Lab Handouts and Lab Report Formats

CH342-01, Summer 2007

Dr. Hathaway

Schedule of Experiments

Dates / Experiment / Pages / Report Due Date*
Weds June 13 / Introduction to Lab, Lab Safety, Calculation of Theoretical Yields, Check-In, Introduction to Melting Points, Thermometer Calibration / 2-5 / June 20
Weds June 20 / Separating the Components of Aspinol, Recrystallization of the Unknown. / 6-12 / June 29
(Aspinol)
Weds June 27 / TLC of Recovered Aspinol Products; Simple and Fractional Distillations of a Binary Mixture / 8-10
13-16 / July 6
(Distillation)
Fri July 6 / Multi-Step Synthesis of Methyl ?-Nitrobenzoate – Step 1: The Oxidation of Acetophenone to Produce Benzoic Acid / 17-18 / July 13
Weds July 11 / Step 2: Preparation of Methyl Benzoate / 19-20 / July 20
Weds July 18 / Step 3: Nitration of Methyl Benzoate / 21-22 / July 27
Weds July 25 / Reduction of 2,6-Dimethylcyclohexanone with Sodium Borohydride / 23-26 / August 3
(before final)
Weds August 1 / Check out and Finish up
Friday,
August 3, 8AM / Final Exam

* Lab reports are by NOON on that date, unless otherwise indicated.


Introduction to Melting Points

Melting point (although more accurately it should be called melting range) is a fundamental physical property of a substance. A pure substance should have a melting range of one degree of less. The melting range should also be close to the reported value in the chemical literature. Impure substances usually have wide melting ranges (over several degrees), and generally melt lower than the reported value.

There are several techniques and pieces of apparatus that can be used to take a melting point. We will be using the Meltempâ apparatus. Although rather simple-looking, this apparatus costs over $300 to replace now, so handle it carefully!

The melting point of a substance is determined in the following manner.

1. Introduce a small amount (about 1-2 mm) of dry, finely powdered crystals into a capillary tube. Be sure that the crystals pack tightly. This can be accomplished by tapping the closed end of the capillary tube on the benchtop.

2. Place the capillary tube (closed end down) in the slot of the Meltemp®. Be careful not to break the tube in the apparatus. Notice that the Meltemp® can hold three tubes at once.

3. Heat the sample and record the melting range. This range starts when the sample just begins to liquefy, and ends when the sample has totally liquefied. You will have to look in the eyepiece and watch the sample. When the sample just begins to liquefy, you will have to look up at the thermometer and record the temperature. You then look back down at the sample and watch it until it has totally liquefied, then look back up at the thermometer, and record this temperature.

The rate of heating is critical for obtaining a good melting point. If you heat the apparatus too fast, you may miss the end of the melting range, because the sample will have completely melted before you can look back down at it. Therefore, you should set a rate of heating of no more than about 5° per minute while your sample is melting. This is done by adjusting the voltage appropriately.

For example, let’s assume you have a sample that melts at 150°. Looking at the table of heating curves, you can see that some voltage settings would not be appropriate. Voltages of less than 40 would never reach 150°. Voltages of 80 or higher would have the temperature increasing so rapidly, you would miss the melting point. A voltage in the range of 50-60 would have a reasonable rate of temperature increase, and would probably work well. Notice that at 50 volts, it would take approximately 12 minutes to reach 150°.

So what do you do if you don’t know what the melting point is supposed to be? One approach is to start with a reasonably low voltage (such as 40), then gradually increase the voltage to maintain a level of heating of about 5° per minute. The disadvantage of this approach is that it will probably take a long time if the melting point is >150°. A second approach would be to take a melting point at a high voltage, such as 90, first. This melting point would be inaccurate, but would give you a rough idea of what range you are looking for. You would then go back and take a second melting point, using a more appropriate voltage setting. The disadvantage of this approach would be having to use two samples, and the need to let the Meltemp® cool back down to about 20° below the melting point before you could use it again.

Precautions:

1. The heating block of the Meltemp® gets very hot (surprise!). Therefore, do not touch it with your fingers or nose (yes, your nose can get close to it) when taking a melting point.

