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Phenol-formaldehyde reaction intermediates

Although the condensation of phenol with formaldehyde has been known for more than 100 years, it is only recently that the reaction could be studied in detail. Recent developments in analytical instrumentation like GC, GPC, HPLC, IR spectroscopy and NMR spectroscopy have made it possible for the intermediates involved in such reactions to be characterized and determined (1.-6). In addition, high speed computers can now be used to simulate the complicated multi-component, multi-path kinetic schemes involved in phenol-formaldehyde reactions (6-27) and optimization routines can be used in conjunction with computer-based models for phenol-formaldehyde reactions to estimate, from experimental data, reaction rates for the various processes involved. The combined use of precise analytical data and of computer-based techniques to analyze such data has been very fruitful. [Pg.288]

Figure 2.2 Formation of chelate intermediate for the phenol/formaldehyde reaction in the presence of a metal salt catalyst... Figure 2.2 Formation of chelate intermediate for the phenol/formaldehyde reaction in the presence of a metal salt catalyst...
A brilliant summary of the progress in the resin industry was published in 1926 by Barry, Drummond and MorreU [39]. A.A. Dmmmond recmited N.J.L. Megson of the British Government Department of Scientific and Industrial Research to study the detailed pathways of the phenol-formaldehyde reaction. The basic philosophy was that if the proposed intermediates could be synthesized by rational... [Pg.25]

The type of catalyst influences the rate and reaction mechanism. Reactions catalyzed with both monovalent and divalent metal hydroxides, KOH, NaOH, LiOH and Ba(OH)2, Ca(OH)2, and Mg(OH)2, showed that both valence and ionic radius of hydrated cations affect the formation rate and final concentrations of various reaction intermediates and products.61 For the same valence, a linear relationship was observed between the formaldehyde disappearance rate and ionic radius of hydrated cations where larger cation radii gave rise to higher rate constants. In addition, irrespective of the ionic radii, divalent cations lead to faster formaldehyde disappearance rates titan monovalent cations. For the proposed mechanism where an intermediate chelate participates in the reaction (Fig. 7.30), an increase in positive charge density in smaller cations was suggested to improve the stability of the chelate complex and, therefore, decrease the rate of the reaction. The radii and valence also affect the formation and disappearance of various hydrox-ymethylated phenolic compounds which dictate the composition of final products. [Pg.405]

Benzoxazines are heterocyclic compounds obtained from reaction of phenols, primary amines, and formaldehyde.98,99 As described previously, they are key reaction intermediates in the HMTA-novolac cure reaction.40,43 Crosslinking benzoxazine monomers at high temperatures gives rise to void-free networks with high Tgs, excellent heat resistance, good flame retardance, and low smoke toxicity.100 As in HMTA-cured novolac networks, further structural rearrangement may occur at higher temperatures. [Pg.416]

The commercial importance of phenol-formaldehyde resins has resulted in extensive studies of these systems, with the aim of identifying the reaction mechanisms and intermediates that occur during subsequent polymerization reactions. However, the complexity of Novolac-type systems has made a detailed understanding of the subsequent chemical processes and their relationship to the physical properties of the final polymerized product difficult. Thus, it is necessary to simplify the system in order to more readily unravel this complexity. Model compounds are frequently used to understand complicated chemical systems and their application to phenol-formaldehyde systems has been well documented . ... [Pg.1637]

Acid-Catalyzed Reactions. When an acid catalyst is used and the pH of the phenol/formaldehyde mixture is lowered to 0.5-1.5, somewhat less complicated products are formed. The initial reaction of addition of formaldehyde to the aromatic ring results in an unstable intermediate that rapidly condenses to three possible dihydroxydiarylmethanes. [Pg.1147]

