ternary mixture separation

Separation Of Ternary Mixture Using DCM

This can be represented as:

Liquid-liquid Extraction

     Liquid-liquid extraction involves the distribution of a substance between two immiscible liquid phases. The two liquid phases are usually, but not always, an aqueous solution and an organic solvent. Most extraction operations in the organic laboratory are carried out in separatory funnel (Figure 1).

Distribution Coefficient

 One of the most important properties of the solvent is its solubility for a particular organic compound. In an extraction, the organic compound is distributed between two different liquid phases: the organic solvent and water. The efficiency of extraction will depend upon the solubility of the compound in the two solvents. The ratio of solubility is called the distribution coefficient (K_D). 

The magnitude of K_D is an indication of the efficiency of extraction:

The larger the value of K_D, the more efficient the extraction.

If a compound has a low K_D for a given extraction, it is better to search for a different organic solvent in which the compound is more soluble in order to do liquid-liquid extraction. If this is not feasible, doing multiple extractions can increase the amount of compound extracted.

General Experimental Considerations

 Choice of Extraction Solvent

Although water is almost always one of the liquids in the liquid-liquid extraction process, the choice of organic solvent is quite wide. A good extraction solvent needs five essential features:

• has high solubility for the organic compound.
• be immiscible with the other solvent (usually water).
• has a relatively low boiling point so as to be easily removed from the compound after extraction.
• extract little or none of the impurities and other compounds present in the mixture.
• be nontoxic, nonreactive, readily available, and inexpensive.

         
 Table 1 below shows some organic solvents used in extraction.

Table 1: Some common extraction solvents.

Thus DCM is the good solvent for ternary mixture separation, its has some advantages over other solvent like Diethyl ether these are :

• It is inflammable, so safe for use in lab.
• Very slight soluble in water, so avoid mixing in Aqu. layer
• Some what  economical cheaper than Diethyl ether.

Salting-out

To improve the extraction of organic compounds from aqueous mixtures, it is advisable to saturate the aqueous phase with a salt such as NaCl or Na₂CO₃. This phenomenon which is called salting-out has the following effects:

• Decreases the solubility of organic compounds in the saturated aqueous phase.
• Decreases the solubility of the organic and aqueous phases in each other, thus improving their separation. This is particularly useful in breaking up emulsions.

Emulsion

 In certain cases, the two immiscible phases do not separate cleanly into two distinct layers; instead, they form an emulsion. It is advisable to prevent its formation by avoiding vigorous shaking of the layers whenever an emulsion is expected to form (e.g., when alkaline aqueous solutions are extracted with chloroform or dichloromethane).

If an emulsion still forms one can often break it by:

1. Stirring the mixture gently with a glass rod.
2. Saturating the aqueous layer with a salt.
3. Centrifugation.

Drying Agents

 Since the organic solution has been extracted or washed with aqueous solutions, it will contain some water. The last traces of water have to be removed by treatment with a drying agent. Common drying agents are anhydrous inorganic salts which readily take up water to become hydrated (as shown in the equation below). At the end of the drying process, the hydrated salt is removed from the organic solutions by filtration. When dry, the organic phase becomes clear. Anhydrous CaCl₂, MgSO₄, or Na₂SO₄ are some common drying agents.

MgSO₄ +  H₂O  à MgSO₄.7H₂O

Important Precautions And Obervations taken During the Mixture Seperation :

1. Stirr  well ternary mixture after DCM addition as all DCM soluble compounds are soluble.
2. There are possibility of one, two or all three compounds are soluble or one or two compounds are insoluble in DCM.
3. Filter the tenary mixture DCM sol., Filterate contain DCM soluble compounds and Residue contain DCM insoluble compound(s).

 Analysis of DCM Soluble compounds ( Filterate)

1. Transfer the filterate in seperating funnel, there is homogeneous layer (only one Layer) appeares.
2. Now add NaHCO₃, formation of two layers (immisible), if Acid is present in given mixture then it dissolve in Sod. Bicarbonate and present in Aqous layer and other compounds are in DCM solⁿ
3. Dencity of DCM solvent is more than water, so that DCM layer appears bottom in seperating funnel and Aqu. Layer at the top.
4. Seperate the layers in seperate beakers. One Aqu. & other DCM.
5. In Aqu. Layer add Conc. HCl, if Ppt. Form or two layer formation (for Liquid)then ACID present.
6. If given organic acid is liquide then formation of two layers by addition of Conc. HCl in Aqu. Layer.
7. Now this organic mixture i.e. DCM + Phenol / Base / Neutral transfer in seperating funnel.
8. Add NaOH in funnel sheak well. Keep constant, formation of two layers (immisible), if phenol present in given mixture it soluble in NaOH and present in Aqu. Layer and other componds (Base / Neutral) present in DCM soln. i.e. in organic layer which is apperas at the bottom of seperating funnel.
9. Seperate the layers in seperate beakers. One Aqu. & other DCM.
10. In Aqu. Layer add Conc. HCl, if Ppt. Form or two layer formation then PHENOL present.
11. If given phenol is liquide then formation of two layers by addition of Conc. HCl in Aqu. Layer.
12. Now this organic mixture i.e. DCM + Base / Neutral transfer in seperating funnel.
13. Add HCl in funnel sheak well. Keep constant, formation of two layers (immisible), if base present in given mixture it soluble in HCl and present in
14. Aqu. Layer and other componds i.e. Neutral present in DCM soln. i.e. in organic layer which is apperas at the bottom of seperating funnel.
15. Seperate the layers in seperate beakers. One Aqu. & other DCM.
16. In Aqu. Layer add NaOH, if Ppt. Form or two layer formation then BASE present.
17. At last Evaporate the DCM from organic layer, NEUTRAL compound remains in the beaker that may be solid or liquid.
18. If one or two the compound(s) seperate from DCM layer, for third compound Keep the DCM solution for evaporation of DCM at any stage. 

Analysis of DCM insoluble (water soluble) compounds (Residue)

1. Residue contain One or two compounds ie. May be Acid/ Phenol/Base/ Neutral.
2. Analysis residue by taking small amount of compound in Test Tube and detect the nature.
3. Nature detection by chemical method i.e. by reacting with NaHCO₃/NaOH/ HCl first it soluble then reappears by addintion of Con. HCl / NaOH respectivally.
4. For ACID it soluble in NaHCO₃ with effervanses of CO2 and reappears by adding Con HCl.
5. For PHENOL it soluble in NaOH and reappears by adding Con HCl.
6. For BASE, it soluble in HCl and reappears by adding NaOH.
7. For seperation of two compounds in residue use flow chart of chemical method.

  List of DCM soluble and DCM insoluble compounds: