Alkaline phenol-aldehyde condensation

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... 

Reaction uniformity in phenol-aldehyde condensations is obtained by careful control of reaction conditions such as temperature of condensation [39], catalyst concentration, and pH. At the early stages the reaction is exothermic, and the temperature must be controlled to prevent a runaway reaction [40]. Gel permeation chromatography offers a means to monitor product uniformity. Specific catalysts (usually 1-6%) are used to obtain either a resole (alkaline catalysts or basic salts) or novolac (acid catalysts). 

Reaction XXVII. Condensation of Chloroform with Phenols and simultaneous Hydrolysis of the Product (Reimer-Tiemann). (B., 15, 2585.) —This is a well-known method for the preparation of phenolic-aldehydes. The phenol is treated with chloroform and an alkaline hydroxide, when — CHC12 enters the ortho- and to a lesser extent the para-position to the hydroxyl group hydrolysis to an aldehyde then takes place. 

Other aldehydes used for the synthesis of phenolic polycondensates include butyraldehyde, furfural or chloral. Efficient AO, e.g. polycondensate 129, were prepared with sulfur containing aldehydes [161]. Linear polycondensates of phenols and aldehydes were tested as AO in mineral oils, PE, PP, poly (ethylene-co-propylene), PS, PA and/or diene based rubbers [159, 162]. Cyclic phenolic condensates, calixarenes (130) posses interesting properties. Calixarenes were synthesized from 4-acyl-, 4-methyl-, 4-tm-butyl- or 4-phenylphenol in alkaline catalysed processes. Cycles containing 4 to 7 phenolic units were formed and tested as AO in PE or PP [163,164], Nickel(II) salt of 130 (R = lerf-butyl, n = 1)... 

Resols are obtained as a result of alkaline catalysis and an excess of formaldehyde. A resol molecule contains reactive methylol groups. Heating causes the reactive resol molecules to condense to form large molecules, without the addition of a hardener. The function of phenols as nucleophiles is strengthened by ionization of the phenol, without affecting the activity of the aldehyde. 

In general 3-benzylidenechroman-4-ones are prepared by condensation of chroman-4-ones with aromatic aldehydes (72). Strong alkaline (55) or acidic (75) conditions can be applied only if eventual sensitive substituents are suitably protected. Using dry hydrogen chloride in acetic acid Boehler and Tamm synthesized 5,7-di-O-methyleucomin (33) from 5,7-dimethoxychroman-4-one and anisaldehyde (9). Later Krishna-MURTY et al. (45) observed the simultaneous formation of a C-6 or C-8 a-chlorobenzylated product (34) in this reaction. Starting from O-benzoylated compounds 5,7-di-O-benzoyleucomin (35) and 4, 5,7-tri-0-benzoyl-4 -demethyleucomin (36) are easily prepared by this method using diethyl ether and ethyl acetate as solvents respectively (45). The unprotected phenolic compounds can be condensed successfully in boiling acetic anhydride (23, 24). The relatively low yield of 5,7-di-O-... 

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