Chemistry of natural products - PowerPoint Presentation

Slide1

Chemistry of natural products

Islamic University in

MadinahDepartment of Chemistry

Prepared ByDr. Khalid Ahmad ShadidChemistry Department – Islamic University in Madinah

Part-2Slide2

Volatile

Oils

It has been known for many centuries ago, that different organs of certain plants contain volatile odoriferous substances that affect the olfactory sense and are responsible for the odour and the fragrance. Because they evaporate readily when exposed to the air at ordinary temperature, they are called volatile oils, ethereal oils or essential oils. The last term is applied since volatile oils represent the essences or the active constituents of such plants.Several points of differentiation exist between volatile oils and fixed oils

and they differ entirely from each other in both chemical and physical properties. Volatile oils, being capable of volatilization may be distilled from their natural sources, while fixed oils not. They do not consist of glyceryl esters of fatty acids, and hence they do not leave a permanent grease spot on paper, and cannot be saponified with

alkalies

. Volatile oils do not become rancid as fixed oils, but instead, on exposure to light and air, they will oxidize and

resinify.

2Slide3

Distribution and

Occurrence

Depending on the plant family, volatile oils may occur different structure parts on the plant, In secretory structures, glandular hairs, oil cells, oil tubes (ducts), as well as in internal lysigenous or schizogenous glands.In the conifers, volatile oils may occur in all the tissues, in rose, they appear in appreciable quantities only in the petals; in cinnamon, only in the bark and in the leaves, in the umbelliferous fruits only in the pericarp, in the mints in

the glandular hairs of the stems and leaves, and in the orange, one kind of oil in the flower petals and another kind in the rind of the fruit.3Slide4

the volatile oil of the bark of

Cinnamomum zeylanicum, is rich in cinnamic aldehyde, while the volatile oil prepared from the leaves of the plant contains eugenol as the main constituent.

The volatile oil obtained from the fruit of the same plant, is rich in camphor.It should be noted that the chemical composition of volatile oil prepared from the same organ of one species varies to some degree according to the environmental conditions under which the plant has grown.4

Distribution and

OccurrenceSlide5

Uses of volatile

oils

volatile oils play an important role in the economy of man. They may be used for their therapeutic action e.g. local stimulant, expectorant, appetite stimulant, carminative , sedative, antiseptic, disinfectant, circulation stimulant, diuretic, anthelementics, parasaticides, antinflammatory, deodorant, insecticide, insect repellent.They may be also used as spices and for flavoring of foods

, confections, beverages, pharmaceuticals, cosmetics and many food products. In addition they are most widely used in perfumery.

5Slide6

Preparation of volatile

oils

The principal methods used in the preparation of from plants depend on :1- Distillation in water or steam ( Hydro-distillation).2- Scarificatication and expression.3- Extraction with solvents.

4- Enzymatic hydrolysis. 5- Extraction by supercritical gasses

6Slide7

1. Distillation

in water or steam ( Hydro-distillation)

This distillation method is the most economical method of preparation of volatile oils. It is based on the fact that when water is mixed with another liquid which is immiscible with it and the two liquids are boiled, they will boil at a temperature lower than that of the high boiling point component and nearly equal or slightly lower than the boiling point of water; because at this temperature the vapour pressure of the two components will

be equal to the vapour pressure of the atmosphere. For example, turpentine oil which boils at 160c°., when mixed with water, it will begin to boil at 95.6c°., at this temperature, the vapour pressure of water is 64.7cm.

Mercury,

and the

vapour pressure of turpentine is 11.3cm mercury. The resulting

vapour

pressure

of the two is 76cm/Hg, which is the

atmospheric pressure

, and thus the liquid

begins

to boil.

7Slide8

The contribution to the total vapour pressure made by the volatile oil and the

water in the from of steam causes the oil to be carried over as vapour with the steam at a temperature far below the normal boiling point of the oil. This

allows for the distillation of volatile oils at temperatures considerably below their decomposition points.There are three types of hydro distillation may be used:1- Water distillation.2- Water and steam distillation.3- Direct steam distillation.

81. Distillation in water or steam ( Hydro-distillation

)Slide9

1- Water distillation.

