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Isolation of Essential Oils by Distillation

Introduction

Most spices have distinctive odors. Not surprisingly, these odors are the result of specific organic chemicals, often in very small concentrations. In this lab, we will be isolating the main organic chemicals giving cumin and caraway that give their distinctive odors. We will isolate these compounds by a process known as steam distillation. In steam distillation, we will be distilling these compounds out of the spices with boiling water. A similar process can be used to decaffeinate coffee.

We will be isolating these compounds as part of a mixture. The mixture of compounds is a liquid, often termed the “essential oil”. We will isolate the odor-producing compound from the mixture by doing chemical reactions which react with the C=O functional group of the aldehyde or ketone. These reactions produce solids, which we will purify by recrystallization. We can take melting points of the solids to verify their identities, since the melting points of the solids are known.

Cumin: The main constituent of the oil of cumin is cumaldehyde, more systematically named as 4-isopropylbenzaldehyde. Oil of cumin also contains limonene.

4-IsopropylbenzaldehydeLimonene

Caraway: Oil of caraway contains carvone and limonene.

CarvoneLimonene
The solid derivatives we are preparing are the 2,4-dinitrophenylhydrazones (DNP’s for short). These are prepared by reacting the aldehyde or ketone with an acidic solution of 2,4-dinitrophenylhydrazine in ethanol. The DNP’s separate as yellow to red solids, which are filtered off, washed with sodium bicarbonate solution, then recrystallized from ethanol.

Aldehyde2,4-dinitrophenylhydrazineDNP derivative

or ketone

Procedure

Isolation of the Essential Oil

Place 8-10 grams of the selected ground spice in a 500 ml 3-neck round-bottomed flask, and add 150 ml of water, along with a few boiling stones. Assemble the apparatus for a direct steam distillation, using a 125 ml Erlenmeyer flask cooled in an ice bath as a receiver. Heat the mixture to boiling with a Thermowell and variable transformer, setting the variable transformer at 8-9. Continue distilling until no further drops of oil can be seen coming over with the water. At least 50-60 ml of liquid should be collected.

Pour the distillate into a 250 ml separatory funnel and extract it twice, using 15 ml portions of methylene chloride. After shaking each time, separate the lower methylene chloride layer into a pre-weighed 100 ml round-bottomed flask. Evaporate the solvent using a rotary evaporator. Reweigh the flask to determine the yield of your essential oil.

Preparation of the DNP derivative.

Dissolve the oil in 2 mL of ethanol, and pipette it into a small beaker. Add 2 mL of DNP reagent (caution: contains sulfuric acid), stir briefly, and allow the mixture to stand for 5 minutes. Collect the solid by suction filtration, wash it with two, 5 mL portions of sodium bicarbonate solution, then with 10 mL of water. Transfer the solid to your 100 mL beaker, add 20 mL of 95% ethanol, and heat it to boiling on the hot plate. If all of the solid does not dissolve, add 95% ethanol in 5 ml portions and keep boiling until it all does dissolve. Remove the beaker from the hot plate, and let it cool for 5 minutes. Place the beaker in an ice-water bath, and let it cool for 10 minutes more. Collect the solid by suction filtration (see the Aspinol Operations Handout), and wash it with 5-10 mL of cold ethanol. Allow it to dry for a few days, then take a melting point of it. The literature melting point of the DNP of carvone is 191º. The literature melting point of the DNP of 4-isopropylbenzaldehyde is 241º.

Steam Distillation Apparatus

CH234 Essential Oils ReportName: ______

Spice Used
Weight of Spice Used
Weight of Oil Isolated
Odor of Your Oil

Weight of DNP Derivative

Melting point range of DNP derivative

Calculate the percent yield of your essential oil from your spice. Show your work.

Write a balanced chemical equation, using structures, for the formation of your DNP derivative.

Calculate the percent yield of your DNP derivative from your essential oil. There is 2.9 grams of 2,4-dinitrophenylhydrazine in 100 mL of the DNP reagent. Assume the oil was 100% 4-isopropylbenzaldehyde or carvone (actually wrong, but we need to assume something for you to do the calculation). Show your work.

a. Calculate the grams of 2,4-dinitrophenylhydrazine you used.

b. Calculate the moles of 2,4-dinitrophenylhydrazine you used.

c. Calculate the moles of 4-isopropylbenzaldehyde or carvone you used.

d. What is the limiting reagent? Explain.

e. Calculate the theoretical yield of the DNP derivative.

f. Calculate the percent yield of the DNP derivative.