Jan., 1058
RADONSOLUBILITY IN FATTY ACIDSAND TRIGLYCERIDES
substituent(s) increases. Furthermore, the values of AS* agree qualitatively with the anticipated steric effects of the substituent(s). The remaining aniline derivatives release electrons to the nitrogen atom by means other than simple inductive effects. I n o-anisidine (line 17) and o-phenetidine (line 19) the decrease in AH* may be attributed to the 4 E effect of the alkoxy group. The values of A S * for these solvents are qualitatively consistent with anticipated steric effects. Halogen derivatives of aniline present a situation more difficult to explain. The halogens exhibit a -I effect which withdraws electrons from nitrogen, and are also capable of a +E effect which furnishes electrons to nitrogen. If the -I effect alone were operative AH* would be larger for the halogen derivatives than for aniline itself. If the +E effect were alone operative AH would be lower for the halogen derivatives than for aniline, and AH* would be expected to be lower for the chlorine derivative than for the corresponding bromine derivative since chlorine has a larger +E effect than bromine. However, according to the data, AH* for m-chloroaniline (line 2) is slightly lower than for aniline, indicating that a +E effect is operative. With the chlorine in the orthoposition the effect is stronger (line 5 ) . With bromine in the ortho-position (line 18) the value of AH* is much lower than for chlorine, exactly the opposite relationship to that which would be predicted on the basis of the +E effect alone. This result, however, is not too surprising if both the -I effect and the +E effect are taken into consideration. The larger steric effect of the bromine atom as compared with chlorine is revealed by comparing AS* for these two solvents (lines 5 and 18).
*
81
Some of the solvents listed in Table I1 are basic type solvents other than aromatic amines (lines 8, 11, 16 and 21). A consideration of the data suggests that with these solvents malonic acid also forms a transition complex, the electrophilic atom of the acid coordinating with the nucleophilic atom of the soIvent. Particularly suggestive in this respect are the data on dimethyl sulfoxide and 2,6-xylidine (lines 21 and 22). The values of AH* and AS* for both these solvents are nearly equal. Furthermore, a certain analogy exists between the structures of these two compounds. Both contain two methyl groups symmetrically spaced between an electronegative, nucleophilic atom (a base in the Lewis sense). I n one case the nucleophilic atom is oxygen joined to sulfur, in the other it is nitrogen joined to carbon. It would appear, however, that the attraction between malonic acid and solvent is nearly equal in both cases, and that the malonic acid encounters nearly the same steric hindrance in coordinating with the coveted electrons. I n every case in Table I1 it is observed that the introduction of a substituent group which tends to increase the effective negative charge on the nucleophilic atom, either by a positive inductive or positive electromeric effect, brings about a corresponding lowering of the enthalpy of activation whlch is qualitatively consistent with the predictions which would be made on the basis of the electron theory of organic chemistry. Acknowledgments.-The support of this research by the National Science Foundation, Washington, D. C., is gratefully acknowledged. Valuable assistance was rendered by Miss Dolores Sicilia in purification of the reagents and running the kinetic experiments.
RADON SOLUBILITY I N FATTY ACIDS AND TRIGLYCERIDESlV2 BY E. NUSSBAUM AND JOHNB. HURSH Contribution from the Department of Radiation Biology, University of Rochester, Rochester, N . Y . Received July 19, 1967
Data are given for the Ostwald solubility coefficient CY' of radon in fatty acids, triglycerides, olive. oil and extracted animal fats. Fatty acids having 1-13 carbon atoms per molecule were equilibrated with radon a t 50,37" and at room temperature. Solubility, CY',at 37", increased with increasing number of carbon atoms per fatty acid molecule from 0.96 in formic acid to a broad plateau of 7.2 in the region of heptanoic acid. I n oleic and linoleic acids 01' was 6.7 and 6.3, respectively. I n olive oil and in extracted animal fats CY' ranged between 5.8 and 6.4.
