Water → Pyrazine-2,5-dicarbaldehyde

Reaction equation

[CH:1]([C:9]1[CH:14]=[N:13][C:12]([CH:15]=CC2C=CC=CC=2)=[CH:11][N:10]=1)=CC1C=CC=CC=1.S(=O)(O)[O-:24].[OH2:27]>CO>[N:13]1[CH:14]=[C:9]([CH:1]=[O:27])[N:10]=[CH:11][C:12]=1[CH:15]=[O:24]

Participants

Procedure

A solution of pyrazine-2,5-dicarboxaldehyde in water is prepared by ozonolysis of 2,5-distyrylpyrazine in methanol. The ozonide is decomposed with aqueous bisulfite and the reaction mixture evaporated under vacuum at 30°. The residual aqueous solution of the dialdehyde is purified by extraction with ether--first while acidic, then while basic. From 2 g. of starting material there is obtained 15 ml of asolution of the dialdehyde (theory 0.96 g.). The pH isadjusted to pH 10-11 and 5 ml. of 2% aqueous potassium cyanide is added with cooling and stirring to dissipate the heat of reaction. There is an instantaneous formation of a red-brown precipitate turning black. Up to this point all operations have been conducted under an inert atmosphere and below 30°. The reaction mixture is heated 5 minutes on a steam bath. The pH is adjusted to 6.5. The product is collected as a red-brown solid and is dried in vacuum at 55° to give 0.3 g. of a black solid, soluble in alkali to give a deep maroon solution and soluble in acid. Anal. Calcd. for the nonamer (Formula I, n=7, X and Y=COOK) as its dodecahydrate: C54H33N18O20K3.12H2O: C, 40.80; H, 3.27; N, 15.87. Found: C, 41.16; H, 3.26; N, 15.78. Acid-base titration establishes the isoelectric point at pH 6.5. In acid, K of the formula is replaced by H.