Reactions of Phenyl Substituted Barbiturates in Concentrated Sulfuric AcidThree reactions of phenobarbitone in concentrated sulfuric acid were investigated.(1) With sodium nitrite in concentrated sulfuric acid phenobarbitone forms an orange EDAcomplex (Ph. Eur.).(2) With an excess of formaldehyde in 83,7 % sulfuric acid phenobarbitone gives a ruby colour (DAB 7) which is due to the formation of carbenium ions. The final product of the reaction is a yellow substance with methylene-and oxymethylene bridges. (3) The reaction of phenobarbitone with piperonal in sulfuric acid (DAB 7-DDR) is in reality areaction with formaldehyde, whichis formed as an intermediate. Only 1/13 mole of formaldehyde is formed per mole of phenobarbitone. The green colour is due to a quinone structure without methylene-or oxymethylene bridges. In this reaction piperonal can be replaced by hexamethylentetramine or trioxane.Phenobarbital wird nach der Ph. Eur. durch die Orangefarbung identifiziert, die esmit Natriumnitrit in konzentrierter Schwefelsfiure gibt. Das DAB 7 lie13 Phenobarbital zur Identifizierung mit Formaldehyd-Schwefelsfiure umsetzen, wobei eine Weinrotfarbung entsteht. Das DAB 7-DDR identifziert Phenobarbital durch die Griinfarbung, die bei der Behandlung mit Piperonal in konzentrierter Schwefelsfiure auftrit t . Me *) Teil der Dissertation von Reinhard Srreck, Tiibingen 1976.