Dr. Roger K. Murray

I. Introduction

A. Objective

The purpose of this experiment is to perform a microwave assisted Diels-Alder reaction of 2,3-dimethyl-1,3-butadiene with maleimide. This reaction will take place inside a microwave reactor, which will assist the Diels-Alder reaction and make it happen much faster and more efficiently than it normally would.

B. Materials and Safety

C. Experimental Procedure

First, a microwave reaction vessel and small magnetic stirring bar will be obtained from the teaching assistant. The stir bar will be placed into the vessel. Next, 1.28 g of maleimide, 3.00 mL of 2,3-dimethyl-1,3-butadiene, and 3.75 mL of water will be added to the reaction vessel. The teaching assistant will fit the reaction vessel with the top and tighten it with a pre-set torque wrench. The teaching assistant will then help place the reaction vessel into a protective sleeve and into the microwave turntable. The position of the vessel in the turntable will be recorded. The teaching assistant will then turn the microwave reactor on, and the vessels will be heated for 10 total minutes. The reactor will be allowed to cool for 20 minutes after completion of heating. The vessel will then be removed from the reactor and brought to the work area under the hood. The cap of the vessel will be loosened and the vessel will be allowed to vent and cool to room temperature. The white solid inside the vessel will be collected via vacuum filtration. Once the product is dry, it will be weighed and its melting point will be determined using the Mel-Temp apparatus.

II. Experiment and Results

A. Data

First, a microwave reaction vessel and a small magnetic stirring bar were obtained. Then added to the vessel were 1.281 g of maleimide, about 3.75 mL of water, and 3.00 mL of 2,3-dimethyl-1,3-butadiene, in that order. The cap of the reaction vessel was fastened using a pre-set torque wrench and it was placed into the microwave reactor. The microwave reactor was then turned on a set to its programmed heating method, in which the temperature was increased to 110 ºC over a 5 minute period and was held at 110 ºC for 5 more minutes. The vessel was then allowed to cool in the reactor for about 25 minutes. The vessel was then brought to the work area and the cap was removed. The vessel was allowed to cool for a few more minutes, then the solid in the vessel was collected using vacuum filtration. The vessel was washed with cold water to help transfer the product to the filtration device. The product was allowed to air dry for two weeks, and was then weighed and its melting point was determined using a Mel-Temp device.

Moles of maleimide was calculated by dividing the weight by the molar weight. The molecular weight of the product was calculated by adding the molecular weight of the two reagents. The theoretical moles of product recovered is the same as the moles of maleimide, which is the limiting reagent. The theoretical weight of the product was found by multiplying the molecular weight by the number of moles. The percent recover was determined by dividing the actual weight recovered by the theoretical weight recovered and multiplying by 100.

III. Conclusions

This was a fairly straightforward lab. I expect the percent recovery to be very high because the microwave reactor is very efficient at speeding up chemical reactions. Microwaves do not produce a lot of excess waste from reactions, so this means most of the chemical reaction that we wanted to take place should have happened, which would result in a high percentage of desired product. The only things that would throw our results off are if we were not able to get all of the product out of the reaction vessel or if cold water was not used in washing it out. If warm water was used, the product would become soluble and it would wash away, leaving a low percent yield.

I. Introduction

A. Objective

The purpose of this experiment is to identify an unknown proprietary drug using thin-layer chromatography. The unknown’s behavior in thin-layer chromatography will be compared with that of its possible component analgesics. The possible unknowns and their analgesic ingredients will be Anacin (aspirin, caffeine), Excedrin (acetaminophen, caffeine, aspirin), Motrin (ibuprofen), and Tylenol (acetaminophen).

B. Materials and Safety

C. Experimental Procedure

First, five 13×100 test tubes will be labeled 1-asp, 2-ace, 3-unk, 4-caf, and 5-ibu. Then

About 20-30 mg of each of the four known compounds will be added to the appropriate test tube, and 20-30 mg of the unknown will be added to the test tube marked 3-unk. Next, 0.5 mL of methanol will be added to the four test tubes with known compounds and they will be swirled until all the solid has dissolved. The test tube with unknown will receive 1.0 mL of methanol and a glass stirring rod will be used to mix the sample. Any insoluble material will be allowed to settle.

Next, two 3” x 1” sheets of fluorescent TLC silica gel plates will be obtained. Capillary tubes will be used to spot the samples of 1-asp, 2-ace, and 3-unk on the coated side of one plate. The spots are to be evenly spaced, 0.5-1.0 mm in diameter, 1 cm from the bottom of the plate, and at least 0.5 cm from the side of the plate. The plate will be viewed under UV light to make sure that enough of each sample has been applied. Capillary tubes will also be used to spot 3-unk, 4-caf, and 5-ibu on the other plate in the same manner. Again, UV light will be used to make sure enough of each sample has been applied.

