The Sense of Smell - Practical workresources.schoolscience.co.uk/ICI/periodictable/downloads/smellpracs.pdfcourse need to follow the usual safety procedures required by your employer

The Sense of Smell - Practical work

CONTENTS

Extraction of Natural Perfume Ingredients

Activity 1 Limonene from citrus fruitsPart A: Expression

Part B: Steam distillation

Part C: Solvent extraction

Part D: Determination of yield

Part E: Description of fragrance characteristics

Part F: Determination of boiling point

Part G: Thin layer chromatography analysis of the oil samples

Activity 2 Chemical reactions of limonene

Activity 3 Investigating the chemical stability of limonene

TEACHERS’ NOTES

Extraction of NaturalPerfume Ingredients

Activity 1 Limonene from citrusfruitsThe outer, coloured rind of citrus fruitscontain oil glands, which you may just beable to see in the cross-section of the rindfrom a freshly cut fruit. Each oil glandcontains the essential citrus oil and thecells that produce it. Limonene is a majorcomponent of citrus oils and makes somecontribution to their odours. If youdamage the rind the glands break openand release their contents.

D-limonene L-limonene

You can demonstrate that the rindcontains these oils by making the glandsrupture near a Bunsen flame. Cut asection of rind forming an arc. Use adarkened room for the next step. Holdthe rind at a distance of about 10 cm froma colourless Bunsen flame. With the outerlayer facing the flame, bend the rind sothat the outer layer becomes moreconvex. You should see small jets ofyellow flame appear as the oil glandsrupture and squirt the flammable oils intothe flame.

In this series of experiments you willextract the citrus oil (containing limonene)from orange rind using the threetechniques: expression, steam distillationand solvent extraction. These are themain methods used in the fragrance

industry for extracting essential oils fromnatural materials. You can extend thework by extracting and investigating thecitrus oils produced from other fruit, e.g.lemons, grapefruit and limes.

Part A: ExpressionRequirements

eye protection2 or 3 orangesnutmeg gratergarlic pressspatula2 x 250 cm3 beakers2 x 250 cm3 conical flasks1 x 100 cm3 conical flaskfilter funneldistilled water wash bottlecentrifuge and centrifuge tubes100 cm3 separating funnel10 cm3 of petroleum ether (b.p. 60-80 ºC)anhydrous sodium sulphate

Safety

Make sure you grate the peel and notyour fingers.

Make sure the centrifuge tubes arebalanced and the lid is secure while thecentrifuge is spinning. If there is not aninterlock to prevent the lid opening whenpower is on, do not use it.

The Sense of Smell - Practical workActivity 1 Part A page 1 of 2

All the practicals on this website havebeen carefully screened for hazards, andchecked by the Laboratory SafeguardsCommittee of the Association for ScienceEducation. Specific hazards and safetyprocedures are identified in the practicalconcerned. Nevertheless, you will ofcourse need to follow the usual safetyprocedures required by your employer. Inparticular you will need to make a RiskAssessment for each practical, as you haveto with all practical work done in yourschool or college.

We are advised that the practicals arecovered by Standard Risk Assessments.

Additional points to note:

Eye protection should always be wornwhenever there is any risk to the eyes.

Whenever students are carrying out anopen-ended investigation, they should be warned to check their plans and riskassessments with the teacher beforestarting any practical work.

Safety note to teachers and lecturers

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Petroleum ether is highly flammable andharmful, there should be no naked flamesin the laboratory. Avoid inhaling thepetroleum ether vapour.

Work in a fume cupboard, at least duringheating.

What you do

1. Weigh a clean, dry 250 cm3 beaker.

2. Working over the 250 cm3 beaker, usethe grater to remove only the outer,coloured rind from the oranges.

3. Scrape the materials from the graterinto the beaker with a spatula.

4. Re-weigh the beaker to determine themass of grated rind you are startingwith.

5. Gather some of the gratings into thegarlic press and squeeze into theconical flask, fitted with a filter funnel.

6. Empty the squeezed pulp from thepress into the flask.

7. Repeat the process until all of thegrated rind has been pressed.

8. Use a total of about 20 cm3 of distilledwater to wash any residue from thegrater and the press into the flask.

The flask now contains a mixture ofessential oil, water and solid debrisfrom the rind. In the next stage youwill isolate the oil by removing thedebris and water.

9. Use a centrifuge to separate the solidmaterial. Make sure that the tubesyou use are balanced by mass.Centrifuge for a longer period of timeif the initial separation isunsatisfactory.

