in pentane byproducts: HCCMe; pentane and carboxylic acid addn. to Sn-compd. (three-nacked flask, stirrer, reflux condenser), mixt. boiling for 30 min; ppt. filtration off (argon atmosphere), washing (pentane or petroleum ether), recrystn. (hexane/benzene 4:1); elem. anal.;