Acidic ionic liquid 1- butyl -3- methyl imidazole hydrogen sulfate ([bmim]+ HSO4-) was prepared by using 1- methyl imidazole as a starting material through alkylation by n-butyl bromide and anion exchange with H2SO4. The synthesis of gramine from indole was investigated by employing the ionic liquid as catalyst with the yield of 81.6%

and the catalyst can be used continuously 4 times with keeping the yield essentially unchanged. The results demonstrated that the ionic liquid catalyst has excellent performance of environmental friendly

and the catalytic activity is more acceptable

reusable than the proton acid catalyst.