55058 chemistry basic laboratory ii (organic...

34
55058 Chemistry basic laboratory II (Organic chemistry) Organic chemistry laboratory Department of Chemistry University of Helsinki 2016

Upload: others

Post on 24-Jul-2020

9 views

Category:

Documents


0 download

TRANSCRIPT

Page 1: 55058 Chemistry basic laboratory II (Organic chemistry)reagenssi.kemia.helsinki.fi/nettilabra/tiedostot... · synthesis products or solid isolated organic compounds are always impure

55058

Chemistry basic laboratory II

(Organic chemistry)

Organic chemistry laboratory

Department of Chemistry

University of Helsinki 2016

Page 2: 55058 Chemistry basic laboratory II (Organic chemistry)reagenssi.kemia.helsinki.fi/nettilabra/tiedostot... · synthesis products or solid isolated organic compounds are always impure

2

ContentGeneral 3

Glassware etc. 6

Working practices 10 How to perform a reaction 10 Heating reaction mixture 10 Mechanical stirring 11 Isolation 12 Suction filtration 12 Extraction 12 Purification 13 Recrystallization 13 Distillation 14 Sublimation 18 Chromatography 19 Synthesis reports 21Synthesis 24

meso-1,2-Dibromo-1,2-diphenyl ethane 24 Acetyl salicylic acid 25 Ethyl propionate 26 Benzoin 27 Reduction of benzoin with NaBH4 28

p-Methyl acetophenone 29p-Benzoquinone 30

IR-spectroscopy 32

Page 3: 55058 Chemistry basic laboratory II (Organic chemistry)reagenssi.kemia.helsinki.fi/nettilabra/tiedostot... · synthesis products or solid isolated organic compounds are always impure

3

GENERAL

Location: Room B147 and B151 (First floor wing B in Chemicum)Instructors' room telephone number 02941 50426

The laboratory hours 8.30 - 16.45 daily. The laboratory period lasts 2 weeks.

You must be present on the first day of the course at 8.30 o'clock when the work benches areallocated. You must check the contents of bench drawers according to the list given by thetechnician. You are responsible for the broken or lost glassware and will have to pay for them in theend of the lab period. When you are finished you must check out your glassware (with the laboratorytechnician, see the main stockroom) by the last day of the course. If you fail to do the checking-outyou will be required to pay € 40 fine.

Please print the course material before you come to the laboratory. Mandatory absence due toexams etc. must be agreed with the teacher of the group in advance. The synthesis form and theproduct should be given to the teacher for checking as soon as possible.

The course Chemistry basic laboratory II contains seven synthesis. The theory (reaction mechanism)and the execution as well as the safety matters of the laboratory work is examined in the morninggroup wise led by the assistant. It is therefore important to be present right from the start of thework session. The participants of the course will be divided into groups in such a way, that everygroup works on a different synthesis. The members of the group carry out the same synthesisindividually. The student receives a grade for the four last synthesis. The grade is based on theproduct yield and purity.

During the synthetic lab work a test on work methods and laboratory safety will be held, whichconsists of questions related to safety at work.

Follow the safety regulations: wear safe glasses at all times, no fire in the lab etc. Keep your workingarea clean.

The paymentsAfter you have finished working and checked with the assistant that all the experiments have beencorrectly entered on your lab card, you should go to the main stockroom (BK 149, 9-11 and 13-15)to get the bill for the course fee and the broken glassware etc. This must be paid to a bank. Whenyou show the receipt of the payment to Leena Kaisalo (B213 or by email [email protected] the course is entered as passed in the study register of the university(WebOodi).

Page 4: 55058 Chemistry basic laboratory II (Organic chemistry)reagenssi.kemia.helsinki.fi/nettilabra/tiedostot... · synthesis products or solid isolated organic compounds are always impure

4

For the course you need• lab coat• notebook

Essential safety rulesCheck the location of:• exit routes• fire-extinguishers• fire-blankets and safety showers• waste containers• Find out the properties of the chemicals you are handling

Always:Handle all chemicals with great careKeep you working area cleanAttend to spills immediately

Never:Eat or drink in the laboratory

Always wear eye protection, gloves and laboratory coat in the laboratory

All experiments must be done in fume hoods

Fire safety• flammable liquids: ether, acetone, petroleum ether etc.• danger of fire, danger of explosion, fire-fighting equipment• electrical safety• how to handle electrical equipment’s safely

Apparatus• Never heat a closed apparatus• When heating use stirring or boiling stones. Don’t heat the oil bath over 200°C, use thermometerin oil bath

• don’t use flame for heating• don’t evaporate solvents from open vessels.

Page 5: 55058 Chemistry basic laboratory II (Organic chemistry)reagenssi.kemia.helsinki.fi/nettilabra/tiedostot... · synthesis products or solid isolated organic compounds are always impure

5

Waste handle and dishwashingNever pour water immiscible organic solvents down the sinkWaste solvent should be poured into appropriately labelled containersWater soluble waste like discarded water layers from aqueous-organic extractions, ethanol,neutralized acids and bases can be poured down the sinkUse acetone to rinse your glassware

Hazardous chemicals• Corrosive reagents: strong acids and bases, oxidizing, reducing, and explosive chemicals andcarcinogens.• Br2, Na, AlCl3, KCN, NaOH, KOH, LiAlH4, H2, NaBH4, KBrO3, SOCl2, Hg• Aniline, methanol, phenol, chloroform, methyl iodide, isoforone• Sodium hypochlorite, H2O2, benzoylperoxide, silica dust.Br2 can be neutralized with Na2CO3 (aq) and ethanol • Cyanides can be neutralized by oxidation. Under basic conditions cyanide ion oxidizes for examplewith sodium hypochlorite first to cyanate (OCN-) and further to nitrogen gas and carbon dioxide.

