Nov 1958
NOTES
with active hydrogen, as is the case with N,N'dimethylformamide, then I could have one of its four hydrogen bridges substituted by a nitrogen bridge and a strongly-acidic proton before the tautomeric equilibrium is affected in the manner described above.
8
%
1459
6
THE SOLUBILITY OF SOME CHLOROMETHANES I N WATER' BY JAMES E. BOGGS AND A. ERWIN BUCK,JR.
4
Department of Chemistry, The University of Tezas, Austin id, Texas Received M a y 29. 1968
2 4
I
I
6 8 Meq. of base per gram of sample. 2
4
Fig. 1.-Titration
of decaborane in acetonitrile.
2 4 6 8 Meq. of base per gram of sample. Fig. 2.-Titration
of decaborane in N,N'-dimethylformamide.
In connection with certain kinetics studies we have determined the solubility of CHsCl, CHzFCl and CHFzClin water as a function of temperature. Experimental
A flask, of accurately known volume, was supported in a
thermostated oil-bath and connected to a vacuum line, a manometer and a second smaller flask containing water. After evacuation, the flask was fi11ed with gas to a desired pressure and allowed to stand until temperature equilibrium was established. The connections from the flask were made of capillary tubing so that their volume was negligible. Then an accurately measured volume of boiled distilled water was drawn in (the pressure inside the flask still being less than atmospheric). The flask and contents were then shaken until the indicated pressure became constant. If P I is the pressure of the gas alone in the flask. at .the temperature of the experiment, P2is the final equillbrrum pressure, Pa is the vapor pressure of water at the temperature of the experiment, VI is the volume of the flask and VB is the volume of water admitted corrected for the temperature change, the pressure of gas in equilibrium with the solution is PO - Pa and the molar concentration of the gas dissolved is C - P'Vl - (Pz - Pd(V1 - Vd VzRT It is assumed that the gases obey the ideal gas law, that a t the low concentrations involved the va or pressure of water from the solution is the same aa that $om pure water, and that the volume change in the liquid phase is negligible. The authors wish to express their appreciation to Dr. W. B. McCormack of E. I. du Pont de Nemours and Co. for supplying us with a sample of CHZFC1.
Results fourth the stoichiometry of the second inflection The results of the solubility measurements are at pH 6.0. These facts permit several speculations about the structure of decaborane molecules. shown in Table I, which lists values of K = (molar A tautomeric equilibrium between form I, con- concentration of solution)/(gas pressure in atmostaining four hydrogen bridges, and form 11, con- pheres). From 2 to 5 determinations were made taining two hydrogen bridges, exists in decaborane, a t each temperature, the average deviation of the individual results from the mean being a little over as 1%. At the low concentrations resulting, all of the solutions showed excellent agreement with Henry's law. It will be noted from Table I that, over the temperature range studied, CHzFCl is a little more f - H soluble than CHaCl but CHFzCl is appreciably less soluble than either. The solubility of CFaCl is too low to be measured by our techniques. The thermodynamic quantities AFO, ASo and AHo, for the transference of one mole of organic chloride from the gas phase a t unit pressure to a I I1 111 hypothetical solution of unit activity have been Whenever a nitrogeneous solvent is used, the evaluated and are shown in Table 11. equilibrium is shifted to the right, the two electronFigure 1 shows a plot of A H 0 vs. absolute temperadeficient hydrogen bridges of I1 being replaced by ture. It can be seen that within experimental an electron-donating nitrogen bridge. If the nitro(1) The authors are grateful to the Research Corporation for finangeneous solvent is capable of hydrogen bonding aid support of this investigation.
1460
NOTES
Vol. 62
gas and water is independent of temperature. From the graph, AC, is 70 cal. deg.-l for CH3CI, 45 csl. deg.-' for CHZFC1, and 85 cal. deg.-' for CHF2C1. -2 Discussion The large values of ACp observed for the dissolution process probably can be attributed almost entirely to the effect of increased temperature on the extent of hydration of the dissolved organic chloride. The fact that ACp is essentially constant for a given substance implies that, for the tempera-4 ture and concentration range we have covered, the product AH,(dn/dT) is also constant, where AHr is the differential heat of reaction for the dehydration process and dn/dT is the number of moles of organic halide dehydrated per degree increase in temperature. Over a small enough range both of these may be essentially constant, but even if they vary individually they will vary in opposite directions so that -6 the net effect will be minimized, As the dehydration proceeds, the most loosely bound molecules of water will be lost first, so that AHr will gradually increase with temperature and dn/dT will decrease. / 0 CHFICl There is a rough correlation between the solubility of the fluorinated chloromethanes and their di-0 pole moments. The dipole moments of CHaCl, 290 310 330 350 CHFzCl and CF3C1are 1.87,21.413and 0.4,4respecT tively. The dipole moment of CH2FCl has never Fig. 1.-Heat of solution as a function of temperature. been measured. The dielectric constant measurements of Boggs, Crain and Whiteford5 a t a freTABLE I quency of 9400 megacycles would indicate a miniSOLUBILITY OF FLUORINATED CHLOROMETHANES. mum value of the dipole moment of CHzFCl of K = C/P 1.82, but because of the effect of inversion dispersion6 CHsCl CHaFCl CHFnCl CFaCl T , OK. the true dipole moment must be somewhat higher 283.4 0.167 0.244 0.0606
