Phenoxide Anion Research Articles

Thermodynamics of hydration of 3-substituted and 3,5-disubstituted phenols

The enthalpies of transfer of 3-chloro-, 3-nitro-, and 3-t-butyl-phenol and their 3,5-disubstituted analogues from the gas phase to aqueous solution are reported together with the corresponding free energies and entropies of transfer for 3-nitro-, 3,5-dinitro-, 3-t-butyl-, and 3,5-di-t-butyl-phenol. The results support previous conclusions that the entropies of ionization of phenols in water are not solely explicable in terms of the electronic effects of ring substituents on the hydration of phenoxide anions. The hydration of the neutral phenols must also be considered and in some cases becomes the predominant factor influencing the effect of substituents on entropies of ionization. Contrary to current theories the solvent ordering effect of phenoxide anions does not always become weaker if substituents are replaced by other substituents which withdraw electronic charge more strongly from the ring position at which the phenoxide oxygen is sited.

The N→O and N→S Migrations of the s-Triazinyl Groups of N,N-Di-s-triazinyl Derivatives of o-Aminophenol and o-Aminothiophenol

Abstract N,N-Bis(dichloro-s-triazinyl)-2-aminophenol reacted with an excess of dimethylamine or methylamine to give N,O-bis(s-triazinyl)-2-aminophenol and N-s-triazinyl-2-aminophenol upon the aminodechlorination, N→O migration, and cleavage of the s-triazinyl group. However, N-(dimethoxy-s-triazinyl)-N-(dichloro-s-triazinyl)-2-aminothiophenol reacted with an excess of dimethylamine to give merely a disulfide of N-s-triazinyl-2-amino-thiophenol upon the aminodechlorination and cleavage of the dimethoxy-s-triazine nucleus. On the other hand, N,N-bis(s-triazinyl)-arylamines containing no ortho-OH or -SH group were stable to the attack by amines, while phenoxy-dimethoxy-s-triazine or phenylthio-dimethoxy-s-triazine reacted readily with dimethylamine to give dimethylamino-dimethoxy-s-triazine upon the fission of phenol or thiophenol. From these resutls, the reactions of the N,N-bis(s-triazmyl) derivatives of both o-aminophenol and o-aminothiophenol with amines to give the corresponding N-s-triazinyl derivatives are considered to proceed by means of an intramolecular nucleophilic attack by the phenoxide or thiophenoxide anion on the s-triazine ring carbon to give the N,O- or N,S-bis(s-triazinyl) derivative upon the N→O or N→S migration of the s-triazinyl group, followed by the cleavage of the O- or S-s-triazinyl group to give the final product. However, when the intermediary derivative is stable to amine, the intermediate is obtained as the major final product.

Effects of Substituents on the Smiles Rearrangement of O-s-Triazmyl-2-aminophenoIs

Abstract Several 4- or 5-substituted O-(s-triazinyl)-2-aminophenols were synthesized, and the kinetics of the Smiles rearrangement of these compounds have been studied spectrophotometrically in methanol, ethanol, and 2-propanol in order to make clear the effects of substituents on the rearrangement. Substituents in the s-triazine nucleus were found to affect the progress of the reaction to a great extent by changing the positive character of the triazine-ring carbon. On the other hand, a substituent in the aminophenol moiety affects both the nucleophilic reactivity of the attacking amino group and the stability of the leaving phenoxide anion or the reactivity of the s-triazinyl group, but the effect on the amino group was found to be predominant, the effect of a substituent in the aminophenol moiety was smaller than that of the substituents in the s-triazine nucleus.

The thermodynamics of hydration of phenols

The solubilities and enthalpies of solution in water of 2-cresol and 4-cresol at 25 °C and the solubility of 4-t-butyl-phenol in water at four temperatures have been measured. The thermodynamic parameters for solution of the three phenols are combined with the parameters for sublimation to give information on the transfer of the phenols from the gas phase to aquous solution. The free energies of hydration of seven substituted phenols are linearly related to the Hammett σ-parameters for the substituents. Either electron accepting or donating substituents in phenol make the enthalpy of hydration more negative. The greater the dipole moment of the phenol the stronger is the attractive solute–solvent interaction. The increment to the entropy of ionization of phenol produced by alkyl substitution results from partial compensation of larger increments to the entropies of hydration of both the phenoxide anion and the neutral phenol.

Effect of 4-substitution on the thermodynamics of hydration of phenol and the phenoxide anion

Enthalpies, entropies, and free energies of sublimation of phenol, 4-bromophenol, 4-formylphenol, and 4-nitrophenol have been evaluated from measurements of the vapour pressures of the solid phenols as a function of temperature. Heats of solution of the phenols in water have been determined calorimetrically and together with solubility data allow calculation of the entropies of solution. Enthalpies, free energies, and entropies of hydration are deduced and are discussed in relation to the effect of 4-substituents on the thermodynamics of ionization of phenol in water. Enthalpies of solution and solvation of the four phenols in methanol have also been measured.

Oxidation of alkoxyphenols. Part XIX. Base-induced coupling of halogenophenols

6-Bromo-4-t-butyl-o-cresol reacts with alkali to give a trimeric spiro-acetal (IV), and 2-bromo-4,6-di-t-butylphenol gives a dimeric benzoxet (VIII). 2-Bromo-4-methoxy-5-t-butylphenol gives some of the corresponding spiro-acetal (XII) but is partly demethylated. These reactions can be explained by an electron transfer from the phenoxide anion to the keto-tautomer of the phenol, and loss of bromide from the resulting radical-anion. A chain reaction ensues involving debromination of an intermediate bisbromocyclohexadienone to a dipheno-2,2′-quinone [bi(cyclohexa-2,5-dien-1-ylidene)-2,2′-quinone]. Evidence is presented in support of these proposals.