Page 6: 55058 Chemistry basic laboratory II (Organic chemistry)reagenssi.kemia.helsinki.fi/nettilabra/tiedostot... · synthesis products or solid isolated organic compounds are always impure

6

Glassware withconical joints

erlenmeyer (29/32) erlenmeyer (14/23)

round bottom flask (29/32)

3-necked flask

round bottom flask (14/23)

pear shaped flask

distillation head

Claisen distillationhead

receivingadapter

dropping funnel

condencer (bulp)

condencer (Liebig)

thermometer

Page 7: 55058 Chemistry basic laboratory II (Organic chemistry)reagenssi.kemia.helsinki.fi/nettilabra/tiedostot... · synthesis products or solid isolated organic compounds are always impure

7

Glassware without conical joints

knee tube

CaCl2 tube(14/23)

stopper(29/32))

stopper(14/23)

adapter 29 to 14

erlenmeyerflask

beaker

graduated cylinder

imupulloimupullon korkki

extractionfunnel

Büchner-funnel

gasket

glass funnel

mortar andpestle evaporation dish

suction flask andits stopper

Page 8: 55058 Chemistry basic laboratory II (Organic chemistry)reagenssi.kemia.helsinki.fi/nettilabra/tiedostot... · synthesis products or solid isolated organic compounds are always impure

8

glass dish watchglass

chromatographyjar

test tubes andrack

pincers

spatula

clamps

magnet bar

CaCl2 tube

magnetic stirrer steel pan (oil bath)

plastic tubewashing bottle

vacuum desiccator

Page 9: 55058 Chemistry basic laboratory II (Organic chemistry)reagenssi.kemia.helsinki.fi/nettilabra/tiedostot... · synthesis products or solid isolated organic compounds are always impure

9

lifting table

Page 10: 55058 Chemistry basic laboratory II (Organic chemistry)reagenssi.kemia.helsinki.fi/nettilabra/tiedostot... · synthesis products or solid isolated organic compounds are always impure

10

WORKING PRACTICESHow to perform a reaction

Heating reaction mixturesHeating reaction mixtures (reflux), recrystallization etc. is done with the apparatus on the followingpicture. The condenser prevents the evaporation of the liquid during the heating. In the condenserthe solvent vapours condense into a liquid and the liquid returns into the flask. To prevent overheating the mixture must be stirred or 1-2 boiling stones should be added into the mixture. If theboiling point of the heated liquid is under 80 C the water bath is used for heating. In case the boilingpoint of the liquid is higher silicon oil bath is used. Use thermometer in an oil bath. Never heat anoil bath over 200 °C. Avoid getting water in the oil bath because it causes splashing of the hot oil.Never use closed apparatus for heating because closed system may explode.

H2O

bulbcondencer

clamp

flask

heathingbath

liftingtable

magneticstirrerH2O

supportstand

Page 11: 55058 Chemistry basic laboratory II (Organic chemistry)reagenssi.kemia.helsinki.fi/nettilabra/tiedostot... · synthesis products or solid isolated organic compounds are always impure

11

Mechanical stirringIf the reaction mixture is stiff mechanical stirring is used for the efficient stirring for example inFriedel-Crafs reaction. Fix the stirrer firmly to the support stand. Cautiously test run the emptyapparatus before adding the starting materials.Note! If you use a dropping funnel with a bypass use a stopper instead of CaCl2 tubing.

Apparatus for Friedel-Crafts reaction (p-Methyl acetophenone)

PVC-hose

Mechanical stirrerHoseRod

Cotton wool

Addition funnel

3-neck flask

Page 12: 55058 Chemistry basic laboratory II (Organic chemistry)reagenssi.kemia.helsinki.fi/nettilabra/tiedostot... · synthesis products or solid isolated organic compounds are always impure

12

Suction filtration

When solid material is isolated from the reaction mixture (like product precipitates from thereaction mixture) the suction filtration is used (see the apparatus above). Both suction flasks areconnect to the support stands with clamps. In the Bühner funnel a filter paper of correct size shouldbe used. The paper should not turn up the edges of the Bühner funnel. Moisten the filter paper withthe same solvent which forms the filtrate. Turn the water aspirator tab on completely and close thesuction flask stopper and start filtering. When the filtration is switched off first release the normalpressure into the apparatus by opening the suction flask stopper. When drying agent is removedfrom the solvent use glass funnel with a small amount of cotton wool.

ExtractionIn order to move the reaction product from the water solution into the organic solvent the watersolution is shaken with organic solvent e.g. ether in an extraction funnel.

A separatory funnel is usually made of thin glass and it should be handled carefully. The stopcock ofthe separatory funnel is either glass or Teflon. Glass stopcock should be lightly greased before useso that it turns easily. Support the separatory funnel in a metal ring clamped to a stand. Get into thehabit of placing an Erlenmeyer or beaker under the separatory funnel as soon as you put it in itsring. Check that the stopper fits well for the glass joint. With the stopcock closed (check!) pour the

suction flask

stopper for suction flask

clamp

Büchner funnel

clamp

thick wall tubing

water aspirator

Page 13: 55058 Chemistry basic laboratory II (Organic chemistry)reagenssi.kemia.helsinki.fi/nettilabra/tiedostot... · synthesis products or solid isolated organic compounds are always impure

13

mixture to be extracted and the extraction solvent into the separatory funnel. As a general rule,never fill the separatory funnel more than two-thirds full.

To carry out the extraction, the aqueous and organic layers have to be thoroughly mixed. Afteradding the liquids to the funnel, and before inserting the stopper, it is good idea initially to swirl theseparatory funnel gently. This swirling causes some preliminary mixing of the layers, and isparticularly important when aqueous carbonate or bicarbonate is being used to extract or neutralizeacidic components. Preliminary swirling will reduce the problems from excessive pressure buildingup during the extraction. After swirling insert the stopper. More vigorous shaking is needed to mixthe layers. Foe holding a separatory funnel the following method is recommended (see the picturebelow). Hold the funnel with both hands. Hold the stopper with one hand and hold the funnelaround stopcock with the other hand, so that you van open the stopcock quickly with your fingers.If doubt, practise your grip with an empty funnel.

To carry out the extraction, lift the separatory funnel of its support, adjust your grip and invert thefunnel. Immediately open the stopcock to release any pressure. When venting a funnel, never pointthe stem towards your neighbours or yourself. After the first venting, close the stopcock and swirlthe inverted funnel for few seconds and repeat the venting procedure. Repeat until the pressurebuild-up diminishes. Then shake the funnel 10-20 seconds and vent the funnel at least once duringthe shaking process.

