How to distinguish between phenol and benzyl alcohol

1. basic structure and molecular composition

From the molecular structure, the difference between phenol and benzyl alcohol is very obvious. Phenol has the formula C6H5OH, where a hydroxyl group (-OH) is attached to the benzene ring, while benzyl alcohol has the formula C6H5CH2OH, where an ethyl group (-CH2OH) is attached to the benzene ring. This subtle structural difference makes them significantly different in many properties.

Due to the different molecular structure, the physical properties of phenol and benzyl alcohol are also different. For example, phenol has a slightly higher density than water, while benzyl alcohol has a slightly lower density than water. The solubility of benzyl alcohol in water is slightly higher than that of phenol, and the melting point and boiling point of benzyl alcohol are also slightly lower than that of phenol.

2. physical property differences

In addition to the differences in molecular structure, phenol and benzyl alcohol also have obvious differences in some physical properties. For example, phenol is liquid at normal temperature, and has a melting point of 77°C and a boiling point of 181°C at standard atmospheric pressure; while benzyl alcohol is liquid at normal temperature, but has a melting point of 80°C and a boiling point of 156°C. These differences in physical properties can be used as a preliminary basis for identification in some cases, especially in the absence of other complex conditions.

The water absorption of phenol and benzyl alcohol is also different. Phenol in the face of water will be due to the large electronegativity of hydroxyl groups and quickly combined with water molecules, showing a strong water absorption; and benzyl alcohol although there is a certain water absorption, but relatively weak.

Reactions with alkaline substances

Phenol and benzyl alcohol exhibit different chemical characteristics when reacting with alkaline substances, which is one of the key points of their difference. As a strong acidic substance, phenol reacts with alkaline substances (such as NaOH) to generate corresponding salts and release water at the same time. The specific reaction formula is:

C6H5OH NaOH → C6H5OONa H2O

because of its hydroxyl structure, benzyl alcohol reacts with strong oxidants (such as acidic potassium permanganate) to form the corresponding salt of benzyl alcohol. The reaction formula is:

C6H5CH2OH KMnO4 (acidic condition) → C6H5CH2O2K MnO2 H2O

by observing the products of the reaction and the change of the reaction conditions, we can further confirm whether the sample is phenol or benzyl alcohol.

3. in Chemical Reactions

Phenol and benzyl alcohol also behave differently in chemical reactions. For example, phenol can react with calcium carbonate to generate white precipitated carbonic acid phenol; while benzyl alcohol cannot react directly with calcium carbonate, and can only react with calcium carbonate under specific conditions (such as acidic environment) to generate the corresponding salt.

Phenol is easily hydrolyzed under alkaline conditions to generate phenolate, while benzyl alcohol is relatively stable under alkaline conditions and is not easily hydrolyzed. This can be used in certain laboratory settings to distinguish between the two substances.

4. use chemical reagents for identification

In order to more accurately distinguish between phenol and benzyl alcohol, specific chemical reagents can be used to complete the identification. For example, the sample to be tested can be added to the NaOH solution to observe whether bubbles are generated or whether a precipitate is generated. If a white precipitate is generated, it can be preliminarily judged as phenol; if only bubbles are generated, it may be benzyl alcohol.

Samples can also be tested for oxidation by using an acidic potassium permanganate solution. Phenol will undergo redox reactions with potassium permanganate under acidic conditions, while benzyl alcohol will not undergo such reactions. Therefore, the type of sample can be judged by whether the reaction proceeds.

5. summary

Phenol and benzyl alcohol are different in many properties, especially in acid-base, reactivity and oxidation. By analyzing their molecular structure, physical properties and their performance in chemical reactions, a variety of effective identification methods can be found. Which method to choose depends on the experimental conditions and available reagents. Whether by observing the difference in physical properties, or through the observation of chemical reactions, as long as the method is appropriate, can effectively distinguish between phenol and benzyl alcohol.