Preparation and Purification of an Alkyl Halide DOCX

Title	Preparation and Purification of an Alkyl Halide
Author	Konrad Magboo
Pages	2
File Size	165 KB
File Type	DOCX
Total Downloads	154
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Page |1 Preparation and Purification of an Alkyl Halide Konrad Frederick Magboo1 and James Daniel Corpuz2 1 Department of Food Science and Nutrition, College of Home Economics, University of the Philippines Diliman, Quezon City, Philippines 2 Institute of Chemistry, University of the Philippines Dil...

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P a g e " 1 Preparation and Purification of an Alkyl Halide Konrad Frederick Magboo1 and James Daniel Corpuz2 1 Department of Food Science and Nutrition, College of Home Economics, University of the Philippines Diliman, Quezon City, Philippines 2 Institute of Chemistry, University of the Philippines Diliman, Quezon City, Philippines A B S T R A C T To demonstrate the formation of an alkyl halide, tert-butyl alcohol was reacted with cold, concentrated HCl to form tert-butyl chloride. The tert-butyl chloride was then dried with anhydrous CaCl2 and decanted to a 25-mL round-bottom flask. The supernate which contained the crude tert-butyl chloride was then distilled at 49-52 and was collected in a pre-weighed vial and cooled in an ice bath. 0.3 mL of tert-butyl chloride was collected through distillation. The experiment had a 6% yield of 0.3 mL of the alkyl halide prepared from the 5 mL of tert-butyl alcohol. 1. Introduction Alcohols undergo a nucleophilic substitution with HX (X is Cl, Br, I) to yield an alkyl halide and water. Tertiary alcohols such as Tert- butyl alcohol readily react with Alkyl Halides because the reaction starts first by the protonation of the OH- group and the formation of the tertiary carbocation which is a stable carbocation. The carbocation will then bond with the Halide anion forming the Alkyl Halide. Alkyl halides are compounds formed from the replacement of a hydrogen atom of an alkane with a halogen (F, Cl, Br, I). They are classified according to the Carbon in which the halogen is bonded. Primary, Secondary, and Tertiary classifications are given. The more acidic the alkyl halides, the more reactive they are. This is because the conjugate bases of hydrogen halides are very weak (except F). The heavier the halogen, the less electronegative they become, thus making them more willing to become ionized. The most reactive hydrogen halide is Hydroiodic acid. In the experiment, cold concentrated Hydrochloric acid will be used. (Solmons, Fryhle, 60-61) The reaction to be studied is the conversion of alcohols into alkyl halides. Alcohols (R-OH) are organic compounds bonded to an OH- group. They are also classified the same way as the alkyl halides. They are classified according to the Carbon in which the hydroxyl group is bonded. Primary, Secondary, and Tertiary classifications are given. In the experiment, the tertiary tert-butyl alcohol was the specimen to be converted. Alcohol reactivity increases with number of substituents of the Carbon where the OH- is bonded. Therefore, tertiary alcohols are the most reactive to hydrogen halides. (Solomons, Fryhle, 481) The equation below is what the experiment aims to demonstrate: (Wikipedia)* 2. Materials and Methods 2.1. Reacting and Preparing the Alkyl Halide solution 10 mL Cold concentrated HCl was mixed with 5 mL tert-butyl alcohol in a dry 50-mL separatory funnel. It was then left undisturbed then the aqueous layer was removed. The organic layer was transferred to a dry flask containing a small amount of solid NaHCO3 to neutralize the excess HCl solution. It was decanted again to another dry flask. The decanted filtrate was finally dried with a small amount of anhydrous CaCl2. 2.2. Purification of the Alkyl Halide solution The crude tert-butyl chloride was transferred into a dry 25-ml round bottom flask and was added with a few boiling chips. It was distilled at 49-52 and was collected at a pre-weighed and pre- cooled vial. 3. Results and Discussion 3.1. Reagent Analysis and Use in the Reaction The experiment used cold concentrated HCl, solid NaHCO3, and anhydrous CaCl2. Cold concentrated HCl was used because tertiary alcohols readily form an alkene with an acid at relatively mild heat through E1 mechanism. It is also added in excess because the tert- butyl alcohol is the limiting reagent for the reaction. HCl is the excess reagent. (Solomons, Fryhle, 280) The concentrated NaCl solution was used to facilitate the separation of layers. This is because NaCl is aqueous and that it will help differentiate the aqueous layer from the organic layer. It is not miscible with the organic layer. Therefore it will go with the aqueous layer. Solid NaHCO3 is used to neutralize the acid HCl. Sodium bicarbonate when reacted with HCl will form Sodium Chloride, and Carbonic acid, which forms water and carbon dioxide in an equilibrium reaction. The solution will still be acidic, although it will only contain the weak acid H2CO3. (Analytical Chemistry Academic Group, Analytical Chemistry 2013 ed.). Anhydrous CaCl2 is used to absorb most of the water in the tert- butyl chloride solution. The H2O will not be fully removed through decantation. On the other hand, anhydrous CaCl2, will absorb water and reduce the number of water in the crude tert-butyl chloride solution. Since this will reduce the amount of water, it will shift the equilibrium reaction of Carbonic acid forming water and carbon dioxide towards the formation of more products. The boiling chips were used in the distillation set-up because they have holes to trap air and allow the formation of bubbles of solvent vapors. This reduces the incidence of bumping which reduces the loss of solution. (University of Colorado, Organic Chemistry at CU Boulder) *For demonstration purposes of the picture only E-mail address: [email protected]...