Allow the funnel to stand until the layers separate. Remove the stopper and run off the lower layerinto the flask. Before removing the lower layer make sure which layer is which. Check the densitiesfrom literature e.g. CRC Handbook of Chemistry and Physics. Label the flask immediately. Pour theupper layer out though the neck of the funnel into a clean Erlenmeyer flask, which should belabelled. Always keep both solutions until you have isolated your organic product.

shaking hold release pressure

Page 14: 55058 Chemistry basic laboratory II (Organic chemistry)reagenssi.kemia.helsinki.fi/nettilabra/tiedostot... · synthesis products or solid isolated organic compounds are always impure

14

PurificationRecrystallizationRecrystallization is an important purification method for solid organic compounds. The method isbased on the differences of the solubility between purified compound and impurities. The solidsynthesis products or solid isolated organic compounds are always impure. The impurities aretrapped between the crystals. In practice this type of impure material is purified by dissolving thecrystals into a minimum volume of such hot solvent from which the compound recrystallizes uponcooling. Due to the small amount of impurities present they stay in solvent which is dilute relativeto the impurities. If the hot solution contains undissolved impurities it must be filtered before thesolvent is cooled down. It is possible to remove coloured impurities from the hot solution by activecharcoal. It is important not to cool the solution too fast. With slow cooling the crystals grow biggerand are more pure.

If the recrystallization solvent is not known it must be chosen by testing. The ideal solvent forrecrystallization should not react with the compound to be recrystallized, should have a boiling pointthat is lower than the melting point of the compound to be recrystallized and most importantly thecompound should be very soluble in hot solvent and insoluble in cold solvent. Unfortunately thereis no rule of thumb how to choose the solvent for recrystallization. Recrystallization of nonpolarhydrocarbons can be tested from hexane or light petroleum. In the case of ethers and halogenidescan dichloromethane be the solvent of choice. If the compound to be recrystallized has OH-groups(alcohols, phenols and carboxylic acids) it is worth to try to use ethanol as solvent. Good alternativescan be found from the CRC Handbook of Chemistry where the solubilities of organic compounds tothe most common solvents are listed.

If suitable recrystallization solvent cannot be found, then a mixture of solvents may have to be used.A mixed solvent system is a pair of miscible solvents. The solvents should be chosen so that one ofthem dissolves the compound readily, and the other one (poor solvent) does not. One method is todissolve the solid in the minimum volume of the hot good solvent, then add the poor solventdropwise until the solution starts to become slightly cloudy, and the set the solution aside tocrystallize. You can try the following mixed solvent systems:

Class of compound Suggested solvent (betterdissolving)

Additional solvent (poorsolvent)

carboxylic acid ethanol waterdicarboxylic acid ether, toluenephenol ethanol, toluene wateramine ethanol waternonpolar compound hexane, dichloromethanepolar compound propanol water

Page 15: 55058 Chemistry basic laboratory II (Organic chemistry)reagenssi.kemia.helsinki.fi/nettilabra/tiedostot... · synthesis products or solid isolated organic compounds are always impure

15

Recrystallization problems: Crystallization does not always work. What if the solvent has beencorrectly chosen but no crystallization occurs after cooling in an ice bath? The reason may be oversaturation of the solution. You can attempt to induce the crystallization by adding a seed crystal (isavailable) or scratch the side of the flask with a glass rod when the produced micro-fragments ofglass serve as nuclei to induce crystallization. If this fails, try cooling the solvent in ethanol-solid CO2

bath (-76 °C), and then scratch the sides of the flask as the solution warms up to room temperature.If the substance still refuses to crystallize, you can concentrate the solution with a rotavapor- andhope for the best.

Sometimes during the recrystallization the substance separates as an oil rather than as crystals. Thisis known as oiling out, and even if the oil solidifies the compound will not be pure, and the materialshould be redissolved by heating the solution. You may need to add a little more solvent at thisstage. In this case the stirring may be left on during the cooling and first a dispersion is formedbefore the compound crystallizes. The use of seed crystals is also recommended.

Distillation

Distillation is one of the main techniques for purifying volatile liquids in organic chemistrylaboratory. It involves vaporizing the material by heating and subsequently condensing the vapourback to liquid, the distillate. There are various ways in which the distillation can be carried out. Thechoice of the distillation procedure depends on the properties of the liquid that will be purifiedand on the properties of the impurities present. The most common distillation methods are:simple distillation, fractional distillation, distillation under reduced pressure, steam distillation andso called Kugelrohr distillation. In addition, sublimation, the purification of a solid, without goingthrough a liquid phase, is also a kind of distillation.

Distillation under normal pressure

Page 16: 55058 Chemistry basic laboratory II (Organic chemistry)reagenssi.kemia.helsinki.fi/nettilabra/tiedostot... · synthesis products or solid isolated organic compounds are always impure

16

thermometer with a conical joint

distillation head

distillation flask

receiving flask

water outwater in

receiving adapter

Liebig condencer

Transfer the liquid to be distilled to the distillation flask and warm the liquid until the more volatilecompound starts to boil. At this point the boiling point of the compound is measured from thethermometer. The vapour finds its way into the condenser where it condenses back to liquid anddrops through the receiving adapter into the receiving flask. After the distillation ends or there is arisk that the liquid is distilled to dryness the distillation is finished or the receiving flask is changedfor the higher boiling compound. Never distil to dryness. The picture of the apparatus for simpledistillation is above. Choose the distillation flask so that the liquid to be distilled fills at least half ofthe flask but no more than 2/3. Use magnetic stirring or boiling stones. When the boiling point ofthe liquid is under 120 °C use running water in the condenser. When the boiling point is 120-150 °Cuse stagnant water and if the boiling point is over 150 °C remove the water from the condenser (aircooling). Heat the flask first mildly until the liquid starts to boil. When the liquid starts to distil adjustthe heating so that the distillate drops into the receiving flask in a rate 1 drop/second. Stop thedistillation before the distillation flask is completely dry. Many liquids especially alkenes and ethersmay contain peroxides which concentrate in distillation residue and may explode.

