Organic compounds are those which contain carbon as well as a select other elements. An organic acid however, is an organic compound which contains acidic properties. An ester is an example of being a derivative of these organic acids. Esters can be prepared by the reaction of carboxylic acids and alcohols, with an inorganic acid used as a catalyst which is dubbed esterification. With o-hydrobenzoic acid, or salicylic acid, we are able to create acetylsalicylic acid otherwise known as aspirin as well as methyl salicylate, which is a component of oil of wintergreen. Both of which are used for pain relief/soreness.
Salicylic acid is a member of the phenol class as their hydroxyl group (OH) is attached to a phenyl ring (benzene) and many phenols react with ferric chloride to cause a colour change. And so, in this investigation we are to prepare the two esters and compare their reactions with ferric chloride compared to the reaction between salicylic acid and the ferric chloride in order to identify phenolic properties. Materials Lab Equipment 125 ml Erlenmeyer flask 10 ml Graduated cylinder Small watch glass Thermometer Filter paper 600 ml Beaker Large test tubes Hot plate Funnel Chemicals Acetic anhydride 1% Ferric Chloride Solution Salicylic Acid.
Ice Ethanol Methyl Alcohol Concentrated Sulfuric Acid Distilled Water Procedure Synthesis of Aspirin
- Place 3 grams of Salicylic acid in a Erlenmeyer flask and record the mass
- Add 6 ml of Acetic anhydride to the flask of salicylic acid
- Add 5 drops of concentrated sulfuric acid to the flask of salicylic acid
- Swirl the flask in order to mix the reagents
- Heat a beaker of water on the hot plate to 80-90 degrees Celsius, use the thermometer to check temperature
- Place the flask of reagents into the beaker of heated water for 20 minutes
- Remove the flask after 20 minutes and allow flask to cool to room temperature
- Measure and add 40 ml of distilled water to the mixture in the Erlenmeyer flask and mix the contents
- Place flask in an ice bath in order to complete crystallization
- Prepare filtration process by placing filter paper in funnel
- Filter crystals in funnel and wash slight by using ice cold water
- Press crystals between paper towels and allow crystals to air dry Testing Crystals for Purity
- Dissolve a few crystals of aspirin into 5 ml of water inside a test tube
- Dissolve a few crystals of salicylic acid into 5 ml of water inside of a separate test tube
- Add a drop of 1% ferric chloride and note the reaction Purification by Recrystallization
- Measure mass of aspirin
- Calculate volume of ethanol needed provided 6g of aspirin dissolves in 20 ml of absolute ethanol
- Prepare water bath in a beaker on top of a hot plate
- Place Erlenmeyer flask containing aspirin and appropriate ethanol in the water bath
- Add 50 ml of 50° C distilled water in the flask once aspirin has been dissolved
- Place watch glass at mouth of flask and allow to slowly cool
- Repeat filtration process in steps 10-12 23.
Record mass of aspirin after it has completely dried Synthesis of Methyl Salicylate
- Place 1 g of salicylic acid and 5 ml of methyl alcohol in a test tube
- Add 3 drops of sulfuric acid in the test tube
- Prepare beaker of water to 70°c and then place test tube in beaker for 15 minutes
- Waft the odour of the methyl salicylate
- Add a drop of 1% ferric chloride solution into the test tube and note any change
Results Synthesis of Aspirin Mass (g) Molar weight Moles used Theoretical mass Percent yield Salicylic Acid 3. 0g 138 amu 1/46 mol (mass/molar weight) = =22. 25% yield Dry recrystallized aspirin 0. 87g 180 amu 1/46 mol moles salicylic acid X [Theoretical] 3.91 g (1/46 moles x 180amu/mole) Reaction with FeCl3 Salicylic Acid Purple/ Magenta Aspirin Light Purple/pink Dry recrystallized aspirin Pale Pink Synthesis of Methyl Salicylate Odor Reaction With FeCl3 Methyl Salicylate Minty Dark Purple Data Analysis Prelab Questions What are esters? What is their general structure? Esters are derivatives of organic acids (carboxylic acids), whilst carboxylic acids contain the carboxyl group (COOH), in an ester the hydrogen is replaced by an alkyl group. Therefore they are said to be the result of a reaction between a carboxylic acid and an alcohol with water as a side product.
Their general structure is: What is the role of the inorganic acids in the esterification process? The role of inorganic acids in the esterification process is to act as a catalyst; that is to speed up the reaction whilst not being used up itself From what substances can esters be prepared? Esters can be prepared from carboxylic acids in a reaction with an alcohol and a inorganic acid used as a catalyst. What is one general physical property of esters? A general physical property of esters is that they have (typically) pleasant odours. Describe a test for phenols.
A test for phenols would be to place a drop of 1% Ferric chloride in the solution and see if it reacts with a colour change as many phenols form colored complexes ranging from green through blue and red through violet with ferric chloride. What is the carboxylic acid group? The carboxylic acid group is characterized as COOH (carboxyl group) and is responsible for some acidic properties. What is the purpose of recrystallization?
