--%>
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 : What are isotonic and hypotonic

    The two solutions which are having equivalent osmotic pressure are called isotonic solutions. The isotonic solutions at the same temperature also have same molar concentration. If we have solutions having different osmotic pressures then the solution having different

    		•
  • Q : Raoults law Give me answer of this

    Give me answer of this question. Provide solution of this question. Which one of the following is the expression of Raoult's law: (a) P-P1/P = n/n+N (b) P1-P/P = N/ N+n (c)P-P2/P1= N/ N-n (d) P1-P/P2= N-n/N

    		•
  • Q : How haloalkanes are prepared from

    Alkyl halides can be prepared from alkanes through substitution and from alkenes through addition of halogen acids or through allylic substitution.    From alkanesWhen alkanes are treated with halogens, chlo

    		•
  • Q : Determining mole fraction of water in

    A mixture has 18 g water and 414 g ethanol. What is the mole fraction of water in mixture (suppose ideal behaviour of mixture): (i) 0.1  (ii) 0.4  (iii) 0.7  (iv) 0.9 Choose the right answer from abo

    		•
  • Q : Problem on molarity-normality-molality

    Can someone please help me in getting through this problem. The solution ofAl2(SO4)3 d = 1.253gm/m comprise 22% salt by weight. The molarity, normality and molality of the solution is: (1) 0.805 M, 4.83 N, 0.825 M (2)

    		•
  • Q : Coordination compounds discuss the

    discuss the practical uses of coordination compounds, give reactions involves and explain whats happening in the process

    		•
  • Q : Molarity based question Help me to

    Help me to solve this problem. 4.0 gm of NaOH are contained in one decilitre of solution. Its molarity would be: (a) 4 M (b)2 M (c)1 M (d)1.5 M

    		•
  • Q : Difference in Mendeleevs table and

    Briefly describe the difference in the Mendeleev’s table and modern periodic table?

    		•
  • Q : Solutions The relative lowering of

    The relative lowering of vapour pressure of 0.2 molal solution in which solvent is benzene

    		•
  • Q : Vapour pressure of benzene Give me

    Give me answer of this question. The vapour pressure of benzene at a certain temperature is 640mm of Hg. A non-volatile and non-electrolyte solid weighing 2.175g is added to 39.08g of benzene. The vapour pressure of the solution is 600,mm of Hg . What is the mo

    		•