由邻硝基甲苯合成邻氨基苯甲酸

College of Chemistry and Molecular Science,

Wuhan University

Report of Organic Chemistry Experiment

Designed Experiment：Synthesis of 2-Aminobenzoic Acid

from 2-Nitrotoluene

Tutor: Ying Xiong

Student’s Name: Wenxin Lu

Major: Chemistry Class of Hongyi School

Student ID: 2012301040179

Date: Apr. 24th to May 29th, 2014(5 weeks in total, once a week)

Ⅰ. Purpose of the Experiment

1. Initiate the progress of the syntheses with the raw material, 2-nitrotoluene, to prepare the important organic synthetic raw material, 2-aminobenzoic acid, by the oxidation of potassium permanganate and the reduction of Fe/HCl.

2. Learn to use IR and 1HNMR to analysis and represent the intermediate and product, determine the purity and the structure of them.

3. Review some operations in fundamental organic chemistry experiment, such as reflux, simple distillation and recrystallization.

4. Know the common oxidation and reduction methods in organic synthesis, to strengthen the basis of theoretical study.

5. By comparing different synthesis methods, determine a simple one which has a characteristic of high yield and less pollution, to understand the idea of “Green Chemistry”.

Ⅱ. Principle of the Experiment

2-Aminobenzoic acid is an indispensable organic synthetic raw material and intermediate. In the aspect of dye, it is used to prepare anthraquinone dyes, azo dyes and indigoiddyes, in the aspect of medicine, it is used to make pontal, pyrozoline, benzydamine, tardan, etc. 2-Aminobenzoic acid is also used in organic synthesis, for example, to prepare compound like 3-hydroxyindole and methyl anthranilate. As a chemistry reagent, it is used to test cerium, cadmium, cobalt, copper, lead, magnesium, mercury, nickel, nitrite, palladium, zinc, silver and uranium.

Step 1: Oxidation of 2-Nitrotoluene

2-nitrotoluene is a derivative of arene, which has an nitryl and an adjacent methyl on benzene ring. There are some α-H atoms on the C atom directly attached to benzene ring, which can be oxidized to a carboxyl group by many kinds of oxidation.

There are various methods of preparing 2-nitrobenzoic acid from 2-nitrotoluene, and several of them are widely applied [1]:(1)Potassium permanganate method. The advantages of this method

are that the yield is as high as 80%, the oxidizing progress is fast, and the operation is easy, whereas, it has weaknesses of low selectivity, high cost and much waste. (2)Sodium dichromate method. 2-nitrobenzoic acid can be prepared by mixing 2-nitrotoluene, sodium dichromate and sulfuric acid in water and keep them slightly boiling for half an hour. The cost of this method is lower than (1), but its yield is inferior to that, moreover, the chromium(Ⅲ) ion produced is severely harmful to environment. So this method is gradually abandoned. (3)Nitric acid oxidizing method. The reduzate of nitric acid is gas and easy to separated, meanwhile, no heavy mental ion is generated. But the using of nitric acid will make picric acid mixed in the product which amount cannot be ignored, regardless of the concentration of nitric acid. Also, nitric acid is corrosive to the facility, so this method can hardly be popularized now. (4)Sodium hypochlorite method. Expensive ruthenium tetroxide will be used in this method, restricted by the condition of the experiment, this method can’t be used. (5)The method of air liquid phase oxidation. This is the most potential and attractive method nowadays, restricted by the condition of the experiment, this method can’t be used.

Comprehensively considering the condition of this experience, the author will adopt the potassium permanganate method to prepare 2-nitrobenzoic acid from 2-nitrotoluene:

Step 2: Reduction of 2-Nitrobenzoic Acid

2-Nitrobenzoic acid is a kind of aromatic nitro compound, which nitryl on the benzene ring can be reduced to amino by reductant.

There are also many ways to reduct aromatic nitro compound to arylamine[2]: (1)Catalytic hydrogenation by using Pd-C catalysis. NaBH4 is a substitute. The reaction is easy to proceed and to be controlled due to its gently extent, and its yield is considerable. But the Pd-C catalysis is not available on the condition of this experiment. (2)Hydrazine reduction. Mix 2-nitrobenzoic acid, methyl alcohol, solution of sodium hydroxide and Raney-Ni, heat to reflux, then drop hydrazine into the system, continue to reflux, high-yield 2-aminobenzoic acid will be gained. (3)Zn-NH4Cl method. In this method, barium 2-aminobenzoate is reacted initially with zinc and ammonium chloride, then with alcohol solution of potassium hydroxide, 2-aminobenzoic acid will be gained.

