Lab F: Fischer Esterification

Question 1

Draw out the reaction scheme for this lab

Answer 1

Refer to notes

Question 2

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.

Answer 2

Refer to notes

Question 3

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 ___________________

Answer 3

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.

Question 4

Why is the Fischer esterification a reliable method to make esters?

Answer 4

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.

Question 5

Why do we reflux the reaction?

Answer 5

To increase the rate of the reaction

Question 6

When a reaction is refluxed in an organic solvent, the boiling point of the solvent is

Answer 6

the reaction temperature

Question 7

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?

Answer 7

1. using an excess of one of the reagents(glacial acetic acid) since it is more economical
2. refluxing for 50 minutes

Question 8

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

Answer 8

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.

Question 9

After removing all the acetic acid, you re left with what three things? What is the next step after this?

Answer 9

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.

Question 10

What are the two steps in the drying process?

Answer 10

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.

Question 11

What is the drying agent, generally and specifically for this experiment.

Answer 11

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.

Question 12

After you have separated the anhydrous CaCl2 from the organic solution by gravity filtration, what is left?

Answer 12

isopentyl acetate and maybe a trace of isopentyl alcohol

Question 13

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

Answer 13

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.

Question 14

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.

Answer 14

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.

Question 15

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

Answer 15

a simple distillation.

Question 16

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

Answer 16

note the temperature range during which your product distills over

Question 17

The product, isopentyl acetate, will be any liquid that distills(during the distillation) from

Answer 17

125-138 degrees celsius

Question 18

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?

Answer 18

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

Question 19

What is the safety hazard associated with concentrated sulphuric acid?

Answer 19

extremely corrosive, health(rating 3)

Question 20

Describe the general procedure for this experiment

Answer 20

1. Mix the 3-methyl-1-butanol with glacial acetic acid and sulfuric acid. Add two boiling stones.
2. Reflux for 50 mins with the variac set to 65
3. Cool the RBF, then pour the reaction mixture into the separator funnel.
4. 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
5. Add sodium bicarbonate and wait until most of the bubbling subsides. Then shake the funnel and drain off the lower layer into beaker #2.
6. Add water and brine, drain the lower aqueous layer into beaker #1.
7. Drain the top organic layer into an Erlenmeyer flask with anhydrous CaCl2.
8. do a gravity filtration adn add two new boiling stones
9. do a simple distillation. collect the liquid that starts to distill at 125 degrees C and keep collecting for the next 2 mins.

Question 21

What is the acid catalyst in this reaction?

Answer 21

Concentrated sulfuric acid

Question 22

What is the purpose of boiling stones?

Answer 22

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

Question 23

What is the literature boiling point of isopentyl acetate

Answer 23

142 degrees

Question 24

What is the literature boiling point of isopentyl alcohol

Answer 24

132 degrees celsius

Question 25

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 _____________.

Answer 25

100 degrees celsius 125-138 degrees celsius

Question 26

What is the equipment required for a simple distillation?

Answer 26

1. 3-way distillation adapter 2. thermometer adaptor 3. keck clips 4. thermometer 5. vacuum adapter 6. labeled vial(for product) 7. boiling stones

Question 27

What are keck clips for

Answer 27

connecting glass on glass joint

Question 28

Draw a simple distillation schematic

Answer 28

Refer to notes

Question 29

What is the placement of the thermometer in the thermometer adaptor

Answer 29

the bulb is completely submerged by the sidearm of the three-way distillation adaptor

Question 30

What is the smell and appearance of the final product

Answer 30

Smell: bananas appearance: clear, colourless liquid

Question 31

When does the reflux start?

Answer 31

When the solution comes to a boil

Question 32

What should you observe in the condenser as the solution is boiling?

Answer 32

The solvent vapours climbing up into the water-cooled condenser and then they are re-condensed back into the RB flask

Question 33

What should you have at the end of the reflux?

Answer 33

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.

Question 34

what is the density of glacial acetic acid?

Answer 34

0.87 g/mL

Question 35

What is the purpose of adding the sodium bicarbonate?