Then, each TLC plate will be placed spotted end down into a developing jar containing a pool of ethyl acetate that is about 0.5 cm deep. The jar will be capped and when the ethyl acetate rises within 1-2 cm of the top of the TLC plate, the TLC plate will be removed from the jar and allowed to dry. Once dry, the TLC plate will be analyzed under the UV light and the appearance of the spots will be drawn in a laboratory notebook.

II. Experiment and Results

A. Data

First, five clean test tubes were labeled 1-asp, 2-ace, 3-unk, 4-caf, and 5-ibu. Twenty to thirty mg of each of the four known compounds were added to the appropriately labeled test tube, and all of the unknown in our given vial, labeled “K”, was added to the vial labeled 3-unk. Next, 0.5 mL of methanol was dispensed into the four test tube containing known compounds, and the test tubes were swirled until the solid had dissolved. Then 1.0 mL of methanol was dispensed into the test tube with the unknown, and it was also swirled until the solid was dissolved. A spatula was used to help mix any solids that were having trouble dissolving.

Next, two fluorescent TLC silica gel plates measuring about 3” x 1” were obtained. Micro capillary tubes were used to spot 1-asp, 2-ace, and 3-unk on the coated side of one plate. The spots were evenly spaced and about 1 cm from the bottom of the plate and 0.5 cm from the side of the plate. On the second plate, 3-unk, 4-caf, and 5-ibu were plated in the same manner. The plates were then placed spotted side down in a developing jar that contained a 0.5 cm high pool of ethyl acetate. The lid of the jar was screwed on and the plates were allowed to sit in the jar until the ethyl acetate rose to about 2 cm from the top of the plate. The plates were then removed from the jar and then analyzed under an ultraviolet light. The appearance and measurements of the spots were recorded in a lab notebook.

III. Conclusions

It appears that the unknown contained caffeine and acetaminophen judging by the R­_f numbers. The average R_f for unknown spot #1 was 0.24, which is very close to the R_f of caffeine (0.22). The average R_f for unknown spot #2 was 0.58, which is fairly close to the R_f of acetaminophen (0.52). However, none of the unknown drugs contain only caffeine and acetaminophen. Excedrin contains caffeine, acetaminophen, and aspirin, which leads me to believe that we may have misinterpreted our gel when looking at it. It was hard to tell if there some of the streaks actually had spots in them or not, so we may have missed on what should have been a third spot above the acetaminophen spot on our gel plate. This third spot would have been aspirin. I do not remember even seeing a streak above our second spot on the gel plate for the unknown, so this means we may not have spotted enough of the solution on the plate. It could also mean that there is a very low concentration of aspirin in Excedrin, which would account for why we could not see it on the gel plate.

I. Introduction

A. Objective

The purpose of this experiment is to compare the efficiency of simple distillation versus fractional distillation for separation of a mixture of toluene and cyclohexane. The mixture will first be separated using fractional distillation. A fractional distillation apparatus will be set up and a Thermowell heater containing sand will be used as the heat source. The mixture will be brought to a boil and slowly condensed. The temperature as a function of the number of drops will be recorded along with boiling point versus the number of drops distilled. Three fractions will be collected representing “pure cyclohexane”, changeover fraction, and “pure toluene”. These three fractions and the undistilled sample of the original mixture will then be analyzed using gas chromatography. A simple distillation apparatus will then be set up and a Thermowell heater containing sand will also be used as the heat source. The mixture will be slowly heated and condensed. The temperature as a function of the number of drops will again be recorded. Only one fraction will be collected for the simple distillation.

B. Materials and Safety

C. Experimental Procedure

Fractional distillation will take place first. A 10 cm column will be packed with steel sponge. Then 3 mL of the unknown mixture of cyclohexane and toluene will be added to the 5 mL short-necked flask along with several boiling chips. The unknown mixture given will be recorded. The fractional distillation apparatus will be set up with a cooled vial as a receiver. A Thermowell heater containing sand will be used as the heat source. The mixture will be brought to a boil over the hot sand bath. When the vapor reaches the thermometer bulb, heat will be reduced by shifting some of the sand. The distillation is to take place at a rate no faster than five drops per minute. The temperature as a function of the number of drops will be recorded along with boiling point versus the number of drops distilled. Three separate fractions will be collected representing “pure cyclohexane”, changeover fraction, and “pure toluene”. The receiver will be changed for the first time after the temperature begins to rise after a plateau. The receiver will be changed for the second time after the temperature begins to plateau after the rise. The distillation will be stopped when about 0.3 mL of mixture remains in the flask.

