Docsity
Docsity

Prepare for your exams
Prepare for your exams

Study with the several resources on Docsity


Earn points to download
Earn points to download

Earn points by helping other students or get them with a premium plan


Guidelines and tips
Guidelines and tips

synthesis of aspirin, Schemes and Mind Maps of Chemistry

Complete explanation of synthesis of aspirin

Typology: Schemes and Mind Maps

2018/2019

Uploaded on 07/31/2019

eknathia
eknathia 🇺🇸

4.4

(26)

264 documents

1 / 6

Toggle sidebar

This page cannot be seen from the preview

Don't miss anything!

bg1
Los Angeles City College Chemistry 51 Fall 2005
3093
1
Experiment 11
Synthesis and Analysis of Aspirin
INTRODUCTION
Aspirin is most widely sold over-the-counter drug. It has the ability to reduce fever (an antipyretic), to
reduce pain (an analgesic), and to reduce swelling, soreness, and redness (an anti-inflammatory agent). One of
the first recorded accounts for the discovery of aspirin appeared in England, in 1763, crediting the bark of
willow trees with a beneficial effect in alleviating distress due to fevers, aches, and pains. Later, the compound
salicylic acid (named for the Latin word for willow, salix) was isolated from willow bark. It proved to be the
active ingredient. By 1860, organic chemists were able to synthesize salicylic acid from basic starting materials,
this furthered the therapeutic use of the substance, but there were problems. Salicylic acid proved to be irritating
to the membranes of the throat, mouth, and stomach. These problems are directly associated with the high
acidity of the compound, but a simple remedy was discovered, namely, replacement of the acidic phenolic
hydrogen atom with an acetyl group.
When interpreting the structures of the above organic compounds, note the following characteristics of these
molecules. Organic molecules are complex compounds of carbon. Carbon always shares four pairs of electrons
in bonds with other molecular groups or atoms. When the structure of an organic molecule is drawn using the
condensed method, carbon rings are represented with simple geometric shapes, such as a hexagon. Each corner
of the hexagon represents a carbon atom and the number of hydrogen atoms required to share 4 pairs of
electrons with the carbon. If the “corner” has no other marks, that means there is a carbon atom bonded to 2
other carbon atoms (in the ring) plus 2 hydrogen atoms. The hydrogen atoms are implied, not show. If a carbon
to carbon double bond (C =C) is present and the carbons are attached in a ring, each of the two carbon atoms is
bonded to two others with 6 pairs of electrons, and only one hydrogen is attached to each of these carbons give
the full compliment of four bonds. If a triple bond is present then only one other atom may be attached. Check
the structures below to see that each carbon has four and only four bonds. Oxygen, on the other hand, will bond
covalently to only two atoms, and hydrogen bonds to only one.
A useful synthesis of acetylsalicylic acid was developed in 1893, patented in 1899, marketed under the trade
name of “aspirin” by the Bayer Company in Germany. The name aspirin was invented by the chemist, Felix
Hofmann, who originally synthesized acetylsalicylic acid for Bayer. More than 50 million 5-grain tablets of
aspirin are consumed daily in the United States. In Part I of this experiment, you will prepare aspirin by reaction
of salicylic acid with acetic anhydride, using concentrated sulfuric acid as a catalyst.
pf3
pf4
pf5

Partial preview of the text

Download synthesis of aspirin and more Schemes and Mind Maps Chemistry in PDF only on Docsity!

Experiment 11

Synthesis and Analysis of Aspirin

INTRODUCTION

Aspirin is most widely sold over-the-counter drug. It has the ability to reduce fever (an antipyretic), to

reduce pain (an analgesic), and to reduce swelling, soreness, and redness (an anti-inflammatory agent). One of

the first recorded accounts for the discovery of aspirin appeared in England, in 1763, crediting the bark of

willow trees with a beneficial effect in alleviating distress due to fevers, aches, and pains. Later, the compound

salicylic acid (named for the Latin word for willow, salix) was isolated from willow bark. It proved to be the

active ingredient. By 1860, organic chemists were able to synthesize salicylic acid from basic starting materials,

this furthered the therapeutic use of the substance, but there were problems. Salicylic acid proved to be irritating

to the membranes of the throat, mouth, and stomach. These problems are directly associated with the high

acidity of the compound, but a simple remedy was discovered, namely, replacement of the acidic phenolic

hydrogen atom with an acetyl group.

When interpreting the structures of the above organic compounds, note the following characteristics of these

molecules. Organic molecules are complex compounds of carbon. Carbon always shares four pairs of electrons

in bonds with other molecular groups or atoms. When the structure of an organic molecule is drawn using the

condensed method, carbon rings are represented with simple geometric shapes, such as a hexagon. Each corner

of the hexagon represents a carbon atom and the number of hydrogen atoms required to share 4 pairs of

electrons with the carbon. If the “corner” has no other marks, that means there is a carbon atom bonded to 2

other carbon atoms (in the ring) plus 2 hydrogen atoms. The hydrogen atoms are implied, not show. If a carbon

to carbon double bond (C =C) is present and the carbons are attached in a ring, each of the two carbon atoms is

bonded to two others with 6 pairs of electrons, and only one hydrogen is attached to each of these carbons give

the full compliment of four bonds. If a triple bond is present then only one other atom may be attached. Check

the structures below to see that each carbon has four and only four bonds. Oxygen, on the other hand, will bond

covalently to only two atoms, and hydrogen bonds to only one.

