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solid-line data for regions a and b are similarly recommended. Acknowledgment.-This work was made possible, in large part, by financial support received from the U. S. Air Force, Office of Scientific Research, Air Research and Development Command, Washington, D. C. ISOTOPE EFFECTS I N THE METHYLENE TSSERTION REACTIOS. I. PROPANE us. 2,%DIDEUTERIOPROPSX E JOHN P. CHESICK Department of Chemistry, Haveiford College, Haverford, I’ennxylva?&aa AND
As. ROBERTWILLCOTT
Department o,f Chemzstry, Emory Cnivarsaty, Atlanta $2, Georgaa
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Received J u n e 6 , 1968
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Fig. Z.--Molal heat capacity of Ag?iOt: 0, Smith, Brown, and Pitzer2; 0, this investigation;
-.-.-a
conditions (Tf (lO,OOOo atm.) = 58OoK.).l8 This is conventionally understood to be a result of variation in the contribution which repulsion forces make to the total lattice energy (see, e.g., ref. 19). At still higher pressures there appear at least two further modifications,20for which the crystal structures are unknown. The rearrangement produced on fusion is less easily identified. It is obviously one which is energetically (L economical” (in view of the low melting point: AH, = (Tf) A&) and in which the “free space” (conventionally postulated to explain physicochemical and electrical properties of liquids) is attained M-ith negligible volume increase in the bulk phase. The presence of “association complexes’’ in molten silver nitrate conveniently explains many of these anomalies. While measurement of macroscopic properties (entropy, volume, and specific heat changes) emphasizes the importance of fusion, investigations into the local environment of ions in silver nitrate (e.g., through ultraviolet absorption studies) suggest that the solidstate transition is more significant as a precursor of the melting process than is often realized. The present results complete the heat capacity curve for silver nitrate from 3 to 6OOOK. Previous data in the range 400-600°K.’~10~21 showed discrepancies, and left something to be desired.22 Values of C, obtained in this investigation are (in cal. deg.-‘ mole-‘) 24.7 f 1 (425); 20.7 f 0.5 (433483); 28.0 i 0.4 (483574OK.). These values are shown in Fig. 2. It is clear that the present value of Cp at 425OK. is more acceptable than either of those previously published; the (19) P. W. Bridgman, “The Physics of High Prrasiirrs,” Bell, London. 1949. (20) P. W. Bridgman, Proc. Am. Acnd. Arts S??., 72, 48 (1937). (21) K. IC. Kelley, U. S. Bureau of Nines ’Bull. 581, 1960, (22) K. S. Pitzer, private communication, 19GO.
Direct insertion reaction of methylene (CH,) into carbon-hydrogen bonds has been demonstrated‘ and has been the subject of a considerable number of investigations in both gaseous and condensed phase. However, no studies have been reported dealing with isotope effectsin this reaction. The addition of methylene to a double bond to yield a cyclopropane ring appears to be a very efficient process2 and the insertion reaction is apparently only slightly less efficient. A bimolecular reaction which occurs on every collision would be expected to exhibit only a small change in rate if an isotopic substitution were made in the reactant species. However, if many collisions are required and carboii-hydrogen bonds are made and broken in the transition state, a large deuterium isotope effect might be observed. Since the carbeiie insertion reaction might present ai1 interesting intermediate case and since the data would be of value in consideration of another proposed insertion r e a ~ t i o n a, ~study was made of the deuterium isotope effect iii the insertion of methylene into the secondary carbon-hydrogen bonds of propane using the primary insertion reaction as an internal reference. In the absence of methyl and propyl radical recombination reactions, the ratio of n-butane to isobutane measured the relative reactivity of primary and secondary carbon-hydrogen bonds. Some radical reactions occur, howerer. It was found in the insertion reaction of methylene with isobutene that 16% of the 2-methyl1-butene formed came from radical reactions. It is presumed that the secondary propyl radicals would be more difficult to form by a hydrogeii abstraction from propane than would the allylic system resulting from hydrogen abstraction from isobutene, and hence, noninsertion processes should be less important in thc methylene-propane system. Frey4 has studied this system and has reported a value of 2.6 for the butaiieisobutane ratio which was independent of pressure in the region 200-1200 mm. In a later paper6 he also reported a study of abstraction reactions of methylene in which a small yield of hexanes, resulting probably from propyl radical recombinations, was suppressed by small additions of oxygen. He estimates that 22% of the methylene attack on propane results in hydrogen atom (1) W . y o n E. Doering and H. Prinzbach, Tetrahedron, 6 , 24 (1959). (2) 11. hi. Frey, Proc. Roy. Sac. (London), A260, 409 (1959). (3) J. P. Chesick, J . A m . Chem. Soc., 8 4 , 2448 (1962). (4) H. hf. Frey, abzd., 80, 5006 (1958). (6) H. M. Frey, Proc. Chem. Soc., 318 (1959).
