NAME:__________________________ Chemistry 231L/232L LAB Final
12/14
——pts
Fall 1999
Assistant Professor: D. D. Gergens, Ph. D. GIVE BRIEF ANSWERS TO THE FOLLOWING QUESTIONS 1. (16)
Aspirin Synthesis. A student in second semester organic chemistry synthesized a mixture of
impure aspirin, polymer by-product, and acetic acid. Using the data below, assist the student in preparing a isolation and purification scheme for pure aspirin. O C-O-H
O
O C-CH3 O
polymer by-product
CH3C-OH
aspirin
a)
All three compounds are significantly soluble in methylene chloride.
Aspirin is soluble in ethanol,
insoluble in cold water, and is soluble in hot water. The polymer is insoluble in ethanol and water. Acetic acid has a high solubility in both water and ethanol. Flow chart a separation scheme for the both the isolation and purification of pure aspirin. Your scheme should include an acid-base extraction and recrystallization, as well as any other necessary steps and laboratory techniques. You may use any other reagents (e.g., acids, bases) as needed in your separation scheme.
Be specific in identifying
additional reagents used in your separation scheme.
b)
A student used the Thiele micro melting-point technique to determine the melting point of aspirin reported it to be 135 °C. Is this value believable? Explain why or why not.
c)
How could you prove or disprove that the compound in part b is in fact aspirin? Give the two best methods. Physical analysis may be conducted only with instrumentation present in our laboratory at Mesa College. Chemical analyses may include any tests that you are familiar with.
page 2 2. ( 4 )
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Give four of the most important NEVER'S to be observed during a distillation.
Draw the set-up and label all glassware for a vacuum filtration.
4. ( 4 )
Draw the set-up and label all glassware for a reflux apparatus. Include water hoses, etc.
5. ( 4 )
Describe how you would go about selecting the best solvent for recrystallization of aspirin, or
for any compound.
page 3 6. ( 4 )
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Explain why eugenol is acidic in aqueous solutions where as methanol is not.
CH3 O
CH2CH=CH2
CH3OH methanol
HO eugenol
7. ( 3 )
Besides eugenol, oil of cloves contains caryophyllene and other terpenes. After the steam
distillation of cloves, how was eugenol isolated and caryophyllene and other terpenes eliminated in the work-up and purification of eugenol from cloves? CH3 CH3
CH3
CH2 eugenol caryophyllene
8. ( 3 )
What should one observe when eugenol is reacted with Br 2 in CH 2Cl 2? Give a detailed explanation.
9. ( 3 )
What should one observe when eugenol is reacted with KMnO4? Give a detailed explanation.
10 ( 3 )
What should one observe when eugenol is reacted with Na2CO3? Give a detailed explanation.
page 4
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11. (6) Redox reaction Balance in acid. Show the half reaction for the oxidation and the reduction.
MnO4
COOH
CH3
-
MnO2 Cl
Cl
Balance the reaction in base
12. (6) A 0.2042-g sample of KHP (MM = 204.2) is dissolve in 25 mL of water. If 20.45 mL of NaOH solution are required to reach the equivalence point, what is the normality of the sodium hydroxide solution?
b) If 20.45 mL of the above standardized base is required to neutralize 20.4 mg of an unknown organic acid, what is the molar mass of the carboxylic acid?
page 5
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FTIR Spectroscopy 12. (10) In the synthesis of aspirin, salicylic acid is acylated to aspirin (acetylsalicylic acid). O C-OH
O C-O-H O
OH
salicylic acid
+
O
CH3C-O-CCH3 acetic anhydride
O +
H
O C-CH3 O
+
CH3C-OH
aspirin
a. Clearly mark all identifiable peaks in each FTIR spectrum that correspond to the appropriate functionality. salicylic acid
Aspirin
b. Interpret all pertinent stretching frequencies and give a detail description of the changes that have occurred between the FTIR of the starting material and the final product.
Make inferences for each
component. Write complete and concise sentences that support the student's claims that in fact aspirin had been synthesized.
page 6 13.
(10)
a.
Give approximate proton chemical shift and spin-spin splitting for two alcohols
——pts
Spectroscopy. A.
OH
B.
OH
C.
OH
D.
OH
of your choice on the right. Clearly mark your choices.
b.
Match the letter of the isomeric alcohol to the correct spectrum. D
