Aldehyde,ketones and carboxylic acid

• Aldehydes and Ketones are compounds containing carbon-oxygen double bond, called carbonyl group.
• The reaction of carboxylic acids with mineral acids like H2SO4 or with P2O5 results in the formation of acid anhydrides.
• In aldehydes, the carbonyl group is bonded to a carbon and hydrogen while in ketones, it is bonded to two carbon atoms.
• The carbonyl compounds in which carbonyl group is bonded to oxygen are known as carboxylic acids, and their derivatives (e.g. esters, anhydrides).
• In compounds where carbon is attached to nitrogen and to halogens, they are called amides and acyl halides respectively.
• The general formulas of these compounds are as follows: Aldehydes and Ketones.
• The common names of most aldehydes are derived from the common names of the corresponding carboxylic acids by replacing the ending – ic acid with aldehyde.
• The position of the substituent in the carbon chain is indicated by Greek letters α, β, γ, δ, etc.
• The α-halocarboxylic acid can undergo a reaction with Cl2 and Red P to form 2-chloropropanoic acid.
• The α-halocarboxylic acid can also undergo a reaction with H2O to form CH3-CHCl-COOH + HCl.
• The α-halocarboxylic acid undergoes electrophilic substitution reactions, where the –COOH group acts as a deactivating group and meta-directing.
• α-halocarboxylic acid is represented as CH3-CH2-COOH.
• During electrophilic substitution reactions, nitration and bromination, the carboxylic acids do not undergo Friedel-Crafts reactions because the carboxyl group is deactivating and the catalyst aluminium chloride (Lewis acid) gets bonded to the carboxyl group to form salts.
• Propanoic acid is also known as 2-chloropropanoic acid.
• The common names of ketones are derived by naming two alkyl or aryl groups bonded to the carbonyl group and by suffixing ketone.
• Aldehydes and ketones add ammonia followed by elimination of a water molecule to give imines.
• Carbonyl compounds condensed with hydroxyl amine to give oximes.
• Carbonyl compounds condensed with hydrazine to give hydrazone.
• Aldehydes and ketones can be reduced to alkanes on treatment with zinc amalgam and concentrated hydrochloric acid, a process known as Clemmensen reduction.
• Carbonyl compounds condensed with semicarbazide to yield semicarbazone.
• Carbonyl compounds add amines to give substituted imines (Schiff’s bases).
• Carbonyl compounds condensed with 2,4 - dinitrophenyl hydrazine to give 2,4 - dinitrophenyl hydrazone, also known as Borsches reagent.
• Carbonyl compounds condensed with phenyl hydrazine to give phenyl hydrazone.
• When reduced using sodium borohydride (NaBH 4 ) or lithium aluminium hydride (LiAlH 4 ) or H 2 in presence of Ni, Pd or Pt catalyst, aldehydes give primary alcohols, while ketones give secondary alcohols.
• The positions of the substituents in ketones are indicated by Greek letters, α α′, β β′ and so on.
• The IUPAC names of open chain aliphatic aldehydes and ketones are derived from the names of the corresponding alkanes by replacing the ending – e with ‘ – al’ and ‘ – one’ respectively.
• In case of aldehydes, the longest carbon chain is numbered starting from the carbon of the aldehyde group while in case of ketones, the numbering begins from the end nearer to the carbonyl group.
• Mild oxidising agents like CrO3, Tollens’ reagent and Fehlings’ reagent can also oxidise aldehydes.
• The aldol or ketol on heated undergo dehydration to give α,β-unsaturated aldehyde or ketone.
• This reaction is called Aldol condensation.
• During this reaction carbon-carbon bond cleavage occurs.
• The name aldol or ketol is used for the product formed.
• This reaction does not affect a carbon-carbon double bond, if present in the molecule.
• Aldehydes and ketones having at least one α-hydrogen atom when treated with dilute alkali, we get β-hydroxy aldehydes (aldol) or β-hydroxy ketones (ketol) respectively.
• Carbonyl group can also be reduced to methylene group, by treating with hydrazine followed by heating with sodium or potassium hydroxide in high boiling solvent such as ethylene glycol.
• Aldehydes are easily oxidised to carboxylic acids on treatment with common oxidising agents like nitric acid, potassium permanganate, potassium dichromate etc.
• Aldehydes or ketones having CH3CO- group or CH3CHOH- group, when treated with sodium hypohalite or halogen in presence of NaOH, we get a haloform (CHX3).
• During this reaction, the methyl group is converted to haloform.
• Ketones when oxidised using strong oxidising agents and at high temperatures, we get a mixture of carboxylic acids having lesser number of carbon atoms.
• The product formed contains both aldehydic (ketonic) and alcoholic group.