Lab F: Fischer Esterification Flashcards
Draw out the reaction scheme for this lab
Refer to notes
Many lower molecular weight esters have fruity or sweet smells, and are responsible for the doors of common natural and synthetic food and drinks. Give the six examples listed in the lab manual.
Refer to notes
Fischer esterification is an ________________, __________________ reaction between a(n) ______________ and a(n) ________________ in the presence of a __________ acid catalyst, to produce the corresponding ester and water as a by-produc. The reaction is _____________ as the ester can react with eh acid and water to go back tot he starting materials. In order to get a good yield of the product it is necessary to ___________________
acid catalyzed
equilibrium
carboxylic acid
alcohol
strong
reversible
push the equilibrium by either removing water as it forms or by using an excess of one of the reagents.
Why is the Fischer esterification a reliable method to make esters?
it required very simple reagents and the reaction can be driven to completion by using a large excess of whichever starting material is less expensive.
Why do we reflux the reaction?
To increase the rate of the reaction
When a reaction is refluxed in an organic solvent, the boiling point of the solvent is
the reaction temperature
What are the two things we are doing in this reaction to drive the equilibrium reaction to the product side and attain a good yield of the ester?
- using an excess of one of the reagents(glacial acetic acid) since it is more economical
- refluxing for 50 minutes
In order to remove all of the acetic acid we can take advantage of the fact it is what functional group? Explain this concept further
Carboxylic acid
Carbxoylic acids typically have pKa values near 5, and can be easily deprotonated. The organic layer will be washed with sodium bicarbonate to convert acetic acid into sodium acetate salt. In this way, we can move all of the acetic acid into the aqueous layer, were sodium acetate has greater solubility. The deprotonation reaction that occurs generates carbon dioxide, making it important to vent your separator funnel frequently.
After removing all the acetic acid, you re left with what three things? What is the next step after this?
You are left with isopentyl acetate, and maybe a trace amount of isopentyl alcohol, and a trace amount of water.
After this step, you will begin by washing the organic layer with a saturated brine solution. All extractions are then dried with an inorganic drying agent.
What are the two steps in the drying process?
Saturated salt solutions are often used to draw water out of the organic layer as a first step in the drying process. An inorganic drying agent is then used to complete the drying process.
What is the drying agent, generally and specifically for this experiment.
The drying agent is an anhydrous inorganic salt(devoid of water) that binds to the water and can then be filtered away. Because we want to lose as little as possible of our product in the drying step without using additional solvent, we will be using anhydrous CaCl2 as the drying agent.
After you have separated the anhydrous CaCl2 from the organic solution by gravity filtration, what is left?
isopentyl acetate and maybe a trace of isopentyl alcohol
You are assuming that your final product, isopentyl acetate, may contain trace amounts of isopentyl alcohol(the starting material). Essentially, you have two products that have boiling points only 10 degrees celsius apart. A difference of this much would require
a fractional distillation
however the difference is so small that even a fractional distillation would need a vigreuz column with many theoretical plates(or indentations), and in using such a column, we would lose a large amount of material/product to column holdup and the vapor that is left in the system. hence, we do a simple distillation to isolate isopentyl acetate on the assumption that if we have any leftover isopentyl alcohol, the amount of isopentyl alcohol may be small enough or none compared to losing a large amount of isopentyl acetate if we were to do a fractional distillation instead.
In order to make this separation easier, we want to significantly limit the amount of isopentyl alcohol that we have to separate from the product. there are two basic strategies to drive an equilibrium reaction.
One strategy is to remove products as they form in order to continue pushing the equilibrium toward more products and the second is to sue an excess of one of the starting materials. We will use more than two equivalents of acetic acid in order ot drive the equilibrium towards the products.
By driving the equilibrium to the products, we may only have a small amount of isopentyl alcohol, if any at all, to remove, which can be accomplished by
a simple distillation.