I. Introduction Shortly after the discovery of radon by Dorn in 1900, solubility studies indicated that radon behaved as other inert gases with regard to its absorption by liquids. Yon Traubenberg was one of the first to investigate radon solubility in water. Studies on the temperature dependence of radon solubility in water and petroleum were conducted (1) Abstracted in part from a thesis submitted by E. Nusabaum to the Graduate School of the University of Rochester in partial fulfillment of the requirements for the Ph.D. degree. (2) This report is baaed on work psrfornled under contract with the U. S. Atomic Energy Commission at the University of Rochester Atomio Energy Project, Rochester, New Pork. (3) H. Rausch v. Traubenberg, Physik. 2.. 6 , 130 (1504).
by Hofmann4 who observed an inverse relationship between temperature and solubility. Koflers investigated radon solubility in aqueous, inorganic salt solutions and noted that in general the solubility decreased as the concentration of the solution or the molecular weight of the salt increased. Lurie6 investigated radon solubility as a function of temperature in water, in organic liquids, e.g., xylene, toluene, alcohols and vegetable oils. A high affinity for radon by the vegetable oils was noted and his observations have given rise to the frequently (4) R. Hofniann, ibid., 6, 337 (1005). ( 5 ) M. Kofler, ibid., 9, 6 (1508). (6) A. Lurie, Ph.D. thesia, Univ. of Grenoble, 1510.
82
E. NUSSBAUM AND JOHN B. HURSH
cited statement that radon is 125 times as soluble in olive oil as in water. In the absence of specific information regarding radon solubility in body fat, many investigators assumed it to be approximately equal to Lurie's value for radon solubility in olive oil as reported in the International Critical Tables' (a' = 18.3 at 40'). Recent reports have indicated that at 37' radon solubility as measured by a' in rat omental fatty tissue8 and in egg lecithingis 4.8 and 6.4, respectively, instead of the generally assumed value of 19. These reports have made it desirable to reexamine the value of radon solubility in olive oil as first reported by Lurie and as more recently confirmed by Strasburger'o and by Schrodt.ll I n seeking a possible explanation for the large difference in the values reported for radon solubility in vegetable oils as compared to animal fats, it may be noted that, in general, the constituent fatty acids in vegetable oil triglycerides contain a higher percentage of unsaturated acids, particularly oleic and linoleic, than do the animal fats. If radon solubility in unsaturated fatty acids were found to be markedly higher than in saturated fatty acids, this fact would help to explain the difference in reported results. Experiments were undertaken t o investigate radon solubility in fatty acids, in triglycerides and in several reference fatty substances including olive oil. 11. Experimental The equilibration apparatus consisted of a 220-ml. cylindrical glass vessel with a stopcock at either end. Radon a t a concentration of approximately 1 p c . per liter of nitrogen was admitted into the evacuated equilibration vessel. Five ml. of fatty acid was introduced, and the vessel was rotated about its long axis at 6 r.p.m. for 2 hours in a thermo-regulated water-bath. Samples of equilibrated fatty acid and duplicate samples of gas were withdrawn from opposite stopcocks of the vessel into evacuated 1-ml. glass bulbs. The use of a water-filled Lucite jacket surrounding the equilibration vessel retarded temperature changes when it was removed from the bath for withdrawing samples. The above sampling procedure is similar in principle to that described by Boyle.12 T o verify that a state of equilibrium was obtained in 2 hours, experiments were performed (i) for prolonged equilibration periods up to 24 hours, and (ii) under conditions in which the liquid lost radon to the gas phase during reequilibration. Radioactivity was assayed by counting the y-rays emitted by the short lived decay products in radioactive equilibrium with radon. Counting was done by means of a well-type sodium iodide crystal scintillation counter. Samples were generally counted sufficiently long to obtain a t least 10,000 counts. A t pica1 counting rate for gas samples was 2,000 counts/min./Yml.; normal background was 110 counts/min. (Less than 0.3% reduction in liquid sample count was caused by self absorption of -prays.) Solubility values.are expressed as the Ostwald solubility coefficient, a', equivalent to the ratio of net counts per min./ml. of fatty acid divided by the net counts per min./ml. of gas. A six hour waiting period was imposed between sample collection and counting to allow for decay of the large excess of radon decay products initially present in the equilibrated liquid. Experiments were carried out a t 50", and to the extent (7) E. W. Washburn, editor, "Intern. Critical Tables," 1st Ed., Vol. 3, McGraw-Hill Book Co.,New York, N. Y., 1928, p. 257. ( 8 ) E.Nussbaum and J . B. Hursh, Sci., 126, 552 (1957). (9) M. Tasca, Radiol. med. ( M i l a n ) , 2 T , 721 (1940). (IO) J. Strasburger, Deut. med. Wochschr., 49, 1459 (1923). (11) 0.Schrodt, Rdntgen-Praxis, 10, 743 (1938). (12) R. W.Boyle, Phil. Mag., 88, 840 (1911).
