Über die Entstehung von α‐Keto‐carbonium‐Ionen bei der säurekatalysierten Hydrolyse von Diazoketonen. (Vorläufige Mitteilung)

Secondary deactivated aliphatic diazo compounds (diazo‐ketones RCOCN2R′; diazo‐esters ROOCCN2R′; 1, 1, 1‐trifluoro‐2‐diazopropane) are hydrolysed by the ASE2 mechanism comprising rate determining protonation of the substrate, followed by decomposition. Product analysis shows that the decomposition of the secondary diazonium ions is monomolecular, without intervention of a nucleophile. The corresponding primary diazo compounds (RCOCHN2, ROOCCHN2 and CF3CHN2) are hydrolysed by the A‐2 mechanism comprising preequilibrium protonation; the primary diazonium ion reacts with a nucleophile in a bimolecular displacement step. The only exception observed is found in p‐nitrophenyl‐diazomethane, which follows ASE2 mechanism. The observations are discussed in terms of the stability of the corresponding secondary resp. primary α‐keto‐carbonium ions.