Advanced organic chemistry preparatory classesdo.chem.uni.wroc.pl/system/files/Preparatory...

Advanced organic chemistry – preparatory classes

P1. SEPARATION OF ORGANIC COMPOUNDS MIXTURE

Objectives:

to train basic organic laboratory techniques

to learn basic procedures for isolation and purification of organic compounds

to use acid-base chemistry for separation of organic compounds

Topics of study:

acid-base chemistry of carboxylic acids and amines

extraction as a separation and purification technique

Suggested textbooks:

Extraction, filtration, melting-point determination:

J. W. Zubrick, The Organic Chem Lab Survival Manual: A Student's Guide to Techniques, Wiley,

eight edition, chapters: 12 (The melting-point experiment); 13 pages 107-110 (Gravity Filtration),

110-113 (The Büchner Funnel and Friends), 114-115 (The Water Aspirator: A Vacuum Source),

117-118 (Salting Out), 118-119 (World-Famous Fan-Folded Fluted Paper); 15 (Extraction and

washing) or

R. J. Fessenden, J. S. Fessenden, P. Feist, Organic Laboratory Techniques, Brooks/Cole Publishing

Company, third edition, chapters: Technique 2 (Melting Points), Technique 3 (Extraction)

Acid-base chemistry of carboxylic acids and amines:

K. P. C. Vollhardt, N. E. Schore, Organic Chemistry: Structure and Function, W. H. Freeman and

Company, New York, fifth edition, chapters: 19-4 (Acidic and Basic Character of Carboxylic Acids),

21-4 (Acidity and Basicity of Amines) or

J. McMurry, Fundamentals of organic chemistry, Brooks/Cole Publishing Company, fourth

edition, chapters: 10.3 (Acidity of Carboxylic acids), 12.3 (Amine Basicity)

Apparatus and materials:

separating funnel with stopper

beakers

graduated cylinder

funnel and filtration paper

Büchner funnel and filter flask

watch glass

laboratory stand and jacks

metal ring

round-bottomed flask

Chemicals:

a sample of benzoic acid, m-nitroaniline

and naphthalene suspended in water

diethyl ether

concentrated hydrochloric acid

sodium hydroxide

anhydrous magnesium sulfate

brine


Procedure:

1. Mount a metal ring to a laboratory stand. Make sure the size of the ring is adjusted to the size

of separating funnel. Place the separating funnel into the metal ring.

2. Place the sample of organic compounds suspended in water in the separating funnel.

3. Start pouring small portions (10 mL) of diethyl ether to the suspension until solids inside

separating funnel fully dissolves. Shake the suspension gently to facilitate the dissolution

process. Remember which layer (upper or lower) is diethyl ether.

4. Pour 10 mL of 3 M hydrochloric acid into the mixture in separating funnel and plug it with a

stopper. Shake the separating funnel vigorously for a while. Remember to equalize the pressure

couple times by slow opening of the stopcock. The amine was transformed into water-soluble

salt in the course of the reaction.

5. Mount the separating funnel into the metal ring, remove the stopper and wait until the

emulsion separate into two distinct layers.

6. Slowly open the stopcock and drain the lower layer into the beaker no. 1.

7. Pour 10 mL of distilled water into the solution in the separatory funnel and shake it for a while.

After the full separation of emulsion into two layers, drain the lower one into the beaker no. 1.

8. Pour 10 mL of 1.5 M NaOH into the mixture in separating funnel and plug it with a stopper.

Shake the separating funnel vigorously for a short time. Remember to equalize the pressure a

couple of times by slow opening of the stopcock. Repeat instructions from procedure 5. Organic

acid was transformed into water-soluble salt in the course of the reaction.

9. Slowly open the stopcock and drain the lower layer with sodium benzoate into the beaker no.

2.

10. Pour 10 mL of distilled water into the solution in the separatory funnel and shake it for a while.

After the full separation of emulsion into two layers, drain the lower one into the beaker no. 2.

