Titration of alkyllithiums with a simple reagent to a blue endpoint

Reaction of readily available N-benzylbenzamide (1) with a slight excess of BuLi produces a deep blue dianion. Under suitable conditions (THF, −40°C), 1 may be used as a stoichiometric reagent to titrate n-BuLi, s-BuLi, and t-BuLi with good precision. Less reactive alkyllithiums (MeLi and MeLi·LiBr), aryllithiums, and LDA may be titrated at higher temperatures (−20 to 0°C). Titres are comparable to those obtained using the Gilman double titration method, and there appears to be no interference from alkoxides.