Title: Conversion of Alcohols to Alkyl Halides
Abstract: In this experiment the conversion of alcohols to alkyl halides are investigated through reflux and simple distillation. These are common procedures used to separate substances. After the reflux and distillation is complete 13C NMR and IR spectrum is used to identify the product or products for each reaction: 1a, 1b, and 2. Every individual in the group was assigned either 1a (1-propanol) or 1b (2-pentanol), and 2 (1,4-dimethyl-3-pentanol). The purpose of this experiment was to understand and become familiar with the reaction mechanisms and be able to observe and compare the product or products for each of the reactions using 13C NMR and IR. The reaction of 1-propanol (1a) with NaBr/H2SO4 was 1-bromopropane, the reaction of 2-pentanol (1b) with NaBr/H2SO4 was 2-bromopentane and the reaction of 2,4-dimethyl-3-pentanol with HCl/ZnCl2 was 2,4-dimethyl-3-chloropentane. Background: Alcohols are capable of being converted to metal salts, alkyl halides, esters, aldehydes, ketones, and carboxylic acids. In this experiment the conversion from alcohol to alkyl halides was investigated. Alkyl halides are a group of chemical compounds derived from alkanes containing one or more halogens. They are used as flame retardants, refrigerants, propellants, solvents, and pharmaceuticals. As a group, students convert three alcohols to alkyl halides under acidic conditions and record the 13C NMR spectrum in each case. The reaction that takes place in the conversion is a bimolecular nucleophilic substitution, or SN2 reaction. Alcohols do not undergo the same SN2 reactions commonly observed with alkyl halides. There are four aspects that determine the rate of the SN2 reaction: nucleophile, substrate, solvent and the leaving group. This reaction requires a lone pair from a nucleophile to donate an electron-pair in the formation of a chemical bond; it then attacks the bonds to an electrophilic center. Once the carbon is attacked by the nucleophile the bond between the necleophile and carbon becomes strong and between the carbon and the leaving group the bond becomes weak. The carbon is then bonded to the nucleophile and partly the leaving group. Halide anions are a negative charge and therefore are best for the leaving groups. The SN2 reactions of each reaction accomplished in this experiment can be found below.
The possible products of 1a, 1b, and 2 can be found below. This experiment, in particular, dealt with the conversion of 1-propanol, 2-pentanol, and 2,4-dimethyl-3-pentanol. Each had the possibility of two products. Both products had different resonances. 1a possible products
2 possible products 1b possible products
The reaction that takes place in this experiment is and SN2 reaction where 3 alcohols are converted to alkyl halides. The rate of SN2 reaction is bimolecular because it depends strictly on the concentration of the substrate and the nucleophile. In this reaction, a lone pair from a nucleophile, donator of an electron-pair in the formation of a chemical bond, attacks and bonds to an electrophilic center. This reaction can be seen below under the substitution. An elimination reaction takes place frequently where the arriving anion performs as a base instead of a nucleophile, the outcome is an alkene.
SN2 reaction for 1a: 1-propanol:SN2 reaction for 1b: 2-pentanol:
SN2 reaction for 2: 2,4-dimethyl-3-pentanol:
Experiment (Methods): This experiment was done in two procedures. The first was the reaction of 1-propanol or 2-pentanol with NaBr/H2SO4. And the second was for the reaction of 2,4-dimethyl-3-pentanol and 6.5 ml of “Lucas reagent.” Both procedures in this experiment involve the conversion of alcohols to alkyl halides are investigated through reflux and simple distillation. These are common procedures used to separate substances. Reflux is a technique for heating a reaction some kind of...