The final product is characterized by recording a boiling point range. In order to characterize a compound by its boiling point range, you will need to
note the temperature range during which your product distills over
The product, isopentyl acetate, will be any liquid that distills(during the distillation) from
125-138 degrees celsius
You will not obtain pure alcohol out of the distillation, and the material that distills will be mostly isopentyl acetate which may be contaminated with a small amount of the isopentyl alcohol. why do we still use a simple distillation?
Because there is only a very small amount of isopentyl alcohol contaminant, the amount of isopentyl acetate lost in this case is most likely less than what would be lost to column holdup and the vapor pressure in a fractional distillation with a sufficient number of theoretical plates to obtain pure separation
What is the safety hazard associated with concentrated sulphuric acid?
extremely corrosive, health(rating 3)
Describe the general procedure for this experiment
- Mix the 3-methyl-1-butanol with glacial acetic acid and sulfuric acid. Add two boiling stones.
- Reflux for 50 mins with the variac set to 65
- Cool the RBF, then pour the reaction mixture into the separator funnel.
- Add cold water and drain the lower aqueous layer into Beaker #1. The top organic layer is the glacial acetic acid while the bottom layer is water
- Add sodium bicarbonate and wait until most of the bubbling subsides. Then shake the funnel and drain off the lower layer into beaker #2.
- Add water and brine, drain the lower aqueous layer into beaker #1.
- Drain the top organic layer into an Erlenmeyer flask with anhydrous CaCl2.
- do a gravity filtration adn add two new boiling stones
- do a simple distillation. collect the liquid that starts to distill at 125 degrees C and keep collecting for the next 2 mins.
What is the acid catalyst in this reaction?
Concentrated sulfuric acid
What is the purpose of boiling stones?
Made of porous material to allow the reaction mixture to go in and out to allow for uniform boiling.
The pores in the boiling stones prevent the solution from bumping to vigorously during the boiling process and helps maintain even boiling of the solution
What is the literature boiling point of isopentyl acetate
142 degrees
What is the literature boiling point of isopentyl alcohol
132 degrees celsius
In the lab, we use alcohol thermometers, and these thermometers are not well calibrated at temperatures over ___________. Thus, even though the literature boiling point of isopentyl acetate is 142 degrees C, the product, isopentyl acetate, will be any liquid that distills(during the distillation) from _____________.
100 degrees celsius
125-138 degrees celsius
What is the equipment required for a simple distillation?
- 3-way distillation adapter
- thermometer adaptor
- keck clips
- thermometer
- vacuum adapter
- labeled vial(for product)
- boiling stones
What are keck clips for
connecting glass on glass joint
Draw a simple distillation schematic
Refer to notes
What is the placement of the thermometer in the thermometer adaptor
the bulb is completely submerged by the sidearm of the three-way distillation adaptor
What is the smell and appearance of the final product
Smell: bananas
appearance: clear, colourless liquid
When does the reflux start?
When the solution comes to a boil
What should you observe in the condenser as the solution is boiling?
The solvent vapours climbing up into the water-cooled condenser and then they are re-condensed back into the RB flask
What should you have at the end of the reflux?
At the end of the reflux process, we would have the product isopentyl acetate, excess glacial acetic acid, the regenerated acid catalyst, and some unreacted isopentyl alcohol.
what is the density of glacial acetic acid?
0.87 g/mL
What is the purpose of adding the sodium bicarbonate?
The NaHCO3 will neutralize any leftover glacial acetic acid in the micture
What should the color of the pH paper be when you check it after adding sodium bicarbonate/
orange or green
What is the purpose of adding brine and water?
The purpose of brine is to begin the drying process. Being a saturated solution, brine draws out large amount of water mixed with he organic layer.
What does the anhydrous CaCl2 do?
Caps the drying process by drawing out any residual water mixed in with your organic layer. It traps any traces of moisture before vacuum filtration.
What does the RBF contain after gravity filtration?
isopentyl acetate and true amounts of isopentyl alcohol
Draw the schematic of a reflux reacition
refer to ntoes
Draw the schematic of a gravity filtration
refer to notes
Where do you dispose of the low boiling distillate, if any?
