The current experiment is a combination of various different parts of organic chemistry experimental syllabus. It integrates functional group analysis, separation of a mixture and regeneration of the components on the basis their functional group/s, skills related to synthesis and thin layer chromatography. The experiment tests the students on some known skills and some new skills are learnt in the process of carrying out the experiment.

Prerequisite:Theory

Identification functional group.

Qualitative separation analysis

Aldol reactions conditions and important parameters

Stoichiometric calculations involved in organic reactions

Techniques and Skills

Quantitative separation of components in a mixture

Slow addition of one solution to another with stirring

Filtration of product using suction

Thin Layer Chromatorgraphy (A-guide-to-thin-layer-chromatography-technique)

Further reading

https://en.wikipedia.org/wiki/Dibenzylideneacetone

https://pubs.acs.org/doi/abs/10.1021/ed078p226

http://www.orgsyn.org/demo.aspx?prep=CV2P0167

 

Part I: Identification of functional groups in compounds A and B 

Droppers 4
Cavity plate 1
Chemicals
Compound A and B
Sat. NaHCO3
10% aq. NaOH
neutral FeCl3 solution
Aq. KMnO4,
ammoniacal solution of AgNO3

 

Part II: Separation of the Given Mixture of Compounds A and B

Beakers 2
Dropper (plastic) 2
Filter paper (circles) 1
Funnel 1
Glass rod 1
Measuring cylinder (10mL) 2
(25 mL) 1
Syringe (2 mL) 1
Wash Bottle 1
Chemicals
Sat NaHCO3, 30 mL
1:1 HCl, 15 mL
pH paper
Mixture of Compound A and B

Part III: Preparation of Derivative

Conical Flask 2
Cork 1
Filter paper (circle) 1
Funnel 1
Glass rod 1
Ice bath 1
Measuring cylinder (50 mL) 1
(10mL) 1
Syringe (1mL) 1
Wash Bottle 1
Chemicals
Acetone, 5 mL
Ethanol, 30 mL
NaOH, 35 mL

 

Part IV: TLC 

Beaker 1
Fusion Tubes 2
Capillary 2
TLC plate 1
Watch glass 1
Chemicals
Pet Ether and Chloroform mixture (90:10)
(solvent system for TLC)
acetone (solvent for dissolution of sample)

 

Glassware

 

Chemicals

 

 

 

Hazard Symbols

Corrosive to skin 

 Oxidizing 

Toxic 

Irritant 

Harmful to environment 

Flammable 

                     

Organic qualitative analysis, separation of compounds and preparation of derivative

Chalcones are 1,3-diphenyl-2-propene-1-one, in which two aromatic rings are linked by an aliphatic three carbon chain.  These are found in edible plants and are considered to be important in various biological compounds. It is also of great importance in pharmaceutical industry as a variety of novel heterocyclics can be designed.

Chalcones are generally coloured compounds because of the presence of the chromophore -CO-CH=CH-, which depends in the presence of other auxochromes. Chalcones and their derivatives are known for their anti-diabetic, anti-inflammatory, anti-parasitic, anti-histaminic, anti-malarial, anti-oxidant, anti-fungal properties.

The current experiment tests the student on various aspects of organic chemistry, such as functional group analysis, separation of two compounds and their regeneration, synthesis and thin layer chromatography. Some of the skills are known to the students and some skills are learnt in the process of carrying out the experiment. The students are also asked to check the purity of the product synthesized using TLC technique.

 Part I

You are expected to complete Part I of this task in the first 30 minutes and return the paper to the laboratory expert. At the end of this part, you will be given the paper for part II.

Part I: Identification of functional groups in compounds A and B 

You are given two compounds Compound A (molecular mass 122) and Compound B (molecular mass 106). Following reagents are given to you: Sat. NaHCO3, 10% aq. NaOH, neutral FeCl3 solution, aq. KMnO4, ammoniacal solution of AgNO3.

Conduct appropriate tests with the reagents provided to you and identify the functional groups present in compound A and B. Write your observations in the following table.

