Improved, Highly Efficient, and Green Synthesis of Bromofluorenones and Nitrofluorenones in Water

Abstract

A series of bromo-, nitro-, and bromonitrofluorenones were synthesized chemo- and regioselectively in 90–98% yield via electrophilic aromatic bromination and nitration under mild conditions using water as the sole solvent. These synthetic methods involve simple workup procedures and use only minimal amounts of organic solvents during the purification of products. The newly developed methods have the advantages of being cost-effective and environmentally friendly and could potentially be used for the large-scale synthesis of fluorenone derivatives.

Keywords:

• Aromatic bromination
• aromatic nitration
• fluorenones
• green chemistry
• water

ACKNOWLEDGMENT

This work was supported by the Natural Science Foundation of Shanxi Province (2006011014).

Notes

^a Br₂ was added in three portions with 4–5 h of interval for each addition. The pH of the reaction was maintained at ∼7 by adding aqueous NaOH to neutralize the HBr released during the reaction.

^a HNO₃ and H₂SO₄ were premixed before being added to the reaction media.

^b The following concentrations of HNO₃ were used: A, 65%; B, 85%; C, 95%.

^c Conc. H₂SO₄ (96%) was used.

^d Refers to pure product after recrystallization.

^e The acid mixture was added in two portions, with the second batch being added after 1 h.

^f The temperature in parentheses refers to that of the heating oil bath.