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Benzaldehyde (C6H5CHO) is an organic and simplest aromatic aldehyde consisting of a benzene ring with a formyl substituent. A colourless liquid having characteristic almond-like odour. The primary component of benzaldehyde can be extracted from a number of other natural sources. Synthetic benzaldehyde forms the flavouring agent in imitation almond extract, which is used to flavour cakes and other baked goods.
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Key Terms: Benzaldehyde, Aromatic, Aldehyde, Benzene ring, Carbon, Hydrogen, Oxygen
Discovery of Benzaldehyde
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Benzaldehyde occurs in various natural items such as almonds or cherries. The isolation of benzaldehyde from bitter almonds occurred in 1803 and is credited to a French pharmacist Martrès. Later it was studied by the German chemists Justus von Liebig and Friedrich Wöhler, first to synthesise it successfully in the 1830s. This ultimately led to the establishment of the structural theory of organic chemistry.
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Structure of Benzaldehyde
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The structure of benzaldehyde consists of a benzene ring substituted with an aldehyde unit, which has one atom of carbon, hydrogen, and oxygen. The number of benzaldehyde sigma bonds is 14, which are formed by the head-to-head overlapping of atomic orbitals.
Properties of Benzaldehyde
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Formula: C7H6O
Density: 1.04 g/cm3
Boiling point: 178.1 °C
Melting point: -26 °C
Molar mass: 106.124 g·mol−1
Soluble in: Water
Reactions of Benzaldehyde
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Benzaldehyde can be oxidised to benzoic acid, as it readily undergoes autoxidation to form benzoic acid on exposure to air at room temperature producing a common impurity in laboratory samples. Since the boiling point of benzoic acid is much higher than that of benzaldehyde, it is purified by distillation.
Benzyl alcohol can be formed by means of hydrogenation, reaction of benzaldehyde with anhydrous sodium acetate and acetic anhydride yields cinnamic acid. Whereas, alcoholic potassium cyanide can be used to catalyse the condensation of benzaldehyde to benzoin. Benzaldehyde undergoes disproportionation upon treatment with concentrated alkali (Cannizzaro reaction), where one molecule of the aldehyde is reduced to the benzyl alcohol and another molecule is instantaneously oxidised to benzoic acid.
Benzaldehyde in Environment
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Benzaldehyde is naturally present in almonds, peaches, cherries, apricots kernels, and other fruits that have pits containing significant amounts of amygdalin.
This glycoside decomposes under enzymatic catalysis into benzaldehyde, hydrogen cyanide and two equivalents of glucose. Benzaldehyde is naturally found in essential oils like hyacinth, cinnamon, citronella, orris, sassafras, labdanum and patchouli. It is also found in grapes, tea, whiskey, firewood, cars and truck exhausts, tobacco smoke.
Uses & Storage
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- Benzaldehyde occurs naturally in many foods, most of the benzaldehyde people eat comes from natural plant foods, such as almonds or cherries . Benzaldehyde has a variety of uses such as:
- It is used in fragrances (perfumes, deodorants, etc.), pharmaceuticals (medicines), personal care items (shave gels, moisturising gels/creams, bath soaps, etc.), dyes, artificial flavour and as an additive to one or more types of tobacco products. It is also used as a solvent for oils, cellulose and resins.
- One of the important uses of benzaldehyde odour is as a bee repellent. It is used to remove bees from a honeycomb to extract honey from these structures.
- Benzaldehyde is also used in the production of dyes (acridine and aniline dyes), soaps, cakes and baked goods as almond extract.
- Benzaldehyde is used in additives such as antibacterial and antifungal preservatives. It is an intermediate product in the formation of compounds such as cinnamic acid, benzoic acid, etc.
- The aroma and fragrance of benzaldehyde are the reason for its widespread use in various sectors. Benzaldehyde is generally stable but should be stored under recommended conditions. It should be properly stored in a sealed container away from heat and light and kept away from reactive substances such as acids and reducing agents. It can also be stored under nitrogen.
Health effects of Benzaldehyde
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If inhaled, benzaldehyde affects your lungs and your skin and might also be able to cause mutations, that is why it is highly recommended to handle it with most care. It likely causes irritation, skin allergy itchiness, etc when it comes to contact. Exposure to benzaldehyde might make one feel lightheaded or dizzy, in extreme cases, getting a seizure or passing out is also possible.
Things To Remember
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- Benzaldehyde (C6H5CHO) is an organic and simplest aromatic aldehyde.
- Benzaldehyde consists of a benzene ring with a formyl substituent.
- It is a colourless liquid with an almond like odour.
- Benzaldehyde can be produced naturally and synthetically.
- In nature, benzaldehyde is found in many foods, and it is mostly found in natural plant foods, such as almonds or cherries.
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| Class 12 Chemistry Related Concepts | ||
|---|---|---|
| Gattermann – Koch Reaction | Williamson Ether Synthesis | Electrophilic Aromatic Substitution |
| Ester Hydrolysis | Reimer Tiemann Reaction | Gabriel phthalimide synthesis |
Sample Questions
Ques. What is benzaldehyde and how is it used? (2 Marks)
Ans. Benzaldehyde is a colourless aromatic liquid that gives off a pleasant almond odour. It rapidly evaporates (turns from liquid to gas) on exposure to air. Benzaldehyde is primarily used as a food additive and can be found in many foods, including baked goods, frozen dairy, fruit juice, soft candy, gelatin pudding, non-alcoholic alcoholic beverages, hard candies and chewing gum.
