Supercritical water phenol alkylation

The anti-Markovnikov alkylation of phenol (PhOH) with /-butyl alcohol (/-BuOH) can be achieved in supercritical water at 673 K in the absence of an added catalyst. 

Alkylation of phenols using primary, secondary and tertiary alcohols was achieved using supercritical water (at the near-critical region, 250-350 °C). This process eliminates the need for environmentally hazardous organic solvents and acid catalysts. Both ortho-and para-alkylphenols were formed in these reactions, their ratio being dependent on the... 

The hydrolysis of aniline to phenol in supercritical water by Patat [5] is accredited as the earliest reported study of a simple reaction in a supercritical medium. The reaction is catalysed by hydrogen ions formed from dissociation of phosphoric acid. Close to the critical point of water the catalyst has limited solubility, but as the conditions of the flow reactor were raised towards 450°C and 710 bar, the reaction rate was observed to increase by an order of magnitude. The mechanism was unaffected by the phase change it was from the better contact between reactants and catalyst that the rate improvement was derived. Townsend has taken advantage of homogeneity to study the reaction of a series of coal model compounds (alkyl-aryl hydrocarbons and ethers) in supercritical water [6]. For the hydrocarbons a free-radical pyrolysis route does not take advantage of the medium. However, for the ethers enhanced rates of reaction through a hydrolysis route occurs. 

The tuning of solubility with a relatively small jump or fall in pressure can possibly bestow many benefits with respect to rates, yields, and selectivity. Reaction parameters can be changed over a wide range. Replacement of solvents with high boiling points by supercritical (SC) fluids offers distinct advantages with respect to removal of the solvent. SC fluids like CO2 are cheap and environmentally friendly the critical temperature of CO2 is 31 C and the critical pressure 73.8 atm (Poliakoff and Howdle, 1995). Eckert and Chandler (1998) have given many examples of the use of SC fluids. Alkylation of phenol with tcrt-butanol in near critical water at 275 °C allows 2- erf-butyl phenol to be formed (a major product when the reaction is kinetically controlled 4-rert-butyl phenol is the major product, when the reaction is... 

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