In Stecker aminoacid synthesis, a cyanide is supplied in salt form that protonates at the beggining: NH4Cl + NaCN = NH3 + HCN + NaCl (Info source - http://www.organic-chemistry.org/namedreactions/strecker-synthesis.shtm) That seems okay, because HCN is weak acid. According to the source, the carbonyl and imine addition is then initiated by an acid. The acid is not mentioned. I don't believe HCN can protonate either carbonyl or imine due to its weakness. What is this acid? I have learnt that cyanide anion can only initiate its addition to carbonyl and proton from any acid cannot do that (that is from HCN (it's too weak) + from any stronger acid (then (CN-) is immediately protonated prior to additon)). Is this correct?