(4)Electrolysis reduction. Use lead, tin or zinc amalgam to electrolyze 2-nitrobenzoic acid, then high yield of 2-aminobenzoic acid will be generated even without catalysis. (5)[3]Fe/HCl or Fe/HOAc reduction. If hydrochloric acid and iron powder are used as reductant, 2-nitrobenzoic acid can be reduced to 2-aminobenzoic acid within 3 hours. Besides, tin chloride (specificity reductant) and lithium aluminum hydride (strong reductant) can be used, but tin salts are toxic and lithium aluminum hydride is inflammable in wet air, so they are both abandoned.

The synthesis methods above are mostly aimed to 4-nitro compound, while the report of synthesis of 2-aminobenzoic acid is relatively less. Considering the similarity between 2-nitrotoluene and 4-nitrotoluene, the author will use the synthesis method of 4-aminobenzoic acid for reference to synthesize 2-aminobenzoic acid. Fe/HCl reduction is adopted in this experiment to reduce 2-nitrobenzoic acid to 2-aminobenzoic acid:

Recrystallization

重结晶是提纯物质的一种实验方法，有两种方式：单一溶剂法和混合溶剂法。单一溶剂法是利用被提纯物质在不同温度下的溶解度差异，将稍过量的样品溶于某一种溶剂中，加热溶解后，缓慢冷却至有晶体析出，得到纯度更高的产品。混合溶剂法是利用被提纯物质在不同溶剂中的溶解度差异，将样品溶于某种溶剂（称为“良溶剂”）中形成接近饱和的溶液，再缓慢滴加另一种溶剂（称为“不良溶剂”），使之析出晶体，冷却即可得到纯度更高的产品。

本实验中中间体（邻硝基苯甲酸）和产物（邻氨基苯甲酸）均为极性较强的物质，且在水中的溶解度不太大，考虑它们的极性，均采用混合溶剂法进行重结晶：对于邻硝基苯甲酸，良溶剂为乙酸乙酯，不良溶剂为石油醚；对于邻氨基苯甲酸，良溶剂为乙醚，不良溶剂为石油醚。

Thin Layer Chromatography (TLC) [4]

薄层层析（thin layer chromatography），也叫薄层色谱、薄板色谱或薄板层析，属层析技术中的一类，常用TLC代表。其原理与柱层析类似，将粒度细小（通常为200目）的吸附剂（硅胶或氧化铝）均匀涂布于玻璃板、塑料板或金属箔上形成一定厚度的薄层，此为固定相。被分离鉴定的样品制成溶液，用毛细管点在薄层上靠近某一端处，则样品中各种物质都会受到吸附剂或强或弱的吸附而附着在表面。将薄板样品点下端浸入展开剂（某一种溶剂或混合溶剂，作为流动相）中，溶剂靠毛细作用从点有样品的一端向另一端运动并带动样品点前进，各组分分子即在展开剂中发生溶解竞争。经过反复多次的吸附和溶解竞争后，受吸附力较弱而溶解度较大的组分将行进较长的路程；反之受吸附较强或溶解度较小的组分行进的距离则较短，从而使各组分间在板上拉开距离。

薄层层析主要应用于化合物的鉴定和其它分离手段的效果检测，并可监测反应进程、作为柱层析的先导，它作为常用分离方法之一，具有微量、快速、操作简便等优点，通常可分离的量在0.5g以下，最低可达10-9g。

作为检测手段，其理论依据为同种分子在记性、溶解度、分子大小和形状等方面完全相同，因而在同一块板上随展开剂爬升的高度亦应相同；不同种分子在这些方面总会有一些差别，因而其爬升高度不会完全相同。若用其它分离手段所得的某一个组分在薄层板上经样点展开后仍为一个点，则说明该组分为同种分子，即原来的分离方法达到了预期效果；如果展开后变成了几个斑点，则说明该组分中仍有数种分子，即原分离手段未达到预期效果。

本实验中，TLC将作为检测反应进程的一种手段。定期取反应液体点在层析板上，用展开剂（乙酸乙酯∶石油醚=1∶3）展开，在紫外灯下显色，因为反应物与产物的比移值不同，故可根据样点的位置确定反应是否进行完全。

