  Chemical composition of the massive cores forming high-mass stars can put
some constrains on the time scale of the massive star formation: sulphur
chemistry is of specific interest due to its rapid evolution in warm gas and
because the abundance of sulphur bearing species increases significantly with
the temperature. Two mid-infrared quiet and two brighter massive cores are
observed in various transitions (E_up up to 289K) of CS, OCS, H2S, SO, SO2 and
of their isotopologues at mm wavelengths with the IRAM 30m and CSO telescopes.
1D modeling of the dust continuum is used to derive the density and temperature
laws, which are then applied in the RATRAN code to model the observed line
emission, and to derive the relative abundances of the molecules. All lines,
except the highest energy SO2 transition, are detected. Infall (up to 2.9km/s)
may be detected towards the core W43MM1. The inferred mass rate is 5.8-9.4
10^{-2} M_{\odot}/yr. We propose an evolutionary sequence of our sources
(W43MM1-IRAS18264-1152-IRAS05358+3543-IRAS18162-2048), based on the SED
analysis. The analysis of the variations in abundance ratios from source to
source reveals that the SO and SO2 relative abundances increase with time,
while CS and OCS decrease. Molecular ratios, such as [OCS/H2S], [CS/H2S],
[SO/OCS], [SO2/OCS], [CS/SO] and [SO2/SO] may be good indicators of evolution
depending on layers probed by the observed molecular transitions. Observations
of molecular emission from warmer layers, hence involving higher upper energy
levels are mandatory to include.

Solar and Stellar Astrophysics