Effect of Initial Substrate Concentrations and Temperature on the Oscillatory Behavior of Phloroglucinol-Based Belousov-Zhabotinsky Reaction Usma Gull, Ghulam Mustafa Peerzada,* Nadeem Bashir Ganaie, and Nisar Ahmad Dar Department of Chemistry, University of Kashmir, Srinagar J&K-190006, India Received August 15, 2012; E-mail: peerzada_gmp@yahoo.co.in, nadeemganaie@rediffmail.com The present study introduces the use of phloroglucinol (1,3,5-trihydroxybenzene) as organic substrate in BZ reaction for the first time. This work has been carried out to assess the influence ofinitial reagent concentrations on the behavior of phloroglucinol-bromate-ferroin-based BZ reaction in a stirred batch reactor. The oscillations are followed by observing the change in redox potential.Different oscillatory parameters like induction time (t in ), time period (t p ), amplitude (A), frequency (v), and number of oscillations (N) show different changes with respect to changes in the initial concentrations of organic substrate, bromate and sulfuric acid, and these observations have been explained on the basisof FKN mechanism. The behavior of the aforesaid system indifferent aqueous acid media has been reported and it is found that sulfuric acid is the best medium for studying the system as it shows a wide oscillatory window compared to that of nitric acid. In phosphoric and perchloric acids the system does not show any oscillatory behavior. Activation parameters of the reaction have been derived by studying the reaction over a temperature range of 15 to 40 « 0.1 °C. The effect of different catalysts on the oscillatory behavior has been studied and it is found that the system gives good oscillatory behavior with ferroin and Ce(III) whereas a poor response is seen when Mn(II) and Ce(IV) are used as catalysts. The dimensions of nonequilibrium chemistry, especially the study of systems far from equilibrium, are growing continu- ously on account ofinterests in real systems such as living systems. The oscillatory chemical reactions are the best examples of systems far from equilibrium that display many unusualfeatures. These chemical reactions have been widely studied in the areas of theoretical and experimental kinetics over last the few decades 1,2 and have potential applications in various areas like physics, chemistry and biology. Biochem- ical reactions such as glycolytic oscillations and peroxidase- catalyzed oxidation of nicotinamide adenosine dehydrogenase (NADH) have generated considerable interest in this field. 3-5 The Belousov-Zhabotinsky (BZ) reaction 6-8 is one of the most studied oscillatory chemical reactions in both batch and CSTR modes which involves the oxidation of an organic substrate by bromate ion in acidic medium. The reaction can be catalyzed or uncatalyzed. The reaction is catalyzed by metalions in free form e.g, Ce 3+ /Ce 4+ , 1,9,10 Mn 2+ /Mn 3+ , 11 as complexes [Ru- (bpy) 3 ] 2+ /[Ru(bpy) 3 ] 3+ , 12-15 [Fe(phen) 3 ] 2+ /[Fe(phen) 3 ] 3+ , 16 or in the form of macrocyclic complexes. 17,18 The famous FKN mechanism 19 proposed by Field, Koros, and Noyes isof special interest in explaining the complex nature of BZ reactions. A simple mathematical 3-variable model 20 formulated by Field and Noyes can describe many of the complex dynamic behaviors of the system including excitability, 21,22 bistability, 23 target or spiral pattern 24,25 in a thin unstirred reaction layer, stirring effects, 26,27 and chaos. 28 The uncatalyzed bromate oscillators do not involve any metalion catalyst and the organic substrate is usually a polyphenol or a polyaniline deriva- tive 29-31 which plays the roleof catalyst as well. These bromate oscillators are explained by a slightly modified FKN mecha- nism known as OKN mechanism given by Orban, Koros, and Noyes. 32 Long-term behavior of BZ reaction inaclosed reactor, 33 self-oscillating gels driven by BZ reaction, 34 and pulse-coupled oscillators 35 are some of the recent advance- ments in this field. Tikhonova et al. (1978) were the first to consider the quantitative use of oscillatory reactions for ana- lytical purposes. 36 Thus, the introduction of pulse perturba- tion technique (APP) gave a new and vast dimension to the analyticalinvestigation of BZ reaction. In the present study, the oscillatory behavior of the ferroin- catalyzed BZ reaction using phloroglucinol (1,3,5-trihydroxy- benzene) as organic substrate has been investigated. This substrate has not been used so far as organic substrate in BZ reaction. Its isomer pyrogallol (1,2,3-trihydroxybenzene) 37-39 has been investigated in both catalyzed and uncatalyzed BZ reactions. Phloroglucinol has sufficient solubility in aqueous acid media and shows a broad oscillatory region with respect to initial reagent concentrations. Phloroglucinolitself or in combination with other substances as well as its derivatives have a vast array of activities like anticancer, antispasmodic, anti-inflammatory, antibacterial, antitumor, neuro-regenerative, and antioxidant properties. 40-42 A detailed study of the reaction system has been carried out at 30 « 0.1 °C. An attempt has been made to study the dynamics of the reaction over a temperature range (15 to 40 « 0.1 °C) with respect to its effect on different oscillatory parameters like induction period (t in ), time period (t p ), amplitude (A), and number of oscillations (N). As medium has a profound effect in a BZ reaction, 43 phloroglucinol-based BZ system has been studied indifferent aqueous acid media like nitric acid, sulfuric acid, perchloric acid, and orthophosphoric acid. A systematic study of the © 2013 The Chemical Society of Japan Published on the web February 9, 2013; doi:10.1246/bcsj.20120217 Bull. Chem. Soc. Jpn. Vol. 86, No. 2, 266-272 (2013) 266