alkyl chain or an aralkyl group containing 6 carbon atoms in the ring and from 1 to 4 carbon atoms in the alkyl substituent. Particularly preferred are the orthoborates wherein each R is a straight chain alkyl group containing from 1 to 4 carbon atoms such as triethyl borate. Representative ortho borate esters suitable for use in this invention include, for example, trimethylborate, triethylborate, tri-2-chloroethyl borate, tritolyl borates, tri-methoxybenzyl borates, tri-chlorobenzyl borates, tri-benzyl borate, tri-4-butylphenyl borate, tri-n-propyl and tri-isopropyl borates, tri-(1,3-dichloro-2-propyl) borate, tri-n-butyl, tri-s-butyl and tri-t-butyl borates, tri-(.beta.,.beta.,.beta.-trichloro-t-butyl)borate, triphenyl borate, tri-o-chlorophenyl borate, tri-n-amyl borate, tri-t-amyl borate, tri-(o-phenylphenyl) borate, tri-n-hexyl borate, tri-3-heptyl borate, tri-3-pentyl borate, tri-n-octyl and tri-isooctyl borates, tri-(2-ethylhexyl)borate, tri-(methylisobutylcarbonyl) borate, tri(diisobutylcarbinyl) borate, tri-(2,5-dimethylbenzyl) borate, etc.

The dialkoxycycloalkanes, which are the preferred dehydrating agents for use in the present invention, in at least stoichiometric quantities, conform to the general formula ##STR9## wherein R is a substituted or unsubstituted alkyl group containing from 1 to 4 carbon atoms and x is an integer of from 4 to 9. R may contain substituents such as amido, alkoxy, amino, carboxy, cyano, etc. radicals. In addition, the cyclic ring may be substituted with alkyl groups of up to 4 carbon atoms. Dimethoxycyclohexane is the most preferred. Representative dialkoxycycloalkanes include for example, dimethoxy-, diethoxy-, dipropoxy- and dibutoxycyclopentanes, and the corresponding dimethoxy, diethoxy, dipropoxy and dibutyoxycyclohexanes, heptanes, octanes, nonanes and decanes, as well as 4-ethyl-1,1-dimethoxycyclohexane, etc. A general postulated equation for the reaction using dimethoxycyclohexane in the oxidative carbonylation of butadiene may be represented as follows: ##STR10##

The platinum group metal compounds which may be employed in the process of this invention as catalyst are the palladium, platinum, rhodium, ruthenium, iridium, and osmium salts or mixtures thereof. Among the chemical forms of the platinum group metal salt compounds which can be used as such or as mixtures or formed in the reaction system from the metals per se are, for example, the palladium, platinum, rhodium, ruthenium, iridium and osmium, halides, sulfates, nitrates, oxides, oxalates, acetates and trifluroacetates, preferably the palladium (II) halides, particularly palladium (II) iodide. Representative catalytic platinum group metal salt compounds include, for example palladium (II) iodide, .pi.-allyl palladium iodide, platinum (II) iodide, rhodium (III) iodide, ruthenium (III) iodide, palladium (II) sulfate, palladium (II) acetate, palladium (II) trifluoroacetate, palladium (II) bromide, rhodium (III) bromide, iridium (III) chloride, platinum (II) sulfate, osmium (II) chloride, palladium (II) oxide, osmium tetroxide, iridium (III) sulfate, etc. As indicated above the metals as such may be added to the reaction as part of the catalyst mixture, the salt compound being formed in situ from at least a portion of the platinum group metal under reaction conditions.

