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

Significance of the Topic

The Briggs-Rauscher oscillating reaction is a classical example of chemical self-organization that exhibits visible color changes over time. Understanding its kinetics provides insights into reaction mechanisms, thermodynamic parameters, and catalytic processes. Temperature-controlled UV-Vis spectroscopy enables real-time monitoring of fast color transitions and quantification of rate constants, advancing fundamental research and applications in chemical education, reaction engineering, and quality control.

Objectives and Study Overview

The primary goal was to characterize the temperature dependence of the Briggs-Rauscher reaction by simultaneously recording kinetic data at four temperatures (5, 10, 20, and 30 °C). Using an Agilent Cary 3500 UV-Vis spectrophotometer equipped with a Multicell Peltier sampling module, the study aimed to:

• Identify characteristic absorption bands of reaction intermediates via full-spectrum scans.
• Measure oscillation periods and amplitude at a fixed wavelength for different temperatures.
• Determine the activation energy through an Arrhenius analysis.

Methodology and Instrumentation

Sample Preparation

• Solution A: 10.75 g KIO₃ in DI water with 1.125 mL H₂SO₄ (250 mL total).
• Solution B: 3.9 g malonic acid, 0.85 g MnSO₄·H₂O, and ~1 g starch in DI water (250 mL total).
• Solution C: 100 mL 30 % H₂O₂ diluted to 250 mL.
• Reaction initiation: mixing 0.75 mL each of Solutions A, B, and C in quartz cuvettes.

Applied Instrumentation

• Agilent Cary 3500 UV-Vis spectrophotometer with xenon flash lamp (250 Hz) and interchangeable sample modules.
• Multicell Peltier sampling module: eight cuvettes, four independent temperature zones (0–110 °C), air- and N₂-cooled Peltier control, optic-fiber source delivery, individual stirrers and probes.
• Acquisition parameters (scanning kinetics): 290–950 nm; scan rate 60 000 nm/min (1.65 s/spectrum); SBW 4.0 nm; signal averaging 4 ms; stir speed 800 rpm.
• Acquisition parameters (single-wavelength kinetics): 610 nm; SBW 4.0 nm; signal averaging 4 ms; sampling rate 250 Hz; stir speed 800 rpm.

Main Results and Discussion

Full-spectrum scans at 5 °C revealed:

• An absorption edge at 300 nm (H₂O₂).
• A growing peak at 460 nm (amber I₂ intermediate).
• A transient band at 610 nm (starch–I₃⁻ complex, dark blue).

Single-wavelength kinetics at 610 nm showed rapid absorbance rise (0→1.5 AU) in ~1.4 s at 5 °C and ~0.65 s at 30 °C, followed by biphasic decay. Oxygen bubbles induced spikes, which were minimized by increasing signal averaging up to 0.1–1 s. Oscillation periods shortened with temperature:

• 5 °C: steady-state period ~69 ± 3 s.
• 10 °C: ~47.6 ± 0.4 s.
• 20 °C: ~20 ± 1 s.
• 30 °C: ~8.8 ± 0.6 s.

An Arrhenius plot of ln(k) vs. 1/T yielded a linear fit (R² = 0.9987) and an activation energy of 58 kJ/mol.

Benefits and Practical Applications

The multizone UV-Vis setup allows parallel kinetic experiments at different temperatures, accelerating data collection and reducing sample-to-sample variation. High temporal resolution captures millisecond-scale transitions, and precise Peltier control ensures stable conditions. This methodology is applicable to rapid reactions, catalytic studies, and teaching demonstrations.

Future Trends and Potential Applications

Emerging directions include:

• Integration with chemometric and machine-learning tools for automated kinetic modeling.
• Microfluidic and lab-on-a-chip platforms for reduced volumes and faster mixing.
• Coupling UV-Vis with spectroelectrochemical or Raman probes for complementary mechanistic insights.
• Expansion to more temperature zones and multiplexed detection for high-throughput screening.

Conclusion

The Agilent Cary 3500 UV-Vis spectrophotometer with Multicell Peltier sampling module enables detailed multi-temperature investigation of the Briggs-Rauscher oscillating reaction. The approach combines full-spectrum identification of intermediates with rapid single-wavelength kinetics, yielding reliable oscillation periods and an activation energy of 58 kJ/mol. This workflow offers a robust platform for studying fast reaction kinetics.

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