10. Carefully transfer the liquid to theseparating funnel, taking care not todisturb the solid pellet at the bottomof each centrifuge tube.

11. Once you have allowed the liquid tosettle you should see two layers. Theuppermost is an emulsion of citrus oiland water. Add 10 cm3 of petroleumether to dissolve the oil, shake themixture and allow it to separatebefore discarding the lower layer,which is mostly water.

12. Run off the remaining layer (citrus oildissolved in petroleum ether) into aseparate, dry conical flask and addenough anhydrous sodium sulphate toabsorb any water, leaving the solutionclear.

13. Transfer the solution into a clean, dry100 cm3 conical flask, leaving thesodium sulphate behind.

14. Working in a fume cupboard with nonaked flames, evaporate thepetroleum ether by placing the conicalflask in a beaker of boiling water.(Heat the water using an electrickettle.)

15. Weigh a stoppered, clean, dry sampletube.

16. Transfer the oil into the tube, stopperit and weigh to determine the mass ofoil you have extracted. Keep the oil ina cool, dark place, ready for analysis(see Part D).







The Sense of Smell - Practical workActivity 1 Part A page 2 of 2


Activity 1 Limonene from citrusfruitsPart B: Steam distillation

Requirements

See requirements for Part A, but include,in addition:

steam generator

tripod and gauze

2 x Bunsen burners

2 x stands and clamps

2 x 100 cm3 conical flasks

1 x 250 cm3 beaker

250 cm3 round-bottomed (or pear shaped)flask

Leibig condenser and rubber tubing

100 cm3 measuring cylinder

Safety

Make sure that the water in steamgenerator does not evaporate awaycompletely.

Make sure there is a vent tube in thegenerator and that there are no kinks inthe tubing carrying the steam to theround-bottomed flask.

Petroleum ether is highly flammable andharmful, there should be no naked flamein the laboratory. Avoid inhaling thepetroleum ether vapour by using a fumecupboard at least when it is heated.

What you do

1. Carry out steps 1 to 8 in Part A, but usea 250 cm3 pear-shaped or round bottomflask to collect the extract from the rindand the squeezed, pulped rind itself.

2. Add a further 100 cm3 of distilled waterto the flask and set up the steamdistillation apparatus as shown in thefigure below.







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The Sense of Smell - Practical workActivity 1 Part B page 1 of 2

3. Heat up the water in the steamgenerator to boiling, using a full Bunsenflame, then reduce the flame until it issufficient to produce a steady supply ofsteam to the contents of the round-bottomed flask. At this point use asecond Bunsen burner to gently heatthe contents of the flask.

4. Collect at least 50 cm3 of distillate. Atthis stage the citrus oil should form anoily emulsion on top of the aqueouslayer in the receiver.

5. Continue the extraction following steps11 to 16 in Part A.







You can obtain good yields without a separate steam generator.

The Sense of Smell - Practical workActivity 1 Part B page 2 of 2


Activity 1 Limonene from citrusfruits

Part C: Solvent extractionIn Part A and Part B you used a solventhelp you handle small quantities of oil youhave already extracted. In this experimentyou will use the same solvent to helpperform the initial extraction from thegrated rind.

Requirements

See requirements for Part A, but include,in addition:

1 x 250 cm3 beaker

1 x 500 cm3 beaker

1 x 250 cm3 conical flask, fitted with aground glass or plastic stopper

30 cm3 of petroleum ether (b.p. 60-80 oC)

Access to a fume cupboard

Tea strainer

Safety

Petroleum ether is highly flammable andharmful, there should be no naked flamein the laboratory. Avoid inhaling thepetroleum ether vapour by using a fumecupboard at least for the evaporationstage.

What you do

1. Carry out steps 1 to 7 in Part A.

2. Carry out step 8 (Part A), but use a 250 cm3 flask as the container.

3. Add 10 cm3 of petroleum ether solventto the flask, stopper and shake itvigorously for one minute. Remove thestopper from time to time to release thepressure created by the solventevaporating.

4. Remove the stopper and allow the solidmaterial to settle.

5. Without disturbing the solid, pour theliquid (both layers) through a filterfunnel and into a separating funnel.You may find it necessary to place a teastrainer in the filter funnel to preventsolid material entering the separatingfunnel.

6. Allow the liquid in the separatingfunnel to form two separate layers.







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The Sense of Smell - Practical workActivity 1 Part C page 1 of 2

7. Run off the lower, aqueous layer backinto the conical flask containing thesolid residue from the orange rind. Ifyou have used a tea strainer return thesolid material from it into this flask aswell.

