D Pharmacy First Year

1. Distillation
Mr. G.A.Shete

2.  Distillation is the process of converting liquid into its vapours by heating &
reconverting it again into liquid by condensing by vapours.
 Apparatus for Distillation:
Still, (in which volatile material is boiled)
Condenser, (in which vapours are condensed)
Receiver, (in which distillate is collected)
 Different types of distillation
1) Simple distillation
2) Distillation under reduced pressure
3) Fractional distillation
4) Steam distillation
5) Destructive distillation

3.  Simple Distillation
It involves simple equipment like an evaporating still, for vaporization of liquid, and
condenser. Usually a glass assembly is used for this purpose. The distillation flask has a
side arm, sloping downward to attach condenser and the liquid obtained is collected in
the receiver. Small pieces of porcelain are added in the flask to avoid bumping of the
liquid. Thermometer is fitted in the distillation flask to note and control the temperature.
It is important because distillation of the various components occurs at different specific
temperatures.
 Applications of simple distillation in pharmacy
It is used for the preparation of distilled water and water for injection.
Preparation of many volatile oils and aromatic water.
Purification of organic solvent.
Preparation official compound like spirit of nitrous ether.
Preparation official compound like spirit of aromatic spirit of ammonia.
To separate volatile and non-volatile solvents

4. Fig: Simple Distillation

5.  Method of distillation of two immiscible liquids.(Steam Distillation)
 In pair of immiscible liquids , each liquid exerts its own vapour pressure & neither
liquid has any appreciable effect on the vapour pressure of the other.
 The vapour pressure of the mixture at given temperature is equal to the sum of the
vapour pressure of two pure components at that temp.
 A mixture of immiscible liquids begins to boil, when sum of their vapour pressure is
equal to atmospheric Pressure.
 Thus in case of water & liquid which boils at much higher temp. than water, the
mixture boils below the boiling point of pure water.
 For eg. Boiling point of turpentine is about 160 ºc, but when mixed with water &
heated, the mixture boils at about95.5 °c.
 At this temp. 95.5 ° c, the vapour pressure of water is 647mm & that of turpentine is
113mm of mercury, the sum is 647 + 113 = 760 mm which is equal to normal
atmospheric pressure

7.  From this, it will be seen that a high boiling substance may be distilled with water at
temp. much below its boiling point.
 For substances which are insoluble in water & are not decomposed by water , this
provides an alternative to distillation under reduced pressure

8.  Fractional distillation
 When the substance dissolved in a liquid, the vapour pressure of the liquid is lowered.
 When two miscible liquid are mixed together, each will act as solute or solvent for the
other. So, when mixture of such two liquid is heated, vapour pressure of each is
lowered.
 The pressure exerted by each liquid is known as “partial pressure”.
 The liquid boils when the sum of partial pressure equals the atmospheric pressure.
 It differs from simple distillation in that Partial condensation of vapour is allowed to
occur in a fractionating column through which the vapour must pass before reaching
the condenser.
 This column enables ascending vapour from the still to come in contact with the
condensing vapour returning to still. This results in enrichment of the vapour in the
more volatile component.

9. Fig: Fractional Distillation

10.  Distillation under reduced pressure (VACCUM DISTILLATION)
 The liquid boils when its vapour pressure is equal to the atmospheric pressure. The
boiling point of the liquid may be lowered to the desired temperature by reducing
the pressure on its surface.
 It consists of double neck distillation flask known as claisen flask. In one of its
neck thermometer is fitted & in the second neck a capillary tube is fitted which
prevents bumping of heated liquid. The capillary should be so fine as to permit
only a slow stream of bubble which can be controlled with a pinch cock. Thick
walled glass apparatus with inter-changeable standard glass joints are used for
vaccum distillation. The claisen flask is connected to the receiver to attain the
desired degree of vaccum. Heating of claisen flask is not started until the desired
vaccum has been attained.

11.  Applications
 It is used for the concentration of extracts containing thermolabile, in order to
prevent their destruction.
 It is used for the separating substances which undergoes decomposition when
heated under normal atmospheric pressure.
 It is used for obtaining a light porous mass on distillation of the liquid extract.
Fig: Vaccum Distillation

12.  Vaccum Still
 A vaccum still is generally made of stainless steel or any other metal which can withstand a
high vaccum. The still is connected to a condenser. The vaccum is created by means of a
vaccum pump. The vaccum still is filled by attaching a pipe to tap in the lower part of the
hood & the pump is started. The other end of the pipe dips into the liquid to be distilled so
that it can be drawn into the still. An observation window in the hood is very helpful to the
operator to see the progress of distillation & also the level of content of the liquid to be
distilled. Two receivers are generally attached to the condenser in order to collect the
distillate without stopping distillation. However, they may be used alternately by a suitable
arrangement of the cocks.
 Application
 Distillation of substances that have a high boiling point at atmospheric pressure.
 Distillation of thermolabile substances that get damaged by a high temperature.
 Removal of the last traces of a volatile solvent.

13. Fig: Vaccum Still

14.  Purified water I.P.
 Water which is free from volatile & non-volatile impurities is called purified water.
 It is prepared by distillation, ion-exchange treatment, reverse osmosis or any other
suitable process. It is liable to get contaminated by micro-organism, hence purified
water should not be used in the preparation meant for parental administration.
 Water for Injection
 Water which is free from volatile and non-volatile impurities, micro-organisms and
pyrogens which is prepared by distillation and reverse osmosis called as water for
injection.
 It is used for preparation of parenteral preparation.