Chapter 16: Problem 16
From \(\mathrm{B}_{2} \mathrm{H}_{6}\), all the following can be prepared except (a) \(\mathrm{B}_{2}\left(\mathrm{CH}_{3}\right)_{6}\) (b) \(\mathrm{NaBH}_{4}\) (c) \(\mathrm{B}_{2} \mathrm{O}_{3}\) (d) \(\mathrm{H}_{3} \mathrm{BO}_{3}\)
Short Answer
Expert verified
Option (d) \( \mathrm{H}_3 \mathrm{BO}_3 \) cannot be directly prepared from \( \mathrm{B}_2 \mathrm{H}_6 \).
Step by step solution
01
Understanding the Problem
The problem asks which of the options cannot be prepared from diborane, \( \mathrm{B}_2 \mathrm{H}_6 \). To solve it, we need to understand the chemical reactions diborane can undergo and the products that can be derived from it.
02
Assessing Preparation of Option A
Option \( a \), \( \mathrm{B}_2(\mathrm{CH}_3)_6 \), can be prepared using diborane by its reaction with trialkylboranes. Therefore, this option can be prepared from \( \mathrm{B}_2 \mathrm{H}_6 \).
03
Assessing Preparation of Option B
Option \( b \), \( \mathrm{NaBH}_4 \), is formed by reacting \( \mathrm{B}_2 \mathrm{H}_6 \) with an alkali metal hydride such as \( \mathrm{NaH} \). Hence, this compound can be prepared from diborane.
04
Assessing Preparation of Option C
Option \( c \), \( \mathrm{B}_2 \mathrm{O}_3 \), can be prepared from diborane by oxidizing it in air. As such, this compound can also be obtained from \( \mathrm{B}_2 \mathrm{H}_6 \).
05
Assessing Preparation of Option D
Option \( d \), \( \mathrm{H}_3 \mathrm{BO}_3 \) (boric acid), is typically formed from boron trioxide, \( \mathrm{B}_2 \mathrm{O}_3 \), by reaction with water. Although \( \mathrm{B}_2 \mathrm{O}_3 \) can be formed from \( \mathrm{B}_2 \mathrm{H}_6 \), the direct transformation of diborane to \( \mathrm{H}_3 \mathrm{BO}_3 \) is not feasible without intermediate steps.
06
Conclusion
After analyzing each option, we find that option \( d \), "\( \mathrm{H}_3 \mathrm{BO}_3 \)," cannot be directly prepared from \( \mathrm{B}_2 \mathrm{H}_6 \) without going through \( \mathrm{B}_2 \mathrm{O}_3 \). Therefore, it is the correct answer to the question.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Diborane
Diborane, whose chemical formula is \( \mathrm{B}_2 \mathrm{H}_6 \), is one of the simplest boron hydrides. It is a colorless gas at room temperature and has a repulsive sweet odor similar to ether. This compound plays a significant role in the chemistry of boron, showcasing various reactions due to its instability and reactivity.
When diborane decomposes, it can interact with other chemicals to form numerous boron-containing compounds.
When diborane decomposes, it can interact with other chemicals to form numerous boron-containing compounds.
- It reacts with various alkyl boranes to form organoboron compounds.
- When exposed to air, diborane rapidly oxidizes.
- It can also react with alkali metals to form borohydrides, such as sodium borohydride (\( \mathrm{NaBH}_4 \)).
Boron Compounds
Boron compounds exhibit a range of structures and properties due to boron's ability to form stable covalent bonds with other elements. Many boron compounds contain boron-oxygen bonds, which can be formed through oxidation.
Here are some common boron compounds derived from diborane:
Here are some common boron compounds derived from diborane:
- **Trialkylboranes**: By reacting diborane with alkenes, trialkylboranes (e.g., trimethylborane) are produced.
- **Sodium Borohydride (\( \mathrm{NaBH}_4 \))**: This compound is formed when diborane reacts with sodium hydride. It is widely used as a reducing agent in chemical synthesis.
- **Boron Trioxide (\( \mathrm{B}_2 \mathrm{O}_3 \))**: Produced by burning diborane in the presence of oxygen, it serves as a precursor for various borates and glassmaking industries.
Oxidation
Oxidation is a fundamental chemical reaction involving the loss of electrons by a molecule, atom, or ion. In the context of boron chemistry, oxidation of diborane leads to various transformations.
For instance, diborane undergoes a vigorous oxidation process in the air to yield boron trioxide (\( \mathrm{B}_2 \mathrm{O}_3 \)). The \( \mathrm{B}_2 \mathrm{O}_3 \) can further react with water to form boric acid (\( \mathrm{H}_3 \mathrm{BO}_3 \)), but this requires two distinct steps:
For instance, diborane undergoes a vigorous oxidation process in the air to yield boron trioxide (\( \mathrm{B}_2 \mathrm{O}_3 \)). The \( \mathrm{B}_2 \mathrm{O}_3 \) can further react with water to form boric acid (\( \mathrm{H}_3 \mathrm{BO}_3 \)), but this requires two distinct steps:
- The initial oxidation of diborane to form boron trioxide.
- The subsequent reaction of boron trioxide with water to obtain boric acid.