Vol. 62
that the acid was in the liquid phase, also at 37" and a t room temperature. Fatty acids and triglycerides used in the solubility studies were Eastman'3 grade (highest purity) except for hexanoic (practical), oleic (technical) and linoleic14(60%).
111. Results Table I presents the measurements of CY' at three temperatures in fatty acids, triglycerides, olive oil and extracted animal fats. Values given represent the mean16of from two to six experiments conducted at the temperature indicated except that at room temperature (18-28') values were normalized at 25' by first plotting the data as described below. Lannungl' has reported that a semi-logarithmic plot of the solubility a' vs. 1/T yields a straight line for a noble gas dissolved in an organic solvent. A straight line drawn through the data of Table I, thus plotted, gives a reasonably good fit except in the cases of acetic, propionic and octanoic acids. Results obtained with unsaturated fatty acids, oleic and linoleic, indicate that both the magnitude of CY' and the slope of the solubility-temperature curve are approximately the same for these acids as for the saturated fatty acids having six or more carbon atoms per molecule. It is seen from Table I that the solubility in fatty acids increases by a factor of six to seven as the carbon chain length increases from 1 to 4 carbon atoms per molecule. It appears that a broad plat,eau in radon solubility is attained in the region of 6 to 7 carbon atoms per molecule. TABLE I RADONSOLUBILITY COEFFICIENT IN FATTY ACIDSAND TRIGLYCERIDES
-
Substance
25'
370
50'
Formic acid Acetic Propionic Butyric Valeric Hexanoic Heptanoic Octanoic Nonanoic Decanoic Undecanoic Lauric Tridecanoic Acrylic Oleic Linoleic Triacetin Tributyrin Trihexanoin Trioctanoin Olive oil (USP) Olive oil (Italian) Butterfat Rat fatty acids (extracted) Human fat (extracted)
1.05 4.43 6.52 7.52 8.64 9.03 8.75 9.03 8.32
0.95 3.30 5.47 5.99 6.06 6.16 6.33 6.16 6.00
..
0.96 3.53 5.23 6.82 6.82 7.23 7.15 6.89 6.89 7.13 6.86
..
..
..
..
.. 8.10 7.96 3.42 6.42 7.25 7.55 7.70 7.71
.. ..
..
..
5.01 6.72 6..32 2.88 5.01 6.10 6.12 6.26 6.24 5.91 5.85 6.33
.. ..
5.93 5.95
.. 5.86
..
..
..
5.17 5.63
..
..
(13) Distillation Products Industries, Rochester, New York. (14) Nutritional Biochemioala, Cleveland, Ohio. (15) Detailed information regarding individual experimental temperatures and results is available elsewhere.*e (16) E. Nussbaum. Univ. of Rochester Atomic Energy Project Report, UR-503,1957. (17) A. Lannung, J . Am. Chem. Soc., 62, 68 (1930).
