Lab F: Fischer Esterification for chris fixed

yo chris did yk ily ?! (pls make more sets (u left while the class was still young))

Purpose

synthesizing Isopentyl acetate (3-methylbutylacetate ) using a Fischer esterification reaction between acetic acid and isopentyl alcohol (3‐methyl‐1‐butanol).

Scheme 1. Synthesis of Isopentyl acetate

example of lower molecular weight esters

What is Fischer esterification?

is an acid‐catalyzed equilibrium reaction between a carboxylic acid and an alcohol in the presence of a strong acid catalyst, usually sulfuric acid, to produce the corresponding ester and water as a by‐product.

Is the reaction reversible or irreversible?

reversible. The ester can react with the acid and water to go back to the starting materials.

In order to get a good yield of the product

it is necessary to push the equilibrium by either removing water as it forms, or by using an excess of one of the reagents

The Fischer esterification is a reliable method to make esters

on an industrial scale,

because it requires 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 rxn

to increase the rate of rxn

When a reaction is refluxed in an organic solvent,

the boiling point of the solvent is the reaction temperature.

what is the excess reagent we use in this experiment

glacial acetic acid

By using an excess of one of the reagents (glacial acetic acid, in this experiment) and refluxing for 50 minutes,

we will be able to drive the equilibrium reaction to the product side and attain a good yield of the ester.

After an initial purification by extraction,

the crude product will be distilled to give pure Isopentyl acetate.

In order to remove all of the acetic acid, we can take advantage of the fact

It is a carboxylic acid. Carboxylic 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, where sodium acetate has greater solubility

The deprotonation reaction that occurs generates

carbon dioxide, making it important to vent your separatory funnel frequently. If you fail to do so, your stopper may pop out, leading to a large loss in yield.

After removing the acetic acid, you are left with

isopentyl acetate, and maybe a trace amount of isopentyl alcohol, and a trace amount of water.

You will begin by washing the organic layer with

a saturated brine solution. Saturated salt solutions are often used to draw water out of the organic layer as a first step in the drying process

All extractions are then dried with

an inorganic drying agent. The drying agent is an anhydrous inorganic salt (devoid of water) that binds to the water and can then be filtered away.

what is the drying agent we use and why do we use it.

anhydrous CaCl2. Because we want to lose as little as possible of our product in the drying step without using additional solvent

how should the anhydrous CaCl2 be seperated

gravity filtration

what do you have at this point

isopentyl acetate with maybe a trace of isopentyl alcohol —two products that have boiling points only 13 oC apart.

what would a difference of 13 oC require

a fractional distillation. However, the difference is so small that even a fractional distillation would need a Vigreux column with many theoretical plates, and in using such a column, we would lose a large amount of material to column holdup and the vapor that is left in the system.

to make seperation easier

we want to significantly limit that amount of isopentyl alcohol that we have to separate from the product.

two basic starategies to drive an equilibrium reaction

One strategy is to remove products as they form in order to continue pushing t h e equilibrium toward more products, and the second is to use an excess of one of the starting materials.

what strategy will we use

We will use more than two equivalents of acetic acid in order to 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

will pure alcohol be obtained

No. the material that distills will be mostly isopentyl acetate which maybe contaminated with a small amount of the isopentyl alcohol.

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.

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

why will our bp be different from literature

Unfortunately, the alcohol thermometers that we use tend to be poorly calibrated at temperatures over 100 °C. Our bp will be about 125-138, while literature is 142.

concerted sulfuric acid hazard

extremely corrosive

since this is an equilibrium rxn

we use glacial acetic acid in excess to push the rxn toward the formation of the product, isopentyl acetate.

why do we use concentrated sulfuric acid

serves as acid catalyst

this rxn is

acid catalyzed esterifcation rxn

do we add stir bar

NO.

do we add boiling chips

YES. add 2

do we use a stir plate

no because don't use stir bar. have heating mantle sitting on base of ring stand.