IR[5]

红外光是一种电磁波，波长在0.78 ~ 500μm范围，可分为三个区段：近红外区（泛频区），0.78 ~ 2.5μm；中红外区（基本转动-振动区），2.5 ~ 25μm；远近红外区（骨架振动区），25 ~ 500μm。

原子和分子所具有的能量是量子化的，称之为原子或分子的能级，有平动能级、转动能级、转动能级和电子能级。基团从基态振动能级跃迁到上一个振动能级所吸收的辐射正好落在红外区，所以红外光谱是由于分子振动能级的跃迁而产生的。一般来讲，红外光谱主要是指中红外光

谱。

分子的振动可以分为伸缩振动和弯曲振动。两个原子之间的伸缩振动可看做简谐振动，由Hooke（虎克）定律，其频率可用如下公式近似计算：

υ=

1

2π√

k

m1m2

m1+m2

代入频率、波数、光速的关系可得

σ=

1

2πc

√

k(m1+m2)

m1m2

k为力常数，其大小与键能、键长有关，键能愈大，键长愈短，k值就愈大，因此k值和振动频率或波数成正比。

不同有机物的结构不同，它们的原子质量和化学键的力常数也不相同，因此会出现不同的吸收频率，从而产生特征的红外吸收光谱。利用已得到的红外光谱，结合可查到的各个官能团的特征振动频率及吸收峰的特点，可推测样品的分子结构。

1HNMR

原子核是带正电的粒子，不能自旋的核没有磁矩，能自旋的核有循环的电流，会产生磁场，形成磁矩。当自旋核处于某一外加磁场中，两不同自旋的原子核的能量具有一定差异，且磁场强度越强，差异越大。

使用某一频率的光入射，当光子能量与两自旋情况的原子核能量之差相同时，电磁波就会被吸收，以此来检测两能态的能量差值。而由于分子内电子屏蔽的作用，不同化学环境的氢原子自旋基态与激发态能量差值不同，在固定的照射频率时，不同的氢原子核会在不同的磁场强度下显示吸收峰，即不同化学环境的氢原子化学位移不同。根据吸收峰的化学位移值来推断该峰对应的氢原子的化学环境，从而判断待测样品中官能团的种类；通过积分计算不同峰的面积来计算不同氢原子的数量比，从而推断出待测分子具体的结构。

Ⅲ. The Physical and Chemical Constant of Major Organic Chemicals Table 1 The Physical and Chemical Constant of Major Organic Chemicals[6]

Ⅳ. Major Chemicals and Apparatus

2-Nitrotoluene(A.R.), potassium permanganate(A.R.), TBA bromide(A.R.), sodium hydroxide(A.R.), hydrochloric acid(A.R.), iron powder(A.R.), acetic acid(A.R.), ethyl ether(A.R.), anhydrous sodium sulfate(A.R.), ethyl acetate(A.R.), petroleum ether(60 ~ 90℃, A.R.).

Three necked flask(19#×3), round bottom flask(100mL/19#), conical flasks(50mL/19#, 25mL/19#), reflux condenser(19#×2), Liebig condenser(19#×2), air condenser(19#×2), distillation head(19#×3), vacuum adapter(19#×2), ground glass stoppers(19#), filter flask(150mL), Büchner funnel, conical funnel, beakers(250mL, 100mL, 50mL), graduated cylinders(50mL, 10mL), thermometer(150℃), thermometer adapter(19#), separatory funnel, tubes, pipettes, watch glass, glass rod, pH test paper, chromatoplates(8cm×2.5cm), developing chamber, sealed melting point capillaries, spotting capillaries, stainless steel spatula, stirring bar, iron clamp, water bath pot, platform scale, ruler.

Constant temperature magnetic heating stirrer, heating mantle, adjustable closed electric stove, portable UV lamp, RY-1 optimelt.