Jan., 1958
RADON SOLUBILITY IN FATTY ACIDSAND TRIGLYCERIDES
83
Radon solubility as defined by a' in the simple, where MI,dl and M z , dz refer to the molecular short chain triglycerides is 10-2570 lower than in weights and the densities of formic acid and the the constituent fatty acids. The data indicate comparison fatty acid, respectively, a t the reference that there is a convergence in value of a' in the tri- temperature. The values for a ' ~and 01'2 are obglycerides and the corresponding fatty acids as the tained from Table I. carbon chain length increases. I n fatty acids and triglycerides of biological prominence the difference in solubility may be insignificant. StrasburgerlO 20.0 Rn found that radon solubility in body fats was not different from that in the constituent fatty acids. 10.0I The value 5.85 for a' in fatty acids extracted ci from pooled samples of rat omental fat is in good agreement with the value 4.83 reported8 for a' in intact fatOy tissue inasmuch as theconstituent fatty acids were found to comprise 80-8570 of the volume of the tissue. Duplicate determinations of a' in fat extracted from one specimen of human abdominal fatty tissue yielded a mean value of 6.33. Imported Italian edible olive oil and USP grade were not significantly different in the quantity of radon they dissolved. IV. Discussion The values obtained for the solubility coefficient a' of radon in the fatty acids permit one to draw two inferences regarding the expected radon solubility in olive oil. (i) If radon solubility in olive oil is determined, largely, by the solubility of radon MOLECULAR WEIGHT. in the constituent fatty acids, an estimated value of Fig. 1.-Inert gas solubility in olive oil as a function of a' in olive oil at 37" is between 6 and 7 instead of 19 molecular weight of the gas, data from Lawrence Or as previously reported. (ii) The relative uniform- the Lurie I,and this report 0 . ity of a' in fatty acids containing 6 or more carbon atoms per molecule causes one to expect little djfference in solubility in oils from olives grown in different geographical areas and consequently having 451 characteristically different fatty acid composition. 40 Radon and other inert gases can be related with 35 regard to their solubility in olive oil. The data 6 compiled by Lawrence, et a1.,'8 for the solubility of ' 0 30nitrogen, argon, krypton and xenon in olive oil satIn isfies the linear relationship a = 0.00005M2~107 25 where a is the Bunsen solubility coefficientlg and M is the molecular weight of the inert gas. Our value for radon solubility in olive oil (a' = 6.25, a = 5.58) agrees well with the value which one would predict from such a plot shown in Fig. 1. The previous value for the radon solubility in olive oil 5 (a = 17) as determined by Lurie, departs markedly from the value predicted by this method. o ~d l l l , , l l l l l l l l To aid in understanding solubility a t the molec1 3 5 7 9 1 1 1 3 ular level, it is useful to determine the quantity20 of radon dissolved per molecule of solvent rather NO. CARBON ATOMS/MOLECULE. than per unit volume. At a given temperature, Fig. 2.-Radon solubility, SM(radon dissolved per molerelative radon solubility, SM,(quantity of radon cule of fatty acid relative to that of formic acid) is plotted dissolved per molecule of a fatty acid relative to the against the number of carbon atoms per molecule for a quantity dissolved per molecule of formic acid) can series of naturated fatty acids. be obtained as Figure 2 shows SMplotted against the number of Illid2cu'z carbon atoms. It is seen that a linear relationship SM = d42dia'i exists between the number of carbon atoms and the quantity of radon dissolved per molecule for fatty (18) J. H. Lawrence, et a[., J . Phueiol., London, 108, 197 (1946). acid molecules containing 4 to 13 carbon atoms. (19) T h e Bunsen solubility coefficient a is defined as the volume of gas reduoed t o 0' a n d 1 atmosphere which dissolves at the temperaV. Conclusions ture of the experiment in unit volume of solvent when the partial pressure of the gas is 1 atmosphere. This differs from a' which docs The solubility of radon per molecule of fatty acid not reduce the gas t o standard conditions. as measured by the Ostwald solubility coeficient (20) At the radon concentrations used in the experiments "quanappears to change in a regular fashion with the tity" of radon denotes a magnitude of 10-10 atoms of radon per molecule of fatty acid. number of carbon atoms per molecule.
I0l B
si
E. G. VASSIANAND W. H. EBERHARDT
For reasons advanced in the discussion of the paper it is concluded that the Ostwald solubility
Vo1. 62
coefficient for olive oil is 6.25 a t 37' rather than Lurie's earlier determined value of 19.
THE SPECTROPHOTOMETRIC DETERMINATION OF THE DISSOCIATION CONSTANT OF A CADMIUM-NITRITE COMPLEX1 BY E. G. VASSIANAND W. H. EBERHARDT Contribution from the Xchool of Chemistry of the Georgia Institute of Technology, Atlanta, Georgia Received J u l y SI, 1967
Spectrophotometric observations on mixtures of cadmium and nitrite ion giveOstrong indication of the formation of a complex or complexes between the cadmium and nitrite ions. The occurrence of an isosbestic point at 337 mp indicates that only a single cadmium-nitrite complex is formed within the range of concentrations studied. All measurements were made a t 25' in the pH range 3 to 6 in solutions at an ionic strength approximately 0.05 and also with the ionic strength adjusted to unity by addition of NaClO4. The experimental data are interpreted unambiguously in terms of a complex of formula CdNOZ+ with a classical dissociation constant of 2 X 1 0 - 2 in solutions of unit ionic strength.
