CHAPTER - II
T
HEORETICAL
THEORETICAL
II.1
CHAPTER II
INTRODUCTION TO GRAVIMETRIC ANALYSIS
Gravimetric analysis describes a set of methods in analytical chemistry for the
quantitative determination of an analyte based on mass of the solid. Gravimetric
analysis is potentially one of the most accurate classes of analytical method available,
as weight can be measured with greater accuracy than almost any other fundamental
property.
It involves isolation and weighing of an element or a definite compound of the
element in as pure a form as possible
(1)
. A large portion of the determination in
gravimetric analysis is concerned with the transformation of the element or radical to
be determined in the pure stable compound which can be readily converted into a
form suitable for weighing. The weight of the element or radical may then be readily
calculated from the knowledge of the formula of the compound and the atomic weight
of the constituent elements. It can be satisfactorily employed in the concentration
range of decigram to milligram of actual weight and hence is a macro-analytical
technique.
TYPES OF GRAVIMETRIC ANALYSIS
There are four fundamental types of gravimetric analysis (2): physical gravimetry,
thermogravimetry, precipitative gravimetry and electrodeposition. These differ in the
preparation of the sample before weighing of the analyte as given below:
a)
Physical gravimetry: It is the most common type used in environmental
engineering. It involves the physical separation and classification of matter in
environmental samples based on volatility and particle size. Most common
analytes are total solids, suspended solids, dissolved solids, surfactants, oil and
grease.
b)
Thermogravimetry: It is a technique in which the mass of a substance is
measured as a function of temperature, while the substance is subjected to a
controlled temperature programme. They are used in a wide range of disciplines,
from pharmacy and foods to polymer science, glasses and volatile solids.
c)
Electrodeposition: It involves the electrochemical reduction of metal ions at a
cathode and simultaneous deposition of the ions on the cathode. The cathode is
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weighed prior to and after electrolysis and the weight difference corresponds to
the mass of analyte initially present in the sample. It is generally used in
environmental engineering analysis.
d)
Precipitative gravimetry: As the name implies, precipitative gravimetry relies on
the chemical precipitation of an analyte. This method is discussed below in
detail.
II.2
PRECIPITATIVE GRAVIMETRY
Precipitation methods are perhaps the most important with which the analysts are
concerned in gravimetric analysis. It is the key chemical reaction involved in
gravimetric method because it can be a highly selective means for separating the
component of interest from the matrix.
II.3
IDEAL CONDITIONS FOR PRECIPITATIVE GRAVIMETRY
The factors which determine a successful analysis by precipitation are
(2)
:
1) Precipitate must be formed quantitatively. 2) Precipitate must be formed within a
reasonable time. 3) Its solubility should be low enough for quantitative separation. It
should be so slightly soluble, that its amount left behind in the solution should not
exceed 10-6 mol. 4) Weighed form of the precipitate must be in the form of a
stoichiometric compound of known composition. Failing this, it must be possible to
convert the precipitate to a stoichiometric weighable form (usually by ignition).
5) Particle of the precipitate must be of such size that they do not pass through the
filtering medium and is unaffected by the washing process. 6) It should be easily and
quickly filterable and it should be possible to remove the soluble contaminations by
washing the precipitate. 7) The precipitate must be free of impurities.
II.4
OPERATIONS INVOLVED IN PRECIPITATIVE GRAVIMETRY
Operations involved in gravimetric analysis are (3): Sample pretreatment, precipitation,
digestion, testing for completion of precipitation, filtration, washing, drying and
igniting, weighing and calculation.
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II.4.1 SAMPLE PRETREATMENT
The first step in performing gravimetric analysis is to dissolve the given sample and to
prepare the solution. Some form of preliminary separation may be necessary to
eliminate interfering materials
(4)
. Also, adjustment of the solution conditions is
necessary to maintain low solubility of the precipitate and to obtain it in a form
suitable for filtration.
