The Chemical Importance of Purity Acquired Through Recrystalization and Analyzed by Melting Point

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1 The Chemical Importance of Purity Acquired Through Recrystalization and Analyzed by Melting Point Codi Gail Hefner 1 and Brenton Matulka 1 1 University of Northwest Missouri State University Abstract: The subject of this study was to successfully recrystallize vanillin after contamination with sucrose and dust then to analyze the melting point to determine its purity. The melting point of the recrystallized vanillin should be close to the melting point provided by chemical literature and the contaminated sample should be significantly lower. The impure mixture was dissolved in hot water and subjected to gravity filtration to remove the impurities. The sample of aqueous vanillin was then left to recrystallize in an ice bath and then vacuum filtered using a Buchner funnel. Analyzation through melting point provided data showing that the crystalized vanillin was more pure than the original mixed sample. Mixed melting point is lower than a pure sample, implicating that there are stronger intermolecular forces that hold a pure crystal lattice together; therefore, making the melting point higher while an impure melting point will have lower intermolecular forces and a lower melting point. With proper recrystallization methods, recovery of a pure product can be determined by comparison to the melting point provided by the chemical literature. The significance of reaching purity by recrystallization of a mixture could be commercially important in the formation of medicines, food products, and cosmetics. Introduction: Recrystallization is a process used to recover a contaminated sample because of chemical properties of: solubility in water and ability to reform a crystal lattice. Separation of vanillin from insoluble impurities and sucrose can be used to demonstrate this process. The first step to recrystallization is choosing an appropriate solvent. Water is used because it will saturate well with vanillin and sucrose at higher temperatures. However, at 25 C sucrose remains dissolved in water because of water s polar properties, while vanillin does not. Water also readily passes through filter paper and is inexpensive. Second, dissolve solutes in water till saturation. Sucrose should mostly be dissolved because of its solubility at room temperature. However, vanillin needs to be dissolved at higher temperatures. This may be accomplished though boiling the solution on a hot plate and occasionally swirling. An Erlenmeyer flask is ideal to use during this step. Pour the solution through filter paper while the solution is still hot to remove the insoluble impurities. If the solution is allowed to 1 - Codi Gail Hefner and Brenton Matulka: Northwest Missouri State University

Solutes: Vanillin Sucrose Organic Structures: Melting Point: 80 º C 186 º C Solubility: Soluble in hot water Soluble in hot and cold water Table 1: Properties of vanillin and sucrose: meltinng point,

cool before it is poured, it is possible for the vanillin to come out of solution and start crystalizing; therefore, the filtrate would contain some sucrose but not vanillin.

2 Solutes: Vanillin Sucrose Organic Structures: Melting Point: 80 º C 186 º C Solubility: Soluble in hot water Soluble in hot and cold water Table 1: Properties of vanillin and sucrose: meltinng point, solubility, and structure. cool before it is poured, it is possible for the vanillin to come out of solution and start crystalizing; therefore, the filtrate would contain some sucrose but not vanillin. A process called decantation can be used to pour off the liquid solution while leaving behind the insoluble solids which may be helpful. Now, the solution should be allowed to cool slowly to room temperature. Because vanillin is insoluble in cold water, it will start to fall out of solution and form crystals. The speed of this process is critical for the purity of the product: slow cooling optimizes crystal formation. As the crystals of vanillin start to form, the sucrose and water molecules will be pushed out and not be trapped allowing for the purest and largest crystals. After the solution has cooled to room temperature it can be placed in an ice bath. Do not swirl or cause many movements during crystal formation because it will disrupt the lattice positioning between adjacent molecules causing small crystals and many nuclei with large surface areas. Additionally, a sample of water should also be cooled during this process. Finally, after crystals have formed, a Buchner funnel can be used to filter the crystals out of the sucrose and water. Gently pour the solution contain crystals into the funnel head and apply a vacuum to suck the water into the flask. The remaining sucrose should be dissolved in the water and should ideally follow into the flask. However, some sucrose is always left behind between or on top of crystals; therefore, it is necessary to rinse the crystals with the water that was cooled earlier. Do not use warm water because it will dissolve the vanillin. Expectantly, this is sufficient enough to drag the sucrose into the flask leaving behind pure water and vanillin crystals. The vanillin crystals are now only contaminated by water, but sufficient drying (evaporation) should resolve this problem. After all the water evaporates, the sample can be evaluated a melting point apparatus: Mel Temp. Two samples must be packed tightly the closed ends of capillary tubes, one for a quick run and one for a slow run. Identification of a compound can be achieved by running a pure melting point versus a mixed melting point of a sample. 1 The quick run for melting point should be increased by 8 C every minute to provide a general idea of where an actual melting point for the material is. The slow run should be increased within 20 C of the quick run s melting point results and increased by 1-2 C per minute to allow the sample s internal temperature to match the temperature reading for more accuracy. 2 - Codi Gail Hefner and Brenton Matulka: Northwest Missouri State University

