Photometric titration of weak acids in nonaqueous media.Determination of phenols in isopropyl alcohol

Abstract

k~ Photometric titrations of 16 weak acids, mainly phenols, were performed in commercial isopropyl alcohol using tetra-n-butylammonium hydroxide in isopropyl alcohol as titrant. In favorable cases, up to four components in a mixture were resolved if a suitable change in wave length setting was made during the titration. Nonlinear phoiometric titration curves for phenols provide new evidence for complex formation between phenols and phenolate ions.

Electrochemical Oxidation of the Phenolic Benzotriazoles UV‐234 and UV‐327 in Organic Solvents

“…As the phenolic BZTs are oxidized at relatively positive potentials and the use of faster scan rates did not lead to the detection of any chemical reversibility in the oxidation process, voltammetric studies were conducted in basic conditions to test for the existence of the phenoxyl radicals. Several studies have demonstrated a simple and fast procedure of preparing phenolate anions in a 100 % conversion by adding a stoichiometric amount of an organo‐soluble base such as Et 4 NOH to the phenol solutions . A large shift in the oxidation potential towards more negative values by approximately 1–2 V is typically observed for most phenols when they deprotonate to form their corresponding phenolates.…”

“…Several studies have demonstrated a simple and fast procedure of preparing phenolate anions in a 100 % conversion by adding a stoichiometric amount of an organo-soluble base such as Et 4 NOH to the phenol solutions. [28][29][30][36][37][38][39][40][41] A large shift in the oxidation potential towards more negative values by approximately 1-2 V is typically observed for most phenols when they deprotonate to form their corresponding phenolates. Figure 2 shows the CVs recorded before and after the addition of 1 mol equiv.…”

Photometric Titrations

“…Mixtures.-One of the advantages of selfindicator photometric titrations appears to be their ability to distinguish between closely related components in a mixture. Hume and his co-workers have explored the applicability of the method (11,13,14). Restricting attention to acid-base titrations (though similar conditions should be applicable to other systems), two kinds of binary mixtures described below may be encoun tered.…”

“…. &-Titration of diphenyl phosphate, 2.4dinitrophenol, p-nitrophenol, and m-nitrophenol with tetrabutylammonium hydroxide in isopropyl alcohol(14).…”

Factors Affecting Stability of Nonaqueous Quaternary Ammonium Titrants.

“…As would be expected, potassium hydroxide shows the greatest tendency to form ion pairs and this behavior is reflected in the shape of its content, and temperature on the stability of nonaqueous quaternary ammonium titrants has been studied. A comparison of the decomposition rates of 12 titrants of widely differing structure has shown tremendous differences in stability. For example, tetraethylammonium hydroxide in isopropyl alcohol has a half life of about 0.2 days at 50°C , while tetramethylammonium hydroxide has a half life of approximately 26 days under the same conditions.…”