Cage Effect in Supercritical Fluids and Compressed Gases in the Photolysis of an Asymmetrically Substituted Diazene

Abstract

We studied the photolysis of (1-biphenyl-4-yl-1-methyl-ethyl)-tert-butyl diazene in supercritical CO(2) and Xe, as well as in compressed Kr. The compound has good solubility in the mentioned fluids, allowing the photolysis measurements to be performed in CO(2) at 1.4 K above T(c) and at pressures as low as 70 bar. We monitored relative cage effect after nanosecond laser pulses by measuring the absorbance at 320 nm (DeltaA(t-->0)) corresponding to the total amount of out-of-cage 1-biphenyl-4-yl-1-methyl-ethyl radical (BME.) produced after nitrogen loss of the diazene. In supercritical CO(2) and Xe, isothermal values of DeltaA(t-->0) showed an increase-decrease behavior with increasing pressure at constant temperature, a typical feature of the transition from the solvent energy transfer to the friction controlled regimes. The comparison of the behavior of DeltaA(t-->0) in CO(2) at reduced temperatures between 1.004 and 1.027, in Xe, and in Kr points to an absence of enhanced cage effect near the critical point. Compatibility with spectroscopic data is analyzed.

Proton Transfer from 2-Naphthol to Aliphatic Amines in Supercritical CO2

“…The following chemicals were used as received: 2-Methoxynaphthalene (Aldrich, 99%), N -ethyldiisopropylamine, DIEA, (Fluka, ≥ 98%), morpholine, MP, (Merck, for synthesis, ≥ 99%), triethylamine, TEA, (Sigma-Aldrich, ≥ 99.5%), cyclohexane (Aldrich, spectrophotometric grade), and CO 2 (AGA, Coleman 99.99%). It is estimated that the oxygen content of the carbon dioxide used in all measurements is lower than 1 ppm …”

“…It is estimated that the oxygen content of the carbon dioxide used in all measurements is lower than 1 ppm. 5 Absorption and Emission Spectra. For all spectroscopic measurements, a high-pressure optical cell made of stainless steel was used, as described in previous work.…”

“…For all spectroscopic measurements, a high-pressure optical cell made of stainless steel was used, as described in previous work. 5 A Shimadzu UV3101PC spectrophotometer and a PTI-Quantamaster spectrofluorometer were used for the absorption and steady state fluorescence measurements, respectively. The absorption spectra were recorded between 200 and 350 nm with a bandwidth of 1 nm.…”

“…Therefore, understanding the factors controlling elementary reactions in scCO 2 has an importance which parallels its use as a processing solvent. We recently investigated the cage effect in geminate radical production, escape, and recombination in scCO 2 5 and we now undertake the study of proton transfer reactions because of their above appointed importance.…”

Critical Effects on Attractive Solutes in Binary Liquid Mixtures Close to Their Consolute Point: A New Experimental Strategy

“…For the case of simple solutes in pure solvents, the effect of solvent criticality on equilibrium and dynamic properties was investigated by measuring shifts in electronic absorption spectra, − or in the frequency of vibrational transitions, , fluorescence emission spectra, − fluorescence anisotropy, free radical reaction, , Raman bandwidth, and rotational and vibrational relaxations . Some of these studies indicate that, near the solvent’s critical temperature, many properties show a plateau in their density dependence, i.e., there is a density range in which the properties of the solute are practically independent of solvent density.…”