Reagent for distinguishing between benzene and cumene

In chemical production and scientific research, benzene and cumene are the two most common organic compounds, which are often confused because of their similar chemical properties. There are significant differences between the two in appearance, physical properties and chemical reaction characteristics, but for laymen, it is often difficult to distinguish accurately with the naked eye. This article will analyze in detail how to identify these two substances through reagents for reference by professionals in the chemical industry.

1. Benzene and Cumene Basic Properties

Before entering the identification method, we first understand the basic characteristics of these two substances.

1. Appearance color Both are colorless liquids, but cumene is slightly yellowish, while pure benzene is a transparent or nearly colorless liquid. This subtle difference is easily detected by the naked eye in actual operation.

2. density and boiling point Cumene has a slightly higher density than benzene, about 0.573g/cm³, while benzene has a density of 0.876g/cm³. Both are volatile liquids, but the boiling point of cumene is about 80 ℃, while the boiling point of benzene is as high as 80.1 ℃. The boiling points of the two are similar, but the volatility is different.

3. Chemical properties Benzene is insoluble in water, while cumene is slightly soluble in water. Both of them can react with bromine water, but the degree of reaction and the phenomenon are different.

2. Identification Reagent Selection

In order to accurately distinguish between benzene and cumene, we used the following reagents:

1. Water Water is one of the most basic identification reagents. The liquid to be tested was poured into water and its solubility was observed. If the liquid can be easily dissolved in water, it is cumene; if there is no obvious dissolution phenomenon, it may be benzene.

2. acidic potassium permanganate solution Acidic potassium permanganate solution is a commonly used oxidant. The liquid to be tested is added to acidic potassium permanganate. If bubbles appear on the surface of the liquid, it indicates that it has reducibility. Benzene itself is not reductive, while cumene will oxidize with potassium permanganate under acidic conditions, releasing brown manganese dioxide precipitate.

3. Bromine water and bromobenzene Bromine water is added to the liquid to be tested, and the mixture is allowed to stand after shaking. If the liquid density is less than that of water, bromine water will be layered in the upper layer without obvious reaction; if the liquid density is greater than that of water, bromine water will be miscible or brown precipitate will appear in the lower layer, indicating that it is cumene. Bromobenzene can be added as another reagent to observe the difference in the phenomenon.

4. microscope observation The particle morphology of the liquid to be tested was observed under a microscope. The molecular structure of cumene is somewhat different from that of benzene and may show subtle particle differences under the microscope.

3. experimental steps and phenomenon analysis

1. water identification Pour the liquid to be tested into water. If the liquid can dissolve quickly, it is cumene; if there is no obvious dissolution, it is benzene. This is because the solubility of cumene in water is slightly higher than that of benzene.

2. acid potassium permanganate identification Take about 1-2 drops of the liquid to be tested, add acidic potassium permanganate solution (H₂ SOO4 KMnO, concentration 1-2 times), and observe the phenomenon. If the color of potassium permanganate solution changes from purple to brown, the liquid is cumene; if there is no obvious change, it is benzene. This is because cumene has reducibility and is oxidized under acidic conditions.

3. Bromine water and bromobenzene identification Bromine water is added to the liquid to be tested, and the mixture is allowed to stand after shaking. If there is no obvious reaction of bromine water, it is benzene; if the color of bromine water fades rapidly, it is cumene. This is because cumene has a property of reacting with bromine water, while benzene does not react. If a small amount of liquid to be tested is added to bromobenzene, and if the color of bromobenzene changes obviously, it is further confirmed to be cumene.

4. microscope observation The particle morphology of the liquid to be measured was observed using an optical microscope. The molecular structure of cumene is C≡H∞CH₂, so its particles may show certain structural characteristics, while the particles of benzene are more uniform. This method is rarely used in the laboratory, but it is an effective means of identification for researchers familiar with microscope operation.

4. Considerations

When conducting identification experiments, the following points need to be paid attention:

1. Safe use of reagents Acidic potassium permanganate solution is corrosive to a certain extent, and gloves and goggles should be worn during operation. Although bromobenzene is non-toxic, it has a certain volatility. A good ventilation system should be ensured when it is used.

2. Control of the operating environment The identification experiment is usually carried out at room temperature to avoid the experiment phenomenon is not obvious due to the temperature is too high or too low.

3. Avoid direct contact Identification reagents such as bromobenzene and acidic potassium permanganate solution have a certain irritation, it is recommended to wear protective equipment.

4. Experimental records When conducting identification experiments, the observed phenomena and the use of reagents should be recorded in detail to ensure the accuracy of the experimental results.

5. practical application of the identification significance

In chemical production, the identification of benzene and cumene is of great significance. For example, in petroleum refining and chemical synthesis, the separation and purification of these two substances is a common operation. Through the identification of the above reagents, the quality of the raw materials can be ensured and production problems caused by mixing can be avoided.

Benzene and cumene also play an important role in the environment and human health. For example, cumene is a solvent and industrial raw material, but its high toxicity may cause serious harm to human health. Therefore, it is necessary to strictly control its use and storage.

Through the above analysis, we can clearly see that selecting suitable reagents and combining various observations is an effective method to distinguish benzene from iso (isopropyl) benzene. Mastering this skill will not only help production management in the chemical industry, but also play an important role in scientific research and laboratories.