Claudio Giomini

Electrochemistry of organic acceptor compounds: aromatic anhydrides

Abstract The electrochemistry of some aromatic anhydrides (A; I-IX) is presented. Voltammetric experiments on I-IX at a glassy carbon electrode in dry dimethylformamide + 0.1 M Et 4 NClO 4 were used to assign the relative electron-acceptor properties of the anhydrides concerned and to reveal compounds for which persistent radical ions A − and dianions A 2− can be prepared in the solvent system used. Some results of large-scale controlled potential electrolyses of tetraphenylphthalic anhydride (IV) at a mercury pool electrode at an applied potential E of −2.2 V in the presence of weak proton donors are also reported. Phthalide (X) can be isolated among the products, albeit in a very low yield. Quenching of the electrolysed solution with a strong acid leads to dimeric lactones XI and XII.

Electrochemical screening for electron acceptors: aromatic esters

Abstract Voltammetric experiments on some aromatic esters, A, at a glassy-carbon electrode in dimethylformamide are used to study the relative electron-acceptor properties of the molecules investigated and to detect compounds for which the corresponding radical ions A.− and dianions A2− are persistent in the solvent system used. The molecules chosen include the trimethylbenzene tricarboxylates (I)-(III), tetramethylbenzene tetracarboxylate (IV), methyl-1-naphthalene carboxylate (V) and the dimethylnaphthalene dicarboxylates (VI) and (VII), as well as the methylanthracene carboxylates (VIII) and (IX). Esters (II), (III), (IV) and (VII) provide examples of two-step reductions of A, A + e−A.-, A.− + e−A2−, which are reversible even at low potential scan rates. A larger equilibrium constant for the reaction 2A. A + A2− is observed in molecules where steric interactions inhibit some CO2Me groups from being coplanar with the aromatic nucleus. The electron affinity of dimethyl-1,8-naphthalene dicarboxylate is higher than the E.A. of 2,6-naphthalene dicarboxylate. Further consideration of the voltammograms has led us to regard esters (I)-(IX) as each having some distinctive feature in its electrochemical behaviour, particularly where chemical reactions following electron transfer are thought to occur.

GASEOUS EQUILIBRIA: SOME OVERLOOKED ASPECTS

For some gaseous equilibria, with particular stoichiometric characteristics, the addition of some reactant or products, as large as it may be, when operated under constant temperature and pressure, cannot cause a (practically) complete shift of the equilibrium to the right, or to the left. The effect of the addition is counteracted by the increase of volume that the system undergoes to keep constant the pressure. [Chem. Educ. Res. Pract. Eur.: 2000, 1, 145-149]

An always‐converging, successive‐substitution, fast algorithm to perform chemical equilibrium calculations

The equation to find the equilibrium value ξe of the degree of advancement for a chemical reaction is rearranged to the form of a successive‐substitution algorithm, which, over the previously described algorithms of the same kind, has the advantage of being always convergent to ξe and, usually, at very fast rate. How to perform the rearrangement is explained in detail, and the proof of the convergence of the algorithm thus obtained is given. A numerical example to test the performance of the algorithm is presented.

pH of simple ampholytes and related compounds. A general, always‐converging, iterative algorithm

For the aqueous solutions of those electrolytes whose acid‐base behaviour is completely described by only one acid andonly one basic ionization process, a new, original, iterative algorithm for the calculation of their pH values is derived from the exact, electroneutrality equations, in a unitary fashion, although these electrolytes belong to different classes. The fact that this algorithm always converges to the root of these equations is given a qualitative proof.

Hydrolysis of salts

From a series of letters dealing with a paper from an earlier issue in this Journal (November 1987, page 957).

Two further simple methods for calculating the critical compressibility factor for the Redlich-Kwong equation of state

The authors believe that the method suggested here can profitably replace, at a didactic level, the conventional approach, which involves the first and second derivatives of the equation of state for a real gas.

Boiling Temperature vs. Composition. An Almost-Exact Explicit Equation for a Binary Mixture Following Raoult's Law.

A simple method that leads directly to the boiling temperature of a binary mixture as a function of its composition.