Chirality-Isolation of Limonene from Citrus Fruits

Project 5: Chirality-Isolation of Limonene from Citrus Fruits

Organic Chem I Laboratory - CHM 2210L

Introduction:

Steam distillation is used in the extraction of essential oils. The hot steam helps to release the aromatic molecules from the orange peels by forcing the pockets to open where the oils are kept. The oils escape from the peels and evaporate into the steam. If the temperature is too high, the essential oil can be burned. The steam of the oil goes through the cooling system to condense and forms a liquid containing the water and the oil. The steam distillation was used to extract terpenoids to obtain the essential oil. "This distillation technique is used because it is based on the balance of immiscible liquids, leaving the boiling point of two liquids to be lower than the actual boiling point of them individually" (Steam Distillation of Essential Oil Manufacture). Terpenoids are immiscible with water, leaving the boiling point to be lower. The terpenoids decompose at the boiling point.

Limonene is a clear monoterpene liquid. It is found in essential oils of citrus fruits and other plant species. It occurs in two active forms, l-limonene and d-limonene. These two isomers have very different odors: l-limonene smells piney and d-limonene has an orange scent. In the isomerization of limonene, the cyclohexane ring is chiral. Chirality is when the geometric property of a molecule is non-superimposable on its mirror image. An atom will have four non-equivalent atoms attached to it. The enatiomeric excess of a substance is a measure of how pure the substance is.

Polarimetry is utilized in this experiment. This measures the extent to which a substance interacts with a plane of polarized light. If the plane rotates to the left or right, then it is called optically active. If this occurs then it is said that the compound must have a chiral center. If the compound does not rotate at all, then it does not have a chiral center. This is based off of its optical rotation, which is the turning of a plane of linearly polarized light about the direction of motion as the light travels through certain materials.

Refractive index is a physical constant that is used to characterize a liquid. It is the ratio of the velocity of light in air over the velocity of light in liquid. It is measured by using a refractometer and a few drops of liquid.

Table of Chemicals:

Compound

Melting Point

Boiling Point

Density

Molecular Weight

IUPAC

Limonene -74.35oC 176oC 841.10kg/m3 136.24g/mol C10H16

Results:

mL of distillation Temperature mL of distillation Temperature

Initial 96oC 20 mL 100oC

5 mL 100oC 30 mL 100oC

10 mL 100oC 35 mL 100oC

15 mL 100oC 40 mL 100oC

Table 1: This table shows the amount of solution that was distillated and temperature at that point.

Compound Weight of 250mL Flask Weight of flask with oil Total weight of oil Weight of orange peels Percent yield of limonene

Limonene 136.03g 136.69g 0.66g oil 73.40g 0.89%

Table 2: Weights recorded for limonene oil and orange peels.

Percent Yeild:

Mass of oil x 100 = % Recovered 0.66g oil x100 = 0.89%

Mass of peels 73.4g peels

Specific rotation: [α]DToC= α = 5.1 = 77.27

(1*c) (1.0dm)(0.066g/mL)

Where α is the observed angle of rotation;

1= length of the light path in dm;

c= is the concentration of the sample in g/mL;

ToC=