--%>
Assignment Help - homework help

Explain polyhalogen compounds with examples.

Carbon compounds containing more than one halogen atom are called polyhalogen compounds. Most of these compounds are valuable in industry and agriculture. Some important polyhalogen compounds are described as follows:

    
Dichloromethane or methylene chloride, CH3Cl2

Dichloromethane is prepared industrially by direct chlorination of methane. The mixture of CH3Cl, CH2Cl2, CHCl2 and CCl4 so obtained is separated by fractional distillation.

Properties

Dichloromethane is a sweet smelling volatile liquid and its boiling point is 313 K.

Dichloromethane harms the human central nervous system. Exposure to lower levels of dichloromethane in air can lead to slightly impaired hearing and vision. Higher levels of dichloromethane in air can cause dizziness, nauses and numbness in the fingers and toes. Direct skin contact with methylene chloride causes strong burning and mild redness to the skin. Direct contact with eyes can burn cornea.

Uses
    
Because of its low boiling point and low inflammability it is used as extraction solvent in pharmaceutical and food industries. It is also used as solvent for carrying out many organic reactions in research laboratories.
    
It is used as a metal finishing and cleaning solvent.
    
It is also used as a propellent in aerosols.
    
Trichloromethane (Chloroform), CHCl3 

Preparation
    
From methane: chloroform is manufactured by chlorination of methane in the presence of light or catalysts.
1278_polyhalogen compounds.png                                     


The mixture of CH3Cl, CH2Cl2, CHCl3 and CCl4 can be separated by fractional distillation.
    
From chloral hydrate, pure chloroform can be obtained by distilling chloral or chloral hydrate with concentrated aqueous solution or KOH solution.
                    
NaOH + CCl3CHO  1950_electrode potential.png  HCOONa + CHCl2
             
NaOH + CCl3CH(OH)2  1950_electrode potential.png  HCOOna + CHCl3 + H2O
    
Laboratory method: in this method chloroform is obtained from ethanol or acetone by reaction with a paste of bleaching powder and water.

In this reaction, bleaching powder serves as a source of chlorine which first oxidizes ethanol acetaldehyte, which is then further chlorinated to chloral. Chloral reacts with Ca(OH)2, given by CaOCl2, to give chloroform and calcium formate.

   Related Questions in Chemistry

  • Q : Explain the process of adsorption in

    The process of adsorption can occurs in solutions also. This implies that the solid surfaces can also adsorb solutes from solutions. Some clarifying examples are listed below: (i) When an aqueous solution of ethano

    		•
  • Q : Infrared Adsorption The adsorption of

    The adsorption of infrared radiation by diatomic molecules increases the vibrational energy fo molecules and gives information about the force constant for the "spring" of the molecule.;The molecular motion that has the next larger energy level spacing aft

    		•
  • Q : Preparation of ammonium sulphate Select

    Select the right answer of the question. Essential quantity of ammonium sulphate taken for preparation of 1 molar solution in 2 litres is: (a)132gm (b)264gm (c) 198gm (d) 212gm

    		•
  • Q : Significance of the organic chemistry

    Describe some of the significance of the organic chemistry in brief?

    		•
  • Q : Problem based on molecular weight

    Select the right answer of the question. Molecular weight of urea is 60. A solution of urea containing 6g urea in one litre is : (a)1 molar (b)1.5 molar (c) 0.1 molar (d) 0.01 molar

    		•
  • Q : Q what is the basicity of primary

    what is the basicity of primary secondary and tertiary amines in chlorobenzene

    		•
  • Q : Problem on solutions The 2N aqueous

    The 2N aqueous solution of H2S04 contains: (a) 49 gm of H2S04 per litre of solution (b) 4.9 gm of H2S04 per litre of solution (c) 98 gm of H2S04

    		•
  • Q : Dipole moment direction for the methanol

    Briefly describe the dipole moment direction for the methanol?

    		•
  • Q : Question based on vapour pressure While

    While a substance is dissolved in a solvent, the vapour pressure of the solvent is decreased. This results in: (a) An increase in the boiling point of the solution (b) A decrease in the boiling point of solvent (c) The solution having a higher freezing point than

    		•
  • Q : Describe the properties of the

    Briefly describe the properties of the carbohydrates?

    		•