Reaktion #54234

Reaktionsgleichung

pyrazole

bromoacetic acid ethyl ester

sodium hydride

tetrahydrofuran

tetrahydrofuran

tetrahydrofuran

→

2-(1-pyrazolyl)-acetic acid

Lösungsmittel

ethanol

Reaktionsbedingungen

Aufarbeitung

1. 1
   workup.STIRRINGThe reaction mixture is stirred for a further 3 hours at 40°
2. 2
   workup.STIRRINGStirring
3. 3
   workup.STIRRINGstirring
4. 4
   Einengenthe suspension is subsequently concentrated by evaporation
5. 5
   workup.ADDITIONTo the residue is added a solution of 74 g of NaOH tablets in 600 ml of 60% methanol (aqueous)
6. 6
   Temperaturrefluxing
7. 7
   workup.WAITis carried out for 40 minutes
8. 8
   TemperaturThe solution is then cooled
9. 9
   Waschenwashed twice with 200 ml of ether
10. 10
    Sonstigeat 5°
11. 11
    Temperaturwith cooling
12. 12
    Extraktionthe solution is continuously extracted during 24 hours with methylene chloride
13. 13
    EinengenThe extract is concentrated by evaporation
14. 14
    Sonstigerecrystallised from ether/tetrahydrofuran
15. 15
    Sonstigemelt at 167°-169°

Vorschrift

50 g of pyrazole in 250 ml of abs. tetrahydrofuran is added dropwise in a nitrogen atmosphere within 1/2 hour at 20°-30°, with stirring and cooling, to 38.7 g of sodium hydride in 100 ml of abs. tetrahydrofuran. The reaction mixture is stirred for a further 3 hours at 40°; it is then cooled towards 5° and, with good cooling, 160.7 g of bromoacetic acid ethyl ester in 100 ml of abs. tetrahydrofuran is added dropwise at 0°-10° during 1 hour. Stirring is maintained overnight at room temperature; there is then added dropwise 150 ml of ethanol; stirring is continued for 1 hour, and the suspension is subsequently concentrated by evaporation. To the residue is added a solution of 74 g of NaOH tablets in 600 ml of 60% methanol (aqueous), and refluxing is carried out for 40 minutes. The solution is then cooled, and washed twice with 200 ml of ether. The aqueous phase is made acid to a congo-red indicator (about pH 2) with conc. hydrochloric acid at 5° with cooling, and the solution is continuously extracted during 24 hours with methylene chloride. The extract is concentrated by evaporation, and recrystallised from ether/tetrahydrofuran. The crystals melt at 167°-169°.

Quelle