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Apple-tab-span {white-space:pre}ol.ol1 {list-style-type: decimal}Emilia TannerMary Parrish, Malyssa CalarcoKhalilia TillettJanuary 27, 2018Experiment 2: Acid-Base Extraction – Separation of an Organic Acid, a Base, and a Neutral CompoundIntroduction/Background Acid-base extraction is a common procedure used to separate organic compounds from each other based on their acidic or basic properties. An acid-base extraction is a form of a liquid-liquid extraction and usually involves varying solubility levels in water and organic solvents. Organic solvents may be any carbon-based liquid that is mostly insoluble in water. In this experiment the carbon-based liquid used is ether.

Many reactions of organic compounds require extraction at a stage of product purification. Extraction results from the unequal distribution of a solute between two immiscible solvents (2).  Certain requirements and principles must be met when choosing a solvent for the experiment. Solvents must be immiscible and have a favorable distribution coefficient in order for the component to be separated. Solvents also cannot react chemically with the components of the mixture and the solvent must be able to be readily removed from the solute post-extraction. The solvent must be nontoxic and nonreactive in order for the extraction to be effective (3). The two immiscible solvents will form separate and distinctive layers that can be removed and separated using the separatory funnel.  The solubility properties of organic bases and acids and their salts allow us to separate materials from each other and other neutral organic molecules.

 Experimental SectionA 3g amount of a solid mixture containing equal parts benzoic acid, 4-chloroaniline, and naphthalene was weighed in a 125 mL Erlenmeyer flask. The mixture was dissolved in 30 mL of diethyl ether and transferred into a 125 mL separators funnel using 20mL fresh ether to complete the transfer. 30mL of 5% HCl was added and capped then shaken vigorously. The cap was unscrewed to vent. The lower layer was drawn off into a 125 mL Erlenmeyer flask labeled flask #1. 3M NaOH was added dropwise in order to generate the amine. pH paper was used to ensure the solution was basic.

The flask was then cooled on ice for 15 minutes. After the precipitate was formed, the solid was collected by vacuum filtration. The remaining product was rinsed with small amounts of cold ice water and the dry crystal was shaped out of the buchner funnel. The crystal was pressed dry between two pieces of filter paper.

50 mL of 5% NaOH was added to the ether solution. The solution was capped and shaken vigorously with frequent venting. The stopper was removed and the aqueous later was drawn off into a flask labeled #2.

6M HCl was added to acidify the contents of flask #2 while cooling in an ice bath. The precipitate, benzoic acid, was collected by vacuum filtration and washed with iced water. The product was dried between filter paper.

The organic layer in the separatory funnel contained naphthalene and 20mL of saturated sodium chloride was added in order to remove any traces of residual water present. The bottom layer was collected and discarded into the aqueous waste container. The ether layer was drained into a 125 mL Erlenmeyer flask labeled flask #3. Anhydrous sodium sulfate was added in order to dry the organic layer. The drying agent was filtered into a 125 mL vacuum flask and rinsed with fresh diethyl ether and then added to the vacuum flask. The ether was evaporated using a vacuum pump evaporator. The dry naphthalene product was weighed and the melting points of each precipitate were determined.

To conclude the experiment the melting points of each were compared to the literature values in order to determine their respective purities. Table of Chemicals Results Discussion Since the percent recoveries of the benzoic acid and the 4-chloroaniline were less than 50% we can assume that an error was made during the experiment. The melting point for benzoic acid was between 68 and 71 degrees Celsius, about ten degrees lower than the actual melting point of benzoic acid, thus we can conclude that our product was not pure benzoic acid. The melting point of 4-chloroaniline was approximately 122 degrees Celsius, three degrees higher than the melting point of pure 4-chloroaniline. Napthalene had the greatest percent recovery but the melting point was about three degrees lower than the actual melting point of pure Napthalene. Sources of error could include extracting more than one layer at a time during the experiment, causing the products to be impure which can affect the melting points. Another source of error could be the original amount of solid that was used to begin the experiment as we measured out 3.68 grams instead of 3 grams.

It is very common to misidentify the layers during extraction which can lead to discarding of the wrong layer. Conclusion Extractions are used as a way to separate a desired substance when it is mixed with other liquids. Extractions result from unequal distribution of solute between two immiscible solvents. They typically involve liquids with differentiable solubility levels in water and an organic solvent. In order for an extraction to be effective the solvents must have a favorable distribution coefficient (1). The information from the data reveals that we were successful in separating/extracting and determining the melting points of the substances however some error did occur causing the percent recoveries to be less than desirable.

The theory of the acid-base extraction is to separate and group certain organic compounds together that have the same functional group. An important part of extraction is to ensure that the desired product dissolves in one of the immiscible solvents (3). ReferencesUMass.

Acid-Base Extraction

pdf (accessed Jan 27, 2018).Libretexts. Acid-Base Extraction (accessed Jan 27, 2018).Weldegirma, S. Experimental Organic Chemistry: Laboratory Manual for CHM2210L and CHM2211L; ProCopy, Inc.


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