Acid-Catalyzed Regioselective Nitration of o-Xylene to 4-Nitro-o-xylene with Nitrogen Dioxide: Brønsted Acid Versus Lewis Acid

Abstract

Nitration of o-xylene with nitrogen dioxide imparts remarkable selectivity to 4-nitro-o-xylene. The addition of Brønsted acids and Lewis acids can effectively improve the selectivity for 4-nitro-o-xylene and/or yield, and the Lewis acids present a better influence on the reactions than Brønsted acids do. A 71% yield of mononitro-o-xylene with high selectivity for 4-nitro-o-xylene (ratio 4-/3- = 3.91) has been achieved by the assistance of bismuth trichloride under solvent-free conditions.

GRAPHICAL ABSTRACT

Keywords:

• Acid catalysis
• nitration
• nitrogen dioxide
• 4-nitro-o-xylene
• regioselective

Notes

^a All reactions were carried out with 5.0 mmol of o-xylene for 12 h, unless otherwise noted.

^b Based on o-xylene and determined by calibrated quantitative GC analysis using an internal standard.

^c Absolute yield (internal standard) based on o-xylene.

^d Reaction time 24 h.

^a All reactions were carried out with 5.0 mmol of o-xylene at room temperature for 12 h, unless otherwise noted. The definitions of conversion and product yield are consistent with Table 1.

^b Relative to o-xylene.

^a All reactions were carried out with 5.0 mmol of o-xylene at room temperature, unless otherwise noted. The definitions of conversion and product yield is consistent with Table 1.

^b Relative to o-xylene.

^c Dichloromethane (3 mL) was added as solvent.

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