The palladium, platinum, rhodium, ruthenium, osmium and iridium compounds employed may be in a homogeneous state in the reaction mixture at reaction conditions. Thus, the compounds may be present in solution, or suspension and may also be on support materials such as alumina, silica gel, aluminosilicates, activated carbon or zeolites or may be anchored to a polymer support. The compounds may be partially or completely soluble under reaction conditions. The reaction is generally carried out in the presence of a catalytic proportion of the platinum group metal salt compound and will proceed with small amounts of the metal salt compounds hereinabove described. Generally the proportions of the platinum group metal salt compound used in the reaction will be equivalent to between about 0.001 to 5 weight percent of the diolefin employed and are preferably employed in amounts between about 0.01 to 2 percent by weight of the diolefin employed. Larger or smaller amounts may be employed at varied pressures and temperatures.

As mentioned hereinabove, alternatively, a ligand or coordination complex compound of the platinum group metal salt compound may be employed in the process of the invention as co-catalyst in the catalytic mixture and thereby also achieve a pronounced increase in the selectivity for the diene monoester. The ligands may be, for example, alkyl or aryl phosphines, arsines, or stibines or salts of the alkali metals, e.g., lithium, sodium, potassium, rubidium, cesium salts, such as lithium bromide, sodium iodide, potassium iodide, lithium acetate, lithium iodide, etc. The complexes of the metal salt compounds which are suitable for use in the process of the present invention include complex compounds of palladium, platinum, rhodium, ruthenium, osmium and iridium. The complex compounds may contain one or more atoms of the salt metals in the molecule and when more than one such atom is present, the metals may be the same or different. The mono- or polydentate ligands which are present in the molecule of the complex compounds and in which at least one of the electron-donating atoms is an atom of phosphorus, arsenic or antimony or a halide ion containing a lone pair of electrons may be, for example, organo-phosphines, -arsines and -stibines and their oxides. Suitable monodentate ligands include alkyl phosphines such as trimethylphosphine and tributylphosphine, arylphosphines such as diethylphenylphosphine and radicals derived from such phosphines, for example the radical having the formula --P(CH.sub.3).sub.2. Hydrocarbyloxy phosphines, i.e., phosphites, such as triphenyl phosphite may also be employed. Suitable polydenate ligands include tetramethyl diphosphinoethane and tetraphenyl diphosphinoethane. Exactly analogous derivatives of arsenic and antimony may be used; however, because of their greater ease of preparation and stability of the derived complexes, the hydrocarbyl derivatives of phosphorus are preferred. It is preferred to employ the alkali metal halides, particularly the lithium halides such as lithium bromide and lithium iodide.

Benzonitrile, acetonitrile, isocyanates, isothiocyanates, pyridine, pyridyls, pyrimidine, quinoline, isoquinoline may also serve as suitable ligands to modify the platinum group metal catalyst activity or catalyst solubility.

The complex compounds suitable for use in the process of the present invention may contain in the molecule, in addition to the ligands discussed above, one or more other atoms, groups or molecules, which are chemically bonded to the metal atom or atoms. Atoms which may be bonded to the metal include, for example, hydrogen, nitrogen, and halogen atoms; groups which may be bonded to the metal include, for example hydrocarbyl, hydrocarbyloxy, carbonyl, nitrosyl, cyano and SnCl.sub.3 -- groups; molecules which may be bonded to the metal include, for example organic isocyanides and isothiocyanates. Examples of suitable complex compounds are those represented by the following formulae: RhBr.sub.3 (PPhEt.sub.2).sub.3 Rh(CO)Cl(AsEt.sub.3).sub.2 Rh I (CO) (PPhEt.sub.2).sub.2 RhCl(CO) (PEt.sub.3).sub.2 Rh(Ph.sub.2 PCH.sub.2 CH.sub.2 PPh.sub.2).sub.2 I PdBr.sub.2 (PPh.sub.3).sub.2 Rh[(PhO).sub.3 P].sub.3 I PdI.sub.2 (PPh.sub.3).sub.2 Li.sub.2 PdI.sub.4 PtCl.sub.2 (p-ClC.sub.6 H.sub.4 PBu.sub.2).sub.2 (PhCN).sub.2 PdI.sub.2 ______________________________________

The complex compounds employed may be introduced into the reaction mixture as such, or they may be formed in situ from a suitable platinum group metal or metal compound noted above and the desired ligand.

