Chlorination with thionyl chloride.
Thionyl chloride (IUPAC: sulfurous dichloride) is a really agressive reagent, it reacts with everything what contains even a little water, especially with your hands.
During the reaction with water (SOCl2 + H2O —> 2 HCl + SO2) it produces hydrogen chloride and sulfur dioxide what are not the best for your health.
Besides of these properties, it is a pretty useful reagent, since it reacts pretty well and could be removed easily since it’s low boiling point (74.6 °C). In organic chemistry it is most often used to prepare alkyl chlorides from alkyl alcohols (RCH2OH + SOCl2 —> RCH2Cl + HCl + SO2) and acyl chlorides from carboxylic acids (RCO2H + SOCl2 —> RC(O)Cl + HCl + SO2). Both reaction produces a lot toxic fumes, so it should be used under a well working fume hood.