Phytochemistry Lecture 3: Volatile Oils

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Questions and Answers

Which of the following components is NOT found in volatile oils?

Oxygenated compounds

Hydrocarbons

Proteins (correct)

Aromatic benzenoids

What is one reason that terpeneless oils are considered more valuable?

They have a stronger turpentine aroma.

They are less soluble in low-strength alcohols.

They contain more terpenoid hydrocarbons.

They are more stable. (correct)

Which method is NOT used for the removal of terpenoid hydrocarbons?

Selective extraction with dilute alcohol

Column chromatography on silica gel

Fractional distillation under reduced pressure

Selective extraction with water (correct)

What characteristic of terpenoid hydrocarbons contributes to their rapid deterioration?

Liability to oxidation and polymerization Signup and view all the answers

Isoprene units are characterized by which of the following?

Being branched five-carbon units with two unsaturated bonds Signup and view all the answers

What is produced when cold dilute acids react with bicyclic monoterpenes?

Terpineol and/or terpin hydrate Signup and view all the answers

Which reaction occurs when Sabinene is exposed to air and light?

Yielding α-thujene Signup and view all the answers

What transformation occurs when bicyclic monoterpenes undergo treatment with acids?

Ring-opening of the second cycle Signup and view all the answers

Which compound is obtained from the fractional distillation of oils from Juniperus sabina?

Sabinene Signup and view all the answers

What type of compounds undergo molecular rearrangement, oxidation, and dehydrogenation?

Bicyclic monoterpene hydrocarbons Signup and view all the answers

Which type of hydrocarbons makes up the majority of unoxygenated constituents in volatile oils?

Acyclic terpenoids Signup and view all the answers

What is the main process used to isolate non-phenolic fractions from volatile oils?

Fractional distillation Signup and view all the answers

Which of the following compounds is recognized as a sesquiterpene analogue of myrecene?

Farnesene Signup and view all the answers

Which component is predominantly found in citrus oils such as orange oil?

Limonene Signup and view all the answers

At what temperature is the fraction containing limonene collected during the fractional distillation process?

176ºC Signup and view all the answers

Which of the following is NOT a use of limonene and dipentene?

Solvents for paints Signup and view all the answers

Which of the following is considered a bicyclic monoterpenoid?

Pinene Signup and view all the answers

Which type of hydrocarbons can be categorized as both monocyclic and bicyclic?

Alicyclic terpenoids Signup and view all the answers

Which of the following statements is true about terpenes?

Terpenes can be either acyclic or cyclic in structure. Signup and view all the answers

What is the molecular formula of monoterpenoids?

C10H16 Signup and view all the answers

Which term describes terpenes that are derived from the oxidation of bicyclic triterpenes?

Irones Signup and view all the answers

Which of the following is NOT a type of volatile oil isolate?

Amino acids Signup and view all the answers

Which of the following categories does NOT represent a classification of terpenes?

Alkyne terpenes Signup and view all the answers

What structural feature is characteristic of phenyl propanoids found in essential oils?

A 6-carbon aromatic phenyl group and a 3-carbon propene tail Signup and view all the answers

What is a common characteristic of acyclic sesquiterpenes and monocyclic sesquiterpenes?

They are both C15 compounds. Signup and view all the answers

Which of the following statements about essential oils is true?

Essential oils can contain both terpenoids and phenyl propanoids. Signup and view all the answers

What is the primary method used to obtain Santalene?

Repeated fractional distillation Signup and view all the answers

Which essential oils are known sources of p-Cymene?

Lemon, sage, thyme, and origanum Signup and view all the answers

Which statement best describes how p-Cymene is formed during hydro distillation?

By cyclization and dehydrogenation of monoterpenoids Signup and view all the answers

What is the parent hydrocarbon that azulene derivatives are related to?

C10H8 Signup and view all the answers

What effect do azulene derivatives exhibit?

Anti-inflammatory and anti-ulcerative effects Signup and view all the answers

Which compound is NOT a product of the reduction of p-Cymene?

Chamomole Signup and view all the answers

What is a common use of chamazulene?

In cosmetic preparations for its anti-inflammatory properties Signup and view all the answers

What is the primary structure of azulene characterized by?

Its highly conjugated structure Signup and view all the answers

What is the main constituent in oil of turpentine?

α-Pinene Signup and view all the answers

Which compound is used in cough mixtures as a mucolytic?

Sobrerol Signup and view all the answers

How is Zingiberene obtained from ginger oil?

Fractional distillation under vacuum Signup and view all the answers

What process is used to convert α-Pinene into Sobrerol?

Auto-oxidation Signup and view all the answers

Which product is obtained from the oxidation of Borneol?

Camphor Signup and view all the answers

Which two forms of oil of turpentine are specified based on their optical rotation?

l-form and d-form Signup and view all the answers

What is a primary use of oil of cade?

