1328
CARLOS h D R A D E A N D
acids (in comparison with those derived from the 2and %systems) also stabilize radical-ions which intervene in reduction of the respective ( N H 3 ) 5 C ~ ( I I I ) complexes. *' Stabilization of a radical-ion intermediate, facilitating electron transfer by adjacent attack, comes to light here, largely because other effects which have been invoked to account for acceleration of electrontransfer reactions in carboxylatocobalt(II1) complexes (,i.e., remote attack, chelation, and increased negative charge on the bridging group) are ruled out in the reduction of the methylated and protonated +pyridinecarboxylato complexes. The lesson to be learned is that specific rate of reduction is a reliable guide neither to the site of attack nor the direction of electron flow. In particular, the "fast" reduction of such complexes as the o-benzoylbenzoato (Table 111) and the pyruvatoI6 derivatives could conceivably be rationalized b y considering stabilimtion of a radical-ion intermediate in attack on the carboxylato group ( e . g . , X I I I ) , rather than b y assuming transient chelation and electron transfer through the carbony1 group. However, the difficulty (271 N-F,thyl-.l-carbethoxypyridinyl, a stable free radical closely related t o o u r N-substituted 2-carboxypyridine complexes, has been isolated recently ( E 11. Kosower and E J. Poziomek, J . A m Cliern S O C . , 88, 2035 (1963)).
HENRYT c l U B E
Vol. 86
-b XI11
J
in reducing the carbonylbenzoato acids in our series, in contrast to the ease in reducing many of the pyridinecarboxylic acids, leads us to favor the radical-ion intermediate in rapid reductions of pyridinecarboxylato complexes but not in reductions of the carbonyl complexes. With the carbonyl complexes, a low-lying vacant orbital, while not low enough to accept an electron from Cr2+, may nevertheless be involved in the resonance transfer of an electron from the reducing agent to the Co(II1) center. Acknowledgment.-The authors wish to thank the donors of the Petroleum Research Fund, administered by the American Chemical Society, for support of this research. Funds to purchase the spectrophotometer were made available by the National Science Foundation under Grant No. 22611.
GEORGEHERBERT JONES LABORATORY O F THE UNIVERSITY O F CHICAGO, DEPARTMENT OF CHEMISTRY, STAXFORD UNIVERSITY, STANFORD, C A L I F . ]
[COSTRIBUTION FROM THE
CHICAGO, I L L . , AND THE
Tracer Experiments on Alkaline Hydrolysis of Some Oxalate Ammonia Cobalt (111) Complexes BY CARLOS a N D R A D E
ASD
HENRY TAUBE
RECEIVED KOVEMBER 12, 1963 LVhen C O ( S H ~ ) ~ releases C ~ O ~ C~ Z O ~in~ -alkaline solution a t 25', C-0 bond breaking takes place in - i n k , S Y , 1961; D H. B u s c h , K S w a m i n a t h a n , a n d TI. W C m k e , i u o r q C'hrrn , 1, 200 (1962)
in water. Analysis showed 20.2070 oxalate (calcd., 20.37Yo) and 46.17% C10,- (calcd., 46.04%). [ C o ( e n ) ~ C ~ O ~ ] (not Cl0~ necessarily anhydrous) was prepared from the chloride3by double decomposition. The perchlorate salt was not analyzed, but a report of analysis of [ C o ( e n ) ~ C ~ 0 ~ 3H20 ] C l ~showed 16.48Yc Co (calcd., 16 .52yc).). Procedure.-For all experiments, salts of normal isotopic composition were used, added to aqueous alkaline solutions enriched in 0 ' 8 . WTith the oxalato complexes as reactants, reaction is so slow that the product complex undergoes serious deterioration ( a s in the case of the pentaammine complex), or it undergoes exchange (as in the case of the bisethylenediamine complex) during the course of the reaction, and isotopic analysis of only the product oxalate is feasible. The solutions after the reaction were filtered t o remove solid material, then acidified to a faint acid reaction, and a solution of i\gNO3 was added to precipitate Ag2CzOi. The .4gtCZ04 was collected by filtration, washed with water of normal isotopic composition and then with CHaOH, and dried a t 40" for 12 hr. and then in a vacuum desiccator for 12 hr. The COZreleased by heating the solid t o complete decomposition was collected and analyzed b y mass spectrometer (.4tlas hdodel M86). The isotopic composition of the solvent was determined by the Anbar-Guttmann, method. ( 2 ) P S a s r and H T a u h e . J A m Chem S o c . , 88, 1 3 (1960) (3) A Werner a n d A Wilmos, Z o n o r g . Chcm , 2 1 , 145 (1899) (4) M . Antmr and S . G u t t m a n n . Iiilprn J . A b p l R a i l i d i o n l ~ o l o P r ~ 6, s, 233 f15159)