2. Check the temperature on the thermometer before you insert your capillary. If the temperature is higher than the melting point of your sample, it will melt immediately, and you will have to prepare another sample.

3. Don’t break off the capillary tubes in the Meltemp®. If you do, or if you find broken tube pieces in a Meltemp®, please notify your instructor so it can be cleaned out. Broken tubes reduce the efficiency of the apparatus.


Melting Point Calibration

Your Name:______

Number of Melting Point Apparatus Used: _____
Standard / Literature Melting Point (ºC) / Your Melting Point Range (ºC)
2,6-Dibenzylidine-4-methylcyclohexanone / 99
2,6-bis(4-Methoxybenzylidine)cyclohexanone / 159
2,5-bis(4-Methoxybenzylidine)cyclopentanone / 212

Using either graph paper or Microsoft Excel, for each standard plot the literature melting points on the Y axis, and the midpoint of your melting ranges on the X-axis. Draw the best straight line through the points (DO NOT CONNECT THE DOTS!) Determine the slope of the line and the Y-intercept. These values will allow you to correct melting points you take on this MeltempÒ apparatus, assuming that the melting ranges you take today are good. Include your graph with this report.

Question:

Redraw 2,5-bis(4-methoxybenzylidine)cyclopentanone in another sheet of paper. Circle and label all of the functional groups in this molecule. See chapter 2 of your lecture text to help you.


Here is a theoretical yield problem for you to do.

Acetic acid Isopentyl alcohol Isopentyl acetate

10.0 mL, d = 1.05 15.0 mL, d = 0.800

1. Calculate the molecular weights of acetic acid, isopentyl alcohol, and isopentyl acetate. Show your work! Use the following atomic weights: C = 12.00, H = 1.00, and O = 16.00.

2. Calculate the number of moles of both acetic acid and isopentyl alcohol. Show your work.

3. What is the limiting reagent? Explain.

4. Calculate the theoretical yield of isopentyl acetate in grams. Show your work

5. If you isolated 5.00 grams of isopentyl acetate in your experiment, what is your percent yield? Show your work.


Professional Strength

ASPINOL®

Ingredients:

Aspirin ...... 1,200,000 mg

Acetaminophen ...... 1,000,000 mg

Inert Material ...... 800,000 mg

Dist. by B&B Pharmaceuticals, Cape Girardeau, MO

“We Sell ‘em Any Way We Can!”

ANALYSIS OF ASPINOL

One of the responsibilities of the U.S. Food and Drug Administration (FDA) is to ensure that over-the-counter drugs are safe and effective. Testing drugs entails identifying and quantitating the amounts of each component in a preparation. In this experiment you are playing the part of a FDA chemist, and your job is to analyze a newly- marketed drug, Aspinol. B & B Pharmaceuticals recently introduced Aspinol, which is reported to contain aspirin, acetaminophen (Tylenol), and some filler, usually sucrose. B & B has been accused of marketing a product which does not meet the approved specifications. In some lots, acetanilide or phenacetin has been substituted for acetaminophen. Acetanilide costs less to manufacture and has similar analgesic properties to acetaminophen, but is somewhat more toxic. Phenacetin is similarly more toxic than acetaminophen. In other lots, the aspirin or acetaminophen, or both, is missing. Your job is to check a sample of Aspinol and determine its composition.

Aspirin / Acetanilide / Acetaminophen / Phenacetin

Since Aspinol is a mixture of compounds you must first separate the components of the mixture before beginning any analysis. To obtain pure compounds from this mixture, you will take advantage of the physical and chemical differences of the individual components. Substances having different solubilities in a given solvent can be separated by extraction or filtration. Acidic or basic compounds can be converted into water-soluble salts, which can then be separated from water-insoluble components. It is this strategy that will be used to separate the components of Aspinol.

The separation is begun by dissolving the Aspinol in dichloromethane (CH2Cl2, sometimes called methylene chloride). The filler material is insoluble in the dichloromethane, and can be filtered away from any aspirin and acetanilide or phenacetin.

