Another tryptophan decarboxylation
(Rated as: excellent)
Copper Chelate of L-Tryptophan
To a solution of 50g L-Tryptophan in water was added an aqueous solution of an excess of Copper(II)Acetate, and the resultant precipitate was washed several times with hot water to give the copper chelate compound, yield 52g.
A suspension of the L-Tryptophan copper chelate in DMSO was heated at 170-175°C for 10 minutes (until the evolution of carbon dioxide had ceased). After cooling, the resultant solution was filtered and to the filtrate was added a suitable amount of water. The reaction mixture was made basic with 30% sodium hydroxide solution and extracted with chloroform. After distillation of the solvent, the product was purified through column chromatography on silica gel, yield 40%. The tryptamine was identified as its hydrochloride salt, mp 246-248°C.
Indole was also formed as a by-product of the reaction. The reaction could not be performed in protic solvents such as water. Other solvents, such as hexamethylphosphoric triamide at the same temp gave 45% yield after 3 minutes, and ethylene glycol gave only 10% yield after 20 min at 190-200°C.
Ref: T. Kametani et al, Synthesis 131-132 (1974)