Introduction The belief that a complex or complexes are formed when cadmium ion and nitrite ion are both present in aqueous solution is based on the differences between the absorption spectrum of mixtures of these two ions and the spectra of the two ions separately. The spectrum of nitrite ion in the spectral range 260-380 mp is well known. Solutions of cadmium chloride did not show any appreciable absorption in this spectral range. Therefore, the variation in spectrum of a solution of nitrite ion upon the addition of cadmium ion was attributed to the formation of a complex or complexes between the cadmium ion and nitrite ion. Figure 1 shows graphically the results obtained from the study of solutions having a constant formality of 0.0221 in potassium nitrite, but varying concentrations of cadmium chloride. The cadmium concentration varied from 0.0000200 to 2.00 F. The pH of all solutions was about 6.0. The existence of an isosbestic point in this system a t 337 mp implies either the existence of only two species containing the nitrite ion or a fortuitously identical molar extinction coefficient at the isosbestic wave length for two different species. Since the latter possibility seems unlikely, it will be assumed that only one complex ion containing the nitrite and cadmium ions exists in solution in the range of the nitrite ion concentration studied. It is well known that cadmium ion and chloride ion form a series of complexes in aqueous solution ranging from CdC1+ to CdCL-. In order to avoid complications resulting from these equilibria in the determination of the dissociation constant of the cadmium-nitrite complex, the cadmium ion was introduced into solution in the form of cadmium perchlorate. The spectrum of a solution of 0.0500 F CdC12 and 0.0221 F KNOl a t pH 5.50 did not differ appreciably from that of a similar solution containing 1 F NaC104 whereas the spectrum of a similar solution containing 1 F NaCl indicated the almost complete destruction of the cadmium-nitrite complex. From this evidence it appears that the presence of perchlorate ion has little effect upon the cadmium-nitrite equilibrium. (1) Based upon a thesis submitted by E. G. V. in partial fulfillment of the requirements for the degree of Master of Science.
Experimental Apparatus.-Spectrophotometric measurements were made with a Beckman DU spectrophotometer equipped with a photomultiplier detector and a thermostated cell compartThe conventional hydrogenment maintained a t 25 f.'1 discharge light source and quartz absorption cells of path length 1.001 and 1.004 cm. were used. The pH was adjusted with perchloric acid and determinations were made with a Beckman model H2 p H meter. Reagents.-Merck reagent-grade potassium nitrite was analyzed for nitrite content according to the method recommended by Kolthoff and Sandell.2 The cadmium perchlorate was prepared by treating J. T. Baker C.P. cadmium carbonate with Baker's 70-72% perchloric acid and boding to remove the HzCOs. The resulting solution of cadmium perchlorate was analyzed by pipetting a measured volume into a platinum crucible, addin several ml. of 9 F H?SOd and evaporating to dryness. Tfe crucible was then heated at 500' in an oven for one hour, cooled, and the contents weighed as cadmium sulfate. The sodium perchlorate was prepared by neutralizing an aqueous solution of sodium hydroxide with perchloric acid.
Results and Discussion Reduction of the Data.-The equilibria which are important in an aqueous solution containing Cd ++, NOz- and Clod- are
+ + +
Cd++ n N O z Cd++ pOHC d + + pC104HNOp = H +
+
= Cd(N02),2-" = Cd(OH)p2-p = Cd(C104)q2-g NOn-
(a)
(b) (0) ( 4
The pH a t which these studies were conducted was chosen as a compromise between equilibria b and d. Values of the pH around 3 to 4 are sufficiently high so that no appreciable decomposition of HNOz is observed during the time of the measurement and equilibrium d introduces little uncertainty in the concentration of the nitrite ion. This equilibrium must, however, be considered in the quantitative treatment of the data. This pH range is also sufficiently low so that equilibrium b may be ignored. Studies in the pH range 3.30 to 3.90 may be interpreted consistently without introducing it. The experiment outlined in the introduction suggests that equilibrium c also may be ignored. In a particular experiment, the formality of the Cd ++ and NOr- is known, the H+ activity is deter(2) I. RI. Kolthoff and E. B. Sandell, "Textbook of Quantitative Inorganic Analysis," The Macmillan Co.. New York, N. Y., 1952. p.
674.
1