A useful synthesis of acetylsalicylic acid was developed in 1893, patented in 1899, marketed under the trade

name of “aspirin” by the Bayer Company in Germany. The name aspirin was invented by the chemist, Felix

Hofmann, who originally synthesized acetylsalicylic acid for Bayer. More than 50 million 5-grain tablets of

aspirin are consumed daily in the United States. In Part I of this experiment, you will prepare aspirin by reaction

of salicylic acid with acetic anhydride, using concentrated sulfuric acid as a catalyst.

Aspirin still has its side effects. Note that the carboxylic acid functional group remains intact.

This may result in hemorrhaging of the stomach walls even with normal dosages. The acidic irritation can

be reduced through the use of buffering agents, like antacids, in the form of magnesium hydroxide, magnesium

carbonate, and aluminum glycinate when mixed with aspirin (Bufferin). While the ester can be formed from

acetic acid and salicylic acid, a better preparative method uses acetic anhydrides in the reaction instead of acetic

acid. An acid catalyst, like sulfuric acid or phosphoric acid, is used to speed up the process.

Part I: Synthesis of Aspirin

Caution! The preparation of aspirin involves the use of two very hazardous materials - concentrated sulfuric

acid and acetic anhydride. Proceed only if you have a fume hood to work in, and after you have listened

carefully to the instructor’s safety directions. As usual, goggles must be worn at all times.

PROCEDURE

  1. Weigh 4.0 g (0.030 mol) of salicylic acid in a 125 mL Erlenmeyer flask. Using this quantity of salicylic acid

to calculate the theoretical yield of aspirin. Record the weigh on the report sheet.

  1. Carefully add 6 mL (0.051 mol) of acetic anhydride to the flask. ( CAREFUL! Acetic anhydride is irritating to

the skin and eyes.)

  1. Using extreme caution, add 5 drops of concentrated sulfuric acid to the flask, swirl gently, and place the

flask in a beaker of boiling water. Clamp the flask to a ring stand and heat for 20 minutes. Constantly stir

with a glass rod; the entire solid must completely dissolve.

  1. Remove the flask from the boiling water bath and allow to cool to room temperature. Crystallization should

occur during cooling. If crystals begin to grow, let the flask sit undisturbed until crystals stop growing then

add the 40 mL of ice water. If crystals do not grow, slowly pour the solution into a 250-mL beaker

containing 40 mL of ice water, mix thoroughly, and place the beaker in ice water and let sit undisturbed

until crystals have grown. The water destroys any unreacted acetic anhydride and will cause the insoluble

aspirin to precipitate out of solution.

  1. Collect the crystals by vacuum filtration (using a Buchner funnel, if available).
  2. Wash the crystals with two 10-mL portions of cold water followed by one 10 mL portion of cold ethanol.

Allow the crude product to dry, then weigh it on the rough balance.

PROCEDURE

  1. Obtain a capillary tube from your instructor, and gently press the open end into the pile of aspirin crystals on

the paper so that a few crystals of aspirin enter the capillary tube.

  1. Tap the closed end of the capillary onto the bench top, so that the aspirin crystals work their way to the

bottom. The aspirin crystals should be firmly packed, and fill the capillary tube to a depth of no more than

1 - 2 mm. Insert the capillary tube containing the sample into the melting point apparatus. Record the

temperature where the melting point is first observed and when it becomes a liquid completely. This is your

melting point range. Melting point of purified aspirin is 135-136 °C.

B. Determination of Purity

Phenols form a colored complex with the ferric ion. If phenol is present in a sample, the resulting color means

the product is impure. The purple color indicates the presence of a phenol group. The intensity of the color

qualitatively tells how much impurity is present.

PROCEDURE

  1. Label three test tubes; place a few crystals of salicylic acid into test tube #1, a small sample of your aspirin

into test tube #2, and a small sample of crushed commercial aspirin into #3. Add 5 mL of deionized water to

each test tube and swirl to dissolve the crystals.

  1. Add 10 drops of 1% ferric chloride to each test tube.
  2. Compare and record your observations.

Experiment 10

ACID/BASE TITRATION

Scientist

Partner(s)

REPORT SHEET

Part I

  1. Theoretical yield:

g salicylic acid ( 138 gsalicylicacid

1 molsalicylic acid )( 1 molaspirin

1 molsalicylic acid )( 1 molaspirin

180 g aspirin ) = g of aspirin

(Theoretical yield of aspirin)

  1. Experimental yield:

Weight of aspirin & watch glass g

Weight of watch glass g

Mass of crude product obtained after suction filtration g

Percent Yield of crude product ( theoreticalyield

experimental yield 100%) %

Mass of re-crystallized product (optional) g

Percent Yield of re-crystallized product ( theoreticalyield

experimental yield 100%) %

Part II

Melting Point of crude product (1st trial) °C (2nd trial) °C

Melting Point of re-crystallized product (1st trial) °C (2nd trial) °C

Ferric Chloride Test (Purity test)

SAMPLE COLOR INTENSITY

Salicylic acid

Your aspirin

Commercial aspirin