New MFI type arseno-silicate molecular sieves (As(V)-MFI), synthesized for the first time, can be crystallized at lower temperature (70-90 degrees C) in 1-3 days under hydrothermal conditions. Interestingly, these As(V)-MFI molecular sieves can be synthesized even faster than the As-free silicalite-l under identical conditions. Further, the crystallization becomes faster with the increase in As content of the reaction mixture, contrary to the observations made on all the other high silica molecular sieves, so far. These microporous As(V)-silicates exhibit significant catalytic activity in (i) phenol hydroxylation using 30% aq. H2O2 (ca. 55% H2O2 efficiency) and (ii) oxidative dehydrogenation of 2-butanol and benzyl alcohol using air under fixed bed vapor phase reaction conditions exhibiting ca. 75-85% selectivity towards 2-butanone and benzaldehyde + benzoic acid, respectively.