Organic Chemistry II Laboratory

This course is meant to re-enforce some of the organic chemistry concepts in CHEM 224, especially characteristic reactions used in identifying the different functional groups in organic chemistry. Demonstrations on physical and chemical experimental methods used to identify organic compounds and some reactions that would synthesize some organic compounds

At the end of this course, students

• Would be able to perform many practical chemical techniques. 
• Should have a better understanding of the preliminary laboratory techniques of organic chemistry.
• Should be able to identify organic compounds by physical and chemical experimental methods.
• Would have developed some experimental skills and research potentials

To satisfy part of the requirement for this course, attendance and participation in all laboratory sessions is mandatory. Assessment would be based on grades from Laboratory assignments (60 points), Lab exam I (20 points) and Lab exam II (20 points).

Grading: 

The labs will be given to students as assignments. Experimental data will be provided for analysis, from which students can make deductions and arrive at conclusions. These will be submitted via turn-it-in in the assignment folder on MyCourses. 

Each lab assignments (labs 2 – 9) will be graded to a total of 10 points per lab.

Best six of eight assignments will count towards final grade: 6 x 10: Total of 60 points from assignments.

Lab Exam 1 (MCQs on ExamSoft) from labs 1 – 5: Total of 20 points.

Lab Exam 2 (MCQs on ExamSoft) from labs 6 – 9: Total of 20 points.

Students cannot re-do the labs that they have missed.

ONLY SIX OUT OF EIGHT LABS WILL CONTRIBUTE TOWARDS THE FINAL GARDE. 

SAS Grading Scale:  Grades will be assigned as follows:

A = 89.5% or better

B+ = 84.5 - 89.4%

B = 79.5 - 84.4%

C+ = 74.5 - 79.4%

C = 69.5 - 74.4%

D  = 64.5 - 69.4%

• Lab Session #1: Introduction & Lab Safety
• Lab Session #2: Melting point determination
• Lab Session #3: Reactions of Alcohols and Phenols
• Lab Session #4: Formation of Ester (Preparation of Ethyl acetate)
• Lab Session #5: Qualitative tests for Aldehydes and Ketones
• Lab Session #6: Determination of an unknown carboxylic acid
• Lab Session #7: Reactions of Amines and carboxylic acid • Lab Session #8: Titration of an amino acid (glycine)
• Lab Session #9: Isolation of Caffeine from team

Lab #1: Introduction and Safety

Students will be introduced to this course content, delivery, and expectations. There will be a discussion on laboratory safety procedures and considerations 

Laboratory Safety:

1. A laboratory coat must always be worn in the lab. This will protect you and your clothes from any contaminants that may be used during the laboratory experiments.
2. Shoes must have closed toes and heals. NO SLIPPERS, NO FLIP-FLOPS, NO SANDALS. You may be asked to leave if you are not dressed properly to conduct an experiment.
3. In general, gloves should be worn during the lab exercises. These will protect your skin from corrosive chemicals. Gloves are NOT worn outside the lab. You do not wear gloves to go to the bathroom, to handle doorknobs, do not handle your pen, do not scratch your face... 
4. NEVER pipette solutions with your mouth, eat, drink, smoke or apply cosmetics in the lab.
5. NEVER pour any chemical or solution into a sink without authorization. 
6.  NEVER use flames with or near volatile solvents 
7. NEVER return reagents to stock bottles. 
8. NEVER smell specimens or chemicals directly. 
9. Use caution when using equipment for heating or melting reagents (e.g. Boiling water baths).
10. ALWAYS report any spillage or accident, however minor, to your instructor
11. Wash hands thoroughly with soap and water after handling laboratory reagents and especially prior to leaving the laboratory when the session is completed.
12. WHEN IN DOUBT ABOUT ANYTHING –ASK YOUR INSTRUCTOR.

N.B: Your Instructor may decide to modify an experiment, change the reagents or change the concentration of reagents based on logistics and experimental trial runs. It is your responsibility to pay attention to detailed instructions for any such modifications during the lab sessions.

LAB 2: Determination of the Melting Point of a Solid Substance.

Aim:  To determine the melting point of given solid substance.

Theory: The change in the state of a compound from solid to liquid when it is heated is called melting, and the temperature at which a solid in its pure form melts is called the melting point. At the melting point, the solid and liquid exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at a standard pressure. 