8. Run the top layer, containing the oildissolved in petroleum ether, into aclean , dry 250 cm3 beaker.

9. Repeat steps 3 to 8 twice using twoseparate 10 cm3 portions of petroleumether. Combine all three extractscontaining the solvent and the oil.

10. Add a spatula measure of anhydroussodium sulphate and swirl thecontents. Continue to add and swirluntil all of the water has beenabsorbed and the extract appears clear.

11. Pour the oil extract into a clean, dry250 cm3 beaker and leave in a fumecupboard and allow the solvent toevaporate – extinguish all nakedflames. You may encourageevaporation by careful use of from anelectric kettle. Avoid prolongedheating as this will evaporate theessential oil you are trying to extract.

12. Weigh a stoppered, clean, dry sampletube.

13. Once the solvent has evaporatedcompletely transfer the remaining oilinto the tube, stopper it and weigh todetermine the mass of oil you haveextracted. Keep the oil in a cool, darkplace, ready for analysis (see Part D).







The Sense of Smell - Practical workActivity 1 Part C page 2 of 2

Comparison of the three differentpreparations on the citrus oil

Now you have obtained the essentialcitrus oil from orange rind you canevaluate the different extraction methodsand compare the characteristics of theproducts you have obtained. Theseexperiments are described in Part D, Part E, Part F and Part G.








Part D: Determination of yield

For each sample you have use the mass ofproduct and the initial mass of the rind tocalculate the percentage yield.

Which method of extraction do you thinkis most effective?

On an industrial scale, what factors, otherthan percentage yield, would a citrus oilproducer need to consider before decidingwhich extraction method to use?

The Sense of Smell - Practical workActivity 1 Part D

3. Smell the dip again after 15 minutesand describe any changes.

4. Smell the dip after a total of 30 minutesand compare with the smell of a freshdip (dip 2). Describe the odour of thefresh dip. This is your impression of thetop notes.

For an impression of body notes

1. Your description of the odour of dip 1at 30 minutes is your provisionalassessment of the body notes.

2. Leave dip 1 for a further 30 minutesthen smell to make a final evaluation ofthe body notes. Compare with dip 2 forany odour differences.

For an impression of dryout notes

1. Continue to smell dip 1 at 30 minuteintervals until the odour remainsunchanged.

2. At this point make an assessment of thedryout notes.

(This is adapted from ‘The Chemistry ofEssential Oils’ David G Williams, MicellePress).


Part E: Description of fragrancecharacteristics

Requirements

5 mm wide strips of filter paper

Samples of the citrus oil extracts

What you do

You will need to approach this in anorganised fashion, labelling each sampledip with its source and the time elapsedsince dipping.

For an impression of top notes

For each sample:

1. Take a strip of filter paper and dip it inthe sample so that the bottom 1 cm iswet with the oil (dip 1).

2. Smell straight away and describe theodour using the terms given in figureonhttp://www.schoolscience.co.uk/content/5/chemistry/smells/smellapa.html (theLignes de Force diagram).

The Sense of Smell - Practical workActivity 1 Part E

http://www.schoolscience.co.uk/content/5/chemistry/smells/smellapa.html

6. At first there will be a slow escape ofbubbles from the open end of themelting point tube as the air insideexpands. When the sample reaches itsboiling point there is a rapid release ofbubbles. Note the thermometerreading when this just occurs.

7. Repeat with the remaining samples ofoil. Comment on the values you obtain.Limonene has a b.p. of 175-176 ºC,which sample do you think is the mostpure?


Part F: Determination of boilingpoint

Requirements


Thermometer (0 – 250oC)

Teat pipette

Melting point tube about 10 cm long andsealed at one end

5 mm diameter tube a little shorter thanthe melting point tube and sealed at oneend

100 cm3 beaker

75 cm3 of medicinal paraffin

Electric hotplate

Safety

CARE! The medicinal paraffin becomesvery hot in this experiment.

CARE! Perform this experiment in afume cupboard.

CARE! Eye protection must be worn.