Factors that must be considered include:
i.
Volume of the solution during precipitation
ii.
Concentration range of the test substance
iii.
Presence and concentration of other constituents
iv.
Temperature
v.
pH – a small amount of acid or alkali may be added as required.
II.4.2 PRECIPITATION
Precipitation is an ionic reaction in which the positive ion of one substance in solution
combines with the negative ion of another substance, also in a solution, to form a
sparingly soluble substance. Most of the precipitates encountered in analytical
chemistry are sparingly soluble salts which behave like strong electrolytes i.e. salt
which are almost completely ionized. The primary condition for precipitation of a
substance to take place from a solution is that the product of the ionic molar
concentrations of the substance should exceed the solubility product of the substance.
Precipitation mechanism is an important step and the completeness of precipitation of
the desired constituent is determined by the solubility of the constituent at
equilibrium. Therefore, the precision of the analytical result depends on the factors
that affect the solubility of a precipitate namely the choice of precipitant, the amount
of precipitant added, the conditions of precipitation, etc. which make the analytical
results incorrect unless the proper steps are taken.
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II.4.2.1
1.
CHAPTER II
FACTORS AFFECTING PRECIPITATION
Choice of precipitant: The precipitant should be such that it produces a
precipitate which is completely insoluble i.e. solubility product should not exceed
10-6 mol. The structure of the precipitate formed should be such so as to allow
rapid filtration and washing. Organic reagents have a special place in inorganic
analysis (generally termed as organic precipitants) because of the following
advantages offered by them (5).
i. Many of the chelate compounds are very insoluble in water, so that metal ions
may be quantitatively precipitated.
ii. The organic precipitant often has a high molecular weight. Thus a small amount
of metal may yield a large weight of precipitate, minimizing weighing errors.
iii. Some of the organic reagents are fairly selective, yielding precipitates with only
a limited number of cations. By controlling factors such as pH and the
concentration of masking agents, the selectivity of an organic reagent can often
be greatly enhanced.
iv. The precipitates obtained with organic reagents are often coarse and bulky and
hence can be easily handled.
v. Further, metal chelates are mostly anhydrous. Hence, the precipitates dry quickly.
This can be accelerated by washing the precipitate with alcohol.
2.
Amount of precipitant: The amount of precipitant added is also of great
importance. If a large excess of precipitant is added, the precipitate formed
redissolves as it raises the solubility of the precipitate and if just enough amount
is added then complete precipitation might not take place as some amount is
required to reach the solubility product value. Hence, in precipitating a substance,
a reasonable, excess of precipitant is invariably added to ensure completeness of
precipitation. The excess precipitant provides excess of common ions and the
solubility of precipitate is decreased. For analogous reasons, the precipitate is
washed with a solution containing common ions.
3.
Effect of temperature: The solubility product of a substance is constant only
when its temperature is unaltered. Usually the solubility increases with the
increase in temperature. When the precipitation is carried out at higher
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temperature, the precipitate formed is of high purity due to better crystal
structure. Hence, wherever possible, precipitation which is carried out at higher
temperature is most advantageous but then it should be cooled before filtration.
4.
Effect of pH: The solubility of the precipitate with the change in pH of the
solution is inevitable. The effect depends on the type of precipitate. Generally,
the precipitate of metal hydroxides and those of sparingly soluble salts of weak
acids are precipitated only in alkaline or neutral pH ranges. Smaller the
dissolution constant for the acid, higher is the pH required for practically
complete precipitation of its salt
(6)
. The selectivity of organic reagents can
always be improved by the control of pH.
5.
Effect of complex formation: In the presence of certain ions, the desired
component is likely to form complex ions having higher dissociation constants
and this will lead to incomplete precipitation. So the unwanted ions should be
prevented from getting precipitated out by masking them. Masking is the
procedure of forming soluble complexes with the unwanted ions and thus
keeping them in solution (7).