Ⅴ. Figures of Experimental Apparatus

Figure 1 Apparatus for Refluxing

Figure 2 Apparatus for Simple Distillation

Figure 3 Apparatus for Vacuum Filtration

Ⅵ. Details of the Experiment (Phenomena are Shown in Brackets)

1. Oxidation of 2-Nitrotoluene [7]

a. Preparation of 2-Nitrobenzoic acid

Add 3.5mL of 2-nitrotoluene and 0.32g of TBA bromide into a 100mL three necked flask. Measure 75mL of water, add two thirds of which into the flask, and attach the reflux condenser, thermometer and constant temperature magnetic heating stirrer, slowly start heating. Use a spatula to add 11.85g of potassium permanganate into the mixture for batches (once a minute)【The solution turned dark violet and became warm, meanwhile there was a little of white powder and oily drops on the inwall of the flask】, and use the remaining water to rush the KMnO4 and some white oily drops back to the flask【The reaction temperature is 90±4℃】. Control the temperature to about 90℃and let the system to react for 1.5h.【Some yellow-white solid adhered to the inwall of the reflux condenser; the solution boiled and turned violet with slightly brown】

After the reaction terminates, add 0.8g of NaOH and cool the mixture to room temperature 【The system turned sepia and became sticky】. Filter it and use 25mL of hot water to wash the residue twice【The residue was brown and the filtrate was light yellow-green】. Combine the filtrate, then acidize the filtrate to pH 1 to 2 by using 6M of HCl【White precipitate and lots of bubbles were generated after adding acid, the solution turned yellow】. Filter it and use cool water to wash the residue【Fine yellow-white powder】. Dry the solid, weigh it【1.37g】and determine the m.p. of it.

Table 2 M.p. Measuring of Crude 2-Nitrobenzoic Acid

The m.p. of 2-nitrobenzoic acid that has not been recrystallized is: 144.5℃.

Make a tiny amount (about 1mg) of crude 2-nitrobenzoic acid dissolve in several drops of ethyl acetate. Use a capillary to suck a little of the solution and point on the plate, then put the plate into a developing chamber containing 3mL of mixture of ethyl acetate and petroleum ether (1:3). When the front of the solvent get close to the top of the plate, take out it and let the solvent to volatilize. Record the spot under the UV light.【There was only one spot on the plate】

b. Recrystallization of 2-Nitrobenzoic acid

Put some crude product in a 50mL beaker, add some ethyl acetate, stir and make the solid to dissolve. Drop in petroleum ether by a pipette to make precipitate appears, cool the beaker in the ice bath. Filter the mixture and the pure 2-nitrobenzoic acid is got【Fine yellow-white crystalline powder, 0.8g】. Dry it at room temperature.

2. IR and 1HNMR Representation of 2-Nitrobenzoic acid

a. IR

Mix about 1mg of 2-nitrobenzoic acid and 200mg of dry potassium bromide in an agate mortar. Under the circumstance of heating by infrared lamp, grind the mixture carefully until there is no shining spot in it, stop grinding. Put some powder in a tabletting container cleaned by ethyl alcohol, then put it under tablet press, keep the pressure of 10MPa for half a minute. Take out the sample

tablet and quickly put it in the sample groove then in the sample room of IR spectrometer which background has been collected. Click “Collect Sample”, the IR spectrum of sample is got, click “Find Peaks” to mark the wavenumbers of every absorption peaks. Click “Replace” to complete marking, click “Full Scare” to show the spectrum in full screen, then the spectrum of 2-nitrobenzoic acid is shown as follows:

Figure 4 IR Spectrum of 2-Nitrobenzoic Acid

b. 1HNMR

Weigh about 40mg of 2-nitrobenzoic acid, and add it to a special NMR sample tube. Drop in 0.5mL deuterated DMSO to dissolve the solid, put the tube in the NMR spectrometer, the 1HNMR spectrum of 2-nitrobenzoic acid is shown as follows:

