The document presents an overview of extraction processes used in pharmachemistry, explaining unit operations and various methods of extraction including infusion, decoction, and percolation. It outlines the properties of ideal solvents and describes specific techniques such as extraction with reflux and counter current extraction. Additionally, it covers the factors affecting the choice of extraction process based on drug characteristics and solvent selection.

1. Unit Operations:
Extraction
Presenter,
Vikas R. Mathad
I – M. Pharm.
Dept. of Pharmachemistry
SJM College of Pharmacy

2. Contents
 Introduction
 Extraction
 Various methods
 Extraction with reflux
 Extraction with agitation
 Counter current extraction
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3. Introduction
 A unit operation is a basic step in a process.
 Unit operations involve a physical change or chemical transformation such as
separation, crystallization, evaporation, filtration, polymerization, isomerization, and
other reactions.
 A process may require many unit operations to obtain the desired product from the
starting materials.
 Arthur Dehon Little propounded the concept of "unit operations" to explain
industrial chemistry processes in 1916.
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4. Extraction
 Extraction may be defined as the treatment of the plant or animal tissues with solvent,
whereby the medicinally active constituents are dissolved, and most of the inert matter
remains undissolved.
 The solvent used for extraction is known as “Menstruum”.
 The inert insoluble material that remains after extraction is called “Marc”.
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5. Ideal properties of solvents
 Be highly selective for the compound to be extracted.
 Should not react with the extracted compound or with other compounds in the plant
material.
 Have a low price.
 Be completely volatile.
 Should have the minimum viscosity.
 Eco-friendly.
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6. Various methods
 Infusion
 Decoction
 Digestion
 Percolation
 Maceration
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7. Infusion
 It consists of pouring water over the drugs and then allowing it to keep in contact with
water for the stated period, usually 15 minutes, with occasional stirring and finally
filtering off the liquid.
 The marc is not pressed.
 The boiling water is commonly used as a solvent, since it has a greater solvent action
than cold water.
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8. Decoction
 In this process, the drug is boiled with water for a stated period usually 10 minutes.
 After boiling, the liquid is strained and water is passed through the content of the
strainer to make the required volume.
 This process is mainly used for vegetable drugs of hard and woody nature having
thermostable water soluble constituents.
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9. Digestion
 The drug is extracted by heating at a particular pressure.
 The apparatus known as “Digestor” is used for extraction of the drug by this method.
 The whole of the drug along with menstruum is placed in the body of the digestor.
 The drug is treated with menstruum under specified conditions of temperature and
pressure.
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10. Extraction with reflux
 A mixture of reactants and solvent is placed in a suitable vessel, such as a round
bottom flask. This vessel is connected to a water-cooled Liebig or Vigreux condenser,
which is typically open to the atmosphere at the top.
 The reaction vessel is heated in order to boil the reaction mixture; vapours produced
from the mixture are condensed by the condenser, and return to the vessel through
gravity.
 The purpose is to thermally accelerate the reaction by conducting it at an elevated,
controlled temperature (i.e. the solvent's boiling point) and ambient pressure.
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11. Simple percolation process
 It is continuous downward displacement of the solvent through the bed of
crude drug material to get extract.
 Most frequently used to extract active ingredients in the preparation of
tinctures and fluid extracts.
 It is the method of short successive maceration or process of displacement.
 A percolator (a narrow, cone-shaped vessel open at both ends) is generally
used. conical cylindrical.
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12. Steps involved in percolation
 Size reduction: The drug to be extracted is subjected to suitable degree of size
reduction, usually from coarse powder to fine powder.
 Imbibition: During imbibition the powdered drug is moistened with a suitable amount
of menstruum and allowed to stand for four hours in a well closed container.
 Packing: After imbibition the moistened drug is evenly packed into the percolator.
 Maceration: After packing sufficient menstruum is added to saturate the material. The
percolator is allowed to stand for 24 hours to macerate the drug.
 Percolation: The lower tap is opened and liquid collected therein is allowed to drip
slowly at a controlled rate until 3/4th volume of the finished product is obtained.
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13. Reserve percolation process
 A part of the percolate, generally 3/4th the volume of the finished preparation.