Continuous feed distillation

water inwater out

Page 17: 55058 Chemistry basic laboratory II (Organic chemistry)reagenssi.kemia.helsinki.fi/nettilabra/tiedostot... · synthesis products or solid isolated organic compounds are always impure

17

Continuous feed distillation is used when alarge volume of solvent is distilled from a smallflask. Usually the situation is like that when thesolvent is separated from the product. Duringthe distillation the liquid is added to the flaskfrom the dropping funnel. The size of thedistillation flask is chosen so that it is suitablefor the distillation of the mixture which is leftover when the solvent has been distilled away.This is how can be avoided the situation whena small amount of compound should bedistilled from a large volume flask. Instead ofcontinuous feed distillation rotavapor can beused to remove the solvent

Fractional distillationIt is possible to separate two liquids by normaldistillation only if their boiling points differmore than 20-50 ºC. If the difference betweenthe boiling points is too small it is not possibleto get pure distillates. It is easier to separatecompounds if a fractionating column (Vigreuxcolumn) is inserted between the distillationflask and the distillation head. As the vapourfrom the distillation flask passes up throughthe fractional column, it condenses on thecolumn packing and revaporizes continuously.This makes it possible to separate the lowerboiling compounds from the higher boilingones efficiently. Different fractions arecollected in own flasks.

Distillation under reduced pressureDistillation under reduced pressure is necessary when the boiling point of the liquid isinconveniently high or the compound to be distilled is solid or when the compound decomposes atelevated temperatures. In order to get vacuum in the distillation apparatus either water aspiratoror oil vacuum pump is used. When the pressure is reduced the boiling point of the compound to bedistilled reduces. The distillation apparatus is show below. Manometer is used to measure thepressure and it is incorporated between the receiver adapter and the suction flask. The reducedpressure within the system is obtained by reading the difference in the mercury levels between thetwo halves of the manometer (mmHg). The suction flask is used to prevent water to enter thereceiving flask in case the water aspirator is closed incorrectly before the normal pressure is

Page 18: 55058 Chemistry basic laboratory II (Organic chemistry)reagenssi.kemia.helsinki.fi/nettilabra/tiedostot... · synthesis products or solid isolated organic compounds are always impure

18

achieved. Always attach the manometer as well as the suction flask with a clamp to support stand.To prevent over heating during the distillation either stirring or vacuum boiling stones is used. If thedistillation is interrupted new vacuum boiling stones must be added before the distillation iscontinued.

The apparatus for vacuum distillation should be tested before the sample is introduced into thedistillation flask. After assembling the apparatus check that all the joints are tight-fitting and that thereare no strains in the apparatus. First open the stopcock of the suction flask, close the stopcock of themanometer and open the water aspirator completely. After this close the stopcock of the suction flask andthe pressure starts to reduce inside the apparatus. Check the pressure by opening the stopcock of themanometer. The reduced pressure within the system is obtained by reading the difference in the mercurylevels between the two halves of the manometer (the scale is in mm). Finally close the manometer stopcockand open the stopcock of the suction flask and you will get normal pressure inside the apparatus.

After testing add the mixture into the distillation flask and add vacuum boiling stones if magneticstirring is not used. Repeat the previous steps and start heating after the reduced pressure is stable.Read the temperature and pressure during the distillation of the compound. Write these valuesdown for the report. When the compound has distilled stop the heating and let normal pressureinto the system and close the water aspirator.

In the organic chemistry laboratory there are two kinds of vacuum pumps in use: water aspirator isin each fume hood and there are couple of oil pumps. With the water aspirator 10-20 mmHg can bereached and with oil pump 0.1-0.001 mmHg (normal pressure is around 760 mmHg). When oil pumpis used the pressure is measured with an electrical pressure meter. Don’t use mercury manometerwith oil pump. In addition when oil pump is used there must be a liquid nitrogen trap between thedistillation apparatus and the oil pump. In order to compare the measured boiling point to the

Page 19: 55058 Chemistry basic laboratory II (Organic chemistry)reagenssi.kemia.helsinki.fi/nettilabra/tiedostot... · synthesis products or solid isolated organic compounds are always impure

19

literature value the readings must be converted to the same pressure. It can be done by usinggraphical nomogram.

Read the boiling point under normal pressure from the scale in the middle and the used pressurefrom the scale at the right hand side. Draw a line through these two points and read the boilingpoint under reduced pressure from the scale on the left hand side (the point where the line crossesthe scale). For example if a compound boils at 200 °C under normal pressure and the reducedpressure inside the distillation apparatus is 20 mmHg the boiling point in 20 mmHg is around 80 °C.

There is a boiling point converter in Nettilabra.

SublimationSublimation is closely related to distillation. A solid is converted into a vapour, without goingthrough liquid phase, which is the recondensed on cold surface in a purified state. Typicalcompounds which sublimate are camphor and selenium dioxide. Sublimation is extremely good wayto purify solid compounds which sublimate under normal or reduced pressure.

Sublimation under reduced pressureUse a sublimator when sublimation is done under reduced pressure. The sample to be sublimed isplaced in the bottom of the outer tube. Use water circulation inside the cold finger. Check that thestopcock of the suction funnel is open, open the water aspirator (fully open), and close the stopcockof the suction funnel. Read the pressure from the manometer and close the stopcock of themanometer. Warm the heating bath to such a temperature that the sublimation occurs. The puresublimated compound sticks on the surface of the cold finger and the impurities stay at the bottomof the outer tube. From time to time the purified solid must be scraped off and to do this you needto stop heating and open the stopcock of the suction flask in order to introduce normal pressure

Page 20: 55058 Chemistry basic laboratory II (Organic chemistry)reagenssi.kemia.helsinki.fi/nettilabra/tiedostot... · synthesis products or solid isolated organic compounds are always impure

20

inside the apparatus. Scrap the pure compound from the cold finger with spatula to weighted watchglass.

