Reaction #50725

Reaction equation

D-Leucine

potassium bromide

H2SO4

water

→

2-Mercapto-4-Methylpentanoic Acid

Conditions

Workup

1. 1
   workup.WAITto proceed for ~14 hours at room temperature
2. 2
   ExtractionThe reaction was then extracted with 75 ml portions of ether three times
3. 3
   ExtractionThe ether extract
4. 4
   Dryingwas dried over anhydrous sodium sulfate
5. 5
   FiltrationThe solution was filtered
6. 6
   Otherthe ether was evaporated
7. 7
   workup.STIRRINGwith stirring at 0° C
8. 8
   workup.STIRRINGThe reaction was stirred for 48 hrs
9. 9
   workup.ADDITIONacidified at 0° C. with judicious addition of 10N H2SO4
10. 10
    ExtractionThe acidified solution was then extracted with 75 ml portions of ether three times
11. 11
    DryingThe ether extracts were dried over anhydrous sodium sulfate
12. 12
    Othersubsequently the ether was removed in vacuo
13. 13
    workup.DISTILLATIONdistilled

Procedure

A solution of D-Leucine (5 g) and potassium bromide (114 g) in 400 ml of 2.5 N H2SO4 was cooled to -5° C. in an ice salt bath. A cold solution of NANO2 (30 g/70 ml water, 0°-50° C.) was added dropwise with stirring. The reaction was allowed to proceed for ~14 hours at room temperature. The reaction was then extracted with 75 ml portions of ether three times. The ether extract was dried over anhydrous sodium sulfate. The solution was filtered and the ether was evaporated. The resulting clear oil, 2-bromo-4-methylpentanoic acid (Martin and Greco, (1968) J. Org. Chem. 33, 1275-1276) (18 g) was committed to a 250 ml solution of 33% sodium trithiocarbonate with stirring at 0° C. The reaction was stirred for 48 hrs and then acidified at 0° C. with judicious addition of 10N H2SO4. The acidified solution was then extracted with 75 ml portions of ether three times. The ether extracts were dried over anhydrous sodium sulfate, and subsequently the ether was removed in vacuo. The resulting yellowish oil (17 g) was vacuum distilled. The final yield was 15.3 g of (S)-2-mercapto-4-methylpentanoic acid; b.p. 92-93 (0.75 mmHg); [α]D 25=-23.2 (cl,MeOH).

Source