CYCLOPROPANEDIAMINES .6. AUTOCATALYTIC CONVERSION OF 1-METHYL-R-1,T-2-CYCLOPROPANEDIAMINE INTO 4-AMINOBUTAN-2-ONE IN AQUEOUS BUFFER SOLUTIONS OF PH-6.5-10 - AZOMETHINE YLIDES AS INTERMEDIATES IN THE CATALYSIS BY ALKYL KETONES

The pK(a) values of 1,2-cyclopropanediammonium dibromides (1-5 . 2HBr) were determined by potentiometric titration with KOH. Corrections for overlapping ionizations and for the varying ionic strength were emplo yed in the calculation of the thermodynamic acidities. The equilibrium constant K-E = 2.9 of the two monoprotonated forms of trans-3b . H+ w as derived from the pK(a) values and the pH dependence of proton spect ra which were interpreted with the help of nuclear Overhauser experime nts. The autocatalytic conversion of trans-3a . 2HBr into 4-aminobutan -2-one (8) in various buffer solutions of pH = 6.5-10 was monitored by proton spectroscopy. This sequence of reactions is subject to a gener al acid/base catalysis and also catalyzed by acetone and butanone.