A solution of l-lysine dihydrochloride (22 g, 100 mmol) in 2 N NaOH (150 ml) is cooled in an ice-water bath and vigorously stirred. Benzyl chlorocarbonate  (53 g = 44 ml, ca. 300 mmol) and 4 N NaOH (125 ml) are added, each in four portions. These additions require about 30 min. Stirring is continued for an additional 30 min then the mixture  is acidified to congo with 6 N hydrochloric acid (about 55–60 ml). Di-benzyloxycarbonyl-l-lysine separates as an oil which is extracted into ether (twice, 200 ml each time). The organic layers are combined and extracted with a 5% solution of KHCO3 in water (three times, 200 ml each time) . Acidification of the combined bicarbonate solutions with 6 N HC1 (60 ml) and reextraction with ether (twice, 150 ml each time), drying the ether extracts over anhydrous Na2SO4 and evaporation of the solvent under reduced pressure leaves di-benzyloxycarbonyl-l-lysine (40 g) as a syrup, which is used without further purification .
KeywordsFoam Recrystallization Anhydride Charcoal Benzyl
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