Abstract:
A Pd/heteropolyacid/boric acid catalyst system, when used with proper diluents, improves the oxidation of olefins to ketones, while reducing scum and deposits on reactor surfaces.

Description:
BACKGROUND OF THE INVENTION 
     The Wacker-type oxidation of ethylene to acetaldehyde using a palladium chloride/cupric chloride/hydrochloric acid catalyst in an aqueous solution has been modified and applied to the synthesis of methyl ketones from terminal olefins. However, major problems have been encountered in using the Wacker-type oxidation in the oxidation of higher olefins and internal olefins. One problem is that of reduced rates of reaction due to the low solubility of the olefin in the aqueous medium. Another major problem is the concomitant secondary oxidation of the ketone product which leads to poor selectivities and poor yield of desired product. 
     The solubility problems encountered in the Wacker-type oxidation of higher olefins have been at least partially solved by resorting to &#34;phase transfer&#34; techniques and the addition of a suitable surfactant. Thus, the prior art teaches that the reaction of the olefinic hydrocarbon reactant to be oxidized in the presence of free oxygen is preferably carried out in a multi-phase diluent system, preferably a two-phase system with one phase aqueous and the other organic. The catalysts known for this multi-phase process are Pd/Cu/alkali metal or alkaline earth metal chloride catalyst or Pd/Cu/boric acid catalyst with the palladium being either free palladium or a palladium compound and the copper component being either a cuprous or a cupric compound. It should also be noted that the HCl used in conventional Wacker oxidation reactions to maintain adequate conversion levels of the olefinic reactant has been eliminated as a component of the multi-phase process. An additional component of this multi-phase prior art reaction system is a suitable surfactant. 
     Corrosion of metallic process equipment is an additional problem when a catalyst containing halide ions such as the conventional Wacker or modified Wacker-type catalysts are utilized in the oxidation process, and a low-corrosion catalyst can be desirable at times. 
     THE INVENTION 
     In accordance with the present invention, an oxidation process described wherein a catalyst with greatly reduced halide content is utilized in a multi-phase diluent system in presence of a boric acid component and with the optional additional of a suitable surfactant. In one embodiment of the invention, a catalyst system containing PdCl 2 , a heteropolyacid H 9  [PMo 6  V 6  O 40  ], H 3  BO 3 , water and decane as a two-phase diluent system, and cetyltrimethylammonium bromide as an optical phase transfer catalyst, show good results in the oxidation of 2-butene to methyl ethyl ketone. 
     ADVANTAGES 
     The catalyst system of the invention is an inexpensive alternative to the use of phase transfer agents in the two-phase oxidation of olefins with PdCl 2  and heteropolyacids. 
     In addition to improvments in selectivity to ketone products, use of the catalysts of the invention means that reactor cleanup is minimal because no scum or deposits are formed when boric acid is used. 
     Furthermore, the palladium/heteropolyacid/boric acid system is amenable to recycle while improving catalyst handling. 
     OBJECTS OF THE INVENTION 
     It is one object of the invention to produce a catalyst useful for the oxidation of olefins to ketones. 
     It is another object of the invention to produce a process whereby ketones can be efficiently produced via the oxidation of olefins. 
     DESCRIPTION OF THE INVENTION 
     I. Catalyst System 
     The catalyst utilized according to the instant invention for the oxidation of olefinic hydrocarbons to carbonyl compounds is made up of three components: (1) a palladium component, (2) a heteropolyacid component, and (3) boric acid component. The use of another component, (4) a surfactant, is optional. 
     (1) Palladium Component 
     The palladium component of the catalyst system of the instant invention can be any palladium-containing material whose properties render it suitable for use in Wacker or Wacker-type reactions. The palladium component of the invention can be palladium metal, e.g., finely divided palladium powder, or a palladium compound. Examples of suitable palladium compounds include allyl palladium chloride dimer [C 3  H 5  PdCl] 2 , dichlorobis(triphenylphosphine)palladium(II), palladium (II) acetate, palladium(II) acetylacetonate, tetrakis(triphenylphosphine)palladium(O), palladium(II) chloride, palladium(II) iodide, palladium(II) nitrate, palladium(II) sulfate, and the like. Mixtures of the above palladium compounds can also be utilized as the palladium component of the instant catalyst system if so desired, thus providing a means to minimize the halide content of the catalyst system. 