Next, gas chromatography will be used to analyze the three fractions from fractional distillation along with an undistilled sample of the original mixture. The procedure for this part of the experiment will be described during the laboratory lecture.

Finally, simple distillation will take place. A simple distillation apparatus will be set up will a cooled vial as a receiver. A 3 mL sample of the unknown mixture of cyclohexane and toluene will be added to the 5 mL short-necked flask along with several boiling chips. A Thermowell heater containing sand will again be used as the heat source. As the vapor reaches the thermometer bulb, the heat will be reduced by shifting some of the sand. The distillation will take place at a rate no higher than five drops per minute. The temperature as a function of the number of drops will be recorded along with boiling point versus the number of drops distilled. Distillation will be stopped when about 0.3 mL of mixture remains in the flask.

II. Experiment and Results

A. Data

First, a simple distillation took place. Four mL of an unknown mixture of cyclohexane and toluene labeled “unknown A” was dispensed into a 5 mL short-necked flask along with a few boiling chips. A simple distillation apparatus was set up using a sand bath as the heating source. A water cooled condenser was used to cool and condense the gas into a vial. The temperature was recorded as after each drop of the liquid into the vial. Distillation was ceased when there was only about 0.3 mL of unknown remaining in the flask.

Next a fractional distillation took place. Four mL of “unknown A” was again dispensed into a 5 mL short-necked flask along with a few boiling chips. A fractional distillation apparatus was set up using a sand bath as the heating source. The 10 cm column was fairly loosely packed with steel sponge. A water cooled condenser was used to cool and condense the gas into a vial. The temperature was recorded after each drop of the liquid into the vial. The temperature rose and plateaued at first, and after it started rising again a new vial was used to collect the liquid. After the temperature began to plateau for a second time, a third vial was used to collect the liquid. Distillation was stopped after there was only about 0.3 mL of unknown left in the flask. The three fractions collected were then analyzed and graphed using gas chromatography, which was performed by Dr. Murray.

Simple Distillation:

Fractional Distillation:

B. Graphs

III. Conclusions

It appears that the fractional distillation was more efficient than the simple distillation. The simple distillation graphed basically as a straight line, but the graph of the fractional distillation actually somewhat shows the plateau where mostly cyclohexane is being condensed and then the rise and second plateau where mostly toluene is being condensed. This can not be really seen in the graph of simple distillation. This may be due in part that the simple distillation was heated too fast. I know that for the fractional distillation it seemed like we heated it at a very steady rate, but the simple distillation was harder to control. This may be why our data did not plot so well.

However, in theory the fractional distillation should be more efficient because of the steel sponge. The sponge acted as surface area for gas to condense on. This prevented some of the toluene from condensing into the vial during fraction A because it would condense onto the sponge and drip back down into the flask. The boiling point of toluene is higher than the boiling point of cyclohexane, so the cooler surface of the sponge helped condense toluene, but the cyclohexane still made it to the vial because of its lower boiling point. The sponge helped improve efficiency of the distillation. The time required for fractional distillation was greater than the time needed for simple distillation, but it was a much more accurate distillation.

The initial composition of the unknown was 46.1% cyclohexane and 53.9% toluene. For fraction A, we ended up with a mixture of 73.4% cyclohexane and 26.6% toluene. I feel that this is a decent result, but it could have been a little better. I think we probably should have switched the vials a few drops earlier, which would have left us with a higher percentage of cyclohexane and lower percentage of toluene. Fraction B ended up with a mixture of 5.5% cyclohexane and 94.5% toluene. The mixture should have ended up more around 50% of each, so this means that we should have switched from vials between fraction B and fraction C sooner. Toward the end of fraction B, pretty much pure toluene was being condensed into the vial, which is probably what threw our numbers off so much. For the final fraction, the mixture ended up being 0.28% cyclohexane and 99.72% toluene. This means that basically pure toluene was all that was left, which is what we were hoping for during the last fraction.

We collected 44 drops for fraction A, 17 drops for fraction B, and 14 drops for fraction C. This does not seem proportional considering the original composition was 46.1% cyclohexane and 53.9% toluene. It should have ended up being about an equal volume for fraction A and fraction C, with a lower volume of fraction B. Something like 27 drops for fraction A, 15 drops for fraction B, and 33 drops for fraction C would have been ideal.

