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Kinetics of Aromatic Bromination

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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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