A
250-mL flask equipped with a
reflux condenser is charged with
6.75 g (0.225 mol) of paraformaldehyde (Note
1) and
16.57 g (0.075 mol) of N-methylanilinium trifluoroacetate (Note
2). A solution of
7.30 g (0.05 mol) of α-tetralone (Note
3) in
50 mL of dry tetrahydrofuran (Note
4) is added at room temperature. The
N-methylanilinium trifluoroacetate dissolves, and the magnetically stirred mixture is refluxed for 4 hr under a
nitrogen atmosphere (Note
5). During this time a red color develops and the paraformaldehyde dissolves after 2 hr. After 4 hr the heating
oil bath is removed and the red solution allowed to cool for 10 min.
Diethyl ether (100 mL) is gradually added under efficient magnetic stirring, which induces the separation of a red gum. The ethereal solution is decanted from the red gum into a
separatory funnel and washed with
50 mL of half-saturated sodium bicarbonate solution. The red gum is triturated with
50 mL of diethyl ether, and the resulting ethereal solution is then used to extract the washing water (Note
6). The combined organic layers are dried over
magnesium sulfate. Filtration and concentration of the extract, first on a
rotary evaporator then under high vacuum, afford
8.05–8.6 g of a heavy red oil (Note
7). Trituration of this oil with
70 mL of diethyl ether precipitates impurities and causes some polymerization. Filtration through Celite and concentration under high vacuum give
6.8–7.2 g (
86–91%) of material that solidifies in a freezer (Note
8). Further purification by column chromatography over silica gel affords analytically pure material (mp
46–46.5°C) but lowers the yield to
70–82%.