Acid-base equilibrium constants for the reaction of tribenzylamine with picric acid and with trinitro-m-cresol in benzene, from spectrophotometric data

Abstract

Th e relative acidic strengths ~o f picric acid and t rinitro-m-cresol in benzene have been measured spectrophotometricall y in terms of their reactivi ty with the base, t ribenzylamine. Th e r espective constants found for the combinat ion of tribenzylamine with picric acid and with trinitro-m-cresol in benzene=a t 25° Care 1.58 X 10 3 and 4.48 X 10 2 • The sam e relative order of strengths would be predicted on theoretical grounds. The constant for picric acid is in close agreement wi th previous m ea surements of the dielectric constant of benzene solutions of t ribenzy lammonium picrate. The method used for a ssessm en t of the relat ive strengths of the two 'acids is superior:to m easurem ents of their ionic dissociation in water.

Behavior of bromophthalein magenta E (tetrabromophenolphthalein ethyl ester) with organic bases and its bearing on the Bronsted-Lowry and Lewis concepts of acidity

“…The suggestion has been made [26 , 27] that tribenzylammonium picrate may exis t in isomeric forms, RaN.HPi and R aNH+Pi-, which are slowly interconvertible, but the arguments used in support of this hypothesis are not entirely convincing. N o anomalies that might b e explained on this basis were observed in spectrophotometric studies of the r eaction of tribenzylamine wi th picric acid in benzene [20], and Maryott, in measuring the dipole moment of tribenzylammonium picrate, could not detect such an equilibrium [25] . Wi tschonke and Kraus [28] were also unable to furnish exp erimental support for such an isomerism.…”

“…50, 40 2, A graphical means of evaluating the association constant is shown in figure 3 (line I ), in which log [1,20]. As required by the reaction postulated, the experimental values fall on or very close to a line of slope -1.…”

“…The shortest cells were made by combining a tubulated endplate with an endplate of crystalline quartz, 3 mm in thickness, having a central indented area 0.1 mm or 0.5 mm in depth. The cells were placed in a thermostated box maintained at 25.0° ± 0.1 ° C [20] half an hour or more b efore measurements were begun. The temperature of the room was au tomatically controlled to stay between 24° and 27° C but was usually b etween 25° and 26° C.…”

Titration of Pharmaceuticals in Nonaqueous Solvents *

“…Among these are Markunas and Riddick (55) who investigated a great number of organic compounds for their suitability to titrations in glacial acetic acid and who reported accuracy and precision obtainable. A review of nonaqueous titrations has appeared in Analytical Chemistry ( T l ) . Davis, et al (11)(12)(13), at the National Bureau of Standards studied indicators and electrode systems in various organic solvents. The application of nonaqueous titrations to acidic and basic compounds has been furthered greatly by Fritz (21).…”

“…Krynitsky, et al (50). and Hochstein (12). who utilized gasometric measurements of the liberated hydrogen for analytical purposes.…”