Methylol derivatives Phenol alcohols

The second phase in resole formation is reaction of the activated phenol with the aldehyde to form the phenol alcohol derivative. When the aldehyde is formaldehyde, the derivative is a hydroxymethyl phenol and the process is known as methylolation. Scheme 2 illustrates this reaction. Since resoles are usually made with excess aldehyde, more than one substitution may be made on the ring. When the reactants are phenol and formaldehyde, up to three methylol groups may be substituted. This reaction has been extensively studied and the rates of... 

The two most important phenol-formaldehyde reactions are (A) the formation of nuclear methylol phenols or phenol alcohols, as they are commonly designated, and (B) the formation of poljmuclear methylene derivatives. 

Phenol Alcohols. As has been previously pointed out, the simplest defimte reaction products of formaldehyde with phenols are the methylol-phenols or phenol alcohols. Although some of these derivath es are too reactive to be isolated, a number have been obtained as pure crystalline products. In some respects they are analogous to the methylol derivatives of aldehydes and ketones, a similarity which is readily demonstrated when the keto- or ortho- and para-quinoidal forms of the phenolic nucleus are designated in the structural formula. The mechanism of their formation from the primary phenolic hemifoniLals may involve tautomeric rearrangements of the sort indicated below ... 

Meta-cresol, which has three positions capable of methylolation, is high reactive with formaldehyde, and the alcohols formed resinify rapidly even under alkaline conditions. As a result, it is extremely difficult to isolate pure phenol alcohols. However, crystalline products beliei ed to be monoalcohols and melting at 105, 110, 117, and 122 C have been reported . The difficulties of isolating pure products are considerable, since three monomethylol derivatives, three dimethylol derivatives and one trimethylol derivative are possible. 

Miscelianeous Substituted Phenols Phenofe containing other substituents than meth l groups and containing free ortho and/or para positions form phenol alcohol derivatives rtth A aiydng degrees of ease vhen subjected to reaction with formaldehyde in the presence of alkah. Numerous examples cd ieolable products obtained by this procedure, such as the 2,6-dimethyloI derivath e of p-ben dphenol and the methylol derivatives of ortho-ehlorophenol, 2,4-dimethylol-l-chlorophenol and 4-methylol-1-clilorophenol, etc., are described. 

Methoxy derivatives of divalent phenols such as guaiacol react like simple monovalent phenols, forming methylol and methylene derivatives. Euler and co-workers- isolated vanillyl alcohol (methjdolguaiacol) and a di-methylol derivative of a methylene-bis-methoxyphenol from the products obtained by reacting guaiacol with formaldehyde under alkaline conditions. Under acidic conditions tw o isomeric methylene-bis-methoxyphenols were obtained. 

These benzaldehydes could then be directly used as a feedstock for various polymeric products or reduced to form phenolic benzylic alcohol derivatives (i.e., p-methylol groups). The p-methylol groups would thus be active sites, whereas in unmodified lignins, the C-l site is blocked and unreactive. In addition, the oxidative-cleavage step will hydrolyze a portion of the lignin interunit ether bonds, and thus increase the total fraction of free phenolic units to further enhance the reactivity. Other possible benefits are that the lignin would be extensively depolymerized and would form a more uniform feedstock material both conditions would give a product that is easier to handle. 

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