Theory & Procedure, Preparation of Organic Compounds Class 12 Notes | EduRev

Chemistry Class 12

Class 12 : Theory & Procedure, Preparation of Organic Compounds Class 12 Notes | EduRev

The document Theory & Procedure, Preparation of Organic Compounds Class 12 Notes | EduRev is a part of the Class 12 Course Chemistry Class 12.
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Objectives

Our objectives are to prepare:

  • A sample of acetanilide from aniline.
  • A sample of dibenzal acetone.
  • A sample of p-nitro acetanilide from acetanilide.
  • A sample of 2-naphthol aniline dye.

The Theory

What is Organic Chemistry?

Organic chemistry is a branch of chemistry that deals with the study of the structure, properties, reactions and preparation of organic compounds. As carbon and hydrogen are the essential constituents of all organic compounds, they are known as hydrocarbons. Organic compounds not only contain carbon and hydrogen, but also certain other elements such as: oxygen, sulphur, nitrogen, and halogens. These are regarded as the derivatives of hydrocarbon.

Which was the first organic compound to be synthesised in the lab and by whom?

Urea was the first organic compound to be prepared in the laboratory, which was by synthesised chance. It was prepared by Friedrich Wohler, a German chemist in the year 1828. Wohler synthesised urea from an inorganic compound, ammonium cyanate.

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What is organic synthesis?

Organic synthesis is a method of preparation of organic compounds. It is concerned with the preparation of organic compounds through organic reactions.

Synthesis of some simple organic compounds.

1. Acetanilide

Acetanilide is prepared from aniline by acetylating it with acetic anhydride in the presence of glacial acetic acid. Aniline or phenylamine is a primary amine with molecular formula C6H5NH2. It is basic in nature. Acetic anhydride is an anhydride of acetic acid and acts as a source of acyl group. Aniline reacts with acetic anhydride by nucleophilic substitution reaction. The reaction between aniline and acetic anhydride is called acetylation. In this reaction, aniline acts as the nuclepohile and acyl (CH3CO-) group from acetic anhydride acts as the electrophile. Here, the hydrogen atom of –NH2 group is replaced by the acyl group. The chemical reaction is shown below.

Theory & Procedure, Preparation of Organic Compounds Class 12 Notes | EduRev

2. Dibenzal acetone

It is prepared from benzaldehyde and acetone by Claisen-Schmidt Reaction.

Claisen Schmidt Reaction is a condensation reaction between an aromatic aldehyde and an aliphatic ketone in the presence of a strong base like NaOH leading to unsaturated ketone. In this reaction, two molecules of water are eliminated.

In the preparation of Dibenzal acetone, two moles of benzaldehyde condenses with one mole of acetone. The chemical reaction is represented as follows;

Theory & Procedure, Preparation of Organic Compounds Class 12 Notes | EduRev

3.  p-Nitro acetanilide

The direct preparation of p-nitroacetanilide from aniline using a nitrating mixture is very difficult. This is because, in the presence of the nitrating mixture, the amino (-NH2) group of aniline is oxidised to the nitro (-NO2) group and forms nitro benzene.

The amino group of aniline is first protected by acylation with acetic anhydride to produce acetanilide which is then nitrated to form p-nitroacetanilide as the major product and o-nitroacetanilide as the minor product. To separate p-nitroacetanilide from this mixture, the reaction mixture is recrystallised in ethanol, so that the more readily soluble o-nitroacetanilide dissolves in ethanol and pure p-nitroacetanilide separates out.

Theory & Procedure, Preparation of Organic Compounds Class 12 Notes | EduRev

4.  2-Naphthol aniline dye

2-Naphyhol aniline dye is an azo compound and it is a scarlet red dye. It is mainly used for dyeing textiles. It contains the characteristic group. Azo compounds have an extended conjugated system and are often coloured and are used as dyes. These compounds are prepared by the reaction known as coupling reaction. 2-Naphthol aniline dye is prepared from aniline.

Aniline is first converted to diazonium salt by treating it with nitrous acid at >5oC. Nitrous acid is produced in the reaction mixture by the reaction of sodium nitrite with hydrochloric acid. The procession of conversion of aromatic primary amines into diazonium salt is known as diazotisation. This benzene diazonium compound undergoes a coupling reaction with 2-Naphthol to form 2-Naphyhol aniline dye.

