ACID-CATALYZED HYDROLYSIS OF PHENYLDIAZOACETIC ACID, EFFECT OF AN ALPHA-DIAZO GROUP ON CARBOXYLIC-ACID ACIDITY

Rates of acid-catalysed hydrolysis of phenyldiazoacetic acid were meas ured in aqueous solution at 25 degrees C across the entire acidity ran ge pC(H+) = 1-13. The reaction was Found to occur through both the non -ionized and ionized forms of the substrate, with the ionized form rea cting faster by a factor of 650. Appreciable solvent isotope effects i n the normal direction (k(H)/k(D)>1) acid the occurrence of general ac id analysis show that hydrolysis occurs by rate-determining proton tra nsfer to the diazocarbon atom of the substrate, Analysis of the rate p rofile for the reaction provides an estimate of the acidity constant o f phenyldiazoacetic acid, pK(a) = 3.70, which is apparently the first determination of the acid strength of an alpha-diazocarboxylic acid. C omparison of this result with the pK(a) of phenylacetic acid shows the diazo group to have a mild (4x) acid-strengthening effect, whose mode st magnitude is attributed to opposing resonance and polar effects.