Overall I feel that what probably cause the most error in this lab was getting the right heat for the sand bath and discerning when to switch vials during fractional distillation. It took a long time before the temperature rose at all, so we could not tell if we were heating the sand bath enough. If we turned the temperature up too much, then the temperature would shoot up when it did begin to rise and that would make it hard to get accurate data. When switching the vials, it seemed that the temperature would hover in a 2 to 3 degree when it plateaued, then it would begin to rise, and I think we let the temperature rise a few degrees too many before switching vials. It was difficult to tell if it was done plateauing or rising.

I. Introduction

A. Objective

The purpose of this experiment is to isolate cholesterol from gallstones via the techniques of extraction and recrystallization. The gallstones will first be dissolved in 2-butanone heated in a hot sand bath. The solution will then be transferred to a micro column using a pipet to filter out the bilirubin, which is the primary impurity of gallstones. The remaining 2-butanone will be removed and the crude cholesterol left over will be recrystallized by dissolving it with methanol and centrifuging it in a Craig tube.

B. Materials and Safety

C. Experimental Procedure

A sample of crushed gallstones weighing about 100 mg will be obtained and weighed. The crushed gallstones will then be placed in a 10 x 100 nm reaction tube along with a boiling stick and 1.5 mL of 2-butanone. This mixture will be gently heated in a hot sand bath. In a second reaction tube also containing a boiling stick, 1.0 mL of 2-butanone will be heated until it is boiling. When the gallstones have disintegrated and the cholesterol has dissolved in the first reaction tube, it will be filtered through a micro column. The micro column will be prepared from a Pasteur pipet packed with a loose wad of cotton, 2 mm of sand, 3-4 mm of anhydrous magnesium sulfate, 1 cm of anhydrous sodium sulfate, 1 cm of Norit RO 0.8 activated carbon pellets, and a very small piece of cotton. The micro column will be clamped in a vertical position and will have a weighed and cleaned 10 x 100 mm reaction tube beneath it.

The solution in the original reaction tube will be transferred into the micro column using a warm Pasteur pipet, which is warmed by immersing it in the hot vapors of the boiling 2-butanone. The 1.0 mL of boiling 2-butanone will be used to wash out the original reaction tube and pipet into the micro column. The filtered hot solution of 2-butanone solution will then be warmed in a sand bath and the 2-butanone will be removed under a gentle stream of nitrogen. The crude cholesterol will be scraped from the reaction tube onto a previously tared piece of a creased, glazed weighing paper. After obtaining the weight of the crude cholesterol, it will be placed into a Craig tube. To recrystallize the cholesterol, it will be first dissolved in the minimum amount of hot methanol. The solution will then be allowed to slowly cool to room temperature, and it will then be cooled in an ice bath. The crystalline cholesterol will be isolated via centrifugation. The cholesterol will then be allowed to air dry. It will then be weighed and its melting point will be determined.

II. Experiment and Results

A. Data

First, a sample of crushed gallstones weighing 0.131 g was obtained. Next, a micro column was prepared using a Pasteur pipet packed with a loose wad of cotton, about 2 mm of sand, about 3 to 4 mm of anhydrous magnesium sulfate, about 1 cm of anhydrous sodium sulfate, about 1 cm of Norit RO 0.8 activated carbon pellets, and a small piece of cotton. One prepared, the micro column was clamped vertically on a ring stand. The crushed gallstones were then placed in a clean glass centrifuge tube along with a boiling stick and 1.5 mL of 2-butanone. The solution was gently heated in a sand bath, along with a separate centrifuge tube containing about 1.0 mL of 2-butanone. One the gallstones dissolved, the solution was transferred to the micro column using a warm pipet. The pipet was warmed by immersing it into the hot vapors of the second tube containing boiling 2-butanone. The reaction tube was rinsed with the hot 2-butanone and the remaining solution was filtered in the micro column.

The filtrate was collected in a clean centrifuge tube. The 2-butanone was removed from this tube under a stream of nitrogen and the remaining cholesterol was allowed to air dry for a week. A minimum amount of methanol was added to the cholesterol and the tube was heated in a sand bath along with a boiling stick until the cholesterol dissolved. The solution was then allowed to cool to room temperature and was then put into an ice bath to cool more. The crystalline cholesterol formed was isolated via centrifugation. The crystals were removed from the tube using a spatula onto filter paper and the crystals were allowed to air dry for a week.

