Nitration of 1-Phenanthrol

Abstract

The nitration of 1-phenanthrol [1] was investigated in relation to the reactivity of the sterically hindered 4-position. Thus, [1] was treated with 65% HNO₃ (1 mol) in AcOH at 45°C for 2 hours yielding 2-nitro- [ 2] (40%), 4-nitro- [3] (trace), and 2, 4 -dinitro-1-phenanthrol [4] (20%) and 1, 4-phenanthrenequinone (5%).
To confirm the structure [2] was reduced with IN.2-14-Pd/C to 2-amino-1-phenanthrol followed by the oxidation with CrOs to give 1, 2-phenanthrenequinone. An authentic sample of [3] was obtained from 4-chloro-1-phenanthrol by the reaction with NaNO₂ in DMF. The further nitration of [ 2] and[3] gave [4] as the common product. When refluxed in an HBrAcOH solution, [3] isomerized to [2], but at a temperature below 90°C the isomerization reaction did not take place.