Dhristi JEE 2022-24

What are Benzaldehyde and its Properties?

The simplest aromatic aldehyde, which consists of a benzene ring with a formyl (-CHO) substituent, is termed benzaldehyde (C6H5CHO). This organic chemical compound has several industrial applications, including dyes, flavouring agents, perfumes and the manufacturing of several other organic compounds. Found naturally in glycoside amygdalin, this aromatic aldehyde is known for its distinct, almond oil-like taste and odour. 


The molecular formula of this compound is C7H6O, and its IUPAC name is benzenecarbaldehyde. It is also referred to as several other names, including benzenedicarboxaldehyde, phenylmethanal, or benzoic aldehyde. It appears as a clear liquid with a smell like almonds. It is miscible with volatile oils, ether, and alcohol. It is denser than and thus only slightly soluble in water and has a solubility of 3 g/L.


Discovery of Benzaldehyde 

Benzaldehyde occurs in a variety of natural items such as almonds or cherries. The isolation of benzaldehyde from bitter almonds goes back to 1803 and is credited to a French pharmacist Martrès. It was later studied by the German chemists Justus von Liebig and Friedrich Wöhler, who first synthesised it successfully in the 1830s. This led to the establishment of the structural theory of organic chemistry.


Structure of Benzaldehyde

The structure of benzaldehyde consists of a benzene ring substituted with an aldehyde unit. This formyl unit has one atom of carbon, hydrogen, and oxygen. The number of benzaldehyde sigma bonds is 14, formed by the head-to-head overlapping of atomic orbitals. 


Preparation of Benzaldehyde

This simple aromatic aldehyde can be derived from a variety of natural sources.

 

It can also be manufactured synthetically from toluene which is found in crude oil, for industrial usage. This is done by a series of chemical reactions in which toluene reacts with chlorine. This leads to the formation of benzal chloride, which can be further treated with water to form benzaldehyde. 


Benzaldehyde can also be synthesised by the oxidation of benzyl alcohol and carbonylation of benzene. Alkaline hydrolysis of benzal chloride also yields benzaldehyde. 


Properties of Benzaldehyde

  • The most distinct characteristics of benzaldehyde are its flavour and odour. Some of the properties of benzaldehyde are:

  • This liquid is colourless to yellow in colour.

  • Benzaldehyde has the odour of almonds.

  • The molecular weight of Benzaldehyde is 106.12 g/mol.

  • It is slightly soluble in water.

  • Benzaldehyde is completely soluble in alcohol and ether.

  • It is generally stable when stored under ordinary conditions. 

  • Benzaldehyde is a neutral compound (neither acidic nor basic).

  • The melting point of benzaldehyde is −26 °C (−14.8 °F).

  • The boiling point of benzaldehyde is 179 °C (354.2 °F).

  • It is highly refractive with a refractive index of 1.5456.

  • The density of benzaldehyde is 1.044 g/mL.

  • Benzaldehyde is considered to be an aromatic aldehyde. 

  • Its carbonyl group is an electron-withdrawing group.


Uses of Benzaldehyde

Benzaldehyde is an aromatic compound with a distinct odour resembling almonds. It can be extracted from a variety of natural sources and can also be synthesised by liquid phase chlorination of toluene. There is no chemical distinction between these two types of benzaldehyde.


Benzaldehyde is a widely used compound in the chemical industry. It also finds usage in several other items. The most common applications of benzaldehyde that make it such an important compound are listed below- 

1. The most common use of benzaldehyde is to provide almond flavouring to items. It is used in food and beverages to provide the scent of almonds.  Various scented products also use benzaldehyde as an additive for having a distinct odour.

2. The industrial usage of benzaldehyde is that it acts as an intermediate in the production of several organic compounds. It is a precursor to various chemical additives, plastics, and pharmaceutical products.

3. Another significant use of the odour of benzaldehyde is as a bee repellent. It is used to draw the bees away from a honeycomb in order to extract the honey from these structures. 

4. Some cosmetic products and personal care products also contain benzaldehyde.

5. Benzaldehyde is also used in the production of dyes (acridine and aniline dyes), soaps, and perfumes.

6. It is also used in cakes and baked goods as almond extract. Benzaldehyde is also used in additives like antibacterial and antifungal preservatives.

7. It is an intermediary product in the formation of compounds like cinnamic acid, benzoic acid, etc.

8. It is used as a solvent for oils, resins, ethers, etc. 

The flavouring and fragrance of benzaldehyde are the reason for its widespread use in several industries.


Storage of Benzaldehyde

Benzaldehyde is usually stable but should be stored as per the recommended conditions. It should be properly stored in a sealed container away from heat and light. It should be kept away from reactive substances such as acids and reducing agents. It is also recommended to store this compound under nitrogen.

FAQs on Benzaldehyde

1. What are the different types of chemical reactions that benzaldehyde can undergo?

Benzaldehyde undergoes all the chemical reactions that aromatic aldehydes undergo, such as electrophilic substitution and the Cannizzaro reaction.

