Isolation & Identification of the Major Constituent of Clove Oil with Steam Distillation

Isolation & Identification of the Major Constituent of Clove Oil with Steam Distillation

The purpose of this laboratory experiment was to isolate and characterize clove oil in order to understand how to isolate organic compounds with high boiling points, how to perform and interpret qualitative tests for organic compound functionality, and to continue to learn how to perform and interpret IR spectrometry. Steam distillation was used in order to prevent the organic compound from decomposing at temperatures approaching the compound's boiling point.

The essential oil of a plant is a mixture of volatile, water-insoluble components that exhibits the odor and other characteristics of the plant. In this experiment the essential oils of clove will be isolated. Cloves contain about 16% by mass of the essential oil, a pale yellow liquid with a sweet, spicy aroma. Clove oil is unusual among essential oils in having only one major component, which comprises about 85% of the oil.

Essential oils are nearly always isolated by steam distillation, in which steam forced through the plant material vaporizes the essential oil which is then condenses into a receiver along with water from the condensed steam. Clove oil was separated from the distillate by extraction with dichloromethane, and its major component was then separated from minor components by extraction with aqueous sodium hydroxide.

The major component of clove oil was a strong-smelling liquid that has the molecular formula C10H12O2. Below are some of the possible structures for the component.

Discussion of Results

1.002 g of fresh whole cloves was weighed but the use of a mortar and pestle to grind them to a fine powder was unnecessary as a better yield was given when larger chunks of clove were used. The cloves were a dark brown color with a tree bark-like texture and a distinct cinnamon odor. The distillation apparatus was assembled using a using a 10-mL round bottom flask, condenser and a Hickman still. Then a 15 mL centrifuge tube was calibrated using cold water marking the levels of 6 to 8 mL for the collection of clove oil. The fresh clove was then combined with water in the distilling flask and distilled until very little liquid remains in the boiling flask. The color of the product began to turn light cloudy yellow as it began to boil indicating the beginning production of clove oil.

With a 9-inch pipet was used to add water through the condenser to keep the flask no more than half way full. Clove oil was extracted from the distillate in 1 mL increments every 5 to 10 minutes. The distillation and extraction process was approximately 37 minutes with 7 mL of distillate recovered. The product recovered was a light yellow liquid color with the same strong, sweet, cinnamon odor as the raw clove. 1 mL of dichloromethane solution was used to rinse the Hickman still and was then transferred to the centrifuge tube. Another 2 mL more of dichloromethane was added and shaken vigorously. Upon shaking the the mixture turned a cloudy white color with two layers resulting. The major component of clove oil was extracted with two more 3 mL portions of dichloromethane solution. The mixture was allowed to cool and left in the hood overnight to dry.

The next day an orange goopy textured product resulted. The extracts were then dried and combined with anhydrous sodium sulfate, then evaporated with dry air under the hood in a warm water bath. The liquid was cooled and had an initial weighing of 0.5887g. It was reweighed several minutes later with a final mass of 0.587g. The mass was constant and was not reweighed.

With the resulting product, an infrared was obtained of the clove oil. One of the most distinctive bands in an infrared spectrum was the one arising from the carbonyl (C=O) stretching mode. This was a very strong peak observed somewhere between 1640-1820 cm-1, and frequently between 1670-1780 cm-1. Its exact location varies between the various carbonyl containing compounds. There was no strong peak due to a carbonyl group in the IR spectrum graph. In fact, the spectrum was practically empty in this region. That was the most pertinent information needed to figure out which compound was the correct one. With the six compounds given as options for the main component in clove oil only one of them lacks a carbonyl group. Among the other five, there is an ester, a carboxylic acid, 2 cyclic ketones and an aldehyde. All of these have a C=O group somewhere in the structure. Therefore, it was easy to conclude that the compound without the C=O group in it was the main compound in clove oil.