Every pure solid has a characteristics melting point therefore determination of melting point helps in identification of the compound. Presence of impurities lowers the melting point of the solid. Thus, Melting point also serves as a criterion of purity of a compound.

Materials required: Given solid organic compound, Thin walled capillary tubes   (8 – 10 cm in length and 2 mm in diameter), Paraffin oil, Laboratory thermometer, Heating medium (Hot plate), magnetic stirrer, 500ml beaker, retort stand, and rubber band

Procedure:

1. Take a fine capillary of length 5-6cm. seal its one end by inserting the end of the capillary tube horizontally into the extreme edge of a small steady Bunsen flame for a few seconds, rotating the capillary meanwhile.
2. Take a small quantity of the compound whose melting point is to be determined on a porous plate and powder it with a spatula.
3. Introduce the powdered compound in the capillary tube by introducing the open end of the capillary tube into the powdered compound and gently rotating it. Gently tap the capillary tube against the porous plate so that the compound sinks into the closed end. Repeat the procedure of introducing and tapping three to four times.
4. Moisten the bulb of thermometer with liquid paraffin and attach the capillary to the lower end of the thermometer.
5. Place the thermometer with the capillary tube in the melting point apparatus containing at least two third of its volume liquid paraffin in such a way that the closed end of the capillary remains below the surface of Liquid paraffin (See fig 1 below)
6. Now heat the beaker gently and note down the temperature from time to time and finally note down the temperature (t ⁰C) at which the compound starts melting (t₁ ⁰C) and completely melts (t₂ ⁰C).
7. Repeat the experiment with a new capillary tube and fresh quantity of the substance.

        Fig1: Set up of the apparatus for melting point experiment

Observations 

Results

Melting points

1. t₁ =  _______________ ⁰C
2. t₂ =  _______________  ⁰C

Mean Melting point = (t₁+t₂)/2 ⁰C

Precautions

1. Use dry and powdered sample for the determination of melting point.
2. Packing of the powder should be uniform without any big air gaps between the solid particles 
3. The capillary tube should be filled one fifth of its length.
4. Maintain uniform temperature of the liquid bath.
5. The rate of heating should be controlled. It should be very slow near the melting point so that the melting point can be recorded accurately.

Question

Assume that the compound provided has a melting point of 80^oC, and you got 75^oC after your experiment, what conclusions can you make about the compound?

LAB 3: Reactions of Alcohols and Phenols

AIM: To observe the reactions of some alcohols and phenols

Principle: Based on the physical and chemical characteristics of alcohols and phenols

Materials required: 10ml each of Ethanol (A), Butan-2-ol (B), 2-methyl butan-2ol (C), and unknown D. Phenol (2g), 20 test tubes, 1% soln. of Sodium dichromate, Glacial ethanoic acid, Conc. H₂SO_4, Conc. HCl, 5% Iron (III) chloride solution, iodine solution, sodium hydroxide and water bath set at 60^oC._.

Precautions

1. Sodium dichromate is a toxic compound. The use of plastic gloves is mandatory.
2. Conc. HCl and H₂SO₄ are very corrosive and most be handled with utmost care
3. Observe all other laboratory safety precautions

Results

• Present results for the reaction of each test reagent as shown in tables below.
• Perform tests a, b, c, on alcohols A, and the unknown provided. 
• To distinguish the various types alcohols, perform tests d and e on all the alcohols provided including the unknown.
• Perform tests f, g, and h on phenol.
• Write equations for tests b, c, d, e, g and h. 

LAB 4: PREPARATION AND PURIFICATION OF ETHYL ACETATE

(ETHYL ETHANOATE)

AIM: To prepare and purify ethyl acetate

THEORY: Esters frequently have distinctive odors and are found in the flavorings of many fruits and plants. An ester is a chemical compound that is formed when an organic acid reacts with an alcohol. Concentrated sulfuric acid, H₂SO₄, can be used to catalyze the reaction. Concentrated sulfuric acid is a strong dehydrating agent and helps the reaction by removing the water molecules as they are formed.

• If acetic acid and ethanol are reacted, the reaction shown below occurs.

  CH₃COOH + CH₃CH₂OH → CH₃COOCH₂CH₃ + H₂O

The product is called ethyl acetate. The systematic name for acetic acid is ethanoic acid, and the product is also known as ethyl ethanoate.

