Acceptor strength of co-ordinated boron halides
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1970
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University of Hawaii at Manoa
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Abstract
The Bronsted and Lewis basicity of R2NBX3- (where R=H, CH3 and X=Cl, F) has been measured using aqueous, non-aqueous, and tensimetric titrations of R2NBX3- or R2HNBX3. Neither (CH3)2HNBF3 nor (CH3)2NBF3- could be successfully titrated in aqueous solution implying a pK for both compounds of about 7. H3NBF3 , CH3H2NBF3 , and (CH3)2HNBF3 could be titrated in pyridine. The experimental half neutralization potentials of 172 mv, 133 mv, and 189 mv respectively demonstrate that the acidity of the amine-BF3 complexes go through a minimum at CH3H2NBF3. This behavior has been rationalized by analogy to the methylammonium ions whose acidity goes through a minimum at (CH3)2NH2+. The methylamine-BH3 complexes could not be titrated in pyridine demonstrating that they are much weaker acids than the corresponding BF3 complexes. Low temperature tensimetric titrations of (CH3)2NBF3- and (CH3)2NBCl3- using as reference acid BF3 indicate that a weak complex, (CH3)2N(BF3)2-, forms while (CH3)2N(BC13)(BF3) cannot be observed. Thus, (CH3)2NBF3- is a stronger Lewis base than is (CH3)2NBC13-. These data have been interpreted to imply that the relative acceptor strengths of the BX3 groups BH3
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Boron compounds, Halides
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Theses for the degree of Doctor of Philosophy (University of Hawaii (Honolulu)). Chemistry; no. 316
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