Highly Efficient Photoinitiation in the Cerium(III)-Catalyzed Aqueous Autoxidation of Sulfur(IV). An Example of Comprehensive Evaluation of Photoinduced Chain Reacions
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文摘
The photoinitiated and cerium(III)-catalyzed aqueous reaction between sulfite ion and oxygenhas been studied in a diode-array spectrophotometer using the same light beam for excitation and detection.Cerium(III) is identified as the photoactive absorbing species, and the production of cerium(IV) initiates aradical chain reaction. To interpret all the experimental findings, a simple scheme is proposed, in whichthe additional chain carriers are sulfite ion radical (SO3-
), sulfate ion radical (SO4-), and peroxomonosulfateion radical (SO5-). The overall rate of oxidation is proportional to the square root of the light intensity perunit volume, which is readily interpreted by the second-order termination reaction of the proposed scheme.It is also shown that the reaction proceeds for an extended period of time in the dark following illumination,and a quantitative analysis is presented for this phase as well. The postulated model predicts that cerium(III)should have a cocatalytic or synergistic effect on the autoxidation of sulfite ion in the presence of othercatalysts. This prediction was confirmed in the iron(III)-sulfite ion-oxygen system. The experimental methodand the mathematical treatment used might be applicable to a wide range of photoinduced chain reactions.
), sulfate ion radical (SO4-), and peroxomonosulfateion radical (SO5-). The overall rate of oxidation is proportional to the square root of the light intensity perunit volume, which is readily interpreted by the second-order termination reaction of the proposed scheme.It is also shown that the reaction proceeds for an extended period of time in the dark following illumination,and a quantitative analysis is presented for this phase as well. The postulated model predicts that cerium(III)should have a cocatalytic or synergistic effect on the autoxidation of sulfite ion in the presence of othercatalysts. This prediction was confirmed in the iron(III)-sulfite ion-oxygen system. The experimental methodand the mathematical treatment used might be applicable to a wide range of photoinduced chain reactions.