Some physical properties of isoprene

Abstract

Isoprene (2-methyl-1,3-butadiene) has been prepared in a state of high purity. Physical properties determined on the freshly purified sample were as follows, boiling point, 34.076 ± .003° C; change of boiling point with change of pressure::~=0.0382° C per millimeter of mercury; freezing point, -146.8 ±.2° C; density at 20° C, 0.6805 ± .0001 g/ml; refractive index at 20° C, 1.42160 ± .00005. The molecular refraction was calculated to be 25.39. The volume expansivity was measured over the entire range of temperature between the freezing point and normal boiling point, giving the following equations: -3t+2.79 X 1O-6t2+ 4.31 X 10-0t3-5.60 X 1O-12t4) p=O. 7002 -0.9754 X 1O-3t-0.592 X 1O-6t2+ O.525 X 10-9t3+ 9.66 X 1O-12 t 4 ,

Heat of combustion of isoprene

“…The amount of isoprene in the vapor phase was calculated in the following three ways: (1) The effect of the factors (a) and (b) mentioned above was neglected. The vapor pressure of pure isoprene at the initial temperature of the calorimeter in each experiment was calculated from a vapor-pressure equation of the form log p=a-b/T, where the constants were determined from values of boiling point and change of boiling point with pressure reported by Beld<:edahl, Wood, and Wojciechowski [3]. The actual pressure of the isoprene vapor in the bomb was assumed to be lower than the vapor pressure of pure isoprene by an amount calculated by means of Henry's law from the amount of impurity (assumed to be water) indicated by the observed values of r (table 2).…”

“…The actual pressure of the isoprene vapor in the bomb was assumed to be lower than the vapor pressure of pure isoprene by an amount calculated by means of Henry's law from the amount of impurity (assumed to be water) indicated by the observed values of r (table 2). The specific volume of the isoprene vapor was calculated by means of the relation PVjT=constant, where the constant was determined from the values of V and T at P= 1 atmosphere [3]. (2) The liquid isoprene was assumed to have absorbed an amount of water sufficient to reduce the density of isoprene in the vapor phase to 80 percent of the density of vapor in equilibrium with pure liquid isoprene.…”

“…Hence the value derived from this investigation for the heat of combustion of liquid isoprene at 25° C and a constant pressure of 1 atmosphere to form liquid water and gaseous CO2 is 3156.9 ± 1.6 international kilojoules per mole. Adding to this the value for the heat of vaporization of isoprene calculated by Bekkedahl, Wood, and Wojciechowski [3], 25.9 ±0.3 kilojoules per mole, there is obtained the value 3182.8± 1.7 international kilojoules per mole for the heat of combustion of gaseous isoprene at 25° C and at a constant pressure of 1 atmosphere, the . products of combustion being liquid water and gaseous CO2•…”

“…The isoprene used was prepared by Bekkedahl, Wood, and Wojciechowski [3] by cracking dipentene vapor and was purified by fractional distillation. Their ebulliometric measurements on the freshly distilled isoprene indicated that the material was of a very high degree of purity.…”

A system of characterization of pure hydrocarbons—Refractometric analysis as a key to the evaluation of structure.

“…No small part of this progress has rested upon the careful synthesis of pure hydrocarbons and the exact determination of their physical and optical properties. Numerous workers at the National Bureau of Standards have gone far toward the ultimate determination of properties of specially purified hydrocarbons (4,23). Upon the foundations provided by these chemists and many others the present system of characterization of hydrocarbons depends.…”