III. Conclusions

Without knowing my final weight and melting point of the crystalline cholesterol, I can only discuss possible sources of error during the procedure. When preparing the micro column, if the wrong amount of any of the materials was added, the bilirubin may not have filtered out. This make the amount of cholesterol recovered be less than expected because the cholesterol may not have crystallized if the bilirubin was still in the solution. If the filtered solution was cooled too fast, that may have prevented the formation of crystalline cholesterol, too.

I. Introduction

A. Objective

The purpose of this experiment is to separate a prepared mixture of benzoic acid, 4-nitroaniline, and naphthalene by the technique of extraction. The compounds will be extracted on the basis of the solubility properties of the acids, bases, and their salts. The given unknown sample will be dissolved with dichloromethane. Hydrochloric acid will then be added and extraction of p-nitroaniline will be performed in two steps: mixing and separation. The extracted p-nitroaniline will then be isolated by adding aqueous sodium hydroxide which will turn the solution basic which will cause the p-nitroaniline to precipitate. The benzoic acid will be extracted by adding sodium hydroxide to the dichloromethane solution and using the process of separation. The benzoic acid will then be isolated using aqueous hydrochloric acid to turn the solution acidic which will make the benzoic acid precipitate. These two precipitates will be collected using vacuum filtration. The 4-nitroaniline will be recrystallized using boiling water, and will then be weighed and measured for its melting point. The benzoic acid will also be recrystallized using boiling water, and will then be weighed and measured for its melting point. Anhydrous sodium sulfate will be added to the left over dichloromethane solution. The mixture will react and then be filtered, and the solid residue of naphthalene will be weighed.

B. Materials and Safety

C. Experimental Procedure

A prepared mixture of unknown relative amounts benzoic acid, 4-nitroaniline, and naphthalene will first be obtained. The weight of the mixture will be taken and recorded. The sample will then be transferred to a 15 mL glass centrifuge tube. 3.0 mL of dichloromethane will then be added to the tube and the mixture will be dissolved by shaking the tube gently. Next, 1.5 mL of 6 M aqueous hydrochloric acid will be added to the centrifuge tube. The mixture will be mixed by capping the tube and shaking it by hand to thoroughly mix the two phases. The centrifuge tube will then be vented by loosening the cap, and then it will be clamped to allow the two phases to separate. The dichloromethane layer will be separated using a pipet with bulb on top. The dichloromethane layer will be sucked into the pipet and transferred to a reaction tube. The left over aqueous layer will be transferred into a 20 x 80 mm vial labeled “aqueous acid extracts” in the same manner using a new pipet. The dichloromethane layer will then be transferred back to the centrifuge tube using a pipet. This technique will be repeated by adding another 1.5 mL of 6 M aqueous hydrochloric acid to the centrifuge tube as before.

Next, 1.5 mL of cold 3 M sodium hydroxide solution will be added to the centrifuge tube with dichloromethane. The same procedure will be followed as above for mixing and separating, except this time the aqueous layer will be transferred to a 20 x 80 mm vial labeled “aqueous hydroxide extracts”.

After that, 12 M aqueous hydrochloric acid will be added to the 20 x 80 mm vial labeled “aqueous hydroxide extracts” dropwise until the solution is acidic. The vial will be placed in an ice bath while this takes place. Next, 6 M aqueous sodium hydroxide will be added dropwise to the vial labeled “aqueous acid extracts” until the solution is basic. This will also take place in an ice bath. The solid formed by these steps will be separately filtered via vacuum filtration using a 25 mL filter flask. The precipitates, benzoic acid and p-nitroaniline, will be transferred to filter paper and allowed to dry, then will be weighed. If specified, 4-nitroaniline and benzoic acid will be recrystallized from boiling water. These samples would then be dried, weighed, and have their melting points determined.

The dichloromethane solution will then be dried by adding about 0.3 g of anhydrous sodium sulfate to the centrifuge tube. The tube will be briefly shaken and allowed to stand for 5 minutes with occasional swirling. Finally, the dichloromethane solution will be filtered or decanted into a tared reaction tube under the hood. The weight of the solid residue in the reaction tube will be determined and the tube will be stoppered. If specified, the solid residue will be purified by column chromatography.