ChromatographyChromatography can be used to separate, purify, or identify compounds. All the chromatographytechniques depend upon differential distribution of various components of the mixture betweentwo phases – the mobile phase and the stationary phase. The mobile phase may be either a liquidor a gas and the stationary phase either liquid or solid. Main types of chromatography are columnchromatography, paper chromatography, thin layer chromatography (TLC), gas chromatography(GC) and liquid chromatography (LC).

TLC-chromatographyDeveloping tank is a jar with a lid and it should preferably have a flat bottom. The inside of thedevelopment tank is lined with filter paper. Sufficient developing solution (eluent) is placed into thetank, a 0.5 cm layer in the bottom of the tank is usually sufficient. TLC-plates are usually aluminiumplates covered with stationary phase (e.g. silica gel) as a thin layer. The plates should be cut downto smaller size (8x2.5 cm is sufficient for 2-3 spots). Handle the TLC-plates with care to avoidcrumbling the delicate absorbent layer.Mark a line (baseline) about 1 cm from one end of the plate. Make a solution of a small quantity ofyour sample in a volatile solvent in which it is soluble (approximately 1 % solution). Dip a TLC-capillaronto the solution and then touch the loaded capillary onto the silica surface and let dry. Repeat thiswith reference compound. Place the TLC plate carefully into the tank making sure that the level ofthe solvent does not reach the level of the sample spotted onto the baseline, otherwise the materialwill simply be dissolved off the plate instead of being carried up it by the eluent.

Page 21: 55058 Chemistry basic laboratory II (Organic chemistry)reagenssi.kemia.helsinki.fi/nettilabra/tiedostot... · synthesis products or solid isolated organic compounds are always impure

21

Allow the solvent front to rise in a horizontal straight line up the plate by virtue of capillary actionuntil it reaches about 1 cm from the top. Finally carefully remove the plate, mark the solvent frontand allow the solvent to evaporate off in the hood. The spots will be visible under UV-light or stainingthe plate with a suitable reagent. A useful measurement that can be made from the developed TLCplate is the relation between the distance moved by the compound spot and the distance moved bythe eluting solvent: this is the retention factor Rf.

Page 22: 55058 Chemistry basic laboratory II (Organic chemistry)reagenssi.kemia.helsinki.fi/nettilabra/tiedostot... · synthesis products or solid isolated organic compounds are always impure

22

Synthesis reports (Basic chemistry laboratory II)

From each synthesis a synthesis form is filled and it is given in with a reaction mechanism,interpreted IR-spectrum and melting point printout as well as TLC-plate in.

Read the chapter How to fill in a synthesis form on page x.Synthesis forms can be found from Nettilabra.

Reaction mechanism: Draw the reaction mechanism clearly to the reversed side of the synthesisform.

How to interpret IR-spectra:You can write the interpretations on the printed spectra.Try to find all the absorptions of the functional groups and bonds present in yourcompound.It is recommended that the fingerprint area (wave number < 1500 cm-1) should not beinterpreted in detail.Write on the spectrum:

The measured wave number (cm-1)Interpretation (functional group and bond)The literature value of the wave numberThe intensity of the absorption s, m, w (from the literature)Literature reference

TLC plates (not from all synthesis):Draw under UV-light the outlines of the visible spotsAttach the TLC plate on the synthesis form with adhesive plastic so that the plasticcovers the whole plate. This prevents the silica layer to crumble.Write next to the plate what was the eluentCalculate the Rf-value

Stable the pages together. The report must be given in as soon as possible.

The synthesis product must be given in to the teacher with the form. Place the synthesis productinto a small vial. Label the vial with your name and the name of the product.

If you get your report back for corrections do them carefully and give the report in within three days.

Page 23: 55058 Chemistry basic laboratory II (Organic chemistry)reagenssi.kemia.helsinki.fi/nettilabra/tiedostot... · synthesis products or solid isolated organic compounds are always impure

23

HOW TO FILL IN THE SYNTHESIS FORM

Fill in all the applicable parts.Name of the synthesis productLiterature reference for the procedure and reaction mechanism

Reaction scheme and to the reverse side reaction mechanism

Information about the starting materials and product

Numerical valuesAccuracy Unit

Molecular weight M integer g/molMass m one decimal accuracy gDensity r (for liquids) accuracy of the literature

value(g/mL)

Volume (for liquids) one decimal accuracy mLMoles with two significant

numbersmol

eqv=mole ratio of startingmaterials

one decimal accuracy -

Yield % integer %Melting point (Mp) one degree accuracy CBoiling point (Bp) one degree accuracy

if measured under reducedpressure also mark thepressure

C / mmHge.g. 75 C /15 mmHg

Refractive index (nD20) accuracy of the

refractometer-

Note! Use precise numerical values when calculating but fill in the form in round numbers.

The yield of a synthesis is the amount of the pure product(s). Theoretical yield (100 % yield) iscalculated according to the equilibrated reaction scheme. Theoretical yield is always calculated fromthe starting material which is used least according to the stoichiometry.

The own yield is expressed as per cents from the theoretical yield.

Determination of purity

It is possible to determine the purity per cent and the purity class of crystalline product with the aidof the melting point. In case of liquid product from the measured refractive index indicates onlywhether the purity class is 1 or 2. If needed the exact purity class of a liquid can be determined bygas chromatography if there are no non-volatile compounds present.

Page 24: 55058 Chemistry basic laboratory II (Organic chemistry)reagenssi.kemia.helsinki.fi/nettilabra/tiedostot... · synthesis products or solid isolated organic compounds are always impure

24

State of theproduct

Difference from the literaturevalue

purity % purity class n

solid ΔT ≤ 1 °C 99 % 11 °C < ΔT ≤ 3 °C over 97 % 23 °C < ΔT ≤ 5 °C around 95 % 3ΔT > 5 °C Technical chemicals

Product must bepurified again

4

liquid ΔnD20 ≤ 0,001

(Basic chemistry lab II ≤0,003) -1

ΔnD20 > 0,001

(Basic chemistry lab II >0,003) -2

Product with purity class n=1 must be of uniform quality and the colour must be the same as in theliterature. Sometimes it is possible to determine by e.g. gas chromatography.

