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
NOTES
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.
2852
NOTES
pressures of highly concentrated solutions of sodium heptafluorobutyrate were up to 3% below the values calculated according to the values of K1 and K2 given in Table I. The experimentally determined surface pressure values of solutions of tetrapropylamnionium bromide were up to 47, higher than the calculated values. Areas occupied by the adsorbed ions were calculated by using Gibbs’ simplified adsorption isotherm6 and the differentiated form of eq. 1.
/
/
4000
Vol. 67
/
TABLE I
3000
COXSTANTS O F SOLUTXS IS FCSED POTASSlb \f T\TITRATE-LITEIUX
f
NITRATEEUTECTIC
$ Solute bodiuiri acetate Sodium in-opionate Sodium trifluoroacetate Sodium pentafluoropropionate Sodium heptafluorobutyrate Tetrametbylarnmonium bromide Tetraethylammomum bromide Tetrapropylammonium bromide Tetraethplammonium chloride
1000
1000
I
200
0
10
I
I
I
I
I
20 30 40 50 60 Surface pressure, dynes/cm.
I
I
70
80
Fig. 1.-Plots of the product of surface pressure times area us. surface pressure. A: 0, sodium acetate; 0 , sodium propionate; B: X, sodium tritluoroacetate; sodium pentafluoropropionate; 0, sodium heptafluorobutyrate; C: 0, tetramethylammonium bromide; 0, tetraethylammonium bromide.
+,
0
Fig. 2.-Plots
22 31
50
87 100 Area, A.Z/ion.
150
of surface pressure vs. area (legend as for Fig. 1).
solution, and K1 and K 2 are constants. Table I gives the values for K1 and KPover the investigated concentration range. The reproducibility of the measured surface pressure ~ the calculated values were values was ~ 0 . 5 7and within 0.5y0of the experimental values. The surface
lii
l i z , mole “/o
078 2 6 78 0 297 40 341 40 017 40 85 X 10-3 133 03 133 286 X 1 0 - 3 133 .275 X 10-6 133 286 X 10-3
Upper limit of Concentration iange investigated, inole % 0
O G 2 6 0 2 04 2 6 0 5 013 .13
Plots of the product of surface pressure times area vs. the surface pressure are shown in Fig. 1. Plots of surface pressure us. area are given in Fig. 2 . The dotted lines represent the extrapolation of the areas occupied by the adsorbed solute ions a t high concentrations to T = 0. The area values for ;he various homologous series were found to be 22 A.2 for the sodium salts of fatty acids, 31 for the sodium salts of perfluorocarbon acids, and 87 A.2 for the alkylammonium halogenides. Discussion Szyszkowski found that the surface pressure-bulk concentration relationship for fatty acids in aqueous solutions can be expressed by eq. 1.6 This relationship holds also for solutions of certain surfactants in other aqueous solvent systems.’ The constant Kl in eq. 1 had the same value for the homologous series of the fatty acids dissolved in water, whereas the constant K z varied by a factor of approximately three for successive members of the series (Traube’s rule). Similarly, eq. 1was found to be applicable to our investigation. It was also found that K1 was a constant for a given homologous series and Kz varied systematically for successive members of the series. There is a direct relationship between the constant K1 and the cross-sectional area of the solute molecules. The calculated values for the area a t c >> K2 were found to be slightly lower than those extrapolated from the experiment (see Fig. 2). These values are close to those given in the The constant K z seems to be related to the polarity of the solute molecule. It is evident from eq. 1 that for a given bulk concentration with K1 constant for a homologous series, the surface pressure increases with de(5) I.. I. Osipow, “Surface Chemistry,” Reinhold Publ. Gorp., Nen York, N. T 1962, p. 121. (6) B. v. Saysakowski, 8. physsh. Chem., 64, 385 (1908). (7) A. Lake, A. S. C. Lawrence, and 0. S &fills, Proc. Intern. Conur. Surface Actzirty, @nd, London, 1, 200 (1957). (8) N. I
