Acid-Base Extraction ● Introduction: Chemical separations in liquids such as oils, salt water, and alcohol is traceable throughout our civilization. This has led to multiple methods and processes to separate compounds. One separation/purification example is acid-base extractions. this is useful for when a compound does not have the specific properties or isn't a dominant material in a mixture and purity methods like recrystallization would be a poor choice and other methods such as partitioning by means of extraction a far more effective choice. In this acid-base experiment, an unknown mixture consisting of a solid neutral compound and a solid carboxylic acid. Both compounds are soluble in ether and insoluble in water. The extraction solvent will be an aqueous solution of 10% NaOH since its pH properties are ideal in creating two immiscible layers of a base extract and a neutral organic. It is my hypothesis, that by utilizing methods for drying out the two separated solutions and recrystallizing them, we can successfully identify the solutions and their purity by taking their melting point temperatures and correlating it to a known data table of MP ● Chemical Properties and safety As with any experiment, safety is crucial in the lab. The chemicals used in this experiment are listed below. An itemized list for each compounds individuals hazard(s) is listed in Table A. Chemical formulas, structures and other relevant data can be found in Table B Table B ● Mechanisms Deprotonation using sodium Hydroxide Protonation using HCl ● Procedure: Take 2 g unknown compound dissolved in (30 ml) ether and place in separatory funnel. Extract solution twice, each with (15 ml) 10% NaOHaq ensuring first base extraction is removed into separate glass container before start of second extraction. Transfer the neutral organic upper layer to clean glass container and use anhydrous sodium sulfate to remove any water in solution. Add (25 ml) of 3M 10% HCl to the base extract to form benzoic acid. Test acid strength for proper pH level. Allow to cool and recrystallize. Decant the upper layer neutral organic compound and evaporate to form a solid. When both compounds are crystallized, filtered and dry, then record compounds individual weight, determine % recovered and take MP to identify compounds. ● Data and observations Unknown Initial Weight MP Final Weight Compound (P) 2.039 g 120-123 C .988 g Natural Organic ----------- 61 C .96.9 g 𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑒𝑎𝑐ℎ 𝑐𝑜𝑚𝑝𝑜𝑢𝑛𝑑 . 988 𝑔 % 𝑅𝑒𝑐𝑜𝑣𝑒𝑟𝑦 𝑜𝑓 𝑢𝑛𝑘𝑤𝑛 = ( )=( ) 𝑥 100 = 𝟗𝟔. 𝟖% 2029 (𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑚𝑖𝑥/2) 2 % 𝑅𝑒𝑐𝑜𝑣𝑒𝑟𝑦 𝑜𝑓 𝑁𝑎𝑡𝑢𝑟𝑎𝑙 𝑂𝑟𝑔𝑎𝑛𝑖𝑐 = ( ● . 912 ) 𝑥 100 = 89.4% 2.039 2 Discussion/Conclusion In this experiment, unknown compounds were identified using liquid acid base extraction methods. The compounds were mixed tighter in an equal 50/50 ratio. Melting points were taking of the extracted compounds to determine identity and purity. Acid base extraction proved to be very successful at doing this. Organic molecules have a degree of solubility not just in water, but in specific organic solvents as well. And since equilibrium is ultimately the goal of any reaction, the solute involved will establish equilibrium concentrations in both the solvents based upon its relative solubility in each of them. This process is called partitioning, and to be effective, then the solutions involved need to be soluble in specific amounts in order to effective and of any practical use. We determine this by utilizing a partitioning coefficient. This coefficient gives a numerical value that shows how much each solute (layer) will be present at equilibrium because even after the partitioning takes place to separate the liquids, some amount of solute will remain unseparated at equilibrium. The larger the coefficient, the more extraction we will get. Partitioning in of itself, is a slow process when solely dependent on molecular randomness. But when partitioning in a controlled setting such as an organic chemistry laboratory, then we can increase the process speed and effectiveness by utilizing the pH of the solutions involved to make the separation process quick and very effective. This idea/process can be controlled by effectively choosing correct immiscible compounds but with specific ideal pH levels in order to yield high extraction amounts with total % ionized being predicted by the partitioning coefficient values Since partitioning coefficients are prescribed by the solubility capabilities and are necessary to effectively obtain results that are of any use, then we needed to employ a liquid solvent that can be able to effectively dissolve. The extraction solvent used in the experiment was an aqueous solution of 10% NaOH because it’s pH properties allowed the deprotonation of the carboxylic acid to form a soluble salt(sodium hydroxide) in the aqueous layer of the two newly formed immiscible layers. To repronate, hydrochloric acid was used with the base extract, because it donates a proton to the salt and reforms benzoic acid which forms a compound that is insoluble in aqueous solution.
