P.J. Das, J. Das / Journal of Molecular Liquids 209 (2015) 94–98
97
Table 4
Comparison of the efficiency of ionic liquid [1-B-4-M-Pyr]Br with some reported IL for the selective O-alkylation of phenols.
Entry
Catalyst
Alkylating agent
Time
Yield (%)
Ref.
1
2
3
4
[Bmim]Cl
DMC
Benzyl chloride
DMC
1.5–6 h
250 min
–
99.4–99.9
–
[29]
[32]
[33]
Phosphonium based ionic liquids
Tributylmethylammonium methylcarbonate
[1-B-4-M-Pyr]Br
⁎
88–94
70–99
DMC
0.5–3.5 h
⁎
High temperature and high pressure continuous flow methylations procedure.
4.3.1.7. 2-Methoxynaphthalene (2h). Mp: 73–75 °C; 1H NMR (300 MHz,
CDCl3, TMS) δH: 7.805–7.749 (3H, m, ArH), 7.465 (1H, t, J = 7.2 Hz,
ArH), 7.358 (1H, t, J = 7.5 Hz, ArH), 7.194–7.162 (2H, m, ArH), 3.944
(3H, s, OCH3); 13C NMR (75 MHz, CDCl3, TMS) δ: 157.58, 134.56,
129.34, 128.95, 127.61, 126.70, 126.32, 123.55, 118.66, 105.77, and
55.24; GC/Ms m/z (relative intensity): 158 ([M]+) (91), 143 (11), 128
(15), 115 (100), 89 (10), and 63 (10).
4.3. Selective O-methylation of phenols and benzyl alcohol
4.3.1. General procedure
A mixture of 1 mmol phenols or benzyl alcohols, 1 mL DMC and
1 mmol of IL was taken in a 10 mL RBF fitted with a reflux condenser
and placed in an oil bath. The reaction mixture was heated to 170 °C
under nitrogen atmosphere for reaction time indicated in Table 2. On
completion of reaction, as monitored by TLC using ethyl acetate and
petroleum ether (60–80 °C) as eluent, the crude product was extracted
with diethyl ether (5 mL × 3), the ether extract washed with water,
dried with anhydrous Na2SO4 and solvent removed by evaporation.
The crude product obtained was purified by column chromatography
on silica gel column and ethyl acetate–petroleum ether as eluent.
4.3.1.8. 4-Nitroanisole (2i). Mp: 48 °C; 1H NMR (300 MHz, CDCl3, TMS)
δH: 8.218 (2H, d, J = 9.3 Hz, ArH), 6.960 (2H, d, J = 9.3 Hz, ArH),
3.918 (3H, s, OCH3); 13C NMR (75 MHz, CDCl3, TMS) δ: 167.08, 141.70,
123.29, 116.58, and 55.89; GC/Ms m/z (relative intensity): 153 ([M]+)
(100), 123 (78), 107 (12), 95 (29), 92 (73), 77 (68), 64 (46), 63 (45),
and 50 (23).
4.3.1.1. 2,6-Dimethylanisole (2a). Colourless liquid; 1H NMR (300 MHz,
CDCl3, TMS) δH: 7.066–6.964 (3H, m, ArH), 3.765 (3H, s, OCH3), 2.335
(6H, s, CH3); 13C NMR (75 MHz, CDCl3, TMS) δ: 156.86, 130.79, 128.74,
4.3.1.9. Anisole (2j). Colourless liquid; 1H NMR (300 MHz, CDCl3, TMS)
δH: 7.380–7.329 (m, 2H, ArH), 7.033–6.955 (m, 3H, ArH), 3.855 (s, 3H,
OCH3); 13C NMR (75 MHz, CDCl3, TMS) δ: 159.45, 129.39, 120.58,
113.80, and 55.03; GC/Ms m/z (relative intensity): 108 ([M]+) (100),
93 (16), 79 (17), 78 (75), 77 (20), 65 (82), 63 (13), 51 (19), 50 (12),
and 39 (28).
123.74, 59.56, and 16.00; GC/Ms m/z (relative intensity): 136 ([M]+
(100), 121 (100), 105 (12), 91 (47), and 77 (45).
)
4.3.1.2. 4-Methoxyanisole (2b). Mp: 54–56 °C; 1H NMR (300 MHz, CDCl3,
TMS) δH: 6.849 (4H, s, ArH), 3.776 (6H, s, OCH3); 13C NMR (75 MHz,
CDCl3, TMS) δ: 153.67, 114.58, and 55.69; GC/Ms m/z (relative intensi-
ty): 138 ([M]+) (95), 123 (100), 95 (52), 92 (7), 80 (7), 77 (6), 65
(11), 64 (12), 63 (14), and 52 (10).
