Half-neutralization potentials

The influence of substituents in mono- and disubstituted 2,3-dimethyl-quinoxalines and their conjugate acids on the UV and NMR spectra have been correlated with a,196 while stretching frequencies of the carbonyl group of 6-substituted quinazolinediones and their half-neutralization potentials have been related to ctp.197... 

Andronati and co-workers reported a detailed study of the A-basicity of compounds 203 (X = H, Me R1 = H R2 = H, Br, Cl, Me) which contain amide, imine, and amine nitrogens in one molecule. The basicities, obtained from the half-neutralization potentials in potentiometric titrations, showed 203 to be monoacidic bases the basicity varied predictably with substitution and fell between the stronger quinoxaline-2-ones and the weaker l,4-benzodiazepine-2-ones. Ultraviolet spectroscopic studies demonstrated that the amino, not the imino, nitrogen was N-protonated (83CHE337). 

Fig. 6.6. Relationship between pKb(water) of N-bases and half - neutralization potential El/2 for potentiometric base titration in glacial acetic acid. 1) 4-aminopyridine (4.83), 2) morpholine (5.30), 3) 2,4,6-trimethylpyridine (6.68), 4) pyridine (8.85), 5) p-toluidine (8.88), 6) o-toluidine (9.61), 7) 3-acetylpyridine (10.82), 8) chloroaniline (11.36), 9) pyrazole (11.47), 10) diphenylamine (13.10) (Pawlak et al., 1985)...

Finally, we have considered the half-neutralization potentials (HNP) of 4-substituted N,iV-dimethylanilines in 2 1 chloroform-acetic acid . The best regression equation is ... 

The end points and half neutralization potentials (HNP) were Identified by the inflections in the EOT (MV) titration curve. A 0.3 thymol blue Isopropanol solution also served as an effective end point indicator (yellow to blue). 

Scheme I. HALF NEUTRALIZATION POTENTIALS IN DMF EMF(iiiv)Hydrogel Derivative...

TABLE 2. Half-neutralization potentials for some silanethiols and silanols23... 

The two-electron reductions of [Fe(CO)2(NO)(>/3-C3H4R)] (R = Cl, Br, or Me) (248) and [Co(CO)2L(>/3-allyl)] (L = phosphine or phosphite) (249) result in metal-allyl bond cleavage. For the cobalt complexes there is a linear correlation between Elj2 and the half neutralization potential of L. The rhodium complex [Rh P(OMe)3 2(fj3-allyl)] reacts with AgPF6 to give [Rh P(OMe)3 2(f 4-C6Hi0)] in which the two C3 fragments have been oxidatively coupled (250). 

A linear correlation is reported between 8p(phosphine) and the change in chemical shift that occurs upon co-ordination of tertiary phosphines with a number of transition metals. The half-neutralization potential, the Taft a, and Sp of the complexes of tertiary phosphines and titanium tetrachloride have been found to be related. The equilibria involving the co-ordination of phosphoryl compounds and water with metal ions such as Al + are sufficiently slow to be studied by n.m.r. and P n.m.r. spectroscopy. Discrete signals from co-ordinated and unco-ordinated ligands are observed. Where this does not occur the equilibrium constant can be estimated from a plot involving chemical shift and concentration of reactant. ... 

Phenylureas. The phenylureas show extremely weak acidic properties in aqueous systems. Partial ionization occurs in basic (4.2N NaOH) solution (355). Although the phenylureas are too weak to be titrated in aqueous systems, Cluett (355) titrated them in an organic solvent and used the half-neutralization potentials (HNP) as an index of acidity (the larger the HNP, the weaker the acid). The HNP values, along with other properties, for several phenylurea herbicides are given in Table IX. The HNP values decrease as water solubilities decrease and parachors increase. 

The nonaqueous titration of trifluproma-zine hydrochloride in acetone with perchloric acid in dioxane as titrant and dimethyl yellow as indicator has been described. 2 jt is suitable for formulation content assays. Titration with perchloric acid was employed to determine the half neutralization potentials (E-1/2) with a Fisher titrimeter in several organic solvents. The following E-1/2 values (in mv) were found acetic acid 234, acetone 455, acetonitrile 424, isopropanol 445, nitromethane 314. 

Glass Calomel RaN p-Me<. SOaH Me-SOaH HCIO4 (in dioxane) half-neutralization potentials 30... 

---