Reaction #1253751

Reaction equation

charcoal

2,5-Dibromo-3-picoline

2-amino-5-bromo-3-methylpyridine

Acetyl chloride

2,5-dibromo-3-picoline

sodium iodide

→

5-bromo-2-iodo-3-methylpyridine

Yield 70.0%

Solvents

hexane

Br2 HBr

acetonitrile

Conditions

Workup

1. 1
   Temperaturethe reaction mixture was gently refluxed for 18 h
2. 2
   OtherThe cooled reaction mixture
3. 3
   Filtrationwas filtered
4. 4
   Washthe solid was washed with acetonitrile until colorless
5. 5
   workup.ADDITIONtreated with aq. Na2CO3 until the pH was 10-11
6. 6
   OtherThe organic layer was separated
7. 7
   Dryingdried over anhydrous sodium sulfate
8. 8
   Concentrationconcentrated
9. 9
   Otherto give a brown oil
10. 10
    Temperatureas above (reflux time 6 h)
11. 11
    OtherA dark brown oil was obtained
12. 12
    Filtrationfiltered
13. 13
    Concentrationconcentrated
14. 14
    Otherto give a light brown oil

Procedure

2,5-Dibromo-3-picoline is commercially available or may be prepared from 2-amino-5-bromo-3-methylpyridine by standard diazotization followed by bromination in Br2/HBr. Acetyl chloride (0.68 mol, 52.7 mL) was added to a stirring solution of 2,5-dibromo-3-picoline (0.45 mol, 113 g) in acetonitrile (600 mL) followed by sodium iodide (1.66 mol, 250 g) and the reaction mixture was gently refluxed for 18 h. The cooled reaction mixture was filtered and the solid was washed with acetonitrile until colorless. It was suspended in methylene chloride and treated with aq. Na2CO3 until the pH was 10-11. The organic layer was separated, dried over anhydrous sodium sulfate and concentrated to give a brown oil. It was subjected to iodination a second time as above (reflux time 6 h). A dark brown oil was obtained using the same work-up as above. A solution of this oil in hexane was treated with charcoal, filtered and concentrated to give a light brown oil. It slowly solidified on standing to give 5-bromo-2-iodo-3-methylpyridine as a light brown solid (95.0 g, 0.32 mol). Yield: 70%.

Source