Abstract:
A method of preparing esters of cinnamic acid comprising catalytically reacting a styrene compound with carbon monoxide, oxygen, and an aliphatic alcohol. The catalyst is a combination of a palladium (II) compound, an alkali metal carboxylate and a copper salt.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a catalytic process for preparing cinnamates by oxidative carbonylation of styrene compounds. 
     Cinnamic acid and cinnamates are used as a material for perfumes, as a cinnamic aldehyde, cyclamen aldehyde, beta-amyl cinnamic aldehyde, and the like. 
     Cinnamates are made conventionally through a Claisen condensation from benzaldehyde and alkylacetate in the presence of sodium alkoxide, as shown in Equation I ##STR1## Another method of making cinnamates is by esterification of cinnamic acid, as shown in Equation II 
     
         C.sub.6 H.sub.5 CH═CHOOH+ROH→C.sub.6 H.sub.5 CH═CHCOOR+H.sub.2 O                                   (II) 
    
     Recently, several methods for preparing cinnamates have been reported, employing palladium catalysts. Heck et al., J. Amer. Chem. Soc. 91, 6707 (1969) and Patel et al., J. Org. Chem., 42, 3903 (1977), show methods of preparing cinnamates using palladium acetate-tertiary phosphine as a catalyst in the reaction of phenyl bromide and an alkyl acrylate. This reaction has the drawback of involving rather expensive raw materials. This reaction is shown in Equation III. ##STR2## 
     Other cinnamates such as methyl cinnamate, can be synthesized in a palladium catalyzed reaction by reacting styrene with carbon monoxide and methanol, as reported by J.K. Stille and his coworkers, J. Amer. Chem. Soc., 98, 1806 (1976) and 98, 1810 (1976); J. Org. Chem., 44, 3474 (1979); and by G. Cometti and G. P. Chiusoli in J. Organometal. Chem., 181, C14 (1979). In Stille&#39;s method, methyl cinnamate could be obtained only in a small amount, with dimethyl phenylsuccinate being the major product. Additionally, a stoichiometric amount of copper (II) salt was required in this reaction. The method of Cometti and Chiusoli has the same disadvantage of using a large excess of copper (II) salt as an oxidant Thus, both methods are unsuitable for industrial applications. 
     Many patents disclose oxidative carbonylation of olefins to alpha, beta-unsaturated esters by reacting an olefin with carbon monoxide, oxygen, and an alcohol in the presence of a catalytic amount of palladium and copper salts, cf. U.S. PAT. NOS. 3,381,030; 3,397,225; 3,397,226; 3,530,168; 3,621,054. None of these patents discloses a satisfactory method for producing cinnamates. 
     Two Japanese patent applications, 21,342 (1982) and 21,343 (1982), disclose that low yields of methyl cinnamate could be achieved through oxidative carbonylation of styrenes, provided that an excess amount of dehydrating agent is used in the reaction. Because the dehydrating agent is an expensive component of the reaction, industrial application of this method is limited. It was disclosed in these two Japanese applications that when styrenes were allowed to react with aliphatic alcohols, carbon monoxide, and oxygen in the presence of palladium and a dehydrating agent, cinnamates could be obtained with a high reaction rate and a high yield. However, this reaction has the disadvantage of requiring an excess of dehydrating agent, which makes the reaction unfeasible for industrial use. 
     SUMMARY OF THE INVENTION 
     Cinnamates can be produced by the oxidative carbonylation of styrene compounds according to the following reaction, in the absence of dehydrating agent: ##STR3## It was unexpectedly found that when a styrene compound was reacted with carbon monoxide, oxygen, and an aliphatic alcohol and in the present of a catalytic amount of a palladium salt, an alkali metal salt of a carboxylic acid and a copper salt, high reaction rates and high yields of alkyl cinnamate could be obtained, along with valuable acetophenone as a byproduct. Moreover, unlike the prior art reactions, this reaction can be carried out smoothly either without any dehydrating agent or using only catalytic amounts of dehydrating agent to increase the reaction rate and total yield of the alkyl cinnamates. 
