用Rosenmund法合成
酰氯經(jīng)催化氫化還原為醛稱為 Rosenmund 法。通常在酰氯的二甲苯或甲苯溶液中，加入喹啉-S 或硫尿等催化劑鈍化劑，加熱通氫并使生成的 HCl 脫離反應(yīng)體系。如果甲硅烷或甲錫烷替代氫，收率可進一步提高。 用Rosenmund 法合成醛反應(yīng)示例
A pressure vessel is charged in order with 600 ml. of dry toluene, 25 g. (0.30 mole) of anhydrous sodium acetate, 3 g. of dry, 10% palladium-on-carbon catalyst, 23 g. (0.10 mole) of 3,4,5-trimethoxybenzoyl chloride, and 1 ml. of Quinoline S. The pressure vessel is flushed with nitrogen, sealed, evacuated briefly, and pressured to 50 p.s.i. with hydrogen. The mixture is shaken with 50 p.s.i. of hydrogen for 1 hour at room temperature, then heated at 35–40° for 2 hours. Agitation is continued overnight while the reaction mixture cools to room temperature. The pressure on the vessel is released, the vessel is opened, and the mixture is filtered through 10 g. of Celite filter aid, and the insoluble material is washed with 25 ml. of toluene. The combined filtrates are washed successively with 25 ml. of 5% sodium carbonate solution and 25 ml. of water. The toluene solution is dried over 5 g. of anhydrous sodium sulfate and filtered. The filtrate is concentrated by distillation at reduced pressure using a water aspirator. The residue is distilled through a 10-cm. Vigreux column with warm water circulating through the condenser, to prevent crystallization of the distillate, yielding 12.5–16.2 g. (64–83%) of 3,4,5-trimethoxybenzaldehyde, b.p. 158–161° (7–8 mm.), m.p.74–75°.
用金屬氫化物還原 最常用的還原劑為氫化三叔丁氧基鋁鋰（LTBA），反應(yīng)在等當量乙二醇二甲醚或其與 THF 的溶液中進行，反應(yīng)溫度盡量低為好。芳香醛的收率較脂肪醛好。 用金屬氫化物還原酰氯合成醛反應(yīng)示例
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. To the flask is added 115.0 g. (0.4989 mole) of 3,5-dinitrobenzoyl chloride followed by 500 ml. of dry diglyme. The solution is stirred vigorously, and the flask is immersed in a cooling bath at ?78°. A diglyme solution of lithium aluminum tri-tert-butoxyhydride 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. 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°. 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. 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.