The ligand or complex compounds may be used in catalytic amounts of from 0 to 3 percent preferably from 0.1 to 1 percent by weight of the diolefin to be reacted although larger or smaller amounts may be employed at varied pressures or reaction rates.

The oxidant salt compounds which may be employed in an essentially anhydrous condition in the process of the present invention and in catalytic amounts of from 0.1 to 10 weight percent preferably 0.50 to 6 weight percent include the iron (II), iron (III), copper (I) and copper (II) salts such as the halides, sulfates, trifluoroacetates, nitrates, oxalates, naphthanates, hex-3-endioates or acetates and preferably copper (I) iodide and iron (II) iodide. Representative oxidant salts include, for example, copper (II) sulfate, copper (II) trifluoroacetate, copper (II) acetate, copper (II) oxalate, copper (II) triflate, copper (II) fluorosulfonate, copper (I) bromide, copper (I) sulfate, iron (III) sulfate iron (II) bromide, iron (II) chloride, iron (III) acetate, iron (III) oxalate, copper (II) penta-2,4-dienoate, iron (II) penta-2,4-dienoate and iron (III) trifluoroacetate.

While not necessary to the reaction of the present invention, it is often desirable to add a small amount of an acid to aid in initiating the reoxidation (by oxygen) of copper (I) to copper (II) or iron (II) to iron (III). Suitable acids include for example hydroiodic, hydrobromic, sulfuric, phosphoric and acetic in concentrations of from 0-2 weight percent of diolefin.

As indicated hereinabove, an alcohol in catalytic quantities may be employed in the process of the invention primarily to aid in initiating the oxidative carbonylation reaction. The alcohols may be employed in concentrations of from 0 to 20 and preferably 0.5 to 10 weight percent of the diolefin employed. The alcohols may be saturated monohydric primary, secondary or tertiary alcohols and conform to the general formula ROH, wherein R is an optionally substituted aliphatic or alicyclic group containing from 1 to 20 carbon atoms and preferably the unsubstituted aliphatic alcohols containing from 1 to 8 carbon atoms. R may also be a substituted or an unsubstituted aralkyl group. In general, the substituents which may be amido, alkoxy, amino, carboxy, etc. radicals, in addition to the hydroxyl group, do not interfere with the reaction of the invention. Representative alcohols especially suitable for use in this invention are saturated monohydric alcohols such as methyl, ethyl, n-, iso-, sec-, and tert-butyl, amyl, hexyl, octyl, lauryl, n- and isopropyl, cetyl, benzyl, chlorobenzyl and methoxybenzyl alcohols as well as, for example, tolylcarbinol, cyclohexanol, heptanols, decanols, undecanols, 2-ethyl hexanol, nonanol, myristyl alcohol, stearyl alcohol, methyl cyclohexanol, pentadecanol, oleyl and eicosonyl alcohols, and the like. The preferred alcohols are the primary and secondary monohydric saturated aliphatic alcohols, such as methanol, ethanol, 1- and 2-propanol, n-butyl alcohol, etc., up to 8 carbon atoms. The R group of the alcohol may be different from the R groups of the dehydrating agents noted hereinabove, resulting in the preparation of mixed diene esters.

Solvents, if desired, which are chemically inert to the components of the reaction system may be employed, and in some cases, especially in the oxidative carbonylation of 1,3-butadiene, will improve the selectivity and conversion to the diene monoester as well as the catalyst solubility or boiling point range for product and catalyst recovery. Suitable solvents include for example, dioxane, dimethylcarbonate, dimethyladipate, benzene, nitrobenzene, acetonitrile, tetrahydrofuran, methyl acetate, ethyl acetate, isopropyl acetate, n-propyl formate, butyl acetates, cyclohexyl acetate, n-propyl benzoate, lower alkyl phthalates, etc. the alkyl sulfones and sulfoxides such as propyl ethyl sulfoxide, diisopropyl sulfone, diisooctyl sulfoxide, acetone, cyclohexanone, methyl formate, etc.