Ques. How is benzaldehyde formed? (3 Marks)
Ans. Toluene is handled with chlorine, due to which, benzal chloride is formed. The benzal chloride is then similarly handled with water. So, industrially, that is how benzaldehyde is made. In the laboratory, the method is manifestly different. Firstly, approximately 10 grams of benzene chloride in conjunction with eight grams of lead nitrate and water (50 ml) are prepared in a flask to make certain that the surroundings of the carbon dioxide stays within the container.
The flask is then heated for so long as 6 hours, after which, the aggregate is cooled after which extracted through ether. Benzaldehyde then enters that ether layer, that is later separated through blending a saturated answer of sodium bisulfate with it because of 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 answer is distilled and the ether is separated, natural benzaldehyde is received at 179°C.
Ques. How is benzaldehyde produced naturally? (2 Marks)
Ans. Benzaldehyde is produced naturally and synthetically. The herbal supply of this natural compound is amygdalin. This chemical compound may be located in gadgets like sour almonds, cherries, peaches and apricot pits. It is likewise located in a plant called Chinese cassica. Amygdalin may be damaged by the enzyme emulsion. This yields benzaldehyde and hydrogen cyanide (HCN). While HCN is a deadly poison, benzaldehyde is a compound that reveals numerous packages which include a flavouring agent and fragrance etc.
Ques. How safe is benzaldehyde for your health? (2 Marks)
Ans. Benzaldehyde is considered to be a Generally Regarded As Safe (GRAS) food additive in the United States by the FDA and is acknowledged as a flavouring substance in the European Union. The Environmental Working Group (EWG)Skin Deep Cosmetic Database lists benzaldehyde as an overall chemical hazard on the low end of the hazard scale.
Ques. What happens to benzaldehyde in your body? (2 Marks)
Ans. Benzaldehyde is absorbed through skin or lungs and is then circulated to high blood flow organs. After being metabolised to benzoic acid, it is naturally eliminated in the urine. It does not bioaccumulate (build up) in any specific tissue type and there was little acute (immediate) toxicity seen in laboratory studies.
Ques. What occurs to benzaldehyde withinside the environment? (2 Marks)
Ans. Benzaldehyde isn't a persistent chemical, that means it does now no longer live lengthy withinside the environment. If released to the atmosphere, benzaldehyde is damaged down quickly via means of the air and daylight and has a half-life of approximately 30 hours. Benzaldehyde may be carried as dust particles withinside the air and can be eliminated via means of rain and fallout. If released to soil or water, it is predicted to biodegrade [Hazardous Substance Data Bank – HSDB].
Ques. What are the specific forms of chemical reactions that benzaldehyde can go through? (3 Marks)
Ans. Benzaldehyde undergoes all of the chemical reactions that fragrant aldehydes go through, which include electrophilic substitution and the Cannizzaro reaction. It also can go through an oxidation reaction to yield benzoic acid.
Benzaldehyde can go through an extra 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 among benzaldehyde, anhydrous sodium acetate and acetic anhydride yields a compound referred to as cinnamic acid. The response of benzaldehyde with potassium hydroxide produces an oxidation and reduction reaction called the Cannizzaro reaction. This reaction yields products together with potassium benzoate and benzyl alcohol.
Ques. What is the product while benzaldehyde undergoes oxidation? (2 Marks)
Ans. When benzaldehyde is exposed to air at room temperature, it quite simply undergoes the method of antioxidation and the chemical product is benzoic acid. The method causes an unusual place of impurity in laboratory samples. It has a tendency to go through oxidation in addition to discounting concurrently with alcoholic potassium hydroxide and offers benzyl alcohol and potassium benzoate as an end result. It is transformed to benzoin while it reacts with potassium cyanide, however with acetic anhydride and anhydrous sodium acetate, the end result is cinnamic acid.
Ques. Is benzaldehyde greater reactive or propanol? Give reasons. (2 Marks)
Ans. When compared with propanol, benzaldehyde is taken into consideration to be much less reactive than the previous or greater stable. This is particularly due to the fact benzaldehyde is a compound that has an fragrant character, whereas, withinside the case of propanol, it has an aliphatic character. The carbon atom of the carbonyl group found in propanol is greater electrophilic than the one of the carbonyl group found in benzaldehyde. As a result of the resonance, the polarity of the carbonyl group is decreased in benzaldehyde, thereby making it much less reactive than propanol typically has a tendency to be.
Ques. What is the significance of benzaldehyde? (2 Marks)
Ans. Benzaldehyde has some of use of like: It functions as an intermediate for the manufacturing of numerous natural compounds and extensively utilised as an intermediate withinside the production method of ampicillin, ephedrine, and different such merchandise withinside the pharmaceutical industry. It is likewise used withinside the manufacturing of soaps, dyes, perfumes, or even positive beauty merchandise. In antibacterial preservatives, it's miles utilized as an additive and additionally usually used as a bee repellent.
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