II.4.2.2
MECHANISM OF PRECIPITATION
The purity and the filterability of a precipitate greatly depend upon the particle size of
the precipitate. The particle size is determined by the relative rates of the two
processes namely (8), nucleation which is the production of extremely small particles
(nuclei) capable of spontaneous growth and particle growth (crystal growth) which is
the growth of the nuclei.
Once the nucleation process starts, it proceeds ultimately to form the precipitate. This
can be represented with the help of actual particle size increase as given below (9):
Ions (10-8 cm) → Nucleation clusters (10-8 to 10-7 cm) → Colloidal particles
(10-7 to 10-4 cm) → Precipitate (> 10-4 cm)
This shows that the nucleation clusters pass through the stage of colloidal particle size
prior to precipitation. Problems which arise with certain precipitates include
coagulation or flocculation of a colloidal dispersion of a finely divided solid to permit
its filtration and to prevent its repeptisation upon washing the precipitate. Hence, the
effect of colloidal state on the process of precipitation is also important.
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The effect of the rate of precipitation on the particle size has been studied by von
Weimarn (10). He found that faster the precipitation, smaller is the particle size. He
also found that the rate of precipitation is dependent on the relative super-saturation.
According to von Weimarn,
Where, Q-S = relative supersaturation,
Q = molar concentration of the mixed reagents before precipitation,
S = molar solubility of the precipitate at equilibrium,
K = a constant.
Applications of the above conceptions are to be found in the following recognized
procedures in gravimetric analysis:
1) Precipitation is usually carried out in hot solutions, since the solubility generally
increases with rise in temperature. 2) Precipitation is effected in dilute solution and
the reagent is added slowly and with thorough stirring. The slow addition results in
the first particles size precipitated acting as nuclei which grow as further material
precipitates. 3) A procedure which is commonly employed to prevent supersaturation
from occurring is that of precipitation from homogeneous solution
(11)
. This is
achieved by forming the precipitating agent within the solution, by means of a
homogeneous reaction at a similar rate to that required for precipitation of the species.
II.4.2.3
PURITY OF THE ANALYTICAL PRECIPITATE
When a precipitate separates from a solution, it is not always perfectly pure. It may
contain varying amounts of impurities due to:
1. Co-precipitation:
If a precipitate is contaminated by substances which are normally soluble in the
solution under the condition of precipitation, then co-precipitation is said to have
taken place. Co-precipitation (12) occurs by the adsorption or occlusion.
2. Post-precipitation:
The process by which an impurity is deposited after precipitation of the desired
substance is termed as post-precipitation. When there is a possibility that post-
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precipitation may occur, directions call for filtration to be made shortly after the
desired precipitate is formed.
II.4.2.4
TYPES OF PRECIPITATE
Precipitates are classified into crystalline, curdy and gelatinous precipitates.
Crystalline precipitates are relatively pure and consist of easily filterable particles.
Curdy precipitates are agglomerates of colloidal particles and are of filterable size.
However, they are more easily contaminated than crystalline precipitates and hence
must be washed with an electrolyte solution. Gelatinous precipitates are flocculated
colloids. The particle size is smaller than that of curdy precipitates and hence is
difficult to filter. They must also be washed with an electrolyte solution to prevent
peptization.
II.4.3 DIGESTION OR AGEING
Generally, the primary precipitate obtained from a hot dilute solution is in the form of
crystals of nearly perfect lattice structure. However, those obtained from concentrated
solutions are generally very small crystals of imperfect structure. There is
considerable variation in particle size for any given primary precipitate. Such a
primary precipitate is subjected to digestion or ageing. This is done by allowing the
primary precipitate to remain in contact with the solution from which it is formed,
normally at higher temperature. The smaller particles exhibit higher solubility and
dissolve. As a result, the solution becomes supersaturated with respect to the larger
particles. This results in the deposition of the dissolved particles on the larger
particles and increase in the average particle size. This is known as digestion, ageing
or Ostwald ripening of the precipitate.
