1、用Rosenmund法合成

酰氯经催化氢化还原为醛称为Rosenmund法。通常在酰氯的二甲苯或甲苯溶液中，加入喹啉-S或硫脲等催化剂钝化剂使钯碳钝化，加热通氢并使生成的HCl脱离反应体系。如果甲硅烷或甲锡烷替代氢，收率可进一步提高。

K. W. Rosenmund, Ber. 51, 585 (1918); K.W. Rosenmund, F. Zetzsche, ibid. 54, 425 (1921).

Reviews: E. Mosettig, R. Mozingo, Org.React. 4, 362 (1948); A. Rachlin et al., Org. Syn. 51,8 (1971); J. A. Peters, H. Van Bekkum, Rec. Trav. Chim. 100, 21(1981). Investigation of reaction parameters: W. F. Maier et al., J.Am. Chem. Soc. 108, 2608 (1986). Modified procedure applied to thesynthesis of esters: V. V. Grushin, H. Alper, J. Org. Chem. 56,5159 (1991).

Rosenmund法合成醛反应示例：

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-carboncatalyst,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 through10 gof 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 over5 gof anhydrous sodium sulfateand filtered. The filtrate is concentrated by distillation at reduced pressure using a water aspirator. The residue  is distilledthrough a 10-cm. Vigreux column with warm watercirculating through the condenser, to preventcrystallization of the distillate, yielding 12.5–16.2 g (64–83%)of 3,4,5-trimethoxybenzaldehyde, b.p. 158–161°C(7–8 mmHg.), m.p. 74–75°C.

Reference: Organic Syntheses, Coll. Vol. 6, p.1007; Vol. 51, p.8

2、用金属氢化物还原

最常用的还原剂为氢化三叔丁氧基铝锂（LTBA），反应在等当量的还原剂的乙二醇二甲醚或其与THF的溶液中进行，反应温度尽量低为好。芳香醛的收率较脂肪醛好。

用金属氢化物还原酰氯合成醛反应示例：

A 3-l.,three-necked, round-bottomed flask is equipped with an efficient stirrer, a pressure-equalizingdropping funnel with a nitrogen inlet, anda Y-tube fitted with a low temperature thermometerand a nitrogen outlet. The outlet is ventedthrough 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 mol) of 3,5-dinitrobenzoylchloride  followed by 500 mL of dry diglyme. Thesolution is stirred vigorously, and the flask is immersed in a cooling bath at−78°. A diglyme solution of lithiumaluminum tri-tert-butoxyhydride is prepared in the followingmanner. Dry diglyme (450 mL)is added with vigorous stirring to an Erlenmeyer flaskcontaining 140.0 g. (0.5512 mol) of lithium aluminumtri-tert-butoxyhydride. After standing overnight, the resultingsuspension is filtered under a blanket of dry nitrogenthrough a thick layer of Celite packed tightly on a Büchnerfunnel. The flask containing the filtrate is kept stoppered until thereducing agent is transferred to the dropping funnel. Dropwise addition of thissolution is started when the contents of the reaction flask reach −72°. Thereis a color change and a temperature rise of a few degrees. The rate of additionis adjusted, maintaining the temperature of the mixture between −78° and −68°.After addition is complete the mixture is stirred at −78° for 30 minuteslonger.  The cold reaction mixture ispoured slowly with stirring into a 3-l. beakercontaining 150 mL of concentrated hydrochloric acid, 300 mL ofsaturated aqueous sodium chloride, and 150 g. of ice. A white precipitate starts toseparate. An additional 150 mL of saturated aqueous sodium chloride is added to the beaker and, after aminute, an upper layer begins to appear. The contents are transferred to a 2-l. separatory funnel and allowed to stand for 15 to 30minutes while an upper brown layer separates. The upper layer is reserved whilethe 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 benzenelayer is washed successively with 100-mL. portions ofaqueous 2% sodium hydrogen carbonate untilthe 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.

Reference: Organic Syntheses, Coll. Vol. 6, p.529; Vol. 53, p.52

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