Phenols, thermochemistry

GASEOUS RADICAL CATIONS DERIVED EROM PHENOLS THERMOCHEMISTRY OE SOME TYPICAL SPECIES AND... 

II. GASEOUS RADICAL CATIONS DERIVED FROM PHENOLS THERMOCHEMISTRY OF SOME TYPICAL SPECIES AND REACTIONS... 

The reaction between OH and phenol lends itself to an analysis of its thermochemistry. On the basis of E7( OH) = 2.3V/NHE and E7(PhO ) = 0.97 V/NHE [42], the formation of PhO and H2O via an electron-transfer mechanism is exothermic byl.33V = 31 kcal mor In spite of this, the reaction proceeds by addition, as outlined in Eq. 24. Again, the propensity of OH to add rather than to oxidize can be understood in terms of the transition state for addition being stabilized by contributions from bond making, in contrast to electron transfer which requires pronounced bond and solvent reorganization which results in a large (entropy-caused) free energy change. 

The enthalpy of formation of all three aminophenol isomers have been measured twice. Two well-respected contemporary organic thermochemistry groups have studied these species76,77. Although disparate, they are closer than some other pairs of competing values cited in this text. Which set, if either, do we choose We prefer those of Reference 76. From the archival enthalpy of formation of gaseous phenol of —96.4 0.9 kJmol-1 and equation 2, the enthalpy of formation of any of the isomers is ca —92 kJmol-1 in the... 

The behaviour of the tyrosyl radicals involved in different processes and environments is not yet well understood Relatively little is known about the structure and selectivity of aryloxylium cations (Ar—0+) that are produced in the phenolic oxidation reactions and implicated in biological processes such as isoflavone synthesis . The thermochemistry which is relevant to the antioxidant properties of phenols as well as the solvent effects on their reactivity ° remain also a largely under-explored topic. Finally, the structure of phenol dimers and oligomers or even of some specific phenols also deserve more attention. We expect that these problems will be subjects for theoretical research in the coming years. 

Thermochemistry of phenols and related arenols to but still discrepant to both sets of contemporary results. 

Arylamines, as phenol precursors 399, 400 O-Arylation 670-673 Arylazonaphthols, thermochemistry of 252 Arylazophenols,... 

Hydroxy-3-methoxybenzaldehyde mass spectra of 296 thermochemistry of 232, 233 2-Hydroxybenzamide, thermochemistry of 232 2-HydroxybenzaniUde, thermochemistry of 232 Hydroxybenzenes—see also Dihydroxybenzenes, Phenols, Polyhydroxybenzenes,... 

Phenol-ketone novolacs 1487, 1488 Phenol-nitrile complexes 377 Phenol radical cations 1101 fragmentation of 289-291 Phenols—see also Biphenols, Bis-phenols, Hydroxybenzenes, Polyphenols acidities of, gas-phase 310-312 acylation of 629-632, 933, 934 Lewis acid catalyzed 631 montmoriUonite-catalyzed 632 pyridine-catalyzed 631 adsorption of 944 alkylation of 606-629, 941 Brdnsted acid catalyzed 612 Lewis acid catalyzed 607-611 solid acid catalyzed 612-621 stereoselective 621-626 under supercritical conditions 621 as antioxidants 139-143, 840-901 ort/io-substituted 845 thermochemistry of 139, 140, 179 autoxidation of 1118, 1119 bromination of 649-651 jr-cation interaction of 322 chlorination of 649 comparison with isoelectronic methyl, amino and fluoro aromatic derivatives 226... 

Sulfonic acids, as phenol precursors 397-399 SulfosaHcyHc acid, thermochemistry of 237 Sulfuryl chloride, as chlorinating agent 649 Supercritical fluid chromatography (SFC) 953, 955... 

The primary causes of accidents in the chemical industry are technical failures, human failures and the chemical reaction itself (due to lack of knowledge of the thermochemistry and the reaction kinetics) [156]. As discussed previously, polymerization reactions are subject to thermal runaway, so that it is not surprising to learn that polymerization reactions (64 from 134 cases) are more prone than other processes to serious accidents [157]. Among the polymerization processes, the phenol-formaldehyde resin production seems to be the worst case, although incidents have been reported for vinyl chloride, vinyl acetate and polyester resins polymerization processes. 

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