Silicaphosphine (Silphos): a filterable reagent for the conversion of alcohols and thiols to alkyl bromides and iodides

Nasser Iranpoor*, Habib Firouzabadi*, Arezu Jamalian and Foad Kazemi

*Department of Chemistry, College of Sciences, Shiraz University, Shiraz 71454, Iran, Email: iranpoorchem.susc.ac.ir, firouzabadichem.susc.ac.ir

N. Iranpoor, H. Firouzabadi, A. Jamalian, F. Kazemi, Tetrahedron, 2005, 61, 5699-5704.

DOI: 10.1016/j.tet.2005.01.115

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Abstract

Silicaphosphine (Silphos), [P(Cl)_3−n(SiO₂)n] is a new heterogeneous reagent that converts alcohols and thiols to their corresponding bromides and iodides in the presence of molecular halogen in refluxing CH₃CN in high to quantitative yields. Separation of the Silphos oxide byproduct can be achieved by a simple filtration.

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Details

The document discusses the development and application of Silicaphosphine (Silphos), a new heterogeneous reagent for converting alcohols and thiols into alkyl bromides and iodides. Silphos, represented as [P(Cl)_3-n(SiO₂)_n], is prepared by reacting silica gel with PCl₃. This reagent offers a practical solution to the common issue of separating phosphine oxide byproducts, as Silphos oxide can be easily filtered out. The study demonstrates that Silphos efficiently converts various alcohols and thiols to their corresponding bromides and iodides in high yields using molecular bromine and iodine in refluxing acetonitrile. The preparation of Silphos is straightforward, involving the reaction of dried silica gel with PCl₃ under argon atmosphere, followed by washing and drying. The reagent is stable and can be stored for extended periods. The document also details the optimized conditions for these conversions and highlights the high selectivity and efficiency of Silphos in competitive reactions between different alcohols. Overall, Silphos is presented as a cost-effective, stable, and easily prepared reagent that simplifies the conversion process and product isolation in organic synthesis.

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Key Words

Silphos, Silicaphosphine, Alcohol, Thiol, Alkyl bromides, Benzyl bromides, Alkyl iodides, Benzyl iodides

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ID: J72-Y2005-2930