Final


 Ammar J. Mohammed /Al-khwarizmi Engineering Journal ,vol.1, no. 1,PP 125-133  (2005)        
                                                                            

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Al-khwarizmi  
Engineering   

Journal       
                      Al-Khwarizmi Engineering Journal, vol.1, no.1,pp 125-133, (2005)         
 

Kinetic and Mechanism of Oxidation of Oxalic Acid by 

Cerium (IV) 
Dr. Ammar J. Mohammed 

Biochemical Engineering Dept./,Al-khwarizmi  Engineering College/ University of Baghdad 

 
Abstract: 

Kinetic and mechanism studies of the oxidation of oxalic acid by Cerium sulphate have been 
carried out in acid medium sulphuric acid. The uv- vis. Spectrophotometric technique was used to 
follow up the reaction and the selected wavelength to be followed was 320 nm. The kinetic study 
showed that the order of reaction is first order in Ce(IV) and fractional in oxalic acid. The effect of 
using different concentration of sulphuric acid on the rate of the reaction has been studied a and it was 
found that the rate decreased with increasing the acid concentration. Classical organic tests was used to 
identify the product of the oxidation reaction, the product was just bubbles of CO2.  
Keyword: Cerium(IV), Kinetics, Oxidation, Oxalic Acid. 

 

Introduction: 
Cerium element is considered as one of 
the most spread lanthanides elements. 
It has numerous oxidation cases (+4, 
+3, +2) [1]. Ce(IV) ion is considered as 
one of important oxidantes, since its 
reduction potential was found in 
sulphuric acid solutions of normality   
(1-8)N equal 1.44 V. this potential 
value is different according to the 
difference of acidic media which 
contains [2]. Ce(IV) solution in acidic 
media is a stable for long time and is 
not influenced by light and increasing 
temperatures for short time [3]. 
Therefore the Ce(IV) solution in acidic 
media is considered as ideal oxidant in 
oxidation reaction. Thus Ce(IV) 
solution in acidic media had region 
been used as oxidant to oxidize many 
organic Compounds [4-7], such as 
carboxylic acids [8]. But there was no 
results reported for oxidation of 
dicarboxilic acid by Ce(IV) except 
malonic acid [9]. Ce(IV) ion in 
sulphuric acid solution gives 
absorption peak in ultra violate at 
320nm      in       which    Ce(IV)     ion  
consumption  can   be   followed   up. 
 

Experimental: 
1- Materials: Cerium (IV) sulphate 

supplied by Riedel-deHean of 96% 
purity, oxalic acid supplied by 
Fluka of 99% purity, sulphuric acid 
supplied by BDH of 98% purity and 
double distillated water had been 
used. 

Method: The reaction was followed up 
throughout consuming the 
concentration of Ce(IV) ion through 
tracing decreasing absorption of 
Ce(IV) ion in ultra violate absorption 
area at wavelength (320)nm. The 
reaction was carried out by adding 2.5 
ml of Ce(IV) solution of different 
concentrations in quartz cell (1×1)cm 
and adding 100 µl of different 
concentrations oxalic acid solutions. 
The absorption was recorded directly 
after mixing the materials quickly. 
Then, the absorption was determined 
in successive intervals. The reaction 
was carried out in.                    
different acidic media of sulphuric 
acid, as shown in Table (1). 
 
   
  
 



 Ammar J. Mohammed /Al-khwarizmi Engineering Journal ,vol.1, no. 1,PP 125-133  (2005)        
                                                                            

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Results and Discussion: 
 
1- Kinetic measurement:  
    The kinetic of oxidation of oxalic 
acid by Ce(IV) was studied under 25C° 
in different concentrations acid media 
of sulphuric acid and by using different 
concentrations of the reacting 
materials. The kinetic study showed 
that the reaction was pseudo first order 
under condition [Ce(IV)]<<[Oxalic 
acid] by using the absorption as 
function for the concentration in first 
order equation: 

