The Acidity of Weak Carbon Acids. Part 4. The Kinetic Acidities of 4-Nitro-, 4,4'-Dinitro- and 4,4',4''-Trinitrotriphenylmethanes

Article abstract of DOI:10.1039/P29900001885

Rate coefficients for the base-catalysed detritiation of 4,4',4''-trinitro-, 4,4'-dinitro- and 4-nitrotriphenylmethanes in dimethyl sulphoxide have been measured at 25.0 deg C.The bases are a series of secondary aliphatic amines and tetramethylguanidine and of benzoate anions.For 4,4'-dinitrotriphenylmethane and piperidine, the rate coefficients for detritiation at 55.0 deg C and for α-<2H₁>-4,4'-dinitrotriphenylmethane and piperidine, dedeuteriation at 25.0 deg C were also measured.The kinetic isotope effect and activation parameters indicate the rate-determining step to be the ionisation process.Bronsted coefficients, β, have been calculated using the known or previously measured pK_a values of the conjugate acids of the bases in dimethyl sulphoxide.The β values for both carbon acids are significantly greater for the benzoate anion than for the nitrogen base catalysis, and those for the dinitro-carbon acid are less than those for the trinitro-acid.No reactivity-selectivity relationship exists.This behaviour is discussed in relation to Marcus and related theories.

Full text of DOI:10.1039/P29900001885

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