DIPOLE-MOMENTS OF 7 PARTIALLY HALOGENATED ETHANE REFRIGERANTS

Dielectric constant measurements have been performed on seven partially halogenated ethanes, currently being considered as alternative refrigerants, in the gaseous state over the range 305-415 K in order to determine their dipole moments. Argon was also studied to test the apparatus. Five of the refrigerants have temperature-independent moments: R125 (CF3CHF2), mu = 1.563 +/- 0.005 D; R134a (CF3CH2F), mu = 2.058 +/- 0.010 D; R143a (CF3CH3), mu = 2.340 +/- 0.010 D; R152a (CHF2CH3), mu = 2.262 +/- 0.008 D; and R124 (CF3CHClF), mu = 1.469 +/- 0.012 D. Two refrigerants have conformer-dependent moments, making their time-averaged moments temperature dependent: R134 (CHF2CHF2), with a moment ranging from 0.991 +/- 0.004 D at 309 K to 1.250 +/- 0.004 D at 413 K; and R143 (CHF2CH2F), where the moment ranges from 1.680 +/- 0.001 D at 309 K to 1.745 +/- 0.001 D at 410 K. Accurate estimation of a molecule's temperature-dependent dipole moment requires an independent determination of its polarizability; this determination has been made from index of refraction measurements. Where possible, the present results are compared with earlier determinations of dipole moments. In all but one instance, the agreement is good.