Aldehydes, Ketones & Carboxylic Acids

  • Common names of different aldehydes and ketones

Aldehydes

  • Aldehydes have the general formula R-CHO
  • Common examples of aldehydes:
    • Formaldehyde (HCHO)
    • Acetaldehyde (CH3CHO)
    • Benzaldehyde (C6H5CHO)
  • Aldehydes are named by replacing the “-e” ending of the parent alkane with “-al”
  • For example, methane becomes methanal

Ketones

  • Ketones have the general formula R-CO-R
  • Common examples of ketones:
    • Acetone (CH3-CO-CH3)
    • Propanone (CH3-CO-CH3)
    • Butanone (CH3-CO-C2H5)
  • Ketones are named by replacing the “-e” ending of the parent alkane with “-one”
  • For example, ethane becomes ethanone

IUPAC Naming of Aldehydes and Ketones

  • IUPAC names are based on the longest continuous chain of carbon atoms
  • The carbonyl group is assigned the lowest possible number in the chain
  • Aldehydes are given the suffix “-al” and ketones are given the suffix “-one”
  • Numbering of the chain starts from the end nearest to the carbonyl group
  • Examples:
    • Methanal (formaldehyde)
    • Ethanal (acetaldehyde)
    • Propanone (acetone)

Common Names of Aldehydes and Ketones

  • Some aldehydes and ketones have common names that are widely used
  • Acetone is commonly known as propanone
  • Formaldehyde is commonly known as methanal
  • Acetaldehyde is commonly known as ethanal
  • Common names are often used in various industries and everyday life

Oxidation of Aldehydes

  • Aldehydes can be oxidized to form carboxylic acids
  • In the presence of an oxidizing agent, the aldehyde is converted to the corresponding carboxylic acid
  • For example, ethanal can be oxidized to ethanoic acid
  • The common oxidizing agent used is acidified potassium dichromate (K2Cr2O7)

Reduction of Aldehydes

  • Aldehydes can be reduced to primary alcohols
  • In the presence of a reducing agent, the aldehyde undergoes reduction to form the corresponding alcohol
  • For example, ethanal can be reduced to ethanol
  • The common reducing agents used are sodium borohydride (NaBH4) and lithium aluminum hydride (LiAlH4)

Nucleophilic addition reactions of Aldehydes

  • Aldehydes undergo nucleophilic addition reactions
  • A nucleophile attacks the carbon of the carbonyl group, resulting in the addition of a new group
  • Examples of nucleophiles:
    • Cyanide ion (CN-)
    • Grignard reagents (RMgX)
    • Hydroxide ion (OH-)

Nucleophilic addition reactions of Ketones

  • Ketones also undergo nucleophilic addition reactions
  • The process is similar to aldehydes, where a nucleophile adds to the carbon of the carbonyl group
  • Examples of nucleophiles:
    • Organometallic reagents (RMgX)
    • Alcohols
    • Amines