Part II: Separation of the Given Mixture of Compounds A and B

A mixture of compounds A and B is supplied to you in a 100 mL beaker. Add 20 mL of saturated NaHCO3 solution to this mixture and stir the solution for 5 minutes (till effervescence ceases).  Carefully, transfer the contents of the beaker to 25 mL measuring cylinder supplied to you. Use another 5 mL of saturated NaHCO3 to transfer the content completely.  Allow the two layers to separate clearly. Remove the organic layer, with the help of a syringe and transfer it to a clean 10 mL measuring cylinder. Note the volume of the organic layer (compound B). You will be using this layer for the preparation of new compound (see Part III).

Volume of the organic layer (compound B)…………………mL

Regeneration of compound A from the aqueous extract

Transfer the aqueous layer from the measuring cylinder to a 100 mL beaker. Add 50% HCl solution in small lots to the beaker with stirring till the solution is distinctly acidic (use pH paper). Note the volume of HCl added. Filter the precipitate (compound A) through filter paper. Use minimum amount of water for transferring and washing of the precipitate. The expert will collect your compound for drying.

Volume of acid needed for regeneration of compound A:…………….mL

 

The organic layer obtained in part II above (in the measuring cylinder) contains compound B, that is, benzaldehyde. You will be preparing dibenzalacetone from benzaldehyde. The reaction is presented below:

 

The density of  benzaldehyde = 1.04 g cm3 and that of acetone =  0.787 g cm3.

Using the reaction given above and the density data, calculate the volume of acetone needed to be added for the preparation.

Volume of acetone needed for derivative preparation:…………………mL

 

Part III: Preparation of Dibenzalacetone from benzaldehyde

To the organic layer in measuring cylinder, add the volume of acetone calculated by you with the help of a syringe supplied to you (Keep the tip of the needle of the syringe immersed in the organic layer while adding the acetone). Add 3 mL of ethyl alcohol to the same flask. In another conical flask, take 30 mL of 10 % NaOH and add 24 mL of ethanol to it.  Stir the contents and keep the flask in ice bath for 5 minutes. With help of a syringe (used for transferring organic layer in part II), add half the quantity of benzaldehyde-acetone-ethanol mixture. Keep shaking the flask intermittently for about 15 minutes, without removing it from the ice bath. After this, transfer the remaining portion of benzaldehyde-acetone-ethanol mixture. Keep shaking the flask intermittently for another 15 minutes.  Filter the product using suction filtration and wash it with 50 mL of water.

Part IV: TLC

Procedure for TLC

Dissolve a drop of benzaldehyde in a small quantity of acetone in a sodium fusion tube. Similarly prepare a solution of your product.  Obtain a TLC plate from a laboratory expert. Draw a faint line, at a distance of about 1cm from the edge of the plate. Using a thin capillary tube, place a drop of the benzaldehyde solution on the line drawn on the plate. Allow it to dry. Then in a similar manner, spot the product solution on the same plate. Take care that the two spots do not merge into one another.  Allow this spot also to dry.  Then place the plate in the beaker, containing the eluent (supplied to you). Cover the beaker with a watch glass, and allow the solvent to rise appreciably (approximately 1 cm away from the top).  Remove the plate from the beaker and mark the solvent front immediately. Mark the spots after exposing the plate to UV light (laboratory expert will help you for UV chamber). Calculate the Rf values using the formula given below and record the results.

a) Rf of benzaldehyde:

b) Rf of dibenzalacetone:

Part II

Mass of the empty butter paper:………………..g

Mass of butter paper + compound A:………….g

Mass of compound A:……………g

Part III

Mass of the empty butter paper……………g

Mass of butter paper + dibenzalacetone………….g

Mass of dibenzalacetone………………..g

(a)        Colour of dibenzalacetone……………….

(b)        Appearance (tick the correct option)

Crystalline ………                              Amorphous…………

Calculate:

(a)        Theoretical yield on the basis of the mass of benzaldehyde

(b)        The yield obtained as a percentage of theoretical yield.

 

Why is the reaction in Part III carried out in an alkaline medium?

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