Problem 26 - A Complete Resource Book in Chemistry for JEE Main

Question

\((\mathrm{Me})_{2} \mathrm{SiCl}_{2}\) on hydrolysis will produce (a) \((\mathrm{Me})_{2} \mathrm{Si}(\mathrm{OH})_{2}\) (b) \((\mathrm{Me})_{2}^{2} \mathrm{Si}=\mathrm{O}\) (c) \(-\left[-\mathrm{O}-(\mathrm{Me})_{2} \mathrm{SI}-\mathrm{O}-\right]_{\mathrm{a}}-\) (d) \(\mathrm{Me}_{2} \mathrm{SiCl}(\mathrm{OH})\)

Step-by-Step Solution

Answer

(a) \((\mathrm{Me})_{2} \mathrm{Si}(\mathrm{OH})_{2}\) is the hydrolysis product.

Step 1: Understanding the Hydrolysis Reaction

Hydrolysis of \((\mathrm{Me})_{2} \mathrm{SiCl}_{2}\), also known as dimethyldichlorosilane, involves adding water to the compound. This reaction substitutes the chlorine atoms with hydroxyl groups (OH). The general reaction for hydrolysis of \({R_2}\mathrm{SiCl}_{2}\) is: \[ R_2SiCl_2 + 2H_2O \to R_2Si(OH)_2 + 2HCl \] where \(R\) represents the methyl group \(\mathrm{Me}\).

Step 2: Forming the Initial Product

Through hydrolysis, each chlorine atom is replaced by an OH group. As a result, the initial product formed is \(\mathrm{Me}_2\mathrm{Si}(\mathrm{OH})_2\). Thus, the structure of the product becomes dimethylsilanediol, as chlorine atoms are fully replaced with hydroxyl groups.

Step 3: Product Analysis and Options Consideration

Evaluate the given options. Option a, \( (\mathrm{Me})_{2} \mathrm{Si}(\mathrm{OH})_{2} \) matches our initial hydrolysis product. Option b, \( (\mathrm{Me})_{2}^{2} \mathrm{Si}=\mathrm{O} \) does not match as it describes a different compound formation, namely involving a double bond (not direct from hydrolysis). Option c, \( -\left[-\mathrm{O}-(\mathrm{Me})_{2}\mathrm{SI}-\mathrm{O}-\right]_{\mathrm{a}}- \), represents a polymer form, which may form further along with polycondensation. Option d, \( \mathrm{Me}_{2} \mathrm{SiCl}(\mathrm{OH}) \), does not match the full hydrolysis reaction.

Step 4: Conclusion

Considering full hydrolysis, option (a) \( (\mathrm{Me})_{2} \mathrm{Si}(\mathrm{OH})_{2} \) is the direct product formed from \( (\mathrm{Me})_{2} \mathrm{SiCl}_{2} \) once it undergoes hydrolysis, as it strictly follows the reaction pattern of replacing chlorine atoms with hydroxyl groups from water.

Key Concepts

Organosilicon Chemistry

Organosilicon chemistry involves the study of compounds containing carbon-silicon (C-Si) bonds. Silicon is located right below carbon in the periodic table, and thus shares some chemical similarities. However, it also has unique properties that lend themselves to distinct chemical behaviors and industrial applications.
In this branch of chemistry:

• Silicon atoms can bond to organic groups such as methyl (Me) groups, leading to many diverse organosilicon compounds.
• These compounds are widely used in industries such as cosmetics, electronics, and construction due to their stability and versatility.
• Organosilicon compounds often exhibit interesting features, such as high thermal stability, hydrophobicity, and high flexibility.

Understanding these fundamental properties is essential for exploring and manipulating organosilicon reactions effectively.

Dimethyldichlorosilane

Dimethyldichlorosilane ( ext{Me}_2 ext{SiCl}_2) is a key compound in organosilicon chemistry that plays a crucial role in the synthesis of silicones and other silicon-based materials. It contains two methyl groups (Me) and two chlorine (Cl) atoms bonded to a central silicon (Si) atom.
The structure can be broken down as follows:

• Each methyl group is bonded to the silicon atom. These groups are non-polar, contributing to the overall hydrophobic nature of dimethyldichlorosilane.
• The chlorine atoms are highly reactive and can be easily replaced through chemical reactions such as hydrolysis.

This compound acts as an important building block in creating more complex silicon-based structures through simple yet effective chemical reactions.

Hydroxyl Substitution

Hydroxyl substitution is a chemical reaction where a hydroxyl group (OH) replaces another atom or group in a molecule. In the case of organosilicon compounds like dimethyldichlorosilane, the chlorine atoms are replaced by hydroxyl groups during hydrolysis.
This substitution occurs as follows:

• Water molecules ( ext{H}_2 ext{O}) react with dimethyldichlorosilane in the presence of moisture.
• Each chlorine atom is replaced by a hydroxyl group, forming the compound dimethylsilanediol ( ext{Me}_2 ext{Si(OH)}_2).

The replacement of chlorine atoms with hydroxyl groups not only alters the physical and chemical properties of the product but also enables further polymerization reactions, forming larger silicone structures.

Reaction Mechanisms

Understanding reaction mechanisms provides insight into the step-by-step process involved in chemical reactions. For the hydrolysis of dimethyldichlorosilane, the mechanism is relatively straightforward.
The mechanism includes:

• The initial attack of water molecules on the silicon-bound chlorine atoms, due to chlorine's ability to leave easily as a chloride ion (Cl⁻).
• The stepwise replacement of each chlorine atom with a hydroxyl group, resulting in the formation of dimethylsilanediol.

Generally, recognizing these steps helps chemists predict the outcomes of similar reactions and synthesize desired materials efficiently. By understanding each phase of a reaction, such as initiation by water and subsequent substitution, scientists can tailor processes in industrial applications.