Trimethylol phenol

Braze, M. 1986. Sensitizing capacity of 2-methylol phenol, 4-methylol phenol and 2,4,6-trimethylol phenol in the guinea pig. Contact Dermatitis 14 32-38. 

Condensation of phenol with formaldehyde is a base-catalyzed process in which one resonance form of the phenoxide ion attacks formaldehyde. The resulting trimethylol phenol is then crosslinked by heat, presumably by dehydration with the intermediate formation of benzylcarbocations. The resulting polymer is Bakelite. Since the cost of phenol is relatively high and... 

Scheme 1.12. The reaction scheme for trimethylol phenol formation.

Resol resins, having very reactive methylol groups (obtained by the condensation of phenol with formaldehyde in basic media), are rarely used as starters for rigid polyether polyols. One reason is the impossibility of melting these resins at the propoxylation temperature, because upon heating they rapidly polycondensate and crosslink. An interesting representative of this group of resin is trimethylol phenol (reaction 15.26). 

Some polycopdensations are preceded by an addition reaction which first creates reactive groups on the monomer molecules. These groups interact then by polycondensation with one another and form large molecules. An example is the reaction of phenol and formaldhyde in aqueous solution, resulting in the formation of mono-, di-, or trimethylol phenols ... 

The reaction of phenol and formaldehyde in alkaline conditions results in the formation of o- and p-methylol phenols. These are more reactive towards formaldehyde than the original phenol and undergo rapid substitution with the formation of di- and trimethylol derivatives. The methylol phenols obtained are relatively stable in an alkaline medium but can undergo self-condensation to form dinuclear and polynuclear phenols (of low molecular weight) in which the phenolic nuclei are bridged by methylene groups. Thus in the base-catalyzed condensation of phenol and formaldehyde, there is a tendency for polynuclear phenols, as well as mono-, di-, and trimethylol phenols to be formed. 

Resole is produced by reaction of a phenol or a phenol derivative with an excess amount of formaldehyde in the presence of a base catalyst. The reaction in basic medium proceeds through the addition of formaldehyde with the phenoxide ion, leading to the formation of o- or p-monomethylol phenol (along with some di- or trimethylol phenol) as established by complexation via cyclodextrin or crown ether [2]. The reaction scheme for the synthesis of resole is shown in Figure 2.3. 

Fig. lA-0. Chemical structures of identified sensitisers in resins based on phenol and formaldehyde. A 2-methylol phenol. B 3-methylol phenol. C 4-methylol phenol. D o-cresol. E 2,4-dimethylol phenol. F 2,6-dimethylol phenol. G 2,4,6-trimethylol phenol. H 4,4 -dihydroxy diphenyl methane. I 2,4 -dihydroxy diphenyl methane. J 2,2 -dihydroxy diphenyl methane. K 4,4 -dihydroxy-3-hydroxymethyl-diphenyl methane. L 4,4 -dihy-droxy-3,5-dihydroxymethyl-diphenyl methane. M 4,4 -dihydroxy-3,3 -dihydroxymethyl-diphenyl methane. N 2,4 -dihydroxy-3, 5 -dihydroxymethyl-diphenyl methane. O 2,4 -dihydroxy-3,3 -dihy-droxymethyl-diphenyl methane... 

Trimethylol phenol is an allergen in resins based on phenol and formaldehyde. Cross reactivity is possible with other phenol derivative molecules. 

More successful, however, was the synthetic approach to resin chemistry, earlier emphasized by Drummond. The first three-ring compound, of the seven theoretically possible, from phenol and formaldehyde was described by Finn et Later Bender and coworkers described the preparation of all seven isomers, three of them being noncrystalline. Some systematic work on the conditions of preparation and the properties of phenolic alcohols was also reported by Finn and coworkers. The isolation of trimethylol phenol was of special interest, because it served as a starting material for the synthesis of branched chain compounds, the presence of which had not been positively detected in resins. 

