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Synthesis of Aspirinequation

Synthesis

Synthesis

Purification

Purification

Characterization

Characterization

Aspirin: some background

Patented by Bayer in 1893

Patented by Bayer in 1893

One of the oldest drugs

One of the oldest drugs

One of the most consumed drugs

One of the most consumed drugs

(Production in the US is 10 million

(Production in the US is 10 million

Kg/year)

Kg/year)

Aspirin: The Molecule

O

OH

HO

O

O

acetyl salicylic acid (aspirin)

Organic backgroundAlcohols

! !

Alcohols Alcohols

! !

Aliphatic alcohols Aliphatic alcohols: Hydroxyl derivatives of saturated hydrocarbons

: Hydroxyl derivatives of saturated hydrocarbons

! !

Enols Enols: Hydroxyl derivatives of unsaturated hydrocarbons

: Hydroxyl derivatives of unsaturated hydrocarbons

R

OH

H

3

C

OH

methanol

OH

ethanol

OH

R

R

enol

OH

phenol

Organic backgroundEsterification

R

1

OH

O

HO

R

2

R

1

O

O

R

2

carboxylic acid

alcool

ester

H

This is an equilibrium!

Organic backgroundEsterification mechanism

R

1

OH

O

HO

R

2

R

1

O

O

R

2

carboxylic acid

alcool

ester

R

1

OH

OH O

H

R

2

H

R

1

OH

OH

2

O

R

2

-H

Reaction

OH

OH

O

salicylic acid

O

O

O

acetic anhydride

O

OH

HO

O

O

acetyl salicylic acid (aspirin)

OH

O

acetic acid

H

2

SO

4

heat

Reaction mechanism

OH

HO

O

O

O O

O

HO

O

O

OH

O

H

O

HO

O

H

OH

O

O

-H

Synthesis procedure

! !

Mix salicylic acid (solid) with acetic anhydride (liquid) and a Mix salicylic acid (solid) with acetic anhydride (liquid) and a catalytic

catalytic

amount of H amount of H

22

SO

SO

44

! !

Heat for 10 min at 90 Heat for 10 min at 90

00

C.

C.

! !

Cool down to room temperature and add water (crystallization Cool down to room temperature and add water (crystallization

solvent). solvent).

! !

Induce crystallization. Induce crystallization.

! !

Filter the crystals. Filter the crystals.

Purification by Recrystallization

WHAT IS

WHAT IS

RECRYSTALLIZATION?

RECRYSTALLIZATION?

Rapid and convenient way of Rapid and convenient way of

purifying a solid organic purifying a solid organic

compound compound

The material to be purified is The material to be purified is

dissolved in the hot appropriate dissolved in the hot appropriate

solvent solvent

As the solvent cools, the As the solvent cools, the

solution become saturated with solution become saturated with

respect to the substance, which respect to the substance, which

then crystallize then crystallize

Impurities stay in solution Impurities stay in solution

METHOD

METHOD

Choose the solvent

Choose the solvent

Dissolve the solute

Dissolve the solute

(Filter suspended solids)

(Filter suspended solids)

Crystallize the solute

Crystallize the solute

Collect and wash the

Collect and wash the

crystals

crystals

Dry the crystals

Dry the crystals

Assessment of purity:

Physical appearance

Physical state (solid? liquid? ..)

Physical state (solid? liquid? ..)

Color

Color

Odor

Odor

Texture

Texture

Homogeneity in composition

Homogeneity in composition

Assessment of purity:

Solubility

In a test tube, transfer a small amount of your

In a test tube, transfer a small amount of your

product (end of a spatula)

product (end of a spatula)

Add ~1/2mL of solvent

Add ~1/2mL of solvent

Determine solubility at room temperature

Determine solubility at room temperature

If not, gently heat and determine solubility at

If not, gently heat and determine solubility at

higher temperature

higher temperature

Test several organic solvents and compare with

Test several organic solvents and compare with

litterature

litterature

Assessment of purity:

Infrared Spectra

Dissolve the product in chloroform and obtain the

Dissolve the product in chloroform and obtain the

IR spectrum.

IR spectrum.

Assign the peaks

Assign the peaks

Do you see impurities?

Do you see impurities?

Compare with the reference spectrum.

Compare with the reference spectrum.

Assessment of purity:

Percent yield

! !

Definition: %Yield = Definition: %Yield = n

n

expexp

/n/n

th th

! !

Write down the reaction with the correct Write down the reaction with the correct stoechiometry

stoechiometry. Ex: A+B

. Ex: A+B

CC

! !

Prepare a chart like below and calculate yield. Prepare a chart like below and calculate yield.

n n

C C

(mol) (mol)

experimental experimental

m m

cc

(g)(g)

experimentalexperimental

n n

C C

(mol) (mol)

theoretical theoretical

m m

CC

(g)(g)

theoreticaltheoretical

nn

BB

(mol)(mol)

m m

B B

(g) (g)

or V or V

BB

( (mL

mL)

)

nn

AA

(mol)(mol)

m m

A A

(g)(g)

or V or V

AA

( (mL

mL)

)