A. J. Charlson, J. S. Shapiro, G. W. Ware, and E. C. Watton MacqLarie University No*h Ryde. N S.W 21 13. Australia
II ABromination Stoichiometric Study in the Gas Phase: of Unsaturated Hydrocarbons
Many college and high school manuals describe a n experiment involving bromine addition t o carbon-carbon double bonds, where decoloration of hromine in carbon tetrachloride is nroduced on the introduction of a easeous or a liouid olefin. " This experiment leaves many questions unanswered and may lead t o confusion with the photo-hromination of hydrocarbons where decoloration of hromine also occurs. For instance, generally n o information is provided about the stoichiometry of the reaction, identity of products, or possible solvent participation. Students may be led to believe t h a t this is a simple reaction; yet considerable research in the area has shown that this is not t h e case ( I ) . T h e mechanism of halogen addition to unsaturated hydrocarbons is known to involve either ionic or radical intermediates d e ~ e n d i n gon experimental conditions (2). Thts pnperdpsrrilws a simple alternativr procedure, hased i,n the w r k d Arhnlad I , . f m stuclyiny the brominarwn of olefins in the gas phase l)rf:rirnries noted in the ronvrntiunol erpcrment are overcome by reacting hromine vapor with excess gaseous olefin to yield liquid products, using the apparatus descrihed below. A clean. dry 1-1 filtration flask was fitted with a rubber stopper through which passed a thermometer and a long glass tuhe connected to a mercury manometer with P.V.C. tubing (Fig. 1). Bromine was introduced in a sealed specimen tube, the base of which had been distended by glass-hlowing to form a breakable blister. Attempts were also made to introduce the bromine with a small buret and syringe through the stopper but problems with leakages and accurate volume measurements were encountered. A "gasometer-typenarrangementtomeasure thevolumeof olefin consumed has been described ( 6 )but it makes no allowance for the vapor pressure of the oroduct and accurate volumetric determination amears dif.. firul~. A techniqur n whwhn imsll rial
