- Methanol (Formaldehyde): Formaldehyde is completely
miscible in water. The aqueous solution of formaldehyde is commercially
sold as formalin. Formalin has a characteristic smell. It is used as a
disinfectant and as a preservative to preserve biological samples.
- Ethanal (Acetaldehyde): Acetaldehyde is
commercially prepared by using Wacker process.
H2C = CH2 + PdCl2 + H2O CH3CHO
+ Pd + 2HCl
It is used in the manufacture of acetic acid and acetic anhydride.
- Uses of Other Aldehydes: As aldehydes are often
sweet smelling, volatile liquids; they are generally used in perfumes
and as flavouring agents. For example,
3-phenyl-2-propenal (cinnamaldehyde) is used
as cinnamon flavour. 3- Methaoxy-4- hydroxy benzaldehyde
(vanillin) is used as vanilla flavour.
- Propanone (Acetone): Acetone is used as a
solvent. For example, during the manufacture of artifical
fibres (like NYLON), the cellulose acetate is
dissolved in acetone.
- Uses of Other Ketones: Like aldehydes, ketones are also sweet smelling liquids. Hence, they
are also used as flavouring agents. For
example, Carvone has a spearmint flavour and Menthone has
- Preparation of Aldehydes and Ketones by
Catalytic Dehydrogenation of Alcohols: Aldehydes are
obtained by heating primary alcohols with Cu/Fe metal at 575 K.
R - CH2OH
RCHO + H2
- Ketones are obtained by heating
secondary alcohols with Cu metal at 575 K.
- Isomerism: Aldehydes
exhibit tautomerism optical and chain
isomerism. They are functional isomers of ketones.
Ketones exhibit tautomerism,
chain, position and optical isomerism. They are functional isomers of aldehydes.
- Tautomerism: The tautomers
are two structural isomers which can be mutually interconverted
by migration of a proton. Example: acetone.
- Fehling's Solution: It is a blue coloured alkaline solution of cupric ion and
Rochelle salt (Sodium Potassium tartarate).