Uses of Dihydric Phenols

The dihydric phenols are speciality products widely used industrially and commercially. Hydroquinone and its relative, 4-methylaminophenol (metol) are the main chemicals used for development in black and white photography. Butylated hydroxyanisole, (BHA) mainly 2,6-di-tert-butyl-4-methoxyphenol (5), an important food antioxidant is synthesised from 2,4,6-tri-t-butylphenol by reaction in methanolic solution with chlorine to give 2,4,6-tri-t-butyl-4-methoxy- 

5-cyclohexa-2,5-dienone which is then dealkylated in acidic methanol. Resorcinol is largely used as a phenol formaldehyde resin for adhesive application in the rubber and tyre industry. Resorcinol or its formaldehyde reaction product can be used as accelerators for curing phenolic resins. The dihydric phenol is an intermediate for azo and triphenylmethane dyes, pharmaceuticals, antioxidants and other industrial chemicals. Two useful derivatives of resorcinol are the ultraviolet absorber, 

4-dihydroxybenzophenone (6), available from the mild mono-benzoylation of 

Catechol is an intermediate for the synthesis of racemic adrenaline which, although quite medicinally active, can be resolved (ref. 36) in 71% yield to afford the more active R(-) enantiomer, the natural form, which can also be derived quantitatively by asymmetric reduction (ref. 37) of the synthetic precursor, adrenalone as the hydrochloride by catalytic hydrogenation in methanol containing the rhodium complex of (R)-o[(S)-1 ,2-bis(diphenylphosphine)ferrocenyl]ethyl alcohol. Adrenalone is obtained by the acylation of catechol with chloroacetyl chloride to afford 3,4-dihydroxy-w-chloroacetophenone followed by reaction with methylamine. 

Catechol is also employed for the industrial antioxidant 4-tert-butylcatechol, and its monomethyl ether, guaiacol is used for the production of vanillin (10). This account is by no means a complete summary of the applications of the dihydric phenols more of which have been listed elsewhere (ref. 38). 

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