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 is benzaldehyde and what is its chemical formula?
Benzaldehyde is the simplest aromatic aldehyde, an organic compound with the chemical formula C₆H₅CHO. It consists of a benzene ring attached to a formyl (–CHO) group. It's a colourless liquid known for its characteristic almond-like odour and is found naturally in almonds, cherries, and apricot pits.
2. How would you describe the structure of benzaldehyde?
The structure of benzaldehyde features a benzene ring where one hydrogen atom is replaced by an aldehyde functional group (–CHO). This makes it an aromatic aldehyde. The molecule contains 14 sigma bonds and its IUPAC name is benzenecarbaldehyde. The carbonyl group (C=O) in the aldehyde is directly attached to the sp² hybridised carbon of the benzene ring.
3. What are the main uses and importance of benzaldehyde in various industries?
Benzaldehyde is a versatile compound with several important applications:
- Flavouring Agent: It is widely used to impart an almond flavour and scent to foods, beverages, and baked goods.
- Industrial Precursor: It serves as a crucial intermediate in manufacturing other organic compounds like dyes (aniline, acridine), cinnamic acid, and benzoic acid.
- Cosmetics and Perfumery: Due to its pleasant scent, it's a common ingredient in perfumes, soaps, and other personal care products.
- Pharmaceuticals: It is used in the synthesis of certain drugs, including ampicillin and ephedrine.
- Other Uses: It also acts as a solvent for oils and resins and is used as a bee repellent to safely extract honey.
4. Why is benzaldehyde less reactive towards nucleophilic addition reactions than an aliphatic aldehyde like propanal?
Benzaldehyde is less reactive than propanal due to two main reasons based on its structure:
- Resonance Effect: The lone pair of electrons on the oxygen atom of the carbonyl group is in conjugation with the benzene ring. This delocalisation of pi-electrons reduces the positive charge (electrophilicity) on the carbonyl carbon, making it less susceptible to nucleophilic attack.
- Steric Hindrance: The bulky benzene ring offers more steric hindrance to the incoming nucleophile compared to the smaller alkyl group in propanal.
5. Why does benzaldehyde not undergo Aldol condensation but does undergo the Cannizzaro reaction?
The key difference lies in the presence of an alpha-hydrogen.
- Aldol Condensation: This reaction requires the presence of at least one alpha-hydrogen (a hydrogen atom on the carbon adjacent to the carbonyl group) to form an enolate ion. Benzaldehyde lacks an alpha-hydrogen, so it cannot undergo Aldol condensation.
- Cannizzaro Reaction: This reaction is characteristic of aldehydes that have no alpha-hydrogens. In the presence of a strong base (like concentrated KOH), one molecule of benzaldehyde is reduced to benzyl alcohol, while another is oxidised to a salt of benzoic acid (e.g., potassium benzoate).
6. What are the primary methods for producing benzaldehyde?
Benzaldehyde can be obtained from both natural and synthetic sources.
- Natural Source: It is extracted from natural glycosides like amygdalin, which is found in bitter almonds and apricot pits. The amygdalin is hydrolysed by enzymes to yield benzaldehyde, glucose, and hydrogen cyanide.
- Industrial Synthesis: The most common commercial method is the liquid-phase chlorination or oxidation of toluene (C₆H₅CH₃). Toluene is first converted to benzal chloride, which is then hydrolysed with water to produce benzaldehyde.
7. What are the potential health hazards associated with handling benzaldehyde?
While widely used, benzaldehyde must be handled with care as it can pose health risks. Exposure can cause irritation to the skin, eyes, nose, and throat, leading to symptoms like coughing or shortness of breath. Repeated or high exposure may lead to skin allergies, dizziness, or lightheadedness. It is recommended to use it in well-ventilated areas and with appropriate personal protective equipment.
