ORGANIC cHEMISTRY - Iv

Experiment 1

Theory

• The practical’s of organic spotting involves identification of the given organic compound.

• The first step to identify the organic compound is to conduct the physical examination of the organic compound.

• Physical Examination of the organic compound involves observing the state of the given organic compound, colour and odour of the given organic compound.

• Compound is also heated on the copper foil to check whether the compound is aromatic or not. Aromatic compound gives sooty flame.

• Solubility of the compound in water is checked and after that litmus test is performed. If the given organic compound is acidic in nature, then it will turn blue litmus to red and if the compound is basic it will turn red litmus to blue.

• After conducting physical examination of the compound, the next step is to perform Laissaigne test to check the presence of nitrogen, sulphur and halogens.

• The knowledge of elements present in the compound is most valuable as that may help to predict the types of functional group that may be present in the compound.

• After performing Laissaigne test, next step is to perform preliminary chemical test or simple test.

• Preliminary tests or simple chemical test involves few tests which are to be performed on given organic compound.

• Tests which are to be done in preliminary chemical tests include checking the reaction of compound in sodium hydrogen carbonate, reaction of compound with dilute sodium hydroxide solution , dilute hydrochloric acid solution, neutral ferric chloride test and tests for unsaturation.

• By these test we can find out whether the compound is acidic, basic or neutral, saturated or unsaturated, phenolic etc.

• With the help of Laissaigne test and preliminary chemical tests, the organic compound is allocated to a particular group. Bearing in mind the elemental group to which compound belongs and the chemical nature of the compound that is acidic, basic or neutral the class reactions are carried out and the class to which the organic compound belong is decided.

• After group allocation, next step is to perform functional group analysis and confirmatory tests. Melting point is a part of confirmatory test.

Procedure

Step by step guidance for the separation of the mixture of the two organic compounds

• You will be given the mixture of two organic compounds

• You need to identify the two organic compounds in the mixture

• So if you want to identify the two organic compounds ,you first need to perform test separately on these two organic compounds

• So it's mandatory that you should separate the two compounds present in the mixture

You will be given the mixture of the organic compounds in the watch glass.

Now before you start adding chemicals to the mixture in order to separate them, you should first try to perform the test in the test tube .

• So first take a small amount of the compound In the test tube. Add saturated sodium bicarbonate solution in the test tube (test tube 1 )

• So your mixture contains two organic compounds. So out of these two organic compounds if one of the compound is carboxylic acid, then that carboxylic acid will react with sodium hydrogen carbonate to release effervescence of carbon dioxide and the sodium salt of carboxylic acid will be formed which will be dissolved in the filterate. ( note - if on adding sodium bicarbonate if there is no reaction then it means carboxylic acid is absent in the mixture. Now check if there is phenol or base present )

• Your second organic compound which is not a carboxylic acid is not going to react with the sodium bicarbonate solution and hence it will remain at the bottom of the test tube.

• Now do filtration.

• So the filterate will be collected in the test tube 2. The second compound which did not react with sodium bicarbonate will remain in the filter paper. Your filterate has carboxylic acid dissolved in it . Now you need to reprecipitate the carboxylic acid which is dissolved in the filerate . So now add concentrated hydrochloric acid solution. You will see that your carboxylic acid will be reprecipitated in the test tube 2 .

Remember - Your second compound which didn't react with the sodium bicarbonate is not carboxylic acid. Since it is not a carboxylic acid, that is why it is didn't react with sodium hydrogen carbonate. So your second organic compound can be phenol, base or neutral

So you have performed the tests in the test tube and you got the result that one of the compound is carboxylic acid. So now you need to perform these test in the WHOLE MIXTURE WHICH YOU HAVE TAKEN IN THE WATCH GLASS SO THAT YOU CAN SEPARATE THE TWO ORGANIC COMPOUNDS COMPLETELY.

• Take 250 ml beaker and now add ALL OF THE MIXTURE WHICH YOU HAVE TAKEN .

• Now you already know that one of the compound is the carboxylic acid .

• Now add 15 ml (approx)of the sodium bicarbonate solution and shake the mixture vigorously. You will see that carboxylic acid has already started the reaction and effervescence of carbon dioxide have started coming. Now add another 15 ml of sodium bicarbonate solution and shake the mixture vigorously. Why we are adding this much amount of sodium bicarbonate? BECAUSE THERE IS ONE CARBOXYLIC ACID IN THE MIXTURE AND ALL THE CARBOXYLIC ACID PRESENT IN THE MIXTURE SHOULD REACT COMPLETELY. Now add just 5 ml of sodium hydrogen carbonate just to make sure that ALL THE CARBOXYLIC ACID HAS REACTED

• YOUR SECOND COMPOUND WHICH DID NOT REACT WITH SODIUM HYDROGEN CARBONATE WILL STAY AT THE BOTTOM OF THE BEAKER. IT HAS NOT REACTED WITH SODIUM BICARBONATE BECAUSE IT IS NOT A CARBOXYLIC ACID. IT CAN BE BASE ,PHENOL OR NEUTRAL

• Now filter the mixture.

• Your second compound which is not a carboxylic acid will be collected on the top of the filter paper.

• Collect the filterate in the beaker 2 .

