Aldehydes, Ketones & Carboxylic Acids - Concept Based Problems - Reaction sequence of aldehydes

  • In this lecture, we will focus on the reaction sequence of aldehydes, ketones, and carboxylic acids.
  • We will solve concept-based problems related to these organic compounds.
  • It is important to have a thorough understanding of the reaction sequence to effectively solve such problems.
  • Let’s begin by reviewing the basic concepts of aldehydes, ketones, and carboxylic acids.

Aldehydes

  • Aldehydes are organic compounds that contain a carbonyl group (-C=O) with a hydrogen atom (-H) attached to it.
  • The general formula for aldehydes is RCHO, with R representing any alkyl or aryl group.
  • Aldehydes can be prepared by the oxidation of primary alcohols.
  • Some common examples of aldehydes include formaldehyde (HCHO) and acetaldehyde (CH3CHO).

Ketones

  • Ketones are organic compounds that also contain a carbonyl group (-C=O), but with two alkyl or aryl groups attached to it.
  • The general formula for ketones is RCOR’, with R and R’ representing different alkyl or aryl groups.
  • Ketones can be prepared by the oxidation of secondary alcohols.
  • Some common examples of ketones include acetone (CH3COCH3) and methyl ethyl ketone (CH3COC2H5).

Carboxylic Acids

  • Carboxylic acids are organic compounds that contain both a carbonyl group (-C=O) and a hydroxyl group (-OH) attached to the same carbon atom.
  • The general formula for carboxylic acids is RCOOH, with R representing any alkyl or aryl group.
  • Carboxylic acids can be prepared by the oxidation of primary alcohols or aldehydes.
  • Some common examples of carboxylic acids include acetic acid (CH3COOH) and formic acid (HCOOH).

Reactions of Aldehydes

  • Aldehydes undergo various reactions due to the presence of the carbonyl group.
  • Some important reactions of aldehydes include oxidation, reduction, nucleophilic addition, and condensation reactions.
  • For example, aldehydes can be oxidized to carboxylic acids using strong oxidizing agents like potassium permanganate (KMnO4) or chromic acid (H2CrO4).
  • Reduction of aldehydes leads to the formation of primary alcohols.

Reactions of Ketones

  • Ketones also participate in similar reactions as aldehydes due to the presence of the carbonyl group.
  • Some important reactions of ketones include oxidation, reduction, nucleophilic addition, and condensation reactions.
  • However, ketones are less reactive compared to aldehydes.
  • Ketones cannot be oxidized to carboxylic acids but can be reduced to secondary alcohols.

Reactions of Carboxylic Acids

  • Carboxylic acids have distinct reactions due to the presence of both a carbonyl group and a hydroxyl group.
  • Some important reactions of carboxylic acids include esterification, decarboxylation, and nucleophilic substitution reactions.
  • Carboxylic acids can react with alcohols to form esters.
  • Decarboxylation involves the removal of carbon dioxide (CO2) from a carboxylic acid molecule, leading to the formation of a smaller molecule.

Reaction Sequence of Aldehydes

  • The reaction sequence of aldehydes involves a stepwise transformation of the carbonyl group.
  • The oxidation of aldehydes leads to the formation of carboxylic acids.
  • Reduction of aldehydes results in primary alcohols.
  • Aldehydes also undergo nucleophilic addition reactions, where a nucleophile attacks the carbonyl carbon atom and forms a new bond.

Reaction Sequence of Ketones

  • The reaction sequence of ketones is similar to that of aldehydes.
  • However, ketones cannot be oxidized to carboxylic acids.
  • Reduction of ketones leads to the formation of secondary alcohols.
  • Ketones also participate in nucleophilic addition reactions, similar to aldehydes.

Summary

  • In this lecture, we discussed the reactions and reaction sequence of aldehydes, ketones, and carboxylic acids.
  • It is important to understand the basic concepts and reactions associated with these organic compounds.
  • By solving concept-based problems, we can deepen our understanding and master the reaction sequence.
  • In the upcoming slides, we will go through several examples to solidify our knowledge.

Oxidation of Aldehydes

  • Aldehydes can be oxidized to form carboxylic acids.
  • This reaction involves the oxidation of the carbonyl group, resulting in the addition of an oxygen atom.
  • Strong oxidizing agents such as potassium permanganate (KMnO4) or chromic acid (H2CrO4) are commonly used.
  • For example, formaldehyde (HCHO) can be oxidized to formic acid (HCOOH). Equation: HCHO + [O] -> HCOOH
  • Other aldehydes can also undergo oxidation to form various carboxylic acids.

