Phenoxide ions, addition reactions

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 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). 

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... 

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-... 

To achieve the selectivity in the mixture of products with different methylene bridges is a critical issue. It is reported that the selectivity of the p-isomer can be boosted by using P-cyclodextrin or crown ether [4]. The basic mechanism is that the additive form complexes with the phenoxide ions and encourages preferential attack at the p-position due to the steric hindrance caused by the attack at o-position. Ortho selectivity can be increased by using a metallic catalyst such as salts of zinc, magnesium, or lead. When the reaction is carried out in the presence of metallic salts, the metal ion forms... 

Resole is produced by reaction of a phenol or a phenol derivative with an excess amount of formaldehyde in the presence of a base catalyst. The reaction in basic medium proceeds through the addition of formaldehyde with the phenoxide ion, leading to the formation of o- or p-monomethylol phenol (along with some di- or trimethylol phenol) as established by complexation via cyclodextrin or crown ether [2]. The reaction scheme for the synthesis of resole is shown in Figure 2.3. 

The rates of dissociation of MeP(OPh)4 and related phosphoranes have been measured by n.m.r. methods, and the association reaction of [OPh] and [RnP(OPh)4 n] shown to proceed at the encounter rate. The hydrolysis of [MeP(OPh)8]+ in aqueous acetonitrile involves a rate-determining addition of water at low acidity (k, but at high acidity a rate-determining loss of phenoxide ion occurs... 

The most widely used approach to the preparation of PESs in both academic research and technical production is a polycondensation process involving a nucleophilic substitution of an aromatic chloro- or fluorosulfone by a phenoxide ion (Eq. (3)). Prior to the review of new PESs prepared by nucleophilic substitution publications should be mentioned which were concerned with the evaluation and comparison of the electrophilic reactivity of various mono- and difunctional fluoro-aromats [7-10]. The nucleophilic substitution of aromatic compounds may in general proceed via four different mechanism. Firstly, the Sni mechanism which is, for instance, characteristic for most diazonium salts. Secondly, the elimination-addition mechanism involving arines as intermediates which is typical for the treatment of haloaromats with strong bases at high temperature. Thirdly, the addition-elimination mechanism which is typical for fluorosulfones as illustrated in equations (3) and (4). Fourthly, the Snar mechanism which may occur when poorly electrophilic chloroaromats are used as reaction partners will be discussed below in connection with polycondensations of chlorobenzophenones. 

One of the most remarkable reactions that has been encountered in this field is the addition of Grignard reagents to phenolic ketones. Here we are dealing with phenoxide ions, which are vinylogs of the corresponding carboxylate ions. 

The complex is additionally stabilised by co-ordination of the phenoxide, and possibly the carboxylate, to the metal ion, illustrating the utility of chelating ligands in the study of metal-directed reactivity. We saw in the previous section the ways in which a metal ion may perturb keto-enol equilibria in carbonyl derivatives, and similar effects are observed with imines. The metal ion allows facile interconversion of the isomeric imines. The first step of the reaction is thus the tautomerisation of 5.28 to 5.29 (Fig. 5-56). Finally, the metal ion may direct the hydrolysis of the new imine (5.29) which has been formed, to yield pyridoxamine (5.30) and the a-ketoacid (Fig. 5-57). 

In contrast to the observed reactivity of phenoxide and aryl alkoxide ions, arene and heteroarene thiolate ions typically couple with aryl radical to generate C—S bonds. The only exception to this regioselective reaction is the addition of 1-naphthalene thiolate ion to p-anisyl radical to render both C- and S-substitutions in 14% and 65% yields, respectively, while with 1-naphthyl radical, 95% of C—S coupling is obtained. In general, PhS- ions react with Arl in liquid ammonia under photostimulation to afford good yields of ArSPh or heteroaryl-SAr (70-100%). Substitution of the less-reactive ArBr can be achieved under photochemical initiation in DMF, MeCN, or DM SO [1],... 

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