Most of the aramid adhesive systems initially used were based on a first-step dip of either an epoxide or a blocked polyisocyanate and then a second or top coat of RFL. Wenghoefer in his patent disclosed a somewhat different first step dip which consisted of bis(j3-azido-formyl oxyethyl)isophthalate. After drying, the cord thus treated, was then dipped in a phenolic adhesive and cured at 230 C for 60 seconds. A patent issued to Van Gils uses a one-step dip based on vinyl pyridine latex, trimethylol-phenol, resorcinol-formaldehyde resin, and... 

The chemistry of melamines and phenoHcs is quite similar. In both cases formaldehyde [50-00-0] is added to the reactive sites on the patent ring to form methylol phenols (3) or methylol melamines (4) (see Phenolresins Aminoresins). There ate six reactive sites on the triazine ring of melamine [108-78-1] (1) so it is possible to form hexamethylolmelamine. However, the most common degree of methylolation is 1.5—2.0. The ortho and para positions of phenol ate active thus phenol can be trimethylolated (2). However, as with melamine, lower degrees of methylolation such as 1.2—2.5 ate... 

The o- and />-methylolphenols are more reactive toward formaldehyde than the original phenol and rapidly undergo further reaction to give di- and trimethylol derivatives. 

Urea (NH2CONH2) reacts with formaldehyde similarly to phenol to produce methylol derivatives that then condense further to yield a cross-linked network (Scheme 1). Actually, at a mole ratio of 1.5-2 mol of formaldehyde to urea and a pH of 7.5, a mixture of the monomethylol, dimethylol, trimethylol, and tetramethylol ureas are formed. For further extensive condensation to take place, the pH of the system must be made acidic. Thus, it is possible to concentrate the initial resin solution or spray-dry it to a soluble powder that can be dissolved and mixed with an acid catalyst at the time of application to induce the curing reaction. The ratio of formaldehyde to urea used in commercial resins varies with the manufacturer, but is always less than 2 1. 

Phenolic resins have been developed to a highly versatile degree as lacquer and paint bases. Pure Novolak is only soluble in polar solvents such as acetone, alcohol, low esters, etc. However, the market potential of alcohol-based lacquers is limited, and such lacquers are too brittle for many uses. For this reason, so-called plasticized and elasticized phenolic resins ( substituted phenolics ) were developed. Plastification is achieved either by partial etherification (e.g., with t-butyl alcohol), esterification (e.g., with fatty acids), or both etherification and esterification (e.g., with adipic acid and trimethylol propanol). These plasticized phenolic resins have increased elasticity, are soluble in aromatics, are compatible with polyvinyl compounds and fatty acids, and are suitable for use as stoving enamels. 

Heat-curing systems are based on a combination of hydroxy-terminated polyesters or polyethers and blocked polyfunctional isocyanates. When the temperature is raised, the blocking agent is removed and the free isocyanate groups react with the hydroxy groups to effect cure. The usual blocking agent is phenol and a typical blocked isocyanate is prepared by reaction of trimethylol-propane (1 mole), tolylene diisocyanate (3 mole) and phenol (3 mole) ... 

Long-chain alkylphenolic acids and their derivatives. Methylol derivatives of 3-pentadecyl phenol have been separated (32) on silica gel G in the solvent light petroleum (60-80 C)-diethyl ether-dimethylformamide-glacial acetic acid (75 85 5 1) as shown in Fig. 3, in which A is the 2-monomethylol derivative B is the 6- C is the 4- D is a mixture of 2-, 2,6-di, and 2,4-dimethyIols E and F are the 4,6-dimethylol G is the 2.4,6-trimethylol H is a mixture of all seven and I is the 6-methylol from a synthesis. 

Meta-cresol, which has three positions capable of methylolation, is high reactive with formaldehyde, and the alcohols formed resinify rapidly even under alkaline conditions. As a result, it is extremely difficult to isolate pure phenol alcohols. However, crystalline products beliei ed to be monoalcohols and melting at 105, 110, 117, and 122 C have been reported . The difficulties of isolating pure products are considerable, since three monomethylol derivatives, three dimethylol derivatives and one trimethylol derivative are possible. 

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