her gratitude to l)r. Jones and Dr. Sorensen for reading the manuscript, and for making available their unpublished data. THEKEWYORKBOTAXICAL GARDES BRONXPARK SEW YORK,S.P RECEIVED OCTOBER 29, 1951
Non-exchange of Radiocyanide and Radiosullide Ions with Aqueous Thiocyanate Ion1 BP ARTHWW. ADAMSOX AND PHILLIP S.MAGEE The exchange reactions of Cl4NN-and S3j=ions with thiocyanate ion have been investigated with essentially negative results.
Ai1 alternative iiiechanisiii, in the case of the cyanide thiocyanate system, might be considered to be an exchange of sulfur through the intermediate NCSCN-2, but one is confronted with the impossibility of writing a structure for this species without exceeding the octet on carbon or invoking an improbable imide formulation for the cyanide group. It is noteworthy, however, that the analogous intermediate 03SSS03-4 has been proposed for the measurable exchange between sulfite and t h i o s ~ l f a t e . ~Here, however, structures of some a priori plausibility can be written since it is not unreasonable to exceed the octet on sulfur. Somewhat similar considerations serve to rationalize the lack of exchange of sulfide and thiocyanate, in contrast t o the measurable exchange of sulfide with thiosulfate.? ( 7 ) D. P. Ames a n d J. E . Willard, THISJOURKAL,73, 164 (1831).
DEPARTMENT OF CHEMISTRY UXIVERSITY OF SOUTHERK CALIFORNIA L O S ANGELES, CALIFORXIA RECEIVED JULY 31, 1951
Experimental The KC1*S solution was prepared from BaCI403 by the method of Adamson,2and that of NazSa5by the addition of sulfate-free BaS35.3 The exchange experiments were carried The Kinetics of the Thermal Decomposition of out by mixing the appropriate solutions in small centrifuge Aluminum Borohydride1 tubes which were then sealed. Those containing sulfate were sealed in a nitrogen atmosphere. 131' k C H . 4 R D s.BROKAXA S D ROBERT s. P E A S E After the elapse of the desired time, the 'separation of radiocyanide and thiocyanate ions was carried out by the Schlesinger, Sanderson and Burg2 have observed precipitation of zinc cyanide. The zinc cyanide was that as the temperature is raised aluminum boropurified by reprecipitation and then treated by the distillation and sample preparation method previously r e p ~ r t e d . ~hydride (AI(BH4),) decomposes yielding hydrogen The separation of radiosulfide and thiocyanate ions was ac- and solid products. This research was undertaken complished by precipitation of cadmium sulfide. The in order to obtain more detailed information as to cadmium sulfide was subjected to a fairly elaborate purifi- the nature of the pyrolysis. Preliminary observacation before being counted, in order to remove coprecipit i o n ~of~ pressure-time curves a t temperatures of tated thiocyanate ion. The samples of zinc cyanide or of cadmium sulfide were counted with a mica end window 130' and higher showed the initial slopes of such counter (2 mg./cm.2 window) and with an atmospheric curves to be proportional to the initial aluminum pressure flow counter, respectively. borohydride pressure, suggesting that the decom$pproximate corrcctioris for self absorption \yere inade. '1'ABL.ll
EXCHASGE
OF
KADIOCYAXIDE
I WITH
'rHIOCYAXA1 E
IN
AQUEOUSSOLUTIOX (KSCK) = 0.19f; ( K C t 4 S ) = 0.59.f P 1%
Temp., "C
Exchange time, hr.
11 10
2-1-
140
12.70
24
:::;1
1'L.iO 14.0 14.0 05
fjr I
Iio
. 'LA
L'I
1%
(iil
16;;
.65 lo
24 Ikfined a i in reference .i.
I ti0
',I
0 . 80 61
2 "fi
The data given in Table I are representative of the rather larger total amount of results obtained, and indicates no measurable exchange, with the possible exception of the \ysteni at pH 0.5. The results with radiosulfide agree with thosc reported in this iswe by Heisig and Holt5 in that no exchange w i ~ sfound i n solutions (1.3 ,f in KSCS and 0.05 f i n Xa2S at room temperature, after 204 hours . L t />ti lL'.ti, :ind after ,554 hours at PH 13.4. These findings of negligible exchange are in accord with the difficulties of formulating potential mechanisms. Thui, the fact that the free energy for the primary dissociation of thiocyanate into sulfur and cyanide ion is positive by 16 kcal.6 is in agreement with the fact that this path does not lead t o exchange. (1) These investigations were carried o u t under contract N6onr23809 between t h e University of Southern California a n d t h e Office of Naval Research. (2) A. W.Adamson, THISJOURNAL, 69, 2564 (1947). (3) T h e tracers were obtained from t h e Atomic Energy Commission. 14! A. W.Adamson, J. P . Walker a n d M. Volpe, THIS JOI:RNAL, 72, 40.30 (1950). 13: CTr. E. Heisig a n d R. Holt, ibid., 74, 1597 (19521 6 ) 11.. &I. Latimer, " l h e Oxidation S t a t e s of t h e I.;lements," I'rentice-Hall, Inc , S e \ r York. S . T , !R%Q p. 12s.
position is essentially a first order process. Products were hydrogen and inhomogeneous solid products containing varying amounts of hydrogen.
Since both aluminum borohydride and the solid products yield hydrogen on heating it is not possible to calculate the aluminum borohydride pressure as a function of time from the total pressure. Instead, borohydride was run into a thermostated reaction bulb4 to the desired pressure, and the clock started. After a predetermined time the thermoitut \vas removed and the reaction bulb rapidly cooled to room temperature. A pressure reading was made, and then the hydrogen evolved was pumped off a t liquid nitrogen temperature. On warming again t o room temperature the pressure of undecomposed borohydride was measured, and from this the pressure at the reaction temperature was calculated. From a series of such runs for different time intervals the disappearance of aluminum borohydride as a function of time was determined. That the condensible residue was in fact undecomposed aluminum borohydride was establishe; by observing ( a ) on exhaustive decomposition a t 45@-600 (by heating in the luminous flame of a torch) about 5.6-5.9 volumes of hydrogen are obtained both with the condensible gaseous residue :tnd with aluminum borohydride and (b) if the residues from several runs are returned to t h e re(1) i u i T a k e n from a theiis submitted b y Richard s. Brokaw i n partial fulfillment of t h e requirements for t h e degree of Doctor of I'hiloso]~hy a t Princeton 1Jnirersity. (b) T h e work described i n this paper was done i n connection with Contract NOrd 7920 with t h e United S t a t e s Kava1 Bureau of Ordnance, as codrdinated b y t h e Applied Physics Laboratory, T h e Johns Hopkins University, a n d Contract N6-ori-105 with t h e Office of Naval Research a n d O 5 c e of Air Research a s codrdinated b y Project Squid, Princeton University. (c) We wish t o acknowledge t h e assistance of Dean H. S. Taylor, who has general supervision of this project. ( d j Reproduction in whole or in p a r t permitted for a n y purpose of t h e United S t a t e s Government. (2) H . T. Schlesinger. R . T. Sanderson and A. B. Burg. THIS JOURNAL, 62, 3421 (1940). (3) E J . Badin and P.C . H u n t e r , unpublished work. 8 ~ 4 ) T h e apparatus w a s t h e one used in studying t h e reactiun u f aluminrim borohydride with r ~ i r f i n s . see E r o k a w a n d Ped.;e T H I S J O T ' K S ~ L . 78, :3237 ( i ! i m