It is applied to plant material that is dried and not subject to injury by boiling. Turpentine oil is obtained in this manner.The crude turpentine oleoresin is introduced into the distilling chamber and subjected to heat until all volatile mater (both oil and

water) is condensed in the condensing chamber, Before distillation the plant material must be disintegrated to some extent i.e comminuted. Flowers, leaves and other thin nonfiberous parts of the plant can be distilled without comminution, seeds and fruit must be crushed, roots and stalksand all woody materials should be cut into short length in order to expose a great number of oil glands. The comminuted material should be distilled at once to avoid loss of oil by

evaporation.9

1. Distillation

in water or steam

(Hydro-distillation)Slide10
Slide11

2- Water and steam

distillation Its is employed for substances (either dried or fresh) that may be injured by boiling with water.In the case of dried materials (cinnamon, clove), the drug is ground

and then covered with a thin layer of water, and steam is passed through the macerated mixture. Since the oil might be impaired by direct boiling, the steam is generated else where and is piped into the container holding the drug.111. Distillation

in water or steam ( Hydro-distillation)

steam distillation require the boiler for vapor increase. the principles are similar to water distillation, but to place the plant on the grid in still and connect pipe with a boiler.Slide12

This method is applicable to all plants. Especially those that may be destroyed

when it is boil. Done by placing wet plants (B)on the grid (C) boiling water (D) steam through the plant with volatile oils evaporates to go to (A)and (H) until the condensation and separation of the water and oil.12

1. Distillation in water or steam ( Hydro-distillation)

2-Water

and steam distillationSlide13
Slide14

3- Direct steam

Distillation:This method resembles the preceding one except that no water is kept in the bottom of the still. Live steam or perforated steam coil, below the charge

and proceed upward through the plant material above the supporting grid.During steam distillation certain components of volatile oil tend to hydrolyse where as other constituents are decomposed by the high temperature as volatile amines and degradation products of carbohydrates (furfural) and pass over during distillation Hydrolysis of ester and loss of water from resulting tertiary alcohols may produce hydrocarbons. These volatile products formed by heat decomposition of

plant substances will often contaminate the oil.14

1. Distillation

in water or steam ( Hydro-distillation

)

FurfuralSlide15

Separation of the components of

distillationThe distillate which consists of mixtures of oil and water is collected in a suitable receiver which is known as

Florentine Flask. The Florentine flask allows the oil to be collected in the upper layer in the flask, while the lower aqueous layer saturated with oil is siphoned off and returned to the steam boiler for the generation of more steam and to recover the dissolved oil. This is called cohobation. For oils heavier than water, the oil is with drawn from the lower outlet and the water from the upper.

In some cases the aqueous layer may be taken and form an article of commerce being sold as" aromatic water", e.g. rose water, orange flower water.15Slide16

2. Scarification

and expression

methods

Some volatile oils cannot be distilled without decomposition. Therefore they should be prepared by other mechanical methods without the application of heat. For oils occurring in the rind of citrus fruits, e.g. peel of orange, lemon, bergamot

, lime etc. the application of

pressure (

squeezing out) is satisfactory.

Expression

can be carried out

by one

of the following methods

:

16

a) The sponge method:

The citrus fruit (orange, lemon, bergamot) is washed, cut into halves and the pulp is removed. The rind is turned out and squeezed when the secretion glands rupture and the oil collected by a sponge, until the sponge becomes saturated with exuded water and oil. The sponge is then periodically squeezed in vessel. The upper oily layer in the vessel is separated.

This process is carried out in a cool and darkened room to minimize the harmful effects of heat and light on oil.Slide17

b- The

écuelle à piquer (ecuelle

a piquer) process:The entire fruits are rotated in a saucer-shaped dish provided with metal pins or sharp metal projections just long enough to penetrate the epidermis and rupture the oil glands.The exuding oil and water are collected in a long narrow depression in the bottom of the saucer. The liquid is poured off into a large vessel, where it is allowed to stand until the oil can be

decanted and separated.2. Scarification and expression

methods

c- Machine Processes:

Much oil is prepared by machines based on the

above principles

and is only slightly inferior to the hand pressed oil.

A centrifuge

may be used to separate the emulsion of oil

and water.

d- Expression of rasping Process:

The outer region of the peel, which contains the oil

glands is

removed by means of a grater. The rasping are placed in

a horsehair

bags and strongly pressed. The liquid obtained is

turbid, but on standing the oil separates and can be decanted and filtered.Slide18

3. The

solvent extraction Methods

: This method is used for the preparation of those oils which decompose by the action of steam (heat), or are present in extremely small quantities in plant organs, that oil removal is not commercially feasible by the previously mentioned methods. The quantities of oil actually distilling over, are lost in the large volume of distillation water from which the oil can

not be recovered. This is applied to flowers such as jasmine, violet, acacia, narcissus, tuberose, gardenia and few others. The methods of extraction are carried out using:-a- Volatile solvents of low boiling points, such as

light petroleum

ether, benzene, or hexane

.

b-

Non- Volatile solvents such as lard, tallow, olive oil etc.

