Question

Acid/Base Extraction

ACID/BASE EXTRACTION Provide a flow chart detailing the acid/base extraction/separation of the compounds shown below. Your answer must employ the following reagents: methylene chloride, hydrochloric acid (1M & 6M), sodium hydroxide (1M & 6M), 10% sodium bicarbonate (aq). Clearly indicate the product(s) and layers formed following each step of your separation scheme. HINT: phenol is soluble in sodium hydroxide solution but insoluble in neutral water or sodium bicarbonate solution. Benzoic acid is soluble in both sodium hydroxide and sodium bicarbonate solutions Use skeletal structures only in your answers: 1. COOH он NH Benzoic acid Phenol Naphthalene aniline 2. During your extraction, you become confused as to which layer is the organic and which is the aqueous. how would you identify them experimentally? 3. Identify which of the following solvents in each pair would constitute the "lower" in a liquid/liquid extraction solution. if layer separation would not be observed, indicate this by stating "miscible." . Ethanol and diethyl ether: . Ethyl acetate and 1M HCL solution (aq): Would it make any difference if the methylene chloride solution containing both the acidic and neutral components was washed with 1M hydrochloric acid rather than 1M solution hydroxide? If so, what would that difference be? Would any layer separation be possible in the solution> would it be possible to isolate the two components from one another using 1M hydrochloric acid rather than 1M sodium hydroxide? Why or why not? 4.

Answer 1

1)

OH i)Dissolve in DCM e*l + Anilin Q)H Se VRovS nIc ha ha Nt

2) Thin layer chromatography is a reliable separation technique that displays individual components of a mixture, separated according to their affinities towards the stationary phase and the compounds' varying solubilities in the mobile phase used. Taking a reference solution containing one of the compounds in the mixture each, using TLC, one can compare the "spots" present in the reference solution to those in the layer taken. The spots that have moved to the same height are identical compounds. This way, from the flow chart, one can primarily determine what compound is expected in the organic layer and check its presence in the unknown liquid layer through TLC.

3) The miscibility of solvents depends on how drastically the intermolecular forces present in the two pure solvents differ.

In case of ether and ethanol, ethanol possesses considerable degree of H-bonding and van der Waals forces while ether has only the latter. But, the oxygen atom of ether is capable of forming H-bonding with ethanol, with the latter's hydrocarbon part also reciprocating ether by its van der Waals forces. This results in the two solvents being in an almost similar environment when mixed, allowing them to be miscible.

In case of ethyl acetate and 1 M HCl, the presence of polar hydrogen chloride in water causes the highly polar water molecules to solvate the ions extensively, thereby increasing the solvent's polarity. Water is a small molecule with an extensive network of H-bonding holding the molecules together while ethyl acetate is a non-polar organic ester which relies on van der Waals forces. Though there is one site for H-bonding in the ester - its carboxyl C=O oxygen, the predominant hydrocarbon part minimizes the interactions possible for the ester with water. So, both the solvent end up having radically different IMFs and so are not miscible. When it comes to which solvent stays above which one, the density of the immiscible solvent decides it. The solvent with a higher density stays below the solvent with a relatively lower density. In this case, ethyl acetate being less dense than 1 M HCl stays above the HCl layer.

4) The extraction technique for separation of acidic, basic and neutral compounds from a mixture relies solely on the compounds' ability to react with acids and bases added, uniquely and form water-soluble salts of the respective compounds, allowing them to be neutralized in the aqueous layers individually and obtained in their pure form.

If a mixture of acidic and neutral compound is washed with HCl instead of NaOH, unlike in the case of latter, no sodium salt of the acid forms and goes into the aqueous layer. Instead, both the acidic and neutral compounds remain in the DCM layer itself, affording no separation.

Irrespective of a basic or acidic solution, DCM is always immiscible with water. So, even if the mixture is washed with HCl solution, the two liquid layers will stay immiscible.