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COMMUNICATIONS TO TEIE BITOR
VOl. 68
TRULKYLSILYL SULFATES
several coexisting species of ions of the same sign in solution could be determined unequivocally Treatment of a concentrated sulfuric acid solu- only if specific electrodes, which are lacking for tion of a hexa-alkyldisiloxane with ammonium many common ions, could be used. Attempts to chloride or fluoride gives the trialkylchlorosilane overcome this ditliculty indirectly have been only Sir:
indifferently successful. I should like to point out that the Gibbs-Donnan membrane equilibrium principle permits a solution of this problem in a general manner by consideration of the ion distribution ann of the membrane potential. Membranes of extreme ionic make the new method widely applicable, permitSOI EtsiOSii +(Mi)2so, ting the measurement of membrane equilibria under particularly favorable conditions with gives a much lower yield. Hexamethyldisiloxane, 100 g., 0.62 mole, was speed and accuracy.z~4~sIt is however not exadded slowly with cooling and vigorous agitation clusively restricted to these simple conditions. A solution I contains the anions R- and NO,-, to 85 g. of fuming sulfuric acid containing 20% the activities SOs. The cold solution was extracted with six and the cations IC+,Na+ and "I+, ) I to be 100-cc. portions of dry pentane. After removal of which (uK+)I, (aNa+)I and ( u ~ , + have of the solvent under reduced pressure, the liquid determined. A "permselective" membrane perresidue changed on cooling to a mass of white meable to all cations and impermeable to all crystals. Treatment of the sulfuric acid layer anionsl.aJJ separates solution I from a KCl soluwith water gave a recovery of 26% of the disilox- tion I1 of known concentration. Solution I1 is iso6smotic with I, or is made isoosmotic by the ane used. The filtered sulfate, m. p. 5f3-58', weigh$d 76 g., 69% yield based on unrecovered addition of non-diffusible non-electrolyte.6 The disiloxane. The sulfate must be handled in a dry volume of I is made S t e l y larger than that of I1 atmosphere as it fumes vigorously in ordinary air. so that the composition of I is not changed signifiTreatment with water gave hexamethyldisiloxane. cantly after equilibration with 11. After the system is equilibrated the membrane Titration of the sulfate with standard alkali gave a neutral equivalent of 117; calcd. 121. Carbon potential E is measured and solution I1 analyzed. was determined by wet combustion with dichro- The final state of the system is mate, sulfuric acid and silver chromate. I I1 Anal. Calcd. for CsHlsSi2S04: Si, 23.1; SO4, [ K + h[Na+11W"H+II[R-II INoI-I1(1 [K+III[Na+l~~[NH,+lxr [C~-~II 39.6; C, 29.6. Found: Si, 22.7; SO, 40.4; C, The activities of the cations in I1 ((LK+)II, 29.7. (aNa+)II and . ( u N ~ + ) I I are calculated from the Triethylsilyl sulfate, b. p. 170' a t 12 mm., @D known analyhcal concentrations according to the 1.4442, was prepared similarly. With water it DebyeHiickel theory. gave the original disiloxane and sulfuric acid. The Gibbs-Donnan theorem postulates for the Anal. Calcd. for CUH&i&O4: Si, 17.2; S04, ion distribution 29.4; neut. equiv., 163. Found: Si, 17.2; SO,, 29.5; neut. equiv., 166. We thank :R. N. Walter of this Laboratory for and for the membrane potential the analyses reported in this Communication. or the corresponding fluor0 compound.' During a study of the mechanism of this reaction we have obtained two tklkylsilyl sulfates, the first examples of sulfuric acid esters of silanols. The trialkylsilyl sulfates are obtained by the action of funiing sulfuric acid on hexa-alkyldisiloxanes. Concentrated sulfuric acid
(1)
Cf. Flood, 'Ims JOURNAL, 56, 1735 (1933).
L. H. SOhWdER DEPARTMENT OR CHEMISTRY E. W. PIETRWA THEPENNSYLVANIA STATE COLLEGE G . T. KERR F. C. WHITMORE STATE COLLEGE, PENNA. RECEIVEDNOVE~~BER 16, 1945
DETERMINATION OF THE ACTIVITIES OF SEVERAL COEXISTING IONS BY THE GIBBS-DONI" EQmLIBRXJM WITHOUT THE USE OF SPECIFIC ELECTRODES
Sir: The electrometric determination of the activities of ions for which speciiic electrodes do not exist has recently become possible in solutions of single electrolytes by the use of "membrane electrodes."lV2 Heretofore, however, the activities of (1) K. Sollner. Tms JOURNAL, 66, 2260 (1943). (2) H. Gregor, 1'h.D. Thesis, Minneapolis, 1945.
The unknown activities of the cations in solution I (uK+)I, (QNP+)I and (UNH.+)I can be evaluated from equation (2). The new method should be of particular interest in colloid chemistry and physiology. D E P ~ T M BOF N TPHYSIOLOGY Umvmw~ OF~MI"E~OTA MINNEAFWLIS 14, MINNESOTA Kaar. SOLLNRR RECEIVEDD R C E ~ ~6,1945 ~ER (3) K.Sollner, J . Phys. Chen., 4S, 47,171 (1945). (4) K.Sollner, ibid., 40,265 (1946). (5) K. Sollner and H. Gregor. Trm JOURNAL. 67,346 (1945).
(13) This precaution is actually unncmssary; cation exchange eqnilibrium is reached mthomt significant osmotic water movement.'
