Organic Chemistry Lab 343
Lab Report 3
24 September 2018
Lab Section 1
Extraction of Acidic and Neutral Compounds
The objective of this experiment is to separate out a neutral compound and an acidic compound from a mixture using acid/base extraction. The main components in this lab are the separation and purification of the components. The method for separation of the components for this lab is liquid/liquid extraction.
Record the assigned unknown. Unknown B
Weigh out approximately 0.5 g (500 mg) of the unknown solid mixture provided by the TA. Record the mass to three decimal places. The weight obtained of Unknown B was 0.5002 g.
In a 25-mL Erlenmeyer flask, dissolve the mixture into 8-10 mL of diethyl ether. Once dissolved transfer the solution to a 125-mL separatory funnel. Rinse the Erlenmeyer with another mL or 2 of ether to complete the transfer. 10.0 mL of diethyl ether was used to dissolve the unknown mixture, then 2 additional mL of ether were used to rinse the flask in order to complete the transfer.
Add 10 mL of saturated sodium bicarbonate solution to the separatory funnel. Note the separation of the two layers… Stopper the funnel, invert, and shake, venting frequently. 10.0 mL of saturated sodium bicarbonate solution were added to the funnel, which was then shaken and vented repeatedly.
After the layers have been thoroughly mixed, return the separatory funnel to the ring stand and allow the layers to settle. When a clear separation of the layers is noted, drain the bottom (aqueous) layer into a clean 50 mL beaker labeled “aqueous.” Leave the ether layer in the separatory funnel. Repeat steps 2 and 3 two additional times, draining the aqueous layer into “aqueous.” Once the solution settled, two distinct layers appeared. While the layers were similar in color, they were very easy to tell apart.
Add 10 mL of saturated sodium chloride solution to the ether layer in the separatory funnel. Stopper the funnel, invert, and shake, venting frequently. After the layers have been thoroughly mixed, return the separatory funnel to the ring stand and allow the layers to settle. When a clear separation of the layers is noted, drain the bottom (aqueous) layer into a beaker or Erlenmeyer flask and set aside for eventual discard. 10 mL of saturated sodium chloride were added to the ether layer in the funnel.
Carefully pour the ether layer into a clean, dry Erlenmeyer flask (25- or 50-mL). Dry the ether extract over anhydrous sodium sulfate. Gravity filter the extract into a clean, dry, tared 50-mL side-arm flask “Ether Extract” and set it (uncapped) under the designated large fume hood while you work with the aqueous solution. The weight of the side arm flask without the extract was 54.3 g. After the gravity fitration was completed, the flask was labeled then placed under the fme hood.
Place the Aqueous beaker in an ice bath and cool for several minutes. Keeping the Aqueous beaker in the ice bath, proceed to the fume hood to add the HCl solution. Working under the hood, slowly add dropwise 6.0M HCl to the Aqueous beaker (keep the beaker in the ice bath during the addition of the acid). Check the pH of the aqueous solution with litmus paper periodically. Note when precipitate begins to form. Continue the HCl addition until the litmus paper indicates that contents of the beaker are acidic and no further formation of precipitate is noted. Allow the Aqueous beaker to cool in the ice bath for an additional 5 minutes at your bench. HCL was added to the beaker at a rate of approximately 2/3 mL. every minute or so. Initially, the solution was very basic (about 12 or so) but after several mL of HCL were added, the pH dropped to closer to 3. Precipitate began to form after approximately 4-6 mL of HCL were added to the solution. The beaker was left to cool for another 5 minutes.
Isolate the precipitated benzoic acid via vacuum filtration, allowing the solid to dry on the vacuum for 10-15 minutes. Record the mass of the benzoic acid. What percentage of the original mass (of the solid mixture) corresponds to benzoic acid? Obtain a melting point range for the benzoic acid. If it is too low or too broad, recrystallize your product from hot water and try again. Vacuum filtration was completed to isolate the precipitate, which was left to dry. The precipitate took approximately 15 minutes to fully dry. The weight of the filter paper was 0.3474 g, and the weight of the filter paper with the benzoic acid was 0.7908 g, indicating that the weight of the benzoic acid was 0.4434 g. The melting point obtained was 121.1 – 122.2 deg C. Because the melting point was close to the recorded melting point of benzoic acid, no recrystallization was performed. The percentage of benzoic acid in the original mixture was approximately 88.68 %.
Remove the “Ether Extract” from the hood. You should note a decrease in the volume of ether. To remove any remaining ether, stopper the side-arm flask and evaporate the ether under vacuum until the solid 1,4-dimethoxybenzene is dry. Record the mass of the 1,4-dimethoxybenzene. What percentage of the original mass (of the solid mixture) corresponds to 1,4-dimethoxybenzene? Obtain a melting point range for the 1,4-dimethoxybenzene. Again, if too low or too broad, recrystallize from hot ethanol/water and try again. The ether extract was taken from the hood, and it was observed that most visible ether had already evaporated out. Just to be precise, however, the ether and 1,4-dimethoxybenzene were further evaporated under a vacuum for several minutes. The mass of the 1,4-dimethoxybenzene was approximately 0.0566 g, and the melting point was 55.2 – 56.4 deg C. Like the benzoic acid, the 1,4-dimethoxybenzene melting point from the sample was significantly close to the recorded melting point, so no recrystallization was deemed necessary. The percentage of the original mass that was 1,4-dimethoxybenzene was approximately 11.32 %.
Final Mass: 0.4434g
% Recovery: 88.68%
Melting Point Range: 121.1-122.2 degrees Celsius
Final Mass: 0.0566g
% Recovery: 11.32%
Melting Point Range: 55.2 – 56.4 degrees Celsius
IR Spectroscopy and setup pictures below
The reason we used a basic substance saturated sodium bicarbonate was to remove the acidic component (benzoic acid) of the ether. This moved it to the aqueous layer which then could be funneled out with the separatory funnel.
The chemical reaction is mixing the benzoic acid in diethyl ether and sodium bicarbonate to produce sodium benzoate and CO2. That chemical reaction is:
C6H5COOH + NaHCO3 —> C6H5COONa + H2O + CO2
The reaction above made benzoic acid into a benzoate ion and made it soluble in water. It seems that a compound, when turned into an ion, makes it more soluble in water.
The reaction of 3-nitroaniline and HCl deprotonates 3-nitroaniline and turns its NH2 into a NH3+. When you extract this now in the aqueous layer, turning it back is just adding sodium hydroxide until the compound turns basic again.
The main differences between the two compound 3-nitroaniline and Benzyl would be as such:
3-nitroaniline would have a peak around 1080-1360 representing C-N Bond, but the Benzyl would not.
3-nitroaniline would have a peak around 3300-3500 representing N-H Bond, but the benzyl would not
3-nitroaniline would have a peak around 1515-1560 & 1345-1385 representing N-O bond, but the benzyl would not.