1177
SINGLEIONCONDUCTANCES IN NONAQUEOUS SOLVENTS
pH dependence of the half-life, but the pH dependence of the yield depends on ionization of OH to 0-. An alternative mode of forrnation from 02-.and an oxygen atom, of which the presencs in irradiated water has been suggested,27would not account for the appearance of this species only a t pFI 3 10. Another possible identity of the species would be 034,the doubly dissociated form of 1 3 2 0 3 , which has been proposed in acid solution. In this case the pH dependence could be explained by a decay through
HOa-.28 Acknowledgment. We are greatly indebted to Mr.
Douglas Harter, whose technical assistance has been very helpful to this investigation. We are grateful also to Mr. E. Backstrom, who operated the linac. The advice of Dr. S. Gordon concerning the use of the xenon lamp was very helpful. It is a pleasure to acknowledge the helpful discussions with our colleagues, Drs. J. Rabani and M. S. Matheson. (27) A. 0. Allen, Radiation, Rea. Suppl., No. 4, 54 (1964). (28) NOTEADDED IN PROOF.-J. W. Boag. in a publication which has recently appeared [ A m . J . Roentgenol., 90, 896 (1963)],reports a transient absorption in oxygenated water with A,, 2450 A. Although no information is given concerning pH, it appears this is 02-, and is in close agreement with our observation.
Single Ion Conductances in Nonaqueous So1vents1p2
by Michael A. Coplan and Raymond M. Fuoss Contribution N o . 1766 from the Sterling Chemistry Laboratory, Yale University, New Haven, Connecticut (Received December 14, 1965)
Conductances in methanol at 25’ are reported for the following salts: sodium picrate, potassium picrate, tetra-n-butylammonium picrate and tetraphenylboride, and triisoamyln-butylammonium iodide, picrate, and tetraphenylboride. Using Gordon’s transference data for sodium and potassium ions in their chlorides in methanol and Ihnee’s value Xo(BPH4’) = 36.50, the following single ion conductances were derived: Xa(Bu4N+) = 39.36 f 0.14, Xo(AmaBuN+) = 36.74 f 0.11, and Xo(Pi’) = 46.87 f 0.03. Triamylbutylammoniurn (TAB) tetraphenylboride is thus shown to be an electrolyte for which Xo+ = Xo- = A o / 2 within 1%, and may therefore be used as a reference electrolyte to establish single ion conductances in other solvents.
Two earlier approximate methods have been proposed to obtain single ion conductances in nonaqueous solvents by halving the limiting conductance of a salt made up of two large ions which were assumed to have equal conductances. Fowler and Kraus3 used tetrabutylammonium triphenylborofluoride and triphenylborohydroxide, and Fuoss and Hirsch4 the tetraphenylboride. A recent determination of the conductance of the tetraphenylboride ion in methanol6 makes it possible to test the assumption. We have determined the conductance in methanol of sodium,
potassium, and tetrabutylammonium picrates, and used Gordon’s values6 for the single ion conductances (1) This paper is based on part of a thesis submitted by Rliohael A . Coplan to the Graduate School of Yale University in June, 1963, in partial fulfillment of the requirements for the degree of Doctor of Philosophy. (2) Grateful appreciation is expressed to the Donors of the Petroleum Research Fund, administered by the American Chemical Society, for support of this research. (3) D. L. Fowler and C. A. Kraus, J . Am. Chem. Soc., 6 2 , 2237 (1940). (4) R. M. Fuoss and E. Hirsch, ibid., 82, 1013 (1960).
Volume 68,Number 6
M a y , 1964
MICHAEL A. COPLANAND RAYMOND M. Fuoss
1178
of sodium and of potassium to evaluate the single ion conductance of the picrate and thence that of the tetrabutylammonium ion in methanol. The result is Ao(Bu4N+) = 39.36 f. 0.14, which is about 8% greater than Kunze's value Ao(BPhe') = 36.50 ==I 0.05. I n order to obtain a salt which would more satis= Ao(-) factorily permit the approximation A,(+) = A0/2, we made triisoamylbutylammonium (TAB) iodide, picrate, and tetraphenylboride. From conductance measurements in methanol on these salts and other results, we find &(TAB) = 36.74 f 0.11, well within 1% of the conductance of the tetraphenylboride. We plan to use this salt as our future reference for single ion conductances in nonaqueous solvents.
