A presentation by

•Basanti Tudu•Sudeshna P. Lenka•Aliva Das

Class XI-A

GUIDED BY ADITI CHAKRABORTY MADAM

Organic chemistry

Methods of purification of organic compounds

Various methods used for purification of organic

compounds are based on

Nature of the compound Impurity present in it

The common techniques used for purification

Sublimation

Crystallisation

Distillation

Differential extraction

Chromatography

SUBLIMATION

Sublimation is the transition from the solid phase to the gas phase without passing through an intermediate liquid phase . This endothermic phase transition occurs at temperatures and pressures below the triple point .

Example: Dry ice is solid carbon dioxide. At room temperature and pressure, it sublimates into carbon dioxide vapour.

 

crystallisation

Crystallization is the (natural or artificial) process of formation of solid crystals precipitating from a solution, melt or more rarely deposited directly from a gas. Crystallization is also a chemical solid–liquid separation technique, in which mass transfer of a solute from the liquid solution to a pure solid crystalline phase occurs. In chemical engineering crystallization occurs in a crystallizer. Crystallization is therefore an aspect of precipitation, obtained through a variation of the solubility conditions of the solute in the solvent, as compared to precipitation due to chemical reaction.

CRYSTALLISED HONEY

DISTILLATION

This important method is used to seperateVolatile liquids from nonvolatile impurities

The liquids having sufficient difference in their boiling points.

Liquids having different boiling points vaporise at different temperatures. The vapours are cooled and the liquids so formed are collected separately.

Simple Distillation

The vapours of a substance formed are condensed and liquid is collected in conical flask.

Fractional Distillation

Fractional distillation is the separation of a mixture into its component parts, or fractions, such as in separating chemical compounds by their boiling point by heating them to a temperature at which one or more fractions of the compound will vaporize. It is a special type of distillation. Generally the component parts boil at less than 25 °C from each other under a pressure of one atmosphere. If the difference in boiling points is greater than 25 °C, a simple distillation is used.

Fractional distillation. The vapours of lower boiling fraction reach the top of the column first followed by vapours of higher boiling fraction.

Different types of fractionating columns

SIMPLE PACKED COLUMN

BUBBLE PLATE COLUMN

Steam distillation

Steam distillation is a method for distilling compounds which are heat-sensitive. The temperature of the steam is easier to control than the surface of a heating element, and allows a high rate of heat transfer without heating at a very high temperature. This process involves bubbling steam through a heated mixture of the raw material. By Raoult's law, some of the target compound will vaporize (in accordance with its partial pressure). The vapor mixture is cooled and condensed, usually yielding a layer of oil and a layer of water.

Steam distillation of various aromatic herbs and flowers can result in two products; an essential oil as well as a watery herbal distillate. The essential oils are often used in perfumery and aromatherapy while the watery distillates have many applications in aromatherapy, food processing and skin care.

 

Commercial use of distillation

In the fossil fuel industry distillation is a major class of operation in obtaining materials from crude oil for fuels and for chemical feedstocks.

Distillation permits separation of air into its components — notably oxygen,nitrogen, and argon — for industrial use.

In the field of industrial chemistry, large ranges of crude liquid products ofchemical synthesis are distilled to separate them, either from other products, or from impurities, or from unreacted starting materials.

Distillation of fermented products produces distilled beverages with a high alcohol content, or separates out other fermentation products of commercial value.