REGENERATIVE ROLE OF THE RED PHOSPHORUS IN THE COUPLE HIAQ P-RED/

The synthesis of ortho-substituted benzoic acid 3 from benzalphthalide 1 in the presence of 'hydriodic acid-red phosphorus' (Hl(aq)/P-red) o ccurs via the formation of benzylphthalide 2 as reaction intermediate. its preparation is optimized by use of the 'supported reaction in dry media' process (Silica/HIaq) under microwave irradiation for 8 min. T he role of the red phosphorus in the reduction reaction is elucidated: it intervenes in a catalytic cycle by an oxido-reductive disproportio nation with the liberated iodine, affording either hypophosphorous aci d in aqueous media, or P2I4 in anhydrous media with concomitant regene ration of HI. Thus, the presence of P-red in the couple 'HIaq/P-red' a llows recycling of the hydriodic acid and enhances its reducing effici ency.