The best way to distinguish between benzaldehyde and acetophenone is using Tollen’s reagent. Benzaldehyde can reduce Tollen’s reagent, giving a red-brown precipitate of Cu2O, whereas acetophenone does not show any reaction towards Tollen’s reagent.
Tollen’s reagent is a chemical reagent useful in the detection of an aldehyde functional group, including aromatic aldehyde functional groups and alpha-hydroxy ketone functional groups. This reagent was named after the German chemist Bernhard Tollens.
CONTENTS
1. Overview and Key Difference
2. What is Benzaldehyde
3. What is Acetophenone
4. Benzaldehyde vs Acetophenone in Tabular Form
5. Summary – Benzaldehyde vs Acetophenone
What is Benzaldehyde?
Benzaldehyde can be defined as an aromatic aldehyde having the chemical formula C6H5CHO. It has a phenyl group attached to an aldehyde functional group. Moreover, it is the simplest aromatic aldehyde. It occurs as a colourless liquid and has an almond-like characteristic odour. Its molar mass is 106.12 g/mol. Its melting point is -57.12 °C, while its boiling point is 178.1 °C.
Figure 01: Benzaldehyde
When considering the production of benzaldehyde, the main routes of production of this compound are liquid phase chlorination and oxidation of toluene. However, this compound occurs naturally in many foods as well, for example, in almonds. Therefore, one of the major uses of this compound is its use as an almond flavour in foods and scented products.
What is Acetophenone?
Acetophenone can be defined as an organic compound having the chemical formula C8H8O. It is a ketone, and it is the simplest ketone among aromatic ketones. The IUPAC name of this compound is 1-Phenylethane-1-one. Other common names include methyl phenyl ketone and phenylethanone.
Figure 02: Acetophenone
The molar mass of acetophenone is 120.15 g/mol; the melting point can range from 19–20 °C, while the boiling point is 202 °C. In addition, this compound occurs as a colourless, viscous liquid. Moreover, we can get it as a byproduct from the oxidation of ethylbenzene to form ethylbenzene hydroperoxide.
When considering the uses of acetophenone on a commercial scale, it is important as a precursor for the production of resins, as an ingredient in fragrances, etc. We can also convert it into styrene, and it is useful for the production of many pharmaceuticals as well.
How to Distinguish Between Benzaldehyde and Acetophenone?
Benzaldehyde is an aromatic aldehyde, while acetophenone is an aromatic ketone compound. Therefore, the easiest method to distinguish between benzaldehyde and acetophenone is using Tollen’s reagent because the aldehyde functional group can form a precipitate with this reagent. Benzaldehyde can reduce Tollen’s reagent, giving a red-brown precipitate of Cu2O, whereas acetophenone does not show any reaction towards Tollen’s reagent.
During Tollen’s test, we need to take three clean and dry test tubes – two test tubes containing the samples and another containing distilled water. Then we need to add Tollen’s reagent to each of these test tubes and then keep them in a water bath for about a minute. We can then observe red-brown coloured precipitate building up in the test tube containing benzaldehyde, but there are no colour changes or precipitate formations in the other two test tubes containing acetophenone and distilled water. Here, we use distilled water as a blank sample to observe any colour difference with the sample.
The following table summarizes the difference between these compounds, making it easier to distinguish between benzaldehyde and acetophenone.
Summary – Benzaldehyde vs Acetophenone
Benzaldehyde is an aromatic aldehyde having the chemical formula C6H5CHO, while acetophenone is an organic compound having the chemical formula C8H8O. The easiest method to distinguish between benzaldehyde and acetophenone is using Tollen’s reagent; the aldehyde functional group can form a precipitate with this reagent. Benzaldehyde can reduce Tollen’s reagent, giving a red-brown precipitate of Cu2O, whereas acetophenone does not show any reaction towards Tollen’s reagent.
Reference:
1. “Benzaldehyde.” National Center for Biotechnology Information. PubChem Compound Database, U.S. National Library of Medicine.
Image Courtesy:
1. “Acetophenone-2D-skeletal” By Chem Sim 2001 – Own work (Public Domain) via Commons Wikimedia
2. “Benzaldehyde” By Wikimuzg – Own work (CC BY-SA 3.0) via Commons Wikimedia