In an Organic Chemistry experiment, where the purpose is to purify commercial ch
ID: 1004600 • Letter: I
Question
In an Organic Chemistry experiment, where the purpose is to purify commercial cholesterol using bromination and debromination, what is the purpose of washing in the debromination steps of each of the compounds in the procedure below:
1. add diethyl either, acetic acid and zinc dust (what is the purpose of each?)
2. stir, wait for white ppt to form
3. add water (why?)
4. Decant solution, put untreated zinc in waste
5. add 5 mL of ether to solution (why??)
6. add 2 mL of water (Why?) and shake
7. pipette out organic layer
8. add 1 mL of 3M sodium hydroxide to organic layer (WHY), cap, shake and pipette out organic layer
9. add 1mL of saturated NaCl to organic layer (WHY), cap, shake and pipette out.
10. add cacl2 pellets
11.add 1mL of methanol (WHY) to solution
12. recrystallize solution and collect crystals.
Explanation / Answer
1) Diethyl ether to be added to get our organic ( product) in upper layer (extraction) and acetic acid in zinc is to be added to remove the bromine from product , in acidic media it forms zinc bromine complex and it forms ppt. or goes into the aqueous layer when addition of water.
2) stirr , wait for white ppt . to form , (zinc bromine complex ppt),
3) add water because formation of two layers ,the complex will goes into the aqueous layer.
4) decant solution because unreacted zinc (solid) will be kept at bottom and removed)
5) addition of 5 ml ether to the solution because extraction of more organic product to the upper layer.
6) addition of 2 ml water because washing of inorganic from organic layer and it will goes to aq. layer,
7) pippete out organic layer ( it contains our product),
8) addition of NaoH Solution to remove excess acid used in the starting (most od if goes to aq. layer) but remaining present in upper layer will be removed by forming salt and goes to lower layer.
9) ADDITION OF 1 ML saturated NaCl to organic layer because to become solution more saturated and most of the organic is extracetd from aq. layer,
10) CaCl2 Pellets to be added to remove moisture (water) content, that is for drying.,
11) addition of one ml methanol to the solution (it must be the solvent for crystallisation).
12) recrystallisation of solution to get pure crystals.
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