The purpose of recrystallization is to purify the solution as suspended insoluble particles are to be filtered out and removed. 0. 980 g of acetylsalicylic acid was obtained from 1.00 g of salicylic acid by reaction with excess acetic anhydride. Calculate the percent yield of acetylsalicylic acid. Salicylic Acid + Acetic Anhydride ? Acetylsalicylic acid + Acetic Acid 1 mole = 7(12g/mol)+6(1. 01g/mol)+3(16g/mol) =138. 06 g/mol 1g = x = 1 mole = 9(12g/mol)+8(1. 01g/mol)+4(16g/mol) =180. 08 g/mol Therefore the percent yield of acetylsalicylic acid is 75% Two esters with empirical formula C3H6O2 may be prepared.
Write the structural formulas for these esters and name them Methyl EthanoateEthyl Methanoate How would you prepare the two esters above? Ethanol + Acetic Acid.
Esters may be saponified through reaction with a strong base. Predict the products of the reaction Give the structural formulas for isopropyl acetate and ethyl salicylate Isopropyl AcetateEthyl Salicylate Post Lab QUESTIONS Why was cold as opposed to warm water used to wash the aspirin you prepared? Cold as opposed to warm water was used to wash the aspirin as cold water would allow the aspirin to crystalize since in colder temperatures, aspirin is less soluble and therefore are able to crystallize and thus allow us to collect more of the aspirin in its crystalized form.
Hot water on the other hand would further dissolve the aspirin. Explain why you would or would not expect to observe a color change if FeCl3 were added to the following: Pure Aspirin Pure aspirin, which is acetylsalicylic acid, is not a member of the phenols class of compound since an OH group is not attached to a benzene ring, and for that reason it does not react with ferric chloride. Salicylic acid however, is a phenol and forms a purple colour when it reacts with ferric chloride.
Therefore it can be understood that if the aspirin is truly pure, it would not have any trace of salicylic acid (as it would be completely reacted) and thus have no colour change in the presence of ferric chloride. Oil of Wintergreen Oil of wintergreen, which contains methyl salicylate, would experience a colour change in the presence of FeCl3. This is because methyl salicylate is a member of the phenol class of compounds as its OH group is attached to a benzene ring. Phenols, when reacted with FeCl3 inhibit colored complexes, and in this case purple. Write the structure of products you would expect from the following reactions:
How would you prepare each of the following? Ethyl Acetate (two ways) 1) Ethanol +Acetic Acid (or Acetic anhydride) with sulphuric acid as catalyst/dehydrating agent CH3CH2OH + CH3COOH CH3COOCH2CH3 + H2O 2) Tishchenko reaction – disproportionation of an aldehyde lacking a hydrogen atom in the presence of an alkoxide (basic salt derived from an alcohol with the hydroxyl hydrogen replaced with a metal, therefore has a negatively charged oxygen atom) to form an ester 2 equivalents of Acetaldehyde in the presence of an alkoxide catalyst: 2 CH3CHO > CH3COOCH2CH3.
Methyl Acetate 1) Methanol+ Acetic acid with inorganic acid as catalyst If your experimental yield of aspirin was greater than 100%, how could this occur? Your experimental yield of aspirin could weigh more than the theoretical mass if your aspirin product is not completely dry as you would therefore also be weighing the solvent and the moisture in the crystals. Furthermore, if the purification process went poorly, there may be some unreacted products in the reactants which you are weighing. Conclusion.
Based on the results of this investigation, we are able to see the similarities and differences between 2 different esters formed from salicylic acid, aspirin (acetylsalicylic acid) and oil of wintergreen (methyl salicylate) based on physical properties such as odour, appearance, colour and chemical such as their individual reactions with ferric chloride (which in fact tells us about its structure and classification). In the esterification with acetic anhydride, the resulting acetylsalicylic acid when in solid form is white in colour and is made up of tiny crystals.
When fully purified, these crystals do not react with ferric chloride. The methyl salicylate however, which was reacted with methanol do react with the ferric chloride and gives a purple colour which indicates that the benzene ring is attached to the hydroxyl group and has phenolic properties. The methyl salicylate also contains a minty odour but like the acetylsalicylic acid is white and is made of tiny crystals. All of these properties are found through observations made throughout the lab.
The process of creating these two esters are also similar in exception to the alcohol added to the salicylic acid (carboxylic acid) as in both scenarios sulfuric acid (an inorganic acid) is added to the flask with salicylic acid and the alcohol and said flask is then heated in a water bath. The solution is then cooled and filtered in order to separate the crystals from the rest of the solvent. This therefore emphasizes the difference which a single carbon atom could make in a reaction. Further looking at my results, it is easy to spot that we had quite a low percent yield of the acetylsalicylic acid at only 22.25%.
Comparing to other groups who had received percent yields upwards of 75%, it is quite alarming to see the difference. This therefore opens up the possibility that experimental error had plagued our investigation. The most logical error would be that the many of the crystals were not filtered out during the filtration process and were thrown out unknowingly with the solvent (acetic acid). It was most likely that this was during the 2nd round of filtration after the purification process as the first time around the aspirin was still at 2.45 g which would have been a still abysmal but higher 62% yield.
The reasoning for this non crystallization would most likely have stemmed from the fact that the solution was not cooled enough to allow complete crystallization (this was due to the time limit of the period) and since the ‘ice cold water’ had warmed up slightly due to the waiting process. This being said, the percent yield of the aspirin does not affect the knowledge and understanding gained from the performance of the lab.