In this experiment we will prepare the ester known as ethyl acetate (ethyl ethanoate) and purify it by distillation.

Chemicals

• Acetic acid, concentrated, 17.4 M (glacial)
• Ethanol (ethyl alcohol, denatured alcohol)
• Sulfuric acid, concentrated (18M)

Equipment

Erlenmeyer flask, 125-mL (2)             

Boiling stones or glass beads

Condenser                                           

Distilling flask

Thermometer                                      

Clamps

Beaker, 400-mL for water bath 

Bunsen burner, ring & wire gauze

Measuring cylinder                             

Capillary dropper

Safety Precautions!

• Wear Chemical Splash Goggles and a Chemical-Resistant Apron.
• The concentrated sulfuric acid used is very hazardous. In case of accidental spillage, wash spills off yourself immediately with large amounts of water. Neutralize spills on the laboratory bench with baking soda.
• The organic acids and alcohols are flammable. Use great care around flames. Do not heat directly with a burner but use a water bath.
• The alcohols are all poisons. Do not ingest them. Wash yourself with soap and water if you spill some on yourself.

Procedure

Preparation of purification of ethyl acetate (ethyl ethanoate).

1. Preparation of ethyl acetate.

Diagram: Showing set up of apparatus for preparation of ethyl acetate

• In one 125-mL Erlenmeyer flask, place 10-mL ethanol, 12 mL glacial acetic acid, 15 drops of concentrated sulfuric acid (18 M), and a boiling stone. 
• The condenser should be clamped in a vertical position, with the bottom of the condenser inside the flask. When the condenser is inserted in this manner it acts as a reflux condenser, allowing the vapors of the mixture to condense and return to the reaction vessel. 
• Slowly run cold water through the condenser, in at the bottom and out at the top. Heat the flask in a hot water bath. 
• Raise the temperature of the hot water until the mixture in the Erlenmeyer flask is gently boiling and continue heating for about 15 minutes. 
• Cool the mixture.

2. Distillation of ethyl acetate.

Diagram: Showing set up of apparatus for distillation of ethyl acetate

• Pour the mixture (including the boiling stone) into a distilling flask and connect the condenser to the side arm of the flask. 
• Insert a thermometer. 
• Heat the bottom of the distilling flask in a hot water bath until no more distillate is coming over. 
• Record the temperature at which the distillation begins and the temperatures during and at the end of distillation. 
• Look up the boiling point of ethyl acetate and compare to the distillation temperature.

QUESTIONS:

1 Write the equation for the formation of ethyl acetate     2 What is the purpose of sulfuric acid?

3. What happens if water is removed from the reaction mixture.            
4. Write the structure of the product formed when ethanol is oxidized by  sodium dichromate

LAB #5: Qualitative tests for aldehydes and ketones

Aim: To distinguish between Aldehydes and Ketones.

Principle: Both aldehydes and ketones contain the carbonyl group, and both undergo nucleophilic addition reactions, with nucleophiles.

However, while aldehydes are easily oxidized to yield carboxylic acids,

RCHO → RCO₂H, ketones are unreactive toward oxidation. This reactivity difference is a consequence of structure: aldehydes have a (CHO) proton that can be removed during oxidation, but ketones do not. In other words, Aldehydes can be oxidized (Removal of hydrogen from it), because the carbon of the carbonyl group has hydrogen attached to it. Ketones have none. Compounds which are oxidized act as reducing agents.

Aldehydes can be distinguished from ketones by their reaction towards the following mild oxidizing agents:

Procedure:

Experiments should be carried out and results presented as indicated below:

LAB #6: Determination of an unknown carboxylic acid

Aim: To determine the molar mass of an unknown monoprotic carboxylic acid by titration and hence identify the acid. 

Principle: At the equivalence point of the titration, the moles of OH (base) are equivalent to the moles of H+ (acid) in the sample. The moles of OH added to the solution from a burette are calculated from the concentration of the base (MOH) and the volume of base (VOH) added, as:

Because it is a monoprotic acid, the moles of acid are equal to the moles of OH at the endpoint of the titration.

The units of molar mass are g/mol. This intensive property is the ratio of two extensive properties, as is shown in the figure below.