Page 25: 55058 Chemistry basic laboratory II (Organic chemistry)reagenssi.kemia.helsinki.fi/nettilabra/tiedostot... · synthesis products or solid isolated organic compounds are always impure

25

SYNTHESISmeso-1,2-Dibromo-1,2-diphenyl ethane

Reaction mechanism is an electrophilic addition to the double bond

Reagents1 g trans-stilbene10 mL of dichloromethane10 mL 10 % (w/v) solutionof bromine indichloromethane bromin(solution conains 0,1 g Br2/1mL)cyclohexene5 mL dichloromethane

Safety notesBromine is extremelypoisonous and corrosive.It has to be handled infume cupboard. Wearprotective gloves.

Equipment50 ml round-bottomedflask (14/29)small graduated cylindersuction filtration apparatuswatch glass

ProcedureDissolve 1.0 g of trans-stilbene in 10 mL of dichloromethane in a 50 mL roundbottomed flask. Stir the solutionwith magnetic stirrer and add 10 mL of a 10% solution of bromine in dichloromethane (0,10 g of bromine/1.0 mL). If the colour of bromine disappears completely, add bromine dichloromethane solution in 1 mlportions until the colour of the bromine stays permanently. The developing dibromocompound precipitatesfrom the solution. Add to the reaction mixture cyclohexene in drops until the extra bromine is destroyed.Stop adding the cyclohexene when the colour of the bromine disappears. Cool the solution in an ice bath tocomplete the precipitation.

IsolationCollect the product by suction filtration. Wash it in the funnel with 5 ml of ice cooled dichloromethane. Drythe product by sucking air though the funnel. Transfer the dry product to a watch glass and weight the dryproduct. The yield of the product is 75%. The melting point of the product is 241-243 °C.

Product characterizationMeasure the melting point and run an IR-spectrum of the product. Check the purity of the product by TLC(1:2 dichloromethane:petroleum ether)

Page 26: 55058 Chemistry basic laboratory II (Organic chemistry)reagenssi.kemia.helsinki.fi/nettilabra/tiedostot... · synthesis products or solid isolated organic compounds are always impure

26

Acetylsalisylic acid (Aspirin)

Reagents· 5.0 mL of acetic anhydride· 2.8 g of salicylic acid· 3-4 drops of conc. sulfuricacid

Safety NotesAcetic anhydride is volatileand a strong irritant.Sulfuric acid is corrosive

Equipment· 100 mL roundbottomedflask (14/29)· magnetic stirrer· water and ice baths· suction filtration apparatus· Büchner funnel· rubber stopper· 2 filter flasks· roundbottomedflask,condenser, oil bath

ProcedurePlace 2.8 g of salicylic acid in a dry 100 mL roundbottomed flask, then add 5.0 mL of aceticanhydride and 3-4 drops of concentrated sulfuric acid. Mix the resulting white slurry with a magneticstirrer, and place the flask in a warm water bath (45-50°C) for 15 min. Allow the flask to cool andadd 50 mL of water and break up any lumps with a spatula.

Isolation and purificationAllow the mixture to stand for an additional five minutes, then chill the flask in an ice bath andremove the crystals by suction. Crystallize the crude aspirin from warm 30% ethanol water mixturenot exceeding 80°C (see experimental note). Allowing the mother liquor to stand overnight mayproduce a second crop of crystals. Airdry the crystals and determine the per cent yield and meltingpoint (mp. for aspirin is 135°C). The yield is 80%.

Experimental note: At temperatures exceeding 80°C, aspirin forms an oil that dissolves organicimpurities from water; in this case it may be difficult to redissolve the aspirin in water.

Product characterizationMeasure the melting point and run an IR-spectrum of the product.

Page 27: 55058 Chemistry basic laboratory II (Organic chemistry)reagenssi.kemia.helsinki.fi/nettilabra/tiedostot... · synthesis products or solid isolated organic compounds are always impure

27

Ethyl propionate

The reaction in question is an acid catalyzed esterification. Propanoic acid is protonated by the acidused as a catalyst. The emerging cation is resonance stabilized. Ethanol acts as a nucleophile as itattacks the cation. This is followed by the transfer of a proton and the loss of water. The reaction isa nucleophilic substitution.

Reagents· 10 mL abs. ethanol· 14 mL propanoic acid· conc. sulfuric acid· 40 mL ether· 2M NaHCO3 solution· MgSO4

Safety NotesConcentrated sulfuric acid ishighly corrosive.Ether is a highly flammableand volatile liquid.Ethanol is a highly flammableand volatile liquid.

Equipment· reflux apparatus· extraction/separationequipment· apparatus for continuousfeed distillation

ProcedureIn a 50 mL roundbottomed flask mix 10 mL of ethanol and 14 mL of propanoic acid. Carefully add2-3 drops of concentrated sulfuric acid (catalyst) and mix the solution well with magnetic stirrer.Reflux the mixture for one hour using an oil bath. Let the reaction mixture cool.

Isolation and purificationPour the cool reaction mixture into a separatory funnel filled with 40 mL of water. Add 40 mL ofether into the funnel, stopper, and shake it gently (wear safety glasses!). Release any pressure insidethe separation funnel by turning the stoppered funnel upside down and opening the stopcock. Letthe funnel rest (upright, stopcock closed) until the layers are separated. Let the aqueous layer (thelower one) drain from the funnel into a different vessel. Wash the ether layer that remains in thefunnel with 20 mL of water (shake it with the added water).

Once the layers have separated, the aqueous layer is drained. Wash the ether solution with 2 MNaHCO3 solution to remove any unreacted acid. It is essential that you are especially careful at thisstage since carbon dioxide is produced when the acid is neutralized. The gas causes pressure insidethe separatory funnel. The pressure is released as described above. The acid is now present in theaqueous layer as the Na salt. Finally wash the ether solution with 20 mL of water. Remove theaqueous layer as thoroughly as possible and then dry the ether solution with anhydrous magnesiumsulfate. After 30 minutes of drying, filter the solution through a regular glass funnel fitted with aclean cotton plug into a dropping funnel. Part of the ether solution is poured into a roundbottomed

Page 28: 55058 Chemistry basic laboratory II (Organic chemistry)reagenssi.kemia.helsinki.fi/nettilabra/tiedostot... · synthesis products or solid isolated organic compounds are always impure

28

flask and magnetic stirrer bar is added. The ether is removed by a distillation procedure used for theremoval of large amounts of solvent (bp. of ether = 35°C). The flask can be heated either in a wateror oil bath.

