A 3-l., three-necked, round-bottomed flask is equipped with an efficient stirrer, a pressure-equalizing dropping funnel with a nitrogen inlet, and a Y-tube fitted with a low temperature thermometer and a nitrogen outlet. The outlet is vented through a bubbler tube, maintaining a slight positive pressure. The flask and dropping funnel are flamed in a stream of dry nitrogen (Note 1). To the flask is added 115.0 g. (0.4989 mole) of 3,5-dinitrobenzoyl chloride (Note 2) followed by 500 ml. of dry diglyme (Note 3). The solution is stirred vigorously, and the flask is immersed in a cooling bath at −78° (Note 4). A diglyme solution of lithium aluminum tri-tert-butoxyhydride (Note 5) is prepared in the following manner. Dry diglyme (450 ml.) is added with vigorous stirring to an Erlenmeyer flask containing 140.0 g. (0.5512 mole) of lithium aluminum tri-tert-butoxyhydride. After standing overnight, the resulting suspension is filtered under a blanket of dry nitrogen through a thick layer of Celite packed tightly on a Büchner funnel (Note 6). The flask containing the filtrate is kept stoppered until the reducing agent is transferred to the dropping funnel. Dropwise addition of this solution is started when the contents of the reaction flask reach −72°. There is a color change and a temperature rise of a few degrees. The rate of addition is adjusted, maintaining the temperature of the mixture between −78° and −68° (Note 7). After addition is complete the mixture is stirred at −78° for 30 minutes longer.

The cold reaction mixture is poured slowly with stirring into a 3-l. beaker containing 150 ml. of concentrated hydrochloric acid, 300 ml. of saturated aqueous sodium chloride, and 150 g. of ice. A white precipitate starts to separate (Note 8). An additional 150 ml. of saturated aqueous sodium chloride is added to the beaker and, after a minute, an upper layer begins to appear. The contents are transferred to a 2-l. separatory funnel and allowed to stand for 15 to 30 minutes while an upper brown layer separates. The upper layer is reserved while the lower layer is extracted with several portions of benzene, totalling 900 ml. The upper layer and the benzene extracts are combined and washed with seven 1-l. portions of water containing 10 ml. of concentrated hydrochloric acid. The benzene layer is washed successively with 100-ml. portions of aqueous 2% sodium hydrogen carbonate until the washings are basic, dried over 100 g. of anhydrous sodium sulfate, treated with 1 g. of charcoal, and filtered. The filtrate is concentrated at reduced pressure, yielding 59–62 g. (60–63%) of crude 3,5-dinitrobenzaldehyde, as a tan solid, m.p. 76–80°. Trituration in an ice bath with cold dry diethyl ether (ca. 0.3 ml./g.) gives a spongy solid, m.p. 85–87° (lit.³ 85°), with losses of 5–10%, sufficiently pure for most uses. Further purification may be effected by recrystallization from toluene-hexane.