what is the purpose of doing boiling stones

the pores in the boiling stone help prevent solution from bumping too vigoursly during the reflux process and helps to maintain an even boiling of the solution

what funnel do we use to add liquids to seperatory funnel

pyrex

why don't we want to transfer boiling stones to sep funnel

to prevent sep funnel from clogging

can boiling stones be reused

NO

at end of reflux process

we will have product, isopentyl acetate, excess glacial acetic acid, re-generated acid catalyst, and maybe some unreacted isopentyl alcohol.

when add water

aq layer (bottom layer): light redish color

organic later (top layer): yellowish-brown color

when add aq sodium bicarbonate

observe fizzing due to formation of carbon dioxide gas. Need to vent

purpose of adding aq sodium bicarbonate

to neutralize any leftover glacial acetic acid in the mixture

when add aq bicarb:

aq layer: clear color

org layer: yellowish color.

what should pH be after add aq bicarb

5 to 6 (neutral

purpose of adding tap water

remove any leftover acid

purpose of adding brine or saturated sodium chloride solution

to begin drying process. Being a saturated salt solution, can draw out large amounts of water mixed in with organic layer.

adding tap water and brine:

same layers as one below.

purpose of adding anhydrous CaCl2 pellets

serves as drying agent to cap drying process by drawing out any residual water that is mixed in with organic layer

after gravity filtration

liquid that drains through will contain isopentyl acetate and trace amounts of any isopentyl alcohol

why carry out distillation

assuming final product may contain isopentyl alcohol. Isopentyl acetate has bp of 142 while bp of isopentyl alchol is 132. a diff of 10 will require fractional distillation. However, diff in bp is so small if use fractional distillation which req using vigerux column which has many indentations or threoretical plates. Each theoretical plate corresponds to simple distillation cycles. This would result in losing a large amount of product due to column holdup and the vapors left in system. Use simple distillation to sep product on assumption that any leftover isopentyl alchol is small enough or none compared to losing product if doing fractional distillation instead.

since final product is liquid

look at bp.

which liquid do we collect

the liquid that distills at 125 and end at 138.

the larger ring of the keck clip goes

on the outermost piece of glassware (condenser on left side)

in simple distillation, heating mantle is supported by

ring clamp

do we foil for simple distillation in this experiment

yes until comes up to a boil

isopentyl acetate appearance

clear. Smells like banana oil

glassware for distillation

3-way distillation adapter, thermometer adaptor, 2 keck clips, thermometer, vacuum adaptor, labeled vial, and 2 new boiling stones

where do we collect liquid that boils at lower temp.

in a different beaker and discard into a C, H, O non-halogenated container.

from which side should we start removing distillation set up

from right side.

where should all aqueous waste be disposed

special container aqueous waste (Fischer Lab)

where should Anhydrous Calcium chloride pellets and gravity filter paper be disposed.

the biohazard box

where should boiling stones be disposed of

biohazard box

where does red bulb of thermometer lie

below 3-way distillation side arm

fischer esterification reaction

lower molecular weight Esters:

- Have pleasant fruity odors

- Used as Flavoring agents and in the Perfume Industry

general method for preparation of esters

reflux, extractions, simple distillation

-

what type of rxn is this

• Acid catalyzed reaction , meaning that the acid is regenerated and is never consumed.

• Impossible to obtain a 100% yield.

Our Esterification Reaction - Synthesis of Isopentyl acetate (Banana Oil)

glacial acetic acid hazard

flammable, corrosive

Fischer Esterification - Reflux Schematic

Flow Chart - Fischer Esterification Reaction

simple distillation set up

why shouldn't we distill to dryness

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.

purpose of reflux

- To heat a reaction mixture at its boiling temperature (the boiling point of the solvent, or in this case, excess reactant used in the reaction) to form the product, without losing any material inside the reaction flask.

Factors affecting Boiling Points

size and intermolecular interactions

-bigger has higher bp

what does it mean for a solution to boil

fractional distillation

-A fractional distillation is used to separate liquid mixtures that are miscible in each other, and that boil at less than 25 oC from each other at 1 atm.

