Synthesis of N , N'-di-sec-butyl-p-phenylenediamine antioxidant

N, N’-di-sec-buty l-p-phenylenediamine was synthesized using p-phenylenediamine, methyl ethyl ketone, and hydrogen as raw materials in the presence of Cu-Cr catalyst. The preparation conditions of the motivation and the effects of the reaction conditions, such as catalyst dosage, reacting temperature, pressure, and reaction time, on the yield of the product were studied. The appropriate preparation conditions of the catalyst were as follows:m(copper nitrate)∶m(chromium nitrate)∶m( barium nitrate)=10 ∶10 ∶1, decomposed for 1. 5 h at 400 ℃, then washed with water and dried at 300 ℃. The optimum reacting conditions were as follows: catalyst do sage 4wt %(based on p-phenylenediamine), responding temperature 160 ℃, reacting pressure 3. 3 ~ 5. 6 MPa, and reacting time 12 h. Under the above conditions, the product yield was over 95 %. When the product (30 μgg- 1)was added to gasoline, the induction time of gasoline became much longer.

For gasoline, oxidative stability is an important index to evaluate its performance. The most effective method to improve gas’s oxidative stability is adding an antioxidant and anti-glue agent. N , N’-di-sec-butyl-p-benzene
Diamine is a good gasoline antioxidant and anti-glue agent and can also be used as a general anti-ozonant for natural rubber and synthetic rubber. Currently, China needs about 100 t of N, N′-di-sec-butyl-p-phenylenediamine every year, which is entirely dependent on imports, and the price is very high. Therefore, it is necessary to investigate and study its synthesis method to find suitable catalysts and reaction conditions and to provide a basis for developing and producing N, N’-di-sec-butyl-p-phenylenediamine in China. In my country, there are relatively few studies on antioxidants, especially amine antioxidants. The technology for producing symmetrically substituted aromatic amine antioxidants abroad is mature, and several commonly used methods are the Harold synthesis method, Fredric synthesis method, Ralph synthesis method, and Hubert synthesis method. In this work, p-phenylenediamine was reacted with aldehyde or ketone to generate imine, which was then synthesized by catalytic reduction under the action of hydrogen. The synthesis method of the catalyst used in the synthesis of N, N’-di-sec-butyl-p-phenylenediamine and the influence of the reaction conditions on the product yield was studied, and the appropriate catalyst preparation conditions and reaction conditions were found.

1.Experimental part

1.1 Experimental equipment and raw materials

Autoclave, Dalian Fourth Instrument Factory, volume 1L, equipped with temperature control system and circulating water cooling system; GC-2001 Gas Chromatograph, Shandong Tenghai Analytical Instrument Factory; Gasoline Induction Period Tester, Dalian Tanaka
Scientific Instruments Ltd. P-phenylenediamine, industrial products; butanone, copper nitrate, barium nitrate, chromium nitrate, etc., are all analytical reagents.

1.2 Preparation of catalysts

Weigh copper nitrate, chromium nitrate, and barium nitrate according to the mass ratio of 10:10:1, dissolve them in as little warm water as possible, evaporate to dryness, put them in a muffle furnace, decompose at a specific temperature for one h, take them out after cooling, wash them
Remove the undecomposed nitrate, put it in a muffle furnace, and bake it at 300 °C for one h.

1.3 Reaction mechanism

The reaction equation is:

N , N'-di-sec-butyl-p-phenylenediamine antioxidant

1.4 Reaction steps

Put 54 g p-phenylenediamine, 360 mL butanone (n (p-phenylenediamine): n (butanone) = 1: 6), and 4 g catalyst into the autoclave, first replace the air in the autoclave with nitrogen four times, then use hydrogen to remove the remaining air in the autoclave, heat it up, and react at 160 °C and 3.3-5.6 MPa for ten h. After the reaction, the catalyst was cooled and filtered to remove the trigger, the excess butanone and the generated sec-butanol were removed by atmospheric distillation, the obtained product was weighed, and its purity was analyzed by gas chromatography. Synthetic N, N’-di-sec-butyl-p-phenylenediamine (30 μg g-1) was added to gasoline, and the induction period was measured.

