Phytochemistry I - Volatile Oils PDF

# Phytochemistry I - Volatile Oils ## Volatile, Ethereal or Essential Oils - **Volatile** or **Ethereal**: As they easily evaporate on exposure to air at room temperature. - **Essential**: As they represent the **"essences"** or principal, active principles of the plants in which they occur. - **...

# Phytochemistry I - Volatile Oils ## Volatile, Ethereal or Essential Oils - **Volatile** or **Ethereal**: As they easily evaporate on exposure to air at room temperature. - **Essential**: As they represent the **"essences"** or principal, active principles of the plants in which they occur. - **Aromatic**: Since most have aromatic odor. ### Major Differences Between Volatile & Fixed Oils | Property | Volatile Oil | Fixed Oil | |---|---|---| | Volatilization at ordinary temperature | Volatile | Non-volatile | | Solubility | Soluble in organic solvents (ether, CHC13) & Alcohol | Limited solubility in organic solvents, almost insoluble in alcohol | | Stain on filter paper | Transient| Permanent & greasy | | Composition | Complex mixtures of hydrocarbons & oxygenated compounds | Triglycerides of fatty acids e.g. palmitic, stearic, oleic...... | | Response to long exposure to air & light (oxidation) | Resinification | Rancidity | | Saponification with caustic alkali (KOH) | Negative | Positive | ## Free & Combined Forms of Volatile Oils - The volatile oil may be **hydrocarbon (terpenes)** or **oxygenated hydrocarbon (terpenoids)**. - They may be present: - **Free**: Aromatic characteristic odor. - **Combined with**: - **Sugars**: Glycosides - **Gums, resins or both**: Oleo-gums, oleoresins or oleo-gum-resins. ### Types of Volatile Oils 1. **Natural volatile oils**: Present as it is and separated from plant parts. 2. **Derived volatile oils**: Don't pre-exist but formed by decomposition of a glycoside. ## Examples - **Bezaldehyde (amygdalin)** in bitter almond (Emulsin E) - **Allyl isothiocyanate (sinigrin)** in black mustard by (myrosin E) ## Distribution, Localization and Function ### 1. Distribution - In higher plants, different families as: Rutaceae, Myrtaceae, Lamiaceae (Labiatae), Lauraceae,..... - Accumulate in all types of vegetable organs: Flowers (rose), Leaves (eucalyptus), Barks (cinnamon), Woods(Sandalwood), Roots (vitiver), Fruits (star anise), etc… ### 2. Localization - Usually in specialized histological structures | Structure | Family | |---|---| | Oil cells | Lauraceae. Zingiberaceae | | Glandular trichomes | Lamiaceae (labiatae) | | Secretory cavities | Rutaceae, Myrtaceae | | Secretory canals | Apiaceae (Umbelliferae), Asteraceae (Compositae) | ### 1) Variation in composition of Vol. oils from different organs of the same plant | Plant Part | Composition | |---|---| | Cinnamon tree bark | Oil rich in cinnamaldehyde | | Cinnamon tree leaf | Oil rich in eugenol | | Cinnamon tree root | Oil rich in camphor | - **Bitter orange tree**: - "Bitter orange oil": from the fresh pericarp of the fruit (rind or zest) - "Neroli oil": from the flowers - "Petit grain oil": from the leaves, twigs & unripe fruits. - **These oils are different in composition & aroma** ## Uses of Volatile Oils 1. **Therapeutic & medicinal uses**: Local stimulants, carminatives, diuretics, mild antiseptics, local irritants, anthelmintics, parasiticides. 2. **Spices & condiments**: In food seasoning (to impart aroma & flavor) or as preservatives. 3. **Flavoring agents**: In food (beverages, soups, bakery products, confectionery) & pharmaceutical industries. 4. **Aromatic agents**: In all types of perfume industries (cosmetics, soaps, Deodorizers, household, cleaners, polishes, insecticides). ## Function to the Plants Itself 1. **Attracting (for pollination) or repelling insects** 2. **Protection from heat or cold** 3. **As antibacterial agents** ## Physical Properties 1. **Possess characteristic odors (lemon and lavender oils)** 2. **Liquids and volatile at ambient temperature** - **Except anise oil** becomes solid at 15.5°C and **rose oil** solidify at 18 °C. 3. **Some oils on cooling deposit a solid substance called "Stearoptene" leaving a liquid called Oleoptene** Ex. Campher, menthol, thymol,... 4. **Soluble in common organic solvents.** Sparingly soluble in water, however sufficient to produce aromatic water. 5. **Specific gravity (0.8-1.17), mostly lighter than water, except clove, winter green & cinnamon oils are heavier (aromatic oxygenated oils)** 6. **Have high refractive index and most of them rotate the plane of polarized light.** ## Methods of Preparation - There are four main methods: 1. **Distillation** - Water distillation - Water and steam distillation - Direct steam distillation - Enzymatic hydrolysis 2. **Scarification and expression** - Sponge method - Ecuelle piquer - Expression of rasping 3. **Extraction with solvents** - Volatile solvents - Non volatile solvents 4. **Selection of the suitable method is done according to:** - The condition of the plant material (moisture content, degree of comminution) - The localization of the oil in the plant (superficial or deep) - The amount of the oil - The nature of the oil constituents ## Distillation Methods **Application**: Preparation of thermostable oils, present in large amounts & not rich in esters (e.g. oils of turpentine, peppermint, cardamom, anise, eucalyptus). **Converts the essential oils into vapor and then condenses the vapor back into a liquid.