• This filterate contains the carboxylic acid .

• Now perform reprecipitation by addition of concentrated hydrochloric acid solution.

• Now once again filter it so that you can collect the carboxylic acid.

Congratulations! Your two organic compounds are now separated.

Procedure for detection of Nitrogen

Take 2-3 ml of prepared laissaigne solution. Now add freshly prepared ferrous sulphate solution. If no precipitates are observed then add little sodium hydroxide solution and then boil the mixture for 2-3 minutes. After boiling the mixture ,cool it under the tap water. Now add dilute sulphuric acid till the precipitates are dissolved. Now appearance of blue or green coloured solution indicates presence of Nitrogen

Procedure for detection of Sulphur.

Take 3-4 ml of Laissaigne solution and add few drops of freshly prepared sodium nitroprusside solution. Purple colouration indicates presence of Sulphur.

Procedure for detection of Halogens.

Take 3-4 ml of Laissaigne solution and add concentrated nitric acid solution till the mixture becomes just acidic. Now add Silver Nitrate solution. Appearance of White or yellowish white curdy precipitates indicates presence of halogens.

Chemistry behind the Lassaigne test- Refer Page number 10, 11 and 12 of RC Book (For Organic Chemistry Practicals)

Tests to be performed under Preliminary chemical tests.

Sodium Bicarbonate test

Take small amount of given organic compound and add 2-3 ml of saturated sodium bicarbonate solution. Bubbles of Carbon Dioxide indicates that given compound has a carboxylic acid. Now you can also check for reprecipitation. Filter the mixture containing the organic compound and sodium bicarbonate and then add 1-2 ml of concentrated hydrochloric acid to the filtrate. Reprecipitation indicates presence of carboxylic acid.

Sodium Hydroxide test.

Take small amount of given organic compound and add 2-3 ml of sodium hydroxide solution. If the given compound dissolves and if there is reprecipitation on addition of concentrated hydrochloric acid then aromatic acids and phenols are present.

Take a small amount of given organic compound and add 2-3 ml of sodium hydroxide solution and then heat it. Smell of ammonia indicates presence of amides and imides. Liberation of oily drops indicates presence of anilides.

Solubility in 1:1 Hydrochloric acid.

Take a small amount of given organic compound and add 2-3 ml of 1:1 Hydrochloric acid solution. If the compound dissolves and there is reprecipitation on addition of concentrated sodium hydroxide solution , then the organic compound is an aromatic amines.

Action of Neutral Ferric Chloride test

If the compound is acidic, then dissolve it in small amount of ammonium hydroxide and then boil off excess of ammonia and then cool. Now add 1 drop of neutral Ferric chloride and observe.

Buff coloured precipitates indicates presence of aromatic acids like benzoic acids and succinic acids.

Violet colouration indicates the presence of phenolic acid. For example – Salicylic

acid.

Action of bromine water.

Take 2-3 ml of bromine water and add small amount of organic compound. If bromine water gets decolourised then it indicates that the given organic compound is unsaturated.

E.g Cinnamic acid

Action of Potassium Permanganate

Take small amount of given organic compound and add alkaline potassium permanganate. If potassium Permanganate gets decolourised then it indicates presence of Unsaturated compound or easily oxidisable compound

Functional group analysis

Theory and the procedure for the analysis for the functional group is already given in RC book

For example for knowing the procedure the for the functional group analysis for aldehydes , you can refer page number 32 and 33 of RC Shah book

To understand the chemistry behind the functional group analysis for aldehydes, refer page number 28 of the RC Shah book.

This is the one example of how to understand the procedure and chemistry behind the analysis for the aldehyde functional group

Similarly you can find the procedure and chemistry behind the analysis for all the different functional groups in your RC Shah book.

Confirmatory test

After performing preliminary chemical test and functional group analysis you come to the conclusion that your organic compound contains aromatic carboxylic acid

Now this aromatic carboxylic acid can be phenyl acetic acid, benzoic acid , cinnamic acid, acetyl salicyclic acid , pthalic acid ( Refer RC shah book , page number 46, 47 and 48)

So in order to determine which carboxylic acid it is , we perform melting point

After performing melting point , you observed that melting point of your organic compound is 123 degree Celsius

So now you can confirm from the melting point that your organic compound is benzoic acid.

Apart from confirming the organic compound from melting point, you also need to perform certain specific confirmatory test for that compound

You can find the confirmatory test for your organic compound from your RC book only

For example confirmatory test for benzoic acid is given on page number 47

Confirmatory test for cinnamic acid is given on page number 47

Similarly you can find confirmatory analysis for other Organic Compounds from RC Book only( For Organic Chemistry Practicals)

Click here to watch Reference Videos (These reference videos are not primary source for study of practicals and they don't cover all the topics. These reference videos are for only quick revision of some topics. You can surely refer this reference videos for quick revision for only some topics but Students are advised to read RC Shah book thoroughly for Organic Chemistry Practicals )

Separation of Organic Compounds

Sodium Bicarbonate test

Pthalein test

Phenyl Hydrazine Test

Laissaigne test

Iodoform Test:

Bromine Water Test

Melting and Boiling Point

Click Here to Download Practical Organic Chemistry by RC Shah

Click Here to Download Lab Manual for Organic Chemistry