Under suitable conditions, the process of ageing also improves the perfection of the
crystal lattice structure to some extent. For various reasons most of the precipitates
carry with them impurities from the solution. During digestion these impurities, to
some extent, return to the solution when smaller particles dissolve.
II.4.4 TESTING FOR COMPLETION OF PRECIPITATION
Accurate values can be obtained only if the precipitation is complete. This is tested by
allowing the precipitate to settle down completely and then adding a drop or two of
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the precipitating reagent. If turbidity develops, then some more of the precipitating
agent should be added and further tested for completion of precipitation (13).
II.4.5 FILTRATION
Filtration is the separation of the precipitate from the mother liquor. The systems
employed are filter papers, Gooch crucibles and sintered-glass crucibles. The choice
of the filtering medium will be controlled by the nature of the precipitate and the cost.
II.4.6 WASHING OF PRECIPITATE
The wash liquid is normally water, sometimes containing an electrolyte. The choice
of the wash liquid depends on the following aspects (14):
1) Higher solubility for the impurities and lower solubility for the precipitate. 2) If the
precipitate is a flocculated colloid, a suitable electrolyte is added to wash the liquid to
prevent peptization of the precipitate. 3) If the ions of the adsorbed impurities are of
non-volatile nature, an electrolyte which can exchange its ions with the impurities to
form a volatile adsorbate is added. These volatile ions may be removed during drying
and ignition.
In addition to the choice of the suitable wash liquid, the mode of washing is also
equally important. The precipitate on the filter paper should be thoroughly stirred
using a jet of wash liquid. This should be followed by washing the edges of the filter
paper with the jet of wash liquid since the precipitate might spread out during
washing. A large number of washes with small volume of wash liquid is more
efficient to remove the impurities than a small number of washes with large volume
of wash liquid.
II.4.7 DRYING AND IGNITION OF PRECIPITATES
The precipitate which has been collected by filtration and washing is dried and/or
ignited to a compound of known composition. This is then cooled under proper
condition to be weighed accurately. Use of ash-free filter papers has greatly simplified
the ignition step. The drying and/or ignition, and finally the weighing are repeated till
constant weight of the residue is obtained to ensure the completion of these two
processes.
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The temperature at which the precipitate should be ignited depends on the following
factors: The precipitate should be ignited at such a temperature range at which it is
converted into a new compound of known and definite composition. Ignition at higher
than the optimum temperature should be avoided, as it may cause loss of the
precipitate due to volatilization, sublimation or decomposition. Most of the
precipitates are dried in an oven at about 373-423 K to remove water if it is only
loosely held, and not strongly adsorbed or occluded. Drying should be done at a
temperature at which antipeptization electrolyte associated with the precipitate is
completely volatilized. In such cases the precipitate will have a known and definite
composition and can be weighed.
Ignited residue must be cooled inside a desiccator containing a dehydrating agent to
remove moisture that might have been adsorbed by the residue when exposed to the
atmosphere during initial cooling. Sometimes, a carbon dioxide free atmosphere
might have to be maintained inside the desiccator if the residue is capable of
absorbing carbon dioxide.
II.4.8 WEIGHING
Modern balances can readily weigh samples directly and masses from several grams
to a few micrograms can be used accurately and quickly. It is essential that the
conditions are the same for the initial weighing as for the final weighing. Temperature
is especially important and hot samples should never be placed directly onto a
balance.
II.4.9 CALCULATIONS
In the usual gravimetric procedure a precipitate is weighed, and from this value, the
weight of the analyte in the sample is calculated with the aid of a gravimetric factor
(GF) (15). The GF is the ratio of the formula weight of the substance sought to that of
the substance weighed.