ktAAInAAIn ot −−=− ∞∞ )()(  
where   A∞, Ao, At are absorption at the  
end of reaction, absorption before 
reaction started, and absorption at 
particular time respectively. The 
results showed that the values of rate 
constant for the first order remained 
constant at changing the concentration 
of Ce(IV) with constant of other 
parameters, as it is shown in Table (1), 
Fig.1. This indicates that the reaction 
is first order with respect to Ce(IV). 
Rate constant of first order was found 
it increase by increasing concentration 
of oxalic acid at constant of other 
parameters, as it shown in Table (1) 
and Fig.2. To find out order of reaction 
with respect to oxalic acid, log of 
observed rate constant (kobs) was 
plotted against log of oxalic acid 
concentration as shown in Fig.3. 
The relation was linear with a slope 
0.66, this value represents order of 
reaction with respect of oxalic acid. 
Kinetic study showed that the first 
order rate constant decrease by 
increasing of sulphuric acid 
concentration, as it is shown in Table 
(1) and Fig.4. 

 
Log observed rate constant 

(kobs) was plotted against log (H2SO4), 
as it is shown in Fig.5. The relation 
was linear with a slope-1.03, this value 
represents the effect of sulphuric acid 
concentration on the rate of reaction. 

The relation was linear with a slope 
0.66, this value represents order of 
reaction with respect of oxalic 
acid.Kinetic study showed that the first 
order rate constant decrease by 
increasing of sulphuric acid 
concentration, as it is shown in Table 
(1) and Fig.4. 

 
2- Stoichmetery: 
 
Stoichmetric measurements, by 
iodometric titration, showed that each 
mole of oxalic acid reacts with 2 moles 
of Ce(IV). 
 
3-Identification of product: 
 

Literature showed that the 
product of oxidation of malonic acid(9), 
methyl malonic acid(10) and glyoxylic 
 acid(12) by Ce(IV) was formic acid 
with release of CO2. In this research, 
CO2release was only observed, and the 
product of oxidation was not 
carboxylic acid, no change observed 
when adding sodium bicarbonate to 
oxidation product. Thus as it is 
expected the oxidation product of 
oxalic acid by Ce(IV) was just CO2. 
 
4-Mechanism suggested and 
concluding law of rate reaction: 
 
Depending on kinetic measurements, 
stoichmetric measurements and 
identification of product, general 
equation for reaction was suggested as 
follows: 
 

↑++→+ + 222)(2)(2 COHIIICeIVCeCOOH

COOH

 
 
The following is the mechanism 
suggested for reaction: 
 



 Ammar J. Mohammed /Al-khwarizmi Engineering Journal ,vol.1, no. 1,PP 125-133  (2005)        
                                                                            

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.
)(

)(
1 
















⇔+

IVCe
COOH

COOH

IVCeCOOH

COOH

K

                                                                       

.                                                     ..(1) 
 
 

)(
)(

2 IIICEHCOOH

COO
IVCe

COOH
COOH slow

k ++









+

•

→

                                              .                                                  
.. (2) 
COO                     O 
 
                             C-O 
 
COOH                 C-O-+H+               
..(3) 
 
                             O 
O 
 
C-O                       O             O 
 
C-O-                  C        O+C     O-    
..(4) 
 
O 
 
     O                                        O              
 

•
C -O-+Ce(IV)              C        O+Ce(III)                                                                  

..(5) 
Basing on earlier explanation, law of 
reaction rate was found out as follow: 
 

] [1
] )][([)(

1

21

acidOxalicK
acidOxalicIVCekK

dt
IVdCe

+
=−

 
                                                      ..(6) 
 
 
Supposing that the reaction was first 
order: 

)]([
)]([

IVCek
dt

IVCed
obs=−        ..(7) 

 

Compare (6) with (7): 
 

] [1
] [

1

21

acidOxalicK
acidOxalickK

k obs +
=             ..(8) 

221

1
] [

11
kacidOxalickKk obs

+=   ..(9) 

 
With using Michaleis Menten plot as 
shown in Fig.6, the plot gave linear 
relation, this proved correctness of the 
law of reaction rate and mechanism 
suggested. 
 