     (2) Heteropolyacid Component 
     The heteropolyacid component of the catalyst system of the instant invention should have a redox potential in excess of 0.5 volt and contain at least two metallic species. It is preferred that it contain molybdenum and vanadium. Such preferred heteropolyacids are defined herein as iso-polymolybdates in which one or more of the molybdenum atoms are replaced by vanadium or an iso-polyvanadate in which one or more of the vanadium atoms are replaced by molybdenum. 
     The polyacid used contains vanadium atoms, for example from 1 to 8, more preferably 6 atoms, in a molecule, and molybdenum. Typical polyacids for use in the present invention are represented by the following general formula: 
     
         H.sub.m [X.sub.x Mo.sub.a V.sub.b M.sub.y O.sub.z ] 
    
     in which 
     X is B, Si, Ge, P, As, Se, Te or I; 
     M is W, Nb, Ta or Re; 
     m, a, b and z are integers; 
     x is zero (for mixed isopolyacids) or an integer (for hetero-polyacids); 
     and y is zero or an integer such that ##EQU1## 
     and m+Nx+6a+5b+N&#39;y≦2z 
     in which each of N and N&#39; is the number of the group of the periodic table to which X and M respectively belong. Examples of typical heteropolyacids are as follows: 
     
         ______________________________________Heteropolyacid     Redox potential, V______________________________________H.sub.9 [TeMo.sub.3 V.sub.3 O.sub.24 ]              +0.80H.sub.4 [As.sub.2 Mo.sub.12 V.sub.6 O.sub.61 ]              +0.65H.sub.3 [AsMo.sub.6 V.sub.6 O.sub.40 ]              +0.72H.sub.6 [SiMo.sub.10 V.sub.2 O.sub.40 ]H.sub.6 [GeMo.sub.10 V.sub.2 O.sub.40 ]H.sub.n [PMo.sub.p V.sub.q O.sub.40 ]*, for example:H.sub.4 [PMo.sub.11 VO.sub.40 ]              +0.65H.sub.5 [PMo.sub.10 V.sub.2 O.sub.40 ]              +0.70H.sub.6 [PMo.sub.9 V.sub.3 O.sub.40 ]              +0.72H.sub.7 [PMo.sub.8 V.sub.4 O.sub.40 ]              +0.75H.sub.8 [PMo.sub.7 V.sub.5 O.sub.40 ]              +0.76H.sub.9 [PMo.sub.6 V.sub.6 O.sub.40 ]              +0.77H.sub.10 [PMo.sub.5 V.sub.7 O.sub.40 ]              +0.79H.sub.11 [PMo.sub.4 V.sub.8 O.sub.40 ]              +0.80H.sub.5 [Mo.sub.r W.sub.m V.sub.2 O.sub.40 ]**H.sub.9 [PMo.sub.3 W.sub.3 V.sub.6 O.sub.40 ]              +0.70______________________________________ *in which n = 3 + q, p = 12 - q, q = 1 to 10 **in which m = 2, 4, 6, or 8 and r = 10 - m. 
    
     The ratios of the various catalyst components can be expressed in terms of a molar ratio of heteropolyacid to palladium. The molar ratio of heteropolyacid component to palladium component in the instant catalyst system is broadly from 1/1 to 50/1. 
     The amount of catalyst employed according to the instant invention can be expressed in terms of the molar ratio of olefinic hydrocarbon reactant to palladium component of the catalyst system. Broadly, the molar ratio of olefinic reactant to palladium component is from about 5/1 up to 1000/1 and preferably from about 10/1 up to 250/1. 
     (3) Boric Acid Component 
     The boric acid component of the catalyst system of this invention can be any boron-containing material that provides a catalytically active boric acid under the conditions of the oxidation reaction of this invention. Suitable boron-containing materials include boric acids, boron oxides, and boric acid esters. Specific examples of suitable boron components include orthoboric acid (H 3  BO 3 ), metaboric acid (HBO 2 ), tetraboric acid, (H 2  B 4  O 7 ), boron oxide (B 2  O 3 ), triethyl borate, tributyl borate, and triphenyl borate. Orthoboric acid (H 3  BO 3 ), is the currently preferred boric acid component of this invention. 
     The amount of boric acid used in the oxidation reaction of this invention can be varied widely. Generally, any amount which assures effective interaction with the other catalyst components and produces the results disclosed herein can be employed. Typically, the molar ratio of boric acid or precursor thereof to palladium component will be from about 0.2/1 up to about 100/1 and preferably from about 5/1 up to about 25/1. 