11. Pour 10 mL of brine into the solution in the separatory funnel and shake it for a while. After the

full separation of emulsion into two layers, drain the lower one into the beaker no. 3 and the

upper one into the beaker no. 4.


12. Place one spatula of anhydrous magnesium sulfate into the beaker no. 4 and stir it for a while.

Place a watch glass on the top of the beaker.

13. To the solution in the beaker no. 1, add dropwise a concentrated solution of sodium hydroxide

until the pH of solution reaches a value of 10 – 11 (use universal indicator papers). Place the

beaker in the crystallizer filled with crushed ice until the solution is cooled down.

14. To the solution in the beaker no. 2, add dropwise a concentrated hydrochloric acid until the pH

of solution reaches a value 1 – 2 (use universal indicator papers). Place the beaker in the

crystallizer filled with crushed ice until the solution is cooled down.

15. Remove the drying agent from the beaker no. 4 using a gravity filtration technique. Transfer the

filtrate into small round-bottomed flask and evaporate the solvent using rotary evaporator.

Transfer the solid residue from the flask into the small vial and protect it with paper. Leave it to

dry in your locker until the next class.

16. Filter both precipitates from beakers no. 1 (m-nitroaniline) and 2 (benzoic acid) using a vacuum-

filtration technique and transfer them into two vials. Protect the vials with paper and leave it

until the next class. At this point, the solution from the beaker no. 3 may be removed.

17. Measure the melting points for all three substances you separated.

Description of the separated compounds

compound 1 compound 2 compound 3

name

formula

Description of the sample of organic compounds


description

mass

Observations and conclusions


The balanced chemical equations

p.4

p.8


p.13

p.14


P2. SYNTHESIS AND PURIFICATION OF ASPIRIN (ACETYLSALICYLIC ACID)

Objectives:

to synthesize aspirin – a physiologically active compound

to practice a simple synthetic and purification procedure

to confirm the identity of the compound using a simple analytical reaction

to determine purity of compound by melting point measurements and NMR technique

Topics of study:

basic reactions of carboxylic acids, anhydrides and phenols

crystallization as a simple and efficient purification method for organic compounds

simple methods for purity control of organic compounds


Basic reactions of carboxylic acids, anhydrides and phenols

K. P. C. Vollhardt, N. E. Schore, Organic Chemistry: Structure and Function, W. H. Freeman

and Company, New York, fifth edition, chapters: 19-8 (Carboxylic Acid Derivatives), 19-13

(Biological Activity of Carboxylic Acids), 20-3 (Chemistry of Carboxylic Anhydrides), Chemical

Highlight 22-2 (Aspirin: A Phenyl Alkanoate Drug) or

J. McMurry, Fundamentals of organic chemistry, Brooks/Cole Publishing Company, fourth

edition, chapters: 8.8 (Synthesis and Reactions of Phenols), 10 (Carboxylic Acids and

Derivatives)

Crystallization, melting-point determination, principles of NMR spectroscopy


eight edition, chapters: 12 (The melting-point experiment); 13 (Recrystallization), 22 (Reflux

and addition), 33 (Nuclear Magnetic Resonance) or

R. J. Fessenden, J. S. Fessenden, P. Feist, Organic Laboratory Techniques, Brooks/Cole

Publishing Company, third edition, chapters: Technique 1 (Crystallization), Technique 2

(Melting Points), Technique 14 (Carrying Out Typical Reactions), Technique 16 (Proton

Nuclear Magnetic Resonance Spectroscopy)

Synthetic procedure is based on: Vogel, A. I., A text-book of Practical Organic Chemistry

including qualitative organic analysis, third edition, 1956, Longman



water bath

laboratory stand

clamps with jacks

round-bottomed flasks (250 mL)

thermometer

glass rod

graduated cylinder

vials

Büchner funnel

filtration flask

filtration paper

reflux condenser

beaker

mortar and pestle

Chemicals:

salicylic acid (10 g)

acetic anhydride (14 mL)

sulfuric acid (few drops)

commercial aspirin

ethanol

distilled water

water solution of iron(III) chloride

Synthetic procedure:

1. Warm the water bath to 60°C.

2. Place salicylic acid and acetic anhydride in a round-bottomed flask.

3. Add few drops of concentrated sulfuric acid to the mixture of reactants and rotate the flask

for a while.