What you do

1. Introduce about 0.50 cm3 of the oilsample into the 5 mm diameter tube.

2. Slide the melting point tube into thesample with the sealed end uppermost.

3. Attach the 5 mm tube to athermometer, so that the bottom of thetube is next to the thermometer bulb.

4. Carefully clamp the arrangement sothat it is held in the 100 cm3 beaker,containing 75 cm3 of medicinal paraffin.

5. Heat the beaker and its contents usingan electric hotplate.







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The Sense of Smell - Practical workActivity 1 Part F


Part G: Thin layerchromatography analysis of theoil samplesIn this experiment you will use thin layerchromatography to investigate thecomposition of the extracted citrus oils.The 20:80 %v/v glacial ethanoicacid:ethanol solvent highlights the polarcomponents in the oils. The 90:10 %v/vhexane:glacial ethanoic acid solventhighlights the non-polar components.

Requirements


10 cm3 20:80 %v/v glacial ethanoicacid:ethanol solvent A

10 cm3 90:10 %v/v 60-80 petroleum:glacialethanoic acid solvent B

t.l.c. plates

250 cm3 beaker

500 cm3 beaker containing iodine crystalsand sealed with cling film

Safety


CARE! Must evaporate only in a fumecupboard.

CARE! Iodine solid is corrosive andharmful if left on skin forsometime.

What you do

1. Take a small t.l.c. plate and place onespot of the sample about 1.5 cm fromthe bottom of the plate. Use a meltingpoint tube and keep the spot below 3 mm in diameter.

2. Run the chromatogram in a coveredbeaker, using solvent A.

3. When ready, remove the chromatogramand allow the solvent to evaporate in afume cupboard. It is important that youdo this thoroughly. If the plate is stillwet you will notice the odour ofethanoic acid remains.

4. Locate the spots, corresponding to thecomponents in the sample, by placingthe plate in a beaker containing a fewcrystals of iodine. Cover this with clingfilm and leave for several minutes.

5. Sketch the appearance of the plateafter you have located the spots.

Repeat with solvent B and with theremaining samples of oil. Which sampleappears most pure? Does your answeragree with your conclusions from thedetermination of boiling point?







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The Sense of Smell - Practical workActivity 1 Part G

Activity 2 Chemical reactionsof limoneneIn this activity you can investigate some ofthe chemical characteristics of limonene.

You will probably not have extractedenough citrus oil to perform all of thesechemical tests. If you need to you may uselimonene from a chemical supplier. Thecheaper sources will contain both the d-and l- isomers of limonene, each with itsown odour characteristics. You can alsobuy essential orange oil from somepharmacists as an aromatherapyingredient.

Requirements

Sample of limonene or extracted oil

3 x test tubes

Test tube rack

Teat pipette

Mixture of 0.005 moldm–3 potassiummanganate(VII) and 2 moldm–3 sulphuricacid (1:1 by volume)

Concentrated sulphuric acid

Approximately 0.5M bromine water

Safety


CARE! Limonene is flammable

CARE! Acidified potassiummanganate(VII) solution is anirritant

CARE! Concentrated sulphuric acid iscorrosive

CARE! Bromine water is toxic andcorrosive

What you do

Reaction with acidified potassiummanganate(VII)

1. Use a teat pipette to transfer about 0.5 cm3 of limonene into a test tube.

Add five drops of the acidifiedpotassium manganate(VII) and shakethe tube until there is no further colourchange.

2. Record the colour change and deducethe reaction that has occurred involvingthe C=C bonds in the limonene.

3. Carefully smell the contents of the tube.How is the odour different fromlimonene?

Reaction with concentrated sulphuricacid

1. Use a teat pipette to transfer about 0.5 cm3 of limonene into a test tube.Add five drops of concentratedsulphuric acid and carefully shake thetube until there is no further change.Do not attempt to smell the product atthis stage.

2. Put 2 cm3 water into a large test tube (aboiling tube). Carefully add to this themixture of limonene and concentratedsulphuric acid.

3. Record the changes and deduce thereactions that have occurred involvingthe C=C bonds in the limonene.

4. Carefully smell the contents of the tube.How is the odour different fromlimonene?

Reaction with bromine water

1. Use a teat pipette to transfer about 0.5 cm3 of limonene into a test tube.Add five drops of dilute bromine waterand shake the tube until there is nofurther colour change.

2. Record the colour change and deducethe reaction has occurred involving theC=C bonds in the limonene. Do notsmell the product.







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The Sense of Smell - Practical workActivity 2

Activity 3 Investigating thechemical stability of limoneneYou will probably not have extractedenough citrus oil to perform all of thesechemical tests. If you need to you may uselimonene from a chemical supplier. Thecheaper sources will contain both the d-and l- isomers of limonene, each with itsown odour characteristics. You can alsobuy essential orange oil from somechemists as an aromatherapy ingredient.

