CHEM 14BL Lecture Notes - Lecture 2: Salicylic Acid, Acetic Anhydride, Crystal Growth

88 views3 pages

redclam353

18 Feb 2017

School

UCLA

Department

Chemistry and Biochemistry

Course

CHEM 14BL

Professor

Russell Arlene

For unlimited access to Class Notes, a Class+ subscription is required.

Document Summary

Salicyclic acid + acetic anhydride aspirin + acetic acid. Salicyclic acid is the limiting reagent in this reaction. % yield = moles of product obtaines / moles of product possible. In this case, % yield = moles aspirin / moles of salicyclic acid. Crystallization: technique to purify a solid compound. It akes advantage of the differing solubility of the compound with temperature. Pure crystals thermodynamically more stable than crystals wiht impurities. Most compounds more soluble in hot solvent than cold solvent. Organic molecule + heat + solvent solution. Most soluble impurities or by-products of reactions have similar solubility properties to the main product. Usually amount of impurity is much less than amount of desired product. Recrystallation of impure solid: dissolve impure product in a minimum amount of hot solvent. This minimizes loss of product in residual cool solution. Actual amount of solvent depends on temperature, rate of solution, quantity of impurity.

Related Questions

Just need answers 1-10. As you can see I attempted them but want to make sure on everything. I believe the odor was odorless but I'm not sure? If aspirin was created would we expect vinegar smell due to acetic acid?

4. Collect the crystals using vacuum filtration. Turn the vacuum off temporarily, pour just enough COLD water to thoroughly wet the crystals, and then turn the vacuum on. Let the vacuum draw air through the crystals for 2 minutes, making certain that the seal with the rubber ring is a good one. Place a small stals on a clean watch glass and spread them thinly to facilitate drying. Using a marker rme on the watch glass and heat the crystals for 15 minutes in an oven set at a temperature of70-80 â Determine the melting point of both your dried aspirin product and pure salicylic acid. Refer to Appendix 4 for instructions on how to take a melting point. *Pure aspirin melts at 135â and pure salicylic acid melts at 156-158 â DATA SHEET/ Questions I. Record the experimental melting ranges for your recrystallized aspirin and the starting material, salicylic acid Recrystallized aspirin Salicylic acid 2. A small melting range usually indicates that: a) The compound generally has a high melting point. 6) The compound has few impurities. c) The compound is highly impure d) The compound is likely to be soluble in water e) The compound is likely to be very unreactive. f) The compound will be difficult to recrystallize. 3. Describe the appearance of your final, recrystallized product. 4. Does the aspirin have a very strong odor, suggesting that it is a very volatile substance? 5. If all of the 2.0 g of the salicylic acid that you started with was converted to aspirin and 100% of the aspirin was recovered, the expected yield of aspirin would be 2.6 g. The isolated yield is always less than this because: (choose all that are appropriate.) Water is trapped inside the crystals. A substantial amount of the aspirin evaporates. Some aspirin remains dissolved in the solvent from the first filtration. Some aspirin remains dissolved in the solvent from the recrystallization. e) The reaction used to create the aspirin does not go to completion. 1 The acetic acid formed in the reaction adversely affects the yield of aspirin. Chem 162-Aspirin tab

Preparation of acetyl salicyclic acid (Aspirin) post-lab questions

1.)At the end of the reaction, you were asked to add ice-cold water to the reaction mixture. What do you think is the reason for this? Explain with chemical equations.

2.)How would the % yield of aspirin be changed if the final rinse of the solid product on the filter paper was done with warm water instead of ice-cold water?

3.)If you run a thin-layer chromatography for a mixture containing salicylic acid and aspirin using a 1:1 solvent mixture of ethyl acetate and hexane, which compound do you think would have more R_f value. Explain why? Bring in the structural features in your explanation.

summary Procedure of lab we did:

- Place approximately 0.300 g of salicylic acid in a tared empty 5 mL conical reaction vial. Record the actual weight of salicylic acid used. Using automatic pipet, add 0.8 mL of acetic anhydride (acetic anhydride vapors are very irritating-handle it carefully, in the hood). Add 2-3 drops of concentrated sulfuric acid using a dropper.

-Clamp the assembly so that the vial is partially submerged in the hot water. Turn on the magnetic stirrer. Once the water bath starts boiling, start timing the reaction. When the mixture has been allowed to react at 100 oC (the temperature of boiling water) for 15 minutes, you can consider the reaction to be complete. During the heating time, take about 20 mL of deionized water in a flask and chill it in an ice-water bath.

- After the reaction has gone on for 15 minutes, add very cautiously, drop by drop, 1 mL of deionized water to the reaction vial. At this point you should have a solution in your reaction vial. Remove the reaction vial form the hot water bath, add another 1-2 mL of DI water and let it stand at room temperature for few minutes. Then, detach the air condenser carefully and remove spin vane with forceps. Place the vial in a beaker and cool down to RT. During this time, the aspirin may begin crystallizing. If not, scratch the walls of the vial with a glass rod. Then, cool the vial in an ice-water bath.

- When the vial appears full of crystals, add about 3-4 mL of ice-cold DI water. Filter the aspirin using vacuum filtration (use Hirsch funnel). Leave the filtration setup in place for few minutes-this will draw air through the sample and will help dry aspirin.

Recrystallization of Aspirin:

- Transfer the rest of the crude aspirin to a 25 mL Erlenmeyer flask and do recrystallization using ethanol.

Purity of Aspirin:

- Using the melting point apparatus, determine the melting point of your crude aspirin and the recrystallized aspirin.

- To do FeCl3 test, get 4 test tubes. Place 1 mL of ethanol and 2 drops of 1% FeCl3 solution in each test tube. Add few crystals of salicylic acid to one test tube. Add few crystals of your crude aspirin product to the second test tube. In the thirst test tube, place a few crystals of your recrystallized aspirin. The fourth test tube will be your âblankâ. Shake each of the test tubes and record your observations.

CHEM 14BL Lecture Notes - Lecture 2: Salicylic Acid, Acetic Anhydride, Crystal Growth

Document Summary

Get access

Related textbook solutions

Chemistry: Structure and Properties

Basic Chemistry

Principles of Chemistry Molecular Approach

Chemistry: Structure and Properties

Principles of Chemistry Molecular Approach

Chemistry: A Molecular Approach

Chemistry: A Molecular Approach

Principles of Chemistry: A Molecular Approach

Chemistry: The Central Science

Related Documents

CHEM 14BL Chapter Notes - Chapter 4: Binary System, Ibuprofen, Intermolecular Force

CHEM 14BL Chapter Notes - Chapter 4: Reagent, Acetic Anhydride

CHEM 232 Lecture Notes - Lecture 4: Acetic Anhydride, Magnetic Stirrer, Aspirin

Related Questions