Reduction of Aldehydes

  • Aldehydes can be reduced to form primary alcohols.
  • This reduction reaction involves the addition of hydrogen gas (H2) or a reducing agent such as sodium borohydride (NaBH4).
  • The carbonyl group is reduced to an alcohol group (-OH).
  • For example, acetaldehyde (CH3CHO) can be reduced to form ethanol (CH3CH2OH). Equation: CH3CHO + 2H2 -> CH3CH2OH
  • Other aldehydes can also undergo reduction to form primary alcohols.

Nucleophilic Addition to Aldehydes

  • Aldehydes can undergo nucleophilic addition reactions with various nucleophiles.
  • This reaction involves the attack of a nucleophile on the carbonyl carbon atom, resulting in the formation of a new bond.
  • The nucleophile can be a negatively charged species, such as cyanide ion (CN-) or a Grignard reagent (RMgX).
  • For example, formaldehyde (HCHO) can react with cyanide ion to form a cyanohydrin. Equation: HCHO + CN- -> HCOH(CN)
  • Other aldehydes can also react with nucleophiles to form different compounds.

Oxidation of Ketones

  • Ketones cannot be oxidized to form carboxylic acids.
  • The presence of two alkyl or aryl groups attached to the carbonyl carbon makes ketones less reactive towards oxidation.
  • Therefore, strong oxidizing agents used for aldehydes, such as potassium permanganate or chromic acid, do not react with ketones.
  • Ketones remain unchanged under these oxidation conditions.

Reduction of Ketones

  • Ketones can be reduced to form secondary alcohols.
  • Similar to the reduction of aldehydes, this reaction involves the addition of hydrogen gas (H2) or a reducing agent such as sodium borohydride (NaBH4).
  • The carbonyl group in ketones is reduced to an alcohol group (-OH).
  • For example, acetone (CH3COCH3) can be reduced to form isopropanol (CH3CHOHCH3). Equation: CH3COCH3 + H2 -> CH3CHOHCH3
  • Other ketones can also undergo reduction to form secondary alcohols.

Nucleophilic Addition to Ketones

  • Ketones, like aldehydes, can undergo nucleophilic addition reactions.
  • The nucleophile attacks the carbonyl carbon atom, forming a new bond and resulting in the formation of a new compound.
  • Various nucleophiles can participate in this reaction, including cyanide ion (CN-) and Grignard reagents (RMgX).
  • For example, acetone (CH3COCH3) can react with a Grignard reagent to form a tertiary alcohol. Equation: CH3COCH3 + R-MgX -> CH3COCHR3
  • Other ketones can also react with nucleophiles to form different compounds.

Esterification of Carboxylic Acids

  • Carboxylic acids can react with alcohols to form esters.
  • This reaction is known as esterification and involves the formation of an ester functional group (-COO-).
  • A condensation reaction occurs, resulting in the elimination of a water molecule.
  • The reaction is usually catalyzed by an acid, such as sulfuric acid (H2SO4).
  • For example, acetic acid (CH3COOH) can react with ethanol (CH3CH2OH) to form ethyl acetate. Equation: CH3COOH + CH3CH2OH -> CH3COOCH2CH3 + H2O
  • Other carboxylic acids can also undergo esterification to form various esters.

Decarboxylation of Carboxylic Acids

  • Decarboxylation is a reaction in which carbon dioxide (CO2) is removed from a carboxylic acid molecule.
  • This process often occurs when carboxylic acids are heated strongly or in the presence of a catalyst.
  • The result is the formation of a smaller molecule.
  • For example, when pyruvic acid (CH3COCOOH) undergoes decarboxylation, it forms acetaldehyde. Equation: CH3COCOOH -> CH3CHO + CO2
  • Other carboxylic acids can also undergo decarboxylation to form different compounds.

Concept-Based Problems

  • Now that we have covered the reaction sequences and reactions of aldehydes, ketones, and carboxylic acids, let’s solve some concept-based problems.
  • These problems will test your understanding of the reactions, reaction sequence, and applications of these organic compounds.
  • We will go through several examples and discuss the solutions step by step.
  • Make sure to grasp the concepts well before attempting these problems.
  • Let’s dive into the problems and deepen our knowledge!

