What is Paraldehyde ? Discuss its Structure, Synthesis, Properties and Uses.
Structure of Paraldehyde
Paraldehyde is a six membered cyclic trimer of acetaldehyde molecules with molecular formula C6H12O3. Paraldehyde exist as diastereomers, known as cis- and trans-paraldehyde. For each diastereomer, two chair conformers are possible. The structures-A, D and structures-B, C are conformers of cis- and trans-paraldehyde, respectively. The structures-C (a conformer of B) and structure-D (a conformer of A) are high energy conformers on steric grounds (1,3-diaxial interactions are present) and do not exist to any appreciable extent in a sample of paraldehyde.
Synthesis of Paraldehyde
The German chemist Valentin Hermann Weidenbusch et.al. synthesized paraldehyde in 1848 by the polymerization of acetaldehyde using sulfuric acid or nitric acid as a catalyst, followed by neutralization with an alkali metal carbonate or hydroxide and distillation to separate the paraldehyde from unreacted acetaldehyde and other byproducts.
The product of the reaction is depend on the temperature of the reaction. At room temperature and higher, the trimer (paraldehyde) is formed, but at lower temperatures, around −10°C, the tetramer (metaldehyde) is produced.
Properties of Paraldehyde
It is a colourless liquid, with sweet odor and boiling point is 128 °C.
It is sparingly soluble in water and highly soluble in chloroform and ethanol.
Paraldehyde slowly oxidizes in air, turning brown and producing an odour of acetic acid.
It quickly reacts with most plastics and rubber.
It regenerates acetaldehyde on distilling with conc. Sulphuric acid.
C6H12O3 → 3CH3CHO
Uses of Paraldehyde
Paraldehyde is used in resin manufacture.
It is used as a preservative.
It is used in the preparation of aldehyde fuchsine dye.
It is also used as solvent in industries.
It has been used in the treatment of epilepsy, alcoholism and certain.
It is used as a sedative, hypnotic, and anticonvulsant.
* The most common side effects of paraldehyde is gastrointestinal discomfort.