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Synlett 2006(16): 2629-2632  
DOI: 10.1055/s-2006-951490
LETTER
© Georg Thieme Verlag Stuttgart · New York

Efficient Demethylation of N,N-Dimethylanilines with Phenyl Chloroformate in Ionic Liquids

Satomi Imoria, Hideo Togo*a,b
a Graduate School of Science and Technology, Chiba University, Yayoi-cho 1-33, Inage-ku 263-8522, Japan
b Department of Chemistry, Faculty of Science, Chiba University, Yayoi-cho 1-33, Inage-ku 263-8522, Japan
e-Mail: togo@faculty.chiba-u.jp;
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Publication History

Received 24 July 2006
Publication Date:
22 September 2006 (online)

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Abstract

Demethylation of N,N-dimethylanilines was carried out in various ionic liquids and acetonitrile as well as under solvent-free conditions. We have demonstrated that their reactivity dramatically depends on the ionic liquid employed; [bmim]Cl showed the best reactivity.

Key words

N,N-dimethylaniline - demethylation - phenyl chloroformate - ionic liquid - phenyl N-methyl-N-arylcarbamate

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Phenyl N -Methyl- N -phenylcarbamate; Typical Procedure: A flask containing [bmim]Cl (2.0 mL) was dried under reduced pressure by a vacuum pump for 2 h at 80 °C. Then, N,N-dimethylaniline (1.0 mmol) and phenyl chloroformate (1.2 equiv) were added to the flask. The resulting mixture was stirred and heated at 80 °C for 3 h. Then H2O (3 mL) was added and the reaction mixture was extracted with EtOAc (20 × 5 mL). The combined extract was condensed to give a residue; the purity of the product was about 50% due to the presence of phenyl chloroformate and a little ionic liquid. The residue was purified by preparative TLC (hexane-EtOAc, 7:1) to give pure phenyl N-methyl-N-phenylcarbamate in 95% yield; colorless oil; bp 155 °C (1 mmHg). IR (neat): 1730, 1600, 1205, 740, 695 cm-1. 1H NMR (CDCl3, TMS): δ = 7.39-7.09 (10 H, m), 3.39 (3 H, s). The following abbreviations are used in 13C spectral data: p, s, t, q, for primary, secondary, tertiary, and quarternary carbon, respectively. 13C NMR (CDCl3, TMS): δ = 153.9 (q), 151.2 (q), 142.8 (q), 129.1 (2 t), 128.9 (2 t), 126.5 (t), 125.8 (t), 125.3 (2 t), 121.5 (2 t), 38.1 (p). HRMS (FAB): m/z calcd for C14H14NO2 (M + H): 228.1025; found: 228.1012. Phenyl N -Methyl- N -phenylcarbamate; Distillation Method: A flask containing [bmim]Cl (4.0 mL) was dried under reduced pressure by a vacuum pump for 2 h at 80 °C. Then, N,N-dimethylaniline (20.0 mmol)and phenyl chloroformate (1.2 equiv) were added to the flask. The resulting mixture was stirred and heated at 80 °C for 3 h. Then the reaction mixture was distilled to give pure phenyl N-methyl-N-phenylcarbamate in 90% yield; bp 155 °C (1 mmHg).Phenyl N -Methyl- N-p -bromophenylcarbamate: Colorless oil; bp 210 °C (1 mmHg). IR (neat): 1720, 1590, 1200, 830, 740, 690 cm-1. 1H NMR (CDCl3, TMS): δ = 7.49-7.45 (2 H, m), 7.34-7.09 (7 H, m), 3.38 (3 H, s). 