Extraction of Carvone

Carvone Extraction Exercise 

Updated 27 th January 2004 

Click here to print in pdf 

Extraction of Carvone 

Click here to print the cover sheet for your lab 

Click here to print the (+) Carvone IR 

Click here to print the (-) Carvone IR 

Objective 

The purpose of this laboratory exercise is to perform extractions by taking a natural product, in this case 

spearmint leaves and caraway seeds, and extract carvone from them. 

Grading 

You will be assessed on 

Completion of the separation of the organic compounds 

Analysis by TLC 

Write up in your Lab Notebook (see Lab Notebook Guidelines) 

TA evaluation of lab procedure 

The pre-lab assignment involves reading and signing both the 

Equipment Responsibility Form and the Safety Rules. There is an additional 

Release Form if you are under 18. These sheets must be completed 

and handed in to your TA at the beginning of lab. 

Lab Notebook Guidelines 

(see Lab Notebook Guidelines) 

Experimental Procedure 

Introduction 

Page 1 of 6 

One of the most fascinating areas in organic chemistry is the study of stereochemistry. The most 

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complicated part of most syntheses is to ensure that your product has the appropriate stereochemistry, 

and an enormous amount of work is expended by chemists to try to ensure better stereochemical control. 

Interestingly, living organisms have no problem producing stereochemically pure products. While it is 

difficult to make an enantiomerically pure compound in the lab, plants and animals do it constantly with 

no error. Living organisms are also much more sensitive to stereochemical differences than many 

laboratory tests. Using most techniques, two enantiomers behave exactly the same: they will have the 

same melting point, boiling point, and density, and will react identically with achiral chemicals. The 

only way to distinguish between different enantiomers in the laboratory is to measure their optical 

activity or treat them with other enantiomerically pure chemicals. Living organisms, on the other hand, 

are excellent at distinguishing between enantiomers. The nose, for example, is one of the most sensitive 

tools for distinguishing some enantiomers--two different enantiomers can smell completely different 

even though they behave the same as one another in many other tests. 

In this lab you will study two naturally produced enantiomers, (-)-carvone and (+)-carvone. Both of 

these chemicals are edible in small quantities and are used as flavoring oils in industry. They have the 

exact same molecular structure, except that they are mirror images of one another. 

One of these enantiomers comes from caraway seeds and the other from spearmint leaves. These 

compounds are responsible for the distinctive smells of the plants, and you can easily determine which 

enantiomer is derived from which plant by its smell. 

You will extract carvone from both caraway seeds and spearmint leaves by soaking the plant matter in 

the proper solvent, and then you will use thin layer chromatography (TLC) and IR to compare the 

compounds you extract. The extraction is based on the fact that carvone is very soluble in methylene 

chloride and in methanol. Therefore, soaking seeds or leaves in either of these will cause it to leach out 

of the plant matter and into the solvent. The reason we do not use the same solvent for both extractions 

is that methanol dissolves the carvone more readily but also dissolves many other substances. There are 

so many materials in caraway seeds that are soluble in methanol that using this solvent would result in a 

highly contaminated sample. In spearmint leaves fewer contaminants are extracted into the methanol, so 

it is an ideal solvent for this extraction. Methylene chloride does not dissolve carvone as well, but it is an 

effective solvent for the extraction of carvone from caraway seeds, where it is abundant. 

Experimental 

NOTE: All TLC plates that have glass backing go into the sharps container. They may not be 

sharp when you use them but odds are the glass will end up that way. 

The technique that will be used to analyze your extracts is explained in the following section. 

THIN LAYER CHROMOTOGRAPHY (TLC) 


TLC is one of the most commonly used techniques in chemistry. It allows a chemist to accurately and 

rapidly analyze very small quantities of material. In this experiment you will use TLC to identify and 

also to check the purity. 


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TLC plates are either glass or aluminum that has been coated with a very thin layer of silica. See text. 

The polar silica is strongly attracted to polar materials, and any polar material on the plate will tend to 

stick to it. When you place a small spot of material at the bottom of the plate, it will be carried up the 

plate by the solvent as capillary action proceeds. The most polar components of the sample will be very 

attracted to the stationary silica gel and not move very far up the plate. The least polar materials will 

have no attraction at all for the silica and will dissolve in the solvent well, thus moving up the plate at 

the same speed as the solvent itself. As time goes on, the compounds within the sample will become 

separated on the plate according to polarity. The most polar molecules will be stuck at the bottom while 

the least polar will flow quickly to the top. 

A TLC plate is prepared as follows. Take a plate and mark two lines on it. Place one line approximately 

1-2 cm from the bottom and one 1-2 from the top. You will spot the sample on the lower line. When the 

TLC plate is being developed the solvent will run up the plate. You will remove the plate when the 

solvent reaches the second line. In about one minute the solvent will evaporate and you will be able to 

check your sample under UV light or stain the plate to determine which compounds appeared. After 

development the plate will look something like the following diagram. 

TLC spots are identified by their Rf value, which is the ratio of the distances the spots ran to the 

distance the solvent itself ran. Thus the Rf is calculated by dividing the distance the spot ran by the 

distance the solvent ran. You can see that the spots on the plate shown above have Rf values of 0.25, 

0.72, and 0.87. 

It can be useful to run several samples on the same TLC plate to easily compare the components of one 

sample with the components of another. If the same molecule is contained in two different samples, 

when you run the samples together on the same plate this molecule will run the same distance for both 

samples and you will see two spots right next to each other. The size and intensity of the spots are 

indicative of the amount of material, so you can see which sample contains more of the material. In this 

lab you will be given two samples of carvone (one + and one -) that were bought from a chemical 

company. You will run these on the same TLC plate as you plant material extracts in order to determine 

whether you actually extracted carvone and how pure this extract is. 

