In this article we are going to focus on chemical profile of essential oils. Essential oils chemical composition and its chemistry plays a significant role in assessing the properties of oil.

We so far know that essential oils are concentrated liquids that are obtained from various parts of the plant. Chemical compounds of plant are classified into primary and secondary metabolites.

Any guesses, essential oil comes under which part? Let me get into details of both terms.

Primary metabolites are those metabolites which are directly involved in the normal growth, development and reproduction of plant. Examples are carbohydrates, vitamins, hormones, flavonoids etc.

Secondary metabolites are those compounds which are not essential to the functioning of the plant. Examples are atropine and antibiotics. Among secondary metabolites, essential oils are very important natural products. Thus, essential oils are secondary metabolites of plant.

Essential oils are volatile oils that are obtained from plant parts using steam distillation or mechanical process. At first glance, essential oil may only be about scents and fragrance. But there is a lot more. They are actually unique domain of study in organic chemistry. Essential oil and chemistry go hand-in-hand.

Essential oils are usually mixtures of volatile compounds which involves non-polar and fat soluble which are produced in plant species.

These plant essential oils are combination of many chemical constituents. Sometimes even over 100 compounds in single oil. Thanks to these chemical constituents which impart oil with various biological activities like antimicrobial, anti-inflammatory, antioxidant etc. It thus becomes very important for everyone who works with essential oil to understand the role of chemistry.

Let us now dive deep into chemistry of essential oils.

Role of chemistry:

Chemistry plays crucial role right from start of extraction process. Extraction of oil is extracted using process of steam distillation or water distillation, solvent extraction or expression. Sometimes other techniques like CO2 extraction or Enfleurage comes into picture.

Distillation itself is an important technique of organic chemistry. Distillation is used for separation of liquids according to their boiling points. Distillation technique is governed by some parameters like temperature, pressure and time of extraction so that the final product obtained is of good quality. Chemical components should not get degrade while extraction process.

Supercritical CO2 extraction process uses carbon dioxide as solvent and it is desirable as it reduces time to extract the oil. This sort of extraction is usually performed under trained chemist and laboratory conditions.

Next segment where chemistry plays unavoidable role is: analysis. Analysis of oil samples is done using gas chromatography-mass spectrometry and nuclear magnetic resonance spectroscopy. Experience individuals in respective machinery can help to determine chemical composition of oils.

Chemical profile of Essential oil

Essential oil is a mixture of low molecular weight constituents that are responsible for the peculiar aroma. The essential oil composition depends on the species of the extracted plant, geographical location of the plant, harvest time and method of extraction. In general, essential oils are divided into 2 distinct groups of chemical constituents:

• Hydrocarbons.
• Oxygenated compounds.

Hydrocarbons:

Hydrocarbons are made up of terpenes which include monoterpenes, diterpene and sesquiterpene. These are considered as most common class of chemical compounds that is found in essential oils.

 I am pretty sure, you have encountered these terms before. Building block of terpene is 5-carbon isoprene unit. Synthesis of terpenes takes place in the cytoplasm of plant cells through mevalonic acid pathway. These are polymers of isoprene units that are joined in a head to tail manner.
Terpenes inhibit the accumulation of toxins and assists in discharging toxins from liver and kidneys.

a) Monoterpenes: The combinations of two isoprene units are called as “terpene unit.” Monoterpenes are formed by attachment of two isoprene units which reflects that it should have at least one double bond. These contribute to various organoleptic properties that are associated with various herbs, spices, and citrus.

They may be cyclic, acyclic or aromatic. Some very widespread monoterpenes are myrcene, Sabinene and terpinolene. One should note that monoterpenes end in –ene.

b) Diterpene:These are formed by combination of 4-isoprene units followed by rearrangement and substitution. They are important component of plant resins. These are present in low concentration in essential oils because of their less volatile nature. These include camphorene, phytane, and labdane etc.  

c) Sesquiterpene: These are second dominant terpenes. These are unsaturated compounds formed from combination of three isoprene units. They can be linear, branched or cyclic.

They are less volatile but have stronger odors. These are highly studied and widespread. Examples are valencene, chamazulene, caryophyllene and selinene etc.

Oxygenated compounds:

Oxygenated chemical compounds contain oxygen as part of their chemical structure. These mainly consist of esters, aldehydes, ketones, alcohols, phenols and oxides.

These compounds are highly odoriferous and they impart plants their fragrance. For instance you must have smelled spearmint oil it has spicy minty odor and credit goes to carvone that is major component of oil.

a) Esters: These compounds results from reaction of alcohol with an acid. The reaction is termed as esterification. They can be frequently found in essential oils. Example: Linalyl acetate and Geranyl acetate.

b) Aldehydes: These are highly reactive with group C-H-O (Carbon, Hydrogen, Oxygen). On topical application, they can cause irritation. Examples are Citral and Citronellal.

c)  Ketones: These compounds are yet other constituents that are present in essential oils. It includes thujone, jasmine, carvone, fenchone etc.

d) Alcohols: These compounds are characterized by O-H group (Oxygen, Hydrogen). It is classified as terpene alcohols and sesquiterpene alcohols. Compounds in this group are Linalool, Geraniol, Bisabolol etc.

e) Phenols: They contain high amount of oxygenating compounds and are responsible for fragrance of oil. These include Thymol, Eugenol, Carvacrol, Anethole etc.

f) Oxides: Those chemical compounds that consist of atleast one oxygen atom. It can also be defined as binary compound of an element or radical with oxygen. It includes cineol, linalool oxide, Bisabolol oxide etc.

Almost all essential oils are made up of these chemical components. Some can be rich in aldehydes and other can be in monoterpenes. It goes like that only. As you know Lemongrass oil is rich in Citral which is aldehydes type of oxygenated compound, Right?

Now consider your favorite Lavender oil it contains linalool and linalool oxide in major amount that is it is both alcohol and oxide rich. All these oils contain some amount of terpenes in it. These components are responsible for providing fragrance as well as biological activities. So understanding the chemistry is a huge part.

Let’s discuss more on these interesting and magical compounds which are adding quality to our life and background. What has been your special interaction and relation with these compounds. Feel free to put any query I’ll try to answer best from my end. Let’s community come together to make it more interesting.

Thank you.