     (4) Surfactant Component 
     Generally, the surfactant component of the reaction system according to the instant invention comprises one or more compounds which exhibit surface-active properties--i.e., surfactants. However, the term &#34;surfactant&#34; encompasses a very broad class of compounds, and it has been discovered that not all surfactants are suitable for use in the instant invention. Nevertheless, for convenience and simplicity, the suitable compounds that can be employed according to the instant invention and described more fully below will be termed surfactants herein. At the present time, it is not known whether, in the catalyst and process of the invention, these compounds functions as phase-transfer catalysts, such as is taught in the art, or whether they function as micellar catalysts, a feature also disclosed in the prior art. Because of this uncertainty in the mode of action of these compounds in the instant invention, and for convenience, the following compounds will merely be described herein as surfactants. 
     A preferred surfactant for use in the reaction system of the instant invention is selected from one of the five following groups: (A) Quaternary ammonium salts of the general formula (R&#34;&#39;) 4  N +  X -   wherein R&#34;&#39; is an alkyl radical of from 1 to 20 carbon atoms and wherein the total number of carbon atoms in said quaternary ammonium salt is from 8 to 30 carbon atoms broadly and preferably from 16 to 22 carbon atoms; and wherein X is selected from the group consisting of Br - , Cl - , I - , F - , R&#34;&#39;, CO 2   - , QSO 3   - , BF 4   - , and HSO 4   - , wherein Q is an aryl, alkaryl or arylalkyl radical of 6 to 10 carbon atoms. It will be noted that a variety of anions are suitable as the X -   component of the quaternary ammonium salts. 
     Useful quaternary ammonium salts according to the general formula given above include cetyltrimethylammonium bromide, 
     hexadecyltrimethylammonium bromide, 
     tetraheptylammonium bromide, cetyltrimethylammonium stearate, 
     benzyltributylammonium chloride, benzyltriethylammonium bromide, 
     benzyltrimethylammonium bromide, phenyltrimethylammonium bromide, 
     phenyltrimethylammonium iodide, tetrabutylammonium bromide, 
     tetrabutylammonium chloride, tetrabutylammonium hydrogen sulfate, tetrabutylammonium iodide, tetraethylammonium bromide, tetrabutyl ammonium fluoride, and tetrabutylammonium tetrafluoroborate. 
     (B) Akali metal alkyl sulfates of the general formula R&#39; v  OSO 3  M, wherein R&#39; v  is an alkyl radical having from 10 to about 20 carbon atoms and wherein M is an alkali metal. Examples of suitable compounds according to the general formula for the alkali metal alkyl sulfates include lithium decylsulfate, potassium dodecylsulfate, sodium dodecylsulfate, sodium hexadecylsulfate, potassium hexadecylsulfate, rubidium dodecylsulfate, cesium dodecylsulfate, sodium octadecylsulfate, potassium octadecylsulfate, potassium eicosylsulfate, sodium eicosylsulfate and the like. 
     (C) Akali metal salts of alkanoic acids of the general formula R&#39; v  CO 2  M, wherein R&#39; v  and M have the same meaning as given above for the compounds of (B). Examples of suitable alkali metal salts of alkanoic acids include lithium deconoate, sodium dodecanoate, potassium dodecanoate, rubidium dodecanoate, cesium dodecanoate, sodium hexadecanoate, potassium hexadecanoate, sodium octadecanoate, potassium octadecanoate, sodium eicosanoate, potassium eicosanoate, and the like. 
     (D) Alkali metal salts of alkaryl sulfonic acids of the general formula ##STR1## wherein R&#39; v  and M have the same meaning as given and wherein R v  is an alkyl radical of 1 to 4 carbon atoms and wherein n is 0 or an integer of from 1 to 4. Typical compounds within the (D) group include sodium dodecylbenzenesulfonate, potassium dodecylbenzenesulfonate, lithium dodecylbenzenesulfonate, sodium tetradecylbenzenesulfonate, potassium hexadecylbenzenesulfonate, rubidium dodecylbenzenesulfonate, cesium dodecylbenzenesulfonate, sodium octadecylbenzenesulfonate, potassium octadecylbenzenesulfonate, sodium eicosylbenzenesulfonate, potassium dodecyltoluenesulfonate, sodium dodecylxylenesulfonate and the like. 
