Question

what criteria would you use to decide whether distillation is an appropriate technique for the purification of a reaction product and what type of distillation method- simple , fractional vacuum or steam - should be used?

Answer 1

The general critera to choose distillation method would be if the indivisual cmponents of mixtures are having a large difference in their boiling point. Distillation is the most useful method for purification of liquids and it is used routinely for purifying solvents and rgents. Through appropriate aparatus, it is possible to seperate liqids whocs boiling points differ by less than 5^oC .

Simple distillation: This is useful only for distilling compounds from nonvolatile residues or for separating liquids whose boiling points differ by at least 50^oC.

Fractional distillation: It is the separation of a mixture into its component parts, or fractions, 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 uses distillation to fractionate. Generally the component parts boil at less than 25 °C from each other under a pressure of one atm. pressure.

Vacuum distillation: Many compounds decomposes when heated to their boiling points, so they cannot be distilled at atmospheric pressure. In this case, it may be possible to avoid thermal decmposition by carrying out the distillation at a reduced pressure. the reduction in bp depends upon the reduction in pressure.

Steam distillation: It is similar to vacuum distillation, steam distillation is a method for distilling compounds which are heat-sensitive and decompose at higher temperature. 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.