ekstraksi senyawa organik asam, basa, netral

8/10/2019 Ekstraksi Senyawa Organik Asam, Basa, Netral

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Experiment 3: Extraction: Separation of an Acidic, a Basic and a NeutralSubstance

Read pp 113-125, 131-132, Technique 11 and pp 132-141, Technique 12, in TOC.View the videos: 4.2 Extraction (Macroscale); 4.6 Drying Organic Liquids; 4.7Separation of Drying Agents (Macroscale) at the bcs.whfreeman.com/mohrig3e website

under Williamson movies.

When separating mixtures of organic compounds that have acidic or basicfunctional groups, such as carboxylic acids, phenols (acidic) and amines (basic), one canexploit the different solubility properties of their protonated and non-protonated forms.For instance, an organic acid is often insoluble in water but soluble in a less polar organicsolvent, such as ether. In a separatory funnel containing ether and water, it would residein the ether layer. When a basic solution is added to the funnel, the acidic compound isdeprotonated and becomes an ionic salt. It is now soluble in water but insoluble in ether.At this point, the de-protonated organic salt would reside in the aqueous layer. A similar"solubility switch" exists for basic organic compounds. A water insoluble organic basecan be protonated by reaction with an acidic solution and can thus move from the etherlayer into the aqueous layer in a separatory funnel.

Many of the carboxylic acids are strong enough that they can be deprotonated bya saturated solution of sodium bicarbonate, a relatively weak base. Phenols, on the otherhand, require a stronger basic solution, such as aqueous sodium hydroxide, to bedeprotonated. Hydrochloric acid is generally used to protonate amines.

The ionic forms of the acidic and basic organic compounds can be recovered fromthe aqueous solution using the same solubility switch principles. When acid is added toan aqueous solution that contains the salt of a deprotonated organic acid, the organic acidis re-protonated. In this form, it is now water insoluble and precipitates from the aqueoussolution as a solid, which can be collected by vacuum filtration. Similarly, the salt of aprotonated amine can be deprotonated by addition of base, at which point it will

precipitate from the aqueous solution and can be collected in its solid form by filtration.

In some cases, a neutral organic compound, one which has neither an acidic nor abasic functional group, is present in the mixture. Such a compound would remain solublein the non-polar organic solvent throughout any extractions with acid and base solutions.At the end of a procedure to separate the components of a mixture, the neutral compoundcan be recovered in its solid form by evaporation of the organic solvent.

The flow chart on the next page outlines a general procedure for separating acidic,basic and neutral organic compounds using the principles of the solubility switch.

You will separate a mixture that contains benzoic acid, 4-chloroaniline andnaphthalene.

C

OH

O

NH2

Cl

Benzoic acidmp 122-123

4-Chloroanilinemp 68-71

Naphthalenemp 80-82


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The 4-chloroaniline is separated first by extraction with hydrochloric acid. Since nophenolic compound is present in this mixture, two extractions with base solution are notrequired; thus, the benzoic acid could be separated from the neutral compound byextraction with either aqueous sodium bicarbonateoraqueous sodium hydroxidesolution. We have chosen to extract the acidic compound into the aqueous layer usingsodium hydroxide.

Outlinethe steps of the following procedure:

Place 3 g of the mixture in a 50 mL Erlenmeyer flask and add 30 mL ofdiethylether. Note: Diethyl ether is highly flammable! Care should be taken whenhandling this solvent. Keep away from flames and direct heat. You will need toswirl and stir the solution with a stirring rod to get everything to dissolve completely.Transfer the solution to a separatory funnel using a little ether to complete the transfer.Pour 10 mL of water into the "sep" funnel and note which layer is organic and which isaqueous. Next, add 10 mL of 3 M HCl. Stopper the funnel, invert it and open thestopcock to vent the vapors. Alternate between gently shaking the funnel and venting the

R COOH Ar OH R NH2 R H

carboxylic acid phenol amine "neutral"

Extract with HCl

R COOH Ar OH R H R NH3+

Cl

Aqueous layerOrganic layer

Extract with NaHCO3

R NH2

R COO

Na+

Ar OH R H


Extract with NaOH

Ar O

Na+R H

R COOH

Ar OH


Add NaOH

Add HCl

Add HCl

collectprecipitate

evaporatesolvent

collectprecipitate

collectprecipitate

Dissolve mixture in ether


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recrystallize the naphthalene, heat about 50 mL of a mixture of 3:1 methanol:wateralmost to the boiling point on a steam bath. Slowly, addjust enoughof the hotmixture tothe compound in the side-arm flask until it just dissolves. The side-arm flask should beheated on the steam bath during this addition of the solvent mixture. Once all of thecompound has dissolved, allow the flask to cool to room temperature then on ice, andcollect the solid by vacuum filtration on a Buchner funnel (see p. 192 in TOC, and Figure

Page, Expt. 1). Wash the crystals with water. Dispose of the filtrate, which containsmethanol, in the Laboratory Byproductsjar.

Collect the basic and acidic products in Flasks A and B by vacuum filtration on aBuchner funnel. Wash with small amounts of ice water. There will not be enough timeto recrystallize the basic and acidic compounds.

The naphthalene will sublime (change directly from the solid phase to the vaporphase) at room temperature; therefore, you should obtain the melting point and weight ofthis compound before leaving the lab. Allow all three products to dry in your drawer.Next week you will obtain the weights and melting points of the acidic and basiccompounds, and you can re-take the melting point of the neutral compound, if any is left.


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Name ______________________________ Date ____________________________

T. A. _______________________________ Lab period ________________________

Results and Calculations (to be handed in two days after the next lab period)

Calculate the percent recovery of 4-chloroaniline from the mixture.

Melting range for 4-chloroaniline __________________________

Calculate the percent recovery of benzoic acid from the mixture.

Melting range for benzoic acid ___________________________

Calculate the percent recovery of (recrystallized) naphthalene from the mixture.

Melting range for naphthalene ____________________________

Comment on your percent recoveries, citing possible reasons for either high or lowpercent recoveries (remember that the original mixture was a 1:1:1 combination of thethree compounds by weight). Comment on your melting points, citing possible reasons ifthe data indicate low purity.


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Write balanced chemical equations for all transferals of the compounds from organic toaqueous phases and for all the precipitation reactions. [Note: If a compound does notmove from one layer to another, no reaction has occurred and no equation can bewritten.] In the equations that you write, indicate the state, solid (s), liquid (l), gas (g) oraqueous (aq), of eachproductformed in the reaction. You must write out the entirestructural formula for each compound. Do not abbreviate an alkyl or aryl group with theletter R.

ekstraksi senyawa organik asam, basa, netral

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