Benzaldehyde Introduction

 I. Basic Information

• Chemical Formula: C7H6O, alternatively written as C6H5CHO.
• Molecular Weight: 106.12.
• CAS Registry Number: 100-52-7.
• EINECS Number: 202-860-4.

II. Physical Properties

• Appearance: Pure benzaldehyde is a colorless liquid, while industrial-grade benzaldehyde may appear as a colorless to pale yellow liquid.
• Odor: It has a characteristic odor reminiscent of bitter almonds, cherries, and nuts.
• Melting Point: -26°C.
• Boiling Point: 179°C.
• Flash Point: 62°C (CC) or 73.9°C (OC).
• Density: 1.04g/cm³.
• Solubility: Slightly soluble in water, but miscible with ethanol, ether, benzene, chloroform, and other solvents.

III. Chemical Properties

• Reducibility: Benzaldehyde can be reduced to benzyl alcohol using reducing agents such as sodium borohydride (NaBH4) or lithium aluminum hydride (LiAlH4).
• Oxidability: Under appropriate conditions, benzaldehyde can be oxidized to benzoic acid using oxidizing agents like potassium permanganate (KMnO4) or potassium dichromate (K2Cr2O7).
• Electrophilic Substitution Reaction: Benzaldehyde can react with various electrophiles to form substituted products. For example, it can react with hydrogen chloride (HCl) to produce chlorobenzaldehyde.

IV. Natural Occurrence and Extraction

Benzaldehyde is widely found in plants, particularly in the Rosaceae family, where it exists mainly as glycosides in the stems, bark, leaves, or seeds of plants, such as amygdalin in bitter almonds. It can also be extracted from apricots, cherries, bay leaves, peach pits, and other sources.

V. Synthesis Methods

• Chlorination of Toluene Followed by Hydrolysis: Toluene is chlorinated under light to produce mixed chlorobenzenes, which are then hydrolyzed and processed further to obtain benzaldehyde.
• Oxidation of Benzyl Alcohol: Chlorobenzenes are hydrolyzed to produce benzyl alcohol, which is then oxidized to benzaldehyde.
• Direct Oxidation of Toluene: Benzaldehyde is an intermediate in the oxidation of toluene to benzoic acid.
• Other Methods: Benzaldehyde can be synthesized from benzene using various catalysts, such as aluminum chloride, in combination with carbon monoxide and hydrogen chloride. Alternatively, it can be obtained by hydrogenating tribenzyl cyanide using platinum chloride as a catalyst. Reduction of benzoyl chloride using palladium on barium sulfate is also commonly used in laboratory preparations of benzaldehyde.

VI. Applications

• Organic Synthesis: Benzaldehyde is an important chemical raw material used in the production of lauryl aldehyde, lauric acid, phenylacetaldehyde, and benzyl benzoate.
• Solvents and Fragrances: Benzaldehyde serves as a unique top-note fragrance ingredient, used sparingly in floral formulas such as lilac, jasmine, and gardenia, as well as in soaps and food fragrances like almond, berry, and cream.
• Pesticides and Dyes: Benzaldehyde is an intermediate in the production of pesticides such as difenzoquat and plant growth regulators like ancymidol. It is also used as an intermediate in the manufacture of dyes, such as those in the triphenylmethane series.
• Other Uses: Benzaldehyde is also used in the production of pharmaceuticals like phenyl glycine; in photochemistry for photographic agents and anticorrosives; as an auxiliary in polyamide dyeing; and as an additive in electroplating baths.

VII. Safety and Storage

• Hazards: Benzaldehyde is flammable and harmful, with irritant properties.
• Storage Methods: It should be stored in a cool, well-ventilated warehouse, away from fire and heat sources. The packaging should be airtight. It should be stored separately from oxidants, acids, and food chemicals.

In summary, benzaldehyde is an organic compound with a wide range of applications in the chemical, pharmaceutical, dye, and fragrance industries. Due to its flammability and harmfulness, special attention should be paid to safety during use and storage.