Potassium borohydride purification

Reaction of the imine-indoline products 157 and 158 with potassium borohydride in acetic acid resulted in rupture of the C-3 -C-7 bond and reduction of the resulting imonium function (Scheme 45). While the initial C-I6 -C-14 PARF imine-indolines 157 and 158 can be isolated, they are less stable on silica gel chromatography than the corresponding l -vincad-ifformine-derived C-16 -C-14 PREF compounds 145, and consequently purification of the vindoline coupling products and separation of dia-stereomers were best carried out at the indole-indoline stage (162, 163). 

This group of reagents has become commercially available in large quantities some of its members - notably lithium aluminium hydride (LiAlH4), calcium hydride (CaH2), sodium borohydride (NaBH4) and potassium borohydride (KBH4) - have found widespread use in the purification of chemicals. 

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