Dipole moments and molecular association of some picrates of primary, secondary, and tertiary amines in benzene and dioxane

Abstract

The dielectric constants of dilute benzene and dioxane solutions of primary, secondar y, and tertiary amine salts of picric acid were measured . Dipole moments are reported fo r the picrates of t h e followingamines ; in benzene: tri-iso-a m yl-(11.9), tTi-n-b uty l-(11.9) , t ri ethyl· (11.7) , di ethylben zyl-(11 .8) , di-n-butyl-(11.5) , di-n-p ropyl-(11. 5) ; in d ioxanc : tr·i-n-butyl-(12.2) , di-n-butyl-(12.1) , n-ocLy l-(12.1), and n-octadecyl-(12.3). The picrates of primary and secondary amincs show a p rono un ced t endency to a s ociate in benzene, as cvidenced by the nonlincar variation in die lectri c constan t with concentration , but not in d ioxane . The efrect of the s ize a nd shape o f th e a lk y lammo nium ion and of hydrogen bo ndin g on t he a ssociation a re d iscusscd .

Conductance and Association of Secondary and Tertiary Alkylammonium Salts in Organic Solvents

“…The extent ofion-pair association of solutes with identical chain length and anion in o-dichlorobenzene decreases with tncs-eaatng substitution on the nitrogen atom. A similar trend has been observed earlier [3,4] for the butylammonium picrate series in nitrobenzene and probably also in benzene [15]. However, the difference of more than three orders of magnitude in K between didodecyl-and tridodecylammonium chloride found in this work, as compared to only a slight difference in K between Bu~H2 Pic and BuaNH Pic, K = 6.5 X lOs and 5.4 X lOS respectively [3,4], suggest that o-dichlorobenzene is a more "differentiating solvent", while nitrobenzene, due to its higher dielectric constant, is more a "leveling-off" solvent.…”

Acid-base behavior in aprotic organic solvents

“…Kraus and co-workers [342] demonstrated that quaternary and tertiary ammonium picrates and halides have large polar (dipole) moments in benzene solution. Subsequently, Maryott [23,343] confirmed this finding and determined the dipole moments of additional salts, including some primary and secondary ammonium picrates. Results of both authors are shown in table 36. It is clear that the dipole moments of the salts are far larger than the moments of the component bases and acids, which are in the range 0-2 D (Debye unit).…”

Acid-base equilibrium constant and dipole moment of tribenzylammonium picrate in benzene from measurements of dielectric constant

“…e/N2, with incr easing dilution indicates tha t the salt is partly dissociated into picric acid and tribenzy1a-mine. The equilibrium constan t for this r eaction , + B Z3NH ... Pi = B z3N + HPi, can be determin ed by a procedure similar to th at describ ed previously [2] . R egarding the change in dielectric constan t as th e sum of three independent contributions that are lin ear functions of the concentrations of the acid, base, and salt, r espectively, • Obtained from least squares solution of eq 3, as shown in figure 1.…”

“…S uch acid-base equilibria are well suited for study because of the r elatively large dipole moment of the sal t compared to that of the component acid and base. In a previous investigation of the picrates of various alkylamines of sufficient basic strength to prevent · measurable dissocia tion into fr ee acid and base [2] , it was found that t he picrates of t ertiary amines, but no t those of primary and secondary amines, showed no significant association in benzene. Consequ en tly, association of th e salt should not be a complicating factor in the reaction with tribcnzylamin e. …”

“…The equipmen t and procedure have been described [2] . Tribenzylammonium picra te was prepared in the sam e manner as the other picrates.…”