4. Place the flask inside a water bath for 15 min. From time to time, stir the reagents using a

glass rod. Make sure the temperature of mixture is between 50 and 60°C.

5. Remove the flask from the water bath and leave it to cool down.

6. Add 150 mL of distilled water and vigorously stir the suspension.

7. Filter the crude product using a vacuum filtration technique.

8. Place a small portion of crude product into an open vial, protect it with a paper and leave it

to dry.

Recrystallization procedure:

1. Place the crude product inside a round-bottomed flask (250 mL) and add 30 mL of ethanol.

2. Mount the reflux condenser on the top of the flask and warm the mixture in a water bath till

solution.

3. Pour the solution into ca. 75 mL of hot water. If the product crystallized at this stage, you

should dissolve it one more time in water bath.

4. Leave the solution for slow cooling.

5. Filter the crude product using vacuum filtration technique.

6. Place the product into evaporator and protect it with paper assigned to you.

7. Place the evaporator with dry product into a desiccator and leave until the next class.


Identity and purity determination:

Analytical test for phenols

1. In four clean and dry test tubes, dissolve salicylic acid, crude aspirin, recrystallized aspirin

and a sample of commercial drug in 2 mL of distilled water.

2. Add 2 – 3 drops of 2.5% water solution of iron(III) chloride. Watch and note down the color

of the solutions at the time of mixing reagents.

Purity determination of aspirin

1. Prepare a sample for NMR measurements: Place 3 – 5 mg of recrystallized aspirin in NMR

tube and add 0.6 mL of CDCl3. The group should additionally prepare two samples of crude

product and commercially available drug.

2. With the assistance of your teaching assistant (TA) go to NMR laboratory and collect NMR

spectra of your samples.

3. Compare NMR spectra you collected with those of your colleagues.

4. Using the melting point apparatus, measure the melting range for crude and recrystallized

aspirin. Melting range is a range of temperature from the point at which first crystals begin

to melt to the point at which the entire sample is liquid.

Reagents

Reagent 1 Reagent 2 Catalyst Solvent

name

Molar weight [g/mol]

density [g/ml]

mass/volume

Melting point/ boiling

point

Safety information

Equipment (fill in the boxes)



Identity and purity determination

Test for phenols

Test tube 1 2 3 4

compound

Color after

addition of FeCl3

Description of product


mass [g]


yield [%]

Theoretical melting point

Experimental melting point

Analysis of NMR data


P3. n-BUTYL ACETATE SYNTHESIS

Objectives:

to train basic organic laboratory techniques

to learn basic procedures for isolation and purification of organic compounds

Topics of study:

extraction and distillation as a separation and purification techniques



eight edition


Publishing Company, third edition


heatnig mantle

laboratory stand

clamps with jacks

round-bottomed flasks (100 mL)

thermometer

glass rod

reflux condenser

beakers

condenser

separatory funnel

funnel

Chemicals:

glacial acetic acid (15 mL)

n-butanol (11.5 mL)

sulfuric acid (0.5 mL)

sodium hydrogen carbonate

anhydrous sodium sulfate


A direct reaction of acid with alcohol, leading to respective ester, proceeds according to the

following mechanism:

As one can notice esterification is an equilibrium reaction, thus to move equilibrium in the

product’s direction, one needs to remove the water or use an excess of one of the substrates.

Direct esterification is catalyzed by strong acids (see the mechanism) e.g. sulfuric, hydrochloric

or p-toluenosulfonic acids.

The experiment consists of a few stages:

Reflux of a substrates mixture

1. In a 100 mL round-bottom flask, mix together glacial acetic acid (15.0 mL), n-butanol (11.5

mL), and add 0.5 mL of concentrated sulfuric acid.

