  Despite the harsh conditions of the interstellar medium, chemistry thrives in
it, especially in star forming regions where several interstellar complex
organic molecules (iCOMs) have been detected. Yet, how these species are
synthesised is a mystery. The majority of current models claim that this
happens on interstellar grain surfaces. Nevertheless, evidence is mounting that
neutral gas-phase chemistry plays an important role. In this article, we
propose a new scheme for the gas-phase synthesis of glycolaldehyde, a species
with a prebiotic potential and for which no gas-phase formation route was
previously known. In the proposed scheme, the ancestor is ethanol and the
glycolaldehyde sister species are acetic acid (another iCOM with unknown
gas-phase formation routes) and formic acid. For the reactions of the new
scheme with no available data, we have performed electronic structure and
kinetics calculations deriving rate coefficients and branching ratios.
Furthermore, after a careful review of the chemistry literature, we revised the
available chemical networks, adding and correcting several reactions related to
glycolaldehyde, acetic acid and formic acid. The new chemical network has been
used in an astrochemical model to predict the abundance of glycolaldehyde,
acetic acid and formic acid. The predicted abundance of glycolaldehyde depends
on the ethanol abundance in the gas phase and is in excellent agreement with
the measured one in hot corinos and shock sites. Our new model overpredicts the
abundance of acetic acid and formic acid by about a factor of ten, which might
imply a yet incomplete reaction network.