18Slide19

a) Extraction with Volatile solvent

:

The drug containing the volatile oil is extracted with the volatile solvent. The solvents used must dissolve quickly the volatile oil present, being chemically inert, with uniform and low boiling point and should be of low price.

19

Preparation

of "floral concretes"

Solvents used:

petroleum ether & n-hexane

Extraction

(

“percolation”

or

“maceration”

at room temperature,

“continuous hot extraction”

in a

Soxhlet

apparatus at constant temperature)

Solvent removal

(distillation under reduced pressure)

Rotary Evaporator

Soxhlet

apparatus

PrecolatorSlide20

Floral concrete

:In preparing volatile oil with solvents, the completely concentrated and purified products represent the so called

floral concretes. These floral concretes contain the odoriferous principles of the natural flower perfumes plus a considerable amount of plant waxes, albuminous material and color pigments, the concretes are therefore of solid consistency and only partly soluble in alcohol 96%. Although their aroma is less concentrated than an Absolute, they are still highly aromatic, and amazingly tenacious and long-lasting.

20

Filtering the concrete

- Cal Pfizer factory - Grasse - 1995Slide21

Absolute:

Although these insoluble concretes are more difficult to work with, some perfumers prefer them to the alcohol soluble absolutes

, which are obtained by precipitating and eliminating the insoluble waxes with strong alcohol and concentrating the filtered alcoholic solutions. The distillation of alcohol from the solution causes the loss of some of the most volatile and delicateconstituent of the natural flower oil.21

Pure essence or absolute

- Cal Pfizer factory - Grasse - 1995Slide22

b- Extraction with non- volatile solvents

:This process is used for the preparation of the very finest of perfume oils. It is used in the preparation of natural

flower oils, where the volatile oil content of the fresh plant parts is so small that oil removal is not commercially feasible by other methods.22

1- Enfleurage process:The

principles of

enfleurage

are simple. As certain flowers e.g. jasmine continue their physiological activities of

developing and

giving off volatile oil even after

picking Fats possesses the ability

of absorption and if brought in contact with

fragrant flowers

, readily absorb the volatile oil

emitted

.

In

this process, quantities of fresh flowers are lightly layered over a specially prepared fat base, as refined lard, tallow or fatty acids of high molecular weight. The fat is spread in a thin layer on both sides of glass plate supported on

a rectangular wooden frame or chassis.Slide23

1

- Enfleurage process:

Several chassis are placed one above the other so that the flowers get sandwiched between the two layers which absorbs the oil as it is given off. Exhausted glowers are removed and replaced by the fresh flowers until the fat is saturated with flower oil. The perfumed fat must then be removed from the glass plates; the final product is called pomade.The pomade is extracted three times with alcohol 95% ( Triple extraction), the clear solution known as extracts. The extract contains a small quantity of alcohol soluble fat. The extract

is concentrated in a vacuum still at low temperature till free from alcohol; the concentrated flower oil is called absolute of enfleurage., absolute of pomade or liquid concretes.

23Slide24

2- The pneumatic

methodThis process is similar in principle to the enfleurage method

and involves the passage of a current of warm air through the flowers. The air laden with suspended volatile oil is then passed through melted fat in which the volatile is dissolved and absorbed. 3- The maceration method The flowers are gently heated in melted fat (lard or fixed oil) being incorporated and rotated in the fluid until exhausted, then they are strained out, squeezed and the exuded fluid

is returned to the fat and so on until a special concentration is reached.The volatile oil containing fat is allowed to cool and the volatile oil is obtained by 3 successive extractions with alcohol. The volatile oil can be obtained in pure form by recovery ofalcohol.

24Slide25

4. Preparation

of volatile oil After Enzymatic Hydrolysis

25Glycosidic volatile oils like bitter almond, mustard oil is obtained by enzymatic hydrolysis of glycosides. In bitter almond seeds amygdalin is acted upon by enzyme emulsin resulting in a mixture of constituents from which the volatile oil may be distilled with steam. In black mustard seeds the glycoside, sinigrin is hydrolysed by the enzyme myrosin with the product of volatile mustard oil

.

For example:

When

gaultherin

is

hydrolysed

with 3% H

2

SO

4

, it forms methyl salicylate, D-glucose and D-xylose.

However

,

gaultherin when hydrolysed by the

enzyme gaultherase it gives primeverose

(6-(β-D-xyloside) – D glucose) a disaccharide and methyl salicylate.Slide26

Presence of volatile of oil can be detected

by following Test.Take thin section of the drug & add a

drop of tincture alkana: –> Red color is produced which indicates presence of volatile oil.

