Phenoxide ions, addition

In addition, Hashida et al. (1971 a) found a linear correlation between log k and the pof fifteen 1,3-dicarbonyl compounds. This indicates that in these cases the nucleophilicity and the basicity of the anions are closely related. The same result was obtained by Hashida et al. (1971b) for the azo coupling reactivity of substituted phenoxide ions. 

Some protonation of the benzyl carbanion by the starting ether (selfprotonation reaction) and other side reactions, such as hydrolysis caused by in situ generation of OH (through protonation of the benzyl anion by traces of water), can be avoided by addition of a suitable acid. Under these conditions, electrolysis leads to an effective conversion of the ether into toluene and phenoxide ion with an electron consumption of 2 F/mol. 

The eourBe of addition of phenols to epicMorohydrin has been a subject of some controversy, since one might suppose the Btrongly nucleophilic character of phenoxide ion to cause indiscriminate attack on the chlorine-substituted carbon atom and tbe epoxide ring... 

The effect of substituents on the reactivity of phenols with epichlorohydrin hot been examined also by Bradley and co-workers.283 In contrast with earlier observations made by Boyd and blade with othyfene oxide and propylene oxide, the most acidio phenols are the ones giving maximum yields with epichlorohydrin. This indicated that in this particular reaction the relative concentration of phenoxide ions rather than their nucleophiBcity is the overriding factor in determining the rates of addition. 

The mesomeric quinonemethides and 0-quinonemethides described above are somewhat more stable than the simple p-quinonemethides whose properties are already well known even from classical studies. The o-quinonemethides XX and XVII do not add on water even in solution in aqueous organic solvents their solution in dioxane/water is stable for months. They do not add on methanol or higher alcohols and react only slowly with phenols and organic acids. The addition of water is not catalyzed by mild alkalies the red color of the phenoxide ion (XVIII) prevails for weeks in soda solution. Addition of water occurs more rapidly in strongly alkaline solution. The addition of mineral acids and reduction by sodium borohydride are instantaneous. The addition of HC1 is rapid even at pH 4.0, the conditions used for determining the carbonyl content of lignin by the hydroxylamine hydrochloride reaction 13). 

However, there are additional structures to be considered. Being basic, oxygen can share more than a pair of electrons with the ring this is indicated by contribution from structures V-VII for phenol, and VIII-X for the phenoxide ion. 

The first slajge can be viewed as both electrophilic substitution on the ring by the electron-deficient carbon of forrnaldehyde, and nucleophilic addition of the aromatic ring to the carbonyl group ase catalyzes reaction by converting phenol into the more reactive (more nucleophilic) phenoxide ion.jj Acid catalyzes reaction by protonating formaldehyde and increasing the electron deficiency of the carbonyl carbon.)... 

A phenoxide ion, therefore, might be expected to undergo certain reactions characteristic of carbanions at the ortho and para positions. One of the best-known examples of such a reaction is the Kolbe synthesis of salicylic acid in which the carbanion form of the phenoxide ion undergoes addition to the carbonyl group of carbon dioxide 49... 

In diols containing both phenolic and alcoholic hydroxyl groups neutral conditions favour the acylation of the latter while the former are selectively acylated in the presence of triethylamine (ref. 57) doubtless due to the more nucleophilic phenoxide ion so formed, which is the basis of the Chattaway procedure originated many years ago. This is exemplified in the preferential formation in 95% yield of the phenolic acetate of estradiol in isopropanol containing 2.9 moles of sodium hydroxide in concentrated solution followed by the addition of 2.9 moles of acetic anhydride and then by stirring of the mixture for SOmins. at ambient temperature with maintenance of the pH at 7.8 (ref.58). 

An important aspect of our studies were the effect of cloud cover, pH, chloride ion, and season on the photolysis of phenol and various chlorophenols. The effect of pH on the photolysis of chlorophenols is due to the higher rate of photolysis of the phenoxlde ion relative to the nonionized compound, due to stronger absorbance by the phenoxide ion ( ). The pK of dichlorophenol, trichlorophenol, and pentachlorophenol are 7.6, 7.0 and 4.8, respectively (.22, 24). Low photolysis rates of chlorophenols in both estuarine and distilled water were obtained at pH below the pK (Table III). At pH 7.6 found in estuarine water 50Z, 80Z, and 99.82 of the dichlorophenol, trichlorophenol, and pentachlorophenol, respectively, is in the form of the phenoxide ion. The photolysis rate of pentachlorophenol in estuarine water was lower than in distilled water (Table I). Addition of chloride ion to distilled water containing pentachlorophenol resulted in a decrease in the photolysis rate. Miille and Crosby ( 5) found that pentachlorophenol had a lower photolysis rate in seawater compared to distilled water due to the photonucleophilic... 

The oxidation of OH by [Fe(CN)6] in solution has been examined. Application of an electrical potential drives the reaction electrochemically, rather than merely generating a local concentration of OH at the anode, as has been suggested previously, to produce both O and [Fe(CN)6] in the vicinity of the same electrode. With high [OH ] or [Fe(CN)6] /[Fe(CN)6] ratio, the reaction proceeds spontaneously with a second-order rate constant of 2.2 x 10 M s at 25 °C. Under anaerobic conditions, iron(III) porphyrin complexes in dimethyl sulfoxide solution are reduced to the iron(II) state by addition of hydroxide ion or alkoxide ions. Excess hydroxide ion serves to generate the hydroxoiron(II) complex. The oxidation of hydroxide and phenoxide ions in acetonitrile has been characterized electrochemically " in the presence of transition metal complexes [Mn(II)L] [M = Fe,Mn,Co,Ni L = (OPPh2)4,(bipy)3] and metalloporphyrins, M(por) [M = Mn(III), Fe(III), Co(II) por = 5,10,15,20-tetraphenylpor-phinato(2-), 5,10,15,20-tetrakis(2,6-dichlorophenyl)porphinato(2-)]. Shifts to less positive potentials for OH and PhO are suggested to be due to the stabilization of the oxy radical products (OH and PhO ) via a covalent bond. Oxidation is facilitated by an ECE mechanism when OH is in excess. 

Alkyl phenyl thioethers RCH2SPh are available by radical-initiated addition of benzenethiol to a terminal olefin or by reaction of an alkyl bromide with thio-phenoxide ion. N -Chlorosuccinimide effects halogenation at the a-site, and the a-chloroalkyl thioether gives the corresponding aldehyde RCHO on treatment with mercury(ll) chloride and cadmium(ll) carbonate in aqueous carbon tetra-... 

In a paper that described a detailed preparation of air-stable cinchona alkaloid-derived chiral quaternary ammonium phenoxides, the Mukaiyama group also used these to enantioselectively prepare 3,4-dihydropyran-2-ones 160 [85]. A low loading of organocatalyst 159 at low temperatures, in a series of solvents, resulted in the formation of the optically active lactone products in high yields with excellent control of enantio- and diastereoselectivity. This process was proposed to go through a phenoxide-ion-catalyzed domino Michael addition and lactonization catalytic cycle as illustrated below. Many variations of the ketene silyl acetals and a, -unsaturated ketones were combined in this domino process (Scheme 7.32). Earlier,... 

Scheme 7.32 Phenoxide-ion-catalyzed domino Michael addition and lactonization.

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