Figure 5 1HNMR Spectrum of 2-Nitrobenzoic Acid

3. Reduction of 2-Nitrobenzoic Acid[8]

a. Preparation of 2-Aminobenzoic Acid

Weigh 1.8g of iron powder and put it into a 100mL three necked flask, add 6mL of water and 1mL of acetic acid successively. Start stirring and gently heat it for 10min to activate iron, which is beneficial to the reaction later【The color of the solution slightly turned dark and red; lots of bubbles was generated】. Add 25mL of 2M HCl, heat to increase the temperature. In the process of temperature heating, slowly add 0.8g of 2-nitrobenzoic acid for many times (once a half minute)【The color turned even darker, ended with brown-black】. Supply 0.2g of iron powder after finishing feeding, keep the temperature to 98 ~ 102℃for 1h【The reaction temperature was 100.5℃; lots of greyish-green precipitate was generated】. Cool to 80℃, adjust the pH to 8.5 ~ 9 by adding 30% solution of NaOH【Black colloidal precipitate was generated】. Filter it and wash the residue by hot water, keep the filtrate and cool it. Add 2M HCl to adjust pH to 3.5 ~ 4【No solid precipitated, but the solution became kind of like jelly】. Extract the organics twice by 40mL of ethyl ether (20mL every time), abandon the water phase. Dry the organic phase by anhydrous sodium sulfate, stewing for 20min【The organic phase is light orange-yellow】. Build the apparatus for simple distillation, vaporize the solvent to about 2mL left, pour it to a watch glass. Crude 2-aminobenzoic acid will separate out after the solvent vaporizes【Yellow powder】. Weigh it【0.52g】and determine the m.p. of it.

Table 3 M.p. Measuring of Crude 2-Aminobenzoic Acid

The m.p. of 2-aminobenzoic acid that has not been recrystallized is: 145℃.

b. Recrystallization of 2-Aminobenzoic Acid

Put some crude product in a 50mL beaker, add some ethyl ether, stir and make the solid to dissolve. Drop in petroleum ether by a pipette to make precipitate appears, cool the beaker in the ice bath. Filter the mixture and the pure 2-aminobenzoic acid is got【Luminous yellow powder, 0.39g】. Dry it at room temperature.

4. IR and 1HNMR Representation of 2-Aminobenzoic acid

a. IR

Mix about 1mg of 2-aminobenzoic acid and 200mg of dry potassium bromide in an agate mortar. Under the circumstance of heating by infrared lamp, grind the mixture carefully until there is no shining spot in it, stop grinding. Put some powder in a tabletting container cleaned by ethyl alcohol, then put it under tablet press, keep the pressure of 10MPa for half a minute. Take out the sample tablet and quickly put it in the sample groove then in the sample room of IR spectrometer which background has been collected. Click “Collect Sample”, the IR spectrum of sample is got, click “Find Peaks”to mark the wavenumbers of every absorption peaks. Click “Replace”to

complete marking, click “Full Scare” to show the spectrum in full screen, then the spectrum of 2-aminobenzoic acid is shown as follows:

Figure 6 IR Spectrum of 2-Aminobenzoic Acid

b. 1HNMR

Weigh about 40mg of 2-aminobenzoic acid, and add it to a special NMR sample tube. Drop in 0.5mL deuterated DMSO to dissolve the solid, put the tube in the NMR spectrometer, the 1HNMR spectrum of 2-aminobenzoic acid is shown as follows:

Figure 7 1HNMR Spectrum of 2-Aminobenzoic Acid

Ⅶ. Calculation of Yield

1. 邻硝基甲苯的氧化产率

取3.5mL（4.06g）邻硝基甲苯进行反应，高锰酸钾过量，理论应得邻硝基苯甲酸的质量为

4.06g×167.12

=4.95g

实际得到邻硝基苯甲酸1.37g，反应产率为

1.37g

4.95g

×100%=27.7%

重结晶后得到纯化邻硝基苯甲酸0.80g，重结晶产率为

0.8g

1.37g

×100%=58.4%

2. 邻硝基苯甲酸的还原产率

第二步还原反应的原料全部来源于第一步氧化反应，且第一步重结晶后的产品全部用于第二部还原，即参与还原反应的邻硝基苯甲酸的质量为0.80g，故理论上应得邻氨基苯甲酸的质量为

0.8g×137.14

=0.66g

实际得到邻氨基苯甲酸0.52g，产率为

0.52g

×100%=78.8%

重结晶后得到纯化邻氨基苯甲酸0.39g，重结晶产率为

0.39g

×100%=75.0%

3. 本实验的最终产率

本实验取原料4.06g，最终得到了0.39g产品，但实验过程中使用了重结晶来纯化中间体及产物，由于重结晶对样品的损失较大，不考虑重结晶的损失，则第一步所得1.37g邻硝基苯甲酸完全用于第二步反应，将得到邻氨基苯甲酸的质量为：

1.37g×0.52g

=0.89g

即若不重结晶，按照本实验的实验步骤，将得到0.89g产品，而4.06g邻硝基甲苯理论上应该得到4.06g邻氨基苯甲酸（邻硝基甲苯和邻氨基苯甲酸分子量相同，是官能团异构体），故本实验的最终产率为：

