Question

Identify the false statement. (1) When ethyl iodide is treated with alcoholic potash, the product formed is ethylene (2) When ethyl alcohol vapours are passed over hot alumina, the product formed is ethylene (3) When ethyl alcohol is heated with conc. \(\mathrm{H}_{2} \mathrm{SO}_{4}\) at \(170^{\circ} \mathrm{C}\), the product formed is diethyl ether (4) Electrolysis of potassium succinate gives ethylene

Short answer

Statement 3 is false.

Step-by-step solution

- Understand the Reactions

Review the reactions given in each statement. It is key to know the general outcomes of these chemical processes.

- Analyze Statement 1

When ethyl iodide (C2H5I) is treated with alcoholic potash (KOH), it undergoes dehydrohalogenation, forming ethylene (C2H4). This statement is true.

- Analyze Statement 2

When ethyl alcohol (C2H5OH) vapours are passed over hot alumina (Al2O3), it undergoes dehydration to form ethylene (C2H4). This statement is true.

- Analyze Statement 3

When ethyl alcohol (C2H5OH) is heated with concentrated H2SO4 at 170°C, dehydration occurs, forming ethylene (C2H4). However, for diethyl ether formation, the temperature should be around 140°C. This statement is false.

- Analyze Statement 4

Electrolysis of potassium succinate produces ethylene as per Kolbe's electrolysis. This statement is true.

Conclusion

Since statements 1, 2, and 4 are true, it is concluded that statement 3 is false.

Key concepts

Dehydration of Ethyl Alcohol

Dehydration, in organic chemistry, means removing water (H2O) from a molecule. When it comes to ethyl alcohol (also known as ethanol, C2H5OH), dehydration can be achieved by heating it in the presence of a catalyst.
One common catalyst for this purpose is aluminum oxide (Al2O3) or concentrated sulfuric acid (H2SO4). The temperature plays a critical role in determining the product formed.

• If ethyl alcohol vapors are passed over hot alumina at around 350°C, ethylene (C2H4) is produced.
• If ethyl alcohol is heated with concentrated H2SO4 at around 170°C, ethylene is still the product due to dehydration.
• For the formation of diethyl ether, the temperature should be approximately 140°C with the same concentrated H2SO4 catalyst.

Thus, the conditions of the reaction, mainly the temperature and type of catalyst, make a significant impact on the product outcome.

Dehydrohalogenation

Dehydrohalogenation is the process of eliminating a hydrogen halide (HX) from an organic compound, typically an alkyl halide. This reaction usually requires a strong base.
For instance, when ethyl iodide (C2H5I) is treated with alcoholic potassium hydroxide (KOH in alcohol), the product is ethylene (C2H4).

• This reaction proceeds via an E2 elimination mechanism.
• Alcoholic potassium hydroxide acts as the base, abstracting a proton (H+) from the carbon atom next to the one bearing the halogen (Iodine in this case).
• As the hydrogen is removed, the halogen also leaves the molecule, resulting in the formation of a C=C double bond (ethylene).

Overall, dehydrohalogenation is an important reaction in organic synthesis, often used to create alkenes from alkyl halides.

Electrolysis of Potassium Succinate

Electrolysis is a method that uses electric current to drive a non-spontaneous chemical reaction. In the case of potassium succinate, electrolysis produces ethylene among other products.
This particular example follows Kolbe's electrolysis, where a carboxylate ion (succinate in this case) is decarboxylated (loses CO2) to form free radicals.

• Potassium succinate (C4H4K2O4) in an aqueous solution undergoes electrolysis.
• The succinate ion (C4H4O4-) splits, releasing carbon dioxide (CO2) and creating ethylene (C2H4) along with other by-products.
• This process efficiently produces ethylene through a relatively straightforward electrochemical pathway.

Kolbe’s electrolysis is a valuable method for synthesizing alkenes like ethylene from carboxylate salts like potassium succinate.

Ethylene Formation

Ethylene (C2H4) is a simple alkene and an essential building block in organic chemistry. Understanding various methods of ethylene formation is crucial.
Here are some common pathways to synthesize ethylene:

• Dehydration of ethyl alcohol: As detailed, heating ethyl alcohol with catalysts like Al2O3 or concentrated H2SO4 at high temperatures (around 170°C) produces ethylene.
• Dehydrohalogenation: Removing a hydrogen halide (like HI from C2H5I) using a strong base like KOH in alcohol can form ethylene via an E2 mechanism.
• Electrolysis of potassium succinate: Kolbe electrolysis of carboxylate salts like potassium succinate results in ethylene formation among other products.

Ethylene serves as a starting material for many industrial chemicals and is vital for producing polyethylene, one of the most commonly used plastics.