     (E) 1-Alkyl pyridinium salts of the general formula ##STR2## wherein R&#39; v  and X -   have the same meanings as described above. Examples of suitable 1-alkyl pyridinium salts are 1-dodecylpyridinium para-toluenesulfonate, 1-dodecylpyridinium chloride, 1-hexadecylpyridinium chloride, 1-hexadecylpyridinium para-toluenesulfonate, 1-decylpyridinium chloride, 1-hexadecylpyridinium bromide, 1-tetradecylpyridinium chloride, 1-octadecylpyridinium chloride, 1-eicosylpyridinium chloride, 1-octadecylpyridinium benzenesulfonate, and the like. 
     The amount of surfactant compound selected from groups (A) through (E) which is utilized according to the instant invention can be expressed in terms of a mole ratio based on the pallidium component of the catalyst system. Broadly, the mole ratio of surfactant to palladium compound will be from 0.01/1 to 10/1. Preferably, it will be from 0.1/1 to 3/1. 
     II. Diluent System 
     As indicated above, the oxidation of the olefinic hydrocarbon according to the instant invention is carried out in the presence of a diluent comprised of at least two liquid pahses, preferably only two, at least one of which is an aqueous phase. 
     The nonaqueous phase will hereinafter be termed the organic phase. Said organic phase should be relatively inert to the oxidation conditions, of course, and also relatively inert to hydrolysis-type reactions. Furthermore, it is apparent that if at least two phases are present, at least one of which is an aqueous phase, that the organic diluent utilized must have somewhat limited solubility in the aqueous phase. In addition, the choice of the organic diluent(s) may be often determined based on the difference in boiling points expected between the product of the oxidation reaction and the organic diluent so as to facilitate separation of the components of the reaction mixture. Within these general requirements, a rather broad range of organic compounds can be utilized to form the organic phase according to the instant invention. 
     Generally speaking, suitable compounds can be found in the classes of compounds described as aliphatic hydrocarbons, aromatic hydrocarbons or alkylsubstituted aromatic hydrocarbons, halogenated aromatic compounds, and esters of aromatic carboxylic acids although the latter may be less preferred because of a tendency toward hydrolysis of the ester group in certain instances. In addition, it has been found that compounds such as nitrobenzene and benzonitrile, commonly utilized as solvents for many organic reactions, show a definite inhibitory effect on the reaction of the instant invention presumably by complexing of one or more catalyst components. 
     Suitable organic diluents include cyclohexane, hexane, octane, decane, dodecane, tetradecane, hexadecane, benzene, toluene, chlorobenzene, methylbenzoate, bromobenzene, 1,2,4-trichlorobenzene, ortho-dichlorobenzene, ortho-xylene, para-xylene, meta-xylene, methylcyclopentane, dimethyl ortho-phthalate, and the like. Mixtures of organic diluents may be utilized in some cases desired. 
     The amounts of the aqueous phase and organic diluent phase based on the starting olefinic reactant can vary over a wide range, and a suitable range includes from about 20 to 0.2 volumes of organic diluent per volume of olefinic hydrocarbon reactant, preferably from about 5 to 1 volumes of organic diluent per volume of olefinic hydrocarbon reactant. Similarly, the broad range for the amount of aqueous phase is from 20 to 0.2 volumes per volume of olefinic hydrocarbon reactant and preferably from 5 to 1 volumes per volume of olefinic hydrocarbon reactant. 
     It is worth pointing out some predictions relating to the expected effects of the volume of aqueous phase on the oxidation reaction of the instant invention. First, if the aqueous phase volume becomes too small, the concentration of the catalyst components in the aqueous phase can cause a decrease in the solubility of the olefinic hydrocarbon reactant in the aqueous phase, thus greatly slowing down the reaction rate wherein the olefinic hydrocarbon reactant is oxidized to the desired carbonyl compound. Secondly, if the aqueous phase becomes too large, the concentration of catalyst components can be so dilute that the reaction with the olefinic hydrocarbon can also be greatly slowed. However, it can be seen that a judicious choice of the optimum amount of the aqueous phase for high conversion levels of the olefinic hydrocarbon reactant can readily be determined by a few well-chosen experiments. 
     At present, it is believed that the primary function of the organic phase in the reaction system of the instant invention is to greatly increase the selectivity to the desired carbonyl compound by effectively removing the carbonyl compound product from the locus of the oxidation reaction thereby preventing side reactions such as isomerization and/or further oxidation of the carbonyl compound. However, this explanation is to be treated merely as one possible theory of the mode of action of the organic phase in the reaction and applicants should not be bound to same. 
