Synthesising organic and biochemical compounds - Preparation of Aspirin.

Chromatography

Mobile phase

Stationary phase

Thin-layer

Liquid solvent

Al2 03 or Si 02 (often bounded together with CaSo3 and supported on a plastic sheet or glass plate this is called a TLC plate)

Paper

Liquid solvent

H20 can the surface of absorbent chromatography paper and therefore support by the cellulose fibres in paper)

Gas layer

Inter gas (usually N2 or Ar )

Liquid often a silicone gum (supported on suitable solid particles in a glass or metal tube)

High performance liquid

Liquid solvent

Small solid particles (packed tightly in a tube usually stainless steel)

attracted to the stationary phase will be held back one strongly attracted to the mobile phase will pass through rapidly. Separated is achieved when components have different relative attractions for the two phases.

When identifying the components some of them will be coloured and so will be visible but often they will not be visible. So then there are a lot of techniques that's can used to see them. Specially pre-treated plates when exposed to ultraviolet light reveal substances as pale purple spots. Be careful not to look at the light for too long.

The distance a component moves relative to the solvent front is called its Rf (relative to the front) value.

Rf = Distance moved by component

Distance moved by solvent front

The Rf of Pure salicylic acid = 2.2cm = 0.31

7.1cm

The Rf of the our sample of salicylic acid = 2.8cm = 0.39

7.1cm

From those results our sample of the salicylic acid is not pure, it has some impurities, and it could possibly be that some the chemicals did not convert to salicylic acid.

Task 3: Comparing methods for making and purifying aspirin.

In this task we are comparing 2 methods of preparing aspirin, there are a number of different measures, to compare 2 different methods, in each method I need to work out a balanced equation and from this I can work the molar proportions of the reactants. This type of reaction is called esterification reaction as an organic acid + an alcohol form an ester with the elimination of water, it requires H+ ions as a catalyst:

The % yield = actual mass x 100

Theoretical mass

Method 1

Apparatus

* 2-hydroxybenzoic acid

* 100ml beaker

* Ethanoic anhydride

* Concentrated sulphuric acid

* Distilled water

* 250ml beaker

* Vacuum filtration equipment (buchiner funnels, buchiner flasks, tubes and Filter paper)

* Ethanol

* Melting point apparatus

Weigh 5.0g of 2-hydroxybenzoic acid in a 100ml beaker. Add 10ml of ethanoic anhydride with care stir to dissolve the solid. Add 12 drops of concentrated sulphuric acid stir continuously to prevent charring. Cool the mixture to room temperature and add it to 150 ml of distilled water to a 250 ml beaker.

Filter the solid produced under vacuum filtration, wash with 50ml of distilled water. Re-crystallise the solid using a 50:50, which means equal quantities of distilled water and ethanoic acid as a solvent say about 10mls each. Filter, dry the product and take the melting points then store the products.

We then had to work out the percentage yield and theoretical yield.

Sample 1

Theoretical yield

(Maximum yield possible) = 138g 180g

1g 180

138

5g 180 X5

138

Theoretical = 6.52

Percentage yield= Actual yield X 100

Theoretical yield

= 0.32 X100

6.52

= 4.91g

Method 2

Apparatus

* Quickfit flask

* 2-hydroxybenzoic acid

* Phosphoric acid

* Reflux apparatus

* Distilled water

* 250ml beaker

* Glass rod

* Ice

* Vacuum filtration equipment

* Melting point apparatus

* Test tube

2-hydroxybenzoic acid and 10 ml of ethanol anhydride was added to a 100 ml quickfit flask. then add 12 drops of 85% phosphoric acid and swirl to mix. fit a reflux condenser, heat the mixture for about 10 minutes in a water bath, without cooling add 5 ml of water down the condenser. When the vigorous reaction has ended, pour the mixture into a 100 ml of cold water in a 250 ml beaker.

Cool to room temperature. Stir and rub the sides of the beaker with a glass rod to start crystallisation. Stand the beaker in an ice bath to complete the crystallisation process. Filter under a vacuum wash with a little water. Re-crystallise the solid from hot water dry the product in a drying cabinet weight the product record its melting point. Calculate the yield and store the product in a labelled test tube.