13C NMR (CDCl3, TMS): δ = 153.5 (q), 151.0 (q), 141.8 (q), 131.9 (2 t), 129.1 (2 t), 127.2 (t), 125.3 (2 t), 121.4 (2 t), 121.4 (q), 38.1 (p). HRMS (FAB): m/z calcd for C14H13BrNO2 (M + H): 306.0130; found: 306.0137. Phenyl N -Methyl- N-p -methylphenylcarbamate: Colorless oil; bp 170 °C (1 mmHg). IR (neat): 1720, 1595, 1205, 820, 740, 690 cm-1. 1H NMR (CDCl3, TMS): δ = 7.33-7.08 (9 H, m), 3.38 (3 H, s), 2.34 (3 H, s). 13C NMR (CDCl3, TMS): δ = 154.0 (q), 151.3 (q), 140.3 (q), 136.4 (q), 129.6 (2 t), 129.1 (2 t), 125.7 (t), 125.2 (2 t), 121.6 (2 t), 38.2 (p), 20.9 (p). HRMS (FAB): m/z calcd for C15H16NO2 (M + H): 242.1181; found: 242.1190. Phenyl N -Methyl -N-m -nitrophenylcarbamate: Colorless oil; bp 240 °C (1 mmHg). IR (neat): 1740, 1600, 1200, 810, 750, 695 cm-1. 1H NMR (CDCl3, TMS): δ = 8.27-8.26 (1 H, m), 8.07-8.05 (1 H, m), 7.75-7.73 (1 H, m), 7.54-7.50 (1 H, m), 7.37-7.33 (2 H, m), 7.20-7.13 (3 H, m), 3.48 (3 H, s). 13C NMR (CDCl3, TMS): δ = 153.3 (q), 150.6 (q), 148.3 (q), 143.8 (q), 131.3 (t), 129.5 (t), 129.2 (2 t), 125.6 (t), 121.3 (2 t), 120.7 (t), 120.1 (t), 37.5 (p). HRMS (FAB): m/z calcd for C14H13N2O4 (M + H): 273.0875; found: 273.0879. Phenyl N -Methyl- N -naphthylcarbamate: White solid; mp 86-87 °C. IR (paraffin): 1720, 1595, 1200, 695 cm-1. 1H NMR (CDCl3, TMS): δ = 8.00-6.92 (12 H), 3.49-3.41 (3 H). 13C NMR (CDCl3, TMS): δ = 154.6 (q), 151.2 (q), 139.1 (q), 134.4 (q), 130.0 (q), 128.9 (2 t), 128.4 (t), 128.1 (t), 126.8 (t), 126.2 (t), 125.6 (t), 125.1 (t), 124.7 (t), 122.2 (t), 121.4 (2 t), 38.4 (p). HRMS (FAB): m/z calcd for C18H16NO2 (M + H): 278.1181; found: 278.1165. Phenyl N -Butyl- N -phenylcarbamate: Colorless oil; bp 150 °C (1 mmHg). IR (neat): 1720, 1595, 1200, 745, 690 cm-1. 1H NMR (CDCl3, TMS): δ = 7.42-7.09 (10 H, m), 3.78-3.74 (2 H, m), 1.66-1.59 (2 H, m), 1.40-1.31 (2 H, m), 0.93-0.89 (3 H, t, J = 7.3 Hz). 13C NMR (CDCl3, TMS): δ = 153.8 (q), 151.3 (q), 141.5 (q), 129.1 (2 t), 129.0 (2 t), 127.3 (t), 126.9 (t), 125.1 (2 t), 121.5 (2 t), 50.6 (s), 30.2 (s), 19.8 (s), 13.7 (p). HRMS (FAB): m/z calcd for C17H20NO2 (M + H): 270.1494; found: 270.1488.Phenyl N -Ethyl- N -phenylcarbamate: Colorless oil; bp 160 °C (1 mmHg). IR (neat): 1720, 1595, 1200, 750, 690 cm-1. 1H NMR (CDCl3, TMS): δ = 7.42-7.08 (10 H, m), 3.83-3.79 (2 H, m), 1.24-1.21 (3 H, m). 13C NMR (CDCl3, TMS): δ = 153.6 (q), 151.3 (q), 142.8 (q), 129.1 (2 t), 129.0 (2 t), 127.3 (t), 126.9 (t), 125.1 (2 t), 121.5 (2 t), 45.8 (s), 13.8 (p). HRMS (FAB): m/z calcd for C15H16NO2 (M + H): 242.1181; found: 242.1170. Phenyl N -Methyl- N -dodecylcarbamate: Colorless oil; bp 180 °C (1 mmHg). IR (neat): 1730, 750, 690 cm-1. 1H NMR (CDCl3, TMS): δ = 7.36-7.37 (2 H, m), 7.20-7.09 (3 H, m), 3.43-3.31 (2 H), 3.06-2.98 (3 H), 1.63 (2 H), 1.32-1.26 (18 H, m), 0.91-0.86 (3 H, m). 13C NMR (CDCl3, TMS): δ = 153.6 (q), 151.3 (q), 142.8 (q), 129.1 (2 t), 129.0 (2 t), 127.3 (t), 126.9 (t), 125.1 (2 t), 121.5 (2 t), 45.8 (s), 13.8 (p). HRMS (FAB): m/z calcd for C20H34NO2 (M + H): 320.2590; found: 320.2596.