SOTES
April, 1963
921
calculated from this approximate equation are shown in the last line of Table I, and are in reasonable agreement with the experimental values, particularly considering the fact that the vapor pressure of 98.1% tritium oxide I n view of the fadctthat a plot of the reciprocal of the time of the accumulation of a given charge in the elecis used for that of the pure component. It will be noted that the standard deviation of the trometer vs. the tritium activity of the gas in the hydrogen sample in the ionization chamber is linear, the exexperimental values of the separation factors would inpression for the separation factor becomes simply dicate a precision of approximately 0.02%, while the tabulated values suggest an accuracy of only 0.1%. (0s This is due to the fact that the vapor samples taken for c y = (01 analysis were removed from the cold trap (0') without recovery of the water from the chemical traps. Addiwhere t represents the time necessary to cover a set tional fractionation could occur in the cold trap, and range on the electrometer scale with a constant presthis would lead to low values of the separatioiz factor, sure of hydrogen in the ionization chamber. the error being greater a t the lower temperatures. One The calculated values of the separation factor at can calculate that the error from this source would have various temperatures are given in Table I. a maximum value of a few tenths of one per cent, and could be negligible. Furthermore, the trend in the difTABLE I ferences between the observed values and those calcuSEPARATION FACTORS FOR VAPORIZATION OF MIXTURES OF PROTIUM OXIDE-TRITIUM OXIDEAT VARIOUSTEMPERATURESlated from the approximate relationship would be in the opposite direction. t, "C. 20.03 30.01 40.02 50.00 60.01 (H/T)p 1,1130 1,0966 1.0760 1,0632 1,051O Acknowledgment.-This work was performed with a=(H/T)i 1.1136 1.0961 1.0764 1.0636 1.0521 funds supplied by the United States Atomic Energy 1.1167" 1.1037" 1.0761 1.0635 1.0521 Commission. The authors are grateful for this sup1.1130 1.0962 1.0761 1.0634 1.0523 port. a = -(TI1 (T),
1.1132 1.0963 1.0762 1.0635 1 0521 1.1134 1.0961 1.0761 1.0636 1.0523 1.1151" 1.1054a 1.1132 1.0963 1.064 1.052 1.096 1.076 Av. a: 1.113 0,00022 0.00017 0.00014 0.00014 0.00014 Stand. dev. 1.065 1.055 1.095 1.075 1.108 CalcdSba: a These values aye not included in calculating the average or the standard deviation. Calculated from the approximate equation o1 = V ' P ~ ~ ~ ~ ~ / P O T ~ O .
Discussion It has been shown2 that the separation factor for deuterium oxide-protium oxide mixtures is given approximately by the relationship
$-z 3-
a =
This expression. may be derived if one assumes random distribut4ionof the isotopic hydrogen atoms among the oxygen atoms, and hence an equilibrium consta,nt of 4 for the reactdon
€LO
+ TSO
2HT0
It is also necessary to assume that the mole fraction in the gas phase is directly proportional to the partial pressure of each component, and that Raoult's law applies to each component in the liquid-vapor equil i b r i ~ r n . Using ~ ihe same assumptions, it can be shown that for protium oxide-tritium oxide mixtures, the separation factor accompanying vaporization is approximated by the equa,tion -I
The vapor pressure of tritium oxide of 98.1 mole o/o purity has been reported6 over the temperature range included in the experiments reported here. The values (4) G. N. Lewis and R. E. Cornish, J . A m . Chem. Sac., 65, 2616 (1933). (5) M. M. P o p o v and F. I. Tazedinov, At. Energ., 8, 420 (1960).
RADIOLYSIS PRODUCTS OF C8 AKD GREATER CARBON CONTENT FROM ?2,!2,4-TRIiVIETHYLPENTANE BY J. A. KNIGHT,R. L. MCDASIEL,AND FREDSICILIO Nuclear Sciences Divzsion, Engineerany Experiment Station, Georgia Instztute of Technologu, Atlanta, Georgia Received September $6, 1968
Work current in this Laboratory is concerned with a detailed study of the radiation chemistry of branched hydrocarbons. Radiolysis products, hydrogen and hydrocarbons through C?, from the X-irradiation (50 kvp.) of 2,2,4-trimethylpentane have been reported.' I n addition to hydrogen, G = 2.2, there were 17 radiolysis products in the Cl-C7 range, total G 5.6. Radiolysis products Cs and greater from the X-irradiation of 2,2,4-trimethylpentane have been investigated mainly with gas chromatographic techniques, and the results are reported in this paper.
-
Experimental Materials.-The 2,2,4-trimethylpentane, Eastman, used in this work waB percolated through activated alumina. The infrared spectra of the "treated" 2,2,4-trimethylpentane and of a sample of Phillips research grade material were identical. Authentic hydrocarbon samples for identification purposes were obtained mainly from Phillips, Eastman, and Xational Bureau of Standards. The 2,2,4,4,6,8,8-heptamethylnonanewas obtained from Humphrey-T'Vilkinson, Inc. X-Ray Apparatus and Irradiation Cell.-The X-ray apparatus and irradiation cell have been previously described .1 All investigations were performed a t 50 kvp. and 50 ma., at a dose rate of 8.2 X l O I 7 e.v./g./min. for the volumes of samples studied. Irradiation Technique.-During the irradiations, the sample was stirred and helium gas at a known flow rate in the range of 5 to 10 ml. per min. was bubbled continuously through the hydrocarbon. This served to remove volatile radiolysis products constantly after buildup to steady-state conditions. Hydrocarbon Radiolysis Products in the C8 and Greater Range.-Samples of the irradiated 2,2,4-trimethylpentane were fractionally distilled with a 1.2 by 33 cm. column packed with (1) J. A. Knight, R. L. McDaniel, R. C. Palmer, and E'. Sicilio, J . Phys. Chem., 65, 2109 (1961).
