Conductimetric studies in ketonic solvents. Part V. Quaternary ammonium salts in ethyl methyl ketone

Abstract

Conductances in ethyl methyl ketone a t 25" are reported for a series of quaternary alkylammonium salts including the tetra-n-alkylammonium iodides and bromides from methyl up to n-octyl. Single-ion conductances have been evaluated by use of n-butyltri-isopentylammonium tetraphenylboride as the reference electrolyte. Hydrodynamic radii give no evidence of solvation of the cations while association parameters indicate anion penetration of the cations in association.

Conductivity and Dissociation Constants of Quaternary Ammonium Perchlorates and Picrates in 4-Methyl-pentan-2-one

“…Indeed, it is natural to expect (and is repeatedly proved experimentally – ) that the Λ 0 values of N( n -C n H 2 n +1 ) 4 X salts with fixed X − ion or of the individual cationic mobilities, Λ + , decrease along with the increase in n . However, the data for n > 5 are few in number. ,,,,, On the other hand, the asymmetrical cations, for example, N( n -C 18 H 37 )(CH 3 ) 3 + or N( n -C 18 H 37 )( n -C 4 H 9 ) 3 + , exhibit a smaller mobility as compared respectively with N(CH 3 ) 4 + and N( n -C 4 H 9 ) 4 + . ,– However, there is a lack of data for making firm conclusions about such properties of symmetrical and asymmetrical cations of equal total van der Waals size. Probably, the sole exception is the report of Hughes and Price on the mobilities both of symmetrical TAA + ions (C 1 to C 8 ) and asymmetrical ones, such as N( n -C 4 H 9 ) 3 (CH 3 ) + and N( n -C 7 H 15 ) 3 (CH 3 ) + in methyl ethyl ketone.…”

“…However, the data for n > 5 are few in number. ,,,,, On the other hand, the asymmetrical cations, for example, N( n -C 18 H 37 )(CH 3 ) 3 + or N( n -C 18 H 37 )( n -C 4 H 9 ) 3 + , exhibit a smaller mobility as compared respectively with N(CH 3 ) 4 + and N( n -C 4 H 9 ) 4 + . ,– However, there is a lack of data for making firm conclusions about such properties of symmetrical and asymmetrical cations of equal total van der Waals size. Probably, the sole exception is the report of Hughes and Price on the mobilities both of symmetrical TAA + ions (C 1 to C 8 ) and asymmetrical ones, such as N( n -C 4 H 9 ) 3 (CH 3 ) + and N( n -C 7 H 15 ) 3 (CH 3 ) + in methyl ethyl ketone. Interestingly, some authors state that in media of low relative permittivity the conductivity of tetraalkylammonium salts is not greatly affected by the length of the hydrocarbon chain of the cation …”

“…The values of molar conductivities of a set of TAA + ions with n from 1 (or 2) to 7 (or 8) are available in several solvent systems, ,,, but in the case that the viscosity is high, the Λ 0 values are rather small and relatively close to each other. The same concerns the data in nitrobenzene, 1,2-dichlorobenzene, sulfolane, ethylene glycol, and propylene carbonate .…”

UV–Vis spectrophotometric studies of self-oxidation/dissociation of quaternary ammonium permanganates (QAP) – impact of solvent polarity

“…For symmetrical tetraalkylammonium ions, an inverse relationship occurs between the second-order rate constants and the radius of the cation [15]. Since the ion-pairing stability is inversely dependent upon the inter-ionic distance between the centers of positive and negative charge, the transition state must form a tighter ion pair than the ground state, i.e.…”

“…Moreover, close contact within the ion pair seems to increase the rate of reaction. For example, the rate constants for the oxidation of methyl cinnamate with methyltri-n-octylammonium permanganate are greater than that with tetra-n-octylammonium permanganate because the former allows a greater penetration of the anion into the structure of the cation [12,15,16]. It therefore appears that QAPs may exist as solvent-separated ion pairs in acetone, but as intimate ion pairs in toluene and methylene chloride [17][18][19].…”