Solvent-Free Iodination of Arenes at Room Temperature

Abstract

Silica supported bismuth(III)nitrate pentahydrate [BNP-SiO₂] was prepared under simple co-grinding condition. The iodination of aromatic compounds using BNP-SiO₂ and molecular iodine under solvent-free conditions is described. The reaction occurred in the solid state at room temperature, yielding the corresponding mono-iodo derivative in good yields. However, less activated aromatics required longer reaction time with comparatively less yield.

aromatic iodination - solvent-free - bismuth nitrate pentahydrate - molecular iodine - co-grinding

References

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<A NAME="RG14003ST-10">10</A>

General Experimental Procedure: To a pre-weighed sample of silica-gel [11] (2.5 g) was added Bi(NO₃)₃·5H₂O (1.7 mmol) and iodine (3.0 mmol) which was then co-grinded in an agate mortar. [12] To the free flowing powder thus obtained, was added the organic substrate (5.0 mmol) and the contents were carefully ground to obtain a fine homogenous powder. This mixture was allowed to stand for the specified time (Table [1] ), at r.t. On completion (TLC or GC analysis [13] ) the reaction mixture was desorbed by dichloromethane (3 × 10 mL). The organic extracts were successively washed with aq Na₂S₂O₃ solution, dried over anhyd Na₂SO₄ and then evaporated under reduced pressure. The crude product was purified by column chromatography to furnish the pure iodides. All products are well known in literature. The products were characterised by their physical constants and spectral analysis.

<A NAME="RG14003ST-11">11</A>

SiO₂ (SRL, 230-400 mesh, BET surface 385.6 m²g^-1, pore volume 0.65 cm³g^-1) was used for all reactions without any prior activation. To a pre-weighed sample of silica-gel
(2.5 g) is added the commercially available Bi(NO₃)₃·5H₂O (0.3 or 0.5 equiv) which is co-grinded in an agate mortar. The contents are carefully ground to obtain a fine homogenous powder. BNP/K10 and BNP/KSF were prepared in a similar manner.

<A NAME="RG14003ST-12">12</A>

CAUTION: Special care must be taken when iodine is co-grinded along with the other contents in an agate mortar. This is because it is known that iodine vapours irritate all parts of the respiratory system.

<A NAME="RG14003ST-13">13</A>

An Eshika Gas chromatograph equipped with FID and
SE-30 column (length 2.0 m) was employed for analysis.