The process of the present invention can be suitably performed by introducing the oxygen and carbon monoxide at a desired pressure into contact with the diolefin, dehydrating agent, the platinum group metal salt compound and the copper or iron oxidant salt and possibly a catalytic amount of an alcohol as well as a cocatalytic amount of a ligand or coordination complex and heating to the desired temperature. In general, a carbon monoxide pressure of about 15 psig to about 5000 psig partial pressure and preferably from 100 psig to about 2000 psig is employed. Stoichiometric quantities of carbon monoxide are generally employed. However, an excess of carbon monoxide may be employed, for example, in continuous processes where a large excess of or high carbon monoxide requirements are generally utilized, a suitable recycle of the unreacted carbon monoxide may be employed. The reaction will proceed at temperatures of from about 25.degree. C. to 200.degree. C. It is generally preferred to operate the process at temperatures in the range of 80.degree. C. to 150.degree. C. to obtain a convenient rate of reaction with the particular diolefin. Lower temperatures may be employed but the reaction rate is slower. Higher temperatures may also be used depending on the diolefin to be reacted. At the higher temperatures the diolefin employed may be in the vapor state. Heating and/or cooling means may be employed interior and/or exterior of the reaction to maintain the temperature within the desired range.

At least stoichiometric amounts of oxygen or an oxygen-containing gas such as air may be employed and at any oxygen partial pressure such that the explosive range is avoided. Thus, the concentrations of oxygen should be low enough so that the reaction mixture is not potentially explosive. The Handbook of Chemistry and Physics, 48th Edition, 1967 indicates that the explosive limits of pure oxygen in carbon monoxide is 6.1 to 84.5 volume percent and air in carbon monoxide to be 25.8 to 87.5 volume percent.

The reaction time is generally dependent upon the diolefin being reacted, temperature, pressure and on the amount and type of the catalyst, oxidant and dehydrating agent being charged as well as the type of equipment being employed. Reaction times will vary dependent on whether the process is continuous or batch and may vary from 10 to 600 minutes. Reaction time for butadiene is generally about 120 minutes.

The following examples are provided to illustrate the invention in accordance with the principles of this invention but are not to be construed as limiting the invention in any way except as indicated by the appended claims.

Although the process of the present invention will primarily be directed to the oxidative carbonylation of 1,3-butadiene to produce the diene monoester, methyl penta-2,4-dienoate, which is an important precursor for the preparation of pelargonic and sebacic acid, it is not intended that the process be limited to the butadiene type diolefins and those skilled in the art will recognize that the present invention is broadly applicable to the oxidative carbonylation of other conjugated diolefins, within the formula as hereinabove set forth, to produce other unsaturated monoester products such as a 1,3-pentadiene to methyl 2-methylpenta-2,4-dienoate.

In the examples which follow the reactions were carried out in a 500 ml. nickel-molybdenum (HASTELLOY Alloy) stirred autoclave or 500 ml. titanium lined stirred autoclave. The liquid feed and solid catalyst components were charged into the autoclave as homogeneous solutions where possible. The diolefins were charged into a sight glass and allowed to come to thermal equilibrium before being charged into the autoclave as a liquid under pressure. Carbon monoxide was charged into the autoclave to the desired pressure followed by heating to the desired reaction temperature. Total system pressure was adjusted to the desired level by the addition of more carbon monoxide. Oxygen or air was added and a non-explosive carbon monoxide/oxygen gas mixture maintained. Where oxygen was employed, carbon monoxide was pulsed into the autoclave to sweep the oxygen out of the pressure tubing. Cooling water was circulated through the internal autoclave cooling coils to maintain the desired reaction temperature and to control the reaction exotherm observed upon the addition of reactant oxygen. After each gas uptake levelled out, total system pressure was readjusted and additional oxygen added. The procedure of charging oxygen or air increments and sweeping out the pressure lines with CO was repeated until no more gas uptake was observed or for the desired reaction time.

