Metathesis of fatty acid esters

In metathesis reactions, unsaturated compounds are converted into new compounds via an exchange of alkylidene groups: 2 RCH=CHR′⇌RCH=CHR+R′CH=CHR′ Since its discovery in 1964, this catalytic reaction has found several large‐scale applications in petrochemistry. One of the most promising synthetic applications of metathesis is to functionalized olefins such as unsaturated esters, ethers, amines, etc., because this allows single‐step syntheses of a variety of mono‐ and difunctional hydrocarbon derivatives. Unfortunately, however, most metathesis catalysts are easily poisoned by polar groups. In 1972 in our institute, the WCl 6 ‐(CH 3 ) 4 Sn system was found to be effective as a catalyst for monogeneous metathesis of fatty acid esters. Thus methyl oleate was converted into 9‐octadecene and dimethyl 9‐octadecene dioate, starting materials for the synthesis of valuable chemical products. In 1977 we developed a heterogeneous catalyst system: Re 2 O 7 on Al 2 O 3 , activated with a small amout of (CH 3 ) 4 Sn. Systematic research has led to intersting applications of metathesis and cometathesis reactions with these catalysts. An example is the cometathesis of methyl oleate with ethene, to produce shorter‐chain compounds with terminal double bonds: CH 3 (CH 2 ) 7 CH=CH(CH 2 ) 7 COOCH 3 +CH 2 =CH 2 ⇌CH 2 =CH(CH 2 ) 7 CH 3 +CH 2 =CH(CH 2 ) 7 COOCH 3 Cometathesis of olive oil (mainly triolein) with ethene opens the possibility of producing both α‐olefins in the C 10 range and fatty oils with lower molecular weight (palm oil type). Until now, metathesis of fatty esters has been restricted mainly to synthetic purposes. Large‐scale applications depend mainly on the development of more active and cheaper catalyst systems.