Stephen aldehyde synthesis, a named reaction in chemistry, was invented by Henry Stephen (OBE/MBE). This reaction involves the preparation of aldehydes (R-CHO) from nitriles (R-CN) using tin(II) chloride (SnCl₂), hydrochloric acid (HCl) and quenching the resulting iminium salt ([R-CH=NH₂]Cl) with water (H₂O). During the synthesis, ammonium chloride is also produced.