Reagents used Mass of unknown alcohol used _18.7294_____________________ Mass of acetic anhydride used __26.5369 gram____________________ Fragrance of unknown alcohol ____slightly unpleasant odor (subjective), clear, colorless liquid___________________ Ceric ammonium nitrate test on the alcohol __smelled with great caution – very sharp, acrid, unpleasant, caused eyes to water. Clear, slightly yellow liquid.___
Basics in Organic Reactions Mechanisms
In organic chemistry, the mechanism of an organic reaction is defined as a complete step-by-step explanation of how a reaction of organic compounds happens. A completely detailed mechanism would relate the first structure of the reactants with the last structure of the products and would represent changes in structure and energy all through the reaction step.
Heterolytic Bond Breaking
Heterolytic bond breaking is also known as heterolysis or heterolytic fission or ionic fission. It is defined as breaking of a covalent bond between two different atoms in which one atom gains both of the shared pair of electrons. The atom that gains both electrons is more electronegative than the other atom in covalent bond. The energy needed for heterolytic fission is called as heterolytic bond dissociation energy.
Polar Aprotic Solvent
Solvents that are chemically polar in nature and are not capable of hydrogen bonding (implying that a hydrogen atom directly linked with an electronegative atom is not found) are referred to as polar aprotic solvents. Some commonly used polar aprotic solvents are acetone, DMF, acetonitrile, DMSO, etc.
Oxygen Nucleophiles
Oxygen being an electron rich species with a lone pair electron, can act as a good nucleophile. Typically, oxygen nucleophiles can be found in these compounds- water, hydroxides and alcohols.
Carbon Nucleophiles
We are aware that carbon belongs to group IV and hence does not possess any lone pair of electrons. Implying that neutral carbon is not a nucleophile then how is carbon going to be nucleophilic? The answer to this is that when a carbon atom is attached to a metal (can be seen in the case of organometallic compounds), the metal atom develops a partial positive charge and carbon develops a partial negative charge, hence making carbon nucleophilic.
Esterification of an Unknown Alcohol
Name_______________________ Unknown Alcohol Number___101____________
- Reagents used
Mass of unknown alcohol used _18.7294_____________________
Mass of acetic anhydride used __26.5369 gram____________________
Fragrance of unknown alcohol ____slightly
unpleasant odor (subjective), clear, colorless liquid___________________
Ceric ammonium nitrate test on the alcohol __smelled with great caution – very sharp,
acrid, unpleasant, caused eyes to water. Clear, slightly yellow liquid.___________
- The product
Mass obtained _____12.0336 gram.______________________________
Fragrance _____________strong, somewhat pleasant, almost sweet but otherwise non-descript
odor (subjective)__________________________
Ceric test on product _____small amount of unknown alcohol # 101
was added to yellow ceric ammonium nitrate solution, whereupon the solution
became blood red.__________________________
Please answer these 3 questions.
- What was the purpose of the NaOH wash? Be brief and use chemical equation where necessary.
- What was the purpose of the NaCl wash
- What does the ceric test suggest? Write a reaction.
-
Esterification of an Unknown Alcohol
Safety Precautions
- Assume all organic compounds to be toxic, either through inhalation, ingestion or absorption through the skin. All chemical reagents used are eye, skin and respiratory hazards. All work is to be done with eyewear, lab coats and gloves.
- Both the starting alcohols and products are flammable and toxic.
- The entire procedure is to be done in a fume hood.
- Have the instructor inspect and approve the distillation apparatus before starting distillation.
Procedure
1. Carefully lower a magnetic stir bar to the bottom of a flask, and then add a boiling chip or two. Place flask in an ice/water bath.
2. Add about 5 ½ disposable droppers worth of assigned alcohol to the flask. Initiate stirring. By massing the vial of alcohol when full and then re-massing after the alcohol has been removed, the mass of alcohol used can be determined. This mass is needed to calculate the % yield.
3. To the flask, while stirring, add approximately 8 1/3 disposable droppers’ worth of acetic anhydride. Remember to determine the actual mass used.
4. While stirring, and with caution, add nine (9) drops of conc. sulfuric acid, one drop at a time. Pausing at least 30 seconds between drops. If any “smoking” is observed prolong the pause between drops. The drops should be allowed to fall directly into the reaction mixture without running down the neck. Be patient and add the acid slowly. Otherwise, the contents of the flask may violently erupt with subsequent loss of product. Make sure the glass partition of the hood is down as far as possible when adding the acid.
5. Continue to stir for 15 minutes with cooling.
6. With the aid of a disposable pipette, transfer the contents of the flask to a 125ml separatory funnel. Extract with two 30ml portions of ICE COLD 10% NaOH. Check the last aqueous extract with litmus to be sure it is basic (should turn very blue). If not basic then extract for a third time or until basic. To extract, shake separatory funnel several times with venting, then allow to stand until two distinct layers form. Separate the layers. Which layer is the ester? What can be done to make sure?
7. In the separatory funnel, extract the ester with 45ml of saturated NaCl solution. What is observed? Which layer is the ester? To make sure, add water to what is thought to be the aqueous layer.
8. Transfer the ester into a clean, dry flask and dry the ester over anhydrous CaCl2.
With the aid of a disposable pipette, transfer the ester to another clean, dry flask and dry over molecular sieves. When dry, transfer ester to a labeled vial.
9. Note the odor of the ester and all the others in the class, including the starting materials. Be careful when smelling acetic anhydride.
10. Run chemical tests, IR and NMR on the product and starting materials.
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