Dec., 1963 abstraction, the other 78% giving insertion products. The actual yield of butanes from propyl-methyl recombinations should be less than this figure to the extent of propyl-propyl recombination and disproportionation reactiops, and the propyl-methyl disproportionation reaction. In this study photolysis of propane-diazomethaiie mixtures were carried out in a 200-ml. Pyrex bulb using Phillips research grade propane or Merck of Canada 2,2-dideuteriopropane of better than 98yo isotopic purity. Propane pressures ranged from 3.2 to 4.2 cm. and diaxomethane pressures were 1.5 to 6.1% of the propane pressures. The mixtures were irradiated with a General Electric RS-12 275-w. sunlamp to complete decomposition of the diazomethane. Product mixtures were analyzed by g.1.p.c. using a 12-ft. column packed with G.E. SF-96 silicone oil-on-firebrick. Butane and isobutane, identified by mass spectral cracking patterns as well as by g.1.p.c. retention times, comprised over 90% of the volatile hydrocarbon products. These products were trapped and passed through a silver nitrate-in-glycol-on-firebrick columii to test for olefins unresolved in the silicone oil column analysis. Only about 2-3% of butene-1 was observed, and a second passage of the butane peaks through the silicone oil columii after the silver nitrate separation showed no significant change in the n-butane-isobutane ratio. In a series of seven runs the n-butane-isobutane ratio was 2.18 f 0.10. The ratio of 2,3-dimethylbutane to total butanes was 0.015. ilddition of 1.1 cm. of air in each of two runs increased the n-butane-isobutane ratio to 2.45. S o hexanes were observed in these scavanged runs. Three runs made with the 2,2-dideuteriopropaiie yield the value of 3.0 f 0.15 for the n-butane-jsobutane ratio. The mass spectra of these products showed no signal a t m/e = 61 other than that expected for the C13 isotope contribution in the butanes, leading us to conclude there was no observable C4&D3 formation. Small amouiits of C4H9D would not have been detectable in the mass spectra. Therefore, if a radical attack is occurring a t either primary carbon to form 2,2dideuterio-n-propyl radicals with subsequent n-butane formation, no secondary radical attack can be significant or there would be CHzD as well as CH3 radicals in the system and C4H7D3 mould result. The presence of a primary hydrogen abstraction without a secondary deuterium abstraction occurring seems unlikely. Therefore, all n-butane observed in the runs made with deuterated propane must have originated in the insertion reaction. Taking the primary hydrogen insertion reaction as independent of secondary deuterium substitution, the primary-secondary insertion ratios of 3.0 and 2.45 indicate that methylene inserts in the secondary carbon-hydrogen bonds 1.23 times faster than in comparable carbon-deuterium bonds. A deuterium isotope effect of 1.37 is calculated if the unscavanged nbutane-isobutane ratio is used for the runs with C3Hs. However, we believe that the only significant radical attack is occurring a t secondary CH bonds in our system, and that 1.23 is the preferred number for the isotope e-rfect. This number can be compared with the ratios of 1.55 a,iid 1.69 found for insertion of methylene
2851
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in the vinylic and allylic bonds of cis-butene-2 and eisbutene-Bd8, respectively.6 The small magnitude of the isotope effect observed in our work corroborates the previously held point of view that the insertion reaction is a very efficient reaction taking place with a near zero activation energy. Acknowledgment.-This work was performed under the support of the U. S. Pubiic Health Service Research Grant RG8973, Yale University. (6) J. W. Simons and B. S. Rabinovitoh, J . A m . Chem. Soc., 86, 1023 (1963).
SURFACE ACTIVITY I N FUSED POTASSIUAP NITRATE-LITHIUM NITRATE EUTECTIC BY KLAUSF. GUENTHER Armour Research Foundation, Illinois Instztute of Technology, Chicago, Illinois Received June 8, 1963
Fused salts are highly ionic solvents and it is therefore to be expected that organic compounds of ionic character are soluble in these melts and produce a pronounced surface activity effect. Practically .no data concerning the solubility of organic solutes in fused salts are available, nor are data pertaining to a systematic investigation of surface tension of organic solutes in salt melts. The objective of this investigation was to study the behavior of some organic solutes in fused salts in more detail with emphasis on the surface tension-concentration relationship. Experimental The solvent used was the potassium nitrate-lithiam nitrate eutectic (56 mole yo KNO, and 44 mole % LiNOa, m.p. 125"). These substances were recrystallized and dried at 200' under vacuum for at least 12 hr. The first members of the homologous series of the sodium alkylates, sodium perfluoroalkylates, and alkyl ammonium halogenides were used as solutes. The solutes were of reagent grade purity. Surface tension was determined by the maximum bubble pressure method. The measuring cell was designed essentially according to Sugden.',? The other parts of the apparatus wcre designed according t o the experimental arrangement described by Peake and Bothwell.a P , which is the pressure difference (in dynes/cm.2) for the generation of bubbles in the two c:ipillaries., was measured and the surface tension determined udng the formula, y = AP(1 0.69r?gd/P), where TIis the diameter (in cm.) of the large capillary, g the gravitation constant, ::nd d the density (in g./cc.) of the melt ( d , ~ , o = 1.9494). The constant of the measuring cell, A , was determined by measuring P with water and benzene as standard liquids. I n a check experiment the surface tension of pure molten silver nitrate was found to be in good agreement with the values given in the 1iterat~i-e.~ All experiments i n fused potassium nitrate-lithium nitrate eutectic were performed at 166'.
+
Results It was found that the surface pressure-bulk coiiceiitration relationship call be expressed by a Sxyszkowskitype forniula of the form
where ?r is the surface pressure (in dynes/cm.), yo the surface tension of the pure solvent (120.5 dynes/cm. a t 166O), c the bulk concentration (in mole %) of the (1) 8 . Sugden, J . Chem. Soc.. 121,858 (1922). (2) R. Sugden, z f d , 126, 27 (1924). (3) J. S. Peake and AI. H. Bothwell, J . Am. Chem. SOC.,7 6 , 2656 (1954). (4) J. O'M. Boekns, "Modern Sspects of Electrochemistry. KO.2," Butterworths Scientific Publications, London, 1959, p. 198.