Theory & Procedure, Preparation of Organic Compounds Class 12 Notes | EduRev

Learning Outcomes

  1. Students understand the concepts of organic compounds, classification of organic compounds, functional groups, substitution, addition, elimination and rearrangement reactions.
  2. Students acquire the skills to prepare:
    • Acetanilide
    • Dibenzal acetone
    • p-Nitro acetanilide
    • 2-Naphthol aniline dye 
  3. Students understand the chemicals required for the preparation of the above compounds.
  4. Students understand the theory behind the formation of acetanilide, dibenzal acetone, p-Nitro acetanilide and 2-Naphthol aniline dye.
  5. Once they understand the different steps, students can perform the experiment in the real lab more accurately and quicker.
  6. Students understand important safety precautions before using hazardous chemicals. 

A. Preparation of acetanilide from aniline

Materials Required 

  • Aniline -10ml
  • Acetic anhydride - 10ml
  • Glacial acetic acid - 10ml
  • Conical flask
  • RB flask
  • Funnel
  • Filter paper
  • Buchner funnel
  • Water condenser
  • Wire gauze
  • Tripod stand
  • Burner
  • Measuring jar

Procedure

Real Lab Procedure

  1. Take 10ml of acetic anhydride in a clean dry 250ml RB flask and add 10ml of glacial acetic acid and shake the contents thoroughly.
  2. To this mixture add 10ml of aniline and fit a water condenser.
  3. Boil this mixture over a sand bath for 10min.
  4. Pour the liquid from the RB flask into 200ml ice-cold water taken in a beaker. While adding stir the contents of the beaker vigorously using a glass rod.
  5. Filter the white precipitate formed and wash it with cold water.
  6. Recrystallisation of Acetanilide: Take the crude acetanilide in the beaker and add 50ml of a mixture of 1 volume of acetic acid and 2 volumes of water. Heat to dissolve the solid. Filter the hot solution into a conical flask and cool the filtrate in ice. Filter off the crystals of acetanilide formed and dry them by pressing them between the folds of a filter paper and measure the weight of the crystals.

Observation

The weight of acetanilide= __________ g.

Precautions

  • Handle the chemicals with care.
  • Freshly distilled aniline should be used to get good results.
  • Prolonged heating and use of excess of acetic anhydride should be avoided.
  • Reaction mixture should first cooled and then poured in ice-cold water otherwise hydrolysis of acetanilide may take place.

B. Preparation of dibenzal acetone

Materials Required

  • Benzaldehyde - 2.5ml
  • Acetone - 1ml
  • 10% NaOH solution - 5ml
  • Rectified spirit - 25ml
  • Conical flask
  • Beaker
  • Test tube
  • Funnel
  • Filter papers
  • Burner 

Procedure

Real Lab Procedure

  1. Take 2.5ml of benzaldehyde, 10ml of acetone and 25ml of rectified spirit in a conical flask. Cork the flask and shake it to obtain a clear solution.
  2. Take 5ml of 10% NaOH solution in a test tube and add this to conical flask drop by drop by shaking the flask. Maintain the temperature of the reaction mixture between 20-25oC while adding the sodium hydroxide solution.
  3. Cork the flask again and shake vigorously for about 10min, releasing the pressure time to time.
  4. Allow it to stand for about 20min at room temperature and then cool in ice water for a few minutes.
  5. Filter the yellow coloured solid and wash it with water.
  6. Recrystallisation of Dibenzal acetone: Dissolve the above yellow coloured crude solid in minimum amount of hot rectified spirit and then allow it to cool slowly. Pale yellow crystals of dibenzal acetone separate. Filter the crystals and dry them by pressing them between the folds of a filter paper, and then measure the weight of the crystals.

Observation

The weight of Dibenzal acetone = ___________ g.

Precautions

  • Handle the chemicals with care.
  • Add NaOH dropwise to the reaction mixture while shaking of the flask continously.
  • Wash the precipitate with water to remove traces of NaOH sticking to it.
  • Use minimum amount of rectified spirit to dissolve the crude sample for crystallisation.

