Phenoxide ions formaldehyde

Free Phenolic Structures Containing /3-Ary I Ether Bonds The first step of the reaction involves the formation of a quinone methide from the phenolate anion by the elimination of a hydroxide, alkoxide, or phenoxide ion from the a-carbon (Fig. 7-25). The subsequent course of reactions depends on whether hydrosulfide ions are present or not. In the latter case (soda pulping), the dominant reaction is the elimination of the hydroxymethyl group from the quinone methide with formation of formaldehyde and a styryl aryl ether structure without cleavage of the /8-ether bond (Fig. 7-26). When hydrosulfide ions are present (strong nucleophiles) they react with the... 

Condensation of phenol with formaldehyde is a base-catalyzed process in which one resonance form of the phenoxide ion attacks formaldehyde. The resulting trimethylol phenol is then crosslinked by heat, presumably by dehydration with the intermediate formation of benzylcarbocations. The resulting polymer is Bakelite. Since the cost of phenol is relatively high and... 

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.)... 

As described above, formaldehyde exists as trimethylene glycol in aqueous solution. Phenol reacts quickly with the alkali-hydroxyl group and produces resonance structural phenoxide ion, and trimethylene glycol is added to the O and P positions in the phenoxide ion. This quinoid-transition-state is stabilized by the movement of proton. The monomethylene-derivative produced in this way reacts further with formaldehyde and produces two types of dimethylol derivative and one type of trimethyl derivative. These reactions are expressed as second-order reactions ... 

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. 

Under basic conditions, phenols can undergo electrophilic substitution, even with very mild electrophiles, through intermediate phenoxide ions. An industrially important application is the reaction with formaldehyde, which leads to o- and p-hydroxymethylation. 

Because quinomethanes are a,j8-unsaturated carbonyl compounds, they may undergo Michael additions (Section 18-11) with excess phenoxide ion. The resulting phenols can be hydroxymethylated again and the entire process repeated. Eventually, a complex phenol-formaldehyde copolymer, also called a phenolic resin (e.g., Bakelite), is formed. Their major uses are in plywood (45%), insulation (14%), molding compounds (9%), fibrous and granulated wood (9%), and laminates (8%). 

It should be noted, however, that the identity of the actual hydroxyalky-lating species has not been established and it is not clear how formaldehyde, as methylene glycol, reacts with the phenoxide ion.) The resulting 0- and p-methylolphenols are more reactive towards formaldehyde than the original... 

ButylatedPhenols and Cresols. Butylated phenols and cresols, used primarily as oxidation inhibitors and chain terrninators, are manufactured by direct alkylation of the phenol using a wide variety of conditions and acid catalysts, including sulfuric acid, -toluenesulfonic acid, and sulfonic acid ion-exchange resins (110,111). By use of a small amount of catalyst and short residence times, the first-formed, ortho-alkylated products can be made to predominate. Eor the preparation of the 2,6-substituted products, aluminum phenoxides generated in situ from the phenol being alkylated are used as catalyst. Reaction conditions are controlled to minimise formation of the thermodynamically favored 4-substituted products (see Alkylphenols). The most commonly used is -/ fZ-butylphenol [98-54-4] for manufacture of phenoHc resins. The tert-huty group leaves only two rather than three active sites for condensation with formaldehyde and thus modifies the characteristics of the resin. 

We recall that enolates undergo condensation reactions with the carbonyl carbon atom of aldehydes (Section 21.7). Enolates tend to react to give alkylation at carbon. A similar reaction occurs between the phenolate ion and formaldehyde. Because both C-2 and C-4 are nucleophilic, two possible condensation products may result. The following reaction shows condensation at C-4, producing a conjugation-extended enolate. Subsequent tautomerization generates the enol form, which is a phenol. Solvent-mediated proton transfer also occurs, giving a phenoxide rather than the more basic (and less stable) alkoxide ion. 

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