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A mixture of 4 (5.00 g) and N-ethylaniline (4.7 g) in n-heptane (200 mL) was refluxed in a Soxhlet extraction apparatus (Figure 1) containing 4A molecular sieves (22.9 g). The reflux was stopped after 2.0 hours and the mixture was cooled to room temperature. The crystalline suspension was filtered. The precipitate was washed with n-heptane and dried in vacuum to furnish 5.53 g (82 percent) of N-ethyl-N-phenyl-5-ethyl-l,2-dihydro-4-hydroxy-l-methyl-2-oxo- quinoline-3-carboxamide (A). 1 H-NMR analysis on the isolated product revealed 2percent remaining ester. 1 H-NMR (d-DMSO), all broad peaks; 11.1 (1H), 7.41 (1H), 7.29 (2H), 7.21 (3H), 7.14 (1H), 6.96 (1H), 3.80 (2H), 3.42 (3H), 3.08 (2H), 1.07 (3H), 1.06 (3H).When the same reaction was performed by the traditional distillation from n-heptane (Entry 22) during 2 hours according to prior art US patent No. 6,875,869 the product was isolated in 85 percent yield (based on compound A) and found by 1H-NMR to be a mixture of compound A (75 molpercent) and the ester used as starting material (25 molpercent).
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A mixture of 4 (5.00 g) and N-ethylaniline (4.7 g) in n-heptane (200 mL) was refluxed in a Soxhlet extraction apparatus (Figure 1) containing 4A molecular sieves (22.9 g). The reflux was stopped after 2.0 hours and the mixture was cooled to room temperature. The crystalline suspension was filtered. The precipitate was washed with n-heptane and dried in vacuum to furnish 5.53 g (82 %) of N-ethyl-N-phenyl-5-ethyl-l,2-dihydro-4-hydroxy-l-methyl-2-oxo- quinoline-3-carboxamide (A). 1 H-NMR analysis on the isolated product revealed 2% remaining ester. 1 H-NMR (d-DMSO), all broad peaks; 11.1 (1H), 7.41 (1H), 7.29 (2H), 7.21 (3H), 7.14 (1H), 6.96 (1H), 3.80 (2H), 3.42 (3H), 3.08 (2H), 1.07 (3H), 1.06 (3H).When the same reaction was performed by the traditional distillation from n-heptane (Entry 22) during 2 hours according to prior art US patent No. 6,875,869 the product was isolated in 85 % yield (based on compound A) and found by 1H-NMR to be a mixture of compound A (75 mol%) and the ester used as starting material (25 mol%).