Answer 35

The NaHCO3 will neutralize any leftover glacial acetic acid in the micture

Question 36

What should the color of the pH paper be when you check it after adding sodium bicarbonate/

Answer 36

orange or green

Question 37

What is the purpose of adding brine and water?

Answer 37

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.

Question 38

What does the anhydrous CaCl2 do?

Answer 38

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.

Question 39

What does the RBF contain after gravity filtration?

Answer 39

isopentyl acetate and true amounts of isopentyl alcohol

Question 40

Draw the schematic of a reflux reacition

Answer 40

refer to ntoes

Question 41

Draw the schematic of a gravity filtration

Answer 41

refer to notes

Question 42

Where do you dispose of the low boiling distillate, if any?

Answer 42

C, H, O non-halogenated waste container

Question 43

Where should boiling stones, anhydrous CaCl2 pellets, gravity filter paper be disposed of?

Answer 43

biohazard box

Question 44

where should capillary tubes be disposed of

Answer 44

red sharps container

Question 45

All aqueous waste should be disposed of in

Answer 45

"Aqueous waste(Fischer lab)"

Question 46

Draw the flow chart for Fischer esterification reaction

Answer 46

refer to notes

Question 47

Write out the general method for preparation of esters.

Answer 47

Refer to notes

Question 48

What is the real-life application for esters?

Answer 48

- Have pleasant fruity odors - Used as flavouring agents and in the perfume industry

Question 49

What does it mean for a reaction to be acid-catalyzed?

Answer 49

The acid is regenerated and is never consumed.

Question 50

Why is it impossible to obtain a 100% yield with an esterification reaction?

Answer 50

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.

Question 51

What are the health hazards associated with glacial acetic acid?

Answer 51

Flammable(rating 2), health(rating 3), corrosive

Question 52

Why is glacial acetic acid named glacial?

Answer 52

Glacial acetic acid is a name for water-free (anhydrous) acetic acid.

Question 53

What is the purpose of a reflux reaction?

Answer 53

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

Question 54

What are the advantages of a reflux?

Answer 54

1. Maintains a constant temperature in the reaction flask 2. reaction is able to reach equilibrium with minimal evaporation of material inside the reaction flask

Question 55

What is distillation?

Answer 55

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.

Question 56

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.

Answer 56

(1) 20-30 degrees Celsius (2) 1 atm (3) miscible

Question 57

If a volatile compound is being distilled, what can be done to minimize loss of material through vaporization?

Answer 57

The receiving contained can be chilled in an ice-water bath

Question 58

Do you distill to dryness?

Answer 58

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

Question 59

When is vacuum distillation used?

Answer 59

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.

Question 60

Draw the schematic for a vacuum distillation

Answer 60

Refer to slideshow

Question 61

During a distillation, when should you read the thermometer?

Answer 61

when the material starts collecting

Question 62

What is a variac? When the boiling point of a substance is higher, what happens to the voltage setting required on the variac?

Answer 62

1. 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.

Question 63

What factors affect boiling points?

Answer 63

1. Size(molecular weight) 2. intermolecular interactions

Question 64

What is a fractional distillation and when is it used?

Answer 64

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.

Question 65

For a fractional distillation: The efficiency of a fractionating column is expressed by ______________. One theoretical plate is equivalent to ______________.

Answer 65

the number of theoretical plates one simple distillation cycle

Question 66

Draw the schematic for a fractional distillation

Answer 66

Refer to slideshows

Question 67

What is the definition of "Normal boiling point"

Answer 67

The temperature at which. liquid vapour pressure equals 1 atm.

Question 68

What is the vapor pressure of water at 100 degrees celsius?

Answer 68

1 atm(760 mmHg)

Question 69

What is another word used to describe vapor pressure?

Answer 69

atmospheric pressure

Question 70

What is the Clausius-clapeyron equation?

Answer 70

refer ot notes

Question 71

What does the vapor pressure vs temp of H2O look like?

Answer 71

Refer to notes

Question 72

What is the real-life application of isopentyl acetate?

Answer 72

Used to flavour soft drinks