Question

MSISTRY 203-204 Grganic Chemistry Lab Manual 3 4 EXPERIMENT #9 The Preparation of t Butyl Chloride A tertiary carbonium ion is more rapidly formed than a secondary or primary carbonium ion. Once formed, a tertiary carbonium ion is stabilized by charge dispersal to a greater extent than a secondary or primary carbonium ion. It therefore has a longer life expectancy. Primary carbonium ions, protons, may exist in solution only in solvated form have any free existence, they dehydration reaction and the replacement of the alcoholic hydroxy group, therefore, occurs most easily for a tertiary alcoho Generally, the dehydration or the hydroxy replacement reaction of a secondary or primary alcohol requires elevated temperatures and/or more strongly acidic conditions. like . If they are very short-lived. The The best experimental procedure for the preparation of a tert. -alkyl chloride from a tertiary alcohol should minimize the most troublesome competing reaction which is dehydration. The simplest expedient is to carry out the reaction at low temperature. At 0-5°c, the competing dehydration reaction is much less extensive than at room temperature. The tert. -butyl chloride is easily separated from the reaction mixture because it is insoluble in water and forms a separate upper layer as it is formed. The crude product is separated from the reaction mixture by means of a separatory funnel and washed to remove acidic contaminants. Funner A lustrates the presence of acidic impurities in the top product layer. By vigorously shaking the crude product with water and then a 5s sodium bicarbonate solution, the acidic impurities are extracted from the top product layer into the bottom layer impurities in the bottom ground- glass stopper at the . The layer following top of the separatory funnel should be held firmly in place with the finger while shaking. Pressure due to gases formed duri the shaking operation may be released by inverting the funnel and continuously opening the stopcock. The actual separation of the layers is affected by opening the stopcock at the bottom of the separatory funnel, thus drawing off the bottom layer. The stopper must first be removed in order to allow equalization of the pressure inside the funnel before draining off. After the extraction washing the crude product to remove acidic contaminants, it is dried using Drierite and finally purified by distillation after decantation of the drying agent Ken 35- CHEMISTRY 203-204 organic Chemistry Lab Manual CH, CH, CH, CH Liquid: liquid extraction and washing Experimental: The tertiary alcohol (tert.-butyl alcohol) is added in small mt portions (until 0.2 moles have been used) with swirling to chilled (0-5°C) conc. HC1. About 80 ml of conc. HCl with specific gravity 1.19 is required. The addition may be completed in about 5 minutes. After the alcohol has been added, the mixture is taken from the ice bath, stoppered loosely, and shaken occasionally for a period of 20-25 minutes. The mixture is thern transferred to a small separatory funnel. The aqueous layer is separated and discarded. The crude product is washed (shaken) CHEMISTRY 203-204 Organic Chemistry Lab 36 Manual with about half its volume of cold water. The product layer is again separated and then washed with 5% sodium bi carbona te solution (2 or 3-20 ml portions) until the washings remain alkaline· The product is finally was small portions of water. It is then dried over Drierite while apparatus for simple distillation is set up. After the product has been thoroughly dried (about 15 minutes), it is filtered through a small glass wool plug in a funnel into a small distilling flask with two relatively A boiling stone is added and the product is distilled collecting the constant boiling fraction in a previously weighed narrow mouth sample bottle immersed in ice water. Since the product is very low boiling (-50c), a beaker of hot water (or H20 bath, rather than a free flame or heating mantle is the best source of heat. The purity of the t-butyl chloride must be evaluated by examining the refractive index. VPC analysis decomposes t-butyl chloride. Questions: 1. Explain the purpose of the first water wash, the sodium bicarbonate washes, and the final water wash in the work up of the crude product. Write equations for any reactions involved. 2. Write equations for any side reactions that might occur: A. during the main reaction B. during your work up of the product carbonate instead of calcium chloride as a drying agent for the crude product? 3. What would be the objections with use of anhydrous potassium 4. Suggest two other common preparative routes to alkyl halides. 5. How can one tell which of two layers in a separatory funnel is aqueous?

Answer 1