Today:
Expt. #8
Dehydration of 2-Butanol
and
Dehydrobromination of 2-Bromobutane;
Analysis of Products by GC
Structure of 2-butanol?
How many 2-butanols are there….?
Structure of 2-bromobutane?
Dehydration of 2-Butanol
Reaction equation?
Mechanism?
Rate equation?
Energy Diagram?
What intermediate(s) is(are) formed?
What product(s) can we expect?
Dehydration of 2-butanol
Reaction Products
CH3 H H H
C C C C
H CH3 CH3 CH3
trans 2-butene cis 2-butene
MW 56.11 MW 56.11
H H
BP 0.9oC BP 3.7oC
C C
CH3 CH 2 H
1-butene MW 56.11, BP -6.3oC
Dehydrohalogenation of 2-bromobutane B: = Base
E2 Mechanism:
B
B:
H H H b H
CH3 CH3
C C C C
CH3
CH3
H Br
H Br
Reaction Diagram?
Transition State
Rate equation?
CH3 H H H
C C + C C
H CH3 CH3 CH3
Similarly: leading to 1-
trans 2-butene cis 2-butene
butene
K. L. Williamson, Macroscale and Microscale Organic Experiments, 2 nd. Edition, D.C. Heath, 1994, p.275
Use this Set-up:
Rubber
Teflon
Rubber septum
tube
septum Butenes
Collection
Reaction tube
tube
H2O
Sand bath
K. L. Williamson, Macroscale and Microscale Organic Experiments, 2 nd. Edition, D.C. Heath, 1994, p.269
Gas Chromatography
mixture With packed column
1)
2)
3)
4)
compounds B A
GC Conditions:
Sample injection volume: 5 - 10 mL
GC column: 2m x 2mm (I.D.)
Stationary Phase: 0.19% Picric acid on Carbograph 2,
80/100
Oven temperature: 60oC
Moving Phase: Helium
Column head pressure: 35 psi or more
Injector temperature: 66oC
Detector temperature: 100oC
Detector: Thermal Conductivity Detector (TCD)
GC Chromatogram of products of the
dehydration of 2-butanol reaction
3
2
Air Peak
1
Peak Area
Time (min)
r.t. (min)
Report Form #8 Part III, Question 2:
What is the maximum volume at STP of the butene
mixture that could be obtained by the dehydration
of 160 mg of 2-butanol?
STP?
PV = nRT
Units! Use correct R…
Next Friday: no classes (Veterans Day)
Following Friday Lab Lecture:
Exp.9, “Separation and Identification of
an Unknown Mixture” (3 lab periods);
IR, recryst., mp. s and other techniques you learnt this
semester