This autoxidation property of carbons leads to a continuous loss of catalyst. When spherical carbon particles of 30 to 100 p,m were used in the oxidation with air of aqueous cyclohexanone solutions at 393 K in a trickle-bed reactor, a weak loss of carbon was observed after four weeks, and the originally smooth particles appeared rough and porous in scanning electron microscopy (SEM) [165]. The catalysts used with a nitrogen content of < 1% had been prepared from nitrogen-containing phenol-formaldehyde resin [166]. In this reaction cyclohexanone is oxidized to adipic acid and other dicarboxylic acids. 2-Hydroxycyclohexanone seems to be an intermediate. A carbon loss of several percent was also reported for other wet-air oxidation reactions of pollutants, mainly of phenol [167-169]. [Pg.254]

Sir Gilbert Morgan discovered phenol-formaldehyde polymers in the early 1890s while attempting to make artificial dyestuffs, but it was Leo Baekeland in the USA that exploited the reaction and obtained a patent for a commercial synthetic polymer in 1907. Phenol and formaldehyde were reacted in alkaline conditions with loss of water which formed an intermediate solid or liquid... [Pg.49]

Formaldehyde also reacts with aromatic hydrocarbons or amines at various ratios and forms relatively small molecular weight reaction intermediates [6]. These are multifunctional and easily form crosslinks by heating with appropriate hardeners. Phenolic resin, urea resin, and melamine resin are typical examples and 3D networks are formed by addition condensation reactions that repeats the addition and condensation... [Pg.99]

Reaction of phenyl metaborate with formaldehyde, followed by catalytic oxidation, has been reported to give sahcylaldehyde selectively and directiy from phenol without isolation of any intermediate products (63). [Pg.506]

Phenolic Resins. PhenoHc resins [9003-35 ] (qv) are thermosets prepared by the reaction of phenol with formaldehyde, through either the base-cataly2ed one-stage or the acid-cataly2ed two-stage process. The Hquid intermediate may be used as an adhesive and bonding resin for plywood, particle board, ftberboard, insulation, and cores for laminates. The physical properties for typical phenoHc laminates made with wood are Hsted in Table 1. [Pg.328]

These resins are prepared by an addition reaction of formaldehyde with either phenols, urea or melamine to prepare an intermediate such as the following ... [Pg.676]

Novolacs are prepared with an excess of phenol over formaldehyde under acidic conditions (Fig. 7.6). A methylene glycol is protonated by an acid from the reaction medium, which then releases water to form a hydroxymethylene cation (step 1 in Fig. 7.6). This ion hydroxyalkylates a phenol via electrophilic aromatic substitution. The rate-determining step of the sequence occurs in step 2 where a pair of electrons from the phenol ring attacks the electrophile forming a car-bocation intermediate. The methylol group of the hydroxymethylated phenol is unstable in the presence of acid and loses water readily to form a benzylic carbo-nium ion (step 3). This ion then reacts with another phenol to form a methylene bridge in another electrophilic aromatic substitution. This major process repeats until the formaldehyde is exhausted. [Pg.378]

Since a small amount of water is always present in novolac resins, it has also been suggested that some decomposition of HMTA proceeds by hydrolysis, leading to the elimination of formaldehyde and amino-methylol compounds (Fig. 7.15).42 Phenols can react with the formaldehyde elimination product to extend the novolac chain or form methylene-bridged crosslinks. Alternatively, phenol can react with amino-methylol intermediates in combination with formaldehyde to produce ortho-or para-hydroxybenzylamines (i.e., Mannich-type reactions). [Pg.389]

Baekeland had to make important discoveries before he could bridge the gap between the initial concept and final products. In particular, he found that the base-catalysed condensation of phenol and formaldehyde can be carried out in two parts. If the process is carefully controlled, an intermediate product can be isolated, either as a liquid or a solid, depending on the extent of reaction. At this stage, the material consists of essentially linear molecules and is both fusible and soluble in appropriate solvents. When heated under pressure to 150 °C, this intermediate is converted to the hard, infusible solid known as bakelite . This second stage is the one at which the three-dimensional cross-linked network develops. [Pg.14]

The complex batch reaction between formaldehyde. A, and sodium p-phenol sulphonate, B, proceeds in accordance with the following complex reaction scheme. All the reactions follow second-order kinetics. Components C, D and F are intermediates, and E is the final product. [Pg.286]


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See also in sourсe #XX -- [ Pg.24 ]




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