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SYNTHESIS AND CORROSION INHIBITION STUDIES OF BENZOYLTHIOUREA DERIVATIVES ON MILD STEEL IN
1.0 M HCI
Siti Najihah binti Md Hashim
UNIVERSITI SAINS ISLAM MALAYSIA
SYNTHESIS AND CORROSION INHIBITION STUDIES OF BENZOYLTHIOUREA DERIVATIVES ON MILD STEEL IN
1.0 M HCI
Siti Najihah binti Md Hashim
(Matric No. 3140208)
Thesis submitted in fulfillment for the degree of
MASTER OF SCIENCE
Faculty of Science and Technology
UNIVERSITI SAINS ISLAM MALAYSIA
Nilai
December 2016
1
AUTHOR DECLARATION
p.; ýý11 Cjý, t11 Jul ý ý;
I hereby declare that the work in this thesis "Synthesis and Corrosion Inhibition Studies of
Ben_oylthiourea Derivatives on Mild Steel in 1.0 M HCl " is my own research except for
quotations and summaries which have been duly acknowledged.
Date: 29th December 2016 Signature :...... ''"- .......................
Name : Siti Najihah binti Md Hashim
Matric No. : 3140208
Address : Bt. 22, Kg. Cherana Puteh,
78000 Alor Gajah, Melaka.
11
APPROVAL
This thesis entitled "Synthesis and Corrosion Inhibition Studies of
Benzoylthiourea Derivatives on Mild Steel in 1.0 M HCI" submitted to the Faculty
of Science and Technology, USIM and accepted as fulfillment of the requirements to
the degree of Master of Science.
I' JULIANA JUMAL, Ph. D, Faculty of Science and Technology, Universiti Sains Islam Malaysia
Date : 29°i December 2016
111
ACKNOWLEDGEMENTS
In the name of Allah, the Most Gracious and Most Merciful. All praises to Him for all
the favors bestowed upon mankind and for giving me health to complete this study. I
would like to express my most sincere gratitude and appreciation to my helpful
supervisor who has been a constant source of knowledge and inspiration, Dr. Juliana
Jumal and for her valuable guidance, advice and constant encouragement throughout
the course of my research study. Her constructive criticisms and suggestions provided
me with the strength and perseverance to complete this thesis despite several obstacles
encountered throughout the period of this research, which at times seemed
insurmountable.
Deep appreciation also goes to my kind co-supervisor, Dr. Karimah Kassim (UiTM)
for her support and invaluable suggestions to guide me during my study especially in
providing research facilities to conduct the analysis. The supervision that she gave,
truly help the progression and smoothness of this study from the beginning until the
end. I also wish to express my gratitude to all members of the postgraduate student
and staff of the Faculty of Science and Technology, USIM especially to Mr. Syamsul
Kamar and Mr. Mohd Nazarali, for providing me technical assistance throughout the
study.
I am greatly indebted to my beloved husband, parents, sisters, brothers and friends for
their love, moral encouragement and support in completing my master study. Last but
not least, the Ministry of Higher Education Malaysia for FRGS research grant
(USIM/FRGS/FST/32/51114) and also MyMaster scholarship, FST, Universiti Sains
Islam Malaysia and FSG, Universiti Teknologi MARA, Shah Alain.
IV
ABSTRAK
SINTESIS DAN KAJIAN PERENCATAN TERBITAN BENZOILTIOUREA
PADA KAKISAN BESI KELULI LEMBUT DALAM 1.0 M HCl
Sebanyak lapan sebatian benzoiltiourea iaitu: 1-sikloheksil-3-(4-fluorofenil)tiourea
(T1), 1-(4-fluoro-benzoil)-3-(4- fluorofenil)tiourea (T2), 1-(4-fluoro-benzoil)-3-(4-
nitrofenil)tiourea (T3), 1-(4-kloro-benzoil)-3-(4-nitrofenil)tiourea (T4), 1-(4-
bromofenil)-3-(4-kloro-benzoil)tiourea (T5), 1-(4-kloro-benzoil)-3-(4-fluoro-
fenil)tiourea (T6), 1-(4-kloro-benzoil)-3-(3-kloro-2-fluoro-fenil)tiourea (T7), dan 1-
(4-kloro-benzoil)-3-(6-kloro-2-fluoro-3-methoxi-fenil)tiourea (T8), telah beijaya
