Apolar versus Polar Solvents: A Comparison of the Strength of Some Organic Acids againstDifferent Bases in Toluene and in Water

The constants of ion-pair formation with 3-nitroaniline (3NO2A) for eight halogenoacetic acids (HAAs, 3a-h:TFA, TCA, TBA, DFA, DCA, DBA, MCA, and MBA), and five 2,2-dichloroalkanoic acids containing 3-8carbon atoms (HAs, 5a-e: DCPA, DCBA, DCMBA, DCVA, and DCOA) have been determined in TOL at298.1 K. The results obtained brought to evidence for HAAs the formation of ion-pairs with two differentstoichiometries (base-acid, 1:1 or 1:2), while in contrast the HAs furnish only the 1:1 pairs. The differentsteric and electronic requirements of HAAs and HAs seem to be responsible for such an unlikely behavior.At the same time, the acid-catalyzed MRH of the (Z)-phenylhydrazone of 5-amino-3-benzoyl-1,2,4-oxadiazole(1) into (2,5-diphenyl-2H-1,2,3-triazol-4-yl)urea (2) in the presence of the five HAs above has been investigatedin TOL at 313.1 K. Thus, in contrast with previous results in the presence of several HAAs, a unique pathwayfor the rearrangement has been observed, again pointing out the importance of the above effects on the initialacid/base interactions. Finally the acidic strength of TFA against seven nitroanilines (NA, 4a-g: 4NO2A,3NO2A, 3Me4NO2A, 4Me3NO2A, 2Me3NO2A, 2NO2A, and 3,5diNO2A) characterized by a very differentbasicity has been measured in TOL at 298.1 K.