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Wednesday, December 12, 2012

Hydration Reaction of Alkenes - Reaction of Organic Chemistry

Hydration Reaction of Alkenes

In organic chemistry, hydration reaction is used to produce alcohol from alkene. And it is very useful to produce cyclohexanol from cyclohexene in industrial chemistry.

Total Reaction

Mechanism

Side Reaction



Chemical
1. Potassium carbonate anhydrous: ~2g
2. Cyclohexene: 4.100g
3. Diethyl ether: 10mL
4. NaCl: 10g
5. Sulfuric acid: 4mL

Procedure
1.      Take 1.7mL water into a flask and add 3.5mL sulfuric acid in the water carefully.
2.      Put the flask in ice bath
3.      Add 4.100g cyclohexene and stopper the flask
4.      Shake the flask vigorously for 10 minutes until the mixture no longer form two phase when standing. Stand the flask for about 30 minutes.

 The mixture would turn dark brown

5.      Use 60mL water to transfer the mixture into a distillation flask.


 Color was changing when added water into the mixture

6.      Distillate the mixture and collect 35~50mL distillate


 Some unreacted cyclohexene(the upper layer) will be distillated at this step
 
 A part of cyclohexene was carbonated during distillation process

7.      Add 10g NaCl into distillate

 The mixture looks very turbid because of cyclohexanol separate in water

8.      Use 10mL to extract the solution twice

 
9.      Collect the organic layer and add some potassium carbonate anhydrous to remove the water inside

 Potassium carbonate anhydrous is not only as desiccant but it could 
also react with the sulfuric acid which might be distillated from the solution

10.  Separate potassium carbonate from the solution
11.  Distillate the solution again to remove diethyl ether and cyclohexene


 12.  Test the refractive index of the final product to determine the purity.

Experimental Record


Theory weight of cyclohexanol
4.940 g
Weight of cyclohexanol
1.450 g
Yield
29.4%
nD20 (theory)
1.4641
nD20
1.4613




9 comments:

  1. hi, what is the concentration for sulfuric acid u used, thank you.
    syuhada, malaysia.

    ReplyDelete
    Replies
    1. It's 98% sulfuric acid 3.5~4.0mL and diluted with 1.7mL of water.

      Delete
  2. thank you =)
    syuhada, malaysia.

    ReplyDelete
  3. 1. at what point do u add diethyl ether?
    2. i would like to carry out hydration for used cooking oil (free fatty acid), what are the things u suggest i should consider?

    ReplyDelete
    Replies
    1. 1. Add the diethyl ether to extract at step 8. .
      2. Do you mean you want to hydrate the alkene on the unsaturated fatty acid? If so, you should not distill extraction because the high boiling of fatty acid. You should only vaporize the solvent(ether) with a rotavapor or heat the extraction gently and carefully(use electric heater, never use flame. It may cause fire because ethyl ether is highly flammable).

      Delete
  4. can this procedure be useful for other alkenes also?

    ReplyDelete
  5. why did you have to use NaOH?

    ReplyDelete