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Purification Techniques: In Application to impure Organic Compounds

Name: Elio Reyes ID: 010644549

Because there is an enormous variety of new and unknown compounds which are made by either mixing different substances or extracted from natural resources, it is crucial to separate and purify these compounds in order to identify an unknown organic compound or their chemical composition, molecular or structural formula. Thus, purification is a crucial technique that is useful when the solubility of impurities is quite dissimilar from the compound. The purification of a compound is important because not only does it lead to results that are on a telescope perspective but such purification can lead to efficient ways to lead the medical industry. The most common purification techniques in the organic chemistry industry are sublimation, crystallization and distillation. Sublimation can be defined as the transition state from solid to gas without going through the liquid state. The use of sublimation as a purification technique requires condensation from the gas phase to recover the solid phase. However, sublimation is not a process that can be considered an analytical technique instead it is a procedure in which compounds or mixtures can be purified or separated. One of the advantages of this purification technique is that it is applicable to a range of solids of inorganic or organic compounds and might be very useful when heat-labile materials are involved (Rao, 1996). Throughout the year’s sublimation as method of purification has been used to obtain high-purity materials as analytical standards. To illustrate, let ´s imagine you fill your ice cube trays with water and put them in the freezer for a night. The next day you check your freezer and you have ice cubes due to the process called freezing. Then, accidently you drop those ice cubes on the floor, and they will have melted in just seconds. Freezing and melting are very mutual phase transitions, sublimation is another too, excluding, and in this case it is a solid changing into a gas. Therefore, sublimating materials never experienced the liquid state. Techniques as such, will purify certain substances by the help of atmospheric pressure created by heat in closed containers such as pans, in which dissociation occurs. In other words, sublimation technique is used to purify the solids that have large high vapor pressures and high melting points. Another technique used in the organic chemistry labs that are used to seek purifications of compounds is Crystallization. This crystallization technique is most commonly used for the purification of solid compounds, which is influenced by solutes. Such compounds can and will be affected by the compounds physical properties such as saturation, the relationship is mainly based on the solutes and solvents and the help of heat. For example, when a saturated compound is set out to reduce its temperature than the used solvent will no longer dissolve, creating crystal that are of pure compound. The impurities are usually formed in the layer of pure crystals which is later removed by filtration. In order to crystallize and impure solid a hot temperature solvent

is added to help it dissolve at its fullest and both the impurities and desired compound will loosely travel through the high tempered solved; however once the solvent reduces its temperature the impurities and desired compound will began to create solid crystals and remains on the crystal surface. This process can be speed up by placing in an ice bath, and this solution is then filtered in order to remove the pure crystals and another solvent is later use to rinse one again and make sure that no impurities are present. In some cases, the extraction of impurities does not give a great percentage yield, and Recrystallization may be used. This is the process of dissolving in a solute the present crystal and recrystallizing. The success of recrystallization is usually based on the solubility of the crystals, and concentration of crystals. Most of the time the solvents that are commonly used are the very polar organic solvents such as ethanol and methanol, and this is because they have a high evaporation energy and are capable to dissolve compounds that are both polar or nonpolar . Water is also used in such and this is because water is polar, so it is easier for it to dissolve nonionic compounds. Another type of solvent that is used is the solvents with low polarity such as acetate. But working with such lab technique requires precaution, since the solvents used are highly flammable. One of the best ways to remember how solvents work in such process is “Like Dissolves Likes,” in other words a polar compound is more like to dissolve in a polar solvent. And lastly to determine the result, calculations are made and figured percent yield, if you yield is higher than increase by optimizing, if so then the technique used was a success (Kumana, 1990). The last technique of purification usually used in Organic Chemistry Lab is Fractional Distillation. This technique has been used for the separation of mixture of two or more liquid compounds whose boiling points differ by less than 60°-75°C. Moreover, a lot of vaporizations and condensations are done before the distillate is collected; as a result, both cause the vapor to become enriched in the more volatile compound. In other words, the components of a mixture may be separated due to their vapor pressure differences only if there is a considerable number of vaporization/condensation cycles are carried out in a fractionating column (McCabe, 1993). To clarify, the fractionating column is inserted between the distillation flask and the distilling head of the distillation apparatus and generates a large surface area where liquid-vapor equilibria can happen. As long as a vapor travels up, it cools, condenses into a liquid and then it evaporates again after it become into contact with hotter vapor rising. Consequently, if the fractionating column is efficient, the vapor that finally reaches the distilling head at the top of the column is composed of the component with the lower boiling point.

Cited Page

Kumana JD (1990) Run batch distillation processes with spreadsheet software. Chemical Engineering Progress 6: 53. McCabe WL, Smith JC and Harriott P. (1993). Unit Operations of Chemical Engineering, 5th edn. New York: McGraw-Hill. Rao S (1996). Engineering Optimization. New York: John Wiley....