Usually, the purpose of a quantitative analysis is to determine the percentage of a
certain element or ion (A) in a sample, which can be calculated as:
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II.5
CHAPTER II
ERRORS IN CHEMICAL ANALYSIS
It is impossible to perform a chemical analysis (16) in such a way that the results are
totally free of errors or uncertainties. Unfortunately, there is no simple and widely
applicable method for determining the reliability of data with absolute certainty. It
requires as much effort to estimate the quality of experimental results as it requires
collecting them.
Mean: When carrying out replicate analysis the quantity obtained by dividing the sum
of the results by the number of measurements in the set is called as mean.
N
X = Σ Xi
i=1
-------------N
… … … … (iv)
Where,
Xi = individual value of x
N = set of N replicate measurements
Precision and accuracy: Precision describes the agreement between two or more
measurements that have been made in exactly the same way. Accuracy indicates the
closeness of a measurement to its true or accepted value and is expressed by the error.
Accuracy means agreement between a result and its true value.
Precision is determined by simply replicating a measurement. In contrast, accuracy
can never be determined exactly because the true value of a quantity can never be
known exactly. An accepted value is used instead.
Standard deviation: Standard deviation is a statistical term, scientists and engineers
use as a measure of precision. Standard deviation is determined as follows:
N
___
S = Σ (xi – X) … … … … (v)
i=1
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Where,
_____
______
xi – X = deviation from the mean (X) of the ith measurement.
The precision of a measurement is readily determined by comparing data from
carefully replicated experiments. There are three types of errors:
1.
Indeterminate (random) error: causes data to be scattered more or less
symmetrically around a mean value.
2.
Determinate (systematic) error: causes the mean of the set of data to differ from
the accepted value.
3.
Gross error: usually occur only occasionally but are often large and may cause a
result to be either high or low, this leads to results that differ markedly from all
other data in a set of replicate measurements.
Determinate errors:
They have a definite source that usually can be identified. They cause all the results
from replicate measurements to be either high or low because they are unidirectional.
Determinate errors are also called systematic errors.
Sources of determinate errors:
The 3 sources of errors are instrumental errors, method errors and personal errors.
1.
Instrumental errors: All measuring devices are sources of this type of error.
For e.g. pipettes, burettes and volumetric flasks may have slightly different volume
capacity from those indicated by their graduations. These differences may result from
using glassware at a temperature that differs significantly from the calibration
temperature, from distortion in container walls due to heating or from errors in the
original calibration. Calibration eliminates most determinate errors of this type.
2.
Method errors: The non-ideal chemical or physical behavior of the reagents
and the reactions upon which an analysis is based can introduce determinate method
errors. In gravimetric analysis sources of non-ideality include simultaneous
precipitation, co-precipitation or post-precipitation effects, the presence of side
reactions, poor selection of desiccant, weighing of hot crucibles and contents, etc.
Errors inherent in a method are difficult to detect and are thus the most serious of the
three types of determinate error.
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3.
CHAPTER II
Personal errors: Many measurements require personal judgments. Examples
include loss of precipitate during filtration, e.g. precipitate in a colloidal state, overwashing and under-washing during filtration process, insufficient drying or ignition,
etc.
II.6
SIGNIFICANT DEVELOPMENTS IN GRAVIMETRY
Some of the significant developments in this area are as follows:
a) The use of multidentate organic chelating agents
(17)
as precipitants has
substantially widened the scope of analysis.
b) The use of masking agents renders the method more selective. Masking is one of
the most widely used techniques for preventing interference and it binds the
interferent as a soluble complex, preventing it from interfering in the analyte’s
determination.
The auxiliary ligand preferentially binds with the species to be masked and forms
highly stable complexes with the potential interference. Cyanide, thiocyanide,
ammonia, fluoride, tartarate, oxalate, etc. find wide use as masking agents. Hence,
selectivity is usually not a problem (18).
c) The application of substoichiometric precipitation avoids chemical yield
determination. Substoichiometric procedure was first proposed by Ruzicka and
Stary (19). It is based on the use of sub-equivalent amount of reagent corresponding to
the amount of metal ion taken. It offers a possibility of selective separation which
could be fruitfully adopted for the estimation of inorganic ions. When observing the
advantages of the substoichiometric precipitation, analysis can be performed in a
more rapid and simpler way as compared to those carried out by using classical
procedures (20).
