1. 5-Ethyl-4-hydroxy-1-methyl-2-oxo-1,2-dihydroquinoline-3-carboxylic acid methyl ester (5.00 g) was dissolved in n-heptane (200 mL) with N-ethylaniline (4.7 g), 4A molecular sieves (22.9 g) were added and placed in a Soxhlet extraction device under reflux.
2. After refluxing for 2.0 hours the heating was stopped and the reaction mixture was cooled to room temperature.
3. The crystalline suspension in the reaction mixture was filtered and the solid product was collected.
4. The precipitate was washed with n-heptane and subsequently dried under vacuum to afford N-ethyl-N-phenyl-5-ethyl-1,2-dihydro-4-hydroxy-1-methyl-2-oxoquinoline-3-carboxamide (A) in a yield of 5.53 g (82% yield).
5. The isolated product was analyzed by 1H-NMR and was shown to contain 2% unreacted ester. 1H-NMR (d-DMSO) data were as follows: broad peaks appeared at 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) ppm.
6. According to U.S. Patent No. 6,875,869, a 2 hour reaction from n-heptane by conventional distillation under the same reaction conditions resulted in a product yield of 85% (based on Compound A). 1H-NMR analysis showed the product to be a mixture of Compound A (75 mol%) and the feedstock ester (25 mol%).