disintesis dan dicirikan melalui analisis mikro unsur (CHNS), spektroskopi infra
merah (FTIR) dan resonan magnetik nuklear (NMR). Daripada data spektrum yang diperoleh, sebatian mempunyai frekuensi getaran regangan v(NH) dalam lingkungan
3500-3 100 cni', v(C=0) pada 1660-1720 cm-1, v(C=S) pada 680-1440 cm-' dan v(C- N) pada 1350-1000 cm-'. Tiga daripada lapan sebatian iaitu T6, T7 dan T8
kemudiannya dipilih untuk dikaji secara lanjut dalam aktiviti anti kakisan. Ciri
perencatan kakisan pada besi keluli lembut dalam larutan 1.0 M asid hidroklorik telah
dikaji pada suhu bilik menggunakan teknik kehilangan berat, ukuran polarisasi
potentiodinamik dan elektrokimia spektroskopi impedans (EIS). Didapati, kesemua
terbitan tiourea ini berkebolehan dalam merencatkan proses kakisan pada besi keluli
lembut. Didapati, peratus perencatan meningkat dengan pertambahan kepekatan
larutan dan kecekapan maksimum diperoleh pada kepekatan 0.0004 M. Antara
perencat yang dikaji, T8 menunjukkan kecekapan perencatan yang terbaik dengan
peratus perencatan tertinggi melebihi 90%. Spektrum impedans menunjukkan bahawa
proses perencatan adalah disebabkan oleh pembentukan lapisan filem terjerap yang
melindungi permukaan logam terhadap medium yang mengkakis. Kajian
potentiodinamik juga mendedahkan bahawa sebatian yang dikaji pada dasamya
bertindak sebagai perencat berjenis campuran yang menghalang kedua-dua bahagian
katod dan anod dalam tindak balas kakisan.
Kata kunci: tiourea, teknik kehilangan berat, polarisasi, kakisan perencatan, keluli
lembut
V
ABSTRACT
SYNTHESIS AND CORROSION INHIBITION STUDIES OF
BENZOYLTHIOUREA DERIVATIVES ON MILD STEEL IN 1.0 M HCI
Eight derivatives of thiourea namely: 1-cyclohexyl-3-(4-fluorophenyl)thiourea (Ti),
1-(4-fluoro-benzoyl)-3-(4-fluorophenyl)thiourea (T2), 1-(4-fluoro-benzoyl)-3-(4-
nitrophenyl)thiourea (T3), 1-(4-chloro-benzoyl)-3-(4-nitrophenyl)thiourea (T4), 1-(4-
bromophenyl)-3-(4-chloro-benzoyl)thiourea (T5), 1-(4-chloro-benzoyl)-3-(4-fluoro-
phenyl)thiourea (T6), 1-(4-chloro-benzoyl)-3-(3-chloro-2-fluoro-phenyl)thiourea
(T7), and 1-(4-chloro-benzoyl)-3-(6-chloro-2-fluoro-3-methoxy-phenyl)thiourea (T8),
were successfully synthesized and characterized via micro elemental analyzer, FTIR,
1H and 13C NMR spectroscopy methods. From the FTIR spectral data, the compounds
are common to have the vibration frequency of stretching of v(N-H) around 3500-
3100 cmi1, v(C=O) around 1660-1720 cm-1, v(C=S) around 680-1440 cm-1 and v(C-N)
in the range of 1350-1000 cm-1. Three of the eight compounds which are T6, T7 and
T8 were selected for further study on their anticorrosion activity. The inhibition
property of the resulted compounds on the corrosion of mild steel in 1M hydrochloric
acid has been investigated at room temperature using weight loss, potentiodynamic
polarization measurements and electrochemical impedance spectroscopy (EIS). It was
found that, all the synthesized thiourea derivatives are capable to inhibit the corrosion
of mild steel. It was found that the inhibition efficiency increases with inhibitor
concentration and maximum efficiency was obtained at concentration 0.0004 M.
Among the studied inhibitors, T8 shows the best inhibition efficiency of greater than
90 %. The impedance spectra indicate that the inhibition process was attributed to the
formation of an adsorbed film that protects the metal surface against corrosive
medium. The potentiodynamic study reveals that the compounds studied acts
essentially as mixed type inhibitor which inhibits both the cathodic and anodic parts of
the corrosion reaction.
Keywords: thiourea, weight loss, polarization, corrosion inhibition, mild steel.