II.7
APPLICABILITY
OF
GRAVIMETRY
AND
ITS
ADVANTAGES
It is many a times the preferred technique because very often the precipitate can be
weighed, so that precipitation may be at the same time the basis of both the separation
and determination steps. One of the most important advantage is that gravimetry is an
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absolute method. It provides very little room for instrumental error and do not require
a calibration or standardization step because the results are calculated directly from
the experimental data and atomic masses. Also, these methods often do not require
expensive equipment. Another advantage is that the constituent is isolated and may be
examined for the presence of impurities, and a correction applied.
Gravimetric methods compare favorably with other analytical techniques in terms of
accuracy attainable. If the analyte is a major constituent (> 1% of the sample)
accuracy of few parts per thousand can be expected if the sample is not too complex.
These methods, when followed carefully, provide for exceedingly precise analysis
(0.1-1%). In fact, gravimetric analysis was used to determine the atomic masses of
many elements to six figure accuracy.
A gravimetric method for almost every element in the periodic table has been reported
in the chemical literature. Also, a number of pharmaceutical compounds are
determined gravimetrically either by isolating the pure form of the medicinal agent
without a chemical reaction or by conversion of the sodium salt to the acid form. The
elemental analysis of organic compounds can be done gravimetrically. The analysis of
rocks, ores, soils, metallurgical and other inorganic samples for their major
components has depended very much on gravimetric methods. One of the most
important application is the analysis of standards used for the testing and calibration
of those instrumental analytical techniques which one may consider to have replaced
gravimetry. Indeed, gravimetric methods are among the most widely applicable of all
the analytical procedures.
II.8
PROBLEMS ASSOCIATED WITH THE PRACTICE OF
GRAVIMETRY
1) Its disadvantage is that they are generally time-consuming.
2) Also, they lack in selectivity of precipitating reagents as there is no specific
precipitant for any specific cation or anion at present. So the precipitant may
precipitate more than one ion, unless great care is exercised.
Focusing on these two limitations, an attempt has been made to develop new
gravimetric methods which are more rapid and selective.
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II.9
CHAPTER II
SELECTION OF ORGANIC LIGAND
Ligand selection is an important consideration in many areas of chemistry, including
analytical, organic, inorganic and environmental chemistry. But the choice of ligand
becomes more critical especially when quantitative and selective separation of metal
ions is the aim of the study. Just as a sculptor chooses a starting piece for shape and
grain and assesses surmountable versus fatal defects, all with an eye towards his final
purpose, so the analyst must plot a route to his goal by proper selection of ligand in
developing a new gravimetric method.
Literature survey revealed that metallo-complexes of 2-MBT and their related 2-MBT
compounds have proved a fertile area for the study over years, stimulated both by the
diversity of their commercial application and the richness of their structural
chemistry. In heterocyclic thiones, both the endocyclic nitrogen atom and exocyclic
sulphur may act as donor atoms (21) and hence these ligands have great ability to adopt
different bonding modes, unidentate, bidentate or bridging sometimes in more than
one way in the same compound(22). This led to interest in the coordination chemistry
of heterocyclic thiones. 2-MBT has a high molecular weight and has been proved as
an excellent chelating agent
(23-28)
and hence was selected as an organic precipitant in
this study to develop new gravimetric methods.
II.10
2-MERCAPTOBENZOTHIAZOLE
II.10.1
INTRODUCTION
Synonyms
: 2(3H)-Benzothiazolethione, 2-Benzothiazolethiol,
1,3-Benzothiazole-2-thiol, 1,3-Benzothiazole-2-thione, 2-MBT,
Accelerator
M,
Benzothiazolethiol,
Mercaptobenzothiazole,
MBT,
Captax,
Mebetizole,
2-Benzothiazolinethione,
Benzothiazole-2-thione and numerous other trade names.
