Preparation of KTpmenthyl
Menthylpyrazole (18.2 g, 0.1 mol) and KBH4 (1.98 g, 0.037 mol) were put in a
round-bottomed flask fitted with a condenser and were slowly heated under an
atmosphere of dinitrogen in the absence of solvent to 220 oC. H2
evolution was monitored using a wet-test meter. After 0.75 h. at 220
oC, 2.22 litres (0.098 mol) of H2 had evolved. Further heating to
240 oC did not cause any more gas to evolve. After cooling, a yellow
glassy solid had formed which was extracted with CH2Cl2 (300 cm3)
and filtered through a Celite pad. Solvent was removed under reduced pressure
to leave a foamy tan solid. 1H NMR showed 3 major peaks in the d
7.4-7.1 ppm region, suggesting that a range of poly(pyrazolyl)hydroborates had
been made. Attempts made to separate the products by vacuum sublimation proved
unsuccessful.
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