Occasionally the reaction mixture turns red, which we believe stems from a slight excess of isoprene. Although it is difficult to decolorize through crystallization (below), even a colored solution is spectroscopically clean and displays reactivity that is indistinguishable from the pale-yellow stock solutions. After stirring the mixture overnight at ambient temperature, the bulk of the potassium dissolved, and the remaining solid settled once the stirring was stopped. The titer of the approximate 1.0 M solution of KBTA can be checked by 1 H NMR spectroscopy after adding a measured aliquot of cyclopentane to serve as a 1 H NMR standard.