2. To prevent overheating, add a few boiling chips into the flask.

3. Prepare a setup for a reflux procedure. Turn on cooling water flow, connect your reaction flask

and turn the heating mantle on.

4. Allow the mixture to reflux for 30-60 min.

Extraction of an organic product and drying

1. After reaction refluxing, turn the heating off.

2. Add approx. 50 mL of water into a separatory funnel and pour the cooled reaction mixture

into it.

3. Collect the upper layer of crude ester and wash it again with water, then with saturated

solution of sodium hydrogen carbonate (be careful with evolving and CO2 – degas the funnel

and shake it gently), and once again water.

4. Collect the organic layer and dry it with anhydrous sodium sulfate for at least 30 min (it is

important to get rid of any water residues).

Simple distillation

1. After drying, filter the drying agent (you should wash it with a small amount of

dichloromethane) directly into a 50 mL distillation flask.

2. Add a few boiling chips.

3. Prepare a distillation apparatus, turn on the water flow and mount your distillation flask.

4. Slowly start to heat the mixture.

5. When it starts to boil, begin to collect of forerunning fraction until you achieve temperature

equal to the boiling point of ester.

6. Collect the main ester fraction, within a range of two Celsius degrees, to a weighed vessel.


7. Note all amounts and temperatures. Do not distill the mixture to dryness.

Examination of the obtained product

1. Carefully check odor of the product.

2. Calculate the yield of the reaction.

3. Measure the refractive index of obtained product and compare to the literature value.

Equipment (part 1)

The balanced chemical equation

Equipment (part 2)


Name/formula


mass/volume [g or mL]

Density [g/mL]

Melting/boiling point [°C]

Safety information


Calculations

Temperature at which you start to collect the main fraction ...................... °C

Temperature at which distillation is stopped .............................................. °C

Appearance and odor of distillate .......................................................................................................

Measured refractive index ......................; Literature value .............................................................

Weight of empty dry vessel ......................... g


Weight of vessel plus product ...................... g

Net weight of n-butyl acetate ...................... g; Yield ......................%


P4. SYNTHESIS AND ISOLATION OF MESO-TETRAPHENYLPORPHYRIN

Objectives:

to synthesize meso-tetraphenylporphyrin from pyrrole and benzaldehyde

to practice small-scale synthesis, thin-layer and column chromatography

Topics of study:

thin-layer chromatography

column chromatography

Suggested literature:

Synthesis of porphyrin

Lindsey, J. S., Hsu, H. C., Schreiman, I. C. Tetrahedron Lett. 1986, 27, 4969

Lindsey, J. S., Schreiman, I. C., Hsu, H. C., Kearney, P. C.; Marguerettaz, A. M. J. Org. Chem.

1987, 52, 827

Chromatographic techniques


eight edition, chapters: 21 (The rotary evaporator), 26 (Chromatography: some generalities),

27 (Thin-layer chromatography), 28 (Wet-column chromatography) or


Publishing Company, third edition, chapters: Technique 11 (Column Chromatography),

Technique 12 (Thin-layer Chromatography)


magnetic stirrer

magnetic stirring bar

laboratory stand

clamps with jacks

round-bottomed flask (50 mL)

beaker (200 mL)

septum, balloon

aluminum foil

syringes (two 5 mL and one 1 mL)

two needles

chromatography column

TLC plates

TLC chamber

Pasteur pipettes


Chemicals:

solution of pyrrole in dichloromethane

(4.5 mL)

solution of benzaldehyde in

dichloromethane (4.5 mL)

solution of boron trifluoride-diethyl ether

complex in dichloromethane (1 mL)

2,3-dichloro-5,6-

dicyanobenzoquinone (DDQ) (171 mg)

aluminium oxide (basic, grade II) for

chromatography

dichloromethane for chromatography

n-hexane for chromatography

Procedures:

Synthetic procedure:

1. Using 5 mL syringes, place solutions of pyrrole and benzaldehyde in 50 mL round-bottomed

flask equipped with a magnetic stirring bar (Figure 1).

