鐵粉還原硝基制備胺是什么機(jī)理? 硝基的還原是一種常用的合成伯胺的方法特別是芳香伯胺，一般而言，最干凈和簡便的還原方法就是通過Pd/C或Raney Ni加氫，但是當(dāng)分子內(nèi)存在對(duì)加氫敏感的官能團(tuán)，如：鹵素(Cl, Br and I; F 對(duì)加氫不敏感)，雙鍵，三鍵，氰基，羰基時(shí)，我們不得不采用其他方法， 最為經(jīng)典的要數(shù)鐵粉的還原。

化學(xué)試劑斯坦利公司認(rèn)為，鐵粉還原一般在鹽類電解質(zhì)(氯化銨)或烯酸條件下進(jìn)行，此條件可以將芳香硝基，脂肪硝基，亞硝基和羥胺等基團(tuán)還原為氨基。鐵粉還原芳香硝基化合物時(shí)，芳基上有吸電子基團(tuán)時(shí)，有利于硝基獲得電子，反應(yīng)容易進(jìn)行。常用的還原條件是：

一、鐵粉/HCl，THF體系或乙醇體系;

二、鐵粉/AcOH;另外常用的條件還有，鐵粉(5eq)，氯化銨(10eq)，在甲醇和水混合溶液(4：1)中回流，但此條件很容易形成偶氮化合物，致使反應(yīng)變黑，氮?dú)獗Ｗo(hù)可以減少偶氮化合物的生成，上述兩種酸性條件很少生成偶氮類副產(chǎn)物。此類反應(yīng)的后處理，一般情況下都是趁熱過濾，防止冷卻后，產(chǎn)品吸附到剩余的鐵粉和氧化鐵上。反應(yīng)機(jī)理鐵粉還原為單電子轉(zhuǎn)移機(jī)理，反應(yīng)中需要轉(zhuǎn)移六個(gè)電子，理論上還原硝基至少需要3倍當(dāng)量鐵粉，實(shí)際反應(yīng)操作中一般加入4倍當(dāng)量以上鐵粉。

反應(yīng)實(shí)例

To the starting material (3.1 g) was added acetic acid (24.4 mL) and then, reduced iron powder (9.15 g), and the mixture was stirred for 16 hours at room temperature. The mixture was filtered with Celite, and washed with ethyl acetate. The solvent was removed under reduced pressure, and water was added to the obtained residue, and the mixture was extracted with ethyl acetate. The organic layer was washed with saturated brine, and dried over magnesium sulfate. The solvent was removed under reduced pressure, and the obtained residue was purified by silica gel column chromatography, to give 1.4 g of the desired product.

To 80 percent ethanol (5.0 mL), the starting material (300 mg, 1.76 mmol) and concentrated hydrochloric acid (0.45 ml, 5.28 mmol) were added to stir for 10 minutes at 20°C. Then, iron powder (500 mg, 8.95 mmol) was added to the mixture to further stirring for 1 hour at 20°C. Insoluble matters were filtered off and the filtrate was concentrated, adding 0.5N NaOH (10 mL) to the residue, filtering the solution to further remove insoluble matters, extracting the filtrate with chloroform, drying the extract over anhydrous sodium sulfate, concentrating the extract, and distilling the resulting crude product to afford 224 mg of the desired compound (91% yield).

鐵粉還原硝基制備胺是什么機(jī)理? 化學(xué)試劑斯坦利公司認(rèn)為，另外由于鐵粉反應(yīng)后氧化物的顏色較深，不好純化，有時(shí)會(huì)用鋅粉代替鐵粉進(jìn)行反應(yīng)，條件類似，鋅粉的另外一個(gè)優(yōu)點(diǎn)是利用磁力攪拌器就可以進(jìn)行較大量的反應(yīng)。