922
NOTES
Podbielniak Heli-Pak 3013 stainless steel packing. The distillations were performed very slowly in order to concentrate the radiolysis products of carbon content CS and greater in the final fraction. Gas Chromatographic Analysis .--The hydrocarbon radiolysis products in the CS-CIOrange aere analyzed with two columns, one a 28-ft. column of 25% (by weight) tri-m-cresyl phosphate and the other a 32-ft. column of 15% di-2-ethylhexyl sebacate. The support was 50-GO mesh Chromosorb in both cases. The gas chromatographic unit was calibrated for thermal response for each of the products identified, except as noted in Table I. Qualitative identification waq made by use of retention times and enrichment techniques. The hydrocarbon radiolysis products in the C11-cl6 range were analyzed with two columns, one a 20-ft. column of 157, Apiezon L and the other a 23-ft. column of 15% Ucon oil LB-550-X, both with 50-60 mesh Chromosorb as the solid support. The gas chromatographic unit was calibrated for thermal response to 2,2,4,6,6-pentamethyIheptane,which was used in determining G-values for products in the Cl2 range, and 2,2,4,4,6,8,8-heptamethylnonane for products in the Clerange. AI1 peak areas were measured with a planimeter. Molecular Weight Determinations.-The higher molecular weight radiolysis product was isolated by removing the parent hydrocarbon, 2,2,4-trimethylpentane, under vacuum. Molecular weight determinations were made on this material with benzene as a solvent on a semimicro seaIe with a thermistor thermometer.2 The quantity of the higher molecular weight product isolated was determined by the pressure (15 to 30 mm.) and the length of time (6-24 hr.) employed for isolation. Most of the molecular weight determinations of the radiolysis products isolated in this manner were in the range of 200-216. Unsaturation.-Unsaturation was determined by measuring volumetrically the amount of hydrogen absorbed by a known amount of the irradiated material. Glacial acetic acid was used as the solvent, and 5% Pt oh carbon was used as a catalyst. The apparatus employed waa very similar to that of Ogg and Cooper.* It was necessary to use fairly large samples for analysis, and the most successful technique employed for introducing a large sample was the use of a sample hslder similar to a separatory funnel with a pressure-equalizing tube. Measurements were made on: (1) irradiated 2,2,4-trimethylpentane after removal of radiolysis products of carbon content less than Cs;and (2) irradiated 2,2,4-trimethylpentane after removal of radiolysis products of carbon content less than CSand greater than Clz. The difference between the two gave a measure of the unsaturation in the products of Clzand greater. The radiolysis products of carbon content less than CSwere removed by slowly distilling about of a sample through the distillation column described above. Samples from which products of less than CSand greater than Cla %'ereremoved were obtained by first removing the products of less than C Sby thermal distillation. Then, the material remaining in the flask was vacuum distilled a t 15 mm. for about 14 hr. This separated the 2,2,4-trimethylpentae along with radiolysis products in the CS-Cn range from the major portion of the products of C12 carbon content and greater. Qualitative infrared evidence for unsaturation in the Cl2 to CUJrange products was obtained with a Perkin-Elmer 221 spectrophotometer with a NaCl prism. Dosimetrv.-The method of dose determination has been described predously.1
Results and Discussion The radiolysis products of C8 and Cg carbon content are listed in Tables I and 11. Radiolysis Products in the Cs-Clo Range.-The radiolytic saturated hydrocarbon products in the c8-clO range could form by a *combinationof two appropriate intermediate fragments which are derived from the parent hydrocarbon by either carbon-carbon or carbonhydrogen bond fission. It is also possible that some CS products could form from 2,2,4-trimethylpentane by rearrangement processes involving a methyl group. Of the six Cs products listed in Table I, all can be (2) J. A. Knight, B. Wilkins, Jr., D. K . Davis, and F. Sicilio, Anal. Chim. Acta, 26, 317 (1961). (3) C. L. Ogg and F. J. Cooper, Anal. Chem., 21, 1400 (1949).
Vol. 67
TABLE I RADIOLYSIS PRODUCTS C8-c~ FROM 2,2,4-TRIMETIIYLPEXTANE Producta
Ub
2,2-Dimethylhexane 2,QDimethylhexane 2,5-Dimethylhexane 2,2,3,3-Tetramethylbutane" 2,3,4-Trimethylpentane and/or 2,3-diniethylhexane 2,2,3-TrimethyIpentane 2,2,3,4-Tetramethylpentane 2,2,4,4-Tetramethylpentane 2,2,5-Trimethylhexane 2,2,4-Trimethylhexane 2,4,4- and/or 2,3,5-Trimethylhexane
0.05 .Ol .I3 .03
