Synthesis of an Alkyl Halide

Synthesis of an Alkyl HalideFrances Abegail G. Quezon and Felipe D. Garcia Jr.

Institute of Chemistry, University of the Philippines, Diliman, Quezon City 1101 Philippines

Date/s Performed: July 12, 2013; Date Submitted: July 19, 2013

Introduction

The aim of the experiment was to synthesize an alkyl halide and to purify it by distillation. This experiment made use of the different boiling points of the starting reagent, tert-butyl alcohol, and the product, tert-butyl chloride. A tertiary alcohol was used because it reacts more readily with HX compounds compared to other alcohols.[1]

The reaction involved was

OH

Cl(1)

+ HCl (This reaction is a substitution reaction, particularly an SN1 reaction.

The yield from distillation was measured with a graduated cylinder. After converting the volume of the initial reagent and the final product to grams using their corresponding densities, the percent yield was calculated using the formula below:

(1)

Experimental Details

In the first part of the experiment, 10 mL tert-butyl alcohol was made to react with 20 mL cold concentrated HCl in a separatory funnel. Tert-butyl alcohol was used because tertiary alcohols react more readily with HX compounds such as HCl, compared to other alcohols.[1]

The type of reaction was a substitution reaction, type SN1. This type occurs in less reactions than the other type, SN2. SN1 reactions occur only in tertiary substrates, provided that the solvent is hydroxylic, such as water or alcohol, and the that the reaction happens under neutral or acidic conditions.[1]

This was the rationale behind the choice of reagents in this experiment. Also, SN1 reactions depends on the concentration of the substrate and not on the nucleophile. The substrate is tert-butyl alcohol while the nucleophile is the Cl- ion. Therefore, the nucleophile should be added in excess since the substrate was the limiting reagent in the experiment.

The reaction involved in the experiment, reaction (1), yielded a volatile product. The boiling point of this being 50.7(C. Because of its nature, tert-butyl chloride needed to be kept chilled and tightly covered[2] so HCl should be reacted cold in order to avoid loss of yield due to premature volatilization.

After these, the mixture was gently swirled and the internal pressure was relieved from time to time to avoid pressure build up. It was then allowed to stand for 20 minutes to allow the layers to separate. NaCl or any other inorganic salt solution may be added to facilitate layer separation. This technique is called salting out. It reduces the solubility of the organic compound in the aqueous layer so that it preferentially dissolves in the non polar layer.[3]

After separation, the bottom layer was released in a receiving flask. This layer was the aqueous layer, the layer to be discarded. However, if unsure of which is the aqueous layer and which is the non polar layer, a few drops of water may be added. The water is immiscible in the non polar layer and would form two layers.

Figure 1. separatory funnel set-up[4]References

(1) McMurry, J. Fundamentals of Organic Chemistry, 7th ed; Brooks/Cole: USA, 2011; pp 222-245.

(2) Organic Chemistry Group Organic Chemistry Laboratory Manual 2008, 34-37.

(3) Chulalongkorn University Department of Chemistry Separation by Solvent Extraction http://www.chemistry.sc.

chula.ac.th/home.htm (accessed July 15, 2013).

(4) Universtiy of Sydney, School of Chemistry E28 Extraction of Organic Compounds http://firstyear.chem.usyd.edu. au/prelab/e28.shtm (accessed July 15, 2013).PAGE 2

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