 

It can also undergo an oxidation reaction to yield benzoic acid. Benzaldehyde can undergo additional reaction with hydrocyanic acid and sodium bisulfite. It reacts with alcoholic potassium cyanide to form benzoin. The hydrogenation of benzaldehyde produced benzyl alcohol.

 

The reaction between benzaldehyde, anhydrous sodium acetate and acetic anhydride yields a compound called cinnamic acid. The reaction of benzaldehyde with potassium hydroxide produces an oxidation and reduction reaction known as the Cannizzaro reaction. This reaction yields products including potassium benzoate and benzyl alcohol.

2. How is benzaldehyde produced naturally?

Benzaldehyde is produced both naturally and synthetically. The natural source of this organic compound is amygdalin. This chemical compound can be found in items like bitter almonds, cherries, peaches and apricot pits. It is also found in a plant known as Chinese cassica. 

 

Amygdalin can be broken down with the enzyme emulsion. This yields benzaldehyde and hydrogen cyanide (HCN). While HCN is a lethal poison, benzaldehyde is a compound that finds several applications such as a flavouring agent and perfume etc.

3. What is the product when benzaldehyde undergoes oxidation?

When benzaldehyde is exposed to air at room temperature, it readily undergoes the process of antioxidation and the end product is benzoic acid. The process causes a common impurity in laboratory samples. It tends to undergo oxidation as well as reduction simultaneously with alcoholic potassium hydroxide and gives benzyl alcohol and potassium benzoate as a result. 


It is converted to benzoin when it reacts with potassium cyanide, but with acetic anhydride and anhydrous sodium acetate, the result is cinnamic acid.

4. How is benzaldehyde formed?

Toluene is treated with chlorine, as a result of which, benzal chloride is formed. The benzal chloride is then further treated with water. So, industrially, this is how benzaldehyde is made. 


In the laboratory, the process is obviously different. Firstly, about 10 grams of benzene chloride along with 8 grams of lead nitrate and water (50 ml) are put together in a flask to ensure that the atmosphere of the carbon dioxide remains in the container. 


The flask is then heated for as long as 6 hours, after which, the mixture is cooled and then extracted by ether. Benzaldehyde then enters that ether layer, which is later separated by mixing a saturated solution of sodium bisulfate with it due to which crystals of benzaldehyde sodium bisulfate are formed. These crystals are filtered and dried and upon heating them with sulfuric acid, benzaldehyde is released. Lastly, the ether solution is distilled and the ether is separated, pure benzaldehyde is obtained at 179°C.

5. Is benzaldehyde more reactive or propanol? Give reasons.

When compared with propanol, benzaldehyde is considered to be less reactive than the former or more stable. This is mainly because benzaldehyde is a compound that has an aromatic character, whereas, in the case of propanol, it has an aliphatic character. The carbon atom of the carbonyl group present in propanol is more electrophilic than the one of the carbonyl group present in benzaldehyde. As a result of the resonance, the polarity of the carbonyl group is reduced in benzaldehyde, thereby making it less reactive than propanol generally tends to be.

6. Are there any hazards associated with benzaldehyde? If so, what are they?

Yes, there are certain health hazards when it comes to benzaldehyde. They are as follows: 

  • If inhaled or breathed in, benzaldehyde can affect your lungs and/or your skin. 

  • It might also be able to cause mutations, which is why it is highly recommended to handle benzaldehyde with utter care. 

  • Coming into contact with it is likely to cause irritation, itchiness, etc. It may irritate one’s nose and/or throat, eventually leading to coughing, shortness of breath, etc.

  • Coming into contact can also cause itchiness in the eyes.

  • Repeated exposure can lead to a skin rash.

  • It can also lead to a skin allergy.

  • Exposure to benzaldehyde might make one feel lightheaded or dizzy. In extreme cases where the exposure is too much, getting a seizure or passing out is also a possible scenario.

  • Benzaldehyde is not only considered to be hazardous when it comes to human contact; it is also said that if this particular compound is released into the water or the soil, it might just biodegrade. 

7. What is the importance of benzaldehyde?

Benzaldehyde has a number of uses and it is this versatility that makes it such a useful compound. Here are some of its key purposes: 

  • Industrially, it tends to serve as an intermediate for the production of various organic compounds.

  • It is also used as an intermediate in the manufacturing process of ampicillin, ephedrine, and other such products in the pharmaceutical industry.

  • It is also used as a vital ingredient when it comes to the production of soaps, dyes, perfumes, and even certain cosmetic products.

  • One of the most common uses of benzaldehyde is associated with food as it helps to bring the flavour and/or the scent of almonds in various foods, especially in cakes and other baked goods, and in beverages as well, at times.

  • In antibacterial preservatives, it is utilised as an additive.

  • It is also commonly used as a bee repellent. 

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