Plant Qrowth'Substances 



ring-closure, yielding the required acid. The other was a 

 variation of that of Piccinini (1899), who used it to prepare 

 N-methylindole-3-acetic and 2-methylindole-3-acetic acids: 

 Jackson and Manske (1935) reported that a moderate amount 

 of ethyl diazoacetate acting upon indole yielded mainly 

 indole-3-acetic acid and no 2-substituted compound. "The 

 isolation of the acid proved to be facile enough, and in some 

 respects this synthesis is the most satisfactory yet recorded." 

 Details of this synthesis are quoted from the original paper : 



Procedure 



"A dried ethereal solution of ethyl diazoacetate prepared 

 from 50 gm. of glycine ester hydrochloride was slowly run 

 into a Claisen flask (fitted with a long fractionating column) 

 in which had been placed 19 gm. of indole and a trace of 

 copper powder. The ether was rapidly distilled off as the 

 solution was run in, so that the reaction was thus made to 

 proceed smoothly. Finally the product was heated to ioo''C. 

 in the vacuum of a water pump, transferred to a Claisen flask, 

 and distilled at 2 to 3 mm. There was frequently a second 

 evolution of gas at this stage, and this was particularly pro- 

 nounced in the experiment in which the proportionate quan- 

 tity of diazoester was greatly increased. [This second experi- 

 ment yielded less mono-acetic acid — H.N.] 



The almost colourless distillate was hydrolyzed with an 

 excess of methanolic potassium hydroxide, the solution diluted 

 with water and the methanol distilled off. Thorough extrac- 

 tion of this solution with ether yielded 2 gm. of indole. The 

 alkaline solution was then acidified with hydrochloric acid and 

 again exhaustively extracted with ether. The combined 

 extracts were dried with sodium sulphate and the ether dis- 

 tilled off. The solid, reddish residue was transferred to a 

 suction funnel and washed with cold ether. 



The indolyl-3 -acetic acid readily dissolved in the ether and 

 was recovered from the fiiltrate by removal of the solvent. It 

 was recrystallized from a concentrated solution in ethyl 

 acetate by the addition of benzene, or from hot water. The 

 latter solvent is preferable when the acid is already of good 



106 