Remember to always use pencil when marking a TLC plate. Pen ink will run up the plate along with 

the solvent and render the plate unreadable. 


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Procedure 

1) Measure 2 g of crushed caraway seeks into the 30 mL beaker and add 10 mL of ether. Ether is chosen 

as a solvent because the carvone is soluble in ether. Cover with aluminum foil to prevent evaporation 

and allow to stand for 15-30 minutes. 

2) Measure 2 g of spearmint leaves into the 50 mL beaker and add 10 mL of ether. Again, cover with 

aluminum foil and allow to stand for 15-30 minutes. 

The different containers have no effect on the extraction. It simply allows you to do two extractions 

simultaneously without duplicating your glassware. 

3) Once the seeds have soaked for the appropriate time, use a Hirsch funnel to filter the caraway seed 

solution. This is done by placing a piece of filter paper in the funnel, assembling the Hirsch funnel as 

diagrammed below, and starting the suction so that a vacuum builds up in the filter flask. Pre-wet the 

filter paper with ether, then pipette the liquid from the extraction into the funnel and collect the liquid in 

the receiving flask. When you have filtered the caraway seed solution transfer the filtrate to the cleaned 

30 mL beaker and wash out the receiving flask with acetone. 

4) Repeat step 3 with the spearmint leaves using a clean pre-wetted piece of filter paper. Transfer this 

filtrate into the cleaned 50 mL flask. 

5) Obtain a TLC plate that contains an indicator (metal or glass backed only) and draw a pencil line 

about 1 cm from the bottom on the side coated with silica. Draw a parallel line 1 cm from the top. On 

the lower line draw four small lines evenly spaced along this line to indicate where you will place your 

samples. 


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Label the lines "+" (for (+)-carvone), "-" (for (-)-carvone), "c" (for caraway extract), and "s" (for 

spearmint extract). 

See you TA if you haven't already about preparing a spotter in lieu of using a capillary tube. 

6) Dip the tip of a spotter (or capillary tube) into your caraway extract and quickly dab this tip onto the 

line where it is labeled c. You may find it beneficial to do this under UV light to see how much sample 

you are placing and how large of a spot you are creating. You should see a very small amount of the 

caraway extract soak into the plate. For the two extracts it is a good idea to spot multiple times (or to 

concentrate your sample) as the amount of carvone in the sample is small. Simply spot, let the solvent 

evaporate (leaving the sample on the plate) and spot again at the same location. 

7) Repeat this procedure for the spearmint extract 

8) Now do the same thing with the diluted (+) and (-) carvone standards. These are more highly 

concentrated than your extracts so make sure to just barely touch the plate with the spotter. 


9) When you have spotted all four of your samples, obtain about 5 mL of 10% ethyl acetate in hexane 

in you 250 mL beaker. Place the beaker on your bench top. 

10) Make sure that the solvent is initially below the line you used to spot the plate. Place you TLC 

gently into the beaker. You will see capillary action begin immediately as solvent runs up the plate. 

11) Cover the beaker to prevent evaporation (a watchglass or aluminum foil is appropriate). After a few 

minutes the solvent will reach the upper line. Remove the plate and allow the solvent to evaporate. 

12) Let the plate dry and then take it to the UV light. The spot of carvone will be visible in the UV 

light. Mark the spot by holding a UV light to it and circling all the spots you see in pencil. You should 

see a carvone spot in all four samples, though it may be larger in some than in others. Note any 

differences you see. Be sure to record the plate in your notebook to the correct scale. 

13) You can also stain the plates with a p-anisaldehyde stain. This stain turns carvone a reddish brow 

color and turns most other compounds blue, so it will be easy for you to identify the carvone spot. 

Using forceps, dip your plate into the anisaldehyde solution. Wipe off the glass back of the TLC plate 

with a paper towel, and then use a heat gun the heat the plate. You will see a pinkish color develop over 


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the whole TLC plate and blue or brow spots where the material ran. Be sure not to overheat the plate or 

it may crack. Once done, check your TLC plate with your TA. 

Draw a picture of the stained plates in your notebook and determine the Rf values. Can you find the redbrown 

carvone spot on all four samples? Can you tell by the spots which enantiomer is contained in 

spearmint and which is in caraways seeds? 

14) Go see the IR demonstration and receive a copy of the IR for both pure carvone samples if you 

haven't already. Do the two enantiomers have distinctly different peaks? Could you tell the difference 

between enantiomers based on the IR spectra? 

15) Smell the pure samples of + and - carvone and then smell some unused caraway and spearmint 

leaves. Can you tell by smell which of the enantiomers is from spearmint and which is from caraway? 

Post Lab Questions 


1. In this lab you used three methods to attempt to distinguish between enantiomers. Outside of these 

three, there is a common method used for distinguishing between enantiomers or determining how 

much of one enantiomer is present in excess. What is this method? 

2. Which methods that you used in this lab (IR, TLC, smell) proved to be effective in distinguishing 

enantiomers? 

3. Separating enantiomers from a mixture is difficult but possible. Since these compounds have the 

same melting point, boiling point, and density as well as other properties, there is not much that 

allows a chemist to separate the enantiomers. Think of or find a method that will allow a chemist 

to separate enantiomers. 

4. What functional groups do you observe in the IR Spectrum? 


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Extraction of Carvone

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