I= KINETICS OF METHYLENE BLUE WITH ORGANIC REDUCTANTS
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Title of Thesis
KINETICS OF METHYLENE BLUE WITH ORGANIC REDUCTANTS

Author(s)
Rafia Azmat
Institute/University/Department Details
University of Karachi/ Department of Chemistry
Session
2004
Subject
Chemistry
Number of Pages
236
Keywords (Extracted from title, table of contents and abstract of thesis)
methylene blue, organic reductants, monochromatic radiations, dye reduction, dye, photochemical reaction, laser photolysis, photobleaching

Abstract
The photobleaching of methylene blue with reducing in 50% aqueous methanol using acetate buffer has been investigated with steady-illumination of monochromatic radiations of 661 mm on specially designed optical bench in a dark room. The dye reduction processes were studied at various parameters i) concentrations of dye, ii) concentrations of reductants such as Galactose, D-Mannose, D-(+)-Ribose, Maltose and Lactose, iii) acidity (Ho) of reaction solution iv) temperature as a function of quantum yield (0). Hammett acidity function (Ho) was used to determine acidity of the reaction solution. The optical method was adopted to evaluate the values of Ho.

Bleaching of the dye simultaneously with demethylation has been observed upon irradiation, color recover as the source of irradiation turned off or exposure to air. Reaction follows second order kinetics with respect to dye concentration and reductant and first order with respect to triplet transient with life time of 10.1 us.

A general mechanism has been proposed. Mathematical expressions were established and rations of rate constants were determined from experimental evidences. The tests were put forward to justify the mechanism. The mechanism was also supported by analysis of reaction mixture by TLC and column chromatic graphic techniques. Visible, Infra red and Mass spectrum of isolated product of the triplet transient showed the high reactivity of the dye triplet species towards different reagents present in the mixture

The values of ratios of rate constant appearing in general mechanism were verified and it was found that quantum yield was the consequence of triplet

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S. No. Chapter Title of the Chapters Page Size (KB)
1 0 Contents
88.69 KB
2 1 Introduction 4
137.52 KB
  1.1 Methylene Blue 4
  1.2 Basis Of Colour 6
  1.3 The Effect Of Molecular Energy Levels 8
  1.4 Color Vision 9
  1.5 Affects The Color Quality Of The Dye 10
  1.6 Colour And Constitution 11
  1.7 Dye 12
  1.8 Significance Of Photochemistry 13
  1.9 Photochemical Reaction 14
  1.10 Photochemical Reaction In The Liquid Phase 14
  1.11 Photochemical Kinetics 15
3 2 Literature Survey 18
277.41 KB
  2.1 Variable States Of Methylene Blue 18
  2.2 Methylene Blue-Sensitized Electron Transfer Reaction 19
  2.3 Absorption Studies Of Methylene Blue 22
  2.4 Reduction States Of Methylene Blue 28
  2.5 Photo Reduction Of Methylene Blue By Light 30
  2.6 Photochemical Reduction Of Methylene Blue By Light 30
  2.7 Photochemical Reduction Of Methylene Blue With Inorganic Reductants 32
  2.8 Photochemical Reduction Of Methylene Blue With Organic Reductants 35
  2.9 Photo Galvanic Effect 38
  2.10 Laser Photolysis 40
  2.11 Photobleaching Of Thiazine Dye 42
  2.12 Polymerization Of Methylene Blue 43
  2.13 Aim Of The Present Work 46
4 3 Experimental Aspects 48
151.18 KB
  3.1 Preparation Of Experiment 48
  3.2 Preparation Of Photochemical Research Laboratory 49
  3.3 Circuit For Light Source 51
  3.4 The Optical Bench Arrangement 51
  3.5 Light Filters 53
  3.6 Reaction Cell 53
  3.7 Thermostatic Bath 55
  3.8 Stirring System 55
  3.9 Material And Method 55
  3.10 Glass Wares 56
  3.11 Double Distilled Water 56
  3.12 Solvent 56
  3.13 Preparation Of Stock Solution 56
  3.14 Deoxygenating System 58
  3.15 Measurement Of Light Intensity 59
  3.16 Measurment Of The Acidity Of The Solution 60
  3.17 Measurement Of The Absorption Coefficient 62
  3.18 The Experimental Procedure 63
  3.19 Analysis Of Photochemical Reaction Mixture 63
5 4 Results 66
480.98 KB
  4.1 Optical Absorption Of Methylene Blue 66
  4.2 Maximum Absorbance Values 66
  4.3 Determination Of Quantum Yield For The Photoresuction Of Methylene Blue With Reducing Sugar 73
  4.4 The Inert Atmosphere For Photo Reduction Of Methylene Blue With Reducing Sugars At Two Different Acidities Ho=4.2 And 7.7 87
  4.5 Variation Fo Acidity On Quantum Yield Of Methyulene Blue In Absence Of Reductant 90
  4.6 The Influence Of Acidity On The Quantum Yield Of Photo Reduction Of Methylene Blue With Reducing Sugars 92
  4.7 Influence Of Concentration Of Reducing Sugars On The Quantum Yield Of Photochemical Reduction Of Methylene Blue 92
  4.8 Influence Of Concentration Of Methylene Blue On The Quantum Yield Of Photochemical Reduction 113
  4.9 Influence Of Temperature On Quantum Yield Of Photochemical Reduction Of Methylene Blue With Reducing Sugars 125
  4.10 Analyses Of Irradiated Reaction Mixture Of Methylene Blue With Reducing Sugars 144
6 5 Discussion 147
584.62 KB
  5.1 The Photobleaching Of Methylene Blue 147
  5.2 Visible Absorption Spectra Of Methylene Blue With Different Reductants And At different Acidities 148
  5.3 The Infra Red Spectra Of Isolated Photochemical Products 155
  5.4 Variation Of Acidities On Quantum Yield Of Photochemical Reduction Of Methylene Blue In Absence Of Reductant 167
  5.5 Influence Of Concentration Of Reducing Sugars On Quantum Yield Of Photo reduction Of Methylene Blue 167
  5.6 Photochemical Reduction Of Methylene Blue By Monosaccharides 169
  5.7 Photochemical Reduction Of Methylene Blue By Disaccharides 170
  5.8 Stirring System 171
  5.9 Material And Method 173
  5.10 Glass Wares 175
  5.11 Double Distilled Water 201
  5.12 Solvent 204
  5.13 Preparation Of Stock Solution 213
  5.14 Deoxygenating System 220
  5.15 Measurement Of Light Intensity 221
  5.16 Future Prospective 222
7 6 References 224
136.71 KB