FRACTIONATION OF ISOTOPIC P-XYLENES BY MEANS OF INCLUSION WITH TETRAKIS(4-METHYLPYRIDINE)NICKEL(II) ISOTHIOCYANATE

When a mixture of two isotopic p-xylenes in n-pentane, each of which forms a 1:1 inclusion compound with the host Ni(4-mepy)/sub 4/(NCS)/sub 2/, is shaken with the latter the mole ratio, R/sub S/, of the two p-xylenes in the resulting solid phase differs from that in the coexisting liquid, R/sub L/. Studies of the guest pairs p-(CD/sub 3/)/sub 2/C/sub 6/D/sub 4/-p-(CH/sub 3/)/sub 2/Ca6H/sub 4/ and p-(CH/sub 3/)/sub 2/C/sub 6/H/sub 4/-p-(CH/sub 3/)/sub 2/C/sub 6/H/sub 4/ show that for both pairs R/sub S/ is proportional to R/sub L/. With the more deuterated member of each pair in the numerator R/sub S//R/sub L/ is 1.10 +- 0.03 for the first pair and 1.13 +- 0.04 for the second. Thus the more deuterated of each pair is preferentially included, and the magnitude of the effect is the same for each pair within experimental error. Deuteration of the methyl groups appears to be more effective than deuteration of the aromatic ring. The phenomenon reflects the greater vapor pressure of the more deuterated isomer and has potential for the separation of deuterated from protiated isomers.