3 Melting Point ( C) The melting point of the recrystallized vanillin should be approximately 80 C if it is a pure sample. However, the crude mixture should be lower because of the intermolecular forces held between molecules will be disrupted. Specifically, the intermolecular forces existing between organic molecules that contribute to the specific melting point is mainly dipole-dipole forces which is the attraction between the positive and negative ends of polar molecules or bonds. Hydrogen bonding also contributes to the intermolecular forces by holding molecules closer together in the crystal form. Melting point is higher in molecules that have symmetry because they have larger surface area interactions. Additionally, mixed melting point is a technique used to identify if two unknown samples are the same compound. If two unknown samples are obtained, three melting points can be determined, each sample individually and one mixed. If the two samples do not have similar pure melting points it can be assumed that they are not the same sample. However, many materials have similar melting points; therefore the mixed melting point is important. 4 When one sample in the capillary tube begins to melt, the liquid will disrupt the intermolecular forces between the other molecules causing it to liquefy faster. Additionally, the symmetry between molecules is no longer maintained because generally, their crystal lattices are different. Therefore, the intermolecular forces are decreased because the surface area between molecules is decreased. The mixed melting point is always lower than either of the pure sampled melting points. The importance of obtaining and testing a pure sample is evident in medicines, food products, and cosmetics. If product contamination is suspected, the melting point of the product compared to a pure sample should give evidence of purity or not. 5 Experimentally, aspirin and acetaminophen have been evaluated and plotted for a better explanation as the purity decreases; melting point decreases (Graph 1). Mixed Percentage v. Melting Point High Low Average Mixed Percentage (Aspirin and Acetpminophen) Graph 1: Northwest Missouri State University. Fall 2012: Brenton Matulka and Codi G. Hefner 3 - Codi Gail Hefner and Brenton Matulka: Northwest Missouri State University

4 Discussion - Results Results of recrystallization of vanillin shows that the filtration techniques used with manipulation of the temperatures provided a pure sample (Table 1). Material: Crude Mixture of Vanillin Incomplete Re-Crystallized Vanillin 75º-76ºC Quick Run: Slow Incomplete 80º-82ºC Run: Table 2: Melting points determined by quick and slow run. The recovery of the contaminated crude sample by processes of water solubility, filtration ability, and crystal lattice formation provided a pure sample which supports the original hypothesis. This process can be used commercially to maintain integrity of a product. If contamination is suspected, melting point of the final crystals compared to the melting point of the crude mixture after a recrystallization process, purity can be determined. 5 Furthermore, the crude mixture of vanillin s melting point was determined incomplete. The mixed sample started melting around 74 C, however, through observation it was clear the that vanillin and insoluble impurities began to liquefy but the sucrose crystals remained in crystal lattice because the intermolecular forces creating the octagonal structure do not break until 186 C. Because of time constraints, the experiment could not be completed but was heated to 100 C. However, it was anticipated that the sample would have completely melted under 186 C because of the liquid vanillin wedging between the sucrose molecules and disrupting the intermolecular forces. Again, this occurrence is testable and provable by mixed melting point versus pure melting point experiments. Additionally, the quick run showed a lower melting point possibly because of water contamination. After the vanillin crystals were vacuum filtered using the Buchner funnel, the sample was not allowed adequate time to dry before being packed into the capillary tubes. The time allotted to drying presents a huge limitation. Future experiments could investigate the crude mixture of vanillin s melting point to compare to the recrystallized vanillin. Also, the mixed melting point of an optically pure sample compared to a racemic mixture can be evaluated to determine if diasteriomers or enantiomers have different melting points. 2 This can also be integrated in commercial product integrity: generic verses name brand pharmaceuticals. 3 Experimental: 1. Take a 2 gram sample of vanillin, sugar, and an unknown insoluble impurity. 2. Dissolve the sample by bringing the mixture to a boil on a hot plate. 3. Remove any extra suspended solids by gravity filtration while still hot. 4. Let sample cool to room temperature, then set in ice bath gently (avoid movement). i. If crystals do not form, use a glass rod and scrape the flask or implant tiny seed crystals. 5. Collect the crystals by using a Buchner funnel and rinse with 3-4mL of cold water to wash any leftover impurities. 6. Press the crystals firmly against the filter paper and allow to air dry to minimize any impurities. 7. After sample dries place in capillaries to run quick and a slow melting points. 4 - Codi Gail Hefner and Brenton Matulka: Northwest Missouri State University

5 Sources (1) Brown R. J. C.; Brown R. F. C. J. Chem. Educ. 2000, 77 (6), p 724 (2) Derdour, L.; Skliar, D. Cryst. Growth Des. 2012, 12 (11), pp (3) Ekrem, P.; Aida, S.; Mirza, N.; Bozo, B.; Husein, N.; Safeta, R.; Amir, M.; Cazim, S.; Melita, P.; Majda S. Health Med. 2011, Vol. 5 Issue 6, p , 6p (4) Irving A. K.; Henry Y. J. Chem. Educ., 1970, 47 (10), p 703 (5) Whetton, M.; Baryla, K.; Finch, H. Accreditation and Quality Assurance. August 2012, Vol. 17 Issue: Number 4 p , 5p 5 - Codi Gail Hefner and Brenton Matulka: Northwest Missouri State University

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