Upon completion of the reaction, the reactor was cooled to ambient temperature and vented to ambient pressure and gas samples obtained. Solids were separated from liquids by vacuum filtration. The gaseous product volume was measured and analyzed by mass spectral analysis (MS) and the liquid product was analyzed by gas-liquid chromatography (glc). Material balances on the diolefins were obtained by considering the MS and glc results.

Diolefin conversions were calculated on the basis of moles of diolefin consumed by the reaction. Product selectivities were based on the millimoles of diolefin required to make the monoester and by-products. The amount of unreacted diolefin was obtained by MS analysis of the gases and glc analysis for diolefin in the liquid product.

In Examples 1 to 3 a solution of alcohol and dehydrating agent was charged into the autoclave along with 1.51 g. (4.2 mmole) palladium (II) iodide, 1.98 g. (10.4 mmole) copper (I) iodide and 1.12 g. (8.4 mmole) lithium iodide. 1,3-butadiene was charged into the autoclave as a liquid under pressure. The reaction temperature was 100.degree. C. and the total initial carbon monoxide pressure was 900 psig. The reaction was initiated by a 50 psig charge of oxygen and 50 psig line purging charge of carbon monoxide giving a total system pressure of 1000 psig. A strong exotherm and pressure drop of 75-100 psig over a course of 20 minutes was observed. The oxygen cycle was repeated five more times in increments of 25 psig oxygen and 50 psig carbon monoxide at intervals of 20 minutes during an autoclave residence period of 120 minutes. A total pressure drop of about 600 psig was observed. The reaction was terminated before completion and cooled to ambient temperature. The alcohol and dehydrating agents and amount of 1,3-butadiene employed and analytical results giving the conversion and selectivities to the methyl penta-2,4-dienoate is shown in Table 1. ______________________________________ 1,3- Bu- tadi- ene  Ester 1,3-                Dehy-    Con- Selectivity butadiene           dration.sup.(1) ver- Based Charged   Alcohol.sup.(2) Agent    sion on 1,3- Ex.  g. (mmoles) (mmole)   (mmole)  (%)  Butadiene ______________________________________ 1    27 g. (500) MeOH (32) DMOC (500) 15   81 mole % 2    54 g. (1000) MeOH (32) TMOF (1000) 11   81 mole % 3    54 g. (1000) MeOH (32) DMP (1000) 12   80 mole % ______________________________________ .sup.(1) DMOC  1,1dimethoxycyclohexane TMOF  trimethylorthoformate DMP  2,2dimethoxypropane .sup.(2) MeOH  methyl alcohol

