Electrophilic Addition

ELECTROPHILIC ADDITION

PURPOSE

The purpose of this lab is to learn how to synthesize 2-methyl-2-butene into 2-bromo-2-methylbutane using addition of hydrogen bromide.

THEORY

Chemical Compound Molecular Formula Molecular Weight Boiling Point Melting Point Density

Amylene CH3CH=C(CH3)2 70.13 g/mol 36 oC -134 oC 0.662 g/ml

Hydrobromic Acid HBr 80.91 g/mol 126 oC -11 oC 1.490 g/ml

2-Bromo-2-MethylButane C5H11Br 151.05 g/mol 107 oC 1.18 g/ml

Sodium bicarbonate NaHCO3 84.007 g/mol Decomposes at melting point unknown 2.159 g/ml

Diethyl ether C2H5OC2H5 74.12 g/mol 34.6 oC −116.3 oC 0.7134 g/ml

In this lab we use electrophilic addition of a hydrogen halide to an alkene to make 2-bromo-2-methylbutane. Electrophilic addition is an addition reaction where a pi bond is removed to create two new covalent bonds, Y-Z + C=C → Y-C-C-Z. Electrophilic addictions can also be the reverse of dehydrohalogenation. Dehydrohalogenation is when a double bond is formed between the α- and β-carbon. In this lab the addition of hydrogen bromide produces a more substituted alkyl halide with respect to Markovnikov's rule where the Bromine atom attaches to the more substituted carbon.**

**According to lab manual, www.wikipedia.com

PROCEDURE

First we mixed 25ml of hydrobromic acid and 10mlof amylene in a 50ml flask. Then we attach the apparatus and reflux the solution for 30 minutes by heating the solution until it boils, after this we allow the solution to cool down and then poured it into a125ml separatory funnel to drain and discard the lower spent acid layer. We washed the organic layer with a combination of 20ml of saturated sodium bicarbonate solution and 20ml of ether. Then we drained the lower aqueous layer and we kept the organic layer. We added 4 to 5 pellets of calcium chloride to the organic layer and allowed the solution to dry for 10 minutes. After this we placed the dry ether solution in a 50ml flask and fractionally distilling the solution until the head temperature reaches 90 degrees C. Then we removed the fractionating column and continued the distillation using a short path column. After this we weighted the product and found the IR.

OBSERVATIONS

As the solution boiled in the first step it kept changing color getting darker from clear to yellow to orange. During the boiling I can see the two layers forming separating into organic and aqueous with a line in between, as the solution boiled more and more the organic phase kept growing little by little. In the final filtration, after 20ml of collected organic phase we did a short path column to collect the amount of the liquid wanted but this step took a lot of time