The product is purified by distillation. The boiling point of ethyl propanoate is 99°C (oil bath). Theproduct yield is 60 %.

Product characterizationMeasure the refractive index and run an IR spectrum of the product

Benzoin

Aromatic aldehydes when treated with an alkali cyanide, usually in aqueous solution, undergocondensation to the hydroxyketone or benzoin (called benzoin condensation). α The best knownexample is the conversion of benzaldehyde to benzoin.

For the mechanism see: A. Streitwieser, C. H. Heathcock and E. M. Kosower, Introduction toOrganic Chemistry, 4. edt.; Macmillan, New York 1992, p. 867.

Reagents· 2.5 mL of benzaldehyde· 35 mL of techn. alcohol· 0.25 g of potassium cyanide

Safety NotesPotassium cyanide is apoisonous and corrosive solid.For the disposal of cyanidecompounds see (in Finnish):P. Tilus, ja T. Asikainen,Turvallinen työskentelylaboratoriossa, HelsinginYliopisto 1996, p.40.Benzaldehyde is an irritant.

Equipment· reflux apparatus· water bath· Erlenmeyer flask· suction filtration apparatus

ProcedureIn a 50 mL roundbottomed flask place 5 mL alcohol, 2.5 mL purified benzaldehyde and 0.25 gpotassium cyanide dissolved in 4ml of water (CARE! This preparation must be done in the hood!

Page 29: 55058 Chemistry basic laboratory II (Organic chemistry)reagenssi.kemia.helsinki.fi/nettilabra/tiedostot... · synthesis products or solid isolated organic compounds are always impure

29

Assumed purity of KCN is 96-98%). Attach a reflux condenser and heat on a boiling water bath for30 minutes. Cool the flask in icewater, filter the crude benzoin and wash it with water and drain dry.

Isolation and purificationRecrystallize the crude product from ethanol; the benzoin is obtained as a white crystalline solid,m.p. 137 °C, the yield of the pure product being 2.1 g.

Product characterizationMeasure the melting point and run an IR spectrum of the product.

Reduction of benzoin with sodium borohydride –1,2-Diphenylethane-1,2-diol

The stereochemical course of ketone reductions can be influenced by the presence of hydroxylgroupsclose to the carbonyl function. This experiment illustrates the stereoselective reduction ofbenzoin using sodium borohydride as reducing agent.

For the mechanism see the course folder Orgaanisen kemian perustyöt I in the assistant room.

Reagents· 2.00 g benzoin· 0.40 g sodium borohydride· ethanol· hydrochloric acid (6 M)

Safety NotesBenzoin is irritantNaBH4 is corrosive, flammableEtanoli is flammable,HCl is corrosive

Equipment· magnetic stirrer· suction filtration apparatus· recrystallization apparatus

ProcedureDissolve the benzoin in 20 mL of ethanol in a 100 mL Erlenmeyer flask.1 Stir the solution magneticallyand add the sodium borohydride in small portions over 5 min using a spatula.2 If necessary, rinse inthe last traces of sodium borohydride with 5 mL of ethanol. Stir the mixture at room temperaturefor a further 20 min. and then cool it in an ice bath whilst adding 30 mL of water followed by 1 mLof 6 M hydrochloric acid.3 Add a further 10 mL of water, and stir the mixture for a further 20 min.

1) Warming may be necessary; solution need not be complete.2) Care! Exothermic

Page 30: 55058 Chemistry basic laboratory II (Organic chemistry)reagenssi.kemia.helsinki.fi/nettilabra/tiedostot... · synthesis products or solid isolated organic compounds are always impure

30

3) Foaming may occur!

Isolation and purificationCollect the product by suction filtration, and wash it thoroughly with 100 ml water. Dry the productby suction for 30 min, and record the yield. Recrystallize from ethanol-water(1:1). Yield 90 %.

Product characterizationCheck the purity by tlc (silica plates; eluent ethyl acetatehexane1:1). Measure the melting point andrun a IR spectrum of the product.

p-Methyl acetophenone

Mechanism: A. Streitwieser, Jr., C. H. Heathcock and E. M. Kosower, Introduction to OrganicChemistry, 4. p.; Macmillan, New York 1992, s. 696.

Reagents15 g AlCl325 mL toluene4,8 mL acetic anhydrideanhydrous MgSO4

Safety NotesAluminium chloride producesHCl when it comes intocontact with dampness of theair and reacts violently withwater. AlCl3 dust is harmfulwhen inhaled.Toluene: flammable.Acetic anhydride:lachrymator,corrosive.

Equipment· 100 mL 3-neckedroundbottomed flask· dropping funnel· CaCl2tube· mechanical stirrer· reflux condenser· PVC-tube· glass funnel· 250 mL beaker· oil bath· separation/extractionapparatus· vacuum distillation apparatus

Procedure(A. I. Vogel, A TextBook of Practical Organic Chemistry, 3. edt., Longman, London 1970, p. 730)

In a 100 mL 3-necked flask, equipped with a separatory funnel carrying a calcium chloride tube, amechanical stirrer, and an efficient reflux condenser attached to a gas absorption device, place 15g of finelypowdered, anhydrous aluminium chloride and 25 mL of toluene. Set the stirrer in motionand add 5.1 g (4.8 mL) of acetic anhydride slowly through the addition funnel; the addition requires

Page 31: 55058 Chemistry basic laboratory II (Organic chemistry)reagenssi.kemia.helsinki.fi/nettilabra/tiedostot... · synthesis products or solid isolated organic compounds are always impure

31

15 minutes, during which time the temperature rises to about 90°C and much hydrogen chloride isevolved. Heat the mixture on a water bath, with stirring, for 30 minutes or until there is practicallyno evolution of gas. Cool the reaction mixture to room temperature and pour it into a mixture of 30g of crushed ice and 30 mL of concentrated hydrochloric acid: stir until the aluminium salts dissolvecompletely.

