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1. To the components of a simulated pharmaceutical preparation, Panacetin, and identifying the unknown component of the mixture through extraction and separation methods.
2. To learn how to purify by recrystallization, how to dry them and how to obtain a melting point.
PRECAUTION: ACETANILIDE AND PHENACETIN ARE EYE AND SKIN IRRITANTS. Minimize contact with your unknown compound.
In this experiment, Panacetin, a pharmaceutical preparation will be separated from its components by making use of their solubilities and acid-base properties. Panacetin contains aspirin, sucrose and an unknown component that may be either acetanilide or phenacetin.
Of the three components, only sucrose is insoluble in the organic solvent dichloromethane (CH2Cl2 or methylene chloride). The insoluble sucrose can be filtered out if Panacetin is dissolved completely in dichloromethane by gravity filtration or centrifugation leaving the soluble aspirin, acetanilide and phenacetin in the solution.
Although the acetanilide and aspirin are both quite insoluble in water at room temperature, the sodium salt of aspirin is very soluble in water but insoluble in dichloromethane.
Aspirin, which is a strong acid can be converted to the salt, sodium acetylsalicylate by extraction with an aqueous solution of sodium bicarbonate . This salt will migrate from the dichloromethane layer, in which it is insoluble, to the aqueous layer, in which it is soluble. The unknown component will stay behind in the solution and can be isolated by evaporating the solvent from the dichloromethane solution. Adding HCl to the aqueous solution restores aspirin as an insoluble white solid.
In the third experiment, the identity of the unknown component of Panacetin will be purified.
Purification is necessary because the separation procedure may be imperfect leaving traces of small quantities in the compound after separation or chemical reactions may occur prior to or during the separation adding new impurities. The unknown component can be purified by recrystallization, in which an impure solid dissolves in a hot (usually boiling) solvent then crystallizes from the cooled solution in a purer form.
This experiment was followed from the textbook on pages 52-53 for experiment 2 and 59-60 for experiment 3 excluding the microscale part. First, weigh approximately 3.00 g of Panacetin and transfer it to a clean, dry 125 ml Erlenmeyer flask. Add 50 ml of dichloromethane to the flask , stir the mixture with a stirring rod to break up any lumps. When it appears that no more of the solid will dissolve, filter the mixture by gravity. Collect the undissolved solid on the filter paper and set it aside to dry. Once it has completely dried, reweigh the solid. This compound separated by gravity filtration is known as sucrose.
Next, transfer the filtrate to a separatory funnel and extract it with two 30 ml portions of 5% sodium bicarbonate . For each extraction, use a stirring rod to stir the liquid layer until any fizzing subsides before a stopper is placed on the funnel and shaken. Dichloromethane will be on the bottom layer and will be drained to a different container. Transfer the dichloromethane layer back into the funnel for the second extraction. The upper layer will be transferred in an Erlenmeyer flask and will be used for recovery of acetanilide. Combine the two aqueous solutions in the same container and acidify slowly with 6M HCL to bring it to a pH of 2. Cool the mixture to room temperature or below while swirling the flask occasionally in an ice bath. Collect the aspirin by vacuum filtration. Wash the aspirin on the filter with cold distilled water. Dry the sample thoroughly before weighing and leave it in the hood for the next lab schedule.
Before proceeding to recrystallization, triturate the compound with 20 ml of hexane. Crush the solid with a stirring rod and filter. Recrystallize the unknown drug component from experiment 2 by boiling it with just enough water to dissolve it completely, then letting it cool to room temperature then to 0 C. In order to induce crystallization, it would be helpful to scratch the walls of the flask so that crystals would have a surface to attach to. Use vacuum filtration to isolate the sample then dry the product to a constant mass and weigh in a tared vial.
Grind a small amount of the dry unknown component to a fine powder on a watch glass using a spatula. Divide the solid into four equal portions. Combine portions 1 and 2. Mix portion 3 with an approximately equal amount of finely ground acetanilide and mix portion 4 with an approximately equal amount of finely ground phenacetin. Obtain the melting point ranges of the purified unknown (portions 1 and 2), mixture with acetanilide and mixture with phenacetin. Each melting point should be measured on two samples- more than that if melting points are imprecise or accurate.
Safety Issues: (all of these are taken from MSDSonline.com)
Potential Acute Effects: Hazardous in case of eye contact (irritant), of ingestion, of inhalation. Slightly hazardous in case of skin contact
Potential Chronic Health Effects: Hazardous in case of eye contact (irritant), of ingestion, of inhalation. Slightly hazardous in case of skin contact (irritant).
Eye and skin irritant
Potential Health Effects
Causes irritation to respiratory tract. Has a strong narcotic effect with symptoms of mental confusion, light-headedness, fatigue, nausea, vomiting and headache. Causes formation of carbon monoxide in blood which affects cardiovascular system and central nervous system. Continued exposure may cause increased light-headedness, staggering, unconsciousness, and even death. Exposure may make the symptoms of angina (chest pains) worse. Ingestion:
May cause irritation of the gastrointestinal tract with vomiting. If vomiting results in aspiration, chemical pneumonia could follow. Absorption through gastrointestinal tract may produce symptoms of central nervous system depression ranging from light headedness to unconsciousness.