     The present invention relates to a method for the oxidative carbonylation of styrenes to alkyl cinnamates by reacting styrene compounds with carbon monoxide, oxygen, and aliphatic alcohols in the presence of a catalyst consisting of a palladium salt, an alkali metal salt of a carboxylic acid and a copper salt. The general formula for styrene compounds for use in the present invention can be represented by the following structure: ##STR4## wherein R 1  and R 2  can be hydrogen, halogen, hydroxyl, alkyl, alkoxyl, aryl, aryloxy, or nitro functional groups. R 3  is hydrogen or an alkyl group of one to six carbon atoms. Specific examples for styrenes are styrene, alpha-methyl styrene, p-chloro styrene, p-nitro styrene, m-methoxy styrene, p-phenyl styrene, beta-methyl-p-isopropylstryene, beta-amylstyrene, and the like. 
     The aliphatic alcohols for use in the reaction according to the present invention include aliphatic alcohols having from one to six carbon atoms, such as methanol, ethanol, propanol, isopropanol, t-butanol, n-butanol, hexanol, and the like. It is also possible to use compounds capable of yielding the aforementioned alcohols in reaction systems containing acetals, ketals, orthoesters of carboxylic acids, dialkylcycloaklanes, orthoboric acid esters, and the like. 
     Carbon monoxide and oxygen for this reaction can be used either in the pure state or can be mixed with nitrogen, argon, and other inert gases as the diluents. Air can be used as the oxygen source. In general, carbon monoxide and oxygen can be charged into the reactor through a separated inlet system or can be charged as a mixture with or without inert gases as the diluents. The partial pressure of carbon monoxide or oxygen is adjusted so that the gas mixture in the reactor system is outside the explosive range. 
     The catalyst consists of three components, a palladium salt, an alkali metal salt of carboxylic acid (alkali metal carboxylate) and a copper salt. The palladium salt can be palladium chloride, palladium bromide, palladium iodide, palladium nitrate, or other divalent palladium salts such as palladium acetate, palladium benzoate, palladium acetylacetonate, palladium trifluoroacetate, palladium oxide, potassium tetrabromopalladate, sodium tetrachloropalladate, and the like. Any other forms of palladium which can form palladium (II) salt under the reaction conditions can be used. Examples are supported palladium such as palladium on carbon, palladium on silica, or palladium on alumina, palladium on silica-alumina, magnesia, titania, kieselguhr, active charcoal, graphite, etc., palladium black, and palladium sponge. Further examples of useful palladium compounds are palladium alpha-picolinate, carboxylates of divalent palladium , bis (acetylacetonato) palladium, bis (triphenylphosphine) dichloro palladium, cyclooctadiene dichloropalladium, tetramine dichloro palladium, and the like. 
     The alkali metal carboxylate can be a carboxylate of an alkali metal such as lithium, sodium, potassium, cesium, and rubidium. Specific carboxylic acids which can be ised to make the alkali metal salts for use in the present invention include the C 1  -C 10  carboxylic acids, including straight and branched chain acids, and aromatic and C 1  -C 10  alkyl aromatic acids as well as dicarboxylic acids having from one to 10 carbons in a straight or branched chain or aromatic and alkylaromatic dicarboxylic acids. Specific examples of alkali metal carboxylates for use in the present invention include the lithium, sodium, or potassium salts of acetic, propionic, butyric, valeric acids or dicarboxylic acids such as malic, malonic, succinic, or glutaric acid, or aromatic acids such as benzoic acid or phthalic acid. 
     The copper salts used in the reaction according to the present invention can be either copper (I) or copper (II) salts. Examples of these salts are copper (I) or (II) halides such as copper (II) fluoride, copper (I) chloride, copper (II) chloride, copper (I) bromide, copper (II) bromide, copper (I) iodide, and other non-halide copper salts such as copper (II) nitrate, copper (II) acetate, and copper (II) sulfate. 