-A fractionating column (Vigreux column) is inserted between the 3-way distillation adapter and the round bottom flask (distillation flask) - providing a larger surface area over which a number of separate liquid-vapor equilibria can occur.

-Many vaporizations and condensations take place before the distillate is collected.

one theroetical place is equivalent to

one simple distillation cycle.

Efficiency of a fractionating column

expressed by number of theoretical plates

Vacuum Distillation

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.Only feasible solution for distilling compounds with BPs > 200 oC.

Simple Distillation:

-Used to separate liquids boiling below 50 oC at 1 atm from: a. non-volatile impurities or b. another liquid that boils at least 25 oC higher than the first.

-A technique in which a liquid is vaporized by boiling, then re-condensed back to a liquid (distillate), and collected in a receiving flask.

Schematic -Simple Distillation

What does NRM stand for

Nuclear Magnetic Resonance

What does NMR show

That nuclei posses charge and can spin

Spinning charge generates a magnetic dipole

What are magnetic dipoles

Characterized by nuclear magnetic spin quantum number "l"

What happens as Bo increase

•More nuclei are aligned with the externally

applied magnetic field or the lower energy

α-spin state.

•∆E = Energy difference between α and β-spin states

•Increasing the applied magnetic field = Increasing ∆E

between spin states

•Nuclei can absorb energy and flip from the

α-spin state to the β-spin state. When this happens,

the nucleus is said to be in RESONANCE with the

applied magnetic field, hence the term

“Nuclear Magnetic Resonance”.

•The difference in energy ΔE between the two

spin states corresponds to a frequency in the Radiofrequency

region of the EM spectrum.

What is Plank's equation

∆E = hν

∆E = γ Boh/2π = hν; ν = γBo/2π

γ = gyromagnetic ratio; a constant that depends on the magnetic moment of the nucleus.

What are the conditions for resonance

Larmor equation: ν = γ Bo /2π or

ω = γ Bo; where ν= ω/ 2π

ν is in hertz and ω is in radians/second

Shielding and deshielding nuclei

Electronegative Cl withdraws e-1 density from the 'C' and 'H' atoms - thus DESHIELDING them

Deshielding or Lesser shielding = more of the applied magnetic field strength experienced

= higher (DOWNFIELD) Frequency absorbed

Schematic of an NMR spectrometer

NMR spectrum is

A plot of the intensity of an observed

NMR signal Vs the frequency, measured

relative to a reference compound;

typically Tetramethylsilane (TMS)

Advantages of TMS

1. TMS HAS 12 equiv. H's

2. NMR Signal due to protons in TMS appears as a singlet at 0 ppm (way upfield from other signals).

3. It is low-boiling and inert.

Common NMR solvents

CDCl3 deuterated chloroform

(typically used for non-polar compounds)

(typically used for

polar compounds)

A Typical NMR Sample Prep:

10-20 mg compound + 0.5-0.6 mL CDCl3

Chemical shift (position of the peak)

frequency difference between the resonace observed for the nucleus and the resonance observed for the reference compound (usually TMS)

Degrees of unstaruation

2 (No. of C atoms) + 2 + (No. of N atoms) – (No. of Halogen atoms) - (No. of H atoms)

2

For a DU ≥ 4 = 3 double bonds + 1 ring (= 1 Aromatic ring)

Features of a 1H NMR spectrum that provide information about a compound's structure:

a.Size of/ area under the peak ((Integration) of NMR signals = is indicative of the relative number of identical protons in a particular environment.

b.Number of signals = corresponds to different groups of non-equivalent protons.

c. Position of signals = is indicative of the kind of proton/ s responsible for the signal.

d. Spin-spin splitting of signals = indicates the number of neighboring protons

= calculated using the N+1 rule)

NMR number of signals

NMR intensity signals

•Area under an NMR signal is proportional to the number of absorbing protons.

•Height of each step is proportional to the area under the peak which in turn is

proportional to the number of absorbing protons.