0.89g

4.06g

×100%=21.9%

Ⅷ. Analyses and Discussions of Experimental Phenomena and Results

1. 对部分实验现象的分析与讨论

第一步邻硝基甲苯的氧化步骤中，①反应开始后有少量白色粉末和油状物附着在烧瓶及冷凝管内壁，由于邻硝基苯甲酸是黄白色结晶，因此这应该就是预期产物——邻硝基苯甲酸；②加入NaOH溶液后液体变得粘稠，且产生大量棕褐色沉淀，由于本实验中氧化是在中性条件下进行的，因此可能生成了如MnOOH、Mn(OH)3、MnO2等锰的氧化物及氢氧化物，而这些物质都是棕

色至黑色的；③滤液加酸酸化时产生了大量气泡，这应该是CO2气体，而产生此气体的原因是NaOH部分变质，变为Na2CO3。

第二步邻硝基苯甲酸的还原步骤中，①反应完毕，加碱溶液调节pH时产生大量黑色胶状沉淀，这是Fe(OH)3中夹杂有少量的Fe(OH)2，由于铁粉是过量的，加入的又是强碱，故很有可能产生胶状的Fe(OH)3，给抽滤带来很大困难；②滤液加酸酸化，调节pH至邻氨基苯甲酸的等电点时，并无沉淀产生，这可能是由于产量较少（最终只收到了0.52g），整个还原步骤中水又加得略多，而邻氨基苯甲酸在水中仍可溶解一小部分，故难以得到沉淀。

2. 对熔点测定结果的分析与讨论

对邻硝基苯甲酸粗品的熔点测定结果显示，此样品的熔点与文献值（146 ~ 148℃）接近，故样品的纯度较高，比文献值稍低可能是样品中含水的结果；而TLC分析的结果是板上仅有一个样点，也说明该“粗品”的纯度较高。

对邻氨基苯甲酸粗品的熔点测定结果显示，此样品的熔点与文献值（146℃）接近，故样品的纯度较高，比文献值稍低可能是样品中含水的结果。

以上说明在氧化还原反应中，只要使用合适的氧化剂或还原剂，控制一定反应条件，能够得到纯度较高的产品，副产物较少。

3. 对红外光谱的分析与讨论[5][9][11]

a. 邻硝基苯甲酸

图4是邻硝基苯甲酸的红外光谱。由图可知，波数在1606.02cm-1和1532.86cm-1处分别出现吸收强度中等和很强的吸收峰，这代表C=C的伸缩振动；在波数为3110 ~ 3010cm-1范围出现一组吸收强度中等的宽峰，这代表苯环上C—H的伸缩振动，这与前面C=C的伸缩振动结合起来，能提供芳香环存在的证据。而在2000 ~ 1650cm-1范围出现的泛频峰的形状与731.33cm-1处出现的强吸收峰表明该苯环是1,2-二取代的。

羧基C=O的伸缩振动本应出现在1710cm-1附近，但由于羧酸常以二聚体形式存在，且由于在苯环上是1,2-二取代，能形成分子内氢键，使得C=O的单键性增强，键长变长，化学键力常数减小导致羰基峰向低波数位移，出现在1681.21cm-1处，是一个很明显的强而略宽的吸收峰；在3000 ~ 2500cm-1范围（图中未标出波数值）出现一系列宽而散的吸收峰，这代表O—H的伸缩振动，915.28cm-1、1416.66cm-1处出现的两个吸收峰代表O—H的弯曲振动。

波数在1532.86cm-1处出现的强吸收峰也有可能代表芳香环上—NO2的不对称伸缩振动，由于吸电子集团—COOH的存在，原本在1520cm-1左右的峰向高波数位移，与苯环C=C的伸缩振动吸收峰重叠；波数在1292.12cm-1处出现的双峰代表芳香环上—NO2的对称伸缩振动，同样由于吸电子集团—COOH的存在，原本在1330cm-1左右的峰向低波数位移。

