Goal
Synthesis Salicylic Acid (precursor to Aspirin) from Methyl Salicylate (Winter green Oil) vs. from Benzene
Does production from 1 yield a different product than product from 2? NO they are the same
What is wintergreen oil?
Methyl Salicylate
Natural product (Benzene (Petroleum byproduct) is unnatural)
Procedure
1. Organic Reaction - Heating Under Reflux
2. Separation - Vacuum Filtration
3. Purification - Recrystallization
4. Analysis - Melting Point
What we need to know for reaction:
1. How much starting material and solvent are needed? What should be the limiting reagent?
Why use NaOH in excess?
How does concentration/ amt. of NaOH affect reaction?
Why excess sulfuric acid?
Does a separate solvent n
1. Refer to balanced equation.
a. Methyl Salicylate is the LR (more expensive, not easy to remove because it is organic)
b. Use more NaOH in excess (more than 2 eqv.) to push the reaction toward the products fully
c. More concentrated NaOH in SM = faster
What is a limiting reagent?
What must be considered before choosing one?
How do you "find" the LR?
1. A reactant in a chemical reaction that determines the amount of product produced
Substance that is totally consumed when the reaction is complete.
The amount of product formed is limited by this reagent because the reaction cannot proceed further witho
Heating Under Reflux -
1. Why is it necessary? (3)
2. How do we control temp of heat source?
3. Why "Heating Under Reflux"?
4. What is "Heating Under Reflux"?
1. Organic Reaction: involves actual covalent bonds to Carbon being made/broken
Used to overcome activation energy
Heats reaction efficiently, delivering consistent heat, while never burning
2. Use BP of solvent to control heat energy that is delivered to
Heating Under Reflux Apparatus
1. Thermowell hooked up to Powermite
2. Round Bottom Flask
3. Stir Bar
4. West Condenser
5. Hoses: Top - water out to drain; Bottom - water in from wall
6. Clamps and Ring Stand
7. Silicone Grease from joints
HUR - Why do we heat reactions on a flameless heat source (not bunsen burning)?
Usually organic materials are flammable
HUR - What does it mean to heat under reflux? Why do we choose water as the solvent?
Boiling a solvent to give energy to a run and then condensing the solvent so it can continue the process
Gives enough heat energy and is convenient and easy to remove at the end
HUR - What are boiling chips used for? (boiling stones/ stir bar)
Location: bottom of reaction vessel
Allow for control over boiling process -- promote smooth boiling BECAUSE WATER VAPOR IS RELEASED CONSISTENTLY
Prevent "bumping" and superheating of solution (therefore preventing solution from boiling over, and or explo
HUR - Why do we put a condenser on top of the reaction?
Do we put a stopper on top of the condenser? Why?
Condenser ensures all of solvent is returned to the vessel (vapors) --> condenser converts water and methyl salicylate vapors back to liquids and returns them to the reaction flask so the don't boil away and reaction can continue to be heated
No stopper -
HUR - Why do we add heat and let the reaction stir for 30 minutes?
How do we know it is done after 30 minutes?
30 minutes is about the time needed for reflux --> want highest product yield and purity
30 minutes begin once boiling
Stop after 30 min. and smell the product --> if you still smell wintergreen scent, reaction is not complete - reflux for longer
HUR - Why do we add H2SO4 to reaction after it cools (vs. when its still hot?)
Because the heat generated from adding an acid can possibly super heat the liquid and then the solution may boiling out of the container
After HUR, letting the product cool, and adding H2SO4, what should form?
Precipitate (Salicylic Acid)
Why do we acidify to pH 2 or below?
To produce maximum yield --> all carboxylic acids must be protonated
Why vacuum filtration instead of separatory funnel for extraction?
Because we have a solid and a liquid; Sep Funnel is used for two liquids
Why do you rinse the Salicylic Acid on the filter with ice cold water?
To remove any left over H2SO4 or other left over starting materials from the Salicylic Acid solvent
Prevents loss of product yield
What can you conclude if the Melting Point of the Salicylic Acid you just synthesized (with Wintergreen Oil) is 152-155 and the 1:1 Mix of your product and synthetic (from Benzene) salicylic acid is 151-154?
There is probably little to no difference between the Wintergreen Oil synthesis and the Benzene synthesis. If there was a difference, you would expect a decreased boiling point and a broaden boiling point range from I'm purities in the 1:1 ratio.
Melting Point Analysis Samples
1. Pure Product
2. Product + Synthesized from Benzene (1:1) Ratio
When drawing Mechanisms, the arrows always...?
Show where electrons are moving
What is the primary solvent in this experiment?
NaOH solution
What would happen if I added only enough 3 M H2SO4 to bring the pH down to 4?
The Salicylic Acid would not precipitate out completely
Decreasing product yield
Decreasing purity - decreasing melting point; broadening melting point range
What would happen if my reaction mixture had an oily layer on top when I added the 3M H2SO4?
Oily layer means there were still starting materials in product; therefore product had not formed completely
Decreasing product yield
Decreasing product purity - decreasing the melting point; broadening the melting point range
What would happen if a labeling error, the bottle labeled " Salicylic Acid from Benzene" actually contained Acetylsalicylic Acid (Aspirin)?
Decreased purity - melting point decreased and melting point range broadened because Aspirin would be an impurity in the 1:1 ratio