Limonene C10H16 (IUPAC: 1-Methyl-4-(prop-1-en-2-yl)cyclohex-1-ene) is a cyclic-monoterpene aliphatic hydrocarbon. Monoterpenes are a class of terpenes that consists of two isoprene units bonded in a linear chain or in a cyclic shape. Isoprene is the foundamental unit of all terpenes.
Limonene is the main component of orange and lemon essential oil. Its quantity is variable, depending on the fruit. In orange essential oil, limonene percentage oscillates between 91-97% (depending on the orange’s origin)1 . Other components of orange essential oil are other terpenes (ex. alpha and beta Pinenes) and long chain alyphatic hydrocarbon alcohols and aldehydes. Limonene is a chiral molecule. The (R)- enantiomer (aka D-Limonene) defines orange’s fragrance.
I'm goinf to extract D-Limonene (90+%) from orange peels. The extraction will be performed by Steam Distillation
Steam distillation is a process that involves steam to co-distill a volatile substance. It is one of the most common method to extract natural products from plant materials. Although steam distillation and simple distillation seem to be identical, the theory behind the separation process is quite different. When the components of the starting mixture are immiscibile (ex polar and nonpolar chemicals mixed together), the vapour produced from this mixtures is different. The components act indipendently from one another. The partial pressure of the mixture is no longer defined by the molar fraction of the solute in the solvent, as instead during simple distillation, according to Raoult’s Law. The components of the mixture don’t mix each other in the liquid phase, but in the vapour phase. This allows the co-distillation.
A mixture boils when its vapour pressure reaches the atmospheric pressure (1 atm). Pure water reaches that value at 100°C. Because of the heterogeneous component (orange peels) that contribuites to the total pressure, the mixture is excpected to boil before 100°C. This is an important feature of steam distillation: it allows the extraction of the oil avoiding its decomposition (at high temperature).
Limonene is nonpolar. It’s not miscibile with water. It also has a lower density. Because of this, it forms a layer over the water. The initial mass of peels is 112g. The distillation has been stopped after 4 hours from its beginning. A total of 3ml has been collected. A water drop is observable in the test tube. Because of the much higher density of the water, the drop sinks to the bottom.
Recorded with a NIKON D7500 Digital Camera, DX SWM VR ED IF Aspherical 72 , Edited with Camtasia 9.
References:
Steam Distillation: Lisa Nichols Organic Chemistry Lab Techniques, 2nd edition 2017 [ Ссылка ]
D-Limonene: PubChem [ Ссылка ]
Notes:
1 orange oil, wikipedia [ Ссылка ]
Disclaimer: The following process is shown only for demonstration and entertainment purposes. It should not be replicated without proper knowledge. Limonene is a flammable, irritant and toxic chemical and must be handled carefully and safely.