II. Experiment and Results

A. Data

A sample comprised of a mixture of unknown proportions of benzoic acid, 4-nitroaniline (p-nitroaniline), and naphthalene weighing 0.292 g was obtained. The sample was transferred into a 15 mL glass centrifuge tube along with 3.0 mL of dichloromethane. The mixture was dissolved by gently shaking the tube. Once the mixture was completely dissolved, 1.5 mL of 6 M aqueous hydrochloric acid was added to the centrifuge tube. The tube was capped and shaken to thoroughly mix the two phases. The tube was then uncapped and clamped vertically to a ring stand. A pipet was then used to take a sample of the upper layer of the mixture, which was then put into a separate clean centrifuge tube. An equal amount of water was then put into this test tube to confirm that the upper layer was the aqueous layer. The contents in the second tube were then transferred back into the original tube using the pipet.

The lower layer of the mixture, the dichloromethane layer, was then transferred using the pipet into a clean centrifuge tube. The remaining aqueous layer was transferred using the pipet into a separate clean tube labeled “aqueous acid extracts”. The dichloromethane layer was then transferred back to the original centrifuge tube again using the pipet. Another 1.5 mL of 6 M aqueous hydrochloric acid was added to the tube with dichloromethane and the process of separating the two layers was performed for a second time. The aqueous layer was transferred to the same test tube as before containing aqueous acid extracts.

Next, 1.5 mL of cold 3 M sodium hydroxide solution was added to the centrifuge tube containing dichloromethane. The tube was capped and shaken to thoroughly mix the two phases, just as before. The dichloromethane layer was again separated from the aqueous layer, and this time the aqueous solution was transferred into a clean centrifuge tube labeled “aqueous hydroxide extracts”. This process was repeated a second time by adding an additional 1.5 mL of cold 3 M sodium hydroxide solution to the dichloromethane solution.

After that, about 0.3 g of anhydrous sodium sulfate was added to the left over dichloromethane layer remaining in the centrifuge tube. The tube was shaken allowed to stand with occasional swirling. While the tube was allowed to stand, the tube containing aqueous hydroxide extracts was placed into an ice bath and 12 M aqueous hydrochloric acid was added dropwise to the until the solution turned acidic. A precipitate, benzoic acid, formed which was filtered out via vacuum filtration. The benzoic acid was allowed to air dry for a week. It was then weighed at 0.074 g and its melting point was about 119 ºC.

The tube labeled “aqueous acid extracts” was also placed in an ice bath and 6 M aqueous sodium hydroxide was added to the solution until the solution turned basic. A precipitate, p-nitroaniline, formed which was also filtered via vacuum filtration. The p-nitroaniline was allowed to air dry for a week. The resulting p-nitroaniline was weighed at 0.040 g and its melting point was about 139 ºC. The dichloromethane solution which was allowed to stand was decanted into a clean test tube. The solvent was then removed under a stream of nitrogen in the hood. The solid residue, naphthalene, was allowed to air dry for a week. The naphthalene was weighed at 0.035 g and its melting point was 76 ºC.

III. Conclusions

The compounds extracted seem to be slightly impure. The melting points for benzoic acid, p-nitroaniline, and naphthalene that were found are all slightly lower than the melting points I looked up beforehand. There are not huge discrepancies in the numbers, so this leads me to believe the compounds extracted are the expected compounds, they are just not completely pure, which is to be expected.

Error in this experiment could have come from a few different sources. One step that could have led to error was during separation. It was hard to extract only the dichloromethane layer, so I am sure some of the aqueous layer was picked up with it. This means that the resulting aqueous solution, whether it be acid or hydroxide extracts, would yield slightly less benzoic acid and p-nitroaniline than expected. If the error were to happen the other way around and some of the dichloromethane layer was picked up with the aqueous extracts, which means less naphthalene would have resulted than expected. It was impossible to be precise with the separation, so that means there was going to be error in the final weight either way.

If the 3 M sodium hydroxide added during separation was not cold, I think the benzoic acid would not have been as soluble in the aqueous solution and therefore less benzoic acid would have resulted than expected. A couple other obvious spots where error occurred were during vacuum filtration and decanting of the dichloromethane. Some filtrate could have been lost if it were too close to the edge of the filter paper. During the decanting of dichloromethane, some of the liquid may not have made it would of the tube. Lastly, I know it was hard to get all of the naphthalene out of tube to weigh it, so the weight of naphthalene recovered is low.