Molecular formula: C7H5NS2
Molecular weight : 167.25
Appearance
: Light yellow powder with faint odor
Density
: 1.42
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Melting point
: 179-181 ºC
Solubility
: < 0.1 g/100 mL in water,
also soluble in alkalies, alcohol, acetone, benzene and chloroform
Structure
:
Thiol
Thione
Figure II-I: INTERCONVERSION OF THIONE TO THIOL
II.10.2
LITERATURE REVIEW
2-MBT was reported by Hofmann (29) in 1887. 2-MBT is a potential bidentate ligand
with three donor sites. The bicyclic MBT has the unique feature of having one N and
two S atoms connected to a single carbon in a five membered heterocyclic moiety. It
has a pKa of 6.93 at 20 oC (30) and hence is present in acidic media as the unionized
protonated form (HMBT) which would adopt either the thione or the thiol structure (26)
as shown above. In basic media 2-MBT exists as the thiol ion (MBT-):
Figure II-II: STRUCTURAL REPRESENTATION OF THIOL ION
MBT- has the possibility of attaining aromatic character (6π-electrons) to the five
membered heterocyclic moiety. In such a situation the lone pair of electrons which are
available on the hetero atoms form the potential donor orbitals. The interesting feature
of these donor orbitals is that their orientation permits coordination either through the
two S atoms or through N.
2-MBT
and its metal derivatives have
industry
(31-32)
extensive
applications in the
rubber
, as preventatives for metal corrosion(33), and even as anti-tumour
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agents (34). In recent years, it has been observed that 2-MBT and its derivatives are
some of the most popular floatation collectors which have been synthesized and tested
for their collecting power in sulfide and non-sulfide mineral floatation. The basis of
these applications is apparently associated with the ability of 2-MBT to form metal
complexes, although little is known of the true nature of these compounds, probably
because of their insolubility. Compounds containing thiazole ring often possess
antibiotic activity and a lot of research has been carried out to study the toxic effects
of 2-MBT and their derivatives on several microbes. Investigations carried out
showed that they are used for their fungicidal and anti-microbial effects (35-36).
Another important application of 2-MBT is in analytical chemistry as an extracting
reagent in solvent extraction and as a precipitating reagent in gravimetric analysis. It
has been widely used as an analytical reagent in solvent extraction of Ag(I)(37),
Ru(III) (38), Hg(II) (39), Os(IV) (40), Ir(III) (41), Cd(II) (42), Cu(II) (43), Au(III) (44), etc. It
has been proved to be a successful chelating agent for the gravimetric estimation of
some cations such as Zr(IV) (45), Rh(III) (46), Pd(II) (47), Pt(IV) (48), etc. But, literature
survey reveals that, so far no work has been carried out for the gravimetric estimation
of Ni(II), Co(II) and Zn(II) with this reagent substoichiometrically. Therefore, it is the
aim of this work to develop new, rapid and selective methods employing 2-MBT as a
complexing agent.
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WORKS CITED
CHAPTER II
II.11 WORKS CITED
1. Mendham, J., Denney, R. C., Barnes, J. D. and Thomas, J. K. Vogel’s Textbook
of Quantitative Chemical Analysis. 6th Ed. Delhi : Pearson Education Ltd., 2000.
2. Mendham, J., Dodd, D. and Cooper, D. Classical Methods. Vol. 2., New Delhi :
Wiley India Pvt. Ltd., 1987.
3. Agarwala, S. K. and Keemti, L. Advanced Inorganic Chemistry. Meerut : Pragati
Prakashan, 1990.
4. Christian, G. D. Analytical Chemistry. Singapore : John Wiley and Sons, 2004.
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