Electrostatic catalysis by ionic aggregates. 7. Interactions of dipolar indicator molecules with ionic clusters

Abstract

The spectral changes that lithium perchlorate ions in ether solution impart upon various dipolar molecules have been explored at 25.0 O C . The molecules studied in this investigation all display UV-visible spectra, which are highly sensitive to solvent polarity (solvatochromism). Of the three types of molecules chosen for the present study, only N,N-dimethylindoaniline (phenol blue) displays UV-visible spectra that vary over the entire range of lithium perchlorate concentrations. For phenol blue, a change in the low-energy absorbance band of 104 nm is observed upon changing the solvent from pure diethyl ether to 5.05 M lithium perchlorate in ether. This corresponds to a stabilization of 8.01 kcal/mol for this transition. With the other indicator molecules, 2,6-diphenyl-4-(2,4,6-triphenyl-1 -pyridinio)phenolate (Reichardt's dye) and 8,9-diacylsesquifulvalenes, the lithium ion forms 1:l complexes. The exceptional sensitivity of Reichardt's dye to solvent polarity makes it an extremely discriminating probe for minute amounts of lithium ions in solution. An equilibrium expression was deduced that agrees well with the experimental data and leads to the following equilibrium constants for these molecules. The values for the Reichardt's dye are 5 X lo6 M-' in diethyl ether solutions and 1 X lo5 M-' in tetrahydrofuran solutions. The values for the 8,9-diacylsesquifulvalenes are 2. 39, 5.44,7.31, and 9.35 M-' for the dibenzoyl-, diformyl-, dicarbomthoxy-, and diacetyl-substituted compounds, respectively, in lithium perchlorate-tetrahydrofuran solutions and 15.8, 16.8, and 18.2 M-' for the dibenzoyl-, diformyl-, and diacetyl-substituted compounds, respectively, in lithium perchlorate-diethyl ether solution. The order of participation of lithium perchlorate in the equilibrium expression indicates that 1: 1 complexes are formed between dipolar molecules and lithium ions. Indeed, an order of 1 is displayed for all compounds, with the exception of 8,9-diacetyl-and 8,9-dibenzoylsesquifulvalene at low concentrations and 8,9-(dicarbomethoxy)sesquifulvalene at all concentrations of lithium perchlorate in diethyl ether, which form 2:l complexes with lithium ions. ( 8 ) Brooker, L. G. S.; Craig, A. C.; Heseltine, D. W.; Jenkins, P. W.; Lincoln, L. L.

A phenol-based compartmental ligand as a potential chemosensor for zinc(ii) cations

“…From the absorption profile, the binding constant is calculated to be 2.06 × 10 4 L mol -1 , following the reported equation. 20 The ESI-MS spectrum obtained with the solution containing L and Zn 2+ in a ratio of 1:2 also supports the formation of the dinuclear complex ( Figure 3). The peak at m/z 593.3 corresponds to one positively charged dinuclear species [Zn 2 (L−3H)] + , which agrees with the result of the UV spectra.…”

Highly Selective Synthetic Transformations Catalyzed by Lithium Perchlorate in Organic Media

“…Based on the NMR spectroscopic studies, according to Pocker and co-workers, lithium perchlorate forms a 1:2 etherate (LiClO 4 ⋅2Et 2 O) below 4.25  concentration and a mixture of 2:1 and 1:1 etherates above 4.25 . [16] According to Kabalka and co-workers, based on spectroscopic and chemical evidence, the increased rates of reaction of certain DielsϪAlder reactions and high selectivities are due to the mild Lewis acidity of the lithium ion in ether. [17] According to these authors, the strong and intrinsic Lewis acidity of lithium ion is moderated in diethyl ether due to its complexation with the solvent and the counter ion.…”

Solubilization of Peptides in Non‐polar Organic Solvents by the Addition of Inorganic Salts: Facts and Implications

“…The addition of salts to a non-polar medium such as THF will certainly increase its polarity ('salt effect')''). Thus, the outcome of many reactions in organic chemistry is subject to influenes by Li salts (Wittig reaction [20], conversions of Lienolates [ 11 and other enol derivatives [21], certain Diels-Alder reactions [22], deprotonations and subsequent reactions of CH-acidic compounds by tertiary amines , and other proton-transfer processes [28]), the detailed mechanisms being mostly unknown. Li salts can be used for Lewis-acid-mediated rearrangements [29].…”