C. Preparation of p-nitro acetanilide from acetanilide

Materials Required

  • Acetanilide- 5g
  • Glacial acetic acid- 5ml
  • Conc.sulphuric acid -10ml
  • Fuming nitric acid -2ml
  • Methylated spirit -20ml
  • Test tubes
  • Glass rod
  • Beaker
  • Buchner funnel
  • Filter paper

Procedure

Real Lab Procedure

  1. Take 5g powdered acetanilide and 5ml of glacial acetic acid in a conical flask and stir the mixture using a glass rod.
  2. Take 2ml of fuming nitric acid in a clean test tube and cool it in a freezing mixture taken in a beaker. Carefully add 2ml of conc.sulphuric acid drop by drop while constantly shaking and cooling it.
  3. Add 8ml of conc.sulphuric acid drop by drop into the conical flask containing acetanilide and glacial acetic acid and cool it in a freezing mixture. Stir the contents and wait until the temperature becomes less than 5oC.
  4. To the cooled contents in the flask, add the nitrating mixture prepared in the 2nd step, drop by drop while stirring constantly. While adding the nitrating mixture, the temperature of the mixture in the flask should not rise above 25oC. Remove the conical flask from the freezing mixture and allow it to stand for 30min at room temperature.
  5. Pour the contents of the flask into a beaker containing crushed ice. Stir it well and filter the precipitate obtained and wash it thoroughly with cold water.
  6. Recrystallisation of p-Nitro acetanilide: Dissolve the precipitate obtained above in 20ml methylated spirit. Warm it to get a clear solution. Filter the hot solution and cool the filtrate in ice. P-Nitro acetanilide is obtained as colourless crystals. Wash the crystals with cold water and then dry the crystals and measure the weight of the crystals.

Observation

The weight of p-nitroacetanilide = __________ g.

Precautions

  • Handle the chemicals with care.
  • During the addition of nitrating mixture, the temperature of the reaction mixture should not rise above 25 oC.
  • Addition of fuming nitric acid should be done drop wise.
  • Do not inhale the vapours of nitric acid as they are very corrosive in nature. Addition of nitrating mixture may preferably be done in a fume cupboard.

D. Preparation of 2-naphthol aniline dye

Materials Required

  • Aniline -4.5ml
  • sodium nitrite- 4g
  • 2-Naphthol -7g
  • conc.HCl -10ml
  • glacial acetic acid -40ml
  • Conical flask
  • Beaker
  • Buchner funnel
  • Bunsen burner
  • Filter paper

Procedure

Real Lab Procedure

  1. Take 4.5g of aniline, 10ml of Conc. HCl and 20ml of water in a conical flask. Cool this solution to 5oC by placing the flask in ice-cold water.
  2. In a 100ml beaker, dissolve 4g of sodium nitrite in 20ml water and then cool this solution to 5oC.
  3. Slowly add sodium nitrite solution to the solution of aniline in Conc.HCl. A diazotized solution is formed.
  4. In a 250ml beaker dissolve 7g of 2-naphthol in 60ml of 10% NaOH solution and cool this solution to 5oC.
  5. Then add the diazotized solution to the naphthol solution while stirring constantly. Immediately a deep red colour develops and the 2-Naphthol aniline dye rapidly separates as red crystals.
  6. Allow the above mixture to stand in a freezing mixture for 30minutes, while stirring occasionally. Filter the solution through a Buchner funnel and wash the precipitate with water and dry it.
  7. Recrystallisation of 2-naphthol aniline dye: Take about 40ml of acetic acid in a beaker and add a small amount of the precipitate into it. Warm the contents of the beaker to get a clear solution. Then filter the hot solution and cool the filtrate in ice. Red coloured crystals of 2-Naphthol aniline dye separate. Wash the crystals with ethanol and then dry the crystals by placing them between filter papers and measure the weight of the crystals obtained.

Observation

The weight of 2-Naphthol aniline dye = _____________ g.

Precaution

  • The solution of aniline in hydrochloric acid should be cooled to 5oC, and this temperature should be maintained throughout the addition of sodium nitrite solution.
  • Addition of sodium nitrite should be very slow because the reaction is exothermic and may cause the temperature to rise.
  • Always add diazonium chloride solution to 2-naphthol solution for dye formation and not vice-versa.

