Question

How will you bring about the following conversions? (i) Ethanol to but-1-yne (ii) Ethane to bromoethene (iii) Propene to 1-nitropropane (iv) Toluene to benzyl alcohol (v) Propene to propyne (vi) Ethanol to ethyl fluoride (vii) Bromomethane to propanone (viii) But-1-ene

Short answer

Converting these compounds involves various methods like halogenation, oxidation, and reduction tailored to each transformation.

Step-by-step solution

Ethanol to But-1-yne

First, ethanol is converted to chloroethane using hydrogen chloride (HCl): \[\text{C}_2\text{H}_5\text{OH} + \text{HCl} \rightarrow \text{C}_2\text{H}_5\text{Cl} + \text{H}_2\text{O}\]Then, perform a Wurtz reaction using sodium acetylide to extend the carbon chain:\[\text{C}_2\text{H}_5\text{Cl} + \text{NaC}_2\text{H} \rightarrow \text{C}_4\text{H}_6 + \text{NaCl}\]This reaction forms but-1-yne.

Ethane to Bromoethene

First, perform halogenation of ethane to obtain chloroethane with chlorine gas in the presence of UV light:\[\text{C}_2\text{H}_6 + \text{Cl}_2 \rightarrow \text{C}_2\text{H}_5\text{Cl} + \text{HCl}\]Then, perform dehydrohalogenation of chloroethane to form ethene:\[\text{C}_2\text{H}_5\text{Cl} \xrightarrow{\text{KOH, alc.}} \text{C}_2\text{H}_4 + \text{HCl}\]Finally, brominate the ethene to bromoethene using hydrogen bromide:\[\text{C}_2\text{H}_4 + \text{HBr} \rightarrow \text{C}_2\text{H}_3\text{Br}\]This yields bromoethene.

Propene to 1-Nitropropane

First, perform hydration of propene to form propan-2-ol:\[\text{C}_3\text{H}_6 + \text{H}_2\text{O} \rightarrow \text{C}_3\text{H}_7\text{OH}\]Next, oxidize propan-2-ol to propan-2-one (acetone):\[\text{C}_3\text{H}_7\text{OH} \xrightarrow{\text{oxidation}} \text{C}_3\text{H}_6\text{O} + \text{H}_2\text{O}\]Apply a nitro reaction using nitric acid/ammonium nitrate to convert propan-2-one to 1-nitropropane:\[\text{C}_3\text{H}_6\text{O} + \text{HNO}_3 \rightarrow \text{C}_3\text{H}_7\text{NO}_2\]This gives 1-nitropropane.

Toluene to Benzyl Alcohol

Perform a side-chain oxidation of toluene using KMnO4 to first form benzoic acid:\[\text{C}_6\text{H}_5\text{CH}_3 \xrightarrow{\text{KMnO}_4} \text{C}_6\text{H}_5\text{COOH}\]Then, reduce the benzoic acid to benzyl alcohol using lithium aluminium hydride (LiAlH ext{4}):\[\text{C}_6\text{H}_5\text{COOH} \xrightarrow{\text{LiAlH}_4} \text{C}_6\text{H}_5\text{CH}_2\text{OH}\]This reaction produces benzyl alcohol.

Propene to Propyne

Begin by halogenating propene with chlorine to form 1,2-dichloropropane:\[\text{C}_3\text{H}_6 + \text{Cl}_2 \rightarrow \text{C}_3\text{H}_6\text{Cl}_2\]Next, eliminate the halogens with potassium tert-butoxide (a strong base):\[\text{C}_3\text{H}_6\text{Cl}_2 \xrightarrow{\text{KOC(CH}_3)_3} \text{C}_3\text{H}_4 + 2\text{HCl}\]This yields propyne.

Ethanol to Ethyl Fluoride

Convert ethanol to acetaldehyde via oxidation with a suitable oxidizing agent:\[\text{C}_2\text{H}_5\text{OH} \rightarrow \text{CH}_3\text{CHO}\]Use hydrogen fluoride directly on acetaldehyde to replace the hydroxyl group with a fluoride ion, forming ethyl fluoride:\[\text{CH}_3\text{CHO} + \text{HF} \rightarrow \text{C}_2\text{H}_5\text{F}\]This creates ethyl fluoride.

