The hot molecular core, W3(H2O), contains a massive protobinary system that is cocooned by dense gas (n(H2) ~ 107 cm−3), with about 1 arcsec (~ 2000 AU) separation of the binary system. We investigate chemical properties of the gas components around this binary system using the mm-wave transitions of complex molecules, CH3CN, SiO, HNCO, and CH3CH2CN, observed with the BIMA array. The two protostellar objects, A and C in W3(H2O), can be distinguished using chemical properties, suggesting that the source A may be younger than the source C within the time scale of less than 104 years. The hot core around the source C, traced by CH3CH2CN and the K=6 component of CH3CN, seems to have more time for chemical evolution than the source A. The SiO emission in this region suggests that there was an influence from the outside of the W3(H2O) and W3(OH) hot cores. The nitrogen chemistry may be more active in the later stage than the oxygen chemistry, but the chemical evolution of the protostellar envelopes may not be monotonic as previously suggested.
