CHEM 121 Lab Report 8 - Organic Synthesis Portage Learning

CHEM 121 Lab Report 8 - Organic Synthesis (Portage Learning)

Name:

Date:

Experiment: 8

Title: Organic Synthesis

Purpose: in this lab we will carry out the synthesis of several carbon-containing organic

compounds: 1. Aspirin, 2. Urea and 3. Salicylic Acid

We will synthesize aspirin also known as acetylsalicylic acid.

Procedure:

Aspirin synthesis

• 2 grams of salicylic acid in a flask and 5 mL acetic anhydride in a graduated cylinder. Combine

the two but as we see nothing happens. It needs a catalyst. Small amount of sulfuric acid - 5 drops preferred. Next we heat in the hot water bath. One of the acetyl groups will replace the H on the O of salicylic acid. After 15 mins, we can see the majority of the solid will have dissolved. Next we will add water while it is still hot. To destroy any left over acetic anhydride.Letting the flask cool then add more water to kill the acetic anhydride. Then add 40 mL of ice water. Cannot see through the white solid meaning it has crystallized. Next to cool further more in ice water. While its cooling scratch the bottom to induce crystallization better. Once its cool we will filter it. We will now be doing suction filtration. Once the liquid is off and the slid is trapped on the pad we will wash some more with ice cold water to rinse of any salicylic acid or sulfuric acid that is left.

• Now we are going to do a test. With two test tubes with water in them. When the phenol group

has ferric chloride to it will give a purple color. As we made aspirin we got ride of the phenolic group but was replaced an acetyl group to now have an acetylsalicylic acid. Which will give us a faint purple color. There is proof positive that the phenol groups are gone.

• Next we are going to determine whether you have the substance you want and they do this by

the melting point apparatus. The one that was used in the video is called a Mel-Temp, melting temperature. The device is made up of a shield, a heated cylinder, melting point capillary, Melting point tube, a window to see the substance in the melting point apparatus. The temperature rises from 51.5 degrees Celsius.

• We are now doing the melting point of the sample of aspirin. Starting temperature is 126 C and

aspiring needs more to melt. Now it has risen to 131 and is melted at 133.8 C.

Urea Synthesis

• In this experiment we will synthesis urea. We will first start with two inorganic compounds,

lead cyanate and ammonia.

• Two previously prepared solutions of potassium cyanate and lead nitrate. We are going to mix

them to make lead cyanate. And it will be used to prepare the urea. A white precipitate has formed. Time to cool the solution to get a maximum yield of lead cyanate. After it is cooled we 1 / 2

will filter this solution and obtain the white crystalline lead cyanate, from which we will continue the experiment to make the urea. After 15 mins of cooling of potassium cyanate and lead nitrate, and we can see the white solid on the bottom of the beaker. Now we will filter and isolate the lead cyanate and then we will react with the ammonium hydroxide and that should form urea after about 90 minutes of heating. After filtering, the bed of the filter has the white solid of the lead cyanate. Now we are going to take this and react it with ammonium hydroxide and it will then produce the urea. 90 minutes later, now filtering the suspension. In solution the liquid should be urea. After the liquid is filtered we should have the final product. Now we will cool the cloudy liquid.

• For the melting point of urea we have started with the temperature at 125 and it is still not

melted. Begins to melt at 127.5. it is melted at 133.2 C.

Salicylic Acid Synthesis

• in this experiment we are going to make salicylic acid from its ester, methyl salicylate, which

is oil wintergreen.

• There is an apparatus set up of 50 milliliter round bottom flask above a bunsen burner. 1.3 mL

of methyl salicylate to the flask now we are going to add 6 M sodium hydroxide. Then with that combined a white solid should form then it will dissolve as it is heated. So we can heat we will add a couple of boiling stones to the flask then we are going to put a water cooled condenser above the flask. This water cooled condenser is just a tube.

• We are going to heat this for 30 minutes to allow the reaction to take place producing salicylic

acid from methyl salicylate. Then we will isolate the product then study it then the MP.

• After 30 minutes, we refluxed this mixture of methyl salicylate and sodium hydroxide and now

we are going to take the mixture and cool it for a few minutes. Now there is not white solid but it is now in solution. Now we are going to isolate the salicylic acid product by adding acid till we get it down to a low pH. Now pour the methyl salicylate/sodium hydroxide in a beaker and add a little bit water. Then add 3 M of sulfuric acid to allow the salicylic acid to precipitate out.We are now testing the pH of the liquid and now the pH paper is orange we want it to become red. We want the pH to be either 1 or 2. Now we will filter and isolate it.

Data/Results/Calculations:

• melting point of aspirin is 133.8 C
• Weighing bottle mass = 19.38 g
• The total mass = 20.80 g
• Mass of aspirin = 1.42 g

Aspirin MP nad % yield

MP = 133.8 C

Moles of salicylic acid = 2.0 g / 138 = 0.0145 mole Expected moles of aspirin = 0.0145 mole Expected mass of aspirin = 0.0145 x 180 = 2.61 g Actual mass of aspirin = 1.42 grams % yield = 1.42 / 2.61 x 100 = 54.5 %

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