Fuoss

R. M. Fuoss and F. Accasciua, Electrolytic Conductance, Interscience PubHshers, New York, 1959. 

The importance of the solvent, in many cases an excess of the quatemizing reagent, in the formation of heterocyclic salts was recognized early. The function of dielectric constants and other more detailed influences on quatemization are dealt with in Section VI, but a consideration of the subject from a preparative standpoint is presented here. Methanol and ethanol are used frequently as solvents, and acetone,chloroform, acetonitrile, nitrobenzene, and dimethyl-formamide have been used successfully. The last two solvents were among those considered by Coleman and Fuoss in their search for a suitable solvent for kinetic experiments both solvents gave rise to side reactions when used for the reaction of pyridine with i-butyl bromide. Their observation with nitrobenzene is unexpected, and no other workers have reported difficulties. However, tetramethylene sulfone, 2,4-dimethylsulfolane, ethylene and propylene carbonates, and salicylaldehyde were satisfactory, giving relatively rapid reactions and clean products. Ethylene dichloride, used quite frequently for Friedel-Crafts reactions, would be expected to be a useful solvent but has only recently been used for quatemization reactions. ... 

The most thoroughly investigated compounds are the alkyl-pyridines. Coleman and Fuoss compared the reactions of pyridine, 4-picoline, and 4-isopropylpyridine with n-butyl bromide and found a steady increase in the rate in the order given the activation energies are 16.0,15.95, and 15.6 kcal per mole, respectively. Brown and Cahn carried out a detailed study of the reactions of 2-, 3-, and 4-alkyl-pyridines with methyl, ethyl, and isopropyl iodides in nitrobenzene the results are given in Table II. These data show the higher activation... 

The influence of solvent polarity on the rate of quatemization is well known and recent measurements have supported the general view that the more polar solvents produce a faster reaction. Fuoss and his colleagues determined the rate of reaction in a number of solvents and discovered that the process was twice as fast in... 

A criterion for the presence of associated ion pairs was suggested by Bjerrum. This at first appeared to be somewhat arbitrary. An investigation by Fuoss,2 however, threw light on the details of the problem and set up a criterion that was the same as that suggested by Bjerrum. According to this criterion, atomic ions and small molecular ions will not behave as strong electrolytes in any solvent that has a dielectric constant less than about 40. Furthermore, di-divalent solutes will not behave as strong electrolytes even in aqueous solution.2 Both these predictions are borne out by the experimental data. 

Table 3. Coefficients S, E J, and J, for IcCM evaluations based on the non developed Fuoss-Hsia conductivity equation [96],...

In Eq. (15) 2 qB/r is the coulombic part of the mean force potential, and Wjj is the noncoulombic part. The earlier association constants of Fuoss, Prue, and Bjerrum are special cases of this general chemical model [15]. The importance of noncoulombic interactions is proved [ 16] by ... 

Ion-pair association constants K A determined with the set of conductivity equations (7)—(15) agree with those obtained from Eq. (18) and (19) [100]. Salomon and Uchiyama have shown that it is also possible to extend the directly Fuoss-Hsia equation to include triple-ion formation [104],... 

Conductivity curves (A versus c ) of salts in solvents of low-permittivity commonly show a weakly temperature-dependent minimum around 0.02 molL-1 followed by a strongly temperature-dependent maximum at about 1 mol L 1. According to Fuoss and Kraus [101,102] the increase of conductivity behind the minimum is due to the formation of new charge carriers from the ion pairs. They assume that coulombic forces suffice to form bilateral cationic [C+A-C+] and anionic [A C+A ] triple ions in solvents of low-permittivity ( <15) if the ions have approximately equal radii. 

Fuoss RM, Katchalsky A, Lifson S (1951) Proc Natl Acad Sci USA 37 579... 

Physical Chemistry of Synthetic Polyelectrolytes Eisenberg, H. Fuoss, R. M. 1... 

Gathers and Fuoss have shown that the conductance of poly-(4-vinyl-N-butylpyridinium bromide) increases with the dielectric constant of the medium. The energy of removal of a mobile bromide ion from the electrostatic field of the molecule decreases as the dielectric constant is increased hence the number of free ions and the net charge on the polymeric ion should increase. Both contribute toward increasing the conductance. ... 

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