COMMUNICATIONS TO THE EDITOR
1403
We have obtained kinetic data for the reaction of T N M with hydroxide ion and nitrite ion which will be reported in a later communication. During this study in dioxane-water mixtures (the solvent varied from water to dioxane-water mixtures), it became evident that with insufficiently purified dioxane, an immediate reaction was occurring which could be explained by reaction with peroxides present in the dioxane. By adding a known amount of hydrogen peroxide (1.5 X M final) an immediate reaction occurred producing equivalent quantities of nitroform ion (1.5 X M ) and nitrite ion (1.6 X M ) . The solution was initially 9.2 X M in T N M and 0.1 M in potassium bicarbonate. In a recent report in this journal,2 it was stated that T N M was found not to react with either nitrite or peroxide alone or with both together at pH 5 or above. The results with nitrite ion are contrary with the findings in this laboratory as reported in ref 1. It is not at all obvious why Bielski and Allen2 did not observe the reactions with peroxide. Their experiments involved hydrogen peroxide of the order of 10" M and M . As shown above, nitroT N M of the order of form would be produced equivalent to loF6M a t a pH corresponding to that with bicarbonate ion. The actual rate constant found by Hoffsommer3 for the reaction with hydroperoxide ion was 1.44 X 10* l./mole sec, in water. The results of the kinetic study of T N M with base in dioxane are illustrated by the data in Figure 1. That the autocatalytic reaction is due to nitrite ion is clearly shown. Nitrite ion was added initially and the slow reaction is absent. When nitrite ion was not added, the other products were nitrate ion equivalent to the nitroform produced and nitrite ion equivalent to four times the TNM not going to nitroform. That this latter reaction also gives rise to carbonate ion was shown by S ~ h m i d t . ~Carbonate ion and nitrate ion in the
present study were shown not to affect the reaction, The rate constant for the reaction of TNM with nitrite ion was found by interpolation to 0.46 l./molehr at 24" and explains why Bielski and Allen2 observed no reaction with nitrite ion. With nitrite ion 10-6 M and T N M lova M , a yield of nitroform of 5 x 10-9 M would be expected which could not be detected under their conditions. I n our study, when the base concentration was sufficiently low and the nitrite ion sufficiently high, only nitroform, nitrate ion, and nitrite ion were produced, confirming the catalytic nature of nitrite ion. The reactions studied in our kinetic investigation were
+ 6OH- + f 4NOz- + 3Hz0 C(NO2)4 + 20H- +C(NOz)3- + NO,- + HzO c(NOz)4
c03'-
C(NOz)4 Nz04
+ NOz-+
+ 20H-
c(N02)3-
+ NOz-
+ Nz04
+ NO3- + H2O
(1) (2)
(3)
(4) The product N204,although not identified, explains the results most satisfactorily. (2) B. H. J. Bielski and A. 0. Allen, J. Phgs. Chem., 71,4544 (1967). (3)A detailed kinetic study of the reaction of T N M with various peroxides has been reported by J. C . Hoffsommer, Doctoral Thesis, George Washington University, 1964. The results of this study are also planned for a future communication. (4) E. Schmidt, Ber., 52B, 400 (1919).
u. s. NAVALORDNANCE LABOR.4TORY
DONALD J. GLOVER CHEMISTRY RESEARCH DEPARTMENT ADVANCED CHEMISTRY DIVISION WHITEOAK, SILVER SPRING,MARYLAND RECEIVED FEBRUARY 5, 1968
Homogeneous Periodic Reactions
Sir: Two reactions are known which oscillate and which have been reported to take place in a homogeneous phase. One is the reaction between hydrogen peroxide and periodate in acid solution,' and the other is the series of cool flames observed in hydrocarbon oxidations.2 The reason for the oscillatory behavior of cool flames appears to be that one of the rate-determining reactions has a negative temperature coefficient,* and as the temperature rises, the reaction dies out, restarting again when the system cools. We have performed experiments4 at 60" on the reac-
0.04
0.03
M 0.02
0.01
0
4
8
12
16
20
24
28
32
36
40
TIME (MINUTES)
Figure 1. Formation of nitroform from TNM by reaction with hydroxide in dioxane-water.
44
(1) W. C. Bray, J. Amer. Chem. Soc., 43, 1262 (1921). (2) B. Lewis and G. von Elbe, "Combustion, Flames and Explosions of Gases," 2nd ed, Aoademio Press Inc., New York, N. Y . , 1961. (3) J. H. Knox in "Photochemistry and Reaction Kinetics," P. G. Ashmore, F. S. Dainton, and T. M. Sugden, Ed., Cambridge University Press, Cambridge, England, 1967. (4) We are indebted to Mr. R. I. McLean for assistance with these experiments and to Mr. V. A. LoDato for helpful discussions. Volume 72, Number 4
April 1968
1404 tion of periodate with hydrogen peroxide [B.D.H. 0.5% acetanilide inhibitor] using glass beads to facilitate agitation and confirmed the periodic evolution of oxygen discovered by Caulkins and Bray, under similar concentration conditions. We found that the exclusion of daylight from the system suppressed the oscillations (so did the addition of liquid mercury). Our sample of hydrogen peroxide decomposed monotonically at 60°, unlike some samples previously described,6 and the rate of decomposition doubled when daylight w a s excluded! It seems likely that an excited state of acetanilide is a better inhibitor than the ground state. In our view, the peroxide-periodate oxidation can no longer be considered as an example of a homogeneous oscillating reaction-the mechanism is very complex, and subtle heterogeneous5 and photochemical effects are present. Bak6 discusses the possibility that the Master e q u a tion can have imaginary eigenvalues, leading to a permanently oscillatory behavior, and, more realistically,
The Journal of Physical Chemistry
COMMUNICATIONS TO THE EDITOR that the Master equation should have complex eigenvalues which will lead via damped oscillations to final equilibrium. However, if the individual elementary processes are microscopically reversible (which is necessary if a final equilibrium is to be attained), a transformation can always be found which symmetries the Master equation for an isolated system, so that the eigenvalues are necessarily reaL4 Consequently, a periodic reaction cannot occur in the homogeneous phase in a thermodynamically closed system.
(6) F. 0. Rice and 0. M. Reiff, J . Phya. Chem., 31, 1352 (1927). (6) T. A. Bak, “Contributions to the Theory of Chemical Kinetics,” W. A. Benjamin, Inc., New York, N. Y., 1963.
C.R.E.S.S. D. H. SHAW H. 0. PRITCHARD YORKUNIVERSITY TORONTO, CANADA RECEIVED FEBRUARY 29, 1968
