Introduction

In organic chemistry, there are many compounds with unique properties and a wide range of applications. One such important compound is benzaldehyde. The interaction of benzaldehyde with various reagents is the key to synthesizing a variety of organic compounds. This combination of chemical characteristics makes benzaldehyde a valuable tool in organic synthesis and industry.
Benzaldehyde was first extracted from bitter almonds in 1803 by the French pharmacist Martrès. In 1832, Friedrich Wöhler and Justus von Liebig first synthesized benzaldehyde.
Benzaldehyde is the starting product for the synthesis of phenyl nitropropen, an intermediate of amphetamine, which have a strong stimulating effect. As a result, it is under special control in many countries.
In this article we will consider chemical and physical properties of benzaldehyde, methods of its synthesis and its applications.

Physical and Chemical Properties of Benzaldehyde

The physicochemical properties of benzaldehyde have an important influence on its chemical reactivity. Benzaldehyde is a colorless or slightly yellow liquid with a characteristic odor of bitter almonds. Benzaldehyde with the chemical formula C6H5CHO, is the simplest aromatic aldehyde, with a molecular weight 106.12 g/mol and a density 1.045 g/cm3 at 25°C. The melting point of this compound is -26 °C, its boiling point is 178-179°C and the ignition temperature 190°C. Benzaldehyde is completely soluble in organic solvents such as ethanol, diethyl ether and slightly soluble in water (6,95 g/L at 25°C).

Benzaldehyde Synthesis

Synthesis of Benzaldehyde

There are several ways to obtain benzaldehyde, including classical reactions and modern methods. Here are some of the main ways to produce benzaldehyde:
1. Oxidation of toluene with magnesium oxide. One of the classic methods to obtain benzaldehyde is the oxidation of toluene in an acidic environment. This process is usually carried out with magnesium dioxide. As a result of the reaction, the methyl group is oxidized to the aldehyde group.

2. Oxidation of toluene with air. Another method for producing benzaldehyde is the oxidation of toluene with air in the presence of a vanadium(V) oxide catalyst. Working with this acid catalyst is life-threatening and requires compliance with production technology.

3. Hydrolysis of benzal chloride. Benzaldehyde can be obtained by hydrolysis of dichlorotoluene with sodium hydroxide. The rate of hydrolysis of benzal chloride is constant independent of pH, but the rate of hydrolysis decreases with increasing concentration of chloride ions in solution.

4. Oxidation of alcohols with nitric acid. Oxidation of benzyl alcohol to benzaldehyde in high yield using an aqueous solution of nitric acid as the oxidizing agent. The advantage of the method is that it gives a high yield using more readily available reagents than others.​

5. Oxidation of alcohols with acid in DMSO. This method is often used in laboratories. This method makes it possible to synthesize sufficiently pure benzaldehyde from benzyl alcohol. The HBr/DMSO approach gives a higher yield of high purity benzaldehyde than nitric acid oxidation.

6. Extraction from plant material. Benzaldehyde can be obtained from plant material by solvent extraction (ethanol, diethyl ether), such as almonds, apricots, apples and cherry pits.

The choice of method depends on the cost and availability of reagents, as well as the methodology used.

Chemical Properties of Benzaldehyde

Benzaldehyde is a reactive chemical component. Here are some characteristic chemical reactions of benzaldehyde:
1. Halogenation reaction. Benzaldehyde can react with halogens such as bromine in the presence of a catalyst such as aluminum trichloride. As a result of the reaction, bromobenzaldehyde and hydrogen bromide are formed.

2. Hydrogenation reaction. Benzaldehyde can be hydrogenated to benzyl alcohol using catalysts such as platinum or nickel. The hydrogenation rate of benzaldehyde varies up to one order of magnitude in different solvents (dioxane < tetrahydrofuran < water), but the reaction path does not change.

3. Reactions with alcohols. Benzaldehyde can add alcohol to form hemiacetals and acetals. These reactions are widely used in the synthesis of complex organic molecules. For example, the reaction of benzaldehyde with ethanol produces hydroxy ethoxytoluene.

4. Henry reaction. In an aldol-type reaction between benzaldehyde and nitroalkanes, new nitro compounds are formed. For example, condensation of benzaldehyde with nitroethane gives phenyl-2-nitropropene. Often, primary amines like n-butylamine, methylamine or ethylamine are used as catalysts. This compound is an intermediate for the further synthesis of amphetamine.

5. Oxidation. The oxidation of aldehydes to acids, in particular benzaldehyde to benzoic acid, is an important transformation. Benzaldehyde can be oxidized to benzoic acid in the presence of oxidizing agents such as copper (II) hydroxide or potassium permanganate.

6. Cannizzaro reaction. In an alkaline environment, the carbonyl carbon disproportionates to form alcohol and acid, but the acid is further neutralized. For example, the reaction of benzaldehyde and sodium hydroxide produces benzyl alcohol and sodium benzoate.

