H. C. Mishra and C. M. S i n g h Ranchi Universlly Ranchi-834008 India
I
Belousov's Oscillating Reaction in Acidic Medium Other Than Sulfuric Acid
Various types of reports o n oscillating chemical reactions have aooeared in recent vears. Z h a b o t i n ~ k i ' ,r~e ~ o r t e ds u h stitution of citric acid b y a variety of organic compounds either possessing a methylene group o r easily forming such a g r o u p d u r i n g oxidation (e.g. malonic acid, h r o m o malonic acid, acetoacetic acid. oxalacetic acid. acetonedicarboxvlic acid) a n d a h i u b s t i t u f i o n of rerium catalyst by manganese or ferroin in Helousov's oscillating chemiral reactions. Knsperek a n d Hruicr' found [hat malunir acid can besuhstitured hy malic acid, bromomalonic arid, a n d dihromo malonic acid. Whereas 1)emas and I)irmente4 have s ~ ~ g g e s r substitution ed of ferroin, manganese, a n d cerium by rris 1'2.2'-t~ypyridine~ ruthenium (11) I R u ~ t , i o ~ ~, in ~'+ Helousov's l reaction which can a c t 110th as catalyst as well a s an indicator. N o report o n t h e change of sulfuric acid in this reaction has a p p e a r e d so far. In the present communication we are reporting the existence of oscillatory phenomenon in the Mn2+ catalyzed reaction between &ic acid and potassium hromate (Belousov's reaction) in acidic media other than sulfuric acid and thus we are also ruling on the possibility of the substitution of sulfuric aeid by phosphoric acid, nitric acid in this reaction. It also contradicts the report5 that 'no substitution seems t o be possible for sulfuric acid.'
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Experimental We used phosphoric aeid and also nitric acid in place of sulfuric acid in the Belousov's reaction (Mn2+catalyzed reaction between citric acid and potassium bromate). We performed our experiment in a reaction cell which was kept in a thermostat. The temperature was maintained a t 35%. The reactants of desired concentration were poured into it. A P t electrode was dipped into it and wascoupled with a standard calomel reference electrode. The resultant solution was stirred with a magnetic stirrer. E.M.F. was recorded with a potentiometer a t different time intervals. The ascillation was easily visualized 'Zhabotinskii, A. M, Dokl. Akad. Nauk, USSR, 157,392 (1964). ZZhahotinskii,A. M, Biofizika, 9,306U964). 3Kasperek, G. J., and Bruice, T.C, Inorg Chem., 10.382 (1971). "ernas, J. N., and Diemente, D., J. CHEM. EDUC., 50, 357
with the ehange in color of the solution. In phosphoric acid a t lower concentration the change in color was from deep yellow to colorless. But a t higher concentration the change was from cherry red to colorless and in the case of nitric acid from yellow t o colorless. Conclusion In phosphorie acid it was found that a t lower concentration the time of oscillation was lower e.g. more frequent than a t higher concentration. In 1N phosphoric acid, the time of oscillation was found to be approximately 20 min when the concentration of Br03-, citric acid was 0.04 M and the concentration of manganous sulfate was 0.01 M. In the case of nitric acid at 0.5 N the time of oscillation was 2.5 min. The concentration of BrOs-, citric acid, and manganous sulfate was the same as in the ease of phosphoric acid. Further studies on this reaction are in progress which we think will rive a clear standina on the problem. "
Acknowledgment Authon acknowledge thankfulness t o the Council of Scientific and l,,dustrial ~ ~New Delhi ~ (India)~for awarding ~ a fellowship ~ to~ ofthem (c.M.s.). Table 1. Reactant Concentrations Used t o Produce Orcillation in Phowhoric Acid Medium Reacfanfe
Concentration
Table 2. Reactant Concentrations Used to Produce Orcillatian in Nitric Acid Medium Reactants
Concentration
119721~ ,... . ,.
Tield, R. J., J. CHEM. EDUC., 49,308 (1972).
Volume 54, Number 6, June 1977 1 377
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