Formaldehyde
Aldehydes are family of carbonyl compounds. An aldehyde has an R group (which can be an alkyl or hydrogen substituent) on one side of the carbonyl carbon and hydrogen on the other. Formaldehyde is the simplest aldehyde. It was used as a preservative but is used less now because it is thought to be carcinogenic. It is the starting material for many reactions.
Preparation of aldehydes:
By oxidation of alcohols:
Aldehydes are generally prepared by oxidation of primary alcohols. Oxidation of primary alcohols in presence of oxidizing agents
like K2Cr2O7/H2SO4, KMnO4, CrO3 gives aldehydes.
Ozonolysis of Alkenes
From hydrocarbons:
By ozonolysis of alkenes:
Ozonolysis of alkenes followed by reaction with zinc dust and water gives aldehydes, ketones or a mixture of both depending
on the substitution pattern of the alkene.
Preparation of Aromatic Aldehydes:
Aromatic aldehydes (benzaldehyde and its derivatives) are prepared from aromatic hydrocarbons by the following method:
Chromyl chloride is suitable reagents that convert the methyl group to an intermediate chromium complex, that is difficult to oxidize further, this intermediate on hydrolysis gives corresponding benzaldehyde. This reaction is called Etard reaction.
Formalin(40%) solution used to preserve biological specimens.
Uses
- In chemical industry aldehydes and ketones are used as solvents, starting materials and reagents for the synthesis of other products.
- Formaldehyde is well known as formalin (40%) solution used to preserve biological specimens and to prepare bakelite, urea formaldehyde glues and other polymeric products.
- Acetaldehyde is used primarily as a starting material in the manufacture of acetic acid, ethyl acetate, vinyl acetate, polymers and drugs.
- Benzaldehyde is used in perfumery and in dye industries