Simulator Procedure (as performed through the Online Labs)

Acetanilide

  • Drag the measuring jar to the RB flask to add 10 ml glacial acetic acid into 10 ml acetic anhydride.
  • Drag the RB flask to shake its contents.
  • Drag the measuring jar to the RB flask to add 10 ml aniline to it.
  • Drag the RB flask to shake its contents.
  • Click on the ‘Next’ button to go to the next process.
  • Click on the knob of the burner to turn it on and heat the contents of RB flask for 10 minutes.
  • Click on the ‘Next’ button to go to the next process.
  • Drag the RB flask to the trough to place it in water and cool the contents for 10 minutes.
  • Drag the RB flask to the beaker to pour the contents into 200 ml ice cold water.
  • You can see that white precipitate of acetanilide is formed in the beaker.
  • Click on the ‘Next’ button to go to the next process.
  • Drag the beaker to the Buchner funnel to filter the precipitate of acetanilide.
  • Drag the bottle to the Buchner funnel to wash the precipitate with distilled water.
  • To go to the recrystallization process, click on the ‘Recrystallization of acetanilide’ button.
  • Drag the beaker to the beaker containing precipitate of acetanilide to pour of acetic acid –water mixture (3:1) into it.
  • Drag the beaker to the burner to heat its contents.
  • Click on the knob of the burner to turn it on.
  • Click on the ‘Next’ button to go to the next process.
  • Drag the beaker to the funnel to filter the hot solution of acetanilide into the conical flask.
  • Drag the conical flask to the ice bath to cool the contents for 10 minutes.
  • On cooling crystals of acetanilide separate out.
  • Click on the ‘Next’ button to go to the next process.
  • Drag the conical flask to the Buchner funnel to filter the crystals of acetanilide.
  • Click and drag the spatula to the Buchner funnel to take the crystals and drag it back to the filter paper to transfer the crystals into the filter paper.
  • Click on the ‘Next’ button to go to the next process.
  • You can see the white shining flakes of acetanilide in the watch glass.
  • Click on the inference icon to see the inference.
  • To redo the experiment, click on the ‘Reset’ button.

Note: Click on the ‘HELP’ button to see the instructions.

Dibenzal acetone

  • Drag the measuring jar to the conical flask to pour 25 ml rectified spirit into the mixture of 1 ml acetone and 2.5 ml benzaldehyde.
  • Drag the dropper to the conical flask to add 5ml 10% NaOH solution to it.
  • Drag the conical flask to shake the contents for 10 minutes.
  • To place the conical flask in cold water, click on the button ‘Place the conical flask in dish containing cold water’.
  • Drag the cork to the conical flask to close the flask.
  • Drag the conical flask to shake the contents for 10 minutes.
  • Leave the flask undisturbed for 20 minutes at room temperature.
  • Drag the conical flask to the trough to place it in cold water and cool the contents for 15 minutes.
  • You can see that pale yellow precipitate of dibenzal acetone is formed in the conical flask.
  • Click on the ‘Next’ button to go to the next process.
  • Drag the conical flask to the Buchner funnel to filter the precipitate of dibenzal acetone.
  • Drag the bottle to the Buchner funnel to wash the precipitate with distilled water.
  • To go to the recrystallization process, click on the ‘Recrystallization of dibenzal acetone’ button.
  • Drag the beaker to the beaker containing precipitate of dibenzal acetone to pour 25 ml hot rectified spirit into it.
  • Leave the beaker undisturbed for 20 minutes to slowly cool the hot solution.
  • You can see that pale yellow crystals of dibenzal acetone are formed in the solution.
  • Drag the beaker to the Buchner funnel to filter the crystals of dibenzal acetone.
  • Click on ‘Next’ button to go to the next process.
  • You can see the pale yellow crystals of dibenzal acetone in the watch glass.
  • Click on the inference icon to see the inference.
  • To redo the experiment, click on the ‘Reset’ button.

Note: Click on the ‘HELP’ button to see the instructions.

