United States Patent (19) 11) 4,131,743 Yoshida et al. 45 Dec. 26, 1978 (54) PROCESS FOR PREPARING 3,959,352 5/1976 Onoda .............................. 260/497. A UNSATURATED DESTERS Primary Examiner-James O. Thomas, Jr. 75 Inventors: Yoshinori Yoshida, Yokohama; Assistant Examiner-Michael Shippen Tutomu Kobayashi, Ibaraki; Attorney, Agent, or Firm-Stevens, Davis, Miller & Hironobu Shinohara, Yokohama; Mosher Izumi Hanari, Tokyo, all of Japan 57 ABSTRACT 73) Assignee: Japan Synthetic Rubber Co., Ltd., Unsaturated diesters are produced by a process which Tokyo, Japan comprises reacting, in a flowing gaseous phase, a gase 21 Appl. No.: 702,935 ous mixture comprising a conjugated diene, a carbox ylic acid and molecular oxygen in the presence of (A) a 22 Filed: Jul. 6, 1976 catalyst comprising palladium, vanadium, antimony and (30) Foreign Application Priority Data at least one alkali metal carboxylate, or in the presence of (B) a catalyst comprising palladium, vandium, anti Jul. 17, 1975 (JP) Japan. 50/86657 mony, at least one alkali metal carboxylate and at least Dec. 11, 1975 JP Japan ................................ 50/146902 one alkali metal halide. The catalyst (A) maintains a 51 int. Cl’.............................................. CO7C 67/05 high activity and a high selectivity for a long time. The 52 U.S.C. ........................................ 560/244; 560/1; catalyst (B), in which further the alkali metal halide is 560/112; 252/472 added, shows a higher activity and a higher selectivity 58 Field of Search ................... 260/497 A; 560/244, for a longer time. And its activity and selectivity are 560/1, 112 stable and durable at high temperatures such as 160 - 200 C. Furthermore, the addition of the alkali metal (56) References Cited halide suppresses combustion reaction of dienes such as U.S. PATENT DOCUMENTS butadiene remarkably. Additionally, the catalysts (A) 3,622,620 11/1971 Horiie.............................. 260/497 A and (B), especially (B) can be easily reactivated when 3,637,819, 1/1972 Sennewald ...................... 260/497 A they lose activity. 3,872,163 3/1975 Shimiza ........................... 260/497 A 3,922,300 11/1975 Onoda .............................. 260/497 A 25 Claims, No Drawings 4,131,743 1. 2 Furthermore, the addition of the alkali metal halide PROCESS FOR PRE-PARNG UNSATURATED suppresses combustion reaction of dienes such as butadi DESTERS ene remarkably and also prevents by-production of monobutadienylacetate especially when lowering O2/- This invention relates to a process for preparing or diene ratio in a feed gaseous mixture. producing unsaturated diesters from a conjugated di The compounds, alkali metal carboxylates and alkali ene, a carboxylic acid and molecular oxygen. metal halides, respectively act as activity-promoting And more particularly, it relates to a process for components. producing unsaturated diesters which comprises react The inventors of this invention found also that a cata ing, in a flowing gaseous phase, a gaseous mixture com 10 lyst which has been used and lost its activity can be prising a conjugated diene, a carboxylic acid and molec reactivated by means of a method which comprises ular oxygen in the presence of (A) a catalyst comprising washing out the alkali metal carboxylate and alkali palladium, vanadium, antimony and at least one alkali metal halide when it is used, which acted as activity metal carboxylate, or in the presence of (B) a catalyst promoting component(s), with a liquid comprising comprising palladium, vanadium, antimony, at least one 15 alkali metal carboxylate and at least one alkali metal water and/or alcohol, thereafter sintering at 150-500 halide. C. with a gas containing oxygen and then reducing at Heretofore, there have been proposed various pro 100-500 C. with a reducing gas, and finally readding cesses for preparing esters from olefins or dienes by the said activity-promoting component(s). The result reacting with carboxylic acids and oxygen in the pres ing reactivated catalyst shows surprisingly the same ence of a catalyst comprising palladium as the main high activity, the same high selectivity and the same component. good stability and durability as the original catalyst. For instance, various processes for preparing butene Furthermore, we found an alternative method for diol diesters from butadiene in the presence of a catalyst reactivating a catalyst which comprises treating the comprising palladium have been researched and dis 25 catalyst which has been used and whose activity has closed in many literature. been lowered in our above mentioned processes for However, the catalysts in the conventional processes producing unsaturated diesters with a gas containing are not always satisfactory in respects of the activity, steam at 100-600 C. selectivity, stability and durability. According to said method, when the catalyst is It has been proposed that unsaturated glycol diesters 30 treated in a stage of still retaining more than 50% of the are prepared by reacting, in a gaseous phase, a conju original activity, the treated catalyst recovers the same gated diene, a carboxylic acid and molecular oxygen in activity as the original catalyst. the presence of a catalyst comprising palladium, anti Conjugated dienes represented by the following for mony and at least one alkali metal carboxylate (e.g. mula may be used in this invention, Japanese Patent Application KOKAI No. 4416/1973). 