Phenols condensation with aldehydes

Aromatic aldehydes condense with phenols, e. g. benzaldehyde and naphthol give hydroxy-dinaphthyl-phenyl methane ... 

A. The Basic Series.—In general, aromatic aldehydes condense with aromatic amines in the presence of zinc chloride to form triphenylmethane derivatives (0. Fischer) phenols and phenyl ethers behave similarly in the presence of concentrated sulphuric acid (Baeyer). The products formed are the leuco-compounds of well-known dyes. 

Aldehydes can methylolate phenols with an acid as a catalyst and therefore function as latent electrophiles in the negative resist design based on condensation (Fig. 125) [150]. The methylolated phenolic resin is expected to dissolve more slowly in aqueous base than its precursor resin and therefore this process could be exploited in negative imaging. Furthermore, the methylolated phenol can undergo further condensation with phenol. If the phenol is polymeric, the second reaction results in crosslinking, lowering the dissolution rate even further. 

Epoxy phenolic adhesives are polyepoxy compounds which possess epoxy reactivity and phenolic resin heat resistance. These are prepared by condensing epichlorohydrin and novolac phenolics (phenol/formaldehyde ratio > 1). A recent Japanese patent issued to Mitsubishi Petrochemical Co. describes the preparation of epoxy resins from epichlorohydrin condensation with phenolic resins prepared from phenol and substituted aldehydes, e.g., vanillin. These resins (23) have high epoxy contents (epoxy equivalent weights >200) and relatively high softening points (85-95°C). 

The structure of the aldehyde used for condensation with phenolic compounds can vary from formaldehyde to others [73] as shown below ... 

These aldehydes react on acid condensation with phenols to give novolac-type products. Base-catalyzed condensation is not practical with acetaldehyde since it undergoes rapid aldol condensation and self-resinification reactions. Acid condensations involving acetaldehyde or its trimer paraldehyde and phenol give soluble and permanently fusible resins, comparable to the novolacs. Aldehyde with no a hydrogens react in a manner similar to formaldehyde ... 

The formation of heterocychc amines of the IQ type is effectively inhibited by antioxidants. The presence of phenohc compounds such as flavanones and flavan-3-ols significantly inhibits their formation. The mechanism of the inhibitory effect is partly based on the ehmination of Strecker aldehydes, precursors of IQ mutagens, by condensation with phenols. For example, phenylacetaldehyde, a decarboxylation product of phenylalanine and a precursor of PhIP, produces two adducts, ( )-8-(phenylethenyl)naringenin and ( )-6-(phenylethenyl)naringenin withnaringenin (Figure 12.2). 

Group of plastics whose resins are derived from the condensation of phenols (e.g., phenol and cresol, with aldehydes). 

Uses of Formaldehyde. Formaldehyde is the simplest and most reactive aldehyde. Condensation polymerization of formaldehyde with phenol, urea, or melamine produces phenol-formaldehyde, urea formaldehyde, and melamine formaldehyde resins, respectively. These are important glues used in producing particle hoard and plywood. 

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... 

Triazolopyranopyrimidines can be prepared from the phenol-substituted triazolopyrimidines. Condensation with an aldehyde with the fused dihydropyrimidine such as 181 is followed by cyclization to give benzo-fused trihetero-cyclic compounds 182 (Equation 48) <1996CHE215>. 

Technical Importance of the Aldehydes.—Formalin solution is used as a disinfectant and as a preservative. Caseinogen hardened with formaldehyde is a widely used substitute for vulcanite, as is also the synthetic resin bakelite, which is produced by the condensation of formaldehyde with phenol (p. 243). 

When heated with a strong acid, pentoses and hexoses are dehydrated to form furfural and hydroxymethylfurfural derivatives respectively (Figure 9.20), the aldehyde groups of which will then condense with a phenolic compound to form a coloured product. This reaction forms the basis of some of the oldest qualitative tests for the detection of carbohydrates, e.g. the Molisch test using concentrated sulphuric acid and a-naphthol. 

Phenolics, A class of thermoset resins made by the condensation of phenol or phenol-containing compounds with aldehydes such as acetaldehyde or formaldehyde. 