Anti-eczematic treatment Signup and view all the answers

Which derivative is formed through the reaction of α-Pinene with HCl gas?

Bornyl chloride Signup and view all the answers

Study Notes

Phytochemistry Lecture 3: Chemistry of Volatile Oils Constituents

Volatile oils are complex mixtures of organic compounds.
Crucial components include hydrocarbons (mono and sesquiterpenes), oxygenated compounds (alcohols, esters, aldehydes, ketones), aromatic benzenoids, and compounds with sulfur or nitrogen.
Oxygenated compounds are responsible for the characteristic odor of volatile oils.

Removal of Terpenoid Hydrocarbons (Preparation of Terpeneless Oil)

Oils high in terpenoids are prone to rapid oxidation and polymerization during storage, leading to undesirable (turpentine-like) odors and reduced aroma.
These oils are less soluble in low-strength alcohols and often resenify quickly.
Terpene-less oils are more stable and more soluble in low-strength alcohols, requiring less material to achieve the same aroma strength. They contain richer amounts of oxygenated compounds.
Methods to remove terpenoid hydrocarbons include fractional distillation under reduced pressure, column chromatography (using silica gel and solvents), and selective extraction using dilute alcohol.

Terpenoids

Terpenoids are synthesized from isoprene.
Isoprene is also known as isopentene or 2-methyl-buta-1,3-diene.
Isoprene units are branched five-carbon units containing two unsaturated bonds.
Terpenes arise from the head-to-tail condensation of a variable number of isoprene units.
Different types of terpenes exist, including monoterpenes (C10), sesquiterpenes (C15), and others.
Chemical structures are displayed for various types of terpenes.

Terpenoids in Essential Oils

Monoterpenoids (C10H16) and sesquiterpenoids (C15H24).
These may exist in acyclic (non-cyclic) or alicyclic (cyclic) forms.
Many are hydrocarbons (90% of some citrus oils), as well as oxygenated forms (alcohols, aldehydes, ketones, esters, ethers, oxides, or peroxides).
Many terpenoids are optically active.
Some terpenes break down into other compounds due to oxidation.

Phenylpropanoids in Essential Oils

Natural products in volatile oils.
Contain a 6-carbon aromatic phenyl group and 3-carbon propene tail.
Exhibit pharmacological properties and are used in the pharmaceutical industry.
Examples include various hydrocarbons, alcohols, phenols, phenolic ethers, aldehydes, ketones, oxides, peroxides, and esters.

Hydrocarbons in Volatile Oils

These are unoxygenated constituents.
Includes various types of mono- and sesqui-terpenoids.
Acyclic and alicyclic forms are noted, including monocyclic, bicyclic, and tricyclic forms.
Aromatic hydrocarbons are also present.

Acyclic Terpenoids

Includes monoterpenoid and sesquiterpenoid hydrocarbons, such as myrecene and ocimene.

Alicyclic Sesquiterpenoids

Includes sesquiterpenoid hydrocarbons, such as farnesene and sesquicitronellene.

Alicyclic Terpenoid Hydrocarbons

Forms of monoterpenes (e.g., monocyclic, bicyclic), and sesquiterpenes (e.g., monocyclic, bicyclic, tricyclic)

Monocyclic Monoterpenoid Hydrocarbons

d-Limonene (citrus oils).
l-Limonene (turpentine oil).
Dipentene (dl form – racemic), (turpentine oil)

Bicyclic Monoterpene Hydrocarbons

Thujane derivatives, including sabinene.
ß-Pinane derivatives, including a-pinene and ß-pinene.

Monocyclic Sesquiterpenoid Hydrocarbons

Zingiberene (main constituent of ginger oil).

Bicyclic Sesquiterpenoid Hydrocarbons

Naphthalene derivatives, including cadinene and zingiberene.

Tricyclic Sesquiterpenoid Hydrocarbons

Santalene (obtained from sandalwood oil by repeated fractional distillation)

Aromatic Hydrocarbons

p-Cymene.
Source, isolation, and uses described.

Semi-synthesis

Methods to transform one compound into another.
Example reactions to form new chemical structures are shown.

Azulene Derivatives

Highly conjugated pigments found in mushrooms, guaiac wood oil.
Mostly colorless pro-azulenes
Isolation via adducts with mineral acids.
Parent hydrocarbon is azulene (C10H8).
Naturally occurring azulenes are substituted with alkyl groups (C15 compounds).
Exhibit anti-inflammatory and anti-ulcerative effects.
Example compounds: Chamazulene and Guaiazulene.

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Description

Explore the chemistry of volatile oils and their constituents in this lecture. Learn about the composition of volatile oils including terpenoids and the methods used to prepare terpeneless oils for better stability and aroma. This quiz will help reinforce your understanding of these essential oils in phytochemistry.