الفهرس 
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Abstract
The present thesis is devoted to
of medium, subs ti tuents and to deduce
study the effect
the mechanism of
the electrode reaction for two series of different azo
compounds using DC-polarography and cycl ic vol tammetry
techniques. This work comprises of three chapters:
Chapter (I) includes the literature survey on the
polarographic and cyclic vol tammetric behaviour of the
azo-compounds. Extension of chapter (I) was intended to
the uv-visible absorption spectra of some azo-dyes to
show the effect of solvents and buffer solutions on the
absorption bands.
Chapter (II) includes preparation of the azo-dye
compounds derived from 4-aminoantipyrine and those
derived from sulfanilamide, instruments and solutions
which were used for the measurements using different
techniques.
Chapter (III) comprises six parts. 1- Part (A)
include the results and data obtained from the polarographic
studies of the azo compounds in aqueous buffer
solutions of different pH values (2-12) containing 10%
(v/v) ethanol for antipyrine azo-dyes (first series) and
30% (v/v) DMFfor sulfonamide azo-dyes (second series).
(ii )
The polarographic behaviour of the present azo
compounds of the first series (I f) and second series (II f) a- aexhibi
ted a single polarographic wave wi thin the entire
pH range except for compounds Ie , IIa and
Generall y, the limi ting current (iI) of the reduction
waves of all compounds is considered to be pH-independent,
revealing that the total number of electrons consumed in
the reduction process is the same in both acidic and
alkaline solutions. On the other hand, the half-wave
potential of the waves get shifted to more negative
patentials on increasing pH of the electrolysis medium
denoting that hydrogen ions are consumed in the reduction
process. The plots of the half-wave potential vs.
pH for all the compounds give satisfactory linear correlations
consisting of one or two segments. The breaks
occured at pH values within the range 6-8 and 7-9 for
series (Ia-f) and (IIa-f)’ respectively.
The effect of mercury height on the limiting current
denoted that the reduction process of all compounds is
mainly diffusion-controlled with some adsorption contribution,
since the values of the exponent x in the relation
(il ~ khx) equal to 0.48-0.75 for the first series
(la_f) and 0.44-0.75 for the second series (IIa_f).
Logarithmic analysis of the polarographic waves using
the fundamental equation of polarography confirmed the
irreversible nature of the waves. The plots of Ed. e vs •
log (i/id-i) give linear correlations. from the slopes
of these plots, values of the transfer coefficient (0<:)
were calculated and found to be less than unity at na=2.
The number of protons (ZH+) participating in the rate
determining step was determined from slopes of logarithmic
analysis and those of E~ - pH curves and found to be one
2
for all depolarizers in both acidic and alkaline solutions,
i.e. the rate-determining step involved two
electrons (na=2.0) and one proton (ZH+ = 1.0).
2- Part (B) include the cyclic voltammetric behaviour
of the azo compounds of series (I & II). The vol tammo-
grams of 1x10-4M of the depolarizers of the two series
were investigated and recorded in buffer solutions of pH
values equal to 3.6, 6.7 and 10.0 at different scan
rates (20-500 mVIs). The vol tammograms of compounds Ic’
Id, lIb’ lId and lIe displayed a single cathodic peak,
whereas those of compounds la’ Ib, Ie’ If’ IIa, IIc and
IIf consisted mainly of two distinct cathodic peaks in
all media. The absence of any anodic peak in the reverse
scan and the shift of peak potential (Ep) to more negative
values on increasing scan rate (v ) confirmed the
irreversible nature of the reduction process. The values
of the transfer coefficient (0<-) were obtained from the
slopes of the E -In v plots. These values of ~-parameter p
------- ------------
(iv)
which are less than unity confirmed the irreversible
nature of the electrode process. The linear plots of
peak current (i ) v e , square root of rate (v~) p scan
showed a small deviation from the origin confirming that
the electrode process is mainly diffusion-controlled
with some adsorption contribution.
