Oxidative Degradtion and Associated Complexation of Ethylacetoacetate by cr (VI) Based Oxidant
K. Akhtar1, R. Ranjan1* and M. Alam2
1PG Department of Chemistry, Ranchi College, Ranchi-834008
2University Department of Chemistry, Ranchi University, Ranchi-834008
*Corresponding Author E-mail: rajeevran7@yahoo.com
ABSTRACT:
The present paper investigates the action of di-tertiary butyl chromate (TBC) - a Cr(VI) based oxidant - on ethylacetoacetate with following aims: (a) Whether degradation occurs along with oxidation? (b) Whether Cr in reduced state enters into complexation with the oxidised fragments or with the unreacted substrate itself? (c) Whether the oxidation is selective i.e., does arresting the reaction at different stages (by taking different substrate: TBC molar ratios) result into same product or not.
KEYWORDS: TBC, TBA, FTIR, TLC, TG, DTA
A number of Cr (VI) based oxidants are being used to carry out oxidation of a wide variety of organic substrates. 1-10 Important among these are di-tertiary butyl chromate, di-isopropyl chromate, chromium peroxide etherate, pyridine chromium peroxide and 2,2-bipyridyl chromium peroxide. But owing to several merits11-13 , di-tert-butyl chromate (TBC) has got an edge over other Cr(VI) based oxidants and therefore it is not only exploited to carry out oxidation but also for complex formation taking advantage of the associated degradation during the process14-21.
EXPERIMENTAL:
In each case TBC was prepared by dissolving CrO3 in TBA. Substrate i.e. ethylacetoacetate was dissolved in TBA. These two solutions were mixed, stirred and refluxed, if needed. In all cases solid products separated out. Solid products isolated were washed with TBA/ acetone/benzene/toluene so as to remove impurities and/or excess of the oxidant. Purity of the products was tested with TLC, using silica gel. Pure solid products were then subjected to elemental, spectrophotometric and spectroscopic (FTIR) analyses. Thermal analyses were carried out and TG and DTA curves were recorded.
RESULTS AND DISCUSSION:
Following absorption bands were obtained in the IR spectrums of the compounds ;
KEAA I
|
Wave No.(cm-1) |
Group Assignment |
|
540 |
Cr-O stretching |
|
810 |
HOH wagging due to co-ordinated water |
|
1140 and 1288.4 |
C=O stretching, symmetric in COO- |
|
1548 and 1680 |
C=O stretching, antisymmetric in COO- |
|
3300 and 3743.6 |
O-H stretching |
KEAA II
|
Wave No.(cm-1) |
Group Assignment |
|
518 |
Cr-O stretching |
|
808 and 1060 |
HOH wagging due to co-ordinated water |
|
1140 and 1288 |
C=O stretching, symmetric in COO- |
|
1548,1649 and 1683 |
C=O stretching, antisymmetric in COO- |
|
3514 and 3735 |
O-H stretching |
KEAA III
|
Wave No.(cm-1) |
Group Assignment |
|
518 |
Cr-O stretching |
|
808.1 and 1060 |
HOH wagging due to co-ordinated water |
|
1170,1290 and 1411 |
C=O stretching, symmetric in COO- |
|
1525.6 and 1685.7 |
C=O stretching, antisymmetric in COO- |
|
3400 and 3732 |
O-H stretching |
On the basis of quantitative, spectrophotometric and spectroscopic analyses, the products were found to be complexes of Cr with oxidised fragments of the substrate, mainly acetic acid and/or acetate, acting as ligands along with water that might have been formed during the process. Thermal analyses of the samples
Table-1. Substrate-ethylacetoacetate in TBA
|
Subs: TBC (molar ratio) |
Name of pdt |
Color of pdt |
Empirical formula of pdt |
Formulation of pdt |
For.Wt |
|
1:3 |
(KEAA I) |
brown |
C4H14O11Cr4 |
(CH3COO-)2 4H2O Cr4O3 |
446 |
|
1:1.5 |
(KEAA II) |
brown |
C4H16O12Cr4 |
(CH3COO-)2 5H2O Cr4O3 |
464 |
|
1:1 |
(KEAA II) |
brown |
C6H16O12Cr |
(CH3COO-)3 3H2O Cr4O2 (OH) |
488 |
|
|
|
|
|
|
|
were carried out and TG and DTA curves recorded, which appear to corroborate the conclusion reached. Findings are given in table-1.
CONCLUSIONS:
In the cases cited above, ethylacetoacetate is oxidised to acetic acid and Cr in reduced state (II) enters into complexation with acetic acid and/or acetate, along with water that might have been formed during the process. The substrate does not find place in the co-ordination zone of Cr (found by comparing the spectrums of ethylacetoacetate with those of the products). All are tetranuclear complexes. Of late a number of polynuclear complexes of Cr have been reported particularly with carboxylate anion with so many different networking. The findings should also be seen in that context22-24.
ACKNOWLEDGEMENT:
The authors duly acknowledge the kind co-operation of SAIF-CDRI, Lucknow, RDCIS (SAIL), Ranchi and RDCIS (MECON), Ranchi.
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Received on 14.01.2012 Modified on 12.02.2012
Accepted on 28.02.2012 © AJRC All right reserved
Asian J. Research Chem. 5(2): February 2012; Page 191-192