Purification of Isobutanol

Subject: Purification of Isobutanol Tue Aug 30, 2011 8:21 am

Isobutanol (CAS NO. 78-83-1) is dried by refluxing with CaO and BaO for several hours, followed by treatment with calcium or aluminium amalgam, then fractional distn from sulfanilic or tartaric acids. More exhaustive purifications involve formation of phthalate or borate esters. Heating with phthalic anhydride gives the acid phthalate which, after crystn to constant melting point (m 65 °C) from pet ether, is hydrolysed with aqueous 15% KOH. The alcohol is distd as the water azeotrope and dried with K2CO3, then anhydrous CuSO4, and finally magnesium turnings, followed by fractional distn. The borate ester is formed by heating the dried alcohol for 6h in an autoclave at 160-175 °C with a quarter of its weight of boric acid. After fractional distns under vac the ester is hydrolysed by heating for a short time with aq alkali and the alcohol is dried with CaO and distd.