Isolation and purificationSeparate the toluene layer, wash it with water, then with 10 per cent sodium hydroxide solutionuntil the washings remain alkaline, and finally with water: dry over anhydrous magnesium sulphate.Distill the residue using a Claisen adapter at atmospheric pressure until the temperature rises toabout 125°C, then allow to cool and distil under reduced pressure. Alternatively, toluene may beremoved with a rotary evaporator. Collect the p-methylacetophenone at 93-94° C/7 mm (the b.p.at atmospheric pressure is 225°C); the yield is 5.8 g.

Product characterizationMeasure the refractive index and run an IR spectrum of the product.

p-Benzoquinone

Reagents· 2.5 g of hydroquinone· 1.4 g of potassium bromate· 1.2 mL of sulfuric acid (2 M)

Safety NotesHydroquinone is harmfulKBrO3 is oxidative,explosive

NOTE! The product is highlytoxic and flammable as anairdust mixture.

Equipment· 100 mL flask (14/29) +stopper· suction filtration apparatus· sublimation apparatus

ProcedurePlace potassium bromate (1.4 g), 2 M sulfuric acid (1.2 mL), water (25 mL) and hydroquinone (2.5 g)into a 100 mL roundbottomed flask. Close the flask with a stopper and stir the mixture for about 30minutesat room temperature. The reaction is over when the initially black mixture turns yellow(yellowish green).

Isolation and purification

Page 32: 55058 Chemistry basic laboratory II (Organic chemistry)reagenssi.kemia.helsinki.fi/nettilabra/tiedostot... · synthesis products or solid isolated organic compounds are always impure

32

Filter by suction filtration, wash with ice cold water and spread the product on filter paper until it isdry. Purify the obtained crude product by sublimation under vacuum. p-Benzoquinone gives a yieldof 1.3 g and has its melting moint at 115°C.

Note: The product is water soluble. This means that over eager washing will diminish the amount ofproduct that is left in the funnel. The impure product in particular decomposes easily so that it isimportant that there is no delay in the isolation and purification of the compound.

Product characterizationMeasure the melting point and run an IR spectrum of the product.

Page 33: 55058 Chemistry basic laboratory II (Organic chemistry)reagenssi.kemia.helsinki.fi/nettilabra/tiedostot... · synthesis products or solid isolated organic compounds are always impure

33

Infrared spectroscopy

Interpretation of IR spectrum

Most of the functional groups absorb IR radiation in the region between 4000-1500 cm-1. This regionshould be interpreted first by comparing observed absorptions with literature tables. Polar groupsabsorb often in smaller frequency and the absorption bands are broad due to hydrogen bonding (e.g.hydroxyl and amino groups). Absorptions in the region between1400-900 cm-1 (so called fingerprintregion) are usually hard to interpret because in this region there are a large variety of different kindof absorptions. Absorptions in this region should be interpreted with caution. The substitution patternof aromatic ring can be found under 900 cm-1.

Try to find from the spectrum functionalities like hydroxyl groups (alcohols, phenols), amino group(amines, amides), carbonyl groups (aldehydes, ketones, esters, amides, carboxylic groups (broad OHand carbonyl group). Also try to find out if there is absorptions from the aromatic compound.

On the table below there is a short list of the most common IR-absorptions of organic compounds.

Literature:

T. Hase, Tables for Organic Spectroscopy, Otatieto, Espoo

E. Pretsch, P. Bühlmann, C. Affolter, Structure Determination of Organic Compounds, Springer2000.

D.H. Williams, I.Flemming, Spectroscopic methods in organic chemistry, 5. ed. , McGraw-Hill BookCompany Limited, Maidenhead, 1989.

Page 34: 55058 Chemistry basic laboratory II (Organic chemistry)reagenssi.kemia.helsinki.fi/nettilabra/tiedostot... · synthesis products or solid isolated organic compounds are always impure

34

Most common IR-absorptions for organic compounds.Compound Band (cm-1) Size Bond Absorption type

Alkane 2850-3000

1350-14701370-1390

s

mm

CH3, CH2 & CH2 or 3 peaksCH2 & CH3CH3

n

d d

Alkene 3020-31001630-1680

mv

=C-H & =CH2C=C (symm. weak)

n n

Aromatic 30301600 & 1500690-900

730-770 ja 630-710735-770750-810800-860860-900

vm-ws-m

sss

m-sm

C-HC=C (ring)C-H (ring)substitution:5 adjacent H4 adjacent H3 adjacent H2 adjacent HisolatedH

n n d

d d d d d

Alcohol &phenol

3580-3650

3200-3550

1330-1430970-1250

v

s

ms

O-H (vapaa), sharpO-H (H-sit.), broadO-H

C-O

n

n

d d

Amine 3400-35003300-34001550-1650

ww

m-s

N-H (prim.)2 peaksN-H (sek.) 1 peakNH2

n n d

Aldehyde &ketone

2690-2840 (2 piikkiä)1720-17401710-172016901675

mssss

C-H (aldehydes)C=O (aldehydes)C=O (ketones)Arylketonea,b-unstaur.

n n n n n

Carboxylic acid& derivatives.

2500-3300 (acids)peittää C-H –värähdykset1705-1720 (acids)1210-1320 (acids)1785-1815 (COX)1750 & 1820(anhydrides)1735-1750 (esters)1000-1300 (esters)1630-1695 (amides)1590-16501500-1560

s

sm-s

ss

ssmmm

O-H (very broad)

C=O (H-bonded.)C-OC=OC=O (2 peaks)

C=OC-O (2 peaks)C=O (amide I)N-H (amide II)N-H (amide II)

n

n n n n

n d

Nitriles 2240-2260 m n

Size: s=strong, m =medium, w= weak, v=variable.Absorption type: n=stretsing, d=bending