In Examples 4 to 13 the procedures and conditions, except as noted for Examples 12 and 13, of Examples 1 to 3 were repeated to oxidatively carbonylate 1,3-butadiene employing 0.66 g. (2.5 mmole) palladium (II) bromide, 2.86 g. (15 mmole) copper (I) iodide and 0.67 g. (5 mmole) lithium iodide. In Example 12 the initial carbon monoxide pressure was 100 psig, the reactor was heated to 100.degree. C. and the carbon monoxide pressure adjusted to 375 psig. The reaction was initiated by a 25 psig charge of oxygen and a 50 psig line flushing charge of carbon monoxide giving a total system pressure of 450 psig. A strong exotherm and pressure drop was noted. When the pressure dropped below 375 psig it was readjusted by adding increments of 25 psig oxygen followed by 50 psig CO. The reaction was carried out for 120 minutes, i.e., prior to completion. In Example 13 the procedure of Example 12 was followed with all pressure doubled giving a total system pressure of 900 psig. The alcohol, dehydrating agent and amount of 1,3-butadiene employed as well as the analytical results for Examples 4 to 13 giving selectivities and conversions to the methyl, ethyl or butyl methyl penta-2,4-dienoate is shown in Table 2. __________________________________________________________________________ 1,3-  Ester 1,3-butadiene         Butadiene Selectivity Charged Alcohol.sup.(4) Dehydration.sup.(1) Conversion Based on 1,3- Ex. g. (mmoles) (mmole) Agent (mmole) (%)   Butadiene __________________________________________________________________________ 4  27 g. (500) MeOH (32) DMOC (500) 18    74 mole % 5  54 g. (1000) MeOH (32) DMOC (1000) 15    83 mole % 6  54 g. (1000) EtOH (25) DEOC (1000) 11    80 mole % 7  54 g. (1000) BuOH (25) DBOC (1000) 13    79 mole % 8  54 g. (1000) MeOH (32) TMOF (1000) 13    81 mole % 9  54 g. (1000) MeOH (32) TMOF (1000) 12    78 mole % 10  27 g. (500) EtOH (25) TEOF (500) 14    81 mole % 11  54 g. (1000) MeOH (32) DMP (1000) 11    82 mole % 12.sup.(2) 54 g. (1000) MeOH (32) DMP (1000) 9    85 mole % 13.sup.(3) 54 g. (1000) MeOH (32) DMP (1000) 11    83 mole % __________________________________________________________________________ .sup.(1) DMOC  1,1dimethoxycyclohexane; DEOC  1,1diethoxycyclohexane; DBO 1,1dibutoxy-cyclohexane; TMOF  trimethylorthoformate; TEOF triethylorthoformate; and DMP  2,2dimethoxypropane .sup. (2) Total system pressure was 450 psig. .sup.(3) Total system pressure was 900 psig. .sup.(4) MeOH  Methanol; EtOH  Ethanol; BuOH  nbutanol.

In Examples 14 to 33 which follow in table form, the procedure and general operating conditions of Examples 1 to 3, except as specifically noted, were repeated using various diolefins (2 moles), dehydrating agent (1 mole), platinum group metal compound catalysts (5.0 mmoles) and oxidant salt compounds, with or without a ligand compound and catalytic alcohol. Gaseous and liquid products were analyzed by mass spectral analysis and gas-liquid chromatography respectively.