2. Flush the solution with nitrogen for 15 min.

3. Put the rubber septum at the top of flask neck and protect the mixture from air using a

nitrogen-filled balloon. Cover the flask with aluminum foil to protect reagents from light

(Figure 2).

4. Using 1 mL syringe, place a solution of boron trifluoride-diethyl etherate in the flask.

5. Mix the reagents for 1 h using a magnetic stirrer.

6. Remove the balloon with septum and add DDQ to the solution.

7. Evaporate the solvent under reduced pressure using rotary evaporator.

Column chromatography procedure:

1. Attach the chromatographic column to a laboratory stand using a clamp (Figure 3).

2. Plug a column chromatography with a small piece of cotton. You can use glass rod to tamp

it down.


3. Prepare a slurry of aluminum oxide in dichloromethane.

4. Place the beaker under the column – you will use it to collect the eluate (Figure 4).

5. Load the chromatographic column with an appropriate amount of adsorbent. Make sure the

column does not dry.

6. Dissolve the crude reaction products in small amount (2 – 3 volumes of Pasteur pipette).

7. Carefully transfer the solution to the top of the aluminum oxide layer. Before you load the

sample, make sure that the eluent level is maximum 5 mm under the adsorbent.

8. Once the mixture of products has gone into the adsorbent, carefully pour little amount of

eluent and allow it to enter the adsorbent. Repeat the process until the eluent you add

remains colorless.

9. Carefully fill the column with eluent making sure not to disturb the adsorbent.

10. Watch the separation and collect fractions eluted witch dichloromethane. Make sure there

is an eluent in the column as long as you run the column.

11. Evaporate the solvent from red-purple fraction using a rotary evaporator.

Thin-layer chromatography procedure:

1. Prepare two thin-layer chromatography plates (TLC plates).

2. Using a pencil carefully draw start lines, localized 1 cm under the shorter edge, on both plates

(Figure 1).

3. On this line mark three, equally distant from each other, spots. Make sure that the first and

the last point are about 0.5 cm distant from the longer edge of TLC plate.

4. Using capillaries, apply three samples on the spots in the sequence (Figure 2):

crude mixture after porphyrin synthesis

purple fraction after chromatography

benzaldehyde

5. Leave the plates for three min to dry.

6. Prepare TLC chambers.

7. Fill a small beaker with 2 mL of dichloromethane (eluent 1). Make sure that once you put the

TLC plate into the chamber, the eluent level is about 3 mm below the start line.


8. Prepare the second TLC chamber in the same manner using n-hexane (eluent 2).

9. Put TLC plates into TLC chambers. Be careful – it is very easy to break the adsorbent layer.

You can help yourself by using tweezers (Figure 3).

10. Put a watch glass on the top of a beaker and observe the separation (Figure 4).

11. Once the eluent reach the level 1 cm below the upper edge, take out the plate from the TLC

chamber and mark the solvent line using a pencil.

12. Leave plates for a couple minutes to dry.

13. Put the plates under the UV-lamp and using a pencil, mark

the spots which appeared after the separation (Figure 5).

14. Measure the distance between start line and finish line and

between the start line and the center of each spot after

separation. Calculate the Rf for each spot using the formula:

b

aR f (Figure 5).

15. Repeat your calculations for the plate developed in the eluent 2. Compare the results.

Synthesis of porphyrin Observations and conclusions

Column chromatography Observations and conclusions

Thin-layer chromatography Eluent 1 Observations and conclusions


Rf calculations

Eluent 2 Observations and conclusions Rf calculations

Advanced organic chemistry preparatory classesdo.chem.uni.wroc.pl/system/files/Preparatory...

Documents

Transcript of Advanced organic chemistry preparatory classesdo.chem.uni.wroc.pl/system/files/Preparatory...