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Asymmetrically N,N'-substituted urea (20–25) yields obtained in solvent free conditions and by the traditional reflux method.
| Urea | X | MP (°C) | Reflux procedure Yield (%) | Time (h) | Solvent free conditions Yield (%) 30 min |
|---|---|---|---|---|---|
| 20 | H | oil | 26 | 4 | >99 |
| 21 | 4-CH3 | 65–68 | 30 | 4 | >99 |
| 22 | 4-OCH3 | oil | 40 | 24 | 98 |
| 23 | 4-Cl | 98–100 | 64 | 4 | >99 |
| 24 | 4-Br | oil | 30 | 4 | >99 |
| 25 | 4-F | 75–78 | 25 | 4 | >99 |