另外，波数为2359.11cm-1出现的一个小峰应代表CO2中C=O的伸缩振动，这是空气背景消除不干净或样品片吸附有少量CO2导致的。

b. 邻氨基苯甲酸

图6是邻氨基苯甲酸的红外光谱。与邻硝基苯甲酸的图谱对比，可以发现：①与邻硝基苯甲酸不同的是，原本1600cm-1附近的C=C伸缩振动吸收峰仍在，但1532cm-1的吸收峰变得极弱，几乎消失，表明硝基已经被转化，不存在硝基的不对称伸缩振动，残余的1534.90cm-1可能代表苯环C=C的伸缩振动；②另一点不同是，波数为3472.77cm-1、3373.05cm-1处出现两个尖峰，代表一级胺N—H的伸缩振动，在1249.31cm-1处出现的较强吸收峰代表芳香胺C—N伸缩振动吸收峰，这些吸收峰证明了氨基的存在，且产物是一种芳香胺；③其它结构特征，如苯环C=C伸缩振动（1600cm-1左右）、苯环上C—H伸缩振动（3085.79cm-1周围的一系列宽峰）、1,2-二取代苯的证据（752.92cm-1的一个尖峰）、羧基C=O伸缩振动（1671.83cm-1）、羧基O—H伸缩振

动（2925.19cm-1、2650.93cm-1、2517.50cm-1及周围的一系列宽峰）等均与邻硝基苯甲酸的相同，表明从邻硝基苯甲酸到邻氨基苯甲酸，仅仅发生了硝基到氨基的转化。

4. 对核磁共振氢谱的分析与讨论

分别将邻硝基苯甲酸和邻氨基苯甲酸作为样品，得出1HNMR图谱图5、图7，而以下图8、图9是用ChemDraw模拟计算出的邻硝基苯甲酸和邻氨基苯甲酸分子中不同氢原子的化学位移值：

图8 邻硝基苯甲酸图9 邻氨基苯甲酸

实际上，ChemDraw对苯环质子化学位移的预测是仅根据公式计算得到的[9]，但邻硝基苯甲酸和邻氨基苯甲酸均为邻二取代的苯环，由于空间位阻等效应，预测效果有时不够理想，故以上分子模拟结果只能作为参考，笔者查阅到了邻硝基苯甲酸和邻氨基苯甲酸的标准核磁共振氢谱[10]，和本实验结果比对，以便后续分析。

图10 邻硝基苯甲酸图11 邻氨基苯甲酸

a. 邻硝基苯甲酸

由图5可看出，邻硝基苯甲酸在化学位移值为7 ~ 14的区间内有三个峰，峰位移值分别约

为13.8，7.98（裂分），7.8（裂分且重叠），峰面积比约为0.5∶1∶3。

与图10对比可知，邻硝基苯甲酸分子中有五种化学环境不同的氢原子：δ13.8的峰代表羧基氢，由于羧基氢非常活泼，屏蔽作用很小，处在低场位置；δ7.999、7.993、7.988、7.976、7.968的峰代表硝基邻位的氢原子；δ7.879、7.871、7.861、7.855、7.850的峰代表羧基邻位的氢原子；δ7.837、7.832、7.825、7.807、7.800、7.788的峰代表羧基对位的氢原子；δ7.775、7.768的峰代表硝基对位的氢原子。且五种氢原子个数比为1∶1∶1∶1∶1。但本实验得出的图谱显示其峰面积比却不是严格的1∶1∶1∶1∶1，究其原因，可能因为样品纯度达不到要求，羧基上的活泼氢部分被取代掉，且苯环上有三种氢原子的化学位移值十分接近，在δ8附近发生了重叠，成为一系列无法分辨的峰，这三种氢原子个数加起来也正好为3，符合实验结果。

δ3.347的峰为水中氢的峰（样品干燥程度不够，且久置吸湿），δ2.505的峰为氘代DMSO 中混有的未氘代DMSO中氢的峰（溶剂的影响），δ1.239和δ0.856的峰分别为相转移催化剂中亚甲基氢和次甲基氢的峰（实验后处理不彻底，产品洗涤不充分），δ0.000的峰为硅脂，极有可能是实验中活塞处的硅脂溶于溶剂中导致。

b. 邻氨基苯甲酸

由图7可看出，邻氨基苯甲酸在化学位移值为3 ~ 9的区间内有六个峰，峰位移值分别约为8.579，7.73（裂分为三重峰），7.24（裂分为四重峰），6.75（裂分为二重峰），6.52（裂分为三重峰），3.4（裂分为三重峰）。峰面积比约为2∶1∶1∶1∶1∶1。