     III. Oxygen 
     As indicated previously, the reaction of the instant invention is an oxidation reaction whereby an olefinic reactant is converted to a carbonyl compound in the presence of a catalyst and diluent system described above. Thus, the reaction of the instant invention is carried out in the presence of free oxygen. The oxygen may be supplied to the reaction mixture essentially as pure oxygen or in admixture with other gases which are essentially inert to the reaction conditions. Air can be utilized as a source of oxygen for the oxidation reaction of this invention. 
     As is generally true for most oxidation reactions, the reaction of the instant invention can be exothermic and thus some care should be exercised in controlling the amount of oxygen present in the reaction system. For this reason, and also to improve control of the temperature of the reaction, it is preferred to add oxygen or the gaseous mixture containing oxygen to the reaction zone incrementally so that explosive oxygen concentrations do not develop. The pressure of oxygen utilized for the instant invention can be from about 2 up to 250 psig and, preferably, from about 10 to 100 psig above the autogenous pressure at the temperature utilized. 
     IV. Olefinic Hydrocarbon Reactant 
     The olefinic hydrocarbon reactant which is oxidized according to the process of the instant invention can be selected from the groups consisting of acyclic olefinic compounds containing from 2-20 carbon atoms per molecule and having 1, 2, or 3 olefinic carbon-carbon double bonds per molecule and cyclic olefinic compounds containing from 5-20 carbon atoms per molecule and having 1, 2, or 3 olefinic carbon-carbon double bonds per molecule. Within the limitations described above, suitable olefinic hydrocarbon reactants can be represented by the general formula RCH═CHR&#39; wherein R and R&#39; are selected from the group consisting of hydrogen, alkyl, alkenyl, alkadienyl, cycloalkyl, cycloalkenyl, and cycloalkadienyl radicals and wherein R can be the same or different from R&#39; and wherein R and R&#39; taken together can form an alkylene or alkenylene or alkadienylene radical thus forming a cyclic system. The term &#34;olefinic carbon-carbon double bond&#34; as used herein is not meant to include those carbon-carbon double bonds which are part of an aromatic carbocyclic system of alternating single and double bonds. 
     Examples of suitable monoolefinic compounds are ethylene, propylene, 1-butene, 2-butene, 1-pentene, 2-pentene, 1-hexene, 2-hexene, 1-octene, 1-decene, 1-dodecene, 1-hexadecene, 1-octadecene, 1-eicosene, vinyl cyclohexane, cyclopentene, cyclohexene, cycloheptene, cyclooctene, cyclododecene, 3,3-dimethyl-1-butene, and the like. 
     Examples of suitable diolefinic compounds are 1,3-butadiene, 1,3-pentadiene, 1,5-hexadiene, 4-vinylcyclohexene, 1,5-cyclooctadiene, 1,9-decadiene, 1,7-octadiene, 1,3-cycloheptadiene, and the like. 
     Suitable triolefinic compounds include 1,5,9-cyclododecatriene, cycloheptatriene, 1,6-diphenyl-1,3,5-hexatriene, and the like. 
     While the double bond unsaturation can be internal or non-terminal, it is preferred that at least one olefinic carbon-carbon double bond be in the terminal position. That is, the preferred olefinic reactant has at least one terminal olefinic or vinyl group. Mixtures of olefinic reactants can be employed. 
     V. Reaction Conditions 
     The particular temperature employed may be dependent somewhat on the olefinic hydrocarbon reactant. For example, at relatively high temperatures, a lower molecular weight olefinic hydrocarbon reactant may tend to be very insoluble in the aqueous phase of the two-phase system of the instant invention, thus causing a reduced conversion of the olefinic hydrocarbon reactant. On the other hand, a higher molecular weight olefinic reactant may be able to tolerate a higher reaction temperature and still maintain a reasonable degree of solubility in the aqueous phase and thus achieve a good degree of conversion at the higher temperature. The temperature utilized in the instant invention is broadly from about 20° to 200° C. and preferably from about 60° to 150° C. Most preferably it lies between about 70° and 100° C. 
     The time employed for the reaction according to the instant invention can vary over a wide range and will, to some extent, depend on the desired degreee of conversion of the olefinic hydrocarbon reactant. Generally, a time period such as from 30 minutes to 8 hours will be employed in the instant invention, preferably 1 to 3 hours. 
     Because the oxidation reaction according to the instant invention is carried out in the presence of a diluent system comprising at least two liquid phases, it is expected that good stirring will be beneficial. Conventional means of achieving good agitation and contact between the liquid phases can be employed. 
