NOTES
Nov., 1958
i457 ,
TABLE I:
SWELLINQ OF
Wo OL
Wt. of wool
Solution
(P.1
AND
PREFERENTIAL SORPTION OF WATER FROM SALT SOLUTIONS AT 25’ ---Concn. Initial
(M)Final
Water sorbed preferentiallyG (% on wt. of d r y wool)
Swellingb
(%)
Effective pressure” (bar)
Water 33d 18 0 NazSz03 (2 M ) 5.003 2.004 2.043 29 12 (1700) Na&03 (satd.) 5.010 3.818 3.898 30 6 (3300) Na2S04 (satd.) 1.9 12 1600 NaCl (2 M ) 4.996 2.012 2.039 20 14 540 NaCl (satd.) 5.008 5.193 5.278 24 13 1400 NaNOj (2 M ) 2.0 16 400 NaN03 (satd.) 7.9 11 1600 NaCNS (2 M ) 5.011 2.015 2.013 0 19 (350) NaCNS (satd.) 4.992 8.917 9.086 28 10 (1600) a Calculated from the increase in concentration of salt solution. b The figure given for each solution is the mean of the measured swellings for five fibers. The standard deviations of the means were in all cases f 1. From ref. 10; the figures for NazSz03and NaCNS were calculated assuming the increase in effective pressures per mole to be the same as for NatSOa and NaI, respectively, although NaCNS almost certainly would give lower pressures than NaI. Accepted value for the water sorbed by wool in an atmosphere at 100% R.H. or in pure water.13
havior is similar to gelatin,2 where, however, the CNS- solution showed a decrease in concentration.) The water sorbed by wool from thiosulfate solutions is approximately equivalent to that taken up from pure water if no salt has been sorbed. Although the wool is therefore fully hydrated in thiosulfate solutions, it swells less than in pure water (analogous to the effect of SO4- on gelatin). Wool swells to approximately the same extent in 2 M NaCNS as in water alone, the solution being sorbed as such so that either the water which can be sorbed preferentially by wool now contains 2 M NaCNS, or, alternatively, NaCNS is sorbed a t specific sites a t the same time as water. It is perhaps unlikely that the combination of these latter two effects would lead to the concentration of the solution remaining constant, but the present results do not allow a distinction to be made between the alternative explanations. Saturated Na2S04 solution (1.9 M ) is similar to 2 M NazSz03whereas 2 M NaCl and 2 M NaN03 are intermediate in behavior between NazS2O3and NaCNS. Thus, in electrolyte solutions where ion-water interaction is high (SzO3-), and soluble non-electrolytes are salted out, proteins such as wool and gelatin are prevented from swelling due to the increased internal pressure of water brought about by ionwater forces. In the 2 M solutions studied, swelling increases with decreasing effective pressure of the solution, until, in 2 Af NaCNS, swelling may be slightly greater than in water alone. A further effect would arise from the protein containing a solution of high ionic strength when the effective pressure is low. This would reduce interaction between polar groups and allow the structure to be more easily disrupted. The effect on the swelling of wool of 2 M CNS- is small but might be expected to show up more clearly in other properties of wool or with soluble proteins. When saturated solutions are compared, rather than a series a t given concentration, the solubility of the salts needs to be considered since, even though the increase in effective pressure per mole may be low, the effective pressure of the saturated solution may be large if the salt is highly soluble. This appears to be the case with NaCNS. As(13) P. Alexander and R. F. Hudson, “Wool. Its Chemistry and Physics,“ Chapinan and Hall Ltd., London, 1954, p. 126.
suming a linear relation between effective pressure and molarity, the saturated salts in Table I should give approximately the same pressure and therefore swelling, except Na2S203where the pressure would be much greater and the swelling consequently lower. This is approximately true. It generally has been considered that the properties of wool in concentrated salt solutions are those of wool in an atmosphere a t the relative humidity above the solutions. The wool would then contain less sorbed water and would be swollen less than in dilute aqueous solutions. However, this would mean that the series of 2 M salt solutions should all have had approximately the same effect on wool. Also, the swelling in saturated thiosulfate solution is less than expected from the decrease in vapor pressure (6% found compared with 9% calculated), while the water sorbed (containing no electrolyte) is greater than expected (30% found compared with 18% calculated). Properties of proteins such as swelling, solubility, denaturation, thermal shrinkage, etc., which are influenced by salt solutions, can be thought of simply as general configurational changes. Certain ions in water, e.g., CNS-, I-, promote such changes since the solutions exert a low effective pressure, or the ions may perhaps ‘Lloosen”the water structure, and the protein then contains solutions of high ionic strength. Other ions in water, e.g., SO4=, prevent or considerably retard the rate of these structural changes since the solutions exert a strong effective pressure and the water sorbed by the protein coiitains no electrolyte. Acknowledgment.-I am indebted to Dr. M. Lipson and Dr. J. H. Bradbury for many most helpful discussions and to Miss L. Boardman for assistance with experimental work.