Somewhat different type 2-amino-4H-chromene synthesis is represented by the interaction of CH-acidic nitriles 27 with salicylic aldehyde 157 where the phenolic OH and aldehyde groups are present in the same molecule. A conventional mechanistic scheme is represented (Scheme 58), where in the presence of a base nitrile 27 condenses with the aldehyde to give Knoevenagel intermediate 158. Then nucleophilic addition of the OH group leads to iminochromene 159, which then adds a nucleophile (as a rule, the second equivalent of nitrile 27) at position 4 to form 2-amino-4H-chromene 160. 

One of the oldest known thermosetting synthetic polymers is made by condensation of phenols with aldehydes using basic catalysts. The resins that are formed are known as Bakelites. The initial stage is the base-induced reaction of benzenol and methanal to give a (4-hydroxyphenyl)methanol, and this reaction closely resembles an aldol addition and can take place at either the 2-or the 4-position of the benzene ring ... 

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. 

Reaction XXXVI. Condensation of Carbon Tetrachloride with Phenols and simultaneous Hydrolysis (Tiemann-Reimer). (B., 10, 2185.)—This reaction is closely analogous to that of the formation of hydroxy-aldehydes by means of chloroform and caustic alkali (see p. 104). A mixture of a phenol, carbon tetrachloride and caustic soda or caustic potash solution is boiled. Condensation occurs, chiefly in the para-position, but small amounts of the ortho-acids are also formed. The product, after the excess of carbon tetrachloride has been removed, is saturated with carbon dioxide and the unchanged phenol extracted with ether. The hydroxy acids are then precipitated by acidification with hydrochloric acid. 

Reaction LXV. (a) Reduction of Phenolic Acids to the corresponding Aldehydes by the action of Sodium Amalgam and Boric Acid in the presence of a Primary Aromatic Amine. (B., 41, 4147.)—This is one of the few methods of reducing an acid to the corresponding aldehyde in satisfactory yield. The presence of the primary aromatic base is essential to protect the aldehyde it condenses with it as formed, and inhibits further reduction to the alcohol. A weak acid such as boric acid is used partly because salt formation by the base would hinder condensation and partly to avoid hydrolysis of the condensation product. 

Acid Catalyzed. Although ketonic carbonyl groups are less reactive than aldehydic carbonyls in the presence of basic catalysts, this is not the case with acid catalysts. Thus acetone undergoes aldol addition in the presence of sulfuric acid to give mesityl oxide, which then condenses with a third molecule of acetone to give a mixture ofphorone (2,6-dimethyl-2,6-heptadien-4-one) and mesitylene (1,3,5-trimethylbenzene). Ketones also condense with activated aromatic products in the presence of sulfuric acid to give coupled aromatic products. For example, acetone and phenol condense to bisphenol A (4,4 -isopropylidenediphenol), which is used in the manufacture of epoxy resins (qv) and polycarbonates (qv). 

Triflic acid has been applied in a three-component condensation of phenols or 2-naphthol, aromatic aldehydes, and alkyl nitriles to form amidoalkylphenols under mild conditions in good to high yields922 [Eq. (5.345)]. The reaction involves a Ritter-type step, wherein the intermediate condensation product reacts with the nitrile component. 

A three-component reaction of aromatic aldehydes, malononitrile and phenols leads to 4-aryl-2-amino-3-cyano-4//-chromenes this reaction can be carried out in aqueous media with improvements in yield and obvious environmental advantages (Scheme 35). The aromatic aldehyde undergoes a Knoevenagel condensation with malononitrile, followed by ortho-alkylation of the phenol and cyclization to form the iminopyran intermediate 114, which isomerizes to the 4//-chrorncncs (Scheme 36) <2003SL2001>. High yields for this three-component reaction can also be achieved in aqueous media when mediated by 7-alumina <2004TL2297> or cetyltrimethylammonium chloride <2001T1395>. 

Besides, furfural polymerizes in the presence of an acid catalyst with phenol, urea, and acetone. In this regard, the phenol-furfural and urea-furfural resins are important [221-223], Furfural reacts usually as does all a-substituted aldehydes in this regard, with phenol it condenses in the presence of either alkali or acid to form synthetic resins in a reaction that is very similar to that of phenol with formaldehyde or acetaldehyde [223],... 

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