  We present high angular resolution 1.1mm continuum and spectroscopic ALMA
observations of the well-known massive proto-cluster Mon R 2 IRS 3.The
continuum image at 1.1mm shows two components, IRS 3 A and IRS 3 B, that are
separated by $\sim$0.65$"$. We estimate that IRS 3 A is responsible of $\sim$80
% of the continuum flux, being the most massive component. We explore the
chemistry of IRS 3 A based on the spectroscopic observations. In particular, we
have detected intense lines of S-bearing species such as SO, SO$_2$, H$_2$CS
and OCS, and of the Complex Organic Molecules (COMs) methyl formate
(CH$_3$OCHO) and dimethyl ether (CH$_3$OCH$_3$). The integrated intensity maps
of most species show a compact clump centered on IRS 3 A, except the emission
of the COMs that is more intense towards the near-IR nebula located to the
south of IRS 3 A, and HC$_3$N whose emission peak is located $\sim$0.5$"$ NE
from IRS 3 A. The kinematical study suggests that the molecular emission is
mainly coming from a rotating ring and/or an unresolved disk. Additional
components are traced by the ro-vibrational HCN $\nu_2$=1 3$\rightarrow$2 line
which is probing the inner disk/jet region, and the weak lines of CH$_3$OCHO,
more likely arising from the walls of the cavity excavated by the molecular
outflow. Based on SO$_2$ we derive a gas kinetic temperature of T$_k$$\sim$ 170
K towards the IRS 3 A. The most abundant S-bearing species is SO$_2$ with an
abundance of $\sim$ 1.3$\times$10$^{-7}$, and $\chi$(SO/SO$_2$) $\sim$ 0.29.
Assuming the solar abundance, SO$_2$ accounts for $\sim$1 % of the sulphur
budget.