Since aspirin is a carboxylic acid it will react with dilute sodium bicarbonate solution and form a sodium salt. This salt (see reaction below) is soluble in aqueous solution and thus the aspirin can be separated from any acetanilide which might be present.

Since acetanilide and phenacetin do not react with dilute sodium bicarbonate to form a water-soluble salt and since they are water-insoluble, they remain in the dichloromethane. By evaporating or distilling off the dichloromethane any acetanilide or phenacetin present may be recovered.

Aspirin may be recovered by acidifying the aqueous solution, chilling, and then filtering the solid aspirin.

Procedures for Separating the Components of Aspinol

CAUTION: Dichloromethane may be harmful if ingested, inhaled, or absorbed through the skin. There is a possibility that dichloromethane may induce cancer, but animal tests have been inconclusive to date. Wear gloves, avoid prolonged or unnecessary contact with the liquid, and do not breathe its vapors.

Separation of the Filler

Obtain a sample of Aspinol, weigh it, and transfer it to a 150-mL beaker. Add 50 mL dichloromethane and stir the mixture thoroughly to dissolve as much of the solid as possible. Using a pre-weighed fluted filter paper, filter the mixture to separate the filler material. Set the filter paper aside (you can set it in the hood to minimize your exposure to the dichloromethane vapors - put your initials on the filter paper lightly in pencil) and reweigh it when all the dichloromethane has evaporated. You may wish to weigh this sample more than once to ensure that all the dichloromethane has evaporated. Record the weight of the filter paper and solid, and determine the weight of solid by subtracting the weight of the filter paper. This solid is the filler present in your sample.

Separation of Aspirin

Transfer the dichloromethane filtrate (liquid) to a separatory funnel and extract the aspirin from it with two 25-mL portions of aqueous sodium bicarbonate solution. Dichloromethane has a density greater than that of the sodium bicarbonate solution, so it will be the bottom layer. Separate the two layers. You will have to transfer each layer to a separate container and then return the dichloromethane to the separatory funnel for the second extraction. Label each container so you know which is which!

Save the dichloromethane solution for isolation of acetanilide or phenacetin, below!

Combine the two sodium bicarbonate solutions in 250-mL beaker. Add 10 mL of 6M hydrochloric acid in small portions with vigorous stirring: the solution will bubble as the acid is added. Test the pH of the solution with pH paper: be sure the pH is 2 or lower. If the pH is above 2, add more acid to bring it below 2. Cool the mixture in a ice bath and collect the aspirin by vacuum filtration. Wash the aspirin with only a few mLs of cold water. Let the aspirin dry on the Buchner funnel for a couple of minutes. Scrape out the crystals onto a watch glass and set it aside to air-dry until next laboratory period, when you will weigh it and take its melting point range. The filtrate in the filter flask may be poured down the drain.

Isolation and Purification of the Unknown, Acetanilide or Phenacetin

Pour the dichloromethane solution into a 100-mL round-bottom flask and remove the dichloromethane on the Rotary Evaporator. Scrape out the remaining solid onto a watch glass, allow it to dry, and weigh the dried material.

Acetanilide is much more soluble in boiling water (5g/ 100 mL) than phenacetin (1.2g/ 100 mL). Recrystallize the unknown by placing it into a 125 mL Erlenmeyer flask, then add 20 mL of water and a boiling stone. Heat the flask to boiling on a hot plate. If not all of the white solid has dissolved, add water in 5 mL portions, and heat it to boiling until all of the white solid dissolves. Once all of the solid has dissolved, remove the flask from the hot plate and allow it to cool to room temperature. Cool the mixture in an ice bath to complete crystallization of the benzoic acid product, and isolate this product by suction filtration. Let it air dry on the aspirator for a while and then further dry in your lab drawer until the next lab period. Weigh and take a melting point range of the product then. Pour the filtrate down the drain.

Thin-Layer Chromatography (TLC) Of Recovered Aspinol Components.

Procedure:

Obtain a TLC plate, and draw a light pencil line across the width of the plate, about 1 cm from the edge. Place 5 light “tic marks” on the line, approximately equally spaced.