C, H, O non-halogenated waste container
Where should boiling stones, anhydrous CaCl2 pellets, gravity filter paper be disposed of?
biohazard box
where should capillary tubes be disposed of
red sharps container
All aqueous waste should be disposed of in
“Aqueous waste(Fischer lab)”
Draw the flow chart for Fischer esterification reaction
refer to notes
Write out the general method for preparation of esters.
Refer to notes
What is the real-life application for esters?
- Have pleasant fruity odors
- Used as flavouring agents and in the perfume industry
What does it mean for a reaction to be acid-catalyzed?
The acid is regenerated and is never consumed.
Why is it impossible to obtain a 100% yield with an esterification reaction?
A 100% yield is impossible in esterification reactions because the reaction reaches a chemical equilibrium, meaning some of the reactants will always remain unreacted, converting back to the starting materials, even if the reaction is allowed to proceed for a long time; this is due to the reversible nature of the reaction, where the ester can also hydrolyze back into the carboxylic acid and alcohol, preventing complete conversion to the ester product.
What are the health hazards associated with glacial acetic acid?
Flammable(rating 2), health(rating 3), corrosive
Why is glacial acetic acid named glacial?
Glacial acetic acid is a name for water-free (anhydrous) acetic acid.
What is the purpose of a reflux reaction?
To heat a reaction mixture at its boiling temperature (the boiling point of the solvent, ir in this case, excess reactant used in the reaction) to from the product, without losing any material inside the reaction flask
What are the advantages of a reflux?
- Maintains a constant temperature in the reaction flask
- reaction is able to reach equilibrium with minimal evaporation of material inside the reaction flask
What is distillation?
A technique in which a liquid is vaporized by heating to its boiling point, then re-condensed back to a liquid, called the distillate), which is collected in a receiving flask.
Simple distillation is a technique used to separate liquids where the boiling points differ by more than _______(1) at _____(2). The two liquids must be ____________(3) in each other.
(1) 20-30 degrees Celsius
(2) 1 atm
(3) miscible
If a volatile compound is being distilled, what can be done to minimize loss of material through vaporization?
The receiving contained can be chilled in an ice-water bath
Do you distill to dryness?
No! Leaving a small amount of residue will prevent overheating and breaking the flask, and also prevent formation of pyrolytic tars that are difficult to wash out
When is vacuum distillation used?
Used for compounds that either boil at too high a temperature, or that decompose near their boiling points. Under vacuum, compounds can be distilled at temperatures lower than their atmospheric boiling points. It is the only feasible solution for distilling compounds with BPs > 200 degrees C.
Draw the schematic for a vacuum distillation
Refer to slideshow
During a distillation, when should you read the thermometer?
when the material starts collecting
What is a variac? When the boiling point of a substance is higher, what happens to the voltage setting required on the variac?
- A variac is a variable voltage transformer. It provides a voltage-adjusted source of alternating current. The higher the boiling point, the greater the voltage required.
What factors affect boiling points?
- Size(molecular weight)
- intermolecular interactions
What is a fractional distillation and when is it used?
A fractional distillation is used to separate liquid mixtures where the difference in boiling points is less than 25 degrees C at 1 atm. A fractionating column(vigreux column) is inserted between the 3-way distillation adapter and the RBF(distillation flask) - providing a larger surface area over which a number of separate liquid-vapour equilbria can occur. Many condensations and vaporizations take place before the distillate is collected.
For a fractional distillation: The efficiency of a fractionating column is expressed by ______________. One theoretical plate is equivalent to ______________.
the number of theoretical plates
one simple distillation cycle
Draw the schematic for a fractional distillation
Refer to slideshows
What is the definition of “Normal boiling point”
The temperature at which. liquid vapour pressure equals 1 atm.
What is the vapor pressure of water at 100 degrees celsius?
1 atm(760 mmHg)
What is another word used to describe vapor pressure?
atmospheric pressure
What is the Clausius-clapeyron equation?
refer ot notes
What does the vapor pressure vs temp of H2O look like?
Refer to notes
What is the real-life application of isopentyl acetate?
Used to flavour soft drinks
