A Convenient Method to Aniline Compounds Using Microwave-Assisted Transfer Hydrogenation

Abstract

The reduction of mononitro and dinitro aromatic compounds to their aniline analogues using microwave-assisted transfer hydrogenation has been demonstrated. The optimised conditions used, with some examples, are described herein.

microwave - transfer hydrogenation - nitroaromatic - anilines

References and Notes

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15

Each isomer was separated and characterised by ¹H NMR and ¹³C NMR spectroscopy. For each isomer, an NOE was observed between the NH₂ and the aromatic proton.

16

The conversion of 2-[(E)-2-(4-pyridinyl)ethenyl]aniline to the 2-[2-(4-pyridinyl)ethyl]aniline required microwave conditions of 180 °C, 120 min in EtOH.

17

3-(Ethyloxy)-4-nitroaniline. Synthesised using heating time of 3 min. ¹H NMR [400 MHz, (CD₃)₂SO]: δ = 1.35 (t, J = 8 Hz, 3 H, CH₃), 4.05 (q, J = 8 Hz, 2 H, CH₂), 6.18 (d, J = 8 Hz, 1 H, ArH), 6.24 (s, 1 H, ArH), 6.53 (br s, 2 H, NH₂), 7.78 (d, J = 8 Hz, 1 H, ArH), 7.71 (d, J = 8 Hz, ArH). ¹³C NMR [75 MHz, (CD₃)₂SO]: δ = 14.8, 64.5, 96.9, 105.9, 127.2, 129.3, 156.3, 156.5. MS (EI, 70 eV): m/z (%) = 182.97 (100). HRMS-FAB: m/z calcd for C₈H₁₀N₂O₃ [M + H]⁺: 183.0770; found: 183.0775.
2-(Ethyloxy)-4-nitroaniline.
Synthesised using heating time of 3 min. ¹H NMR [400 MHz, (CD₃)₂SO]: δ = 1.37 (t, J = 8 Hz, 3 H, CH₃), 4.10 (q, J = 8 Hz, 2 H, CH₂), 6.40 (br s, 2H, NH₂), 6.64 (d, J = 8 Hz, 1 H, ArH), 7.54 (s, 1 H, ArH), 7.71 (d, J = 8 Hz, ArH). ¹³C NMR [75 MHz, (CD₃)₂SO]: δ = 14.5, 63.9, 106.3, 110.8, 119.6, 135.4, 143.6, 146.1. MS (EI, 70 eV): m/z (%) = 182.85 (100). HRMS-FAB: m/z calcd for C₈H₁₀N₂O₃ [M + H]⁺: 183.0770; found: 183.0775.
2-[( E )-2-(4-pyridinyl)ethenyl]aniline.
Synthesised using heating time of 90 min. ¹H NMR [400 MHz, (CD₃)₂SO]: δ = 5.51 (s, 2 H, NH₂), 6.55 (t, J = 4 Hz, 1 H, ArH), 6.65 (d, J = 8 Hz, 1 H, ArH), 6.96 (d, J = 16 Hz, 1 H, CH), 7.01 (m, 1 H, ArH), 7.47 (d, J = 8 Hz, 1 H, ArH), 7.57 (br d, J = 4 Hz, 2 H, ArH), 7.67 (d, J = 16 Hz, 1 H, CH), 8.51 (br s, 2 H, ArH). ¹³C NMR (75 MHz, CDCl₃): δ = 115.7, 116.6, 119.4, 120.61, 123.7, 125.7, 128.8, 129.5, 145.1, 146.3, 149.2. MS (EI, 70 eV): m/z (%) = 197.0 (100). HRMS-FAB: m/z calcd for C₁₃H₁₃N₂ [M + H]⁺: 197.1083; found: 197.1079.
1 H -Indazol-6-amine Synthesised using heating time of 15 min. ¹H NMR [400 MHz, (CD₃)₂SO]: δ = 5.18 (s, 2 H, NH₂), 6.48 (dd, J = 8, 4 Hz, 1 H, ArH), 6.50 (s, 1 H, CH), 7.35 (d, J = 8 Hz, 1 H, ArH), 7.71 (s, 1 H, ArH) 12.3 (s, NH). ¹³C NMR (75 MHz, CDCl₃): δ = 89.6, 111.5, 114.7, 119.7, 132.3, 141.1, 146.8. MS (EI, 70 eV): m/z (%) = 134.02 [M + H]⁺ (100). HRMS-FAB: m/z calcd for C₇H₇N₃ [M + H]⁺: 134.0717; found: 134.0718.