Oxidative degradation and
associated complexation study of citric acid by di-tertiary butyl chromate
Renuka Thakur1, Rajeev Ranjan2*
1PG Department of
Chemistry, Ranchi Women’s College, Ranchi-834001
2PG Department of Chemistry, Ranchi College,
Ranchi-834008
*Corresponding Author E-mail: rajeevran7@yahoo.com
ABSTRACT:
Ditertiary
butyl chromate (TBC) has been used to oxidize citric acid in different molar
proportions and the solid products obtained have been isolated and analyzed.
Elemental analysis, IR and thermal studies have been carried out. The thermal
decomposition pattern, mechanism of decomposition and evaluation of kinetic
parameters of the products have been reported in this paper.
KEYWORDS: TBC, DTA, TGA, TLC
Chromium
trioxide is a strong oxidant in non-aqueous solvent and is used successfully to
oxidize variety of organic compounds. So many Cr(VI) based oxidants are being
used to carry out oxidation of a wide variety of organic substrates.1-9 Cr(VI) based oxidants
are not only used to carry out oxidation but also for the complex formation
with advantage of associated degradation during the process.10-23
The
simultaneous DTA, TG curves of the complexes were recorded. Thermal analysis
involves linear heating of the complexes. On increasing the temperature, there
may various chemical and physical changes occur at definite temperature ranges.
Characterization of these complexes helps in ascertaining the products formed
by oxidation of citric acid. The oxidation of citric acid by TBC (di-tertiary
butyl chromate) produces lactic acid acetic acid and formic acid which form
complexes with chromium.
EXPERIMENTAL:
Materials and
Methods:
A
molar solution of tertiary butyl chromate (TBC) was prepared by dissolving 1 gm
of dry CrO3 in 2.2 ml of tertiary butyl alcohol (TBA). This clear
brown solution of di-tertiary butyl chromate (TBC) was added to citric acid
dissolved in minimum volume of dioxan, in different substrate and oxidant ratio
with constant stirring and solid products RBC1, RBC2, RBC3
and RBC4 were isolated. The obtained solid products were washed
several times with dioxan, benzene and finally with acetone. Purification of
these compounds ware done by TLC. Elemental analysis, IR and thermo-gravimetric
analysis of these compounds have been carried out. On elemental and spectral
analysis, these products were identified as complexes of chromium involving
oxidation as ligands (table-1). The weight loss and corresponding heat changes
confirms the expected sequence of reactions on heating.
Table-1
|
CA + TBC |
Symbol |
Colour |
Empirical formula |
Composition of the products |
|
1: 0.25 |
RBC4 |
Ash powder |
C3H7CrO5 |
[(CH3COOH)(HCOOH)Cr] |
|
1: 0.5 |
RBC3 |
Cement ash |
C4H9CrO6 |
OH | [(CH3-CH-COOH)Cr (HCOO-).H2O] |
|
1: 0.75 |
RBC2 |
Dark brown |
C4H10CrO8 |
OH | [(CH3-CH-COOH)CrO2(HCOOH).H2O)] |
|
1:1 |
RBC1 |
Cement ash |
C4H10CrO7 |
[CH3-CH-COOH)CrO(HCOOH).H2O] |
Citric acid: Ditertiary butyl chromate
The
products depend on the strength of oxidant. The complexes RBC1, RBC2,
RBC3 and RBC4 have been analyzed thermogravimetrically
for the evaluation of their thermal decomposition kinetic parameters and
thermal decomposition mechanism by NETZSCH Simultaneous Thermal Analyzer STA
409. These complexes decomposed in two or three steps. The intermediate formed
undergo further decomposition without remaining stable over a significant range
of temperature.
Table-2
Thermal analysis of RBC1
|
Temp. |
Sequence showing change |
Weight Loss |
Parentage Loss |
||
|
|
|
Theo. |
Exp. |
Theo. |
Exp. |
|
Upto 120oC |
OH Step
I -H2O OH |
18 |
18.87 |
8.10 |
8.15 |
|
200-300oC |
OH |
46 |
45.70 |
20.72 |
20.58 |
|
300-400oC |
OH CrO2 |
90 |
93.88 |
40.32 |
42.28 |
|
Total |
|
154 |
158.45 |
69.36 |
71.36 |
Results and Discussions:
The
regular decomposition of complex RBC1(C4H10CrO7)
started at 120oC and it losses one molecule of water at this
temperature in step-I (table-2). The step-II involves loss of one molecule of
formic acid. The step-III involves loss of lactic acid. The DTA graph shows
three distinct exothermic peaks (fig-1). The first one appeared at 120oC
when one molecule of water was completely lost. Second peak appeared at 280oC.
At this temperature formic acid was starting to break. The third major peak
appeared at 350oC at this temperature lactic acid was completely
lost leaving behind CrO2. By this schematic change, we see that the
theoretical total loss percentage almost confirmed the experimental total loss
percentage.
Table-3
Thermal analysis of RBC4
|
Temp |
Sequence showing change |
Weight Loss |
Percentage loss |
||
|
Theo. |
Exp. |
Theo. |
Exp. |
||
|
100-260oC 260-560oC |
[(CH3-COOH) (HCOOH)CrO Step
I - HCOOH (CH3 - COOH) CrO Step II - CH3COOH CrO |
46 60 |
45.67 58.57 |
26.43 34.48 |
26.24 33.66 |
|
Total |
|
106 |
104.24 |
60.91 |
59.90 |
In
the complex RBC4 (C3H7CrO5), the
decomposition started at 100oC. At this temperature one molecule of
formic acid is lost. The second step involves loss of one molecule of acetic
acid. The maximum loss is between 260oC-560oC (table-3). The
DTA graph shows two distinct exothermic curves (fig-2). The first one appeared
at 100oC. At this temperature formic acid was started to break and
was completely lost. Second peak appeared at 340oC. At this
temperature acetic acid was started to break and was completely lost leaving
behind CrO.
From
the above analysis we can conclude that the formula of RBC4 is to be
[(CH3-COOH) HCOOH CrO] which is supported by TG and DTA curves.
Table-4
Prominent IR bands of complexes (in cm-1)
|
Group Assignment |
RBC4 |
RBC3 |
RBC2 |
RBC1 |
|
Cr-O stretching |
632.65 |
628.79 |
501.49 |
509.21 |
|
C=O symmetric stretching in COO- |
1226.73 |
1226.73 |
1238.30 |
1072.42 |
|
C=O antisymmetric stretching in COO- |
1577.77 |
1593.20 |
1566.66 |
1442.75 |
|
O-H stetching (broad) |
3073.53 |
3077.68 |
3086.11 |
3093.82 |
Fig-1
DTA/TG curve of RBC1
Fig-2
DTA/TG curve of RBC4
The presence of
coordinated water in some complexes were indicated by broad band in the region
3500-3200 cm-1.24-25 A number of polynuclear complexes of
Cr have been reported previously with carboxylate ion with many different
framework.26-28 Since the nature of DTA/TG curve of the complexes
are similar, the sequential change and DTA/TG graph of only RBC1 and RBC4 are given(fig-1 and fig-2).
ACKNOWLEDGEMENT:
We
are thankful to the Head, CIF, BIT Mesra, Ranchi, for providing IR Spectra and
elemental analysis. We are also thankful to the Director, RDCIS, SAIL, Ranchi,
for providing TG/DTA analysis.
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Received
on 27.09.2015 Modified on 09.10.2015
Accepted
on 15.10.2015 © AJRC All right reserved
Asian J. Research Chem. 8(11): November 2015; Page 657-660
DOI: 10.5958/0974-4150.2015.00105.4