Problem 120 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following statements is/are correct? 1\. \(\mathrm{CH}_{3} \mathrm{CHCl} . \mathrm{CH}_{3}\) is a secondary alkyl halide. 2\. Acetylene is formed when \(\mathrm{CH}_{2}=\mathrm{CH}-\mathrm{Cl}\) is heated with water. 3\. Iodoform gives a precipitate with \(\mathrm{AgNO}_{3}\) solution on heating, whereas chloroform does not. 4\. Freon \(\left(\mathrm{CCl}_{2} \mathrm{~F}_{2}\right)\) is prepared by the action of \(\mathrm{CCl}_{4}\) and \(\mathrm{SbF}_{3}\) in the presence of \(\mathrm{SbCl}_{5}\) as a catalyst. (a) 1,2 and 3 (b) 2,3 and 4 (c) 1,3 and 4 (d) 3 and 4

Step-by-Step Solution

Answer

Statements 1, 3, and 4 are correct (Option c).

Step 1: Analyze Statement 1

Statement 1 claims that \(\mathrm{CH}_3 \mathrm{CHCl} . \mathrm{CH}_3\) is a secondary alkyl halide. To determine this, identify the carbon atom that is bonded to the chlorine (Cl) atom. This carbon atom is attached to two other carbons, making it secondary. Therefore, statement 1 is correct.

Step 2: Analyze Statement 2

Statement 2 suggests that acetylene is formed when \(\mathrm{CH}_2=\mathrm{CH}-\mathrm{Cl}\) is heated with water. However, acetylene, a molecule with a carbon-carbon triple bond, is not formed via simple hydrolysis of \(\mathrm{CH}_2=\mathrm{CH}-\mathrm{Cl}\). Instead, hydrolysis would generally produce alcohols or related products. Thus, statement 2 is incorrect.

Step 3: Analyze Statement 3

Statement 3 claims that iodoform gives a precipitate with \(\mathrm{AgNO}_{3}\) on heating, while chloroform does not. This is true because iodoform (\(\mathrm{CHI}_3\)) reacts with silver nitrate to form a yellow precipitate of silver iodide (\(\mathrm{AgI}\)), while chloroform does not react this way. Therefore, statement 3 is correct.

Step 4: Analyze Statement 4

Statement 4 claims that Freon (\(\mathrm{CCl}_2 \mathrm{F}_2\)) is prepared by the reaction of \(\mathrm{CCl}_4\) and \(\mathrm{SbF}_3\) with \(\mathrm{SbCl}_5\) as a catalyst. This is the common industrial synthesis of Freon, as the antimony trifluoride (\(\mathrm{SbF}_3\)) reacts with carbon tetrachloride (\(\mathrm{CCl}_4\)) to substitute fluorine atoms in place of some chlorine atoms. Therefore, statement 4 is correct.

Key Concepts

Alkyl Halides

Alkyl halides, also known as haloalkanes, are compounds that contain carbon, hydrogen, and halogen atoms. They are named based on the number of carbon atoms attached to the carbon bonded with the halogen. If the carbon atom is attached to two other carbon atoms, it is called a secondary alkyl halide. This is important for understanding their reactivity and classification.

• In alkyl halides, the halogen atom is typically chloride (Cl), bromide (Br), iodide (I), or fluoride (F).
• The presence of the halogen atom makes the carbon-halogen bond polar, influencing the chemical behavior of these compounds.
• Secondary alkyl halides are known for participating in a variety of chemical reactions, such as substitutions and eliminations.

A common example is the compound \(\mathrm{CH}_3\mathrm{CHCl}\cdot\mathrm{CH}_3\), where the chlorine atom is attached to a secondary carbon, as this carbon is bonded to two other carbon atoms.

Hydrolysis Reactions

Hydrolysis reactions involve the chemical breakdown of a compound due to its reaction with water. This reaction is significant in transforming organic compounds into simpler derivatives, often in the presence of a catalyst or under specific conditions.

• In organic chemistry, hydrolysis can convert alkyl halides to alcohols.
• This process typically requires a strong base to facilitate the nucleophilic substitution, where water or hydroxide ions substitute the halogen atom in alkyl halides to form alcohols.
• An important aspect of hydrolysis is that it cannot produce acetylene, which is a hydrocarbon with a carbon-carbon triple bond, from simple vinyl chlorides.

Understanding the limitations and reactivity involved in hydrolysis is crucial for predicting product formation.

Precipitation Reactions

Precipitation reactions occur when two soluble compounds react to form an insoluble solid, known as a precipitate. This is a type of double displacement reaction where ions in solution form a new compound.

• In organic chemistry, notable examples include the reactions of iodoform, which yields a yellow precipitate when reacted with silver nitrate (\(\mathrm{AgNO}_{3}\)).
• This reaction does not occur with chloroform due to differing reactivity and the absence of iodide ions.
• Reactivity with silver nitrate is a common test to distinguish between various halides, helping in analytical chemistry.

The formation of precipitates is an essential method for confirming the presence of particular ions or functional groups in a compound.

Industrial Synthesis

Industrial synthesis is critical in chemical manufacturing and involves large-scale production of chemical compounds. One of the notable examples in this context is the production of Freon, used historically in refrigeration systems.

• Freon (\(\mathrm{CCl}_2\mathrm{F}_2\)) is synthesized through the reaction of antimony trifluoride (\(\mathrm{SbF}_3\)) with carbon tetrachloride (\(\mathrm{CCl}_4\)), which requires a catalyst like \(\mathrm{SbCl}_5\).
• This industrial process involves the substitution of fluorine for chlorine atoms in the carbon tetrachloride molecule, effectively generating Freon.
• The methodological advancement in synthesizing compounds like Freon enables efficient mass production, crucial for various applications.

Understanding the industrial synthesis process is key to appreciating the practical application of organic chemistry in real-world scenarios.