Accelerating Heat-Initiated Radical Reactions of Organic Halides with Tin Hydride Using Flow Microreactor Technologies

Abstract

We herein report that flow microreactors can promote an efficiency of radical chain reactions. The chain reactions with a fast propagation step can be accelerated by virtue of an efficient heat-transfer character of the microreactors, whereas the yield of those reactions with a slow propagation step was increased by flow microreactors. Moreover, the yield was further increased by a sequential addition of the initiators, which was allowed by a flow-sequential-addition system.

Key words

flow microreactor - flow chemistry - radical chain reduction - reaction acceleration - sequential addition

• References and Notes

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• 11 For the sequential-addition flow reactions with system, a flow microreactor system consisting of two T-shaped micromixers (M1 (φ = 250 μm) and M2 (φ = 500 μm)) and four microtube reactors (R1, R2, R3, and R4) was used. R2 and R3 were dipped in an oil bath (120 °C), and R4 was cooled in an ice bath (0 °C). A xylene solution containing 1-chloroadamantane (0.20 M, 4), tri-n-butyltin chloride (0.24 M), and internal standard (n-tetradecane) was introduced into M1 (0.5 mL/min). Also, a xylene solution of AIBN (0.04 M) was introduced into M1 (F₁ mL/min). The mixed solution was passed through R1 (length L = 100 cm, φ = 1000 μm) and R2 (L = L₁ cm, φ = 1000 μm, residence time = t ₁ s) where the reaction proceeds. Another AIBN solution (in xylene, 0.04 M) was introduced into M2 (F₂ mL/min) and mixed with the reaction solution. The resultant mixture was passed through R3 (L = L₂ cm, φ = 1000 μm, residence time = t ₂ s), and R4 (L = 100 cm, φ = 500 μm) where the reaction was stopped. The sum of F₁ and F₂ is 0.5 (mL/min), and the total reaction time (t ₁ + t ₂) was set as 1885 s by varying L ₁ and L ₂. After a steady state was reached, an aliquot of the solution was collected and analyzed by gas chromatography.