Sept. 19621
ISOPIESTIC ISVESTIGATIOS
O F DI-(2-ETHYLWEXYL)-PHOSPHORIC4 C I D IS ?%-OCTANE
experimental procedures, values for G(-isopropylbenzene) are not very reliable because of the large correction necessitated by incomplete recovery from the solid. I n ten experiments with highsurface solid per cent conversion values ranged from 1 3 4 7 % . Seven of the ten values lay between 21 and 41y0, and the average of all ten was 29%. On low-surface solid the recovery of isopropylbenzene was much better, and no correction was used for isopropylbenzene retained; consequently, the values of G(-isopropylbenxene) used are too large and per cent conversions are minima. The range’ of per cent conversion from five experiments with lowsurface solid was 29-36%, with ai1 average of 37%. AppIication of a quite small correction (10-fold smaller than that measured for high-surface solid) for isopropylbenzene retention on the low-surface solid brings the average per cent conversion to near 50% and reduces the spread in values. It would appear that the per cent conversion on low-surface soljd is appreciably higher than that for highsurface solid. The much lower values for G(hydrogen) add support to this view; however, it is possible that retention by irradiated high-surface solid is greater than the retention correction used and, therefore, that per cent conversions calculated for high-surface solid are low. Conversion in liquid radiolysis is about 3%, and the maximum value in gas radiolysis would appear to be about 18%.1 There appears to be little doubt that presence of the solid has enhanced the selectivity of the radiolysis of isopropylbenzene considerably, as shown particularly by the results for per cent conversion with low-surface solid. Low vdues for G(propene), about 0.2% of G(benzene), may be due to failure to produce pro-
1629
pene or the inability to recover propene from the solid containing adsorbed isopropylbenzene, a8 discussed in the section on experimental procedures. Since thermodynamic equilibrium at loo”, the temperature used for recovery of liquid products, overwhelmingly favors isopropylbenzene relative to benzene and propene, observation of appreciable benzene yields is contingent on failure to produce equivalent amounts of propene or on conversion of propene to other products on the solid. Possible fates of propene are polymerization and formation of diisopropylbenzene. The possibility that propeiie is formed in an amount equivalent to benzene and subsequently disappears in isopropylbenzene alkylation would decrease the amount of G(-isopropylbenzene) attributable to side reactions and impose an upper limit on conversion of 50%; this value appears to be closely approached with low-surface solid. In the blank experiment (cf, Experimental Procedures) less than 8% of unrecovered propene was recovered as diisopropylbenzenes; however, this represents positive evidence for such a reaction, Thus, a radiation-induced, solid-catalyzed unimolecular split into benzene and propene with conversion of propene to diisopropylbenzene could be the major reaction occurrent. The unique behavior of the benzene yields and the higher per cent conversion of isopropylbenzene to benzene on a solid which is a catalyst for thermal dealkylation suggeet the possibility that a solid to some extent may direct absorbed radiation energy into that reaction for which it is a thermal catalyst. It is intended to test this speculation by the use of solids of varying catalytic activity, particularly a very pure silica of little or no catalytic activity,
AX ISOPIESTIC INVESTIGATlON OF DI-(2-ETHYLHEXYL)-PHOSPHORIC ACID (DPA) AND TRI-R-OCTYLPHOSPHINE OXIDE (TPO) I N n-OCTANE’ BY C. F. BAES,JR. Contribution from the Oak Ridge National Laboratory, Oak Ridge, Tennessee Received Februaw 88, 1968
Isopiestic measurements are presented in which octane solutions of di-( 2-ethylhexyl)-phosphoric acid (DPA) and tri-noctylphosphine oxide JTPO) are compared with triphenylmethane (TPM)-octane as the reference solution. In the range 0-0.2 m the results show deviations up to 10 and 20% from ideal solution behavior of DPA dimer and TPO monomer, res ectively. While partial trimerieation of DPA (in qualitative agreement with previous iron( 111) extraction results for 8 P A ) and partial dimerization of TPO (which is not supported by molar polarization results) can account in part for the resuIts, it is evident that non-specific non-ideal behavior of the solutes also is involved. Practical activity coefficients were , , !og estimated on two separate assumptions: ( 1 ) YTPI zz 1, giving log -I(DPA)* = - 0 . 5 2 2 7 m ( ~ p ~ , ~ ~ / 0a . 4 2 0 m ( ~ p ~and YTPO = - 1.168mTpo 0.149m~po2; and (2) log Y(DPA)% --0.6432m(~~a,,’/8 (from iron(II1) extraction results), giving YTPM = -0 737m~pnrand log YTPO = - 1 . 8 8 6 ~ ~ f ~ ~00. 2 4 5 ~ ~ ~ ~ 0 ~ .
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The isopiestic measurements reported here were undertaken in connection with solvent extraction studies of di-(Bethylhexy1)-phosphoric acid (DPA) 2-4 and tri-n-octylphosphine oxide (TPO) . 5 , 6 (1) This communication is based on work performed for the U. S. Atomic Energy Commission a t Oak Ridge National Laboratory, Oak Ridge, Tennessee, operated by Union Carbide Corporation. (2) (a) C. F.Baes, Jr., R . A. Zingaro, a n d C. F. Coleman. J. Phys. Chem., 62, 129 (1958); (b) C. F. Baes, Jr., a n d H. T. Baker, ibid., 64, 89 (1960). (3) C. A. Blake, K. B. Brown, a n d C. F. Coleman, “ T h e Extraction’ and Recovery of Uranium (and Vanadium) from Acid Liquors with Di-
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(2-ethylhexyl) -phosphoric Acid and Some Other Organophosphorus Acids,” ORNL-1903, M a y 1 3 , 1955, p. 106. (4) C. 8 . Blake, D. J. Crouse, C. F. Coleman, K. B. Brown, a n d A. D. Kelmers, “Progress Report: Further Studies of the Dialkylphosphoric Acid Extraction (Dapex) Process for Uranium,” ORNL-2172, Sept. 6, 1956, p. 110. ( 5 ) H. T. Baker a n d C. F. Baes, Jr., “An Infrared and Isopiestic Investigation of the Interaction Between Di-(2-ethylhexy1)-phosphoric Acid a n d Tri-(n-octy1)-phosphine Oxide in Octane.” paper presented a t ACS Meeting, Chicago, Sept. 7-12, 1958, paper in preparation. (6) C. A. Blake, I
