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Extraction of an Unknown Compound

By kirbymk Jul 29, 2013 821 Words
Kate Kirby
June 6, 2013

Title: Extraction of an Unknown Compound
Purpose: The purpose of this experiment was to separate a mixture of two or more unknown compounds and identify them based on their melting point and reactivity with an acid or a base. Compound studied/Reactions: The organic solvent used in this experiment was methyl t-butyl ether (MTBE, 2-methoxy-2-methylpropane). The unknown that dissolved in the MTBE, but was insoluble in water. MBTE is very volatile and flammable. It was determined in the experiment that the unknown was an organic base (an amine) that reacted with aqueous acid (HCl) to form a water-soluble salt. This reaction is seen below: RNH2 + HCl(aq) ( RNH3+Cl-(aq)

Procedure: It was determined prior to carrying out the experiment that the unknown compound that was used contained a basic compound, not the acidic compound. One gram of the unknown was placed into an Erlenmeyer flask with approximately 30mL of MBTE. The solution was swirled and stirred until all of the unknown solid was dissolved, it was then decanted and placed into a separatory funnel. The unknown mixture contained a basic compound so 15mL of HCl was added to the separatory funnel and shaken up to mix. With the stopper in place on the separatory funnel, the two layers separated, the bottom layer was drained into a beaker, this was the water layer of the solution and set aside for further testing later. To recover the neutral compound from the ether solution, 15mL of saturated aqueous NaCl was added to the separatory funnel using the same technique as before. The bottom layer was drained and discarded in the sink. The remaining layer, the ether layer, was poured out of the top of the funnel into a Erlenmeyer flask with several scoops of anhydrous MgSO4 to dry the ether solution. The solution was decanted into a 100mL round bottom flask and the ether was removed using a rotary evaporator. The remaining solid, which was the neutral organic compound, was scraped from the flask onto a piece of filter paper and allowed to dry completely. The aqueous solution that was collected from the separatory funnel earlier in the experiment was placed in an ice bath for a few minutes to cool. After the solution was cooled, approximately 15mL of 3M NaOH were added in small amounts until it was acidic, at which point the solution turned milky white and the solid amine precipitated in the solution. The precipitated solid amine was collected using suction filtration in a Buchner funnel until the solid was dry. The solid collected was the base compound. Finally, the melting points of both of the solids collected were calculated and used to identify the unknowns. Results:

|Solid extracted |Melting Point Range |Identification | |Neutral component |98.6-113.0 (C |Acetanilide (MP: 114-116 (C) | |Amine solid |77.1-82.8 (C |Ethyl 4-aminobenzoate (MP: 88-90 (C |

Discussion: The unknown compound that was used for the extraction contained a basic compound. The first solid that was extracted and collected was the neutral organic compound, which was a white crystal like solid. The solid was dried and several crystals were used to calculate the melting point. The melting point of the neutral compound was then compared to the melting points of three neutral compounds given in the lab manual and it was determined based on this data that the neutral unknown compound was acetanilide. Similarly, another solid was collected through the extraction of the unknown compound after NaOH was added to the aqueous solution collected from the separatory funnel and dried using suction filtration. This solid component was found to be the solid amine. The melting point of the solid amine was taken and compared to the melting points of other basic compounds given in our lab manual. Based on the information collected, the unknown amine solid was determined to be ethyl 4-aminobenzoate. The melting point range of the amine solid did not match the melting point ranges of any of the compounds given in the lab manual, but the melting points most closely related were that of ethyl 4-aminobenzoate so this was the identification that was chosen. The procedure did go as expected and all of the steps were successful with clear results that followed the expected results given in the lab manual. The evidence used to determine a successful experiment were the melting points of the two solids collected which were identified based on the melting points of the expected outcomes given in the lab manual. The unknown compound was made up of acetanilide and ethyl 4-aminobenzoate, which were both successfully extracted through the experiment. Conclusion: The extraction of a neutral component and a basic, amine component, was successful. The melting points of the two solid components lead to the conclusion that the unknown compound was composed of acetanilide and ethyl 4-aminobenzoate.

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