1) Field of the Invention
This invention relates to a process for preparing cinnamate esters by the reaction of styrene compounds, carbon monoxide, alcohols and oxygen.
2) Description of the Prior Art
Cinnamate esters have found wide-spread commercial utility as perfumes and raw materials therefor owing to their inherent aroma. They are also important as raw materials for chemical or biochemical products, for instance, agricultural chemicals, photosensitive resins and phenylalanine.
Cinnamic acid has conventionally been produced on small scales by using benzaldehyde and derivatives of acetic acid as principal raw materials. This process is however not preferred from the industrial viewpoint since it requires such costly raw materials. As processes permitting use of more economical raw materials, several processes have been proposed to prepare a cinnamate ester by reacting a styrene compound, carbon monoxide, an alcohol and oxygen in the presence of a catalyst (see, for example, Japanese Patent Laid-Open Nos. 15242/1981, 70836/1982, 92242/1985 and 169442/1985).
All of these proposals employ as a catalyst at least metallic palladium or a compound thereof, with various compounds added for the purpose of attaining further increased reaction performances.
On account of the use of such an expensive metal as palladium, it is indispensable not only to develop a catalyst system which can afford a high reaction performance and has a prominent catalytic activity but also to establish a process for the repeated use of the catalyst according to which the catalyst components used in the reaction are recovered efficiently and the catalytic activity lost in the reaction is regenerated for its re-use in the reaction, in order to make these processes useful as an industrial preparation process of cinnamate esters.
Several proposals have been made to recover the catalyst components and regenerate their catalytic activity. In Japanese Patent Laid-Open No. 169441/1985, the catalyst components are recovered by filtration together with active carbon from a reaction liquid obtained as s result of the reaction wherein a particular catalyst system that contains palladium supported on active carbon is used as a main catalyst component. The thus-recovered catalyst components are regenerated in catalytic activity by heating them together with an organic acid. This regeneration method is only applicable to the reaction in which a particular catalyst system is used.
Japanese Patent Laid-Open Nos. 231630/1985 and 237046/1985 disclose processes in accordance with which palladium in a reaction liquid after completion of the reaction is adsorbed onto a carbonaceous carrier added prior or subsequent to the reaction, thus permitting recovery of the palladium by filtration. These recovery processes are however applicable only in the presence of a carbonaceous carrier and thus are not universal.
Further, use of a carbonaceous carrier causes the process to be more complicated and in addition, makes it difficult to remove or separate the water and other unfavorable components adsorbed onto the carbonaceous carrier so that the reaction tends to be affected adversely when the catalyst is used repeatedly. Therefore, these processes involve many problems in their industrialization.