Causes irritation, redness and pain. Prolonged contact can cause burns. Liquid degreases the skin. May be absorbed through skin.
Vapors can cause eye irritation. Contact can produce pain, inflammation and
temporal eye damage.
Can cause headache, mental confusion, depression, liver effects, kidney effects, bronchitis, loss of appetite, nausea, lack of balance, and visual disturbances. Can cause dermatitis upon prolonged skin contact. Methylene chloride may cause cancer in humans. Aggravation of Pre-existing Conditions:
Persons with pre-existing skin disorders, eye problems, impaired liver, kidney, respiratory or cardiovascular function may be more susceptible to the effects of this substance.
Moderate Eye Irritation: Signs/symptoms may include redness, swelling, pain, tearing, and blurred or hazy vision. Skin Contact:
Moderate Skin Irritation: Signs/symptoms may include localized redness, swelling, itching, and dryness. May be absorbed through skin and cause target organ effects. Inhalation:
No health effects are expected.
May be harmful if swallowed.
Gastrointestinal Irritation: Signs/symptoms may include abdominal pain, nausea, diarrhea and vomiting. Repeated ingestion may cause:
May be absorbed following ingestion and cause target organ effects. Target Organ Effects:
Prolonged or repeated exposure may cause:
Auditory Effects: Signs/symptoms may include hearing impairment, balance dysfunction and ringing in the ears. Clotting Disorders: Signs/symptoms may include increased blood clotting time and internal bleeding (hemorrhage). Liver Effects: Signs/symptoms may include loss of appetite, weight loss, fatigue, weakness, abdominal tenderness and jaundice.
Central Nervous System (CNS) Depression: Signs/symptoms may include headache, dizziness, drowsiness, incoordination, nausea, slowed reaction time, slurred speech, giddiness, and unconsciousness. Kidney Effects: Signs/symptoms may include reduced or absent urine production, increased serum creatinine, lower back pain, increased protein in urine, and increased blood urea nitrogen (BUN). Pulmonary Edema: Signs/symptoms may include chest discomfort, shortness of breath, significant cough with frothy sputum production, bluish colored skin (cyanosis), increased heart rate, respiratory failure and may be fatal. Single exposure may cause:
Immunological Effects: Signs/symptoms may include alterations in the number of circulating immune cells, allergic skin and /or respiratory reaction, and changes in immune function.
5. Sodium Bicarbonate
Warning! May cause respiratory tract irritation. Causes eye and skin irritation. Target Organs: Blood, kidneys, heart, liver, eyes, skin.
Potential Health Effects
Eye: Causes eye irritation.
Skin: Causes skin irritation. May be harmful if absorbed through the skin. Ingestion: May be harmful if swallowed. Causes gastrointestinal tract irritation. Inhalation: May cause respiratory tract irritation. May be harmful if inhaled. Chronic: May cause liver and kidney damage. Adverse reproductive effects have been reported in animals. Laboratory experiments have resulted in mutagenic effects. Chronic exposure may cause blood effects.
6. Hydrochloric Acid
POTENTIAL HEALTH EFFECTS:
Inhalation: May cause irritation (possibly severe), chemical burns, and pulmonary edema.
Skin contact: May cause irritation (possibly severe) and chemical burns.
Eye contact: May cause irritation (possibly severe), chemical burns, eye damage, and blindness.
Ingestion: Not a likely route of exposure.
Target Organs Effected: Respiratory System, Skin, Eye
Chronic Effects: Repeated or prolonged exposure to dilute solutions may result in dermatitis. Discoloration of the teeth may occur as a result of long term exposure.
Interaction with Other Chemicals Which Enhance Toxicity: None known Medical Conditions Aggravated by Exposure: None known
In Experiment 2, the extraction of substances from one another is based on the differences in their physical and chemical properties. Approximately, 3.0029 g of panacetin was weighed and completely dissolved in 50 ml of dichloromethane and filtered. The residue was left to dry and weighed (sucrose). Then 30 ml of NaHCO3 was added to the filtrate. This solution was transferred into a separatory funnel. This formed two layers. Top layer was the organic layer (NaHCO3) described as a clear liquid. Bottom layer was the aqueous layer and was yellow in color. The filtrate was washed twice with NaHCO3. HCl was added to the aqueous solution until the pH equaled to 2.0. It was filtered through vacuum filtration and allowed to dry until the next week’s lab. This filtrate is known as aspirin. Meanwhile, the unknown in the organic layer was also allowed to settle for the next experiment.