The reaction conditions, reactants, catalysts, oxidants, alcohols and ligands employed in Examples 14-33 are set forth in Table 3 and the results showing main product, percent diolefin conversion and mole percent selectivities are summarized in Table 4. __________________________________________________________________________ (psig)            Dehy- .degree.C. Pres- Time     Alcohol dration (5.0 mm) Oxidant Ligand Ex. Temp. sure Mins. Diolefin (mmole) Agent Catalyst (mmole) (mmole) __________________________________________________________________________ 14 100 1000 120 IP.sup.(1) --   DMOC.sup.(2) PdCl.sub.2 CuCl.sub.2 LiCl 15 100 1800 120 BD.sup.(3) --   DMOC PdI.sub.2 CuI   LiI 12.5  10.0 16 125 1800 100 BD   MeOH.sup.(4) DMOC PtI.sub.4 CuI   LiI 100             12.5  10.0 17 125 1800 120 BD   MeOH DMOC RhI.sub.3 CuI   LiI 100             12.5  10.0 18 125 1800 120 BD   MeOH DMOC RuI.sub.3 CuI   LiI 100             12.5  10.0 19 100 1000 120 BD   MeOH DMOC PdCl.sub.2 FeI.sub.2 LiI 50.0            12.5  10.0 20 110 1000 120 BD   MeOH DMOC PdI.sub.2 CuBr.sub.2 LiBr 50.0            12.5  10.0 21 100 1800 120 BD   MeOH DMOC PdI.sub.2 CuSO.sub.4 LiI 50.0            12.5  10.0 22 110 1000 120 BD   MeOH DMOC PdI.sub.2 CuI   NaI 50.0            12.5  10.0 23 110 1000 100 BD   MeOH DMOC PdI.sub.2 CuI   KI 50.0            12.5  10.0 24 100 1800 120 BD   MeOH DMOC PdI.sub.2 CuBr  -- 50.0            12.5.sup.2 25 100 1800 120 BD   MeOH DMOC PdI.sub.2 Cu(OAc).sub.2 LiI 50.0            25.0  10.0 26 100 1000 120 BD   MeOH TMOF.sup.(5) PdI.sub.2 CuI   LiI 50.0            12.5  10.0 27 100 1000 120 BD   MeOH DMP.sup.(6) PdI.sub.2 CuI   LiI 50.0            12.5  10.0 28 100 1800 120 BD   MeOH TMOB.sup.(7) PdI.sub.2 CuI   LiI 50.0            12.5  10.0 29 100 1800 120 BD   MeOH TMOF PdBr.sub.2 CuI   LiI 50.0            12.5  10.0 30 100  500 120 BD   MeOH DMP  PdBr.sub.2 CuBr.sub.2 LiBr 50.0            12.5  10.0 31 100 1900 120 BD   MeOH DMOC Pd(OAc).sub.2 CuI   LiOAc 50.0            25.0  10.0 32 100 1800 180 BD   MeOH DMOC PdSO.sub.4 CuI   LiI 50.0            25.0  10.0 33 100 1800 120 BD   MeOH DMOC Pd metal CuI   LiI 50.0            25.0  20.0 Key .sup.(1) IP  Isoprene .sup.(2) DMOC  1,1dimethoxycyclohexane .sup.(3) BD  1,3butadiene .sup.(4) MeOH  Methyl alcohol .sup.(5) TMOF  trimethylorthoformate .sup.(6) DMP  2,2dimethoxypropane .sup.(7) TMOB  trimethylorthoborate ______________________________________ Di-     Mole % olefin  Ester %       Selectivity Con-    based on Ex.  Product              version 1,3-butadiene ______________________________________ 14   methyl 3-methylpenta-2,4-dienoate 15      80 15   methyl penta-2,4-dienoate 19      81 16   methyl penta-2,4-dienoate 4      80 17   methyl penta-2,4-dienoate 8      83 18   methyl penta-2,4-dienoate 6      81 19   methyl penta-2,4-dienoate 11      81 20   methyl penta-2,4-dienoate 18      79 21   methyl penta-2,4-dienoate 16      78 22   methyl penta-2,4-dienoate 15      80 23   methyl penta-2,4-dienoate 20      83 24   methyl penta-2,4-dienoate 12      77 25   methyl penta-2,4-dienoate 14      79 26   methyl penta-2,4-dienoate 18      81 27   methyl penta-2,4-dienoate 21      79 28   methyl penta-2,4-dienoate 6      75 29   methyl penta-2,4-dienoate 19      80 30   methyl penta-2,4-dienoate 20      81 31   methyl penta-2,4-dienoate 15      82 32   methyl penta-2,4-dienoate 13      80 33   methyl penta-2,4-dienoate 17      81

## Claims

1. A process for the preparation of a diene monoester having the formula ##STR11## wherein R is an alkyl group of from 1 to 4 carbon atoms and R' is hydrogen or a methyl group, which comprises reacting a diolefin of the formula ##STR12## wherein R' is as above described with a mixture of carbon monoxide and oxygen and a stoichiometric amount of a dehydrating agent selected from the group consisting of acetals, ketals, carboxylic orthoesters, trialkylorthoborates and 1,1-dialkoxycycloalkanes, at a pressure of between about 15 psig and 5000 psig and at a temperature in the range of about 25.degree. C. to 200.degree. C. in the presence of an effective amount of a catalytic mixture of a platinum group metal compound selected from the group consisting of palladium, ruthenium, rhodium, and platinum, halides, cyanates, sulfates, nitrates, oxides, oxalates, acetates, and trifluoroacetates or mixtures thereof, an organic mono- or poly-dentate ligand or coordination complex compound selected from the group consisting of alkyl, aryl and halogen-substituted phosphines, arsines, stibines, and alkali metal salts, and a copper (I), copper (II), iron (II) or iron (III) oxidant salt compound and recovering the desired diene monoester.

