Question

Write the steps involved in the conversion of the following (i) Ethanol to but-1-yne (ii) Ethyl bromide to butan- 2 - one (iii) 2 -chloropropane to propan-1-ol

Short answer

Question: Describe the conversion of the following organic compounds: (i) Ethanol to but-1-yne (ii) Ethyl bromide to butan-2-one (iii) 2-chloropropane to propan-1-ol Answer: (i) Ethanol can be converted to but-1-yne through the following steps: Formation of ethyl chloride, formation of dibromoethane, formation of ethyne (acetylene), and formation of but-1-yne. (ii) Ethyl bromide can be converted to butan-2-one through these steps: Formation of ethanal (acetaldehyde), aldol condensation, and formation of butan-2-one. (iii) 2-chloropropane can be converted to propan-1-ol by the following steps: Formation of 1-chloropropane, and formation of propan-1-ol.

Step-by-step solution

Formation of Ethyl chloride

Convert ethanol (CH3CH2OH) into ethyl chloride (CH3CH2Cl) by reacting it with hydrochloric acid (HCl) in the presence of an anhydrous zinc chloride (ZnCl2) catalyst. The reaction is as follows: \[ CH3CH2OH + HCl \xrightarrow{ZnCl2} CH3CH2Cl + H2O\]

Formation of Dibromoethane

React ethyl chloride with Bromine (Br2) in the presence of Ultraviolet (UV) light to form dibromoethane (CH3CH2Br2). The reaction is as follows: \[ CH3CH2Cl + Br2 \xrightarrow{UV} CH3CH2Br_2\]

Formation of Ethyne (Acetylene)

Perform dehydrobromination of dibromoethane using alcoholic potassium hydroxide (KOH). The reaction is as follows: \[ CH3CH2Br_2 + 2 KOH \xrightarrow{alcoholic} CH\equiv CH + 2 KBr + 2 H2O \]

Formation of But-1-yne

Finally, perform an appropriate nucleophilic substitution reaction by reacting ethyne with 1-bromo butane. The reaction is as follows: \[ CH\equiv CH + CH3(CH2)_3Br \rightarrow CH3(CH2)_3C\equiv CH\] The final product is but-1-yne. (ii) Ethyl bromide to butan-2-one:

Formation of ethanal (acetaldehyde)

Convert ethyl bromide (CH3CH2Br) into ethanal (CH3CHO) by a hydrolysis reaction using aqueous silver nitrate (AgNO3) solution and ethanol: \[ CH3CH2Br + 2[AgNO3 + H2O] \rightarrow CH3CHO + HBr + 2AgBr + 2HNO3\]

Aldol Condensation

Perform aldol condensation by reacting ethanal with sodium hydroxide (NaOH) and water (H2O) to form aldol: \[ 2CH3CHO + OH^- \rightarrow CH3CHOHCH2CHO\]

Formation of butan-2-one

Finally, heat the aldol compound to form butan-2-one through the elimination of water: \[ CH3CHOHCH2CHO \xrightarrow{Heat} CH3COCH2CH3 + H2O\] The final product is butan-2-one. (iii) 2-chloropropane to propan-1-ol:

Formation of 1-chloropropane

Perform a nucleophilic substitution reaction by reacting 2-chloropropane (CH3CHClCH3) with alcoholic potassium hydroxide (KOH) to form 1-chloropropane (CH3CH2Cl): \[ CH3CHClCH3 + KOH \xrightarrow{alcoholic} CH3CH2Cl + KCl\]

Formation of propan-1-ol

Finally, perform a substitution reaction with water (H2O) and a strong base like aqueous sodium hydroxide (NaOH) to convert 1-chloropropane to propan-1-ol (CH3CH2CH2OH): \[ CH3CH2Cl + NaOH \rightarrow CH3CH2CH2OH + NaCl\] The final product is propan-1-ol.

Key concepts

Converting Ethanol to But-1-yne

Understanding organic chemistry conversions is essential for students as it lays the foundation for synthesizing complex molecules from simpler ones. Beginning with the conversion of ethanol to but-1-yne, it's important to grasp each step involved in this transformation.

From Ethanol to Ethyl Chloride: The first stage involves the conversion of ethanol (a common alcohol) to ethyl chloride, using hydrochloric acid with zinc chloride as a catalyst, forming water as a byproduct.

Dibromoethane Fabrication: The next step is the formation of dibromoethane by reacting ethyl chloride with bromine under UV light, which is a radical halogenation reaction.

Ethyne Generation: Then, the dibromoethane undergoes dehydrobromination with alcoholic KOH to create ethyne, an alkyne with a triple bond character, known for its versatility in organic synthesis.

But-1-yne Synthesis: Finally, the ethyne reacts with 1-bromo butane through a nucleophilic substitution to form but-1-yne. This step is pivotal in elongating the carbon chain and completing the conversion process.

By breaking down each stage and understanding the chemical changes that occur, students can appreciate the logic and order of organic synthesis.

From Ethyl Bromide to Butan-2-one

Transitioning from halides to ketones includes several key steps, and the conversion of ethyl bromide to butan-2-one illustrates this effectively. Each transformation applies fundamental organic principles that deepen a student's understanding of functional group interconversions.

Ethanal from Ethyl Bromide: The journey begins by transforming ethyl bromide into ethanal. This is achieved through hydrolysis using an aqueous silver nitrate solution, which not only replaces the bromide but also establishes the aldehyde functional group.

Aldol Condensation Pathway: Next, the aldehyde undergoes aldol condensation in the presence of sodium hydroxide, forming an aldol, an important intermediate for creating carbon-carbon bonds.

Creating Butan-2-one: To finalize the conversion, the aldol is subjected to heating, resulting in butan-2-one through dehydration. This step highlights the significance of temperature control in chemical processes and the ability to manipulate molecular structure via the elimination of water.

Each phase in the conversion of ethyl bromide to butan-2-one is an excellent example of chemical reactivity and the strategic use of conditions to achieve desired outcomes in organic synthesis.

Turning 2-Chloropropane into Propan-1-ol

In the realm of organic chemistry, converting halogenated compounds into alcohols is a staple transformation. For students, the process of turning 2-chloropropane into propan-1-ol showcases essential concepts of reactivity and functional group manipulation.

From 2-Chloropropane to 1-Chloropropane: Initially, this conversion requires an understanding of nucleophilic substitution, as 2-chloropropane is treated with alcoholic KOH to yield 1-chloropropane. Here, rearrangement from secondary to primary halide sets the stage for further reactivity.

Propan-1-ol Synthesis: Subsequently, 1-chloropropane reacts with sodium hydroxide to produce propan-1-ol. This step exemplifies the transformation of a halide to an alcohol, a common and vital process in organic synthesis.

Engaging with the process allows students to familiarize themselves with the subtleties of substitution reactions and the use of various reagents to steer the course of synthesis towards the intended alcohol product.