The initiation of some substituted styrenes by butyl lithium has been studied. In hydrocarbon solvents the rates are given byRi ~k [M][BuLi] n where n lies between ¼ and ~ for benzene solutions and is approximately 0.57 for n-hexane solution. In benzene solution the relative rates of initiation of the meta-and para-substituted styrenes give a linear Hammett plot of slope -t-1"0 with the exception of certain monomers which undergo side reactions. The addition of ethers to systems in hydrocarbon solvents increases the rate of initiation in a manner which may be accounted for by assuming the formation of mono and dietherate complexes of the catalyst.
EXPERIMENTAL
REAGENT grade benzene after standing over concentrated sulphuric acid for a week was washed with dilute sodium hydroxide solution. The product was dried, distilled from phosphorus pentoxide and stored over Linde molecular sieve 4A.
n-Hexane was purified as for benzene. Tetrahydrofuran (THF) was distilled from a reservoir containing sodium benzophenone ketyl and was stored over sodium wire in a dark bottle.
Reagent grade diphenyl ether was used without further purification.
Monomers were freed of inhibitor by washing with dilute aqueous sodium hydroxide. After drying over calcium hydride they were fractionated twice under reduced pressure (N2 bleed) using a 70-cm column fitted with a vacuum jacket and packed with Dixon rings. Final purification was effected by flash distillation from solvent-free butyl lithium. These procedures were shown to be effective by argon vapour-phase chromatography.
Butyl lithium solutions were prepared by the reaction of redistilled butyl chloride with a two-fold excess of lithium. The solutions were freed of insoluble products by centrifuging. Concentrations were determined by hydrolysis and titration of samples with standard hydrochloric acid using phenolphthalein as indicator.