The lab goal is to determine the molar mass of an unknown monoprotic acid. The grams of acid are determined from weighing the acid and the moles are determined from the titration with NaOH. 

Materials required: Weighing balance, Burette, Pipette, Erlenmeyer flasks (3), Methanol (30mls), 0.1M NaOH (150mls), 0.15g of an unknown carboxylic acid (Benzoic acid) and phenolphthalein indicator.

Procedure

1). Accurately weigh 0.15g of your unknown acid and transfer it into a 125ml Erlenmeyer flask. Add 10 ml of methanol and 2 drops of phenolphthalein indicator and swirl the contents to ensure proper mixing.

2). Titrate against a standardized 0.1M NaOH solution. The change in color from colorless to pink can be noted once the equivalent point has been reached. Record your readings.

3). Repeat the titration with a new weighed sample of the same carboxylic acid. The mass used for the second titration should be different from the mass used for the first determination. 

Calculate the molar mass (g/mol) The two values should agree within ±2 amu. If they do not, perform a third titration.

4). Wash the burette after the last titration, while still clamped. Drain the burette, then slowly add about 10 mls of water and drain; then 10mls of dil. HCl and drain; finally add 50ml of distilled water and drain.

Do not place the burette under the faucet in order to wash it 

5). Identify your unknown carboxylic acid by matching your results with the possibilities listed in the table provided

Results:

Tabulate your results as shown below:

Conclusion: My unknown carboxylic acid is -------- Suggest a molecular formula for this acid: 

How many carboxylic acids with this formula are possible?

LAB #7: Reactions of Amines and Carboxylic acids

AIM: To test and observe the reactions of some amines and carboxylic acids.

Reagents:

• Phenylamine (Avoid skin contact. Toxic & harmful because of skin absorption)
• Ethanoic acid
• Red litmus paper
• Sodium nitrite (10%)
• Hydrochloric acid (Conc), 5% and 10% HCl
• Propanol
• Sodium hydroxide
• Sodium carbonate salt (about 0.5g)
• Lime water
• Benzene sulphonyl chloride

Procedure

Experiments to be carried out and recorded as shown below:

LAB #8: TITRATION OF AN AMINO ACID (GLYCINE)

AIM: To study the titration curve of an amino acid (glycine).

Theory: Titration curves are obtained when the pH of given volume of a sample solution varies after successive addition of acid or alkali. The curves are usually plot of pH versus the volume of titrant added.

Amino acids are amphoteric molecules which can be titrated either against an acid or an alkali. They are weak Polyprotic Acids which exist as zwitterions at neutral pH. When an aqueous solution of an amino acid is titrated with an acid, it acts as a base, with a base, it acts as an acid.

In this experiment we are finding out the titration curve of the amino acid Glycine.

Glycine is a diprotic amino acid which means that it has two dissociable Protons, one on the α amino group and the other on the carboxyl group. In this fully protonated form; it can donate two protons during its complete titration with a base.  In the case of Glycine, the R group does not contribute a dissociable Proton.

The dissociation of proton proceeds in a certain order which depends on the acidity of the proton: the one which is most acidic and having a lower pKa will dissociate first.  So, the H+ on the α-COOH group (pKa1) will dissociate before that on the αNH3 group (pKa2).

Chemicals: 

0.1M Glycine

0.1M NaOH

Equipment:

pH meter

250ml conical flask

5ml pipette

PRECAUTIONS:

Observe all laboratory precautions

Procedure:

Pipette 25 cm³ of glycine into the conical flask provided and measure the pH. Now fill the burette to the zero mark with 0.1M NaOH. Using the burette, add 5ml of 0.1M NaOH to 25cm³ of glycine and record the pH of the resulting solution. Continue adding 5 ml of NaOH at a time and measure the pH for every 5ml added. Record your results as shown in the table below.

Results

QUESTIONS:

1. Using the data collected, draw a titration curve with pH on the vertical axis [shorter axis] and the volume of NaOH added on the horizontal             axis [longer axis].
2. What is the mathematical relationship between pKa and PI ?        
3. Obtain the value of pI (isoelectric point) from the graph. 
4. What is a zwitterion?
5. Draw the structure of glycine and state why glycine is unique compared to the other amino acids.

