Cyanohydrins were first prepared by the addition of HCN and a catalyst (base or enzyme) to the corresponding carbonyl. On a laboratory scale the use of HCN (toxic) is largely not encouraged, for this reason other less dangerous cyanation reagents are sought out. In situ formation of HCN can be sourced using precursors such as acetone cyanohydrin. Alternatively, cyano-silyl derivatives such as TMS-CN allows for both the cyanation and protection in one step without the need for HCN. Similar procedures relying on ester, phosphate and carbonate formation have been reported.