Kinetics of Aromatic Bromination
Essay by Michelle Morello • December 1, 2015 • Lab Report • 860 Words (4 Pages) • 2,900 Views
Chemistry 232 Fall 2015 and Spring 2016
Kinetics of Aromatic Bromination
Name: _____________________________________________ Date: ___________________________ Abstract
In this experiment, the kinetics of aromatic bromination were analysed to determine the reactivity different substituents have on aromatic rings. The greatest change of absorbance was found to be benzene, with a change in absorbency of 0.316. Chlorobenzene had the least change in absorbency, which was 0.186. Phenol was found to be the fastest reacting aromatic compound from the experiment. The activation energy (∆G‡) for the bromination of diphenyl ether was 38195.3.
General Equation of Bromination
Procedure Reference
Marrs, P. Organic Chemistry Laboratory Manual. pp. 41-52. (University of Victoria, BC). Fall 2015.
Reagents
Compound | MW | Physical and Safety Data |
Bromine, Br2 | 159.82 | Volatile, highly toxic, oxidizer and corrosive. Bp:58ºC, d: 3.1g/mL |
Acetic acid, C2H4O2 | 60.05 | Bp:118ºC, d: 1.05g/mL. Irritant, corrosive, |
Qualitative Rates of Bromination; Deactivated Aromatic Compounds
Benzene | Nitrobenzene | Chlorobenzene | ||||
Time | A | Time | A | Time | A | |
40 mins | 0.343 | 40 mins | 0.282 | 40 mins | 0.216 | |
80 mins | 0.098 | 80 mins | 0.148 | 80 mins | 0.112 | |
120 mins | 0.027 | 120 mins | 0.067 | 120 mins | 0.030 |
The above results were recorded at ~75°C.
Qualitative Rates of Bromination; Activated Aromatic Compounds
Time taken until disappearance of bromine colour | |||||
Temperature | Phenol | Diphenyl Ether | p-Bromo- phenol | Acetanilide | Anisole |
0 °C | 4.20s | No change | 11.90s | 7.28s | 16.83s |
Room temp. | 4.00s | No change | 4.10s | 2.88s | 9.96s |
50 °C | - | No change | - | - | 2.90s |
Quantitative Rates of Bromination: Diphenyl ether
Reaction at 0°C (ice bath)
Time (minutes) | 0 | .15 | 0.30 | 0.45 | 1.00 | 1.30 | 2.00 | 2.30 | 3.00 |
A | 0.402 | 0.437 | 0.422 | 0.412 | 0.417 | 0.399 | 0.386 | 0.343 | 0.317 |
-ln(A) | 0.911 | 0.828 | 0.863 | 0.887 | 0.875 | 0.919 | 0.952 | 1.070 | 1.149 |
Reaction at ~23°C (room temperature)
Time (minutes) | 0 | 0.15 | 0.30 | 0.45 | 1.00 | 1.30 | 2.00 | 2.30 | 3.00 |
A | 0.330 | 0.300 | 0.277 | 0.247 | 0.266 | 0.178 | 0.136 | 0.102 | 0.069 |
-ln(A) | 1.109 | 1.204 | 1.284 | 1.398 | 1.324 | 1.726 | 1.995 | 2.283 | 2.674 |
Reaction at 50 °C (warm water)
Time (minutes) | 0 | 0.15 | 0.30 | 0.45 | 1.00 | 1.30 | 2.00 | 2.30 | 3.00 |
A | 0.240 | 0.238 | 0.187 | 0.155 | 0.134 | 0.085 | 0.016 | 0.000 | 0.000 |
-ln(A) | 1.427 | 1.435 | 1.677 | 1.864 | 2.010 | 2.465 | 4.135 | - | - |
Include the graphs of the above data, and determine the slope of the line. Calculate k and enter it in the table below.
[pic 1]
Figure 1. Graph of quantitative rates of bromination on diphenyl ether at 0ºC
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