Metal chlorides or sulfuric acid in ionic liquid solvents convert catechol to p-tert-Butylcatechol

• We report a method to transform from acid to super-acid.
• Ionic liquids mediated chloride or sulfuric acid show superior catalytic activity.
• Activity relies on hydrogen bonds changes of molecules and proton-transfer.
• [C4SO3HPy]HSO4 + 7.8%H2SO4 was picked as the best catalyst.

A series of novel acidic ionic liquids (ILs) mediated in metal chloride or sulfuric acid (IL-RClx or IL-H2SO4, R = Na, K, Al, Ba, Ca) were investigated as catalysts in the alkylation of catechol and methyl tert-butyl ether to p-tert-Butylcatechol. Based on the ILs screening, it was found that N-(4-sulfonic acid butyl) pyridine hydrogen bisulfate (IL2) was the most efficient catalyst (in the reaction). Moreover IL2 modified by sulfuric acid showed the best performance with the yield of p-tert-Butylcatechol approximately 81.7% and the selectivity of 92.5%. For a clear perspective to the influence of H2SO4, IL2 ([C4SO3HPy]HSO4) was systematically studied by the Density Functional Theory at 6–31 + G* level and the results showed that hydrogen bonds inside the ILs were probably the key for acidity enhancement of the modifications.