Formaldehyde

formaldehyde

source : study.com

source : slideshare.net

formaldehyde : Methods of preparation –

1. By the oxidation of CH₃OH:

This oxidation is done either by O₂ in presence of a platinized asbestos catalyst or by acidified K₂Cr₂O₇.

2CH₃OH (methyl alcohol) + O₂ ——>  2 HCHO (Formaldehyde) + 2H₂O (at 300 – 400 ^oC)

CH₃OH + (O) ———–> HCHO + H₂O (in presence of K₂Cr₂O₇ + H₂SO₄)

2. By dehydrogenation of CH₃OH :

Vapors of CH₃OH are passed over Cu or Ag at 300 -400 ^oC then H₂ is eliminated with the formation of HCHO.

CH₃OH ———> HCHO + H₂

3. By heating Calcium formate: HCHO is formed.

 

4. From formic acid — By passing vapours of formic acid over heated MnO catalyst at 300⁰C, formaldehyde is formed.

HCOOH +HCOOH ——>HCHO +CO₂+H₂O

 

Lab Preparation :

source : prepchem.com

HCHO is prepared in laboratory by catalytic oxidation of CH₃OH. A round bottom flask is fitted with two tubes bent at right angles. One tube connects the flask with the combustion tube having platinized asbestos. The other end of the combustion tube is fitted with a tube leading into the receiver which is connected to a suction pump.

Methyl alcohol is taken in a round bottom flask which is heated on a water bath to have a temperature about 40^o C. Combustion tube is heated to redness with the help of suction pump, air is sucked in through the apparatus. Vapors of CH₃OH and air come in contact with the heated catalyst, when CH₃OH get oxidized to HCHO which is absorbed in H2O.

The condensate obtained is a mixture of HCHO, CH₃OH and water. Excess of CH3OH is removed by fractional distillation. The resulting mixture is called formalin which contains 40% HCHO , 8% CH₃OH and 52 % water.

CH₃OH + O₂ ——> HCHO + H₂O

Physical properties:

source: ipcs inchem

1. It is a colorless, pungent smelling gas.
2. It is extremely soluble in H₂O. Its solubility in water may be due to hydrogen bonding.
3. Its solution acts as an antiseptic and disinfectant.
4. It causes irritation to skin, eyes, nose and throat.

source: study.com