exp6w08 - Experiment 6: Butene Synthesis by E1 dehydration...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
Experiment 6: Butene Synthesis by E1 dehydration of 2- butanol (GC) : Mohrig, Chapter 16-17 In this experiment, the non destructive technique of gas chromatography will be used to monitor the progress of a reaction over time. In gas chromatography, the mobile phase is a gas rather than a liquid as in liquid chromatography. Separation is achieved by the rela- tive affinities of the various components of a mixture for the stationary phase as it is car- ried by the moving gaseous phase. It has several distinct advantages over other forms of chromatography (greater number of theoretical plates, good sensitivity, very rapid). Ana- lytical scale GC involves the syringe injection of a small volume of liquid or gas through a rubber gasket (injection septum) into a stream of inert gas such as helium, which flows at a pre-adjusted rate. The injection port is maintained at a temperature high enough to vaporize the liquid which is then swept by the helium flow into a heated metal column (6’ x 1/8”) maintained at an appropriate temperature. The column is packed with the solid support. The various components of the sample mixture pass through the column at different velocities depending upon their relative gas-liquid phase partition coefficients. In general, non-polar substrates separate on the basis of boiling points while polar substrates separate more (but not exclusively) on the basis of polarity. This stationary phase, which is commercially produced by Union Carbide, is a non-volatile polymer with structure R- (CH 2 -CH 2 -O) n -H, [n ~100]. The area under the peak recorded by the detector is pro- portional to its quantity in a mixture of similar components.* The retention time T R of a given compound varies for a given column and the flow rate and column. The formation of an alkene from an alcohol catalyzed by acid with loss of water is called a dehydration. In this particular instance, the mechanism is classified as an E1 unimolecular process. In the first step, the oxygen atom of 2-butanol is rapidly and reversibly proto- nated by sulfuric acid to give an oxonium cationic intermediate. In the second and rate- determining step, water dissociates to give a 2° carbocation. In a third rapid step, the cat-
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 04/07/2008 for the course CHEM 6a taught by Professor Pettus during the Winter '07 term at UCSB.

Page1 / 2

exp6w08 - Experiment 6: Butene Synthesis by E1 dehydration...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online