Bromomethane to Propanone

First, convert bromomethane to ethyl magnesium bromide using magnesium in dry ether:\[\text{CH}_3\text{Br} + \text{Mg} \rightarrow \text{CH}_3\text{MgBr}\]Conduct a Grignard reaction between ethyl magnesium bromide and carbon dioxide to form a carboxylic acid intermediate. Finally, reduce this intermediate to propanone using appropriate methods such as carboxylation and reduction:\[\text{CH}_3\text{MgBr} + \text{CO}_2 \rightarrow \text{CH}_3\text{C(O)}\text{OH} \rightarrow \text{C}_3\text{H}_6\text{O}\]Eventually yielding propanone.

But-1-ene

To convert into but-1-ene, consider conducting a dehydration process on a suitable butanol variant. If starting from butanol, dehydrating with sulfuric acid can provide but-1-ene: \[\text{C}_4\text{H}_9\text{OH} \rightarrow \text{C}_4\text{H}_8 + \text{H}_2\text{O}\]This gives but-1-ene as the product.

Key concepts

Understanding Chemical Reactions in Organic Synthesis

Chemical reactions are the backbone of organic synthesis. They involve breaking and forming bonds to transform one chemical compound into another. In the process of converting ethanol to but-1-yne, we first convert ethanol (\( \text{C}_2\text{H}_5\text{OH} \)) to chloroethane by adding hydrogen chloride (\( \text{HCl} \)), resulting in chloroethane (\( \text{C}_2\text{H}_5\text{Cl} \)).
Next, a Wurtz reaction using sodium acetylide extends the carbon chain, forming but-1-yne (\( \text{C}_4\text{H}_6 \)). This sequence exemplifies how carefully chosen reactions can systematically convert one molecule into a completely different one. Understanding each step and the conditions required is critical for successful synthesis in organic chemistry.

• Adding reagents (like HCl) to adjust or enhance the reaction.
• Breaking bonds to form intermediates (like chloroethane) that can be further transformed.
• Stretching carbon chains, often through specific reactions (like using sodium acetylide).

Exploring Reaction Mechanisms

A reaction mechanism is a step-by-step description of how a chemical reaction occurs on a molecular level. It tells us what happens to each atom and bond during the reaction, including formation and breaking of bonds. In the case of converting ethane to bromoethene, understanding the mechanism is crucial.
Initially, ethane reacts with chlorine gas in the presence of UV light to form chloroethane. Here, UV light provides energy for the homolytic cleavage of chlorine molecules into radicals, allowing them to react with ethane. This aligns with a radical substitution mechanism, where radicals substitute a hydrogen atom to form chloroethane. Further down the pathway, dehydrohalogenation of chloroethane with alcoholic KOH forms ethene, and subsequent bromination with HBr yields bromoethene.

• Identifying how radicals form and behave in substitution mechanisms.
• Breaking bonds through energy input (such as UV light) is crucial for radical formation.
• Dehydrohalogenation involves the elimination of hydrogen halide to form a double bond (as seen from ethene).

Grasping Functional Group Transformations

Functional group transformations are key to modifying the chemical behavior and properties of molecules. They involve converting one functional group to another through specific reactions. For example, in converting toluene to benzyl alcohol, we start by oxidizing the methyl group on toluene to a carboxylic acid using potassium permanganate (\( \text{KMnO}_4 \)).
This oxidation is a transformation that provides the platform for subsequent conversion. After forming benzoic acid, reduction with lithium aluminium hydride (\( \text{LiAlH}_4 \)) transforms the carboxylic acid into benzyl alcohol. These transformations rely heavily on reagent choice and reaction conditions, which dictate how and when a functional group will change.

• Understanding functional groups and their reactivity is essential for predictable outcomes.
• Reagents like \( \text{KMnO}_4 \) and \( \text{LiAlH}_4 \) play key roles in inducing transformations.
• Predicting reaction products based on the transformation pathway.

Navigating Organic Chemistry Pathways

Organic chemistry pathways refer to a series of chemical reactions that transform a starting material into the desired product through intermediate compounds. In our exploration from propene to 1-nitropropane, we encounter a series of transformations.
We begin by hydrating propene to form propan-2-ol, followed by oxidation to produce propan-2-one. This compound then undergoes a nitro reaction to form 1-nitropropane. Each step in this pathway requires careful consideration of reaction conditions and intermediates. With each reaction, we move closer to the final product, highlighting the interconnectedness of organic pathways and the elegance of sequential synthesis.

• Each step builds upon the previous one, emphasizing the importance of sequential logic.
• Pathways require precise control over conditions to ensure product formation.
• Creating a roadmap for synthesis involves balancing reactivity and stability of intermediates.