2) Take a thin Section of drug & add alcoholic soln. of Sudan IIIrd:

- >

red color

is produced

, which

indicate presence

of volatile oil

.

Chemical Test for Volatile

oilSlide27

5. EXTRACTION

BY SUPERCRITICAL GASSES

Beyond its critical point, a fluid can have the density of a liquid & the viscosity of a gas

 therefore diffuses well through solids, resulting in a good solvent.

CO

2

is the main gas used

Advantages of CO

2

- It is a natural product

- chemically inert, non-flammable

- non-toxic

- easy to completely eliminate

- selective

- readily available

- InexpensiveSlide28

5. EXTRACTION

BY SUPERCRITICAL GASSES

DISADVANTAGE:

Technical constraints - High cost of initial investment

ADVANTAGES:

- obtain extracts which are very close in composition to the natural product.

- It is possible to adjust the selectivity & viscosity,

etc

by fine tuning the temperature & pressure

- All result in the increase of popularity of this type of methodSlide29

5. EXTRACTION

BY SUPERCRITICAL GASSES

USES:

Initially developed to decaffeinate coffees, prepare hops extracts or to remove nicotine from tobacco, the method is now used to

- Prepare spice extracts (ginger, paprika, celery)

- Specific flavours (black tea, oak wood smoke)

- Plant oils

- To produce specified types of a certain product, e.g.

thujoneless

wormwood oil.Slide30

Purification of volatile oils prepared by steam Distillation

Volatile oils prepared by steam distillation may be dark colored or may contain bad smelling substances

due to decomposition.These oils can be purified by rectification. Rectification procedure include redistillation in steam or dry distillation under reduced pressure, Bad smelling substances can be removed from the volatile oil by aeration, which consist of passing of a stream of air or inert gas in the oil for a short time.For removal of water or moisture which might be present in the prepared volatile oil, anhydrous sodium

sulphate is usually used to dry the oil.30Slide31

Storage of volatile

oil

The following should be considered for the proper storage of volatile oils to guard against spoilage, deterioration represented by change in fineness of odor and color and prevent oxidation and resinification.1- The volatile oil should be dry, free from water or moisture, anhydrous sodium sulphate can be used for drying volatile oil safely.2- The volatile oil should be stored in dark amber bottles

or aluminium containers.3- The oil should be stored away from direct sunlight and in cool dark place.4- The containers should be completely filled and be small as possible.

31Slide32

Determination of percentage of volatile oil in plant material

Miscibility with alcohol

Most volatile oils are miscible with

absolute alcohol

.

Oils

highly miscible

with

alcohol of low concentrations

are usually

rich in oxygenated constituents.

Decreased miscibility with alcohol of low concentrations



adulteration

with non-polar solvents e.g. petroleum ether (turbidity) or fixed oils

% v/w = Vol of oil × 100 / Wt of drugSlide33

Physical Examination:

helps in evaluation of the oil sample

& detection of adulterantsOdor Detection of any abnormal odor (by smelling 1 or 2 drops of the oil applied on a filter paper) 

adulteration or deterioration during storage e.g. orange oil acquires a caraway odor on bad storage due to

autoxidation

of limonene to

carvone

&

carveol

Solubility

Oils are soluble in non-polar solvents as benzene, carbon disulfide & light petroleum.

Any turbidity



moisture

Specific gravity

Apparatus: pycnometer (specific gravity bottle

)

Sp. gr. gives an indication on composition

Oils with sp. gr. < 0.9,

rich in hydrocarbons & aliphatic compounds

Oils with sp. gr. > 1.0,

rich in aromatic & S compounds.

Oils with 0.9 > sp. gr. < 1.0,

contain different types of constituents

Optical rotation

[

Apparatus:

Polarimeter

]

Determination helps in detection of adulteration & identification of the variety of the sample e.g.

French oil of turpentine

is

levorotatory

[

l (-)] as it contains

l-

pinene

in high concentration.

American oil of turpentine

is

dextroratory

[

d (+)] as its major constituent is d-

pinene

.

Gives indication on the method of preparation of the volatile oil isolate:

All

synthetic compounds

are

racemic

(dl).

Natural compounds are generally optically active present in (l) or (d) forms.

Example:

natural camphor is (l) or (d) while synthetic camphor is (dl).

Refractive

index

[A

pparatus: Refractometer]

Refractive Indices of volatile oils range

from 1.4-

1.6 any deviation



adulteration Slide34

Pycnometer

Polarimeter

Abbe refractometerSlide35

THANK YOU

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