Phenols, aldehydes and other reagents

Phenol is the monomer used in higher quantity in the production of phenolic resins. Phenol was initially derived from coal tar, but with the increased commercialization of phenolic resins, the demand for phenol grew significantly. Currently, the peroxidation of cumene is the predominant synthetic route for the production of phenol, accounting for over 90% of world production. In this process, cumene is oxidized with oxygen to produce cumene hydroperoxide. Subsequently, the peroxide is decomposed to phenol and acetone using a strong mineral acid as a catalyst (Fink, 2005 Weber and Weber, 2010). Cumene is in turn produced from the alkylation of benzene with propylene (Weber and Weber, 2010). 

Phenol has unique chemical properties due to the presence of a hydroxyl group and an aromatic ring, which are complementary in that they facilitate both electrophilic and nucleophilic reactions. The aromatic ring of phenol is highly reactive towards electrophilic snbstitntion, which assists its acid-catalyzed reaction with formaldehyde. Phenol is a weak acid and easily forms sodium phenoxide (NaPh) in a base-catalyzed medinm. In the presence of sodium phenoxide, the nucleophilic addition of the phenolic aromatic ring to the carbonyl group of formaldehyde occurs. Thus, phenol can react with formaldehyde under acidic or basic conditions, leading to either novolac or resole resins (Weber and Weber, 2010). 

The use of alkyl phenols such as cresol in phenolic resin production reduces reactivity, hardness, cross-linking density and color formation but increases solubility in non polar solvents, flexibility, and compatibility with natural oils. At room temperature, o- and p-cresol are crystalline solids, while m-cresol is a viscous oil. Cresols are less soluble in water than phenol is (Weber and Weber, 2010). Approximately 60% of cresol is obtained from coal tar and crude oil using classical techniques such as distillation and liquid-liquid extraction. The remaining 40% is obtained synthetically by the alkylation of phenol with methanol (Fink, 2005). In addition to phenolic resins, cresols are also used in the production of herbicides, fungicides, disinfectants, plasticizers, epoxy resins and pharmaceuticals (Fink, 2005 Weber and Weber, 2010). 

Xylenols are available in six isomeric forms, all of which are crystalline at room temperature. Xylenols can be obtained from the same natural sources as cresols and phenol. In addition to phenolic resins, xylenols are used in solvents and disinfectants (Weber and Weber, 2010). 

Bisphenol-A (BPA) or 2,2-i /5(4-hydroxyphenyl) propane is used to produce special phenolic resins for coating applications, but the main use of bisphenol-A is in the production of polycarbonates and epoxide resins (Knop and Pilato, 1985). 

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