Phenol-aldehyde condensations aldehydes used

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... 

Raw Materials. Phenolic resins are formed by the condensation of a phenol with an aldehyde using either base or acid catalysis. Though... 

The calixarenes (from the Greek calix, meaning chalice) are a family of structures that have seen extensive use in many contexts. Shown below is the remarkable, one-step synthesis of the prototype calixarene. This condensation reaction is a variant of the phenol-aldehyde condensation that produces bakelite, the first synthetic polymer. Early workers spent considerable effort to optimize this synthesis, biasing the product toward the calixarene... 

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). 

This book is a useful guide for the industrial, and academic chemist as well as students studying polymer chemistry which involve ureas, melamines, benzoguanamine/aldehyde resins (amino resins-aminoplasts), phenol/aldehyde condensates, epoxy resins, silicone resins, alkyd resins, polyacetals/polyvinyl acetals, polyvinyl ethers, polyvinylpyrrolidones, polyacrylic acids and polyvinyl chloride. 

P-Hydroxy-a-naphthaldehyde, Equip a 1 litre three-necked flask with a separatory funnel, a mercury-sealed mechanical stirrer, and a long (double surface) reflux condenser. Place 50 g. of p-naphthol and 150 ml. of rectified spirit in the flask, start the stirrer, and rapidly add a solution of 100 g. of sodium hydroxide in 210 ml. of water. Heat the resulting solution to 70-80° on a water bath, and place 62 g. (42 ml.) of pure chloroform in the separatory funnel. Introduce the chloroform dropwise until reaction commences (indicated by the formation of a deep blue colour), remove the water bath, and continue the addition of the chloroform at such a rate that the mixture refluxes gently (about 1 5 hours). The sodium salt of the phenolic aldehyde separates near the end of the addition. Continue the stirring for a further 1 hour. Distil off the excess of chloroform and alcohol on a water bath use the apparatus shown in Fig. II, 41, 1, but retain the stirrer in the central aperture. Treat the residue, with stirring, dropwise with concentrated hydrochloric acid until... 

The phenolics are resinous materials produced by condensation of a phenol, or mixture of phenols, with an aldehyde. Phenol itself and the cresols are the most widely used phenols whilst formaldehyde and, to a much less extent, furfural are almost exclusively used as the 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. 

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 ... 

The use of carbodiimides in organic synthesis includes the Moffat oxidation of primary alcohols to aldehydes using a dicyclohexylcarbodiimide/DMSO adduct as reagent. Also, conversion of alcohols or phenols into hydrocarbons via hydrogenation of acylisoureas derived from the corresponding carbodiimide adducts is a useful reaction. Furthermore, aldoximes, on treatment with carbodiimides, are converted into nitriles, and numerous uses of carbodiimides as condensation agents or catalysts are known (see Chapter 13). 

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)... 

The second known possibility is the reaction of (Si a) with aldehyde or acetales under acidic conditions in CHCI3 (Eq. 39) The mechanism of the condensation is analogu-ous to the reaction of phenols with aldehydes. Condensation at the /8-position of 83 a) leads over dimer and trimer to the polymer 85) (yield < 30%). The yield of 85) may be optimized using a solvent with a higher solubility for the polymer. The limitation is the low yield of 4.3% for the one step synthesis of 83 a). 

Other types of resin modifiers compatible with resols may also be used. Examples include UF (urea-aldehyde condensation product) and epoxide. Japanese workers have found that the most effective and economical ingredients as modifiers for phenolic foam are resorcinol, o-cresol, and fulfuryl alcohol. 

The phenolic-based resin compounds are among the most widely used and well-known thermosets. Phenols react with aldehydes to give condensation products if there are free positions in the benzene ring - ortho and para to the hydroxyl group. Formaldehyde is the most reactive and is used almost exclusively in commercial production. The reaction is always catalyzed, either by acids or bases. The nature of the product greatly depends on the type of catalyst and the mole ratio of the reactants. Refer to Novolac Resins. 

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

Synthesis of phenol-formaldehyde oligomers uses as the main raw materials phenol and formic aldehyde. Both are used in the form of aqueous solutions of 90% and 40-45% concentration, respectively [1], Since formaldehyde contains small amounts of formic acid, the condensation process can take place in the absence of catalysts, so that phenol-formaldehyde oligomers can be obtained. The reaction rate is, however, quite low when the process takes place at atmospheric pressure and a temperature around 100°C. The use of acid or basic catalysts is compulsory in industry to produce phenol-formaldehyde oligomers of desired characteristics. Novolac type oligomers are obtained in acid catalysis in basic catalysis, resol type oligomers are produced. 

Phenolic resins are prepared by condensation of phenolic compounds with aldehyde, commonly formaldehyde. Phenol was initially predominantly used to prepare phenolic resins, but subsequently, a greater variety of alkyl or aryl substituted phenols were explored to tailor the properties of resins by controlling functionality to meet diverse requirements of different coatings. An alkyl group substi-... 

The above route also proved to be economically less viable, therefore, we decided to use the commercially available p-amino phenol to carry out a similar set of reactions. p-Amino phenol was condensed with dimethoxy tetrahydrofuran to obtain the i -aryl pynole 41. The phenol 42 was converted to the acetate and that was subjected to die Vilsmeier/Friedel-Crafts acylation conditions to obtain the aldehyde 43. Decarbonylation of the aldehyde followed by Wolff-Kishner reduction and esterification resulted in the formation of con imd 45. Similar results were obtained starting with p-anisidine. In this case demethylation was carried out using boron tribromide. The phenolic group... 

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