4.3.1.10. 4-Chloroanisole (2k). Liquid; 1H NMR (300 MHz, CDCl3, TMS)
δH: 7.291 (2H, d, J = 8.7 Hz, ArH), 6.782 (2H, d, J = 8.7 Hz, ArH),
3.792 (3H, s, OCH3); 13C NMR (75 MHz, CDCl3, TMS) δ: 158.08, 129.90,
126.70, 116.55, and 55.85; GC/Ms m/z (relative intensity): 144
([M + 2]+) (32), 142 ([M]+) (100), 129 (17), 127 (52), 101 (16), 99
(51), 75 (13), 73 (13), and 63 (14).
4.3.1.3. 3-Acetamidoanisole (2d). Mp: 81 °C; 1H NMR (300 MHz, CDCl3,
TMS) δH: 8.531 (1H, s-broad, NH), 7.271–7.133 (2H, m, ArH), 7.021
(1H, d, J = 7.8Hz, ArH), 6.646–6.611 (1H, m, ArH), 3.726 (3H, s,
OCH3), 2.128 (3H, s, COCH3); 13C NMR (75 MHz, CDCl3, TMS) δ:
169.26, 159.79, 139.13, 129.41, 112.24, 109.73, 105.85, 55.04, and 24.20.
4.3.1.11. 4-Chlorobenzyl methyl ether (2n). Mp: 48–50 °C; 1H NMR
(300 MHz, CDCl3, TMS) δH: 7.368–7.303 (4H, m, ArH), 5.127 (2H, s,
CH2), 3.800 (3H, s, OCH3); 13C NMR (75 MHz, CDCl3, TMS) δ: 133.68,
130.26, 129.67, 128.77, 128.45, 68.73, and 54.95; GC/Ms m/z (relative
intensity): 158 ([M + 2]+) (9), 157 (9), 156 ([M]+) (30), 155 (22),
127 (23), 125 (72), 121 (100), 91 (32), 89 (22), and 77 (21).
4.3.1.4. 2,4,6-Trichloroanisole (2e). Mp: 60–62 °C; 1H NMR (300 MHz,
CDCl3, TMS) δH: 7.299 (2H, s, ArH), 3.882 (3H, s, OCH3); 13C NMR
(75 MHz, CDCl3, TMS) δ: 151.30, 129.96, 129.49, 128.70, and 60.78;
GC/Ms m/z (relative intensity): 214 ([M + 4]+) (19), 212 ([M + 2]+)
(61), 210 ([M]+) (61), 199 (26), 197 (100), 195 (83), 171 (12), 165
(41), 167 (42), 111 (8), 109 (12), 107 (9), and 97 (23).
4.4. Reusability of ionic liquid
Before performing the reaction, we investigated the miscibility of
the ILs in water and in other solvents. They were found to be miscible
in water but immiscible in ether and this immiscibility made recovery
of products and the IL simple. After complete extraction of the crude
product with diethyl ether, the insoluble IL was dried under vacuum
and stored in a desiccator for subsequent reuse. The recycled catalyst
could be used for three successive runs without appreciable loss in its
catalytic activity (Table 3).
4.3.1.5. 1-Methoxynaphthalene (2f). Pale yellow liquid; 1H NMR
(300 MHz, CDCl3, TMS) δH: 8.466–8.446 (1H, m, ArH), 7.964–7.934
(1H, m, ArH), 7.648–7.486 (4H, m, ArH), 6.906 (1H, d, J = 7.2 Hz,
ArH), 4.076 (3H, s, OCH3); 13C NMR (75 MHz, CDCl3, TMS) δ: 155.30,
134.37, 127.37, 126.30, 125.79, 125.49, 125.09, 121.89, 120.11, 103.65,
and 55.29; GC/Ms m/z (relative intensity): 158 ([M]+) (80), 143 (43),
115 (100), 89 (12), and 63 (12).
Acknowledgements
4.3.1.6. 4-Chloro 3-methylanisole (2g). Liquid; 1H NMR (300 MHz, CDCl3,
TMS) δH: 7.235 (1H, d, J = 8.7 Hz, ArH), 6.779 (1H, s, ArH), 6.705–6.668
(1H, m, ArH), 3.784 (3H, s, OCH3), 2.357 (3H, s, CH3); 13C NMR (75 MHz,
CDCl3, TMS) δ: 158.02, 136.90, 129.50, 125.70, 116.35, 112.40, 55.35,
and 20.28; GC/Ms m/z (relative intensity): 158 ([M + 2]+) (32), 156
([M]+) (100), 143 (12), 141 (37), 121 (30), 113 (31), 91 (21), 77
(51), 63 (11), and 51 (20).
One of the authors, J. D. thanks CSIR, New Delhi, for the award of
Junior Research Fellowship.
Appendix A. Supplementary data
Copies of 1H, 13C NMR spectra and mass spectra of ionic liquids and
products.