Steric hindrance and acidity. Part I. The effect of 2,6-di-t-butyl substitution on the acidity of phenols in methanol

The acid ionisation constants in methanol at 25° of four 4-substituted phenols and their 2,6-di-t-butyl analogues have been measured by a spectrophotometric method. The increment in pKa produced on introduction of the two 2-t-butyl groups was a function of the electron-withdrawing power of the 4-substituent. The results are in accord with a severe steric inhibition to solvation at the phenolic oxygen atom of the hindered phenoxide anions. The solvation requirements of the 4-substituents are also considered to be of possible importance. The “anomalous” pKa of 4-nitro-2,6-di-t-butylphenol is discussed.

Kinetic Studies of Solvolysis. XI. The Steric Course of the Phenolyses of Optically Active α-Phenylethyl Chloride in Mixtures of Various Phenols and Organic Solvents—A Mechanism for the SN1 Reaction with a Net Retention of Configuration

Abstract The SN1 phenolyses of optically active α-phenylethyl chloride in binary mixtures of organic solvents and certain substituted phenols (i. e., phenol, p-cresol, p-chloro- and p-nitro-phenol) proceed in the presence of aniline and of triethylamine to give the corresponding α-phenylethyl substituted-phenyl ethers with a predominantly-retained configuration. In binary mixtures of benzene and various phenols, the extents of retention for the ethers are slightly reduced at the higher base concentrations. However, in binary solvents of acetonitrile and certain phenols, the optical purities of the ethers with retained configurations decrease continuously with the base concentrations, while at the higher concentrations (∼0.4 m) the steric courses change to the inverted course. The C-alkylated (α-phenylethylated) derivatives of these phenols, isolated along with the phenyl ethers, have inverted configurations, irrespective of the configurations of the corresponding phenyl ethers. These results are all consistent with a mechanism in which a molecule of the phenol reacts with the SN1 ion-pair intermediate of the phenolysis to give a phenyl ether with a retained configuration, probably by SNi-like four-center substitution, whereas the reaction of a phenoxide anion with the SN1 intermediate proceeds predominantly by the Walden inversion mechanism yielding a phenyl ether and α-phenylethylated phenols with inverted configurations.

Solvation of ions. Part VIII. S N2 reactions of phenoxide and carboxylate anions with methyl iodide in methanol and in dimethylformamide

Rate data for the SN2 reactions of methyl iodide with the sodium of lithium salts or some phenols, carboxylic acids, and 4-nitrothiophenol in methanol and in dimethylformamide are reported. The reaction of methyl iodide with methanol containing sodium picrate is shown to be methanolysis, rather than an SN2 reaction of picrate ion as reported in Part II. Hydrogen-bonding solvation of phenoxide and carboxylate ion by methanol decreases as the negative charge on oxygen becomes more dispersed. Both acetate and phenoxide ion are powerful hydrogen-bond acceptors. Nucleophilic tendencies change significantly on transfer from methanol to dimethylformamide.The decrease in enthalpy of activation of the SN2 reaction and the decrease in vmax. of the electronic absorption spectrum of phenoxides, on transfer from methanol to dimethylformamide, are compared.

Ionization of phenol, the cresols, and the xylenols in methanol

The acid ionization constants of phenol, the cresols, and the xylenols in methanol at 25°C have been measured by ultra-violet spectrophotometry. Comparison of the constants with those for aqueous solution suggest that for 2-methyl phenols steric inhibition to the solvation of the phenoxide anions tends to increase the free energy change accompanying ionization. This effect is greater in methanol than in water.

Anodic Reactions of Simple Phenolic Compounds

A study of the anodic reactions of phenols was made using the techniques of voltammetry, coulometry, and controlled potential electrolysis. It was shown that two entirely different anodic reactions are possible with phenolic compounds. The first is an electrophilic attack on the aromatic nucleus of the nonionized phenol with the irreversible removal of two electrons to give a mesomeric phenoxonium ion. As an example of this process an electrolysis of 2,6‐di‐tert‐butyl‐p‐cresol in acetonitrile at a platinum anode resulted in the addition of methanol to form 2,6‐di‐tert‐butyl‐4‐methyl‐4‐methoxy‐cyclo‐hexadienone in 65% yield. The second possible electrode reaction is the reversible removal of one electron from the phenoxide anion to give a phenoxy free radical. This process was illustrated by the electrolysis of the vanillinate anion in acetonitrile at a platinum anode to give dehydrodivanillin in 65% yield. It was found that half‐wave potentials for both electrode reactions could be correlated by Hammett‐type equations. Brief voltammetric experiments in 50% aqueous isopropanol on a carbon electrode indicated that both reactions could also occur in this system, depending on the pH and on the of the phenol being investigated.

キサントヒドロールを用いる呈色反応 (第3報)

In the reaction of phenol and xanthydrol in hydrochloric-acetic acid solution, 9-(p-hydroxyphenyl) xanthene (I) is formed as the intermediate of a pigment formation but when the reaction is allowed to proceed in glacial acetic acid solution, 9-(o-hydroxyphenyl) xanthene (II) is formed in about an equal amount with I. I and II can be separated by alumina chromatography and can be discriminated easily by the marked difference in their coloration behavior to the Gibbs reagent.When hydrochloric acid is present the reaction participated by the free-type phenol is predominant and, since its activation energy is comparatively high, difference between ortho and para substitution is thought to be rather marked. On the other hand, in the glacial acetic acid solution, the reaction participated by the phenoxide anion becomes predominant and its activation energy would be lower than that in the former case, resulting in a small difference between ortho and para substitution. This assumption is endorsed by the fact that para-substitution alone takes place in the case of anisole, which would not form a phenoxide anion, irrespective of the presence or absence of hydrochloric acid.