THE THYROID AND PARATHYROIDS 311 



heavy dark impurities. A small amount of sodium hydroxide is 

 added to the nitrate and carbon dioxide is passed through the 

 solution. The barium and sodium carbonate are removed by 

 filtration, and the alcohol is distilled. The last traces of 

 alcohol are removed by heating in an evaporating dish. The 

 aqueous residue is now acidified with hydrochloric acid. The 

 precipitate is dissolved in alkaline alcohol, carbon dioxide is 

 passed through the solution, the precipitated sodium carbonate 

 is removed, and the alcohol is evaporated. The last traces 

 of alcohol are removed by heating on a water bath and the 

 solution is allowed to stand. The monosodium salt of thyroxin 

 will separate at this point. The yield is not quantitative, and 

 it must be further purified by dissolving in alkaline alcohol, 

 passing in carbon dioxide, distilling the alcohol, and allowing 

 the monosodium salt to crystallize a second time. This may 

 then be precipitated from an alkaline alcoholic solution by the 

 addition of acetic acid. Re- solution in alkaline alcohol and 

 precipitation with acetic acid for five or six times removes 

 the impurities and will yield thyroxin containing the theoretical 

 percentage of iodine." 



Kendall states that he has obtained 33 grammes of 

 thyroxin from 6,550 pounds of fresh thyroid. 



Thyroxin is said to be 4,5.6, tri-hydro, 4,5,6, tri-iodo 

 2 oxybetaindolepropionic acid. It exists in three forms : (1) 

 the keto form with the carbonyl group adjacent to the imino, 

 (2) A tautomeric enol form, and (3) A form with an open ring 

 structure (cp. creatine and creatinine). It can be regarded as 

 a derivative of tryptophane. According to Kendall the third 

 form is that in which iodine occurs in the body. 



I H 



H 

 I 



\ 



C = 



N 



(1) Keto form 



