Phenol Phenoxide ion

Table 27. Selected examples of correlation between observed and calculated UV transitions (Del Bene and Jaffe). (Other studied compounds include benzene, pyridine, 1,2-diazine, 1,3-diazine, 1,4-diazine, cyclopentadienide ion, pyrazole, imidazole, 2-pyrrole-carboxaldehyde, furfural, benzonitrile, nitrosobenzene, phenol, phenoxide ion, pyridinium ion, 1-hydroxy-pyridinium ion, 2-cyano-pyridine, 3-cyano-pyridine, 4-cyano-pyridine, 2-amino-pyridine, 3-amino-pyridine, 4-amino-pyridine.)...

The anions of phenols (phenoxide ions) may be used in the Williamson ether synthesis, especially with very reactive alkylating reagents such as dimethyl sulfate. Using phenol, dimethyl sulfate, and other necessary reagents, show how you would synthesize methyl phenyl ether. 

LSV and DCV mechanism analyses of the protonation of anthracene radical anions by phenol-phenoxide ion buffers in OMF"... 

In the strongly basic medium, the reactant is the phenoxide ion high nucleophilic activity at the ortho and para positions is provided through the electromeric shifts indicated. The above scheme indicates theorpara substitution is similar. The intermediate o-hydroxybenzal chloride anion (I) may react either with a hydroxide ion or with water to give the anion of salicyl-aldehyde (II), or with phenoxide ion or with phenol to give the anion of the diphenylacetal of salicylaldehyde (III). Both these anions are stable in basic solution. Upon acidification (III) is hydrolysed to salicylaldehyde and phenol this probably accounts for the recovery of much unreacted phenol from the reaction. 

Hydroxide ion lies below phenol m Table 1 7 hydrogen carbonate ion lies above phe nol The practical consequence of the reactions shown is that NaOH is a strong enough base to convert phenol to phenoxide ion but NaHCOs is not... 

It IS necessary to keep the acidity of phenols in mind when we discuss prepara tion and reactions Reactions that produce phenols when earned out in basic solution require an acidification step to convert the phenoxide ion to the neutral form of the phenol... 

Many synthetic reactions involving phenols as nucleophiles are carried out m the presence of sodium or potassium hydroxide Under these conditions the phenol is con verted to the corresponding phenoxide ion which is a far better nucleophile... 

A meta nitro group is not directly conjugated to the phenoxide oxygen and thus stabi hzes a phenoxide ion to a smaller extent m Nitrophenol is more acidic than phenol but less acidic than either o or p nitrophenol... 

Reaction with arenediazonium salts Adding a phe nol to a solution of a diazonium salt formed from a primary aromatic amine leads to formation of an azo compound The reaction is carried out at a pH such that a significant portion of the phenol is pres ent as its phenoxide ion The diazonium ion acts as an electrophile toward the strongly activated ring of the phenoxide ion... 

The predominance of a-substituted products in the reaction of 2,4,6-tribromopyridine in phenol solution may result from competitive attack by free phenol in preference to attack by the phenoxide ion reagent involving structures 18 (B = base) or 19. A wealth of chemistry awaits elucidation by physical-organic studies. 

A more proper comparison regarding Vl-group nucleophilic reagents would be between the pairs PhO and PhS , and MeO" and MeS. However, both phenoxide and alkylsulfide ions are more basic than phenylsulfide ion, and their reactions are less amenable to study in alcoholic solution. For dilute solutions of phenoxide in methanol the equilibrium (9) shifts nearly half-way toward the right if a stoichiometric excess of phenol is not present. If phenoxide ion is less reactive... 

The reaction of 2,4,6-tribromopyridine with phenoxide ion illustrates, in our opinion, the effect of hydrogen bonding as discussed in Section II, B, 3. Reaction (150°, 24 hr) in water gave approximately equal amounts (18% yields) of 2- and 4-monosubstitution, but in phenol under the same conditions only the 2-phenoxy derivative (in high yield plus a small amount of the 2,6-diphenoxy compound) was formed. In water, reaction at the adjacent 2- and 6-position is hindered by the hydrogen bonding (cf. 61) of the solvent to the azine-nitrogen, compared to reaction at the 4-position. On the other hand, in... 

Unlike the acid-catalyzed ether cleavage reaction discussed in the previous section, which is general to all ethers, the Claisen rearrangement is specific to allyl aryl ethers, Ar—O—CH2CH = CH2. Treatment of a phenoxide ion with 3-bromopropene (allyl bromide) results in a Williamson ether synthesis and formation of an allyl aryl ether. Heating the allyl aryl ether to 200 to 250 °C then effects Claisen rearrangement, leading to an o-allylphenol. The net result is alkylation of the phenol in an ortho position. 

The rates of bromination of 3-nitrophenol in aqueous solution at 25 °C have been measured at various concentrations of perchloric acid and sodium bromide294. An increase in both caused a decrease in rate the latter again shows that Br is much less reactive than Br2, whilst the former shows that reaction occurs principally on the 3-nitrophenoxide ion and the difference from the observation for phenol in acetic acid (above p. 117) is undoubtedly partly due to the greater stability of the 3-nitrophenoxide relative to the phenoxide ion. The... 

These workers also measured rates of exchange of phenol and phenoxide ion... 

The solvent can also affect regioselectivity. Consider O- vs C-alkylation of phenoxide ion with allyl chloride or bromide. In water, with allyl chloride the O- to C-alkylation ratio is 49 41 with phenol as a solvent it is 22 78 with methanol, dimethylformamide, and dioxane 100% O-alkylation is achieved. The selective solvation of the more electronegative O by the more protic solvents perhaps leads to some C-alkylations. 

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