Its given in my book that alkyl halides react with alcoholic potassium cyanide to give alkyl cyanide through $\mathrm{S_N2}$ mechanism.

But why do we need to use alcoholic $\ce{KCN}$ (potassium cyanide dissolved in alcohol)? My understanding is that polar protic solvent favours $\mathrm{S_N1}$ over $\mathrm{S_N2}.$

  • $\begingroup$ Solubility. Potassium cyanide does not dissolve in non-polar aprotics $\endgroup$ – Waylander Dec 4 '19 at 15:38
  • $\begingroup$ Does alcohol have any role in reaction. Can we have reaction using only KCN $\endgroup$ – Grace Dec 4 '19 at 15:44
  • $\begingroup$ As @Waylander said, alcohol does not participate in the reaction itself. It only dissolves KCN so that it can dissociate to give the $\ce{CN-}$ nucleophile $\endgroup$ – Aniruddha Deb Dec 4 '19 at 15:58
  • $\begingroup$ Then instead of alcoholic can we use aqueous KCN $\endgroup$ – Grace Dec 4 '19 at 16:30
  • $\begingroup$ No because then the alkyl halide will not be soluble $\endgroup$ – Raoul Kessels Dec 4 '19 at 16:37

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