  The Si+SO$_2$ reaction is investigated to verify its impact on the abundances
of molecules with astrochemical interest, such as SiS, SiO, SO and others.
According to our results Si($^3$P) and SO$_2$ react barrierlessly yielding only
the monoxides SO and SiO as products. No favourable pathway has been found
leading to other products, and this reaction should not contribute to SiS
abundance. Furthermore, it is predicted that SiS is stable in collisions with
O$_2$, and that S($^3$P)+SiO$_2$ and O($^3$P)+OSiS will also produce SO+SiO.
Using these results and gathering further experimental and computational data
from the literature, we provide an extended network of neutral-neutral
reactions involving Si- and S-bearing molecules. The effects of these reactions
were examined in a protostellar shock model, using the Nautilus gas-grain code.
This consisted in simulating the physicochemical conditions of a shocked gas
evolving from $i.$ primeval cold core, $ii.$ the shock region itself, $iii.$
and finally the gas bulk conditions after the passage of the shock. Emphasising
on the cloud ages and including systematically these chemical reactions, we
found that [SiS/H$_2$] can be of the order of $\sim$ 10$^{-8}$ in shocks that
evolves from clouds of $t=1\times 10^6$ yr, whose values are mostly affected by
the SiS+O $\longrightarrow$SiO+S reaction. Perspectives on further models along
with observations are discussed in the context of sources harbouring molecular
outflows.
