Phenolic, acid catalysed

This process has been in use since 1958. As the components are relatively cheap, it is mainly used for the production of large parts. It is applicable for all alloy types. The hardening of these resins is more difficult and less regular compared to the fiiran resins. 

The resins are either phenol-formaldehyde (PF), or urea-formaldehyde/phenol-formaldehyde copolymers (UF/PF), both being resols , with a formaldehyde/phenol ratio higher than one. 

The catalysts are strong sulphonic acids, such as paratoluene, xylene or benzene-sulphonic, with sometimes an addition of sulphuric acid, usually used in a diluted form. 

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Stevenson DE, Wibisono R, Jensen DJ, Stanley RA, Cooney JM. 2006. Direct acylation of flavonoid glycosides with phenolic acids catalysed by Cmdida antarctica lipase B (Novozym 435 ). Enzyme Microb Technol 39 1236-1241. 

In contrast to its effect upon the general mechanism of nitration by the nitronium ion, nitrous acid catalyses the nitration of phenol, aniline, and related compounds. Some of these compounds are oxidised under the conditions of reaction and the consequent formation of more nitrous acids leads to autocatalysis. 

Derbyshire and Waters202 carried out the first kinetic study, and showed that the chlorination of sodium toluene-m-sulphonate by hypochlorous acid at 21.5 °C was catalysed more strongly by sulphuric acid than by perchloric acid and that the rate was increased by addition of chloride ion. A more extensive examination by de la Mare et al.203 of the rate of chlorination of the more reactive compounds, anisole, phenol, and />-dimethoxybenzene by hypochlorous acid catalysed by perchloric acid, and with added silver perchlorate to suppress the formation of Cl2 and C120 (which would occur in the presence of Cl" and CIO-, respectively),... 

Carr and England211 investigated the kinetics of the hydrochloric acid-catalysed chlorination of phenol by N-chloro-succinimide, -acetamide, and -morpholine, and found that the latter compound gave third-order kinetics, viz. 

Dihydropyran-4-ones are a source of phenols via an intramolecular [2+2] photocycloaddition reaction and a Lewis-acid catalysed cleavage of the cyclobutane moiety <96TL1663>. 

A very similar rearrangement takes place during the acid-catalysed decomposition of hydroperoxides, RO—OH, where R is a secondary or tertiary carbon atom carrying alkyl or aryl groups. A good example is the decomposition of the hydroperoxide (84) obtained by the air-oxidation of cumene [(l-methylethyl)benzene] this is used on the large scale for the preparation of phenol and acetone ... 

Autoxidation may in some cases be of preparative use thus reference has already been made to the large-scale production of phenol+ acetone by the acid-catalysed rearrangement of the hydroperoxide from 2-phenylpropane (cumene, p. 128). Another example involves the hydroperoxide (94) obtained by the air oxidation at 70° of tetrahydro-naphthalene (tetralin) the action of base then yields the ketone (a-tetralone, 95), and reductive fission of the 0—0 linkage the alcohol (a-tetralol, 96) ... 

The two saturated rings of the cannabinoid nucleus are formed with the correct stereochemistry at C-6, C-6a and C-lOa but without selectivity at C-9 in a single acid-catalysed cyclisation step from the phenol 51. Stabilisation of a cationic intermediate by the alkyne group is proposed to account for the facile cyclisation . 

Electron-rich aromatic compounds, such as phenol, anisole and A,./V-dimethylaniline, add to bis(2-trichloroethyl) azodicarboxylate under the influence of lithium perchlorate, boron trifluoride etherate or zinc chloride to yield para-substituted products 74, which are transformed into the anilines 75 by means of zinc and acetic acid86. Triflic acid (trifluoromethanesulphonic acid) catalyses the reactions of phenyl azide with benzene, toluene, chlorobenzene and naphthalene, to give TV-arylanilines (equation 34)87. 

This is the best known rearrangement reaction of phenylhydroxylamines and is an acid catalysed reaction leading principally to the formation of 4-amino phenols 37, although a little of the 2-isomers 38 are also sometimes formed. Reaction proceeds quite smoothly in relatively dilute acid at room temperature. Reaction is quite general for a range of R and X substituents. Much of the early work was carried out by Bamberger38 and the position up to 1967 has been very well reviewed39. 

In general, it would appear that the process of ipso-intermediate formation of the more reactive substrates such as phenols and amines is dominated by nitrous acid catalysed... 

Aryl glycosides of 2-amino-2-deoxy sugars, as might be expected, can be prepared by similar techniques as was illustrated by the synthesis of phenyl 3,4,6-tri-0-acetyl-2-acetamido-2-deoxy-p-D-glucoside and -D-galactoside by toluene -sulphonic acid catalysed reactions between phenol and the hexosamine penta-acetates These products were then anomerised using zinc chloride as catalyst to provide means of obtaining -anomers. 

This effect cannot be explained by simply considering differences in frontier orbital energies. A useful monofluorinated dienophile has been prepared [364] using metallated difluoroenol carbamate chemistry (Eq. 143) cycloaddition occurred smoothly with a range of dienes, and desulfination could be achieved under mild conditions without loss of the fluorine atom. Wakselman and co-workers [365] synthesised a rare competent difluorinated dienophile. Lewis acid catalysed Diels-Alder reaction with furan afforded an acceptable yield of (unfortunately) unstable cycloadduct which decomposed to a phenolic product via a dehydrofluorination reaction, circumscribing its utility (Eq. 144). 

The mechanism proposed for the acid-catalysed synthesis of bis(aryl)-alkanes [394] [scheme (E)] follows the main features of the aldolisation scheme (H). The protonised form of the carbonyl compound reacts by an electrophilic attack with the quinonoid structure of the aromatic molecule (e.g. phenol), viz. 

The oxidation of diols by quinolinium dichromate (QDC) shows a first-order dependence on QDC and acid.5 The oxidation of phenols to quinones by quinolinium dichromate in aqueous acetic acid is acid catalysed rate-determining formation of a cationic intermediate is indicated by a p value of —3.79 and further analysis shows the rates to be influenced equally by both inductive and resonance effects of the substituents.6... 

The nitrosation of phenol and cresols in buffer solutions involves a diffusion-controlled C-nitrosation followed by rate-limiting proton loss. /r-Crcsol is much less reactive than the other substrates.79 Nitrosation in trifluoroacetic acid or in acetic-sulfuric acid mixtures is regioselective (e.g. 4-nitroso-m-xylene is fonned from m-xylene) and possible non-selective nitrous acid-catalysed nitration can be eliminated by purging reaction solutions with nitric oxide.80... 

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