CARBON ACIDITY .86. LITHIUM AND CESIUM ION-PAIR ACIDITIES OF DIPHENYLAMINE IN TETRAHYDROFURAN - THE AGGREGATION OF LITHIUM AND CESIUM DIPHENYLAMIDE - A NEW METHOD FOR THE DETERMINATION OF AGGREGATION CONSTANTS IN DILUTE-SOLUTION

An investigation of the aggregation of lithium and cesium diphenylamide (LiDPA and CsDPA, respectively) in tetrahydrofuan solution has been carried out. Two independent methods were used; one makes use of the effect of concentration in the observed ion-pair acidity of diphenylamine, and the other is based on a spectral analysis. LiDPA is found to be a monomeric contact ion pair, in agreement with Collum's NMR results. For CsDPA, the two methods yield results that are in agreement only if a monomer/dimer equilibrium is assumed. All other hypotheses can be ruled out with high confidence. At 25-degrees-C, the dimerization constant is found to be 160 +/- 10 M-1. Together with experiments conducted at -15-degrees-C, we find the thermodynamics of dimerization to be approximately DELTAH-degrees = -2 kcal/mol and DELTAS-degrees = 4 eu. At 25-degrees-C, the lithium and cesium ion-pair pKs of diphenylamine are 19.05 and 24.20, respectively.