Cryptophenols and Hindered Phenols

In this section the reactions of 2-tert-butylated and 2,6-di-tert-butylated phenols recently described are considered. The former, the cryptophenols are not completely hindered like the 2,6-di-tett-butylphenols although their reactions are different from those of 2-methylphenols. In both groups the reactions are comparatively straightfonward and comprise substitution or oxidation either at the phenolic oxygen or at the carbon in the 4-position. 

The reactions of this group either at the phenolic hydroxyl or at ring positions have been summarised in Table 6.7 (refs.94-97). 

In the reactions described the tert-butyl group survives comparatively drastic conditions although as might be expected the use of aluminium chloride sometimes causes de-tert-butylation.Thecompound2,4-di-tert-butyl-6-(5-chloro-pyridazin-2-yl)methylphenol in dichloromethane with aluminium chloride (3 equivs.), upon stirring at ambient temperature for 15 mins, followed by careful work-up of the mixture by quenching with water over 30 mins, gave the 4-mono tert-butyl product in 73% yield (ref.98). 

Loss of the tert-butyl groups occurred in the oxidative dimerisation of 2-methyl-6-tert-butylphenol in 54% yield finally to 3,3 -dimethyl-4,4 -dihydroxybiphenyl by heating with a catalytic quantity of ferric manganese naphthoate at 160°C during 6 hours in a stream of dry air to afford first a dimeric intermediate which after acidic washing in xylene solution was dealkylated by refluxing for 6 hours with 4-toluenesulphonic acid (ref.99). 

A mixture of the phenol and tetranitrogen tetrasulphide (1 mole) was refluxed in toluene (6h). Other phenols reacted similarly. 

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