vi
TABLE OF CONTENTS
CONTENTS
AUTHOR DECLARATION APPROVAL ACKNOWLEDGEMENT ABSTRAK ABSTRACT TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURES LIST OF SCHEMES LIST OF ABBREVIATIONS AND SYMBOLS LIST OF APPENDICES
CHAPTER 1: INTRODUCTION 1.1 Problem Statement 1.2 Background of Study 1.3 Significance of Study 1.4 Scope of Study
Page
11
111
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V1
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sill
1 1 1 4 4
CHAPTER 11: LITERATURE REVIEW 6 2.1 Mild Steel 6 2.2 Corrosion 7
2.2.1 Definition of Corrosion 7 2.2.2 Electrochemical Nature of Steel Corrosion 9 2.2.3 Corrosion Control 10
2.3 Corrosion Prevention by Inhibitors 11 2.3.1 Organic Inhibitors 13 2.3.2 Inhibitor Mechanism 16 2.3.3 Environmental Friendly Corrosion Inhibitors 17
2.4 Thiourea 18 2.4.1 Thiourea and Its Derivatives 19 2.4.2 Synthesis of Thiourea Derivatives 22 2.4.3 Applications of Thiourea Derivatives 24
2.5 Thiourea and Its Derivatives as Corrosion Inhibitor 24 2.5.1 Mechanism of Inhibition of Thiourea 27
CHAPTER III: MATERIALS AND METHODS 30 3.1 Chemicals 30 3.2 Instrumentations for Characterization 31 3.3 Synthesis of Thiourea Derivatives Compounds 31
3.3.1 Preparation of 1-cyclohexyl-3-(4-fluorobenzoyl)thiourea (TI) 32
vii
3.3.2 Preparation of 1-(4-fluorobenzoyl)-3-(4-fluorophenyl)thiourea 33 (T2)
3.3.3 Preparation of 1-(4-fluorobenzoyl)-3- 34 (4-nitrophenyl)thiourea (T3)
3.3.4 Preparation of 1-(4-chlorobenzoyl)-3- 35 (4-nitrophenyl)thiourea (T4)
3.3.5 Preparation of 1-(4-bromophenyl)-3- 36 (4-chloro-benzoyl)thiourea (T5)
3.3.6 Preparation of 1-(4-chlorobenzoyl)-3- 37 (4-fluorophenyl)thiourea (T6)
3.3.7 Preparation of 1-(4-chlorobenzoyl)-3- 38 (3 -chloro-2 -fluoroph enyl) thiourea (T7)
3.3.8 Preparation of 1-(4-chlorobenzoyl)-3- 39 (6-chloro-2-fluoro-3-methoxyphenyl)thiourea (T8)
3.4 Characterization of Thiourea Derivatives Compounds 40 3.4.1 Elemental Analysis for CHNS 40 3.4.2 Fourier Transform Infrared Spectroscopy (FTIR) 40 3.4.3 Nuclear Magnetic Resonance (NMR) Spectroscopy 40
3.5 Corrosion Inhibition Studies 41 3.5.1 Weight Loss Measurement 41 3.5.2 Electrochemical cell 42 3.5.3 Potentiodynamic Polarization Measurement 43 3.5.4 Electrochemical Impedance Spectroscopy (EIS) 43
CHAPTER IV: RESULTS AND DISCUSSIONS 45 4.1 Synthesis of Thiourea Derivatives Compound 45 4.2 Micro Elemental Analysis 48 4.3 Fourier Transform Infrared (FTIR) Spectroscopy 49 4.4 Nuclear Magnetic Resonance (NMR) Spectroscopy 55 4.5 Mechanism of the Synthesized Product 61 4.6 Weight Loss Measurement 62 4.7 Linear Polarization Resistance (LPR) Technique 67 4.8 Electrochemical Impeadance Spectroscpy (EIS) 74 4.9 Discussion on Inhibition Characterization 81 4.10 Mechanism of Inhibition by Benzoylthiourea Derivatives 85
CHAPTER V: CONCLUSION 87 5.1 Suggestions and Recommendations 88
REFERENCES 90
APPENDICES 103
viii
LIST OF TABLES
Table Title Page
Table 1: ASM Classifications of Corrosion Types 7
Table 2: List of Some Reported Thiourea Derivatives 21
Table 3: List of Chemicals and Solvents 30
Table 4: Instruments for Characterization 31
Table 5: Physical Data of The Resulted Thiourea Derivatives 46
Table 6: Elemental Analysis Data of The Synthesized Thiourea 48 Derivatives
Table 7: The Important Infrared Absorption for All Compound in 51
cm -1
Table 8: 1H Shifts Analysis in ppm for Compound T6, T7 and T8 57
Table 9: 13C Shifts Analysis in ppm for Compound T6, T7 and T8 58
Table 10: Parameters Obtained from Weight Loss Measurement for 66 Mild Steel in 1.0 M HC1 Containing Different Concentrations of Inhibitors
Table 11: Electrochemical Parameters of Mild Steel Corrosion in 1.0 70 M HC1 Solution in The Absence and Presence of Different Concentrations of Inhibitors