p- Nitroacetanilide

  • Drag the measuring jar to the conical flask to add 5 ml glacial acetic acid into 5 g acetanilide.
  • Drag the conical flask to the trough to place it in water.
  • Drag the dropper to the conical flask to add 8 ml conc. H2SO4 to it.
  • Click on the ‘Next’ button to go to the next process.
  • Click on the glass rod to stir the contents of the conical flask.
  • Drag the dropper to the test tube in the freezing mixture to take the mixture of 2 ml fuming nitric acid and 2 ml conc. H2SO4 from the test tube.
  • Drag the dropper to the conical flask to add the mixture of fuming nitric acid and conc. H2SO4 to it.
  • Drag the conical flask to leave it undisturbed for 30 minutes at room temperature.
  • Drag the conical flask to the beaker to pour the solution into crushed ice.
  • You can see that precipitate of p–nitroacetanilide separates out.
  • Click on the ‘Next’ button to go to the next process.
  • Drag the beaker to the Buchner funnel to filter the precipitate of p–nitroacetanilide.
  • Drag the bottle to the Buchner funnel to wash the precipitate with distilled water.
  • To go to the recrystallization process, click on the ‘Recrystallization of p-nitroacetanilide’ button.
  • Drag the beaker to the beaker containing precipitate of p–nitroacetanilide to pour methylated spirit into it.
  • Drag the beaker to the burner to heat the contents.
  • Click on the knob of the burner to turn it on.
  • Click on the ‘Next’ button to go to the next process.
  • Drag the beaker to the funnel to filter the hot solution of p-nitroacetanlide into the conical flask.
  • Drag the conical flask to the ice bath to cool the hot solution for 10 minutes.
  • On cooling, colourless crystals of p-nitroacetanilide separate out.
  • Click on the ‘Next’ button to go to the next process.
  • Drag the conical flask to the Buchner funnel to filter the crystals of p–nitroacetanilide.
  • Click and drag the spatula to the Buchner funnel to take the crystals and drag it back to the filter paper to transfer the crystals into the filter paper.
  • Click on the ‘Next’ button to go to the next process.
  • You can see the colourless crystals of p–nitroacetanilide in the watch glass.
  • Click on the inference icon to see the inference.
  • To redo the experiment, click on the ‘Reset’ button.

Note: Click on the ‘HELP’ button to see the instructions.

2-Naphthol aniline Dye

  • Drag the measuring jar to the conical flask to add 10 ml Conc.HCl into 4.5 ml aniline.
  • Drag the measuring jar to the conical flask to add 20 ml water to it.
  • Drag the conical flask to the ice bath to cool the contents for 30 minutes.
  • Click on the ‘Next’ button to go to the next process.
  • Drag the beaker to the beaker containing 4 g sodium nitrite to add 20 ml distilled water to it.
  • Drag the beaker to the ice bath to cool the prepared sodium nitrite solution for 20 minutes.
  • Click on the ‘Next’ button to go to the next process.
  • Drag the beaker to the conical flask to add sodium nitrite solution to it.
  • Click on the ‘Next’ button to go to the next process.
  • Drag the beaker to the beaker containing 7 g of 2- naphthol to add 60 ml 10% NaOH to it.
  • Drag the beaker to the ice bath to cool the alkaline solution of 2-naphthol for 20 minutes.
  • Click on the ‘Next’ button to go to the next process.
  • Drag the conical flask to the beaker to add the diazotised solution into the beaker containing alkaline solution of 2- naphthol.
  • Click on the ‘Next’ button to go to the next process.
  • Click on the glass rod to stir the contents of the beaker and cool it for 30 minutes.
  • Deep red precipitate of 2-naphthol aniline dye is formed.
  • Drag the beaker to the Buchner funnel to filter the precipitate of 2-naphthol aniline dye.
  • To go to the recrystallization process, click on the ‘Recrystallization of 2-naphthol aniline dye’ button.
  • Drag the beaker to the beaker containing precipitate of 2-naphthol aniline dye to add 40 ml glacial acetic acid to it.
  • Drag the beaker to the burner to heat the contents.
  • Click on the knob of the burner to turn it on.
  • Click on the ‘Next’ button to go to the next process.
  • Drag the beaker to the funnel to filter the hot solution of 2-naphthol aniline dye into the conical flask.
  • Drag the conical flask to the ice bath to cool the contents for 10 minutes.
  • On cooling deep red crystals of 2-naphthol aniline dye separate out.
  • Click on the ‘Next’ button to go to the next process.
  • Drag the conical flask to the Buchner funnel to filter the crystals of 2-naphthol aniline dye.
  • Click and drag the spatula to the Buchner funnel to take the crystals and drag it back to the filter paper to transfer the crystals into the filter paper.
  • Click on the ‘Next’ button to go to the next process.
  • You can see the deep red crystals of 2-naphthol aniline dye in the watch glass.
  • Click on the inference icon to see the inference.
  • To redo the experiment, click on the ‘Reset’ button.
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