     The charge order of the reaction components and catalyst components is not critical in the process of the instant invention. However, the presence of oxygen in the reaction mixture prior to heating of the mixture to the desired reaction temperature appears to promote higher selectivity to the desired carbonyl compound. 
     The process of the instant invention can be carried out in either a batch or continuous process. 
     Reaction vessels and conduits utilized in the process of the instant invention should, of course, be able to withstand the oxidizing conditions which are present. For this reason, glass-lined, tantalum, titanium or Hastelloy C-clad vessels and conduits are recommended for use in the process of this invention. 
     VI. Reaction Mixture Workup 
     A variety of methods can be utilized to recover the products, unreacted olefinic hydrocarbon starting materials, and the catalyst in the aqueous phase in the instant invention. For example, the entire reaction mixture can be subjected to a fractional distillation to separate the components into various fractions or portions. The bottoms from said distillation can be recycled to the reaction zone as that portion contains essentially all of the catalyst system for the reaction. 
     Another method of treating the reaction mixture is to contact the entire mixture with a lower alkane such as n-pentane, then separate the aqueous phase from the organic phase, with subsequent fractional distillation of the organic phase to recover the products and any unreacted olefinic hydrocarbon reactants. The aqueous phase can be recycled to the reaction zone as described above, since it contains essentially all of the catalyst components. 
     Another method of reaction mixture workup involves admixture of the reaction mixture with a saturated aqueous sodium chloride solution followed by extraction of the mixture into diethyl ether. The ether extract can then be distilled or treated in such a manner as to remove the ether leaving the organic residue containing the product and any unreacted olefinic hydrocarbon reactant. Said residue can then be subjected to fractional distillation procedures to recover the various components. 
     VII. Product Utility 
     As indicated earlier, the reaction of the instant invention provides a process for the conversion of olefinic hydrocarbon reactants to carbonyl compounds. Said carbonyl compounds are ketones, except for the case of ethylene oxidation which yields acetaldehyde. If the olefinic hydrocarbon reactant contains two carbon-carbon double bonds, the product can be an unsaturated monoketone or diketone. Furthermore, the unsaturated monoketone can be recycled to the reaction zone for conversion to the diketone. Similarly a triolefinic reactant can be converted to intermediates such as unsaturated mono- or diketones and ultimately to a triketone. Ketones from the olefinic hydrocarbon reactants described in part IV above have generally well-known utilities. For example, they can be utilized as solvents (methyl ethyl ketone) or as intermediates in the synthesis of other chemical compounds (pinacolone). 
     VIII. Examples 
     In all of the runs that are described in the following examples, the reaction vessels utilized were a 300 cc Hastelloy C magnedrive stirred tank reactor sold by Autoclave Engineers or a 500 mL Fischer-Porter compatability aerosol bottle. The autoclave was heated by an electric heater and controlled by a Thermoelectric 400 temperature controller. The Fisher-Porter bottles were fitted with pressure gauges, vent and chargelines through which oxygen could be added continuously or incrementally. The oxygen line to the reaction vessel was fitted with the appropriate check valves and flame arrestor. The bottle was heated in an ethylene glycol bath, and monitored on an Acromag by a thermocouple placed in the glycol bath. The bottle contents were stirred by a magnetic stirrer. 
     For autoclave runs, the reactor was charged with the catalyst system, the diluents, and then sealed. Thirty psig oxygen pressure was introduced to pressure test the reactor, then vented. The olefinic reactant was then charged, while autoclave stirring was begun to aid olefin dissolution in the organic diluent. Thirty psig oxygen pressure was again introduced and the autoclave heated to the desired reaction temperature before the oxygen pressure was adjusted to the desired operating pressure. The reaction was allowed to take-up oxygen on demand for the duration of the reaction in order to maintain the desired pressure. For runs carried out in the Fischer-Porter bottles, the catalyst, diluents, and olefinic reactant were charged. The bottle was assembled with the proper fittings, placed in the ethylene glycol bath, and stirring begun. An initial pressure of 30 psig oxygen was introduced, the reaction mixture heated to the desired reaction value. As above, the system is allowed to take-up oxygen on demand to maintain the desired operating pressure throughout the reaction. 