     The reaction temperatures can range from about 25° to 250° C., and the preferred temperature range is from about 50° C. to about 150° C. 
     Reaction pressures can range from about 1 to about 1500 psi, although ranges in the amount of about 50 to about 750 psi are preferred. 
     The gas composition, the molar ratio of carbon monoxide to oxygen, can range broadly from about 0.1 to 20. A molar ratio of carbon monoxide to oxygen of from about 0.25 to 10 is preferred. 
     The catalyst composition can range from a molar ratio of copper to palladium of about 1 to 50, although a molar ratio of copper to palladium of about 2.5 to 20 is preferred. 
     The alkali metal carboxylate is present in the catalyst composition in a molar ratio of alkali metal to palladium of about 1 to 100 although a molar ratio of alkali metal to palladium of about 2.5 to 40 is preferred. 
     The molar ratio of styrene compound to palladium can range from about 10,000 to 10. A molar ratio of styrene to palladium of about 1000 to 25 is preferred. 
     The molar ratio of alcohol to styrene can range from 500 to 1, although a molar ratio of alcohol to styrene compound of form about 10 to about 1 is preferred. 
     It has been found that the use of alkali metal carboxylates as catalytic materials in the reaction according to the present invention greatly increases the selectivity of the reaction over and above the selectivity found with the use of any other types of compounds. The use of the alkali metal carboxylates has been found useful in reactions according to the present invention where it is desired to increase the amount of cinnamic acid ester produced to the detriment of production of acetophenone or other undesirable reaction products. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The following examples represent specific methods of producing cinnamates according to the present invention. 
    
    
     EXAMPLE I 
     Styrene (54.0g, 483 mmole), methanol (78.4 g, 2246 mmole), palladium (II) chloride (0.444 g, 2.5 mmole), sodium propionate (2.4 g, 25.0 mmole) and copper (I) bromide (3.586 g, 25 mmole) were charged into a 300 ml Hastelloy autoclave. After the autoclave was sealed, it was purged with a gas mixture containing 12% carbon monoxide in air by bubbling the gas mixture through the liquid contents of the autoclave while stirring for about 10 minutes. After that, the gas flow was adjusted to a 500 ml/min. flow rate, and the pressure in the reactor was adjusted to 500 psig with a back pressure regulator. The autoclave was then heated to 100° C., and the reaction was kept at this temperature for 3.0 hours. 
     After the reaction had gone to completion, the autoclave was cooled and the pressure was released. The reaction mixture was then analyzed using gas chromatography. Analysis of the reaction mixture showed the following composition: 96.1 mmole of styrene, 40.8 mmole, 91.8 mmole of acetophenone, 289.7 mmole of methyl cinnamate, and 3.6 mmole of dimethylphenylsuccinate. This corresponds to 80,1% conversion of styrene and 74.8% selectivity to methyl cinnamate. 
     EXAMPLE II 
     This example illustrates that the addition of a dehydrating agent such as 2,2-dimethoxypropane has little effect on the oxidative carbonylation of styrenes to cinnamates. 
     Example I was repeated with the addition of 2,2-dimethoxypropane (20.2g, 193.8 mmole). After the reaction, the following materials were obtained from gas chromatographic analysis: styrene, 102.7 mmole; acetophenone, 57.8 mmole; methyl cinnamate, 267.4 mmole; dimethyl phenyl succinate, 4.0 mmole. This corresponds to 77.1% conversion of styrene and 77.5% selectivity to methyl cinnamate. 
     EXAMPLES III-XI 
     In these examples, summarized in Table I, the reaction procedure is similar to that shown in Example I. Differences occur in the variation of reaction temperature, pressure, time, and catalyst composition. 