Limonene molecules contain two C=Cbonds and each of these behave in thesame way as the double bond in ethene.This makes samples of citrus oil likely tochange chemically, for the worse, duringstorage due to oxidation andpolymerisation reactions.

In this activity you can investigate thefactors that encourage these reactions tooccur. By using the techniques describedin Activity 1 (Parts E to G) and Activity 2you can investigate how and how quicklythe chemical, physical and odourproperties of limonene change duringstorage.

You will need to compare a fresh sampleof limonene with one that has beenexposed to conditions that encourageoxidation and polymerisation.

Safety

In addition to the precautions listed inActivity 1 (Part G) and Activity 2 take careadditional care since the air oxidation oflimonene produces allergens. Wear plasticgloves to avoid skin contact.

Safety Part G

CARE! The medicinal paraffin becomesvery hot in this experiment.

CARE! Perform this experiment in afume cupboard.


Safety for Activity 2


CARE! Limonene is flammable

CARE! Acidified potassiummanganate(VII) solution is anirritant

CARE! Concentrated sulphuric acid iscorrosive

CARE! Bromine water is toxic andcorrosive

Factors that encourage deterioration ofcitrus oil:

• light

• exposure to air

• transition metal ions

• heat

What you do

Keep the fresh sample in a dark glassbottle in a refrigerator. As a starting pointyou can perform an ‘accelerated storagetest’ by leaving approximately 30 cm3 oflimonene in a 500 cm3 conical flask,loosely plugged with cotton wool and leftexposed to sunlight. At regular intervalsover the following two weeks you canperform the tests, given in Activity 1 (Part E, Part F and G) and Activity 2 todetect how the sample has changed. Inaddition you can get an idea of theviscosity of the sample by pouring someinto a test tube and stoppering it so that asmall air space is left at the top. Whenyou turn the tube upside down the time ittakes for the bubble to rise to the surfaceis an indicator of the viscosity – the longerit lakes, the more viscous the sample.







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The Sense of Smell - Practical workActivity 3 page 1 of 2

Interpretation of the results

increase in boiling point • increased levels of impurities in the limonene• polymerisation

greater number of spots on • oxidation reactions producing new componentsthe developed t.l.c. plate

decreased tendency to react with • reduction in the number of unsaturated molecules manganate(VII), concentrated • due to oxidation and/or polymerisationsulphuric acid and bromine water

increase in viscosity • polymerisation

increase in odour intensity • formation of oxygenates (e.g. carvone, limoneneoxide

Once you have established how quicklythe properties of the limonene samplechange under these conditions you caninvestigate the effect of varying eachfactor in turn.







The Sense of Smell - Practical workActivity 3 page 2 of 2

Limonene from citrus fruits

Part A

The volume of oil obtained in step 1 isquite small. It is important that studentsrealise they are adding solvent to increasethe volume of the oily layer so it can beseparated more easily. The solvent is notextracting material directly from thegrated rind.

Part B

Patience will be rewarded here. About 30 minutes is needed for an effectiveextraction.

Parts A,B and C

The solvent evaporates quite readily in thefinal step. Ensure that students follow thesafety warnings.

Part D

Yields will vary greatly here, dependenton students' technique. On an industrialscale, economic factors need consideration- energy costs, cost of solvents, cost ofmaintaining the plant, labour costs.

Part E

The citrus top note will predominate here.

Part F

Pure limonene has a b.p. of 175-176 oC.The citrus oil extracted is not purelimonene, expect experimental valuesabove 176 oC.

Part G

Solvent extraction produces a colouredsample with many more 'spots' than thesamples from expression and steamdistillation. It therefore produces anextract with more components (includingpigments from the rind). Students mayfind this extract has the highest b.p.

Activity 2

The observations should be typical ofthose obtained from an alkene. Bothmanganate(VII) and bromine water aredecolourised. Concentrated sulphuric acid,followed by water produces an alcoholthat dissolves reasonably well in water.Students may find that treatment withmanganate(VII) and concentratedsulphuric acidlwater produce materialswith greater odour intensity andharshness.

Activity 3

Ensure that students follow the safetywarnings. Students are free to plan theirinvestigation. It is essential that youregularly monitor their plans.

The Sense of Smell - Practical work

TEACHERS’ NOTES







Documents

The Sense of Smell - Practical workresources.schoolscience.co.uk/ICI/periodictable/downloads/smellpracs.pdfcourse need to follow the usual safety procedures required by your employer