Limonene
A colourless, unsaturated hydrocarbon. Volatile liquid at room temperature and pressure, with a boiling point of 176 degree Celsius.
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| Molecular structure of limonene. It is a cyclic monoterpene, containing two isoprene units and having the formula C10H16. |
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| Limonene is chiral, meaning the enantiomers cannot be superimposed on its mirror image. It occurs naturally as the R enantiomer. |
D-limonene has a citrus smell. It occurs in citrus peels such as orange.
L-limonene smells like turpentine and pine. It can be found in pines, conifers, as well as herbs like mint.
Why extract D-Limonene?
D-limonene is an essential oil. Essential oils have important functions in plants, repelling fungi and pests. The sweet fragrances of flowers attract pollinators. In fruits, essential oils attract fruit-eating animals that help to disperse the seeds.
+ fruit peels like orange and lemon are discarded after consumption. Extracting limonene is green because the peels are reused :)
+ combustable, thus can be used as a potential renewable biofuel
+ important medicinal properties: sedative, anti-stress, anti-carcinogenic, relieves heartburn and gastrointestinal reflux
+ useful in chemical synthesis: a precursor to carvone
+ solvent for cleaning products
+ used in cosmetic products, food flavorings and as a fragrance in the perfume industry
+ botanical insecticide, with fewer harmful side-effects compared to other insecticides such as DDT
How to extract D-Limonene?
Orange peel can be separated into two distinct layers: the pith and the skin.
The white pith contains negligible amount of orange oil, and is discarded.
The outer, orange part of the orange peel is the skin, and contains most of the orange oil.
Because limonene is a relatively stable terpene, it can be extracted through steam distillation, without decomposing. This maintains the structure of the limonene molecules, crucial in ensuring the purity of limonene extracted.
Hot steam opens the pockets in orange peel, allowing volatile orange oil to be released. As the temperature increases, these volatile molecules vaporise and condense on the cooler surface of the condenser. Since limonene is volatile, it can vaporise at a temperature lower than its boiling point. Thus, the liquid collected from steam distillation is a mixture of water and limonene.
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| Cut the outer, orange part of the orange peel (skin) |
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| Measure and record mass of orange peel in a pre-weighed container |
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| Add distilled water and homogenise in a blender. |
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| Transfer all of the mixture to a clean 250mL round bottom flask using filter funnel and spoon |
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| Set up apparatus for fractional distillation. Turn on the hot plate and condenser water. Keep watch of the temperature of the vapour. |
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| Collect distillate. |
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| Immerse distillate in a water bath at 80°C. Allow liquid to settle; orange oil rises to the top. Drain orange oil into a pre-weighed clean vial. Measure and record mass of orange oil for subsequent calculations. |
Results
Initial mass of orange peel = 101.0g
Final mass of orange oil = 1.2g
% yield = 1.2g ÷ 101.0g x 100% = 1.19%
Due to the low volume of water added during homogenization, we extracted limonene with a higher purity, but obtained a lower yield.
The yield of limonene is quite high compared to other essential oils, which can range from 0.01-1%.
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| The presence of unsaturated hydrocarbons such as limonene can be tested by adding aqueous bromine to the orange oil. If mixture changes from brown to colourless, unsaturated hydrocarbons are present. |
References
http://en.wikipedia.org/wiki/Limonene
http://www.catalysis-ed.org.uk/asymmetric/asymm1.htm
http://www.reading.ac.uk/web/FILES/chemistry/Limonene.pdf
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