     
                                           TABLE I__________________________________________________________________________       EXAM-            EXAM-                 EXAM-                      EXAM-                           EXAM-                                EXAM-                                     EXAM-                                          EXAM-                                               EXAM-       PLE 3            PLE 4                 PLE 5                      PLE 6                           PLE 7                                PLE 8                                     PLE 9                                          PLE 10                                               PLE__________________________________________________________________________                                               11REAGENTS (mmole)PhCHCh.sub.2       477.7            475.8                 459.6                      497.7                           463.0                                496.2                                     514.9                                          502.3                                               493.4CH.sub.3 OH 2246 2425 2470 2450 2444 2500 2499 2454 2474PdCl.sub.2  2.5  2.5  2.5  2.5  2.5  2.5  2.5  2.5  2.5CuBr        25.0 25.0 25.0 25.0 25.0 25.0 25.0 25.0 25.0C.sub.2 H.sub.5 COONa       25.0 25.0 25.0 25.0 25.0 50.0 12.5 6.25 25.0CONDITIONST (°C.)       100  80   120  120  120  120  120  120  120P (psig)    500  500  500  250  125  250  250  250  250t (min)     180  300  240  240  240  240  240  210  240Gas Flo (ml/min)       500  500  500  500  500  500  500  500  550(12% CO in air)RESULTS (mmole)PhCHCH.sub.2       96.1 83.0 52.0 37.5 145.9                                168.0                                     13.0 77.2 -- ##STR5##   40.8 20.5 30.8 21.9 63.4 48.5 27.0 1.4  78.8PhCHCHCOOCH.sub.3       289.7            280.4                 356.7                      430.1                           183.6                                193.4                                     461.5                                          312.1                                               253.8 ##STR6##   3.6  63.0 3.4  2.5  3.2  --   0.5  9.0  1.9% CONVERSION OF       80.1 82.6 88.7 92.5 68.5 66.1 97.5 84.6 100STYRENE% SELECTIVITY TO       74.8 71.3 87.5 86.4 58.0 59.0 91.9 73.4 71.7CINNAMATE__________________________________________________________________________ 
    
     EXAMPLES XII-XVII 
     In these examples, summarized in Table II, the reaction procedure is similar to that shown in Example I. Differences occur in the variation of oxidant, alkali carboxylate, and the gas phase materials charged into the reactor. The gas phase materials (carbon monoxide and air) were changed, under desired pressure, by controlling the flow rate and through a separated inlet system. 
     
                                           TABLE II__________________________________________________________________________       EXAMPLE 12               EXAMPLE 13                        EXAMPLE 14                                EXAMPLE 15                                         EXAMPLE 16                                                 EXAMPLE__________________________________________________________________________                                                 17REAGENTS (mmole)PhCHCH.sub.2       496.8   502.2    502.2   499.1    498.4   492.5CH.sub.3 OH 2453    2450     2475    2463     2491    2483PdCl.sub.2  2.5     2.5      2.5     2.5      2.5     2.5Cu Salt     CrBr, 25.0               CuBr, 25.0                        CuCl 25.0                                CuCl.sub.2, 25.0                                         FeCl.sub.3,                                                 CuBr, 25.0Sodium Carboxylate       Naprop, 12.5               Naprop, 12.5                        Naprop, 12.5                                Naprop, 12.5                                         Naprop, 12.5                                                 NaBu**, 12.5CONDITIONST (°C.)       120     120      120     120      120     120P (psig)    75      150      150     150      150     150t (min)     240     240      240     240      240     210Gas Flow (ml/min)       CO:30   CO:60    CO:60   CO:60    CO:60   500***       AIR:220 AIR:440  AIR:440 AIR:440  AIR:440RESULTS (mmole)PhCHCH.sub.2       238.7   95.3     17.4    50.4     95.8    17.0 ##STR7##   16.2    13.4     35.9    151.2    117.3   27.5PhCHCHCOOCH.sub.3       162.8   386.5    423.3   160.6    130.1   411.2 ##STR8##   11.9    9.2      8.4     2.1      --      1.9% CONVERSION OF       52.0    81.0     96.5    89.8     80.8    96.5STYRENE% SELECTIVITY TO       63.1    95.1     87.3    35.8     32.3    86.5CINNAMATE__________________________________________________________________________ *Naprop = Sodium Propionate **NaBu = Sodium Butyrate ***12% CO in Air