ALKALINE HYDROLYSIS OF COBALT(III) COMPLEXES
April 5, 1964
-
Results T h e results obtained with Co(NH~)&z04+ and C o ( e n ) G 0 4 + are shown in Tables I and 11, respectively. The symbol E represents the enrichment ratio of the species under consideration, t h a t is, the ratio Ols 016 T A B L EI TRACER RESULTS'o s
THE
T i m e of reaction ( S a O H ) , -11 min
No
HYDROLYSIS OF Co( NH,),C204
+
HyE of drolysis, T e m p , E of % OC solvent oxalate
10 1 4 1 4 5 7600 1 x 10-4 3 21 7600 30,000 3 85 1 X 10F 63 0 25 12 4 7 22 0 25 8 5 2900 > 96 0 25 900 100 14 2 100 14 6 X 20 100
1 2 3 4
5 6
7 8 9 10 11 12
E for complex
25 100 25 25 25 71 25 25 25 25 100 100
7 4 7 9 5
6 4 4 4 3 4 4
86 32 60 25 13
52 30 30 99
07 04 97
n
1 020 0 0 l b 1 023 03b 006' 1 009 1 200 1 742 71' 1 021 Olb 1 024 02 1 067 07 1 34 33 1 29 55 1 067 07 1 021 00
1.000; concentration of complex, -0.02 M; concentration of Na2C204, -0.04 M . Blank experiments taking Sa2CaOaof normal isotopic composition through the exchange procedure. The other values of n in t h e table are corrected for t h e slight pick-up of solvent oxygen indicated by the blank experiments. Experiments 4 and 5 show t h a t exchange of C204*- with H2O in O H - does occur, b u t the reaction is very slow =
TABLEI1 TRACER EXPERMESTS' ON
1 2 3 4 5 6
HYDROLYSIS O F CO(en)2Cs04+
"C.
(h-aOH)a. Jf
Time,b min.
E of solvent
E of oxalate
n
90 90 71 71 71 25
1.97 1.97 0.00273 0.333 1.51 4.96
10 10 60 7 2 7200
7.16 7.16 7.50 6.75 7.34 7.09
3.64 3.58 2.70 5.26 5.27 5.52
1.72 1.68 1 05 2.96 2.70 i n the first step l)resuinatily arises because of the greater straiii i l l the iour-iiienibered coiriparecl to the fiveriieiiihered riiig This suggests that Co -0boriti break+ hydrolyzes in ing will he otiservecl when (NH:i)rCoCO:c alkaliiic solution : this point is a t present under iiivestigatiori in these laboratories. Acknowledgments. 'l'his work was supported by the .l.toriiic: Energy Cotiirnission under Contracts AT(11-1 1-:37h iT-iiiversity of Chicago) arid . - ~ ' ~ ( 0 4 - ~ ~ b ;Wi (Stuxifortl I,Triiversity). C. A. wishes to express thanks, for fellowship support, to the International Cooi)eratioii .~tirriitiistratioii, to the Orgariization of Xiiieric:tri States, ant1 to the University of Chile. ~
isotopic course of the reaction during the iiiit,ial stages, when the effects of the re\,ersal oi reaction 1 are I i o t yet felt. Reaction - 1 coiiipetitig with 2 accounts for the eschaiige. I f this tiiechutiisin i s correct, rcactioii 2 must have a higher activation ener 'y than - 1 to ;ICcount for the decrease in extent o exchxigc. a t high temperature. This requirement is consistelit with the coticlusion reached for Co(KH.,),C,OtCthat substitution a t Co has u higher activation ericqy thnri substitiitior~ a t C For the tnechanism we s u x g e s t for oxyg:cri exchange to lie consistent with the observationh that the rates of hydrolysis, oxalate exchaiige. and loss of optical activity are equal, we tieecl only require that the internietlixte 1x1 tlotss not undergo raceinizatioii or oxalatil rxchatige liefore i t ticcomposes I)? reactioii 2. a rcquirc.trietit that d o e s riot seeni utir I;siiig eq. 1) arid takiiig the tlata for w p t . .1of'Tulile I1 21s showing that coriiplete hytlrolysis lentls to escharige of 1 .!Ni atoms o u t oi :i possihlc o f 13. ki, k,, is calculatctl as 1 I..i:i. The ratio k , , k,. does appear to lie i ~ e a k l y tlepentlent o i i (OH-) ; thus ki, k,. from e x p t . 5 ( ( N a O H ) = I ..-I .\I) is (1.i;. 'This trend is borne o u t a1su h y comparing the result o f e s p t . (iwith those for expt. 1 , 2, aritl .i. From the trend of iz with tetiiperaturc show1 pt. 1 , 2 , arid 5, n for expt. t i is expected to lie close
. l ~ l i ci ~r
n l l h P .
.r
AIIZ ciiuln.
sCIL , 7 5 , M!I:I ( i m j .
:i! i'. irilished.