I. Introduction

A. Objective

The purpose of first part of this experiment is to first recrystallize impure acetanilide that is contaminated with dye methylene blue. Decolorizing charcoal will be used to purify the sample. The starting and ending weights of the acetanilide will be recorded to determine percentage of acetanilide recovered. Also, the melting points of the impure acetanilide and recrystallized acetanilide will then be determined using a Melt-Temp device. During the second part of the experiment, the melting point range of pure naphthalene will be measured using a Mel-Temp device. The will calibrate the machine, and then an unknown compound will be identified by discovering its melting range using the technique of mixture-melting points. During the final part of the experiment, the microscale recrystallization of 50 mg of impure trans-1,2-dibenzoylethylene will take place using ethanol to dilute the solvent and the Craig tube technique for recrystallization. The starting and ending weights of the trans-1,2-dibenzoylethylene will be recorded to determine percentage recovered. Also, the melting points of the impure trans-1,2-dibenzoylethylene and recrystallized trans-1,2-dibenzoylethylene will be determined using a Melt-Temp device.

B. Materials and Safety

C. Experimental Procedure

The first part of the experiment is the recrystallization of impure acetanilide. To begin, 2.5 grams of impure acetanilide will be obtained from the teacher’s assistant. Of that sample, 0.1 grams will be saved for a melting point determination. The remainder will be weighed and placed into a 250 mL Erlenmeyer flask with 50 mL of water and several boiling stones. The mixture is to be heated until the acetanilide dissolves. The heat will then be taken away and 25 mL of cold water and about 2.5 grams of decolorizing carbon pellets will be added to the mixture. The mixture will then be brought to a boil and boiled gently for one to two minutes. An additional 0.5 grams of decolorizing carbon pellets can be added if the blue color has not been completely removed. The solution should be boiled for another five minutes and this process can be repeated until the blue color is completely removed. The solution should then be filtered through a fluted filter into a warmed 125 mL Erlenmeyer flask. The original Erlenmeyer and filter paper will then be rinsed with an additional 10 mL of hot water. The 125 mL Erlenmeyer flask with the mixture is then to be cooled in an ice bath. The crystals will then be collected using vacuum filtration and a Buchner funnel. The crystals are then to air-dry on a watch glass for several days. Then the weights and melting points of the purified and impure samples will be determined using a Mel-Temp apparatus.

The second part of the experiment is melting point determination. Two melting point capillaries with samples of pure naphthalene will be tested with a Mel-Temp device to determine their melting point. An unknown will then be distributed. The unknown will be tested using the Mel-Temp device, first heating at a rate of 10-20 ºC to locate the approximate melting range, and then it will be heated at about 1-2 ºC to determine the exact melting point. To determine the identity of the unknown, the two known compounds with similar melting points will be obtained and be made into mixtures of equal amounts of unknown and known compound. The melting range of these mixtures will be determined to find the identity of the compound.

The last part of the experiment is the recrystallization of trans-1,2-dibenzoylethylene. First, a sample of 50 mg of impure trans-1,2-dibenzoylethylene is to be obtained. The sample will then be transferred to a Craig tube. Next, 0.5 mL of 95% ethanol will be added using a pipet pump and 2 mL graduated pipet along with a wood boiling stick. The mixture will be heated in a hot sand bath until the solvent begins to boil. At this time, additional ethanol will be adding dropwise until the solid completely dissolves. Then, the Craig tube is to be removed from the heat and allowed to slowly cool to room temperature. Once it is room temperature, the Craig tube will cool in an ice bath and then placed in a centrifuge to collect the crystals. The crystals are to then air dry, and the starting and ending weights are to be measured.

II. Experiment and Results

A. Data

First, a 2.443 g sample of impure acetanilide was obtained along with a second sample weighing about 0.1 g, which was later used for a melting point determination. The 2.443 g sample of impure acetanilide was placed into a 250 mL Erlenmeyer flask along with about 50 mL of water, and several boiling stones. The impure acetanilide was a greyish, brownish, flakey powder. When mixed with the water, the water turned a bright transparent blue color. This mixture was then heated in the Erlenmeyer flask on a hot plate until the acetanilide dissolved. After the acetanilide dissolved, the Erlenmeyer flask was removed from the heat and 25 mL of cold water and about 2.5 g of decolorizing carbon pellets were added to the flask. The mixture was then brought to a boil and was boiled for about 2 minutes. The mixture produced a black residue and most of the the blue color disappeared after the decolorizing pellets were added and it was brought to a boil. About an additional 0.5 g of decolorizing pellets were added and the mixture was boiled for another couple minutes to remove any more traces of blue color. The mixture was then filtered through a fluted filter in a stemless funnel into a warmed 125 mL Erlenmeyer flask. The original Erlenmeyer flask was rinsed with hot water to aid in transfering all of the mixture into the fluted filter. As the mixture was filtered, crystals began to form in the filtrate in the 125 mL Erlenmeyer flask. This flask was then put into an ice bath to cool for about 5 minutes. The acetanilide mixture was then filtered via vacuum filtration and a Buchner funnel. Transparent rectangular shaped crystals were collected in the filter paper. The acetanilide crystals collected were set aside to dry for a week. The crystals recovered were weighed and the melting point of the impure acetanilide and pure acetanilide were determined using a Mel-Temp device. The crystals recovered weighed 0.731 g. The melting point of impure acetanilide was 113 ºC and the pure acetanilide melting point was 115 ºC.

