Purification of organic compounds crystallisation

CRYSTALLISATION

Process Most Commonly Employed

For The Purification Of Solid Organic

Compounds. Impure Solid Is

Dissolved In The Minimum Volume Of

A Suitable Solvent. The Soluble

Impurities Pass Into The Solution

While The Insoluble Ones Are Left

Behind. The Hot Solution Is Then

Filtered And Allowed To Cool

Undisturbed Till Crystallisation Is

Complete. The Crystals Are Then

Separated From The Mother Liquor By

Filtration And Dried. The Efficiency Of

The Process Of Crystallisation

Depends On The Skill With Which The

Following Steps Are Carried Out:

( 1 .a)Choice of solvent – For a judicious choice of the solvent, above 50 mg of the solid is taken in a test tube and shaken with a few drops of the solvent. The solvent is unsuitable if whole of the solid goes into the solution at room temperature. If the solid dissolves upon heating and throws out maximum crystals on cooling, the solvent is suitable. This process is repeated with the solvents such as water, benzene ,ether, ethyl alcohol, acetone, etc.., till the most satisfactory one is sorted out. ( 1 .b) Preparation of solution – A suitable quantity of the solid substance is taken in a conical flask fitted with a reflux condenser. A small volume of the solvent selected in step( 1 .a) is also placed in the flask. The quantity of the solvent should be just enough to dissolve the whole solid on boiling. The heating maybe done on a water bath or wire gauze according as the solvent is low boiling or high boiling. ( 1 .c) Filtration of hot solution – The hot solution obtained above is then filtered through a fluted filter paper placed in an ordinary glass funnel. If the quantity of the solution is large, it takes longer and the crystals may form in the funnel during filtration. To prevent this, a hot-water funnel maybe used.

Filtration under reduced pressure using a Buchner funnel Vaccum Desiccator

CRYSTALLISATION

Process Most Commonly Employed

For The Purification Of Solid Organic

Compounds. Impure Solid Is

Dissolved In The Minimum Volume Of

A Suitable Solvent. The Soluble

Impurities Pass Into The Solution

While The Insoluble Ones Are Left

Behind. The Hot Solution Is Then

Filtered And Allowed To Cool

Undisturbed Till Crystallisation Is

Complete. The Crystals Are Then

Separated From The Mother Liquor By

Filtration And Dried. The Efficiency Of

The Process Of Crystallisation

Depends On The Skill With Which The

Following Steps Are Carried Out:

ORGANIC CHEMISTRY-I

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CRYSTALLISATION

Process Most Commonly Employed

For The Purification Of Solid Organic

Compounds. Impure Solid Is

Dissolved In The Minimum Volume Of

A Suitable Solvent. The Soluble

Impurities Pass Into The Solution

While The Insoluble Ones Are Left

Behind. The Hot Solution Is Then

Filtered And Allowed To Cool

Undisturbed Till Crystallisation Is

Complete. The Crystals Are Then

Separated From The Mother Liquor By

Filtration And Dried. The Efficiency Of

The Process Of Crystallisation

Depends On The Skill With Which The

Following Steps Are Carried Out: