Epoxide phenol reaction

Shechter and Wynstra ( ) proposed two possible types of reactions between phenol and a glycidyl ether. One involves direct reaction of the phenol with the epoxide the other involves direct reaction of the aliphatic hydroxyl, generated from the epoxide-phenol reaction, with another epoxide as shown in Reactions 22 and 23 ... 

The basic catalysis of the epoxide-phenol reaction has been studied by a variety of authors (12,13). In general, the conclusion has been that basic catalysis gives selectivity for the phenol-epoxide reaction over the secondary alcohol-epoxide reaction (the secondary alcohol being formed from the opening of an epoxide). Although the base catalyzed reaction has been studied, the specific mechanism for triphenylphosphine Catalysis has not been determined. We propose the mechanism shown in Reaction Scheme 3 which is consistent with our experimental results. 

Two reactions have been proposed, one involving direct reaction between phenol and epoxide (reaction 76) and the other involving reaction between aliphatic hydroxyl, generated from the epoxide-phenol reaction (reaction 76), with another epoxide according to reaction (77). ... 

The existence of reaction (77) has been confirmed by a higher consumption rate of epoxides as compared to phenols.About 60% of the epoxide present has been shown to be consumed in epoxide-phenol reactions and the other 40% is consumed according to reaction (77). Alcohol has been found to be absent at the beginning of the reaction and forms only when phenol reacts with epoxides. The epoxides prefer to react with the so-formed alcohols, in the presence of the catalyzing influence of phenols, rather than with phenols. 

Epoxidized novolacs, 411 Epoxy -phenol networks, 411-416 properties of, 413-416 Epoxy-phenolic reaction kinetics of, 413 mechanism of, 411-412 Epoxy structures, 414 e-Caprolactam, 174... 

We emphasize that the above results have been observed only in the oxidation of sulfides and phenols, reactions known to follow radical mechanisms. A thorough investigation of the catalytic potential of the materials in other oxidation reactions (epoxidation, hydroxylations, etc.) is warranted. 

Subsequently, other workers including O Neill and Cole (4 and Dannenberg (5 ) showed that Reactions 2 and 3 proceed to the exclusion of Reaction 4. The reactivity of a particular epoxide-amine system depends on the influence of the steric and electronic factors associated with each of the reactants. It has been known for some time that hydroxyls play an important role in the epoxide-amine reaction. For example, Shechter et al. ( ) studied the reaction of diethylamine with phenylglycidyl ether in concentrated solutions. They showed that acetone and benzene decreased the rate of reaction in a manner consistent with the dilution of the reactants, but that solvents such as 2-propanol, water, and nitromethane accelerated the reaction (Figure 3). They also found that addition of 1 mol of phenol to this reaction accelerated it to an even greater extent that addition of 2-propanol or water. 

Using model systems, they found that without a catalyst no reaction occurred at 100 °C. At 200 °C epoxide disappeared at a much faster rate than phenol did (Figure 5) about 60% of the reaction was epoxide-phenol and the other 40% was epoxide-formed alcohol. Because alcohol was absent at the beginning of the reaction and only appeared when phenol reacted with epoxide, it was concluded that the phenol preferred to catalyze the epoxide-alcohol reaction rather than react itself. 

The base-catalyzed reaction, however, proceeded readily at 100 C with 0.2% mol of potassium hydroxide and exhibited a high degree of selectivity. As can be seen from Figure 6, disappearance of phenol and epoxide proceeded at the same rate throughout the course of the reaction. This phenomenon indicates that epoxide reacted with phenol to the essential exclusion of any epoxide-alcohol reaction, Shechter and Wynstra (8) proposed a mechanism in which the phenol first is ionized to phenoxide ion as shown in Reaction 24 ... 

Dr. Fred Guengerich at Vanderbilt University has published mechanistic schemata for cytochrome P450 involvement in an extensive array of both common and uncommon oxidative reactions and reductive reactions. Some of those are exhibited later in this chapter in a brief consideration of reductive reactions. Mechanisms for carbon hydroxylation, heteroatom oxygenation, N-dealkylation, O-dealkylation, alcohol oxidation, arene epoxidation, phenol formation, oxidation of olefins and acetylenes, reduction of nitro compounds, reductive dehalogenation, and azo reduction, to name a few, are provided. 

T. Mika Cll) has reviewed the chemistry of curing agents and how these influence the properties of the cured resins. Compounds such as phenol and boron trifluoride are effective accelerators for epoxide-amine reactions, while solvents usually slow down this same reaction due the lower concentration of reactants and/or to specific hydrogen bond interactions. 

TaBTe III illustrates how important it is in practice to choose highly selective catalysts for the polyaddition reaction. With a strong base like TBAH as catalyst very little branching is observed at 100°C. At 150°C, however, k2 is over a 100 times larger than at 100°C. Although this would normally have led to extensive branching, because of a nearly thirtyfold increase in the rate constant, k], for the epoxide/phenolic OH reaction branching is not very extensive. 

Shechter and Wynstra were the first to examine the uncatalyzed epoxy-phenol reaction." They found that no reaction occurred when equimolar quantities of phenol and phenyl glycidyl ether (PGE, a low molecular weight epoxy) were held at 100 C. When held at 200°C, however, epoxide disappeared at a much faster rate than the phenol, with the net result that about 60% of the reaction was epoxide with phenol (Rxn. 1) and 40% was epoxide with secondary hydroxyl (Rxn. 2). The extent of the second reaction is particularly significant when one considers that the secondary hydroxyl concentration was originally zero and became finite only when some epoxide had reacted with phenol. 

