1．前言
硝基化合物，特别是芳香族硝基化合物，是具有悠久历史的一类化合物。硝基化合物是合成染料，香料，药物，和炸药的重要中间体，广泛应用于化学工业，制药和有机合成的各个领域中。因此，硝基化合物的制备是研究地最多，应用也最为广泛的一类有机反应。
同时，由于硝化，特别是芳香类化合物的硝化，需要过量的硝酸及硫酸等强酸，产生大量的废气和废酸，使之成为污染环境的一大因素。
硝基化合物的制备有多种途径，烃类的直接硝化，卤素取代及胺，肟的氧化等，如下图所示：
其中芳烃或脂肪烃的直接硝化是制备硝基化合物最简捷的途径。常见的硝化试剂归纳如下：
• 硝酸 Nitric acid
Alone or in combination with H2SO4, H3PO4, HClO4, HF(BF3), (CH3CO)2O, (CF3CO)2O, CF3CO2H, MeSO3H, CF3SO3H, FSO3H(SbF5), Nafion-H, sulfonated resins, clays, molecular sieves, graphite
• 硝酸盐 Nitrate salts
AgNO3/BF3, KNO3/H2SO4, K(Na)NO3/TMSCl/AlCl3, Cu(NO3)2/(CH3CO)2O, NH4NO3/(CF3CO)2O, (NH4)2Ce(NO3)
• 硝酸酯 Nitrate esters
BuONO2/Nafion-H, MeONO2/BF3, Me3SiONO2, acetone cyanohydrin nitrate
• 硝酰化合物 Nitryl compounds
NO2BF4, NO2PF6, NO2ClO4, NO2Cl(F), MeCO2NO2, CF3CO2NO2, PhCO2NO2, N-nitropyridinium nitrate
•氧化氮 Nitrogen oxides
NO2－O3, N2O3/BF3, N2O4/H2SO4, N2O4/AlCl3, nBuLi/N2O4, N2O5, N2O5/HNO3，N2O5/SO2
• 硝烷 Nitroalkanes
C(NO2)4, CH(NO2)3, (O2N)3CC(NO2)
在有机合成中，通过硝基化合物可以实现多种转换，如下图所示：
接上一篇文章：有机合成中引入硝基的方法有多少？赶紧拿起小本本记下（三）
3．脂肪族硝基化合物的合成
合成脂肪族硝基化合物最便捷的方法是卤素，磺酸酯等的硝基取代。活泼亚甲基的硝化，烯烃的硝化，和胺、肟的氧化，也能合成脂肪族硝基化合物。
3.1 硝基取代反应示例
卤代烃与亚硝酸盐（NaNO2，KNO2，AgNO2等）在极性非质子溶剂DMF或DMS0中或在相转移催化条件下反应，可以得到较好产率的硝基化合物。通常反应伴有副产物亚硝酸酯的生成。磺酸酯类化合物，如Tosylate，也可以发生类似反应。这是合成脂肪族硝基化合物的最常用的方法。
三甲硅基18以及三甲锡基19也能被硝基取代，得到相应的硝化物。
Ethyl α-bromobutyrate (58.5 g., 0.30 mol) is poured into a stirred mixture of sodium nitrite (36 g, 0.52 mol), anhydrous phloroglucinol (40 g, 0.32 mole), and 600 mL of N,N-dimethylformamide (DMF) contained in a 1-L three-necked flask equipped with a sealed stirrer. The flask is closed, except for a tube containing calcium chloride, and immersed in a water bath maintained at room temperature. Stirring is continued for 2.5 hours; then the reaction mixture is poured into ice water (1.2 L) layered over with ether (300 mL) After separation of the upper layer, the aqueous phase is extracted with four 100-mL portions of ether. The combined extracts are washed with four 100-mL portions of water and then dried over anhydrous magnesium sulfate. The magnesium sulfate is removed by suction filtration and washed with four 25-mL portions of ether which are combined with the filtered extract.