     After the desired reaction time had elapsed the reaction was cooled to room temperature before excess oxygen was vented. The combined organic and aqueous phases were subjected to conventional fractional distillation to recover volatile materials (starting material, products and by-products). After distillation, the residual materials were phase separated, decane solvent was recycled to the reactor while the aqueous phase was evaporated to dryness, the residue redissolved in deionized water, H 2  SO 4  added to adjust pH to 1.9 and the resulting solution was then recycled to the reactor. All samples were analyzed by gas-liquid phase chromatography. 
    
    
     EXAMPLE I 
     Preparation of the Phospho-6-molybdo-6-vanadic acid 
     45.5 g Na 3  PO 4 .12H 2  O (0.12 mol), 103.6 g MoO 3  (0.72 mol), 42.0 g V 2  O 5  (0.23 mol) and 22.4 Na 2  CO 3 .10H 2  O (0.09 mol) were dissolved in 600 mL H 2  O. The solution was heated to boiling and stirred vigorously for 40 minutes. The solution gradually turned an intense brownish-red. The solution volume was reduced to 150 mL by evaporation, then allowed to cool to room temperature. The pH of the solution was adjusted to 1.00 with concentrated sulfuric acid, the solution was then filtered and set aside for use as a component in the inventive oxidation process. 
     EXAMPLE II 
     Two control runs were carried out in which 2-butene was oxidized to methyl ethyl ketone (MEK) in the absence of organic diluent and surfactant component. The same heteropolyacid charge was used in each run, with boric acid added to the second run. Both runs were carried out in 300 cc Hastelloy C autoclaves following the general procedure set forth above. One hundred mL of water and reagents in the amounts specified in Table I were treated for 2 hours at 80° C. and 100 psig. 
     
                                           TABLE I__________________________________________________________________________                  Butene                       Butene Selectivity     Heteropolyacid,             H.sub.3 BO.sub.3,                  Charged,                       Conversion,                              to MEK,Run#    PdCl.sub.2, mol     mol     mol  mol  mol %  mol %__________________________________________________________________________1   .01   .05     --   0.48 17.7   77.52   .01   .05     0.25 0.45 10.0   98.4__________________________________________________________________________ 
    
     The results of these experiments demonstrate the poor performance of the palladium/heteropolyacid catalyst system at 80° and 100 psig when carried out in aqueous phase only, with or without added boric acid. 
     EXAMPLE III 
     A control run was carried out in which 2-butene was oxidized to MEK utilizing the palladium chloride-heteropolyacid catalyst system in a two-phase medium in the absence of boric acid or a surfactant component. The reaction was carried out in a 500 mL Fischer-Porter bottle according to the general procedure set forth above. One hundred mL water and 100 g (137 mL) decane containing 0.01 mol PdCl 2 , 0.05 mol heteropolyacid, 0.46 mol 2-butene were reacted for 2 hours at 80° C. and 100 psig. Analysis of the final product revealed a 2-butene conversion of only 2.9% with a selectivity to MEK of 99.6%. 
     The results of this experiment demonstrate the poor performance of the palladium/heteropolyacid catalyst system in two-phase medium in the absence of surfactant or boric acid component. 
     EXAMPLE IV 
     A control run was carried out in which 1-butene was oxidized to methyl ethyl keton utilizing the palladium chloride-heteropolyacid catalyst system in a two-phase medium in the absence of boric acid or a surfactant component. The reaction was carried out in a 500 mL Fischer-Porter bottle according to the general procedure set forth above. One hundred mL water and 100 g (137 mL) decane containing 0.01 mol PdCl 2 , 0.05 mol heteropolyacid, 0.45 mol 1-butene were reacted for 2 hrs. at 80° and 100 psig. Analysis of the final product revealed a 1-butene conversion of only 3.3% with a selectivity to MEK of 90.5%. 
     The results of this experiment demonstrate the poor performance of the palladium/heteropolyacid catalyst system in two-phase medium in the absence of surfactant or boric acid component. 
     EXAMPLE V 
     A control run was carried out in which 2-butene was oxidized to methyl ethyl ketone utilizing the palladium chloride-heteropolyacid catalyst system in a two-phasee medium with cetyltrimethylammonium bromide (CTMAB) surfactant added. The reaction was carried out in a 500 mL Fischer-Porter bottle according to the general procedure set forth above. One hundred mL water and 100 g (137 mL) decane containing 0.01 mol PdCl 2 , 0.05 mol heteropolyacid, 0.004 mol CTMAB, and 0.47 mol 2-butene were reacted for 2 hrs. at 80° and 100 psig. Analysis of the final product revealed a 2-butene conversion of 64.2% with selectivity of 84.5% to MEK. 
