In a
250-ml. Erlenmeyer flask provided with a
magnetic stirrer bar and a
thermometer containing
50 ml. (54 g., 530 mmol.) of acetic anhydride and
4.0 ml. (3.1 g., 41 mmol.) of dry t-butyl alcohol,
7 ml. (39 mmol.) of 40% fluoroboric acid (Note
1) are added, initially very cautiously, and then in
ca. 0.2-ml. portions until all has been added, at such a rate that the final temperature reaches
ca. 100°. A dark yellow-brown color develops. The solution is allowed to cool spontaneously to 80°, and then is chilled to 5° in an
ice bath. Separation of the salt begins and is completed by the addition of
100 ml. of ether. After filtration on a
Büchner funnel the salt is washed with
30 ml. of ether, yielding
3.9–4.1 g. (
47–50%) of a colorless or pale yellow product, m.p.
218–220° (decomp.) (Note
2). The crude product may be recrystallized from
ethanol-methanol 1:1 (ca. 70–80 ml.) containing a few drops of
fluoroboric acid, affording
3.4–3.5 g. (
41–43%) of colorless prisms, m.p.
224–226° (decomp.) (Note
3).