Chloroform forms a very poisonous compound called phosgene ( COCl2) when stored for a long time by reacting with oxygen in presence of sunlight.

CHCl3 + 1/2 O2 →COCl2 + HCl

In order to consume that phosgene gas and make chloroform safe, it is mixed with ethanol.

OCCl2 + 2 HOC2H5→ O=C(OC2H5)2 + 2 HCl

As a result, if your compound contains alcohol aensitive group, such as acid chlorid, do not use use chlorform as solvent.