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

Abstract

In a continuat ion of sp ectrophotometric studies of it s indicator properties in benzene, bromophthalein magenta E (t et rabromophenolphthalein ethyl ester) has been sholVn to react with 1,3-diphenylguanidine and with 1, 2,3-triphenylg uanidine in two s teps t hat correspond to the equations : (1) R 3N + HX<=± R 3NH+ ... X -(magenta) ; (2) R 3NH + . .. -X-+ R 3K <=± (R3NHNR3)+X -(blue). The association constants l{J and l{2 for these reactions with diphen ylguanidine are 2.2 x 105 and 15.5, respectively. For the reactions with triphenylguanidine, l{J is 525 and l{2 is of the same order as t he l{2 for t h e reaction with diphenylguanidine. R eplacing benzene by ethanol or pyridine produces the same kind of effec t a s increasing t he concentrat ioll of di-or t riphenylguanidine. The resul t s indicate t hat the Br\'lllsted-Lowr y formu lat ion of an ac id-base reaction should be modified, and that hydrogen acids should be regarded as a special class of Lewis acids.

Thermodynamic constants for association of isomeric chlorobenzoic and toluic acids with 1,3-diphenylguanidine in benzene

“…The dimer-monomer data used in making the corrections are not known with certainty to be accurate. Self-association of diphenylguanidine, formation of complex anions (RCOOHOCOR) − , the “secondary” reaction of diphenylguanidine with bromophthalein magenta E [ 6 ], and adsorption of solutes on glass-or silicaware are additional possible causes of errors. However, it is believed that experimental uncertainties in the optical data are the main obstacle to the attainment of high accuracy; these have more effect when the association constants are relatively great in magnitude (10 5 to 10 6 ), as in the present work.…”

“… 9 In comparing relative acidic strengths in water and benzene, one must bear in mind that the primary acid-base reaction eq (1) is a shift of the acid proton toward the base to form hydrogen-bonded ion-pairs. Formation of independently moving ions occurs to a very minor extent unless the ions can become hydrogen-bonded to molecules of solvent or solute [ 3 , 6 ]. This “secondary reaction” is likely to hamper study of the main acid-base interaction.…”

Brønsted Acid—Base Behavior in “Inert” Organic Solvents

“…. Equations 6 and 7 are based on the postulate 17 that in aqueous solutions the proton, H + , is likely to be associated with at least two water molecules, and not just the one molecule implied in the familiar formula for the hydronium ion (H 3 0 + h. In actuality, when in dilute aqueous solutions the proton is believed to be associated with four molecules in the manner indicated by I, and the water molecules constituting OH 2 + A"... HOH (6) Adding Eqs.…”

“…17 In all of the investigations cited the authors were convinced that homoand heteroconjugation involve hydrogen bonding. 17 In all of the investigations cited the authors were convinced that homoand heteroconjugation involve hydrogen bonding.…”

Acid-Base Titrations in Nonaqueous Solvents

“…Triethylamine in water is a much stronger base toward such acids as hydrochloric than it is in the gaseous state toward trimethylboron. However, Davis and Hetzer (29) pointed out that in water, as in other media, the proton does not have an independent existence.…”