** - Oil of terpentine boils at 160 °C - Water boils at 100 °C - Oil of terpentine + water = 95.5 °C **1. Water distillation** - Plant material (dried) is completely immersed in water and the still is brought to the boil, when the condensed material cools down. - E.g oil of turpentine. **2. Direct steam distillation** - Plant material (fresh) is placed in a still and steam is forced through the material. - The hot steam helps to release the aromatic molecules from the plant material and carries them (oil droplets) to the condensation chamber. - E.g: oil of peppermint. **3. Water and steam distillation** - Plant material (fresh or dried) is immersed in water in a still, which has a heat source and steam is fed into the mixture (water + crushed plant). - 1pint (=0.75 ml) essential oils are obtained from ½ ton (=225kg) of dried lavender by steam distillation. ### Distillation Methods Table | Method | Plant Material | Other | Advantages | Disadvantages | |---|---|---|---|---| | H₂O Distillation | Dried & fresh (petals), not injured by boiling with H₂O | | -Relatively low. -Least expensive. -Cohobation is allowed. | -Esters are hydrolyzed. -H₂O sol. & high b.p. not constituents are distilled | | H₂O & Steam Distillation | Dried & fresh, injured by direct boiling with H₂O | | Better. -Hydrolysis is reduced. | -Not suitable for powders, crushed | | Direct Steam Distillation | Fresh (i.e. containing moisture) | | The best. -Method suitable for oils rich in esters & high b.p. constituents | -H₂O is absent. -efficient if material entire or | ## Scarification & Expression Methods - **Principle**: Mechanical procedures carried at room temperature & based on puncturing )الخرم & queezing ( of the plant material to liberate the oil, which is collected. - **Applications**: Preparation of heat sensitive oils, present in large amounts in outer peels of fruits e.g. Citrus fruits (Rutaceae) as orange, lemon & bergamot. - **These are cold methods of extraction, mostly used in the extraction of citrus essential oils.** - Thermolabile (heat sensitive) - Room temperature (cold method) - **1. Sponge method** - Citrus fruits are cut into halves, the juice was removed and the pericarp soaked in water, then squeezed against a sponge in a cool dark room to prevent oil oxidation. - The sponge is periodically squeezed in a vessel→ oil + water. - **2. Ecuelle a piquer** - Funnel shaped apparatus made from copper provided with pins and short stem. - The fruits are placed in a device and rotate with puncturing the oil glands in the peel of the fruits. - Rotatory movement makes oil gland rupture the oil gland excluded from glands collected in the stem and separated. - **3. Expression of rasping** - The outer region of pericarp containing oil glands is removed by a grater. - The rasping is strongly pressed in horse-hair bag. ## Extraction with Solvents **For oils:** - **Decompose by the action of steam (thermolabile)** - **Present in extremely small quantities**. E.g. oil of Jasmine, violet, Tuberose. - **For delicate part (petals)** - **Extraction using volatile solvents**: Volatile solvents as pet. ether, hexane, are used by percolation or continuous extraction (Soxhlet) - **Evaporation under reduced pressure**: The volatile solvent will evaporate- leaving residue contains volatile oil and non-polar impurities (Floral concrete). - **Extraction of volatile oil from floral concrete with absolute alcohol** - **Non volatile solvent extraction methods application**: Preparation of delicate flower oilse.g. jasmine, violet and tuberose. - Present in very small amounts, not easily obtained by distillation or expression. - Oils formed of thermolabile constituents (i.e. easily decomposed by heat). - **1) Enfleurage method** - **2) Pneumatic method** - **3) Maceration method** ## Questions 1. Volatile oil leave Permanent & greasy Stain on filter paper (T/F) 2. Oxygenated hydrocarbon called terpenes (T/F) 3. Cinnamon tree have the same V.O in whole plant (T/F) 4. Use of Volatile Oils Attracting (for pollination) or repelling insects (T/F) 5. Clove, winter green and cinnamon oils are heavier than water (T/F) 6. Distillation methods can be used for preparation of thermolabile oils (T/F) 7. In direct steam distillation we can use direct flame (T/F) 8. We can prepare peppermint oil by using water distillation (T/F) 9. When Essential oil is present in small amount we can prepare it by using distillation methods (T/F) 10. Scarification method is used when oil present in large amounts in inner peels of fruits (T/F) ## MCQ 1. Cinnamon tree bark have. - (Cinnamaldehyde- eugenol-camphor) 2. Scarification contains - (sponge method – steam method- water and steam method) 3. For Extraction using volatile solvents we use - (enfleurage method- soxhlet – pneumatic method) 4. Extraction with non volatile solvent contains - (Enfleurage method – pneumatic method- both) 5. Solvent extraction method is used with - (thermostable substances – when oil present in large amounts- Thermolabile constituents)