In experiment 3, before we went to do recrystallization, we first did trituration of the unknown by adding 20 ml of hexane. We crushed the solid and filtered. Even with the addition of approximately 27 ml of boiling water into the compound, it started to dissolve. That was the first clue that we have acetanilide as our unknown. We went ahead and continue heating and swirling the solution over a hot plate. There was the formation of brown oil-like globules. We were then asked to decant the clear liquid from this solution. This clear liquid was allowed to cool to room temperature then to 0 C. There was formation of white crystals at the edge of the beaker. Through vacuum filtration, we were able to filter the product, weighed and used for melting point measurement of the unknown.
The solid was divided into 4 equal parts. First 2 parts were combined, 3rd part was mixed with acetanilide and the last part was mixed with phenacetin. After taking the melting points of all these 3 substances we were able to identify the unknown product to be acetanilide.
No big issues encountered during this experiment. Transferring some products as well as the final crystals from watch glass and filter paper and leaving some products were crucial to get the most final product. This explains why the percent recovery for the unknown was low. Some crystals fell off or didn’t transfer to the filter paper. Even though the % recovery was relatively low (88.4079%), this experiment still produced a 0.6898 g of product.
This experiment was focused on two main objectives. First, the analysis of panacetin to find out what percentages of sucrose, aspirin and the unknown component it contains. Second, to find out whether the unknown is acetanilide and phenacetin. A big part of the composition of panacetin was made up of the unknown. We were able to determine the composition of sucrose to be 17.95 %, Aspirin 26.93% and the unknown to be 55.12% After following the experiment procedures, we were able to purify through recrystallization the end product to be acetanilide. This is an odorless white crystalline solid substance which has a melting point of 114 C. Our experimental value for acetanilide’s melting point was 117 which indicates that the result had a very narrow range and close to the literature value. I would therefore conclude that we had isolated a close to pure product of acetanilide with little impurities present.
1. a. Describe any evidence that a chemical reaction occurred when you added 6 M HCl to the solution of sodium acetylsalicylate
A chemical reaction took place upon the addition of 6M HCl to a solution of sodium acetylsalicylate because a precipitate formed known as aspirin.
b. Explain why the changes that you observed took place.
The observed change took place as a result of the acid reacting with the salt forming a compound insoluble in water.
2. Describe any explain the possible effect on your results of the following experimental errors or variations. In each case, specify the component (s) whose percentage(s) would be too high or too low.
a. After adding dichloromethane to Panacetin, you didn’t stir or shake the mixture long enough
Improper stirring or shaking of the mixture will result in incomplete dissolution of the panacetin mixture. There will be loss of some solid analytes during filtration. The recovered amounts will be lower than they should be leading to a final percentage to be low.
b. During the NaHCO3 extraction you failed to mix the aqueous and organic layers thoroughly.
If the aqueous and organic layers were not thoroughly mixed the acid would remain in the solution and the extraction would be less efficient resulting to a low percentage yield.
c. You mistakenly extracted the dichloromethane solution with 5 % HCl rather
than 5 % NaHCO3.
If 5% HCl is used instead of 5% NaHCO3 that would protonate the aspirin and keep it in the organic solution making the aspirin, acetylsalicyclic acid.
d. Instead of using pH paper, you neutralized the sodium bicarbonate solution to pH 7 using litmus paper
At ph7 the bicarbonate wouldn’t be able to act as a base and extract a proton because at pH of 7 it would protonate itself so it wouldn’t be able to react with aspirin.
5. Write a balanced reaction equations for the reactions involved a. When aspirin dissolves in aqueous NaHCO3
C9H8O4 (aq) + NaHCO3 (aq) —–> C9H7O4Na (aq) + CO2 + H2O Weak acid weak base Strong Base Strong acid
b. When Aspirin is precipitated from a sodium acetylsalicylate solution by HCL
C9H7O4Na + HCl ————-˃ C9H8O4 + NaCl Strong Base Strong acid Weak Acid Weak Base
Assuming that both reactions are spontaneous under the standard conditions, label the stronger acid, stronger base, weaker acid and weaker base in each equation.
1. a. What is the minimum volume of boiling water needed to dissolve 0.200 g of phenacetin?
b. About how much phenacetin will remain dissolved when the water is cooled
to room temperature?
c. Calculate the maximum mass of solid (undissolved) phenacetin that can be recovered when the cooled solution is filtered.
0.200 g-0.0125 g (amount soluble in cold water)= 0.1875 g
2. An unknown compound X is one of the four compounds listed in table 3.2. A mixture of X with benzoic acid melts at 89 C, a mixture of X with phenyl succinate melts at 120 °C and a mixture of X with m-aminophenol melts at 102 °C. Give the identity of X and explain your reasoning.
X is phenyl succinate.
When a compound mixes with a different compound, the melting point of the mixture will be lower than the melting points of either of the pure compounds. Basing from the table, the melting point of pure benzoic acid is 121 C but when mixed to X, it went down to 89 C. Likewise with O-toluic acid and m-aminophenol. Since the melting point of mixture X with phenyl succinate has a melting point of 120 C, the melting point of pure X must be equal or closer to 121. Mixing X with phenyl succinate did not change the melting point thus X must be phenyl succinate.
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