A process suitable for adoption to large scale manufacture of 1-[(2-bromophenyl-sulfonyl]-5-methoxy-3-[(4-methyl-1-piperazinyl)methyl]-1H-indole dimesylate monohydrate, which is a selective 5-HT6 receptor antagonist intended for the symptomatic treatment of Alzheimer's disease and other disorders of memory and cognition like Attention deficient hyperactivity, Parkinson's and Schizophrenia.