Decarboxylation of Tryptophan in Tetralin With a Ketone Catalyst4
L- or DL-Tryptophan (102.1 g, 0.5 mol) was suspended in tetralin (250 ml) containing acetone (2.9g, 0.5 moles) and the mixture was heated to reflux
for 8-10 hours with vigorous stirring until no more carbon dioxide was evolved and the reaction mixture became clear. The solvent was removed under
vacuum, and the residue was distilled under reduced pressure to give a yellow crystalline solid, bp 140-155°C at 0.25 mmHg. This was recrystallized
from boiling benzene to afford faint yellow prisms, mp 116-117.5°C (lit 115-117°C).
The yield with acetone as catalyst was 75%, methyl ethyl ketone 84.4%, 3-pentanone 85% and 2-pentanone 86.2%.
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