3- Part (C) concerned with the calculation of the
kinetic parameters of the electrode reaction, and the
effect of substituents on the reduction mechanism. The
kinetic parameters of the electrode reaction; the rate
• constant (Kf ,h) and the activation energy (AG ) were
evaluated from DC-polarographic and cyclic vol tammetric
measurements. The obtained results revealed that the
values of Kf ,h
the activation
are found to be decreased and subsequently
• energy (.e.G ) increased on increasing pH
of the electrolysis medium, which denoted the more
irreversible nature of reduction process on going from
acidic to alkaline part of the pH range.
4- Part (D) includes the determination of the
diffusion coefficient values of the depolarizers of
series I & II and the total number of electrons consumed
in the overall reduction process using Ilkovic equation.
The results obtained revealed that the roduction process
of the azo compounds (I )
a-e and (II )
a-e consumed 4
-- - _._--------- -------~--------
(v )
electrons Idepolarizer molecule, whereas 10 and 6 electrons
are consumed for compounds If and IIf, respectively.
The results were confirmed by controlled potential
coulometry (cpc) measurements. The thin layer chroma tography
(TLC) of the completely electrolysed solutions of
the azo compounds Ia and II’a confirmed that 4-aminoantipyrine
and sulphanilamide were produced on comparing the
products of the completely electrolysed solutions of
compounds Ia and IIa with the authentic samples, respectively.
Thus, the electroreduction process of these
compounds (series I & II) takes place via the cleavage
of the N;N center. For compound (If) which contains the
electroactive -N02 group, the remaining six electrons
are consumed in the reduction of -N02 to the
group. On the other hand, for compound (IIf), the remaining
two electrons are consumed in the reduction of the
electroactive -CHO group to the -CH20H group. The
suggested mechanistic pathway of the electrode reaction
was established and discussed.
5- Part (E) includes the effect of complexation of
some azo compounds of series I & lIon the polarographic
behaviour of some transition metal ions such as Cu (II) ,
Zn(II) and Ni(II) ions in 0.1 M NaN03 as supporting
electrolyte. The polarographic behaviour of 2xl0-
4
M of
the simple metal ions was investigated. The half-wave
--_.---------
(v i )
potential (E~) as well as the diffusion current of
the simple metal ions were found to be affected by the
gradual addition of different concentrations of the ligand
(10-4 _10-3M). The diffusion current of the metal ions
was decreased on increasing ligand concentration which
may be attributed to the increased bulk of the complexed
metal ions. The half-wave potentials of the metal ions
were shifted to more negative values on increasing the
ligand concentration, denoting to the complex formation.
The values of (0< n) and (Kf ,h) were determined from
logarithmic analysis of the complexed waves and found to
be decreased, revealing that the irreversibility of the
electrode processes is increased on increasing the ligand
concentration. The plots of AE~
correlations of slopes equal to j
v s , log ex give 1inear
(0.0591). The coordinan
tion number (j) was determined from these slope values.
At the same time, the overall stability constants (log
BMX.) of the formed complexes were determined from the
J
intercept of the above plots.
6- Part (F) contains spectrophotometric methods for
structural informations about molecules of the azo dyes
under investigations such as effect of solvent and buffer
solutions on the characteristic absorption bands. The
spectra of azo dyes were found to be affected by the
nature of sol vent, and the displacement of absorption
(vii)
bands to red shift on going from nonpolar solvent to
polar one. The shift may be attributed to physical
properties of solvent or due to the formation of hydrogen
bonding between solvent and solute. The study of different
functions of solvent such as (D--1/D+1)vs.t>)J and
A against the functions F (D) , F2(n) , 0< , IT , 13, E max T
and Z revealed that the red shift of CT band is due to
the increased polarity of the solvent and blue shift is
due to intermolecular hydrogen bond formed between the
solvent molecules and the n-electrons of the azo group.
The absorption spectra of azo compounds under
investigation have been carried out in universal buffer
solutions containing 30% (v/v) ethanol within the pH
range (2-12). All the azo compounds (la_e) and (lIb_e)
exhibited an absorption band in the visible region within
• the range (350-400 nrn ) due to TT: - JL and CT transi tions of
the n-electrons along the whole molecule. On increasing
the pH of the medium, the absorption band located in the
above range of wavelength displayed a red shift which is
attributed to the partial ionization of the OH group.
Determination of the acid dissociation constants (pk) of
the azo compounds under investigation using the variation
of absorbance wi th pH was performed using three
different methods.