Thanks Bandil, I hadn't even considered solubility issues in the substitution.
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"Piperidine, 85 g (99 ml, 1 mole) is carefully mixed with 84 ml of conc. HCl and 200 g of ice-water, and the pH is adjusted to 3-4. To this solution, 98 g (104 ml, 1 mole) of cyclohexanone is added, followed by 68 g (1.0 mole) of KCN in 150 ml of H2O (or 116 ml of 40% aqueous NaCN) without external cooling but with efficient stirring."
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A quick test would tell is the CuCN dissolves, and I think it may, in the presence of such high molarity HCl. HCN in situu?
For some reason I think, solubility issues aside, that the reaction mechanism may be different, with Cu possibly forming some sort of complex in the process. Could well be wrong actually.
Thanks for the tip on HCN generation! I thought that might be a possiblity, prolly, the only way.. And yes, the production of HCN with sulfuric is something I would choose to avoid at an cost. It's not something to play with without strict laboratory protocol and equipment IMHO.