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Alcohols, Phenols and Ethers - Commercial Importance of some Alcohols

Grade 12CBSEChemistry

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Methanol (CH3OHCH_3OH), also known as 'wood spirit', was originally produced by the destructive distillation of wood. Today, it is manufactured by the catalytic hydrogenation of carbon monoxide (COCO) at high pressure (200−300200-300 atm) and temperature (573−673573-673 K) using ZnO−Cr2O3ZnO-Cr_2O_3 as a catalyst.

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Methanol is a colorless liquid and is highly poisonous. Ingestion of even small quantities can cause blindness, while larger quantities can cause death due to its oxidation to methanal and then to methanoic acid in the body.

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Ethanol (C2H5OHC_2H_5OH) is commercially obtained by the fermentation of sugars. The molasses from sugar cane or fruits like grapes are converted into glucose and fructose by the enzyme invertase. These are then converted to ethanol by the enzyme zymase, both found in yeast.

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Fermentation of ethanol is an anaerobic process (occurs in the absence of air). If air enters the fermentation mixture, the oxygen oxidizes the ethanol to ethanoic acid (CH3COOHCH_3COOH), which gives the beverage a sour taste.

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Denatured Alcohol: To prevent the misuse of industrial alcohol for drinking purposes, it is made unfit for human consumption by adding small amounts of copper sulphate (CuSO4CuSO_4, to provide color) and pyridine (to provide a foul smell).

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Uses of Methanol: Primarily used as a solvent in paints, varnishes, and for the production of formaldehyde (HCHOHCHO).

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Uses of Ethanol: Used as a solvent in the drug industry, in the preparation of perfumes, and increasingly as a fuel additive (power alcohol).

📐Formulae

CO+2H2→200−300 atmZnO−Cr2O3,573−673 KCH3OHCO + 2H_2 \xrightarrow[200-300 \text{ atm}]{ZnO-Cr_2O_3, 573-673 \text{ K}} CH_3OH

C12H22O11+H2O→InvertaseC6H12O6⏟Glucose+C6H12O6⏟FructoseC_{12}H_{22}O_{11} + H_2O \xrightarrow{\text{Invertase}} \underbrace{C_6H_{12}O_6}_{\text{Glucose}} + \underbrace{C_6H_{12}O_6}_{\text{Fructose}}

C6H12O6→Zymase2C2H5OH+2CO2C_6H_{12}O_6 \xrightarrow{\text{Zymase}} 2C_2H_5OH + 2CO_2

💡Examples

Problem 1:

Explain why the fermentation of sugars should be carried out in anaerobic conditions.

Solution:

Fermentation must be anaerobic because in the presence of air (oxygen), the ethanol (C2H5OHC_2H_5OH) produced is oxidized to ethanoic acid (CH3COOHCH_3COOH). This not only reduces the yield of ethanol but also ruins the flavor of the product.

Explanation:

The oxidation reaction is: C2H5OH+O2→CH3COOH+H2OC_2H_5OH + O_2 \rightarrow CH_3COOH + H_2O

Problem 2:

What is 'denatured alcohol' and why is it prepared?

Solution:

Denatured alcohol is ethyl alcohol that has been made unfit for drinking by the addition of poisonous or foul-smelling substances like CuSO4CuSO_4 (for color) and pyridine. It is prepared to prevent the illegal consumption of industrial-grade alcohol which is often sold at lower tax rates.

Explanation:

The addition of CuSO4CuSO_4 gives the alcohol a distinct blue color, while pyridine makes it smell repulsive, ensuring it is only used for industrial solvent purposes.

Commercial Importance of some Alcohols Revision - Class 12 Chemistry CBSE