Kinetics of an Oscillating Reaction using Temperature-Controlled UV-Vis Spectroscopy

Significance of the topic

The Briggs-Rauscher oscillating reaction provides a vivid demonstration of complex chemical kinetics through repeated color changes driven by competing radical and non-radical pathways. Precise temperature control and high-speed spectroscopic monitoring enable quantitative insights into reaction dynamics, activation energies, and intermediate species. Such studies are critical for understanding thermally sensitive processes in industrial reaction monitoring, process optimization, and chemical education.

Goals and overview of the study

This application note describes the simultaneous investigation of Briggs-Rauscher oscillation kinetics at four different temperatures using an Agilent Cary 3500 UV-Vis spectrophotometer equipped with a Multicell Peltier sampling module. The primary objectives were to identify key spectral features of reaction intermediates, measure oscillation periods as a function of temperature, and determine the activation energy via an Arrhenius analysis.

Methodology and applied instrumentation

Sample preparation involved three solutions: Solution A (KIO3 in sulfuric acid), Solution B (malonic acid, MnSO4, and starch indicator), and Solution C (30% hydrogen peroxide). Equal aliquots (0.75 mL each) were mixed in 10 mm quartz cuvettes. A mixture of A+B served as reference to isolate peroxide-initiated changes.

Instrumentation:

• Agilent Cary 3500 UV-Vis spectrophotometer with xenon flash lamp
• Multicell Peltier module with four independently controlled temperature zones (5, 10, 20, 30 °C)
• Optic-fiber delivery to eight cuvette positions, individual stirrers, and temperature probes
• Acquisition parameters for kinetic scans at 610 nm: spectral bandwidth 4 nm, signal averaging 0.004 s, stir speed 800 rpm
• Scanning kinetics (290–950 nm) at 60 000 nm/min yielded time-resolved spectra every 1.65 s

Main results and discussion

Scanning kinetics at 5 °C identified three spectral signatures: a UV band near 300 nm (H2O2), an amber peak at 460 nm (iodine intermediates), and a prominent 610 nm band (starch–tri-iodide complex). Single-wavelength monitoring at 610 nm captured rapid absorbance rises (1.4 s at 5 °C to 0.65 s at 30 °C). Bubble-induced spikes from O2 evolution were minimized by increasing signal averaging time.

Kinetic traces revealed periodic absorbance oscillations whose periods shortened with temperature: steady-state values of 69 ± 3 s (5 °C), 47.6 ± 0.4 s (10 °C), 20 ± 1 s (20 °C), and 8.8 ± 0.6 s (30 °C). An Arrhenius plot of ln(1/period) versus 1/T yielded a linear fit (R2 = 0.999) and an activation energy of 58 kJ/mol, consistent with literature.

Benefits and practical applications

• Parallel measurement of four temperatures reduces experimental time and variability
• High temporal resolution captures rapid oscillatory transitions
• Precise Peltier control ensures stable thermal conditions and reproducible kinetics
• Methodology applicable to other fast, temperature-dependent reactions in QA/QC or research

Future trends and applications

The integration of even faster detectors and microfluidic mixing could access millisecond-scale processes. Multiplexed temperature zones combined with machine-learning analysis will facilitate automated kinetic modeling. The approach may extend to photochemical oscillators, enzyme kinetics under temperature gradients, and real-time process monitoring in industrial systems.

Conclusion

This study demonstrates that the Agilent Cary 3500 UV-Vis with Multicell Peltier module enables simultaneous, high-speed kinetic analysis of the Briggs-Rauscher oscillating reaction across four temperatures. Spectral identification of intermediates guided the selection of 610 nm for monitoring, while Arrhenius analysis determined an activation energy of 58 kJ/mol. The system’s modular design and precise control offer a powerful platform for investigating complex reaction mechanisms.

References

• Briggs TS, Rauscher WC. An Oscillating Iodine Clock. J Chem Educ. 1973;50(7):496.
• Kim K-R, Lee DJ, Shin KJ. A Simplified Model for the Briggs-Rauscher Reaction Mechanism. J Chem Phys. 2002;117:2710–2717.
• Richard MN, Stanley DF. The Oscillatory Briggs-Rauscher Reaction. 3. A Skeleton Mechanism for Oscillations. J Am Chem Soc. 1982;104(1):45–48.
• Shakhashiri BZ. Chemical Demonstrations – A Handbook for Teachers of Chemistry, Vol. 2. University of Wisconsin Press; 1985:248–256.
• Dutt AK. Chloride Ion Inhibition, Stirring, and Temperature Effects in an Ethylacetoacetate Briggs-Rauscher Oscillator in Phosphoric and Hydrochloric Acids in a Batch Reactor. J Phys Chem B. 2019;123(16):3525–3534.
• Mahon MJ, Smith AL. Kinetic Absorption Spectroscopy of the Briggs-Rauscher Oscillator. J Phys Chem. 1985;89:1215–1216.
• Singhal A, Grögli P, Geiser B, Handl A. A Briggs-Rauscher Reaction-Based Spectrometric Assay to Determine Antioxidant Content in Complex Matrices. Chimia (Aarau). 2021;75(1–2):74–79.
• Dutt AK, Banerje RS. Studies on Kinetic Parameters of Briggs-Rauscher Oscillating Reaction. Z Phys Chem. 1982;2:298–304.