Phenol base-catalyzed

Phenols Phenol Base catalyzed hydrolysis of chlorobenzene (in autoclave)... 

Stopping the polymer at this point requires the ratio of formaldehyde to phenol to be less than unity. Both methylene and ether bridges are known to be present. The reaction is either acid or base catalyzed, and branching is uncommon at this stage. The products are variously known as A stage resins, novolacs, or resole prepolymers. 

This reaction is carried out under base-catalyzed conditions and with a formaldehyde/phenol ratio greater than unity. The resulting product is called a C state resin or resite. 

The main processes for the manufacture of hydroxybenzaldehydes are based on phenol. The most widely used process is the saligenin process. Saligenin (2-hydroxybenzyl alcohol [90-01-7]) and 4-hydroxybenzyl alcohol [623-05-2] are produced from base-catalyzed reaction of formaldehyde with phenol (35). Air oxidation of saligenin over a suitable catalyst such as platinium or palladium produces sahcylaldehyde (62). 

A cyclic borate can be used to protect a catechol group during base-catalyzed alkylation or acylation of an isolated phenol group the borate ester is then readily hydrolyzed by dilute acid. ... 

Miller et al. [9] hypothesized rules on the regioselectivity of addition from the study of the base-catalyzed addition of alcohols to chlorotnfluoroethylene. Attack occurs at the vinylic carbon with most fluorines. Thus, isomers of dichloro-hexafl uorobutene react with methanol and phenol to give the corresponding saturated and vinylic ethers The nucleophiles exclusively attack position 3 of 1,1-dichloro-l,2,3,4,4,4-hexafluoro-2-butene and position I of 4,4-dichloro-l,l,2,3,3,4-hexafluoro-1-butene [10]. In I, l-dichloro-2,3,3,4,4,4-hexafluoro-l-butene, attack on position 2 is favored [J/] (equation 5) Terminal fluoroolefms are almost invariably attacked at tbe difluoromethylene group, as illustrated by the reaction of sodium methoxide with perfluoro-1-heptene in methanol [/2J (equation 6). 

Comforth has reviewed literature reports and independently studied the special cases of reaction of 1 with salicylaldehyde and with 2-acetoxybenzaldehyde. Coumarins (10) are afforded in the condensation of 1 with salicylaldehyde or its imine, whereas when 2-acetoxybenzaldehyde is used, acetoxy oxazolone 12 is the major product. The initial aldol condensation product between the oxazolone and 2-acetoxybenzaldehyde is the 4-(a-hydroxybenzyl)oxazolone 11, in which base-catalyzed intramolecular transacetylation is envisioned. The product 9 (R = Ac) can either be acetylated on the phenolic hydroxy group, before or after loss of acetic acid, to yield the oxazolone 12, or it can rearrange, by a second intramolecular process catalyzed by base and acid, to the hydrocoumarin, which loses acetic acid to yield 10. When salicylaldehyde is the starting material, aldol intermediate 9 (R = H) can rearrange directly to a hydrocoumarin. Comforth also accessed pure 4-(2 -hydroxyphenylmethylene)-2-phenyloxazol-5(4//)-one (13) through hydrolysis of 12 with 88% sulfuric acid. 

Phenol-formaldehyde resins are the oldest thermosetting polymers. They are produced by a condensation reaction between phenol and formaldehyde. Although many attempts were made to use the product and control the conditions for the acid-catalyzed reaction described by Bayer in 1872, there was no commercial production of the resin until the exhaustive work by Baekeland was published in 1909. In this paper, he describes the product as far superior to amber for pipe stem and similar articles, less flexible but more durable than celluloid, odorless, and fire-resistant. ° The reaction between phenol and formaldehyde is either base or acid catalyzed, and the polymers are termed resols (for the base catalyzed) and novalacs (for the acid catalyzed). 

Phenolic resins were discovered by Baeyer in 1872 through acid-catalyzed reactions of phenols and acetaldehyde. Kleeberg found in 1891 that resinous products could also be formed by reacting phenol with formaldehyde. But it was Baekeland who was granted patents in 1909 describing both base-catalyzed resoles (known as Bakelite resins) and acid-catalyzed novolac products.2... 

Base-catalyzed phenol-formaldehyde reactions exhibit second-order kinetics [Eq. (5)]. Several alkylphenols such as cresols also follow this rate equation ... 

TABLE 7.5 Relative Positional Reaction Rates in Base-Catalyzed Phenol-Formaldehyde Reaction... 

Phenol-formaldehyde reactions, 399, 380 base-catalyzed, 400-402 Phenol-formaldehyde resins, modified, 410-411... 

In base-catalyzed addition to triple bonds, the rate falls in going from a primary to a tertiary alcohol, and phenols require more severe conditions. Other catalysts, namely, BF3 and mercuric salts, have also been used in addition of ROH to triple bonds. 

Fig. 36 Catalytic cycle for the Br0nsted-base catalyzed addition of phenols, hydrazoic acid, or 2-cyanopyirol to ketenes...

