ASynthesis of an alkyl halide
Jade A. Chuahiong and Marika Bianca F. Morioka
Institute of Chemistry, University of the Philippines, Diliman, Quezon City 1101 Philippines
Date Performed: April 25, 2013; Date Submitted: April 30, 2013
Alkyl halides could be synthesized through several processes and using different compounds as reactants. One of the simplest method used is the addition of a hydrogen halide to an alcohol. In this research, tert-butyl alcohol was reacted with cold concentrated HCl to produce tert-butyl chloride. The crude product was distilled to yield a pure tert-butyl chloride. The tert-butyl alcohol, together with HCl, underwent an SN1 nucleophilic substitution reaction, which is composed of three steps—(1) propanation of alcoholic oxygen, (2) formation of carbocation, and (3) attacking of the nucleophile to the carbocation. The experiment was only able to yield 0.504 grams or 5.21% of the theoretical yield of 9.679 grams, which is considered as extremely low percent yield. This result could have resulted from various experiment and experimenter errors and other uncontrollable environmental factors.
An alkyl halide or haloalkane is composed of hydrocarbons with a halogen attached to a sp3-hybridized carbon. It resembles an alkane with a halogen attached to it. Halogens are fluorine, chlorine, bromine, and iodine. Any of these halogens seen to be attached to an alkane, could then be identified as alkyl halides. They are generally polar because of the electronegativity difference of carbon (2.5) with the halogen (2.5-4.0). However, most alkyl halides are found to have low solubility in water. They are miscible with each other and with other non-polar solvents as well. The infamous chlorofluorocarbons (CFCs) that are active destroyers of the ozone layer are probably the most common example of alkyl halides. Common alkyl halides used in the laboratory are dichloromethane or methylene chloride (CH2Cl2), trichloromethane or chloroform (CHCl3), and tetrachloromethane or carbon tetrachloride (CCl4). Many alkyl halides with chlorine as the halogen component are found to be toxic and carcinogenic.6 Researchers are restricted to use these compounds in fume hoods and with great care. Alkyl halides are usually used as the starting compounds for the synthesis process of many compounds in the laboratory or even in the industry.6 In this research, however, alkyl halide was the final product. One of the simplest ways to synthesize alkyl halide was examined in this research. Alkyl halide could be formed using several methods. The first method is through the free radical substitution (FRS) or halogenation using an alkane and a halogen. This method, however, is not highly recommended because of the varying and diverse products it produces, which are not all alkyl halides.3 Another process is through the electrophilic addition reaction of alkenes. One kind of electrophilic addition is the addition of a hydrogen halide to an alkene, called hydrohalogenation.6 In this method, the hydrogen halide is introduced to the alkene either by bubbling the gas phase of the hydrogen halide directly to the alkene or dissolving it to a solvent, which could either be acetic acid or the alkene itself. Another kind is halogenation in which the halogen is added to the alkene. (Take note the use of the same term as FRS, but these two processes are completely different.) Bromine and chlorine readily react with alkene and this reaction produces alkyl halides. Fluorine is too reactive and can be hard to control, while iodine is not that reactive with alkenes.3 Aside from these, alkyl halides could also be synthesized from a reaction between an alcohol and a halogen. There are still different ways to synthesize alkyl halides from an alcohol. One way as patented by Herrick Arnold and Edward Lessig in 1937 is through mixing the halogen acid to the alcohol vapor over a liquid bath that could heat up to the right temperature...
References: (1) Alkyl halides. Retrieved from http://hyperphysics.phy-astr.gsu.edu/hbase/organic/alkhal.html
(2) Arnold, H.R. & Lessig, E.T. Synthesis of alkyl halides. United States Patent Office: 1937.
(3) Bauld, N.L. Alkyl halides. 2001 Retrieved from http://research.cm.utexas.edu/nbauld/teach/halides.html#mechanism
(4) McGraw-Hill Companies. Preparations of alkyl halides. Retrieved from http://www.mhhe.com/physsci/chemistry/carey/student/olc/ch04prepare.html
(5) McMurry, J.E. Organic chemistry, 7th ed.; Thompson Learning, Inc.: California, 2008, pp. 215-218; 335-339; 344-345
(6) Norris, P. Elimination reactions. Retrieved from http://www.hyperconjugation.com/teaching/3719files/mechanisms/elimination.html
(7) Institute of Chemisty, University of the Philippines. Organic chemistry laboratory manual, 2008 ed.; University of the Philippines: Manila, 2013
(8) Solomons, T.W.G. & Fryhle, C.B. Organic chemistry, 10th ed.; John Wiley & Sons, Inc.: New Jersey, 2011, pp. 230-233; 334-335
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