For the second part of the experiment, a sample of pure naphthalene was obtained and loaded into two cappillaries to determine its melting point using a Mel-Temp device. The temperature of the Mel-Temp was raised fairly slowly and the first trial resulted in a melting point of 81.5 ºC. The second trial resulted in a melting point of 81.0 ºC. An unknown sample labelled “4” was obtained and its melting point was determined using the Mel-Temp. During the first trial, which was the fast trial, the temperature of the Mel-Temp was raised about 10-20 ºC per minute and the unknown had a melting point of 104 ºC. During the slow trial, the temperature of the Mel-Temp was raised about 1-2 ºC per minute and the unknown had a melting point of 110.5 ºC, which was comparable to m-toluic acid and resorcinol. Two new samples were made, mixing an even amount of each known compound with unknown “4”. The melting point of these mixtures were again determined using the Mel-Temp. The melting point for the unknown mixed with m-toluic acid was 106 ºC, while the melting point for the unknown mixed with resorcinol was 110 ºC.

For the third part of the experiment, a 0.068 g sample of impure trans-1,2-dibenzoylethylene was obtained an put into a Craig tube along with 0.5 mL of 95% ethanol and a wood boiling stick. The of impure trans-1,2-dibenzoylethylene was a yellow powdery substance that when combing with the ethanol, changed the color of the liquid to a transparent yellow. The tube was heated in a hot sand bath. It was covered in sand up to the level of solution present and it was heated until the solvent began to boil. A few additional drops of 95% ethanol were added until all the solid dissolved. The Craig tube was then removed from the heat and was allowed to cool for about five mintues at room temperature and then another few mintues in an ice water bath. The Craig tube was then put into a centrifuge. The supernatant was discarded and crystals were taken out of the Craig tube and put onto filter paper using a small spatula. The crystals were yellow, thin, and long. The crystals were then allowed to dry for a week. The crystals recovered were weighed and the melting point of the impure trans-1,2-dibenzoylethylene and pure trans-1,2-dibenzoylethylene were determined using a Mel-Temp device.

III. Conclusions

I do not really know how to judge the results from the first part of the experiment. A percent recovery of 29.92% seems low to me, but that could be close to the expected recovery value. I would have to know the molecular formula of the impure acetanilide to figure out how many moles of pure acetanilide were there to begin with, then compare that to the number of moles of acetanilide recovered. I do know that there were many parts of the experiment where error could have occurred. For example, if too many decolorizing carbon pellets were added, they would have absorbed some of the acetanilide along with the impurities. If the mixture of acetanilide, water, and decolorizing pellets was not boiled long enough, there would still be left over impurities and some portion of acetanilide would still be impure and would not yield the expected amount of crystals. If the funnel and filter paper were too cold, some crystals would begin to form in the filter paper and not make it to the filtrate. The filtrate could not have been allowed to cool long enough and some crystals might not have formed. Some of the crystals could have been poured outside of the filter paper and went into the filtrate during vacuum filtration. There were many steps where error could have occurred, so it is highly unlikely to recover the actual amount of acetanilide that was present in the impure sample.

The results from the second part of the experiment seemed accurate. The melting point of the unknown was nearly identical as the melting point of the unknown mixed with resorcinal. The melting point of the unknown mixed with m-toluic acid was lower than that of pure known, which makes sense. Impurities usually make substances have lower melting points. This means the unknown was resorcinal. Error in this part of the experiment could come from using the Mel-Temp incorrectly or not evenly mixing even amounts of unknown and known samples. That could cause the temperature readings to be different.

For the third part of the experiment, error could have come from many different parts. For example, the impure trans-1,2-dibenzoylethylene could have not all dissovled during boiling. Crystals could start to form on the boiling stick before the Craig tube was centrifuged, which would have then been lost. The Craig tube could have not been cooled long enough to form all the crystals. Some crystals could have been poured off along with the supernatant after centrifugation. Some crystals were not recovered from the Craig tube because they were too hard to get out. There were many sources of potential error, so again it is highly unlikely to recover that original amount of trans-1,2-dibenzoylethylene present in the impure sample.