Experimental Materials. Sodium picrate was prepared by neutralizing recrystallized picric acid with sodium hydroxide in ethanol. The product was recrystallized twice from absolute ethanol (7 g./lOO ml.) and once from water (4 g./lO ml.). The monohydrate was dried in an Abderhalden drier a t 132' (chlorobenzene) and 1 p for 5 days (d 1.940). Potassium picrate was prepared in a similar fashion, and was recrystallized three times from water (10 g./lOO ml.). This salt does not form a hydrate; i t was dried a t 100' and 1 p for 1 day (d 1.852). Tetrabutylammonium picrate was from laboratory stock, m.p. 91.6-91.9'. It was dried a t 58' (acetone) and 1 p ( d 1.116). Tetrabutylammonium tetraphenylboride from laboratory stock was recrystallized from petroleum ether (b.p. 60-80')acetone (1 g. of salt in 25 ml. of acetone, add ether to cloud point, filter, and add balance of 100 ml. of ether) to fine white needles, melting a t 236.6-236.8' jn a sealed capillary (d 1.023). Triisoamylbutylammonium (TL4B) iodide was prepared by heating Eastman triisoamylamine and n-butyl iodide in ethanol at 85' for 26 hr. (9.0 g. of amine, 7.3 g. of iodide, and 8 ml. of ethanol). Crude product was obtained by pouring the reaction mixture into 100 ml. of water; the dried precipitate was washed with petroleum ether and then dried a t 50' for 4.5 hr. in the vacuum oven (yield, 60%). Heating a second batch for 46 hr. raised the yield to 80%. The salt was recrystallized three times from 3 : 1 ethyl acetatepetroleum ether (10 g./lOO ml.), m.p. 119O, d 1.229. TAB picrate was prepared from the hydroxide (from the iodide and silver oxide) and picric acid. It was recrystallized three times from propanol (22 g./lOO ml.) ; i t is necessary to cool slowly or the salt may separate as an oil which congeals to lumps, m.p. 94.2-94.8', d 1.139. TAB tetraphenylboride was prepared by adding a 3% solution of TAB iodide in methanolThe Journal of Physical Chemistry
water to a 2% aqueous solution of sodium tetraphenylboride. The precipitate was thoroughly washed, and then recrystallized three times from 3 : 1 acetonewater (1.5 g./lOO ml,), m.p. 274-275') d0.967. Methanol was dried by refluxing 2-1. batches over 12.5 g. of aluminum foil and 2.5 g. of mercuric chloride for a t least 6 hr. under nitrogen. ,4 conductance cell on the end of the condenser monitored the solvent, which mas distilled directly into a solvent storage flask, from which it was pumped into the conductance cell by dry nitrogen. The solvent conductance varied from 1 to 5 X lo-*, d 0.78655 f 2 a t 25'. Methods. Electrical equipment, cells, and general technique were as described by Lind and F ~ o s s . ~ All solutions were made up by weight; volume concentrations c (equivalents per liter of solution) are related to weight concentrations w (equivalents per kilogram of solution) through the density, c = wp. At low concentrations, p = p o ( l rw). Values of y were
+
Table I : Conductance of Picrates in Methanol a t 25" (Superscripts Designate Series of Determinations) 104~ -----NaPi---
4.2338 8.499 12.423 16.308 21.008 4.571b 9.179 13.635 17.996 22.646 4,452O 12.894 17.103 21.837 4.06sd 8.312 12.106 16.017 20.318
A
87.03 84.93 83.46 82.24 80.97 86.80 84.60 83.00 81.71 80.52
86.94 83.32 82.04 80.82 87 20 85.04 83.59 82.37 81.17
---KPi--
4.466a 9.038 13.464 18.450 22.131
93.48 90.90 89.00 87.24 86.12
104~
5.l3lb 10.346 15.346 19.966 25.544 4.081O 8.296 12.177 16.420 20.638 4.713d 9.522 13.883 18.794 23.063 8.524" 13.177 17.133 21.515 25.442 29.762 33.687 38.564 43.144
A
93.13 90.39 88.41 86.84 85.24 93.85 91.38 89.64 88.08 86.69 93.44 90.83 89.01 87.33 86.03 91.37 89.36 87.92 86.56 85.46 84.38 83.47 82.41 81.50
104~
A
4 150"
81 06 78 80 77 40 7
