How to distinguish between benzaldehyde and benzophenone

In chemical production, benzaldehyde and benzophenone are often confused, but in fact they are two completely different compounds with different properties. Distinguishing them not only helps to improve production efficiency, but also avoids safety accidents caused by misuse. This article will analyze the molecular structure, physical properties, chemical reactions and other aspects in detail to help professionals in the chemical industry accurately distinguish between the two.

1. Molecular structure and basic properties

From the molecular structure, the difference between benzaldehyde and benzophenone is obvious. The chemical formula of benzaldehyde is C6H5CHO, and a formaldehyde group (-CHO) is attached to the benzene ring in the molecular structure. The chemical formula of benzophenone is C6H5COH, and a hydroxyl group (-OH) and a methyl group (-CH3) are attached to the benzene ring in the molecular structure. Therefore, there are significant differences in molecular weight, density, melting point, etc.

Specifically, benzaldehyde has a molecular weight of 100.11, a density of 1.048g/cm³, and a melting point of -80°C; benzophenone has a molecular weight of 100.12, a density of 1.046g/cm³, and a melting point of -84°C. It can be seen from these data that the two are close in physical properties, but the subtle differences can still be used as a preliminary basis for identification.

2. Physical properties and identification methods

Through the difference of physical properties, benzaldehyde and benzophenone can be identified. For example, both are colorless liquids, but benzaldehyde is slightly denser and has a slightly higher melting point. The solubility of the two is also different. Benzaldehyde is slightly soluble in water, and its solubility in ethanol is about 0.06g/100g ethanol; while benzophenone has extremely low solubility in water, and its solubility in ethanol is about 0.4g/100g ethanol. By these solubility differences, one can aid in distinguishing the two.

3. Chemical properties and reaction characteristics

Chemical properties are one of the key points to distinguish benzaldehyde from benzophenone. From the reaction characteristics, benzaldehyde is relatively stable, but it may decompose under strong oxidation conditions, while benzophenone has stronger reducibility and is prone to addition reaction. Specifically:

• Chemical reaction of benzaldehyde: Benzaldehyde may react with alkaline substances under acidic conditions, but it is more stable under alkaline conditions. Benzaldehyde may decompose at high temperatures to produce benzene and formaldehyde. This decomposition usually requires a catalyst and high temperature conditions, which do not easily occur under ordinary conditions.

• Chemical reaction of benzophenone: benzophenone is easy to neutralize with alkaline substances under acidic conditions to generate the corresponding salt. Under alkaline conditions, benzophenone is easy to react with aldehydes to generate more complex organic compounds. Benzophenone is prone to polyformaldehyde reaction under alkaline conditions and high temperatures to produce white crystals.

1. Environmental and safety information

From the perspective of environmental protection and safety, there are potential risks in the application of benzophenone and benzaldehyde. But there are significant differences in environmental performance. Benzaldehyde is used as an environmentally friendly material in certain industrial applications, such as as a water-soluble coatings additive, and is favored for its environmental friendliness. Benzophenone is more used as a chemical intermediate, but in some cases may cause a greater burden on the environment.

4. Practical application of identification

In actual production, when it is necessary to distinguish between benzaldehyde and benzophenone, it can be identified by the following methods:

• Reagent identification method: add NaOH solution after sampling, observe the reaction phenomenon. Benzaldehyde is more stable under alkaline conditions, while benzophenone reacts with NaOH to produce a white precipitate.

• Instrument identification method: by infrared spectrum analysis, the characteristic peak positions of benzaldehyde and benzophenone are different. The aldehyde group (C = O) absorption wave peak of benzaldehyde is located at about 1720 cm≡¹, while the hydroxyl group (O-H) absorption wave peak of benzophenone is located at about 3200-3600 cm≡¹.

• Solubility test: Dissolve the test sample in ethanol, and observe its solubility. The solubility of benzaldehyde is lower, while the solubility of benzophenone is higher.

1. Summary

Although benzaldehyde and benzophenone are both aromatic compounds, there are significant differences in molecular structure, physical properties, and chemical reactions. Professionals in the chemical industry should accurately distinguish these two substances through molecular structure analysis, physical property testing, chemical reaction experiments and other methods to avoid accidents caused by misuse. Emphasis should be placed on the selection of environmentally friendly products to provide safer and more sustainable solutions for subsequent production processes.