Phenol is readily alkylated at the ortho positions using alkenes in the presence of a Lewis acid such as aluminium phenoxide:
: CH=CR  +  CHOH  →  RCHCH-2-CHOH 
More than 100,000 tons of tert-butyl phenols are produced annually (year: 2000) in this way, using isobutylene (CH=CMe) as the alkylating agent. Especially important is 2,6-ditert-butylphenol, a versatile antioxidant.