Acidity of Carboxylic Acids

  • Carboxylic acids are weak acids
  • They can donate a proton (H+) and form a carboxylate ion (RCOO-)
  • Acidity increases with the electronegativity of the substituents attached to the carboxyl group
  • Stronger acids have a more stable carboxylate ion
  • Examples:
    • Methanoic acid (HCOOH)
    • Ethanoic acid (CH3COOH)
  1. Common Names of Aldehydes and Ketones
  • Some common names for aldehydes include:
    • Formaldehyde (HCHO) - used as preservative and in resin production
    • Acetaldehyde (CH3CHO) - used in chemical manufacturing and as flavoring agent
    • Benzaldehyde (C6H5CHO) - used in perfumes and flavoring agents
  • Common names for ketones include:
    • Acetone (CH3COCH3) - widely used as a solvent and nail polish remover
    • Acetophenone (C6H5COCH3) - used in the synthesis of pharmaceuticals and fragrances
  1. IUPAC Naming of Aldehydes and Ketones
  • IUPAC names are based on systematic rules for nomenclature
  • The longest continuous chain containing the carbonyl group is selected as the parent chain
  • The carbonyl carbon is assigned the lowest possible number, indicated by the “-al” or “-one” suffix
  • Examples:
    • Methanal (formaldehyde) - IUPAC: methanal
    • Ethanal (acetaldehyde) - IUPAC: ethanal
    • Propanone (acetone) - IUPAC: propanone
  1. Oxidation of Aldehydes
  • Aldehydes can be oxidized to form carboxylic acids
  • The reaction involves the loss of hydrogen from the carbonyl group and the gain of oxygen
  • Common oxidizing agents used include acidified potassium dichromate (K2Cr2O7) or Tollens’ reagent (Ag(NH3)2+)
  • Example: Ethanal (CH3CHO) oxidized to ethanoic acid (CH3COOH)
  1. Reduction of Aldehydes
  • Aldehydes can be reduced to primary alcohols
  • Reduction involves the addition of hydrogen to the carbonyl group
  • Common reducing agents used include sodium borohydride (NaBH4) or lithium aluminum hydride (LiAlH4)
  • Example: Ethanal (CH3CHO) reduced to ethanol (CH3CH2OH)
  1. Nucleophilic Addition Reactions of Aldehydes
  • Aldehydes undergo nucleophilic addition reactions
  • Nucleophiles attack the carbon of the carbonyl group, breaking the double bond
  • Examples of nucleophiles include:
    • Cyanide ion (CN-)
    • Grignard reagents (RMgX)
    • Hydroxide ion (OH-)
  • Products formed depend on the nature of the nucleophile and the reaction conditions
  1. Nucleophilic Addition Reactions of Ketones
  • Ketones also undergo nucleophilic addition reactions
  • The process is similar to aldehydes, where a nucleophile adds to the carbon of the carbonyl group
  • Examples of nucleophiles include:
    • Organometallic reagents (RMgX)
    • Alcohols
    • Amines
  • The products formed depend on the nature of the nucleophile and the reaction conditions
  1. Acidity of Carboxylic Acids
  • Carboxylic acids are weak acids due to the presence of the carboxyl group (-COOH)
  • They can donate a proton (H+) and form a carboxylate ion (RCOO-)
  • Acidity increases with the electronegativity of the substituents attached to the carboxyl group
  • Examples of carboxylic acids:
    • Methanoic acid (HCOOH)
    • Ethanoic acid (CH3COOH)
    • Benzoic acid (C6H5COOH)
  1. Reactivity of Carboxylic Acids
  • Carboxylic acids undergo various reactions due to the presence of the carboxyl group
  • They can undergo esterification reactions with alcohols to form esters
  • They can also react with bases to form carboxylate salts and water
  • Carboxylic acids can undergo decarboxylation under certain conditions, producing carbon dioxide and an organic compound
  1. Preparation of Carboxylic Acids
  • Carboxylic acids can be prepared through various methods:
    • Oxidation of primary alcohols or aldehydes
    • Hydrolysis of nitriles
    • Oxidation of alkylbenzenes
  • Each method has its own set of reaction conditions and limitations
  1. Uses of Aldehydes, Ketones & Carboxylic Acids
  • Aldehydes and ketones are commonly used as solvents, reagents, and intermediates in organic synthesis
  • Formaldehyde is used in the production of resins and plastics
  • Acetone is widely used as a solvent in many industries, including nail polish remover
  • Carboxylic acids are used as preservatives, flavoring agents, and in the production of soaps and detergents
