General procedure for the synthesis of 2,4-dichloro-3-cyanopyridine from 2-chloro-4-hydroxynicotinonitrile:
1. 2-Chloro-4-oxo-1,4-dihydropyridine-3-carbonitrile (238 mg, 1.54 mmol) was dissolved in phosphorochloridic acid (0.7 mL) and heated to reflux for 2 hours.
2. After the reaction was completed, the reaction solution was concentrated and aqueous sodium bicarbonate (10 mL) was added to the residue.
3. The aqueous phase was extracted twice with ethyl acetate (10 mL), the organic phases were combined and dried over sodium sulfate.
4. The organic solvent was removed by pressurized distillation, and the crude product was obtained.
5. The crude product was recrystallized in hexane to give 2,4-dichloro-3-cyanopyridine (167 mg, 63% yield).
Product characterization:
- Appearance: white powder
- Melting point: 107-109°C
- IR (KBr) νmax: 3072, 2235, 1559, 1538, 1444, 1406, 1368, 1220, 820 cm1
- 1H NMR (DMSO-d6, 400 MHz) δ: 7.91 (1H, d, J = 5.5 Hz), 8.65 (1H, d, J = 5.5 Hz)
- HRMS m/z calculated value C6H2N2Cl2: 171.9595, measured value: 171.9598
- MS (EI) m/z: 172 [M], 137, 110, 101, 75, 62, 51
