Aldehyde Functional Group
Aldehyde Functional Group
Aldehyde:
Aldehydes are characterised by the presence of carbonyl group > C = O in their molecules. Aldehydes contain group RCHO . It is formed by the oxidation of alcohol.
Formaldehyde or Methanal (HCHO) : -
Formaldehyde is the first member of the aldehyde series. It is present in green leaves of plants where its presence is supposed to be due to the reaction of with water in presence of sunlight and chlorophyll.
Preparation :
- It can be prepared by the following methods :
(i) By oxidation of methly alcohol : - The oxidation is done either by oxygen in presence of a catalyst like platinised asbestos or copper at or by acidified potassium dichromate.
(ii) By dehydrogenation of methyl alcohol : Vapours of methyl alcohol are passed over copper or silver at when hydrogen is eliminated with the formation of formaldehyde.
(iii) By heating calcium formate : Dry calcium formate is strongly heated to obtain formaldehyde.
Calcium formate Formaldehyde
(iv) By ozonolysis of ethylene : Ethylene is dissolved in an organic solvent such as chloroform or carbom tetrachloride and a stream of ozonised oxygen is passed. The ozonide formed is decomposed by passing hydrogen in presence of palladium as catalyst.
Physical Properties
Which of the following are correct : (a) Aldehyde is colourless, pungent smelling gas. (b) Aldehydes contain group RCHO . (c) Aldehyde is formed by the oxidation of alcohol. | |||
| Right Option : D | |||
| View Explanation | |||
_________________________ is the first member of the aldehyde series. | |||
| Right Option : D | |||
| View Explanation | |||
Which of the following are correct : (a) Vapours of methyl alcohol are passed over copper or silver at (b) Aldehydes are characterised by the presence of carbonyl group > C = O in their molecules. (c) Dry calcium formate is strongly heated to obtain formaldehyde. | |||
| Right Option : D | |||
| View Explanation | |||
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