 The percolate is subjected to evaporation or distillation to convert it into a soft extract.
 The soft extraction is dissolved in the reserve portion of percolate and then sufficient
menstruum is added to produce the required volume.
 The portion of the percolate reserved must be the first percolate because it is more
concentrated.
 The portion of the active constituents of the drug are saved from deterioration.
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14. Continuous hot percolation process
 Its also called Soxhlet extraction.
 The fixed oils from seeds and alkaloids from the drug are extracted.
 Solvents – benzene, chloroform, petroleum ether, alcohol etc.
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15. Continuous hot percolation process
 Limitations:
 Physical character of drug- the drugs which block the Soxhlet apparatus are not
suitable. Ex- opium, gum, resin, orange peel etc.
 Solvent- only pure solvents or constant boiling mixtures can be used for this
process.
 Chemical constituents of the drug- the process is unsuitable for drugs having
thermolabile active constituents such as enzymes, alkaloids, anthraquinone
derivatives, esters etc.
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16. Extraction with agitation
 Agitation is the movement of one or more components of a mixture
to improve contact.
 Putting into motion by shaking or stirring, often to achieve mixing.
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17. Simple maceration
 In this process solid ingredients are placed in a stoppered container with the whole of
the solvent and allowed to stand for a period of at least 3 days (3 - 7 days) with
frequent agitation, until soluble matter is dissolved.
 The mixture is then strained (through sieves / nets), the marc is pressed and the
combined liquids clarified (cleaned by filtration) or by decantation, after standing.
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18. Maceration with adjustment
 The unorganised drug is placed with 4/5th of the menstruum in a closed vessel for a
period of 2-7 days.
 During this period, shaking is done occasionally.
 The liquid is filtered and the final volume is made up by passing the remaining 1/5th
of the menstruum through the filter.
 The marc is not pressed.
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19. Double maceration process
 The drug is macerated twice by using the menstruum which is divided into two parts
in such a manner that the same volume is used for each maceration.
 The whole of the drug is macerated for 48 hours with the quantity of menstruum
required for first maceration.
 Strain the liquid and press the marc.
 Macerate again for 24 hours with the remaining menstruum required for second
maceration.
 Mix the liquids obtained from the two maceration and allow to stand for 14 days and
filter.
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20. Triple maceration process
 The drug is macerated thrice by using menstruum which is divided into three parts in
such a manner that the same volume is used for each maceration.
 The whole of the drug is macerated for one hour with each part of menstruum and
strained.
 Combine the liquids obtained from second and third maceration and evaporate and
mix it with the liquid obtained from first maceration.
 Add alcohol 90% equal to 1/4th of the volume of the finished product and adjust with
water.
 Allow to stand for 14 days and filter.
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21. Counter current extraction
 A method of multiple liquid-liquid extractions is countercurrent extraction.
 It permits the separation of substances with different distribution coefficients (ratios).
 A clever design known as Craig apparatus is used for this purpose (Lyman C. Craig,
1943).
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22. Craig apparatus
 Craig apparatus consists of a series of glass tubes (r: 0, 1, 2..) that are designed and
arranged such that the lighter liquid phase is transferred from one tube to the next.
 The liquid-liquid extractions are taking place simultaneously in all tubes of the
apparatus which is usually driven electromechanically.
 The lower (heavier) phase of the two-phase solvent system (e.g. water, blue layer in
the picture) is the "stationary phase", whereas the upper (lighter) phase (e.g. hexane,
red layer in the picture) is the "mobile phase".
 Here, wet raw material is pulverized using toothed disc disintegrators to produce fine
slurry.
 The material to be extracted is moved in one direction (generally in the form of fine
slurry) within a cylindrical extractor where it comes in contact with extraction solvent.
 Finally, sufficiently concentrated extract comes out at one end of the extractor while
the marc falls out from the other end.
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23. Craig apparatus
A manually operated Craig apparatus consisting of 25 tubes
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24. Factors affecting choice of extraction
process
 Character of drug
 Therapeutic value of the drug
 Cost of drug
 Stability of drug
 Solvent
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25. Reference
 R. M. Mehta (2010). Pharmaceutics I. 5th ed. Delhi: Vallabh Prakashan, pp.150-174.
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