与图11对比可知，邻氨基苯甲酸分子中有六种化学环境不同的氢原子：δ8.579的峰代表氨基氢，氨基氢属于活泼氢，原本其化学位移值应处在高场（0.5 ~ 5）但由于氨基与芳香环相连，芳香环的吸电子作用极大地活化了氨基氢，使得其化学位移值向低场移动；δ7.737、7.734、7.710的峰代表羧基邻位的氢原子；δ7.263、7.260、7.236、7.213的峰代表羧基对位的氢原子；δ6.774、6.747的峰代表氨基邻位的氢原子；δ6.548、6.522、6.498的峰代表氨基对位的氢原子；δ3.468、3.397、3.374的峰代表羧基氢，羧基氢原本由于非常活泼，处在低场位置，但在邻氨基苯甲酸中羧基与氨基处于邻位，能形成强分子内氢键，且羧酸多以二聚体形式存在，无疑使得羧基氢的活泼程度下降，屏蔽效应增强，化学位移值向高场移动。且六种氢原子个数比为2∶1∶1∶1∶1∶1，实验与理论标准预测相符，实验谱图与标准谱图基本一致，表明该化合物为邻氨基苯甲酸，且具有较高的纯度。

δ2.505的峰为氘代DMSO中混有的未氘代DMSO中氢的峰（溶剂的影响），除此之外并无其它杂质峰。

c. 经重水交换的邻氨基苯甲酸

向一份邻氨基苯甲酸样品中加入重水进行活泼氢交换，得到了如下NMR图谱。

图12 重水氘代的对硝基苯胺核磁共振氢谱

与图7对比可以发现，δ7.7、7.2、6.7、6.5的峰仍然存在，且比例仍约为1∶1∶1∶1，说明这四个峰对应的是苯环上的氢的峰，它们不属于活泼氢，不能与重水发生交换。由图12可知，加入重水进行氢交换之后，原本δ8.6和δ3.6的两个峰消失，说明这两个峰对应的是氨基氢和羧基氢，均属于活泼氢。加入重水后，这两个活泼氢被氘取代，因此原有的峰消失。而δ4.363产生了一个新的峰，此峰应为一氘代水（HOD）的峰。

5. 对产率的分析与讨论

经计算发现，邻硝基甲苯氧化这一步骤的产率很低，仅为27.7%，而相关文献[7]显示产率可达80%，分析有如下几点原因：①实验条件所限，所用加热器没有温度探头，无法做到真正恒温，实际可能因为温度的波动造成反应不够充分；②反应时间偏短，使得部分邻硝基甲苯未来得及被氧化；③氧化条件不够合适，笔者未试验反应pH值对产率的影响，但比较不同同学的结果，发现有几个同学令高锰酸钾在碱性条件下氧化邻硝基甲苯，得到了较为可观的收率；④NaOH的量可能不足，没有将全部产物转化成盐。

邻硝基苯甲酸的还原这一步骤的产率尚可，总产率偏低主要由氧化步骤的产率偏低造成。不过实验过程中，制备邻位产物的产率普遍偏低，说明其产率低并不是极为异常的情况，想提高产率是相对困难的一件事。

Ⅸ. References

[1] 余远斌,杨锦宗. 邻硝基甲苯氧化制邻硝基苯甲酸[J]. 杭州化工,1996,26(2):44

[2] 于佩凤. 邻氨基苯甲酸的合成. 专论综述:1-2

[3] 蔡照胜,盛凤军. 邻硝基乙苯直接氧化-还原合成邻氨基苯甲酸的探讨[J]. 广州化工,1997,25(2):30

[4] 武汉大学化学与分子科学学院实验中心. 有机化学实验. 武汉:武汉大学出版社,2004.102-103,193-194

[5] 邢其毅,裴伟伟,徐瑞秋等. 基础有机化学（上册）. 第三版. 北京:高等教育出版社,2005.169-172

[6] 中国试剂网https://www.360docs.net/doc/179877537.html,:666/ScrcBackGroup/reagent/newindex.jsp

[7] 张精安,张忠妍,鲍娟. 2-乙酰胺基苯甲酸合成工艺的改进[J]. 科技创新导报,2008,26:97

[8] 高明勇. 苯甲酸衍生物的合成. 染料与染色,2007,44(1)

[9] 张正行. 有机光谱分析. 北京:人民卫生出版社,2009.180

[10] 物竞化学品数据库https://www.360docs.net/doc/179877537.html,/

[11] Pretsh,E.等. 波谱数据表:有机化合物的结构解析. 荣国斌译. 上海:华东理工大学出版社,2002