PROTON AFFINITIES AND AGGREGATION STATES OF LITHIUM ALKOXIDES, PHENOLATES, ENOLATES, BETA-DICARBONYL ENOLATES, CARBOXYLATES, AND AMIDATES IN TETRAHYDROFURAN

The proton affinities of the title compounds are represented by their heats of deprotonation, DELTA-H(dep), through reactions with lithium bis(trimethylsilyl)amide, LiHMDS, in tetrahydrofuran at 25-degrees-C. Aggregation numbers of the parent acid and of its lithium salt at a concentration of 0.10 M were obtained by vapor-pressure osmometry at 37-degrees-C. Lithium phenolates were also studied by conductivity at 25-degrees-C. DELTA-H(dep)s for 27 oxygen, nitrogen, and carbon acids of varied types correlate fairly well (R = 0.95)with their published pK(a)s in dimethyl sulfoxide although their degrees of aggregation in THF vary from one to over seven. In some cases, the DELTA-H(dep) of an acid is strongly dependent on the concentration ratio of LiHMDS to that of the acid's lithium salt at the time of measurement. Aggregation numbers determined by VPO in this report agree with available published values obtained by previous workers using several techniques. There is no obvious relationship between the aggregation number of the lithium salt and the basicity of the corresponding anion as represented by DELTA-H(dep). This observation along with independent evidence for equilibria betweenmonomers, dimers, tetramers, etc. for a number of compounds indicate that there are only small differences between the relative stabilities of different aggregation states. Conductance data for lithium p-nitrophenolate were treated by Wooster analysis, the results of which suggest equilibria between ion triplets, ion pairs, and free ions in THF. The conductance of LiHMDS in this solvent is surprisingly high, and this property was used to demonstrate an interaction between LiHMDS and lithium omicron-tert-butylphenolate.