2.Experimental results and discussion

2.1 Effect of decomposition temperature on catalyst performance

Figure 1 shows the effect of decomposition temperature on the yield of N,N’-di-sec-butyl-p-phenylenediamine during the preparation of the catalyst.

It can be seen from Figure 1 that under the same conditions, the yield of N, N’-di-sec-butyl-p-phenylenediamine prepared by the catalyst decomposed at 400 °C is significantly higher than that of the catalyst prepared by decomposition at different temperatures. The decomposition temperature was from 400 ℃ to 500 ℃, and the product yield decreased from about 90% to 0. The main reason was the reduction of catalyst activity caused by the accumulation of the active components of the catalyst. For the same catalyst
The activity of the activated catalyst was significantly higher than that of the unactivated one. This may be due to the influence of the incompletely decomposed nitrate on the reaction. After washing, the pore surface area of ​​the catalyst became more extensive, the activity of the catalyst was also enhanced, and the reaction speed was accelerated. Therefore, the decomposition temperature of the catalyst is 400℃, the decomposition time is about 1.5 h, and the activation effect of water washing is good.

2.2 The effect of catalyst dosage on the yield of N,N'-di-sec-butyl-p-phenylenediamine

The effect of the amount of catalyst on the yield of the reaction product was investigated, and the results are shown in Figure 2. It can be seen from Figure 2 that the yield of the product increases with the increase of the amount of catalyst. When the amount of motivation exceeds 2 g, the result exceeds 80%, and the increase gradually decreases. Considering the cost of the catalyst in industrial production, it is better to take 2 g, which is 4% of the mass percentage of p-phenylenediamine.

2.3 Choice of minimum reaction temperature

In order to investigate the minimum reaction temperature of this reaction, the change of the pressure in the autoclave with the temperature was observed, as shown in Figure 3.

It can be seen from Fig. 3 that the initial pressure increases with the increase in temperature. When it exceeds 120 °C, the trend of pressure increases with temperature becomes slow, indicating that the reaction starts to proceed at 120 °C, and when the temperature reaches 155 °C, the pressure no longer increases. On the contrary, it suddenly decreased with the temperature increase, indicating that the reaction started to proceed rapidly when it reached 155 ℃. So, the
The reaction temperature should preferably not be lower than 155 °C. Because the high temperature will cause side reactions (such as the hydrogenation of butanone to sec-butanol), the reaction temperature in this study is 160-170 °C.

2.4 Influence of reaction pressure on product yield

The effect of hydrogen pressure on the reaction product yield was investigated, and the results are shown in Figure 4. It can be seen from Figure 4 that in the range of 3.3 to 5.6 MPa, the product yield increases with the increase of pressure, but with the addition of pressure
The width is not very obvious. The pressure rise puts higher requirements on the pressure-bearing capacity of the reactor and related pipelines. Therefore, it is considered in this study that the average pressure is 5 MPa.

2.5 Influence of reaction time on product properties

The effect of reaction time on the yield of the reaction product was investigated, and the results are shown in Figure 5. It can be seen from Figure 5 that the product yield increases with the increase of reaction time. This experiment takes into account the product yield and reaction time efficiency

The selected reaction time was 12 h.

2.7 Product performance evaluation

The purity of the product synthesized under the optimal conditions reached 98.0%, and the product yield reached 95.9%. In order to evaluate the performance of the product, according to GB256-82 gasoline induction period determination method, the optimal synthesis conditions were

The purity of the synthesized N,N’-di-sec-butyl-p-phenylenediamine was analyzed by gas chromatography, and then added to gasoline to measure the induction period.

The results were compared with T501 and imported antioxidants. The results are shown in Table 1.


Induction period/min

blank gasoline


blank gasoline+T 501(30 μg    g –  1 )


Blank gasoline + imported antioxidant(30 μg    g – 1 )


Blank gasoline + synthetic product(30 μg    g – 1 )


It can be seen from Table 1 that the induction period of blank gasoline was 230 min, and the induction period was increased to 330 min, 480 min and 540 min after adding 30 μg g-1 T501 and imported antioxidants and synthetic products respectively. . After adding the synthetic product, the induction period of gasoline increases obviously, and the effect is better than adding T501 and imported antioxidant.

3 Conclusion

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