For each of the samples we made we had to use tlc to identify any impurities in our products. To do the tlc we needed 250ml beaker with Clingfilm or a lid, 5-10mls of solvent which is ethyl ethanoate mixed with a few drops of ethanoic acid. We had to spot the tlc plate with the following pure aspirin, 2-hydroxybenzoic acid, make the solvent front, remove from the beaker and dry. We then had to look at the plate with a uv lamp and mark out the position of the spots.

Sample 2

Percentage yield= Actual yield X100

Theoretical yield

= 3.34 X100

6.52

= 51.2g

Results

Product 1

Product 2

Weight

0.32g

3.34

Melting point

25

72

TLC

0.85

0.90

.

Task 4: Analysing Aspirin

For each of the samples of aspirin we produced we used TLC to identify any impurities in the preparations.

RF (relative to the front) values

The distance a component moves relative to the solvent front is called its RF value.

The equation is RF= distance moved by component

Distance moved by solvent front

Use a ruler to measure the length from the baseline to A then from the baseline to the solvent front then do the same for the other sample.

Task2: results for TLC

RF = 3.8 =0.5 my sample

8.4

The sample that I made is pure compared to the pure sample that we tested.

Task3 method 1

Solvent front= 8.2 cm

Pure aspirin=7.1cm

Method 1= 7.0cm

Method 2= 7.4cm

2-hydrcxybenzoic acid= 6.4cm

RF= 7.0

8.2 = 0.85 method 1

RF= 7.1 = 0.85 pure aspirin . 8.2

Problems

Some of the problems that I encountered are not filtering the samples properly so when I took it out it was still soggy, so what I did to correct that was I had to put it into an oven for it to dry out. Or I could have filtered it again. Another problem that I had was when I was filtering my products the vacuum didn't have enough pressure for it to work that way it wouldn't of got filtered properly. So what I had to do to correct that problem is I had to open the tap as far as I could push the bunchier funnel into the flask and push in the tubes so that way there would be more pressure.

Interpretation of the results

The thin layer chromatography (TLC) results tell me that my 2-hydrography benzoic acid (Salicylic acid) that I produced is not pure. Some of the reasons could be:

* Some of it didn't get converted properly

* There were same impurities

* I did something wrong in the preparation

My first sample gave me a pure sample compared to the pure aspirin I tested. My second product wasn't pure I think this was because there were some impurities in the product or I did something wrong in the preparation.

My method 1 gave me a very small yield maybe it was because we did something wrong or maybe there were was some impurities in it. I could see all of the crystals in the product. And my product was bright white.

My method 2 gave me a very large yield but for some reason it was discoloured and it was light pink. I also couldn't see any crystals.

My results (TLC, melting points) tell me about my 2 products that the product 1 has a small yield therefore the yield is more pure. Were as my product 2 has a big yield so the yield is not that pure. My results also tells me that maybe the reason why my product 2's boiling point was so high because the impurities that were in it had I high melting point. My results tell me that if you want pure aspirin in small batches you should use method 1, but if you want a lot of aspirin but not that pure you should use method 2. but I think that method 1 is the best method because you don't need to heat it up for that long and the sample is pure.

Evaluation

The literature value of aspirin is 1350C my sample for method 1 had a melting point of 1250C, which is quite close to the literature value, but it is not the same. Maybe this is because there were some impurities in my product or I did something wrong in the preparation stages.

My sample for method 2 had a melting point of 1720C, which is very far from the literature value of aspirin this is mainly because there were some impurities in my sample making the melting point higher.

Comparison with industrial processes

In industrial the production aspirin will require some of the processes that require precision which does that need humans are done by automation which makes the production of aspirin very easy and quicker because the computers controlled everything that would normally done by hand The equipment and chemicals are transported on conveyor belts

Advantages of automation

* Made the process more efficient.

* Saved more money and time in the long run.

* Reduced labours costs by employing less personal.

* Allows them to produce economy of scale: a continuous. process same as mass production which is cheaper than batch production that Ridley use.

Disadvantages of automation

* The automation would cost a lot of money

* The system will consume large a amount electricity