Structure of Colored Compound Formed in the Sullivan Reaction for Guanidine

Abstract

Sullivan 1 found that when guanidine is heated with 1.2 naphtho-quinone-4-sodium sulphonate and alkali a brown colored solution is formed which on acidification with concentrated HCl and concentrated HNO₃ gives a striking red complex while all other compounds tested, amino acids, amines, etc., go to yellow. Even amino guanidine and methyl guanidine are yellow. The formation of the red compound in the presence of HCl and HNO₃ was utilized as a test with a high degree of specificity for free guanidine.

In order to determine the structure of the colored compound formed, one gram of guanidine hydrochloride was dissolved in 10 cc. of water and to this was added 4 gm. of the naphthoquinone in 25 cc. of water, with a little of the quinone still in suspension. The well stirred mixture was made definitely alkaline with 10 cc. of 5N NaOH and the solution was brought to boiling on a water bath, then quickly cooled to 10-15°C. and acidified with 15 cc. of concentrated HCl followed by 15 cc. of concentrated HNO₃. The heavy red precipitate was centrifuged and washed free of acid by water. It was then dried in a desiccator and in an oven at 80°C. Without any attempt to obtain maximum yields the weight of the material purified for analysis w2s 1.8 gm. or 80% of the theoretical yield. The compound was little soluble in cold water, slightly soluble in alcohol and rather insoluble in acetone and ether. It dissolves in dilute NaOH with a strong red color. The M.P. on quick heating was 242-245°C. with decomposition. The nitrogen content was 19.35%. The same decomposition point obtained whether the precipitant was concentrated 132, concentrated HNO₃, or mixtures of these, and mixed melting points of these precipitates showed no change.