A Friedel-Crafts-type reaction of phenols under basic conditions is also possible. Aqueous alkaline phenol-aldehyde condensation is the reaction for generating phenol-formaldehyde resin.34 The condensation of phenol with glyoxylic acid in alkaline solution by using aqueous glyoxylic acid generates 4-hydroxyphenylacetic acid. The use of tetraalkylammonium hydroxide instead of sodium hydroxide increases the para-selectivity of the condensation.35 Base-catalyzed formation of benzo[b]furano[60]- and -[70]fullerenes occurred via the reaction of C60CI6 with phenol in the presence of aqueous KOH and under nitrogen.36... 

Figure 1. Hydrolysis pH-rate profiles of phenyl acetate (lower) and a substituted 2-phenyl-l,3-dioxane (HND). Phenyl acetate profile constructed from data of Mabey and Mill (32), HND profile from data of Bender and Silver (33). Phenyl acetate reacts via specific-acid catalyzed, neutral, and base-catalyzed transformation pathways. The pseudo-first-order rate constant is given by Kobs = K(h+) [H+] + Kn + K(qh-) [0H—]. HND hydrolyzes only via an acid-catalyzed pathway the phenolate anion is some 867 times more reactive than its conjugate acid.

Reactions of aryl halides with phenoxides or phenols (Equation (30)) and base catalyzed by complexes of these ligands occurred in significantly higher yields than did the same reactions catalyzed by complexes of DPPF or BINAP. For example, a large number of diaryl ethers have... 

Still another possibility in the base-catalyzed reactions of carbonyl compounds is alkylation or similar reaction at the oxygen atom. This is the predominant reaction of phenoxide ion, of course, but for enolates with less resonance stabilization it is exceptional and requires special conditions. Even phenolates react at carbon when the reagent is carbon dioxide, but this may be due merely to the instability of the alternative carbonic half ester. The association of enolate ions with a proton is evidently not very different from the association with metallic cations. Although the equilibrium mixture is about 92 % ketone, the sodium derivative of acetoacetic ester reacts with acetic acid in cold petroleum ether to give the enol. The Perkin ring closure reaction, which depends on C-alkylation, gives the alternative O-alkylation only when it is applied to the synthesis of a four membered ring ... 

The dissociation of water coordinated to exchangeable cations of clays results in Brtfnsted acidity. At low moisture content, the Brrfnsted sites may produce extreme acidities at the clay surface-As a result, acid-catalyzed reactions, such as hydrolysis, addition, elimination, and hydrogen exchange, are promoted. Base-catalyzed reactions are inhibited and neutral reactions are not influenced. Metal oxides and primary minerals can promote the oxidative polymerization of some substituted phenols to humic acid-like products, probably through OH radicals formed from the reaction between dissolved oxygen and Fe + sites in silicates. In general, clay minerals promote many of the reactions that also occur in homogenous acid or oxidant solutions. However, rates and selectivity may be different and difficult to predict under environmental conditions. This problem merits further study. 

In HO -catalyzed hydrolysis (specific base catalyzed hydrolysis), the tetrahedral intermediate is formed by the addition of a nucleophilic HO ion (Fig. 3.1, Pathway b). This reaction is irreversible for both esters and amides, since the carboxylate ion formed is deprotonated in basic solution and, hence, is not receptive to attack by the nucleophilic alcohol, phenol, or amine. The reactivity of the carboxylic acid derivative toward a particular nucleophile depends on a) the relative electron-donating or -withdrawing power of the substituents on the carbonyl group, and b) the relative ability of the -OR or -NR R" moiety to act as a leaving group. Thus, electronegative substituents accelerate hydrolysis, and esters are more readily hydrolyzed than amides. 

Fig. 8.12. Activation of hemiester prodrugs of phenols by acid-catalyzed hydrolysis (Reaction a), base-catalyzed hydrolysis (Reaction b), and cyclization-elimination (Reaction c). Enzymatic hydrolysis not shown (adapted from [174]). 

Catechol and related phenolics 13,16,19, 31, and 32 were also isolated after alkaline treatment of D-glucose and sucrose. Several other substituted acetophenones were isolated. The mechanism of formation of phenolic compounds from monosaccharides under alkaline conditions has yet to be thoroughly investigated. The similarity in the types of aromatic products from D-glucose and D-xylose indicates the formation of the same C2, C3, or C4 fragments, with subsequent recombination and cycliza-tion. Base-catalyzed aldol reactions are, no doubt, predominant pathways in the initial formation of these aromatic products. 

Thus, for example, guanidine analogues guanoxyf n (79) and guanochlor (82) also possess antihypertensive activity. Guanoxyfen is synthesized by base-catalyzed condensation of phenol with chloroaceto-nitrile, followed by hydride reduction to amine 78. 

The high-molecular-weight products formed by the condensation of phenols with carbonyl compounds (especially with formaldehyde) are known as phenolic resins. They are mixtures of structurally nonuniform compounds that are initially soluble and fusible but which can become crosslinked (cured) by subsequent reactions. One distinguishes between acid- and base-catalyzed condensations, since they lead to different end products the properties of the condensation polymer are also affected by the mole ratio of phenol to formaldehyde. 

Base-Catalyzed Phenol-Formaldehyde Condensation (Resols)... 

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