     The results of this experiment demonstrate the operability of the palladium chloride-heteropolyacid catalyst for the oxidation of 2-butene to methyl ethyl ketone in the presence of a surfactant such as CTMAB. 
     EXAMPLE VI 
     A series of 1-butene oxidations were carried out utilizing the same catalyst charge for numerous recycles, occasionally recharging palladium (as noted in Table II below) to compensate for handling losses. All reactions were carried out using a 500 mL Fischer-Porter bottle containing 100 mL water, 100 g (137 mL) decane, 0.05 mol heteropolyacid, 0.25 mol H 3  BO 3 , and palladium in the amounts tabulated in Table II. Reactions were carried out for 2 hrs. at 80° and 100 psig according to the general procedure set forth above. 
     
                       TABLE II______________________________________            Butene    Butene    Selectivity            Charged,  Conversion,                                to MEK,Run#  PdCl.sub.2, mol            mol       mol %     mol %______________________________________1     0.01       0.45      66.7      92.02     &#34;          0.44      65.7      97.53     +.0001     0.45      82.0      97.04     &#34;          0.45      59.3      99.15     +.0001     0.46      54.7      99.16     &#34;          0.45      30.6      97.4______________________________________ 
    
     These experiments demonstrate the operability of the process of this invention for the oxidation of 1-butene to methyl ethyl ketone in the presence of a palladium compound, a heteropolyacid and boric acid in two-phase medium. High butene conversions with excellent selectivity to MEK are obtained. These excellent results are maintained through several recycles of the catalyst. 
     EXAMPLE VII 
     A series of 2-butene oxidations were carried out utilizing the same catalyst charge for numerous recycles, occasionally recharging palladium (as noted in Table III below) to compensate for handling losses. All reactions were carried out using a 500 mL Fischer-Porter bottle containing 100 mL water, 100 g (137 mL) decane, 0.05 mol heteropolyacid, 0.25 mol H 3  BO 3 , and palladium in the amounts tabulated in Table III. Reactions were carried out for 2 hrs. at 80° and 100 psig according to the general procedure set forth above. 
     
                       TABLE III______________________________________            Butene    Butene    Selectivity            Charged,  Conversion,                                to MEK,Run#  PdCl.sub.2, mol            mol       mol %     mol %______________________________________1      .01       0.47      87.5      86.82     &#34;          0.44      79.3      88.73     +0.0001    0.45      73.0      92.94     &#34;          0.45      63.8      95.35     +0.0001    0.45      44.1      97.46     &#34;          0.45      40.8      96.3______________________________________ 
    
     These experiments demonstrate the operability of the process of this invention for the oxidation of 2-butene to methyl ethyl ketone in the presence of a palladium compound, a heteropolyacid and boric acid in two-phase medium. High butene conversions with excellent selectivity to MEK are obtained. These excellent results are maintained through several recycles of the catalyst. 
     EXAMPLE VIII 
     A series of 2-butene oxidations were carried out utilizing the same catalyst charge for numerous recycles, occasionally recharging catalyst components (as not in Table IV below) to compensate for handling losses. All reactions were carried out using a 500 mL Fischer-Porter bottle containing 100 mL water, 100 g (137 mL) decane, 0.05 mol heteropolyacid, 0.25 mol H 3  BO 3 , and palladium and surfactant in the amounts tabulated in Table IV. Reactions were carried out for 2 hours at 80° and 100 psig according to the general procedure set forth above. 
     
                       TABLE IV______________________________________                           Butene                    Butene Con-   Selectivity           CTMAB,   Charged,                           version,                                  to MEK,Run#  PdCl.sub.2, mol           mol      mol    mol %  mol %______________________________________1     0.01      0.004    0.52   51.9   91.32     &#34;         &#34;        0.42   59.8   90.43     +0.0001   +0.00003 0.52   51.4   87.74     &#34;         &#34;        0.47   58.9   91.15     +0.0001   +0.00003 0.44   77.3   89.36     &#34;         &#34;        0.45   69.0   90.3______________________________________ 
    
     These experiments demonstrate the operability of the process of this invention for the oxidation of 2-butene to methyl ethyl ketone in the presence of a palladium compound, a heteropolyacid, boric acid and a surfactant in two-phase medium. Excellent butene conversions with high selectivity to MEK are obtained through several recycles of the catalyst. 
     Reasonable variations, such as those which would occur to a skilled artisan may be made herein without departing from the scope of the invention.