Table 12: Electrochemical Impedance Parameters for Mild Steel in 77 1.0 M HCl Solution in the Absence and Presence of Compound T6, T7 and T8 at Different Concentration
ix
LIST OF FIGURES
Figure Title Page
Figure 1: Mechanism of Actuation of Organic Inhibitors, When It Is 14 Adsorbed to the Metal Surface and Forms a Protector Film on It
Figure 2: Theoretical Potentiostatic Polarization Diagram: 15 Electrochemical Behavior of Metal on a Solution Containing a Cathodic and Anodic Inhibitor (A) Compared to the Same Solution Without the Inhibitor (B)
Figure 3: Illustration of a Corrosion Inhibitor Adsorbed onto a Metal 17 Surface
Figure 4: Thiourea 18
Figure 5: Tautomeric Forms of Thiourea 18
Figure 6: Structure of Thiourea and Urea 19
Figure 7: Customary Structure of Thiourea 20
Figure 8: Examples of Carbonyl Thiourea Derivatives 20
Figure 9: Mechanism of Formation of Mono Thiourea Derivatives 23
Figure 10: Reaction Pathway of N-(2-Methoxybenzoyl)-N'-(4- 23 Diphenylamine)Thiourea
Figure 11: FTIR Spectrum for Compound T6 52
Figure 12: FTIR Spectrum for Compound T7 53
Figure 13: FTIR Spectrum for Compound T8 54
Figure 14: 'H NMR Spectrum for Compound T8 59
Figure 15: 13C NMR Spectrum for Compound T8 60
Figure 16: Mechanism of Formation of Benzoylthiourea Derivatives 62
Figure 17: Structure of Compound T6 63
Figure 18: Structure of Compound T7 63
Figure 19: Structure of Compound T8 63
x
Figure 20: Polarization Curve for Mild Steel in 1.0 M HCI in the 71 Absence and Presence of Different Concentration of Compound T6
Figure 21: Polarization Curve for Mild Steel in 1.0 M HC1 in the 72 Absence and Presence of Different Concentration of Compound T7
Figure 22: Polarization Curve for Mild Steel in 1.0 M HCI in the 73 Absence and Presence of Different Concentration of Compound T8
Figure 23: Nyquist Plot for Mild Steel in 1.0 M HCI in Different 78 Concentrations of Compound T6
Figure 24: Nyquist Plot for Mild Steel in 1.0 M HC1 in Different 79 Concentrations of Compound T7
Figure 25: Nyquist Plot for Mild Steel in 1.0 M HC1 in Different 80 Concentrations of Compound T8
Figure 26: List of EDG and EWG Substituent 84
X1
Scheme Title
Scheme 1:
Scheme 2:
Scheme 3:
Scheme 4:
Scheme 5:
Scheme 6:
Scheme 7:
Scheme 8:
LIST OF SCHEMES
Page
Chemical Equation for 1-cyclohexyl-3-(4- 32 fluorobenzoyl)thiourea (Ti) Formation
Chemical Equation for 1-(4-fluorobenzoyl)-3-(4- 33 fluorophenyl)thiourea (T2) Formation
Chemical Equation for 1-(4-fluorobenzoyl)-3-(4- 34 nitrophenyl) thiourea (T3) Formation
Chemical Equation for 1-(4-chlorobenzoyl)-3-(4- 35 nitrophenyl)thiourea (T4) Formation
Chemical Equation for 1-(4-bromophenyl)-3-(4- 36 chlorobenzoyl) thiourea (T5) Formation
Chemical Equation for 1-(4-chlorobenzoyl)-3-(4- 37 fluorophenyl)thiourea (T6) Formation
Chemical Equation for 1-(4-chlorobenzoyl)-3-(3-chloro-2- 38 fluorophenyl)thiourea (T7) Formation
Chemical Equation for 1-(4-chlorobenzoyl)-3-(6-chloro-2- 39 fluoro-3-methoxyphenyl)thiourea (T8) Formation
xii
LIST OF ABBREVIATIONS AND SYMBOLS
ASM American Society for Microbiology
CHNS Carbon, Hydrogen, Nitrogen and Sulphur Analysis
CPE Constant Phase Element
DMSO Dimethyl Sulfoxide
EDG Electron Donating Group
EWG Electron Withdrawing Group
FTIR Fourier Transform Infrared
LPR Linear Polarization Resistance
NMR Nuclear Magnetic Resonance Spectroscopy
OCP Open Circuit Potential
% Percentage
°C Degree Celsius
Ec, Corrosion Potential
et al. And co-workers
g Gram
h Hour
lc°« Corrosion Current
mg Milligram
ppm Part per Million
wt% Percentage of Weight
xiii
LIST OF APPENDICES
Appendix Title Page
Appendix A The FTIR Spectrum for T 1-T5 103
Appendix B The 1H NMR Spectrum for T1-T7 108
Appendix C The 13C NMR Spectrum for T6-T7 115
Appendix D Conferences and Seminar Participated 117