The ether is distilled through a small column, under reduced pressure, from a 1-L flask which is heated by a bath whose temperature is gradually raised to about 60°. The residual yellow liquid is transferred, with the aid of a little anhydrous ether, to a 100-mL flask, and the remaining solvent is distilled through the column under reduced pressure. Rectification of the residue yields 2–3 g of fore-run boiling in the range 33–71°/1 mm. which is followed by (33–36 g, 68–75%) of colorless ethyl α-nitrobutyrate, bp 71°/1 mm., nD20 1.4233. 20
3.2 含活泼亚甲基化合物的硝基取代反应示例
含活泼亚甲基（如苄甲基，含α氢的酯等）的化合物，在强碱（K/NH3, Na/NH3）的作用下，与硝酸酯反应，得到硝基化合物。
To a freshly prepared solution of sodium amide (0.23 mol) in liquid ammonia (300 Ml) was added 2-picoline ((8.4 g, 0.09 mol)) rapidly at –33o. After stirring for 10 min, n-propyl nitrate (29.6 g, 0.28 mol) was added as rapidly as possible while the temperature was kept below –33o. The mixture was stirred an additional 5 min, the ammonia gradually replaced with absolute ether, and the reaction mixture filtered after room temperature was reached (3-5 hr). The crude sodium 2-picolylnitronate was dried in vacuo, dissolved in 20 mL of water, and acidified with 11.0 g of glacial acetic acid at room temperature. Extracting the solution with chloroform, drying (Na2SO2), concentrating the extract in vacuo, and distilling the residue afforded 2-nitromethylpyridine (7.3 g, 55%). 21
3.3 胺和肟的氧化反应示例
胺的氧化，特别是肟的氧化，是合成脂肪族硝基化合物的一个重要手段。因为肟可以方便地由醛酮和羟胺制得。这是由醛酮合成硝基化合物的有效的方法，常用的氧化剂有过酸、臭氧、Oxone，高锰酸钾，高硼酸钠，次氯酸。
A mixture of oxime (1.89 g, 10 mmol) , urea (0.2 g, 3 mmol), NaH2PO4 (7.8 g, 54 mmol) in acetonitrile (25 mL) was stirred and heated to gentle reflux. A solution of peroxytrifluoroacetic acid was prepared by adding, dropwise during 10 min, trifluoroacetic anhydride (3.4 mL, 24 mmol) to a solution of 90% hydrogen peroxide (0.55 mL, 20 mmol) and acetonitrile (6 mL) chilled in ice bath. The peroxytrifluoroacetic acid solution was then added dropwise over 1 h to the stirred, heated oxime miture. In most cases, the mixture turned blue or green as the oxidizing solution was added but became yellow by the time addition was completed. The reaction mixture was then centrifuged, and the yellow supernatant liquid was decanted and concentrated in vacuo. The residue was treated with water (15 mL) and then extracted with 3 portion (15 mL each) of methylene chloride. The combined organic extracts were washed with 5% aqueous sodium bicarbonate, dried over MgSO4, and concentrated residue to give the product (1.95 g, 95%). 22
3.4 烯烃硝化反应示例
烯烃直接硝化生成共轭硝基取代烯烃，是一个合成脂肪族硝基化合物的有效的方法。常用的有 NO，N2O4，NaNO2/CAN, NaNO2/HgCl2 等多种体系。
Sodium-dried diethyl ether (150 mL) is placed in a 1-L, four-necked flask equipped with a fritted gas-inlet extending to its bottom, a sealed mechanical stirrer, a 100-mL, pressure-equalizing dropping funnel, a thermometer, and a dry ice condenser protected with a phosphorus pentoxide drying tube. Cyclooctene (44.4 g, 53.5 mL, 0.404 mol) is placed in the dropping funnel, and the system is swept with dry oxygen. Dinitrogen tetroxide (39.3 g, 27.1 mL at −9°, 0.427 mole) is condensed in a graduated, calibrated trap that is protected with a phosphorus pentoxide drying tube and has been swept with dry oxygen.
The flask is cooled to −10°, and the dinitrogen tetroxide is distilled with a warm water bath from the trap into the ether, with slow stirring; the transfer is aided by a minimal flow of dry oxygen. The solution is allowed to warm to 0–5°, and the oxygen flow rate is increased to 10 mL per minute. The cyclooctene is dropped into the dinitrogen tetroxide solution, with vigorous stirring, over a 30-minute period. The reaction is exothermic, and the temperature is kept at 9–12° by cooling with a methanol–dry ice bath at −20°. The dropping funnel is rinsed with 25 mL of ether, and the yellow solution is stirred for an additional 30 minutes at 10° with continued oxygen flow. Triethylamine (121 g, 1.20 mol) is added, with stirring, over a 12-minute period; the temperature of the reaction mixture is kept at 4–12° by maintaining the bath at −4°. The mixture is kept at room temperature for an additional 30 minutes, diluted with 150 mL of ether, and cooled to 0–5°. The excess triethylamine is neutralized with an ice-cold solution of 72 g of acetic acid in 200 mL of water, with stirring. The reaction mixture is transferred to a 2-l. separatory funnel and extracted with three 400-mL portions of ether. The combined ethereal extracts are washed with two 200-mL portions of water, three 150-mL portions of saturated aqueous sodium hydrogen carbonate, and again with water.
Most of the ether is removed at room temperature with a rotary evaporator. The water that separates is removed with the aid of a small separatory funnel, and the remaining ether, traces of water, and cyclooctane are distilled at room temperature (10 mm) over 3 hours, yielding 59–61 g of the crude 1-nitrocyclooctene as a yellow oil and. Chromatography on silica gel with successive elution with n-hexane and benzene gives 1-nitrocyclooctene (39–40 g, 63–64%). Distillation gave an analytically pure sample, bp 60° (0.2 mm.), nD20 1.5116. 23
Cyclohexene (0.82 g, 10 mmol) was added to the aqueous solution of mercuric chloride (2.71 g, 10 mmol) and sodium nitrite (1.38 g, 20 mmol) and stirred at 25oC for 30 h. The resulting precipitate was filtered to give the nitromercurial compound 2 (2.91 g, 80%). Compound 2 in methylene chloride (30 mL) was added 2.5 N aqueous sodium hydroxide (3.2 mL, 8 mmol) at 25oC, the mixture was stirred for 5 min followed by acidification (1 N hydrochloric acid), the resulting mixture was filtered through Celite (quantitative recovery of metallic mercury), extracted with methylene chloride, the solvent was removed under reduced pressure to give pure l-nitrocyclohexene (1 g, 98%).24
Cyclohexene (0.82 g, 10 mmol) was added to the mixture of ammonium cerium (IV) nitrate (NH4)2Ce(NO3)6 (CAN, 11 g, 20 mmol), and sodium nitrite (6.9 g, 100 mmol) and acetic acid (7.2 g, 120 mmol) in chloroform (100 mL) in a sealed tube. After sonication (600W) at 50oC for 4 h, the resulting mixture was washed with water and brine, extracted with chloroform. The solvent was removed under reduced pressure, the residue was purified by coumn chromatography to give the product (1.2 g, 95%). 25
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