LAB #9: ISOLATION OF CAFFEINE FROM TEA BY EXTRACTION

AIM: To demonstrate the isolation of a natural product from a biological source, using extraction techniques.

THEORY OF EXTRACTION

Extraction with a solvent (Solvent extraction) is a separation technique most frequently employed to isolate one or more components of a mixture. The technique is based on the preferential solubilities of the components of the mixture for two different immiscible solvents. 

It involves the partial removal of a solute from one liquid in which it is less soluble to another immiscible liquid in which it is more soluble. In most cases, an organic solvent is used to remove an organic solute from an aqueous solution or suspension. If a solute is shaken with a mixture of two immiscible solvents at a fixed temperature, the solute will distribute itself in both solvents according to its solubility in each. The solute will partition itself according to the ratio:

K_p = [solute]_A/[solute]_B

Where K_p is the distribution coefficient, [solute]_A is the concentration of the solute (in moles/L) in solvent A (usually the organic solvent) and [solute]_B is the concentration of solute in (in moles/L) in solvent B (usually water).

For example, 6.67g of phenol is dissolved in 100ml of water, while 8.33g will dissolve in 100ml of benzene, the distribution coefficient will be:

Kp = (8.33g/100mL)_benzene /(6.67g/100mL)_water =1.25

Solvent extraction is more efficient if a certain volume of the extracting solvent is used in several portions rather than one.

Caffeine is an alkaloid that is present in coffee, tea, cola, chocolate any many nonprescription drugs. 

Caffeine is soluble in water because it has several polar and basic functional groups. 

This property makes it insoluble in aqueous base. Thus, by adding a weak base (e.g. sodium or calcium carbonate) to an aqueous solution of tea extract, one can decrease its solubility in water  and increase its solubility in a less polar organic solvent ( such as CH₂Cl₂), into which the caffeine can be easily extracted, using a separatory funnel. Any neutral compound will be extracted into the organic phase, but unfortunately, there are a few of these present in tea. Any acidic compounds (such as tannic acid, a major component of tea) will be deprotonated and will remain in the aqueous phase.

Therefore, Sodium carbonate serves two main functions: to place caffeine in a more basic environment so that it has a higher affinity for dichloromethane and to  cause the tannins which are acidic to form phenolic salts in the aqueous solution.

PRECAUTIONS:

Observe all laboratory precautions.

PROCEDURE:

1. In a 400mL beaker, place 10 tea bags and approximately 100mL of water. Bring to boil on the hot plate and continue to boil for about 15 minutes.
2. Carefully remove the beaker from the hotplate, remove and discard the teabags, and dissolve 15g of Na₂CO₃ in the tea solution by stirring 
3. Cool the tea solution in and ice water bath, then transfer it into a separatory funnel, using a funnel.
4. Add 20mL of methylene chloride via a funnel and shake the mixture gently. DO not shake to vigorously, or you will get an emulsion (i.e. a mixture consisting of droplets of one phase suspended into the other). If this happen let it stand for about 15 minutes to allow separation of the layers.
5. Extract the aqueous layer with another 20mL portion of methylene chloride
6. Combine the organic extracts in a 125mL conical flask, and dry them with about 1g of anhydrous MgSO₄
7. Allow the solution to stand for about 10 minutes, swirling it occasionally to complete the drying.
8. Keep the aqueous phase in a beaker – do not discard until you are sure you do not need it anymore
9. Gravity-filter the methylene chloride solution into a small pre-weighed beaker. Add one boiling chip, and carefully evaporate the solvent to dryness in a hot water bath or a large beaker of water on a hotplate in the hood.
10. Remove the boiling chip, reweigh the beaker, and calculate the yield of crude caffeine

QUESTIONS:

1. Tea contains approximately 2% caffeine by weight. Assume that you started with 25g of tea leaves, calculate the percentage yield of your crude extract.
2. Suppose you forgot to add sodium carbonate to the tea solution prior to extraction.  What effect would this have on your yield?
3. What are the advantages and disadvantages of using ether in solvent extraction?
4. Why was the extraction with methylene chloride done twice with 20mL each time, instead of once with 40mL of methylene chloride?
5. Write equations for the reactions between ethanol and Na, phenol and NaOH and between ethanoic acid and Na₂CO_3.

CHEM 225 Laboratory Schedule – Spring 2022