Formal Report - Synthesis of an Alkyl Halide

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Experiment 6: Synthesis of an Alkyl Halide
Maria Alexandria Buraga Ammuyutan
Institute of Chemistry, University of the Philippines, Diliman, Quezon City 1101 Philippines -------------------------------------------------
Department of Food and Science Nutrition, College of Home Economics, Univeristy of the Philippines, Diliman, Quezon City 1101 Philippines -------------------------------------------------

Alcohols react with hydrogen halides (HCl is used in this experiment) to yield the resultant alkyl halides and water. The insolubility of the alkyl halide in water allows the separation of it from the aqueous layer using a separatory funnel. The alkyl halide, then, were purified by a simple distillation apparatus using boiling point differences between the pure tert-butyl chloride and not. In this experiment, tert-butyl chloride is synthesized from tert-butyl alcohol.

Alkyl Halides (also known as halogenoalkanes or haloalkanes) are a group of chemical compounds derived from alkanes containing one or more halogens. They are a subset of the general class of halocarbons, although the distinction is not often made. Alkyl Halides are widely used commercially and, consequently, are known under many chemical and commercial names. A number of methods were developed for its systematic synthesis. The most common preparation method is by reacting alcohol with hydrogen halides in extremely acidic environments. In this production method, tertiary alcohols were recommended to be used because of the stability and relative strength of the tertiary carbocation. Halogens will substitute with the hydrogen atoms to form alkyl halides through SN1 reactions. Experimental Detail

Before all else, the materials and the simple distillation set-up were prepared. 10 mL tert-butyl alcohol and 20 mL cold concentrated HCl was placed in a dry 30 mL separatory funnel while gently swirled. It is important to use cold concentrated HCl because keeping the temperature of the acid low will increase the fraction of the SN1 product so to increase the yield. Keeping it cold will help prevent loss of the volatile product after it is formed. The mixture was relieved by the internal pressure by slowly opening the stopcock from time to time. The mixture remained undisturbed for about 20 minutes then its layers were separated by removing the aqueous layer (To determine which the aqueous layer is, add 1-2 drops of water in each layer. The layer in which the water dissolves is the aqueous layer, which will be discarded into the waste acid bottle). The organic layer was then transferred into a dry flask which contained a small amount of solid NaHCO3. Solid NaHCO3 is the primary standard for acid-base titrations because it is firm and air-stable, making it easy to weight accurately. It is also used to speed up the decomposition of water in electrolysis. Again, it was swirled gently and decanted into another dry flask. The filtrate was then dried with anhydrous CaCl2 and decanted into a dry 25 mL round bottom flask. The crude alkyl halide product must be dried carefully with anhydrous CaCl2 before distillation to prevent hydrolysis of the Alkyl Halide during the distillation of the product. A few boiling chips were added to prevent it from suddenly overheating and the crude tert-butyl chloride was distilled. Without boiling chips, a liquid which is heated in a horizontal container might become superheated and "bump' all of a sudden, and occasionally discharges vapor. This sudden discharge of gas might result in the solution as well as the reagents to be spilled out of the container all of a sudden. A simple distillation set-up was prepared as shown in Figure 1. In simple distillation, the liquid to be boiled is placed in a vessel which is usually made of metal or glass. The vessel is known as a retort. The top of the container is curved downward. At the bottom of the condenser’s cooler,...
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