腈与金属氢化物反应生成醛亚胺的金属盐，由于亚胺的碳氮双键极化比较小，难以被第二个负氢进攻，则可让反应停于此阶段而得醛。Stephen醛合成法（H. Stephen, J. Chem. Soc. 127, 1874 (1925); T.Stephen, H. Stephen, ibid. 1956, 4695）是用SnCl2/HCl将腈转化为醛亚胺的盐酸盐然后水解便得醛。此法只用于芳香醛的合成。
Preparation of 2-chloro-6-methylbenzaldehyde
Toa stirred solution of 2-chloro-6-methylbenzonitrile (1 g, 6.6 mmol) in THF (15 mL) under argon at 0 oC a solution of DIBAL (1 M in THF, 7ML, 7 mmol) was added dropwise over 5 minutes. After 3 hr at 0 oC, the reaction mixture was brought toroom temperature and further stirred overnight. The reaction mixture was quenched with 5percent sulfuric acid at 0 oC, extracted with ether, washedwith brine and dried (MgSO4). Concentration provided2-chloro-6-methylbenzaldehyde (0.92 g) which was used without further purification.
In a 1-liter flask equipped with a stirrer, condenser, dropping funnel, andthermometer is placed 10.2 g(0.3 mol) of lithium aluminum hydride in 300 mL of ether. The flask contains anitrogen atmosphere throughout the reaction period. To the stirred solution is added 39.6 g (0.45 mol) of ethyl acetate over aperiod of 1.25 h at 3-7℃. The reaction mixture is stirred for anadditional 0.5 h and then 24.9 g(0.30 mol) of trimethylacetonitrile is added over a period of 5 min. The temperature rise to 10℃, with the formation ofa highly visous solution. The reactionmixture is stirred for 1 h at 0℃ and then the solution is decomposedcautiously with 300 mL of 5 N H2SO4. The ether layer is separated and the layer isextracted three times with 50 mL portions of ether. The ether extracts are washed with saturatedsodium bicarbonate solution followed by ether washings with 30 mL portions ofcold water in order to remove ethanol. Theether extracts are dried over sodium sulfate and distilled to yield 25.8 g (74%) of pivalaldehyde, bp 70-72.5℃ (747 mm), n20D 1.3794.
Reference:H. Stephen, J. Chem. Soc., 1925, 127, 1874
RaneyNi 的活性作适当调节，可以催化还原腈到醛。通常用亚磷酸钠和甲酸钝化Raney Ni。也有在N，N-二苯基乙二胺或氨基脲共存下制得醛衍生物的方法。
Ranney Ni 加氢还原氰到合成醛
A 2-l., two-necked,round-bottomed flask fitted with a mechanicalstirrer and a reflux condenser is chargedwith 40.0 g. (0.232 mole) of 4-cyanobenzenesulfonamide,600 mL of 75% (v/v) formicacid, and 40 g. of Raney nickel alloy. Thestirred mixture is heated under reflux for 1 hour. The mixture is filtered withsuction through a Büchner funnel coated with afilter aid, and the residue is washed with two 160-mLportions of 95% ethanol. The combinedfiltrates are evaporated with a rotary evaporator.The solid residue is dissolved in 400 mL of boiling water and freed from asmall amount of insoluble material by decantation through a plug of glass woolplaced in a filter funnel. The filtrate is chilled in an icebath, and the precipitate is collected by filtration with suction, washedwith a small amount of cold water, and dried at 50° under vacuum, yieldingabout 32 g. of crude product, m.p. 112–114°C.
The product isdissolved in 800 mL of hot 95% ethanol, 15.5 g. of activated carbon is added, and the mixture is swirled periodically while it is allowed tocool for 1 hour. The activated carbon is removed byfiltration with suction through a bed of filter aid, the filter cake is washedwith 50 mL of 95% ethanol,and the combined filtrates are evaporated with a rotary evaporator. The residueis dissolved in 225 mL of boiling water, and the hot solution is decantedthrough glass wool placed in a filter funnel. The filtrate is cooled to 0°, theproduct is collected by filtration with suction, washed with a small amount ofcold water, and dried in a vacuum oven at 50°C, yielding 25.6–28.0 g. (62.9–68.8%)of 4-formylbenzenesulfonamide, m.p. 117–118°C.
Reference:Organic Syntheses, Coll. Vol. 6, p.631; Vol. 51,p.20
Toa flask containing 0.11 mol of methyl magnesium iodide (prepared from 7 mL ofmethyl iodide in 30 mL of ether containing 2.7 g of magnesium) is added 25 mL of benzene followedby 15 g (0.074 mol) of9-cyanophenanthrene. The reactionmixture is refluxed for 3 h, cooled, and hydrolyzed with cold ammonium chloridesolution. The benzene-ether layer isseparated, shaken with cold dilute hydrochloric acid, and then refluxed for 1 hin order to hydrolyze the ketimine hydrochloride to the ketone. The ketone, which precipitates as an oil, isseperated, distilled under pressure, and then recrystallized from ethanol toyield 9.5 g (58%),mp 73-74℃.
Reference: E. Bachman, J. Am Chem. Soc., 1936, 58, 2098