Summary

  • In this lecture, we discussed the oxidation, reduction, and nucleophilic addition reactions of aldehydes, ketones, and carboxylic acids.
  • Aldehydes can be oxidized to carboxylic acids and reduced to primary alcohols.
  • Ketones cannot be oxidized but can be reduced to secondary alcohols.
  • Both aldehydes and ketones can undergo nucleophilic addition reactions.
  • Carboxylic acids can undergo esterification and decarboxylation reactions.
  • Understanding the reaction sequence and reactions of these compounds is crucial for solving concept-based problems.

Reaction Sequence of Aldehydes

  • The reaction sequence of aldehydes involves oxidation, reduction, and nucleophilic addition reactions.
  • Oxidation of aldehydes leads to the formation of carboxylic acids.
  • Reduction of aldehydes results in primary alcohols.
  • Nucleophilic addition reactions of aldehydes allow the formation of various compounds with the addition of a nucleophile.

Examples

  1. Oxidation of formaldehyde (HCHO):
    • Formaldehyde reacts with potassium permanganate (KMnO4) to form formic acid (HCOOH). Equation: HCHO + [O] -> HCOOH
  1. Reduction of acetaldehyde (CH3CHO):
    • Acetaldehyde reacts with sodium borohydride (NaBH4) to form ethanol (CH3CH2OH). Equation: CH3CHO + 2H2 -> CH3CH2OH
  1. Nucleophilic addition of formaldehyde (HCHO):
    • Formaldehyde reacts with cyanide ion (CN-) to form a cyanohydrin. Equation: HCHO + CN- -> HCOH(CN)

Reaction Sequence of Ketones

  • The reaction sequence of ketones involves reduction and nucleophilic addition reactions.
  • Ketones cannot be oxidized to carboxylic acids.
  • Reduction of ketones leads to the formation of secondary alcohols.
  • Nucleophilic addition reactions of ketones allow the formation of various compounds with the addition of a nucleophile.

Examples

  1. Reduction of acetone (CH3COCH3):
    • Acetone reacts with sodium borohydride (NaBH4) to form isopropanol (CH3CHOHCH3). Equation: CH3COCH3 + H2 -> CH3CHOHCH3
  1. Nucleophilic addition of acetone (CH3COCH3):
    • Acetone reacts with a Grignard reagent (RMgX) to form a tertiary alcohol. Equation: CH3COCH3 + R-MgX -> CH3COCHR3

Reaction Sequence of Carboxylic Acids

  • The reaction sequence of carboxylic acids involves esterification and decarboxylation reactions.
  • Carboxylic acids can react with alcohols to form esters.
  • Decarboxylation involves the removal of carbon dioxide (CO2) from a carboxylic acid molecule.

Examples

  1. Esterification of acetic acid (CH3COOH):
    • Acetic acid reacts with ethanol (CH3CH2OH) to form ethyl acetate. Equation: CH3COOH + CH3CH2OH -> CH3COOCH2CH3 + H2O
  1. Decarboxylation of pyruvic acid (CH3COCOOH):
    • Pyruvic acid undergoes decarboxylation to form acetaldehyde. Equation: CH3COCOOH -> CH3CHO + CO2

Concept-Based Problems

  • Now let’s apply our knowledge to solve some concept-based problems related to aldehydes, ketones, and carboxylic acids.
  • These problems will test your understanding of the reaction sequences, reactions, and applications of these compounds.
  • Make sure to carefully analyze each problem and use the concepts we have discussed.
  • Let’s begin solving the problems one by one.

Problem 1

  • Identify the product formed when benzaldehyde (C6H5CHO) undergoes oxidation. Solution:
  • Benzaldehyde can be oxidized to form benzoic acid (C6H5COOH). Equation: C6H5CHO + [O] -> C6H5COOH

Problem 2

  • Predict the product formed when propanal (CH3CH2CHO) undergoes reduction. Solution:
  • Propanal can be reduced to form propanol (CH3CH2CH2OH). Equation: CH3CH2CHO + 2H2 -> CH3CH2CH2OH

Problem 3

  • A nucleophilic addition reaction occurs between butanal (CH3CH2CH2CHO) and a Grignard reagent (RMgX). Predict the product formed. Solution:
  • The nucleophile attack (RMgX) on the carbonyl carbon of butanal will result in the formation of an alcohol with an additional carbon. Equation: CH3CH2CH2CHO + R'-MgX -> CH3CH2CH2CH(R')OH
  • The product will be an alcohol with a longer carbon chain than the original butanal.