2. A process according to claim 1 wherein the diolefin is selected from the group consisting of 1,3-butadiene, and isoprene.

3. A process according to claim 2 wherein the diolefin is 1,3-butadiene.

4. A process according to claim 1 wherein the dehydrating agent is selected from the group consisting of 1,1-dimethoxycyclohexane, trimethylorthoformate, 2,2-dimethoxypropane, trimethylorthoborate, 1,1-dimethoxyethane, 1,1-diethoxypropane, 2,2-dimethoxybutane, 1,1-dibutoxycyclohexane, 1,1-diethoxyhexane, and triethylorthoformate.

5. A process according to claim 4 wherein the dehydrating agent is 1,1-dimethoxycyclohexane.

6. A process according to claim 1 wherein the pressure is between about 100 psig and 2000 psig.

7. A process according to claim 1 wherein the temperature is in the range of from about 80.degree. C. to 150.degree. C.

8. A process according to claim 1 wherein the platinum group metal compound is selected from palladium (II) iodide, palladium (II) chloride, palladium (II) bromide, platinum (II) iodide, rhodium (III) iodide, ruthenium (III) iodide, palladium (II) acetate, palladium (II) sulfate, sodium iodopalladate, sodium bromopalladate, and potassium iodopalladate, or palladium metal.

9. A process according to claim 8 wherein the platinum group metal compound is palladium (II) iodide.

10. A process according to claim 8 wherein the platinum group metal compound is palladium (II) bromide.

11. A process according to claim 1 wherein the oxidant salt compound is selected from the group consisting of copper (I), copper (II) iron (II) and iron (III) halides, sulfates, trifluoroacetates, oxalates, naphthenates, nitrates and acetates.

12. A process according to claim 11 wherein the oxidant salt compound is selected from the group consisting of copper (II) bromide, copper (I) iodide, copper (II) chloride, iron (II) iodide, iron (III) iodide, copper (II) sulfate, and copper (II) acetate.

13. A process according to claim 12 wherein the oxidant salt compound is copper (I) iodide.

14. A process according to claim 12 wherein the oxidant salt compound is copper (II) bromide.

15. A process according to claim 12 wherein the oxidant salt compound is copper (II) chloride.

16. A process according to claim 1 wherein the ligand or coordination complex is lithium iodide.

17. A process according to claim 1 wherein the ligand or coordination complex is lithium bromide.

18. A process according to claim 1 wherein the ligand or coordination complex is potassium or sodium iodide.

19. A process according to claim 1 wherein the reaction is carried out in the presence of a catalytic amount of from 0 to 20 weight percent based on the diolefin employed of a monohydric saturated aliphatic alcohol containing from 1 to 4 carbon atoms which may contain other substituents which would not interfere with the reaction.

20. A process according to claim 19 wherein the alcohol is methyl alcohol.

21. A process according to claim 19 wherein the alcohol is ethyl alcohol.

22. A process for the preparation of methyl penta-2,4-dienoate which comprises reacting 1,3-butadiene with a mixture of carbon monoxide and oxygen and a stoichiometric quantity of a dehydrating agent selected from the group consisting of acetals, ketals, carboxylic orthoesters, trialkylorthoborates and 1,1-dialkoxycycloalkanes, at a pressure of between about 100 psig and 2000 psig and at a temperature in the range of from about 80.degree. C. to 150.degree. C. in the presence of an effective amount of a palladium metal salt compound and a copper (I) oxidant salt compound.

23. A process according to claim 22 wherein the dehydrating agent is 1,1-dimethoxycyclohexane, the palladium metal salt compound is palladium (II) iodide, and the copper (I) oxidant salt compound is copper (I) iodide.

24. A process according to claim 23 wherein the reaction is carried out in the presence of a catalytic amount of lithium iodide and a catalytic amount of methyl alcohol.