Recovery of Citral from lemon grass oil by steam distillation
By - 07/13/2006
Dr. A. Rajasekaran
Distillation is a purification technique in which compounds
with different boiling points can be separated by controlled heating.
The liquid which has not vaporized is called the residue, and the liquid
which is collected in the receiver is called the distillate. There is
several distillation techniques can be preferred depending on the nature of
constituents to be purified or to be separated. These include simple distillation,
fractional distillation, steam distillation and vacuum distillation.
Simple distillation is a technique that’s widely used to isolate and
purify organic liquids and determine boiling points. Simple distillations
are not effective in removing multiple solvents from one another with a high
degree of success. Fractional distillation is effective in separating
components of liquid mixtures, which have boiling point difference by more than
25◦C at a temp below 200◦C. In fractional distillation, a
fractionating column is inserted between the distillation flask and the distillation
head. The fractionating column provides a large surface area in which the mixture
can be continuously vaporized and condensed.
Steam distillation is a special type of distillation or a separation process for temperature sensitive materials like oils, resins, hydrocarbons, etc., which are insoluble in water and may decompose at their boiling point. The fundamental nature of steam distillation is that it enables a compound or mixture of compounds to be distilled (and subsequently recovered) at a temperature substantially below that of the boiling point(s) of the individual constituent(s). Essential oils contain substances with boiling points up to 200°C or higher temperatures. In the presence of steam or boiling water, however, these substances are volatilized at a temperature close to 100°C at atmospheric pressure. The mixture of hot vapours will, if allowed to pass through a cooling system, condense to form a liquid in which the oil and water comprise two distinct layers. Most (but not all) essential oils are lighter than water and form the top layer. The steam that is used for the distillation is generated either within the vessel that contains the compound or mixture (by boiling water contained at the base) or by an external boiler.
In the present experiment Citral is isolated by steam distillation of lemon
grass oil.
The distillate contains 90% of Citral (Citral-a) and 10% of neral (Citral-b),
the isomer, about 2, 3-bond. Citral exhibits geometrical isomerism.
Citral (C10H16O, Mol wt 152.24 g) is chemically called as 3,7-dimethyl-2,6-octadienal, the aldehyde of geranial, occurs in the volatile oils of lemon grass, lemon, orange, limetta, and pimento. It is also called as lemenal, Geranialdehyde or Geranial. Citral is a pale yellow oily liquid with a pleasant odour of lemons. Specific gravity, 0.893 to 0.897. Boiling-point, 228° to 229°, with slight decomposition. Refractive index, 1.4876 -1.4931 it is optically inactive. Citral is used in commercial synthesis of Vitamin-A, ionone, and methylionone
Procedure
Assemble the apparatus as shown in Figure. Transfer 3 mL of Lemon grass oil, 75 mL of water to a 250-mL round-bottom flask. Place a boiling chip into the flask. Connect the flask to a simple distillation apparatus that has been modified as shown in Figure. Heat the mixture to boiling, carefully at first to avoid excessive foaming, which could spill over into the condenser and into the graduated cylinder. Use graduated cylinder to collect the distillate. Isolate the Citral obtained from mixture of water and Citral by extracting it with diethyl ether Evaporate the ether layer to get Citral. Record the flash point. Store it in a smallest possible container in desiccators for later analysis, FTIR and Refractive index.
Steam Distillation apparatus
Author Contact Information
Dr. A. Rajasekaran,
Additional Professor, School of Pharmacy, Faculty of Medicine and Health Sciences,Asian Institute
of Medicine Science and Technology, Sungai Petani, Kedah, Malaysia
Phone: 006-04-4422884 Fax: 006-04-4422881 email:rsekaran2001in@yahoo.co.in