Friedel-Crafts Alkylation of Benzene with 1-Bromopropane : Study of Carbocation Rearrangement.

Experiement 16

Friedel-Crafts alkylation of Benzene with 1-Bromopropane

: Study of Carbocation Rearrangement.

Jeongmin Lee         

                                                                             03-11-2015

Objective

The goal of this experiment is to exemplify a Friedel-Crfats reaction, to study a reaction involoving carbocation rearrangements, to identify compounds using gas chromatography, and to gain exposure to processing NMR data.

Starting Material

185uL of 1-bromopropane + 2.5mL of dry benzene

Procedure

A triangular magnetic stir bar, 185uL of 1-bromopropane, 2.5mL of dry benzene and a spatula scoopful of anhydrous aluminum chloride was added in a dry 5mL conical vial. A reflux condenser was attached to the reaction vial and the reaction mixture was warmed with stirring on a hotplate to gentle reflux for 20minutes. The reaction mixture was cooled in an ice bath, and 1.5mL of water was added drop wise from the top of the condenser. The vial was capped and shaken vigorously with venting. The layer was separated and the lower aqueous layer was discarded. The organic layer was dried with anhydrous sodium sulfate. The filtrate was transferred into a pre-weighed 5mL conical vial and evaporated on a warm hotplate with gentle stream of air until 0.5-1.0mL of liquid remained. The evaporating continued until there was about 200-250mg of liquid remaining. The final mass was recorded for calculating the GC percent yield.

2 sample for GC was prepared

• Vial 1 : 2 drops of product + 1mL of CH2Cl2
• Vial 2 : 1mL of (2 drops of product + 1 drop of the isopropyl benzene + ~3mL of CH2Cl2 mixture)

Reaction Scheme

Benzene + 1-bromopropane ----AlCl3----→ Propylbenzene (mixture of isopropylbenzene and n-propylbenzene)

Result

1. GC chromatography

Vial 1 : product + CHCl2

                Unknown 1 (benzene) at 1.82min area 87.5 uV.Min (38.325%)

                Unknown 2 (isopropylbenzene) at 3.89min area 84.3uV.Min (36.922%)

                Unknown 3 (n-propylbenzene) at 4.13min area 56.5 uV.Min (24.753%)

1. Proton NMR Spectroscopy – attached

13CNMR : 6 unique carbon

1HNMR : 3 unique hydrogen groups

Indicates isopropylbenzene

1. GC percent yield

38.325% of benzene + 61.675% of propylbenzene