KINETICS OF HYDROLYSIS OF DECABORANE BY R. W.ATTEBERRY High Energy Fuels Division, Olin Mathieson Chemical Corp., Niagara Palls, N . Y. Receiued M a y B 1 , 1968
Kinetic studies of the alcoholysis of decaborane’ show that reactions with secondary alcohols possess
NOTES
1458
lower activation energies than the slower reactions with primary alcohols. Recently, studies of exchange between decaborane and deuterium oxide2 indicate that hydrogen at the bridge positions exchanges very rapidly, and that terminally-bonded hydrogen exchanges slowly in dioxane as solvent. Corroboration of the exchange experiments has been obtained by the following techniques: 0.5-1.0 gram samples, a, of decaborane (B10H14)were added to flasks, equipped with stirrers and water-cooled condensers, immersed in constant temperature baths. At the start of the experiment, ca. 450 ml. of distilled water, pre-equilibrated thermally, was added to each flask. Aliquot samples were removed as a function of time, quenched in ice-water,
Vol. 62 TABLE I HYDROLYSIS RAT^ DATA Temp.,
80
100
OC.
ti/,, hr. k , (sec.)-l
4.5 4.27
x
10-5
13.5 1.43 X
E,,kcal. mole-' 14.5 measured conductimetrically by Guter and Schaeffer for initial dissocciation of decaborane in aqueous dioxane.3 Therefore, of the two mechanisms offered for dissociation of decaborane in aqueous media, a ion-dipole hydroxylation of boronhydrogen bonds appears more plausible. (3) G. A. Guter and G. W. Schaeffer, ibid., 78, 3546 (1958).
TITRATION OF DECABORANE IN NITROGENEOUS SOLVENTS
1-
0.8 I -
BY R. W. ATTEBERRY High Energy Fuels Division, Olin Mathieson Chemical Corp., Niaoara FalEs, N . Y . Received May $1, 1968
Guter and Schaefferl have described the pK titration of decaborane, Bl0HI4,as a strong monoprotic acid in water-dioxane mixtures. The procedure suffers the disadvantage of simultaneous hydrolysis of the decaborane, such that precision of the method is somewhat dependent upon the rate of addition of titrant. Schaeffer2 has described the complex formed between decaborane and acetonitrile. Bridge hydrogen vibrations appearing in the infrared spectrum of decaborane a t 5.3 and 6.4 p disappear in the infrared spectrum of the complex, suggesting that the nitrogen has donated electrons to the electrondeficient bridges of the decaborane. Heating of the complex liberates hydrogen to form bisacetonitrilodecaborane, (CH3CN)2B1oH12. It was found that whenever decaborane was dissolved in an excess of acetonitrile, such that the complex had been formed, the resulting solution I could be titrated quantitatively with aqueous I I I I alkali with a precision of three parts per thousand. 10 20 30 Figure 1 shows the typical pH titration curve, emHours. ploying glass and calomel electrodes. Fig. 1.-Hydrolysis of decaborane. As evident, the pH titration curve of decaborane in acetonitrile is typical of a weak monoprotic acid and titrated with standard base to a phenol- with pKa = 3.5. This titration serves as an admirphthalein end-point. Excess mannitol, ca. 4 g., was able assay for decaborane, with an inherent color then added, and the sample was retitrated to change a t the end-point from lemon-yellow to phenolphthalein end-point to measure X, the con- straw. centration of boric acid Although acetonitrile has an appreciable dielectric constant of 36, the effect of a nitrogeneous solB~oHlr 30Hz0 +10B(OH)3 + 22H2 vent with the same dielectric constant offering Figure 1 is a first-order plot of the data, indicating hydrogen bonding opportunities was sought. Figsimultaneous, or parallel hydrolytic reactions. ure 2 shows a titration curve of decaborane in The more rapid reactions are evidently hydrolyses N,N'-dimethylformamide as such an example. a t the bridge positions, with subtracted half-times Although the precision of titrations of decaborane of ca. 0.25 hour (dotted portions). The slower in N,N'-dimethylformamide is only ca. 4%, it is reactions are dependent upon temperature. strikingly significant that decaborane becomes a This activation energy is similar to the values stronger diprotic acid in this solvent. Moreover, for secondary alcohols1; it equals exactly the value the first inflection at pH 1.2 occurs at exactly one
+
(1) H. C. Beachell and T. R. Meeker, J . A m . Chem. Boc., 7 8 , 1796 (1956). (2) M. F. Hawthorne and J. J. Miller, ibid., SO, 754 (1958).
~~
(1) G. A. Guter and G. W. Schaeffer, J . A m . Chem. (1956). (2) R. Schaeffer, ibid., 79, 1006 (1957).
SOC.. 78, 3546
