Phenol: Synthesis, Formation, Electrophilic, and Hydrolysis
Synthesis of phenols
A lot of the phenol used at this time is produced from benzene, by way of both hydrolyses of chlorobenzene or oxidation of isopropyl benzene (cumene).
Common synthesis of phenols
To make more complicated phenolic compounds, an extra normal synthesis is required. The cumene hydroperoxide response is pretty particular to phenol itself. The Dow course is considerably extra normal, however, the stringent circumstances required typically result in low yields, and so they could destroy every other functional group on the molecule. A milder, extra normal response is the diazotization of an arylamine (a by-product of aniline, C6H5NH2) to present a diazonium salt, which hydrolyzes to a phenol. Most purposeful teams can survive this system, so long as they’re secure within the presence of dilute acid.
Hydrolysis of chlorobenzene
Benzene is definitely transformed to chlorobenzene by quite a lot of strategies, one in every of which is the Dow course. Chlorobenzene is hydrolyzed by a powerful base at excessive temperatures to present a phenoxide salt, which is acidified to phenol.
Formation of phenol-formaldehyde resins
Phenolic resins account for a big portion of phenol manufacturing. Underneath the commerce title Bakelite, a phenol-formaldehyde resin was one of many earliest plastics, invented by American industrial chemist Leo Baekeland and patented in 1909. Phenol-formaldehyde resins are cheap, heat-resistant, and waterproof, although considerably brittle. The polymerization of phenol with formaldehyde entails electrophilic fragrant substitution on the ortho and para positions of phenol (in all probability considerably randomly), adopted by cross-linking of the polymeric chains.
Phenols are extremely reactive towards electrophilic fragrant substitution, as a result of the nonbonding electrons on oxygen stabilize the intermediate cation. This stabilization is best for assault on the ortho or para place of the ring; due to this fact, the hydroxyl group of phenol is taken into account to be activating (i.e., its presence causes the fragrant ring to be extra reactive than benzene) and ortho- or para-directing.
Picric acid (2,4,6-trinitrophenol) is a crucial explosive that was utilized in World War I. An efficient explosive wants an excessive proportion of oxidizing teams reminiscent of nitro teams. Nitro teams are strongly deactivating (i.e., make the fragrant ring much less reactive), nonetheless, and it’s typically troublesome so as to add a second or third nitro group to an aromatic compound. Three nitro teams are extra simply substituted onto phenol, as a result of the sturdy activation of the hydroxyl group helps to counteract the deactivation of the primary and second nitro teams.
Phenoxide ions, generated by treating phenol with sodium hydroxide, are so strongly activated that they endure electrophilic fragrant substitution even with very weak electrophiles reminiscent of carbon dioxide (CO2). This response is used commercially to make salicylic acid for conversion to aspirin and methyl salicylate.