Acetic Anhydride Reacting With Sulphuric Acid Biology Essay

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The aspirin or acetyl salicylic is one of the most common used medicine against headache, pain and also known as anti-inflammatory and analgesic. This substance is part of the group of nonsteroidal anti-inflammatory and has properties of bringing down the high temperature, fever.

In order to synthesize the aspirin we need an acetylating reaction with the salicylic acid, this consists in the esterification with the acetic anhydride, in which the phenolic group has been converted to its acetate ester and the acetic acid thus been eliminated. We use some drops of the sulphuric acid that reacts as a catalyser

Esterification mechanism.

Acetic anhydride reacting with sulphuric acid, the catalyser.

In this synthesis we can see the importance of the phenol group which is obtained industrially from benzene, the acid salicylic is the phenol group also known as hydroxybenzoic acid and carboxylic acid with the presence of acetic anhydride gives us aspirin (acetyl salicylic acid).

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The term synthesis is when 2 or more agents react chemically to obtain a distinct product, in this case the aspirin, we call it a synthetic product. At the final stage of a synthesis process, it is rare to obtain a 100 percent pure product; this is mainly due to unwanted reactions or the synthesis reaction is not been fully completed. Therefore it is necessary to purify the products after the synthesis in order to obtain a purer product we call that a recrystallisation. This process consists in heating ethanol to dissolve the aspirin, which is a solid and cool it slowly to get rid of impurities.

Final product, aspirin (acetyl salicylic acid):

Experimental: as per manual.

Results and discussion:

Salicylic Acid

Acetic Anhydride

Product obtained :

Acetyl Salicylic Acid (Aspirin)

Molecular

formula

Molecular

Weight (g/mol)

138

102

180

Weight in grams (g)

3

6.48

(1.08 g/cm₃x6ml)

Exp A : 2.05

Exp B : 1.09

No. of moles

to be used

0.022

0.064

0.0114

Mole ratio of

reagents

1

1

1

Melting Point

(Celsius)

Exp A : 110

Exp B : 130

Colour /phase of

product

colourless/solid

colourless/liquid

white/solid

Crystal Shape

needle-shaped

needle-shaped

Density

(g/cm₃)

1.08

Calculations:

Theoretical and Percent Yield

http://moodleshare.org/pluginfile.php/8902/mod_page/content/1/Stoichiometry/Images/Topic_7/_Yield_Equation.jpg

Exp A:

Chemical formula of salicylic acid is C7H6O3

Chemical formula of acetyl salicylic acid is C9H8O4

So 1 mole of salicylic acid 138g

1 mole of aspirin 180g

Maximum mass of aspirin that can be produced:

3 g were used in the experiment so,

3/138g = 0.022 mole

0.022x180g = 3.96g

The actual mass obtained of crude product is 2.15g

2.15/3.96 x100 % = 54%

Exp B:

2.15g of crude product but only 1.09g of pure aspirin was obtained after recrystallisation:

1.09/2.15 x 100% = 51%

As it has been already mentioned in the introduction section, there is the need of a reaction with acid salicylic and the acetic anhydride in order to obtain aspirin. The acid sulphuric is used as a catalyser and help to speed up the reaction's process.

In the experiment A so before recrystallisation, the aspirin (crude product) was a solute white with granules then after the purification phase (recrystallation), the acetyl salicylic acid (or aspirin) was pure white (shining) and crystals.

As you can see in the calculations above, the actual yield in exp A and B are almost identical, 54 and 51 % respectively. This can be considered as fair. Chances of having pure product at 100% of theoretical yield are small, and almost impossible. This is can be due to different factors such as losses on filtrations and not having the reaction wanted, the kinetic theory.

Answers to questions:

Exp. A Crude Product:

Calculate the yield of product in grams and % yield based on the original mass of salicylic acid.

See calculations and general discussion above (done).

Explain how the yield could be improved and potential loss points in your experiment.

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Reaction without reaction (synthesis of acetic acid), find ideal conditions?

Potential loss points: vacuum filtration, some of the product remained on the filter?

Compare the melting point with the theoretical value and determine if the crude product is dry.

Theoretical value of melting point: 130C

The melting point of the product: 110C

So the melting point is lower than the theoretical, this means that the product is not dry and pure?

How could the product be purified further?

Recrystallisation?

Show the TLC development results and identify the best eluent system. Calculate the Rf value for the product. Does the TLC show any impurities? Where impurities are shown, calculate their Rf values and predict what these impurities might be.

S - salicylic acid

pure aspirin

the core product

Rf = distance travelled by compound (b) / distance travelled by solvent (a)

Rf S = 2.8/2.9 = 0.82

Rf A = 2.4/2.9 = 0.96

Rf C = 2.5/2.9 = 0.86

We still don't have pure product, still contaminated as the distance travelled is close to salicylic acid… Need recrystillasation?

Exp.B Recrystallisation of aspirin and analysis of pure product:

Calculate the yield of product in grams and % recovery, based on the weight used in recrystallisation.

See calculations and general discussion above (done).

Recalculate the % yield for the pure product, based on the original mass of salicylic acid used in the synthesis.

% yield = 1.09/3.96 x 100% = 27.5%

Explain how the % recovery from recrystallisation could be improved and potential loss points in your purification.

Vacuum filter?

Compare the melting point of pure product with the theoretical value, and determine if the product is dry and pure or not.

Theoretical value of melting point: 130C

The melting point of the product: 127.5C

The product is drier after recrystallisation?

How could the product be purified further?

?

Use the TLC sustem developed for your crude product in Part A. Calculate the Rf value for the pure product. Does the TLC show any impurities? Where impurities are shown, calculate their Rf values and predict what these impurities might be.

S - salicylic acid

pure aspirin

the core product

Rf = distance travelled by compound (b) / distance travelled by solvent (a)

Rf S = 2.5/2.7= 0.92

Rf A = 2.3/2.7= 0.85

Rf C = 2.3/2.7= 0.85

Same distance travelled for our product and pure aspirin so close to purity…?

Explain the results of the ferric chloride test. Explain the rationale behind carrying out of a ferric chloride test on the product?

C:\Users\pacific226\Downloads\ferric chloride test.jpg

Visual results, our product colour is close to the pure aspirin…?

N/A

Calculate the LOD and MC of your samples. Does your meet the following BMR production specifications for your product - LOD <5% and MC <2%? If not then what would you recommend to production?

LOD(Loss On Drying) = weight loss/wet weight x100

MC (Moist Content) = weight loss/dry loss x 100

LOD = 2.44-1.09/2.05 x 100 = 46%

MC = 2.44-1.09/1.09 x100 = 88%

There is a difference of more or less 40% between the 2. ?

Determine the oxygen balance for your product and indicate if it is a potential hazard risk or not.

-[1600 (2x9 + 8/2 - 4)] / 180 = -160

The oxygene balance is between -150 and -200, this compound may show detonation properties under severe confinement?

Calculate the % atom economy of the reaction and hence comment on the efficiency of the reaction.

% Atom Economy = (Mol. Weight of atoms utilized / Mol. Weight of all reactants) x 100

% Atom Economy = (180/480.21) x 100 = 37.5%

Efficiency of the reaction is 37.5%

?

For info: 480.21 = 138.12 + 102.09 + 180 + 60

Conclusion: Please provide a general conclusion…

Compare with industrial scale level

TLC and test colour also shown that it was quite close to the theoretical yield?

Optimal conditions?

Etc…