In their initial studies, Shechter and Wynstra had demonstrated that these catalysts could achieve high selectivity of the epoxy-phenol reaction in a solution of excess phenol. They later reversed the situation and studied the reaction selectivity in a solution of excess glycidyl ether in which the phenol was used as the limiting reagent. The excess of epoxide over phenol was measured until phenol had practically disappeared, and the results in all cases indicated high selectivity towards the epoxy-phenol reaction. The tertiary amine, ben ldimethylamine, was somewhat more effective than potassium hydroxide benzyltrimethylammonium hydroxide was even more powerful. First-order kinetics were observed for all reactions. Since it was postulated that the phenoxide ion was common to all these reactions, the observed diffCTences in reaction rates were linked to the cation. In was not determined, however, whether the cation effect is one of different degrees of dissociation of the phenol salts or of some other phenonomenon. 

It is noteworthy that the activation energies for both reaction propagation and reaction initiation are very similar, 68.0 and 65.6 kJ/mole, respectively. A probable explanation for this is that both the primaiy epojQT-phenol reaction and the complex activation reaction have similar rate-limiting steps, which in all likeUhood is the opening of the epoxide ring. 

Isocyanates form addition products reversibly with compounds which contain moderately reactive hydrogen, such as phenol, oximes, lactams and malonates. Fig. 14 is an example of a typical blocking-unblocking reaction. These addition compounds, called blocked isocyanates, are stable to water. They have been used in place of free isocyanate. The phenol-blocked isocyanates are the most common. In 1957 the DuPont Co. developed an aqueous dip based on blocked isocyanate. This process, called D-417, used phenol-blocked methylene bis(4-phenyl isocyanate) and a water soluble epoxide, the reaction product of glycerine and epichlorohydrin. RFL is used as the topcoat or second step dip ... 

Base-catalyzed reactions are very specific and take place readily at 100 °C. In the presence of about 0.2 mol % potassium hydroxide, the consumption rate of phenols exactly corresponds to the disappearance of epoxides. This suggests that, in this case, the epoxide-alcohol reaction according to reaction (77) is absent. A reaction mechanism according to Scheme 26 has been proposed to explain this behaviour. 

Prepared by epoxidation of styrene with per-oxyelhanoic acid. Reactions are similar to those of aliphatic epoxides (s e, e.g. ethylene oxide). Reacts with alcohols to give mono-ethers, e g. PhCH(0Me)CH20H. Phenols give resins. 

The oxidation step is similar to the oxidation of cumene to cumene hydroperoxide that was developed earlier and is widely used in the production of phenol and acetone. It is carried out with air bubbling through the Hquid reaction mixture in a series of reactors with decreasing temperatures from 150 to 130°C, approximately. The epoxidation of ethylbenzene hydroperoxide to a-phenylethanol and propylene oxide is the key development in the process. 

Methylene chloride is one of the more stable of the chlorinated hydrocarbon solvents. Its initial thermal degradation temperature is 120°C in dry air (1). This temperature decreases as the moisture content increases. The reaction produces mainly HCl with trace amounts of phosgene. Decomposition under these conditions can be inhibited by the addition of small quantities (0.0001—1.0%) of phenoHc compounds, eg, phenol, hydroquinone, -cresol, resorcinol, thymol, and 1-naphthol (2). Stabilization may also be effected by the addition of small amounts of amines (3) or a mixture of nitromethane and 1,4-dioxane. The latter diminishes attack on aluminum and inhibits kon-catalyzed reactions of methylene chloride (4). The addition of small amounts of epoxides can also inhibit aluminum reactions catalyzed by iron (5). On prolonged contact with water, methylene chloride hydrolyzes very slowly, forming HCl as the primary product. On prolonged heating with water in a sealed vessel at 140—170°C, methylene chloride yields formaldehyde and hydrochloric acid as shown by the following equation (6). 

Other modifications of the polyamines include limited addition of alkylene oxide to yield the corresponding hydroxyalkyl derivatives (225) and cyanoethylation of DETA or TETA, usuaHy by reaction with acrylonitrile [107-13-1/, to give derivatives providing longer pot Hfe and better wetting of glass (226). Also included are ketimines, made by the reaction of EDA with acetone for example. These derivatives can also be hydrogenated, as in the case of the equimolar adducts of DETA and methyl isobutyl ketone [108-10-1] or methyl isoamyl ketone [110-12-3] (221 or used as is to provide moisture cure performance. Mannich bases prepared from a phenol, formaldehyde and a polyamine are also used, such as the hardener prepared from cresol, DETA, and formaldehyde (228). Other modifications of polyamines for use as epoxy hardeners include reaction with aldehydes (229), epoxidized fatty nitriles (230), aromatic monoisocyanates (231), or propylene sulfide [1072-43-1] (232). 

Tetrakis (4-hydroxyphenyl)ethane is prepared by reaction of glyoxal with phenol in the presence of HCl. The tetraglycidyl ether [27043-37-4] (4), mp ca 80°C, possesses a theoretical epoxide functionaUty of four with an epoxy equivalent weight of 185—208 (4). 

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