The chemical reactions of benzaldehyde show its ability to form new compounds and molecules, which makes it a valuable component in organic synthesis.

Applications of Benzaldehyde

Benzaldehyde has applications in various fields, here are some of its uses:

1. Pharmaceutics. Benzaldehyde is an important intermediate in the synthesis of many medicinal compounds. It is used to create various pharmaceuticals, including antiseptic, anticancer (in the form of beta-cyclodextrin benzaldehyde inclusion compound) and antispasmodic (benzaldehyde sulphur trioxide as a potential drug for the treatment of Alzheimer disease) agents.
2. Perfumes. The odor of benzaldehyde gives it the value of scented products, including perfumes, fragrance oils and other beauty products. It is used to add a nutty, fruity scent or flavor to many scented products.
3. Food industry. Benzaldehyde is used as a flavoring agent in the food industry to create fruity, nutty, spicy flavors or in imitation almond extract; it is added to drinks, chewing gum, cakes, other baked goods and other products.
4. Chemical synthesis. Benzaldehyde is used as a starting material for organic reactions and the synthesis of other complex molecules. It is used as a raw material for the synthesis of phenylethylamines, aromatic substances like acetals of benzaldehyde, cinnamic aldehyde, cinnamic acid, benzyl benzoate, jasmin aldehyde, hexylcinnamic aldehyde, as well as triphenylmethane, acridine and aniline malachite green dyes.

Health Effects of Benzaldehyde

The health effects of benzaldehyde are an important aspect of its use. Although it is safe for humans in most cases, the potential risks of using it must be considered. Here are some aspects of the health effects of benzaldehyde:

1. Toxicity. May be toxic when handled with large amounts of benzaldehyde.
2. Allergic reactions. In rare cases, benzaldehyde can cause allergic reactions, including irritation of the skin and mucous membranes.
3. Respiratory effects. Prolonged or repeated exposure of benzaldehyde in the respiratory tract can irritate mucous membranes and increase symptoms in people with respiratory conditions such as asthma.

It is important to take precautions, especially when working with large amounts of benzaldehyde.

Safety Precautions

When working with benzaldehyde, it is advisable to follow safety measures to protect yourself and others from possible risks. Here are some guidelines and precautions when working with benzaldehyde:
Ventilation: Work in well-ventilated areas to minimize the concentration of benzaldehyde in the air.
Personal protective equipment: Wear appropriate protective clothing, including goggles, gloves and lab coat. This will help prevent benzaldehyde from getting into your skin and eyes.
Fire safety: Handle benzaldehyde with care, avoiding contact with open flames, sparks and heat sources. When storing benzaldehyde, be aware of its flammability. Store in a fire-resistant container, away from sources of heat and fire.

Following these precautions will help minimize risks when working with benzaldehyde in the laboratory.

Conclusion

In conclusion, benzaldehyde is an organic compound with unique chemical properties and a wide range of applications. Chemical properties allow the use of benzaldehyde in organic synthesis to obtain various compounds.
Benzaldehyde can be synthesized in several ways and is an important starting material for the pharmaceutical, chemical and perfume industries, where its properties are used to create many products. Precautions must be taken when working with benzaldehyde to minimize health risks.

Bibliography

• Benzaldehyde synthesis from benzyl alcohol G.Patton Dec 18, 2021
  Url: https://bbgate.com/threads/benzaldehyde-synthesis-from-benzyl-alcohol.611/
• Benzaldehyde Jarl L. Opgrande, C. J. Dobratz, Edward Brown, Jason Liang, Gregory S. Conn, Frederick J. Shelton, Jan With Kirk-Othmer Encyclopedia of Chemical Technology 04 December 2000
  Url: https://doi.org/10.1002/0471238961.0205142615160718.a01
• Final report on the safety assessment of benzaldehyde. Andersen A International Journal of Toxicology, 01 January 2006, 25 Suppl 1:11-27
  Url: https://doi.org/10.1080/10915810600716612
• Reduction of Benzaldehyde on Metal Oxides D. Haffad, U. Kameswari, M.M. Bettahar Journal of Catalysis Volume 172, Issue 1, November 1997, Pages 85-92
  Url: https://doi.org/10.1006/jcat.1997.1854
• Reactions of Benzaldehyde with o-Nitroaniline Gardner W. Stacy, Bruce V. Ettling, and Anthony J. Papa J. Org. Chem. 1964, 29, 6, 1537–1540
  Url: https://doi.org/10.1021/jo01029a064
• Experimental and modeling study of benzaldehyde oxidation Sylvain Namysl, Matteo Pelucchi, L. Pratali Maffei, Herbinet, Olivier Combustion and Flame Volume 211, January 2020, Pages 124-132
  Url: https://doi.org/10.1016/j.combustflame.2019.09.024