35 In the aforementioned process, however, the cata R1 Rs N / lysts have various disadvantages in respects of activity, CCaCeC selectivity, stability and durability. / N As for a catalyst comprising the three components of R2 R3 R4 R6 palladium, vanadium and an alkali metal carboxylate, it 40 has been noted that the catalyst shows extremely low Wherein R1-R6 individually are hydrogen or hydrocar activity, and therefore it is practically impossible to bon groups, preferably alkyl groups. The number of employ the catalyst in a process for producing the prod carbon atoms of hydrocarbon groups is not limited, but ucts of this invention. preferably 1 to 6. An object of this invention is to provide a commer 45 The above conjugated dienes include butadiene, iso cially useful process for producing an unsaturated dies prene, 2,3-dimethylbutadiene, piperylene and the like. ter, especially an unsaturated glycol diester in which Cyclic conjugated dienes such as cyclopentadiene, acyl-oxy groups have been added to the both side ends alkyl-cyclopentadiene, cyclohexadiene and the like also of the conjugated diene compound. may be used in this invention. Other objects and advantages of this invention will be 50 apparent from the following descriptions. Among such conjugated dienes, butadiene and iso We made research on processes for producing unsat prene are especially preferable. urated diesters by reacting a conjugated diene, a car It is not necessary for said conjugated dienes to be boxylic acid and molecular oxygen in a flowing gaseous pure and they may include other hydrocarbons in a phase, and we found that a catalyst comprising palla 55 ratio not affecting the reaction. dium, vanadium, antimony and at least one alkali metal Carboxylic acids which may be used in this invention carboxylate maintains a high activity and a high selec include aliphatic, alicyclic and aromatic carboxylic tivity for a long time. acids. For commercial application, lower aliphatic car The catalyst comprising the four components, that is, boxylic acids such as acetic acid, propionic acid, butyric palladium, vanadium, antimony and at least one alkali acid and the like are preferable. metal carboxylate, eliminates the above mentioned dis Oxygen acting as an oxidizing agent is not required to advantages of the conventional processes. be pure. It may be diluted by at least one inert gas such Further, we found that a catalyst, in which at least as nitrogen, carbon dioxide and the like. Air is the most one alkali metal halide is added further in addition to the convenient oxygen source, since it is available any above mentioned four components, shows remarkably a 65 where, and not expensive. higher activity and a higher selectivity for a longer When acetic acid and butadiene are employed as the time. Its high activity and high selectivity are stable and starting materials, the main reaction proceeds as foll durable at high temperatures such as 160-200 C. lows: 4,131,743 3 4. Ratio of antimony/vanadium is not limited but is preferably in the range of from 0.1 to 10 in terms of | | | || H. H. H. H. gram atoms. =c-c- + 2CH3COOH + o->H--C=C--h Alkali metal carboxylates include lithium-, sodium-, H. H. potassium-, rubidium-, or caesium-carboxylate and the like. =o =o Alkali metal carboxylates can be fixed on the carrier CH CH in the ratio of 0.01-40 m mol per 1 g of carrier. Butadiene Acetic Acid 1,4-Diacetoxybutene-2 Alkali metal halides include fluorides, chlorides, bro O mides and iodides of lithium, sodium, potassium, rubid According to this invention, 1,4-diacetoxybutene-2 is ium and caesium such as lithium fluoride, sodium fluo produced with a high selectivity, and only a small ratio ride, potassium fluoride, rubidium fluoride, caesium of 3,4-diacetoxybutene-1 and monoacetoxy-1,3-butadi fluoride, lithium chloride, sodium chloride, potassium ene are produced as by-products, chloride, rubidium chloride, caesium chloride, lithium Preparing procedures for our catalysts can be carried 15 bromide, sodium bromide, potassium bromide, rubid out by the conventional methods. For example, the ium bromide, caesium bromide, lithium iodide, sodium metal compounds of the catalyst are dissolved in a sol iodide, potassium iodide, rubidium iodide and caesium vent. Into the resulting solution, a carrier is dipped. iodide. Thereafter the said components are fixed on the carrier Among these alkali metal halides, alkali metal chlo by distilling off the solvent and reduced by hydrogen or rides, especially caesium chloride, are preferable. an organic reducing agent in a gaseous phase or by the Alkali metal halides can be fixed on the carrier in the conventional reducing agents such as hydrazine, form ratio of 0.01-40 mmol per 1 g of carrier.