Radical Halogenation and Gas Chromatography

Topics: Chlorine, Chemical reaction, Gas chromatography Pages: 4 (1325 words) Published: February 11, 2013
In radical halogenations lab 1-chlorobutane and 5% sodium hypochlorite solution was mixed in a vial and put through tests to give a product that can then be analyzed using gas chromatography. This experiment was performed to show how a radical hydrogenation reaction works with alkanes. Four isomers were attained and then relative reactivity rate was calculated. 1,1-dichlorobutane had 2.5% per Hydrogen; 1,2-dichlorobutane had 10%; 1,3-dichlorobutane had 23%; and 1,4-dichlorobutane had 9.34% per Hydrogen. Introduction

Alkanes are relatively unreactive. There are only a few types of reactions commonly performed. In this lab, halogenation was performed. In the methane molecule, the carbon-hydrogen bonds are low-polarity covalent bonds. The halogen molecule has a nonpolar covalent bond. UV light contains sufficient energy to break the weaker nonpolar chlorine-chlorine bond, but it has insufficient energy to break the stronger carbon-hydrogen bond. The fracture of the chlorine molecule leads to the formation of two highly reactive chlorine free radicals (chlorine atoms). A free radical is an atom or group that has a single unshared electron.

This initial reaction is called the initiation step of the mechanism. Once the high-energy chlorine free radicals are formed, the energy source (UV light or heat) can be removed. The energy liberated in the reaction of the free radicals with other atoms is sufficient to keep the reaction running. When a chlorine free radical approaches a methane molecule, the chlorine free radical combines with the liberated hydrogen free radical to form hydrogen chloride and a methyl free radical. This is called a propagation step, a step in which both a product and a reactive species, which keeps the reaction going, are formed. When a reaction occurs between free radicals, a product forms, but no new free radicals are formed. This type of reaction is called a termination step because...
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