  1. Reactions of Aldehydes
  • Aldehydes can undergo various reactions due to the presence of the carbonyl group
  • They can react with nucleophiles to form addition products
  • They can also undergo oxidation and reduction reactions
  • Examples of reactions:
    • Nucleophilic addition reactions (cyanohydrin formation)
    • Oxidation to carboxylic acids
    • Reduction to primary alcohols
  1. Reactions of Ketones
  • Ketones can also undergo similar reactions as aldehydes
  • They react with nucleophiles to form addition products
  • Ketones can be oxidized to form carboxylic acids
  • Reduction of ketones leads to the formation of secondary alcohols
  • Examples of reactions:
    • Nucleophilic addition reactions (hydration)
    • Oxidation to carboxylic acids
    • Reduction to secondary alcohols
  1. Esterification Reactions
  • Carboxylic acids can undergo esterification reactions with alcohols
  • Esterification involves the formation of an ester and water
  • A strong acid catalyst is often used to promote the reaction
  • Examples of esterification reactions:
    • Ethanoic acid + methanol → methyl ethanoate + water
    • Propanoic acid + ethanol → ethyl propanoate + water
  1. Hydrolysis of Esters
  • Esters can be hydrolyzed in the presence of an acid or a base
  • Acid-catalyzed hydrolysis results in the formation of carboxylic acid and alcohol
  • Base-catalyzed hydrolysis gives carboxylate ion and alcohol
  • Examples of ester hydrolysis:
    • Methyl ethanoate + water (acid-catalyzed) → ethanoic acid + methanol
    • Ethyl propanoate + sodium hydroxide (base-catalyzed) → sodium propanoate + ethanol
  1. Nucleophilic Acyl Substitution
  • Carboxylic acids and their derivatives undergo nucleophilic acyl substitution
  • A nucleophile replaces the leaving group on the carbonyl carbon of the carboxylic acid derivative
  • Examples of nucleophilic acyl substitution:
    • Hydrolysis of acid halides, acid anhydrides, and esters
    • Formation of amides from acid chlorides and amines
  1. Decarboxylation of Carboxylic Acids
  • Carboxylic acids can undergo decarboxylation under certain conditions
  • Decarboxylation involves the removal of a carboxyl group as carbon dioxide
  • It often requires heating or a catalyst
  • Examples of decarboxylation reactions:
    • Benzoic acid → benzene (with heating and a catalyst)
    • Pyruvic acid → acetaldehyde (with heating)
  1. Electrophilic Aromatic Substitution
  • Carboxylic acids can undergo electrophilic aromatic substitution reactions
  • The carboxyl group activates the aromatic ring towards electrophilic substitution
  • Examples of electrophilic aromatic substitution with carboxylic acids:
    • Benzoylation of benzene to form phenyl benzoate
  1. Chemical Tests for Aldehydes and Ketones
  • Aldehydes and ketones can be distinguished using various chemical tests
  • Tollens’ test: Detection of aldehydes, where silver mirror formation indicates the presence of an aldehyde
  • Fehling’s test: Detection of reducing sugars, including aldehydes, where the formation of a red precipitate or color change indicates the presence of an aldehyde or ketone
  • 2,4-Dinitrophenylhydrazine (DNPH) test: Formation of a yellow to orange precipitate indicates the presence of an aldehyde or ketone
  1. Chemical Tests for Carboxylic Acids
  • Carboxylic acids can be identified using specific chemical tests
  • Sodium bicarbonate test: Effervescence (bubbling) due to the release of carbon dioxide gas indicates the presence of a carboxylic acid
  • Ester formation test: Reacting a carboxylic acid with an alcohol in the presence of an acid catalyst produces an ester
  • Neutralization reaction: Carboxylic acids react with bases to form carboxylate salts and water
  1. Applications of Aldehydes, Ketones, and Carboxylic Acids
  • Aldehydes are used in the production of resins, plastics, and pharmaceuticals
  • Ketones have applications as solvents, flavors, fragrances, and pharmaceutical intermediates
  • Carboxylic acids find use as preservatives, flavoring agents, and in the production of soaps and detergents
  • Various derivatives of aldehydes, ketones, and carboxylic acids also have important applications in different industries