5-Effect of sulphuric acid on 
reaction rate: 
Literature showed that −342 )(SOCeH  
was active species resulted from 
solving Ce(IV) in sulfuric acid (11): 
 

−⇔+ 3424224 )()( SOCeHSOHSOCe ..(10)                                    

]][)([
)(

*
4224

342

SOHSOCe
SOCeH

K
−

=         

..(11) 
 

][*
)(

])([
42

342
24 SOHK

SOCeH
SOCe

−

=         

..(12) 
Substituting Ce(SO4)2 from (12) to (6) 
 

]
]])[ [1(*
] [)([)]([

421

34221

SOHacidOxalicKK
acidOxalicSOCeHkK

dt
IVCed

+
=−

−

                                                      ..(13) 
The last equation that clarifies the 
negative effect of sulfuric acid on 
reaction rate agrees with experimental 
results. 
 



 Ammar J. Mohammed /Al-khwarizmi Engineering Journal ,vol.1, no. 1,PP 125-133  (2005)        
                                                                            

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References: 
 
1. J.E.Huheey, "Inorganic Chemistry", 

Harper-Row (1972). 
2. F.A.Cotton; G.Wilkinson, 

"Advanced Inorganic Chemistry", 
Jhon Wiley. 4th ed, (1988). 

3. G.Nagy; E.Koros; N. Of tedal; 
K.Tjelfhat; P. Ruoff, "Effect of 
temperature in Cerium-ion 
catalyzed bromate-driven 
oscillators", Chemical physics 
Letters, 250 (1996) 255-260. 

4. R.Dayal; G.V.Bakore, "Kinetics of 
the oxidation of mandelic acid by 
Cerium (IV) sulphate", J.Indian 
Chem. Soc., 49 (11), (1972) 1093-
1095. 

5. R.G. Varma; R.L. Yadav, "Ceric – 
Cerium oxidation of ortho-cersol", 
J. Indian Chem. Soc., LX (1983) 
554-556. 

6. T. Tzedakis; A.J. Savall, " Ceric 
sulphate oxidation of p-
methoxytoluene: Kinetics and 
reaction results", Ind. Eng. Chem.  
Res., 31(11), (1992) 2475-2483. 

7. D.C.Bilehal; R.M.Kulkarni; S.T. 
Nandibewoor, "Kinetics of 
oxidation of pyridylmethylphiny-
benzimidazole by Cerium (IV) in an 
aqueous perchloric acid medium", 
Turk. J. Chem., 27(2003) 695-702. 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 
 
8. B.Singh; P.Kumar; R.K.Shukla; 

B.Krishna, "Kinetics of Ce(IV) 
oxidation of 3-Bromo propionic 
acid in aqueous nitric acid 
Solution", J.Indian Chem.Soc., LIV 
(1977) 378-380. 

9. B.Neumann; O.Stenbock; 
S.C.Muller; N.S.Dalal, 
"Stoichiometric fingerprinting as an 
aid in understanding complex 
reaction : The oxidation of malonic 
acid by Cerium (IV)", J.Phys. 
Chem, 101 (1997) 2743-2745. 

10. P.O.Kvernberg; E.W.Hansen; 
B.Pedersen; A.Rasmussen; P.Ruoff; 
"Oxidation of methylmalonic acid 
by Cerium (IV). Evidence for 
parallel reaction pathways", J.Phys. 
Chem. A, 101 (1997) 2327-2331. 

 
11. P.K.Saxena; B.Singh; 

R.K.Shuka; B.Krishna, "Kinetics of 
Ce(IV) oxidation of diethy ketone in 
sulphuric acid solutions", J.Indian 
Chem. Soc., LV(1978) 56-59. 

12. B.Neuman; O.S.Stefan; 
S.C.Muller; N.S.Dalal, "Oxidation 
of glyoxylic acid by Cerium (IV)", 
J.Phys. Chem., 100(1996) 12342-
12348. 

13.  
 
 
 
 
 



 Ammar J. Mohammed /Al-khwarizmi Engineering Journal ,vol.1, no. 1,PP 125-133  (2005)        
                                                                            

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Table (1)The values of concentration of reactors and rate constant 

 

104[Ce(IV)]/M 102[Oxalic]/M [H2SO4]/M Kobs/min-1 

0.3125 
0.625 
1.25 
2.5 
5 

 
3.8 

 
0.125 

1.41 
1.42 
1.42 
1.35 
1.41 

 
1.25 

0.24 
0.48 
0.96 
1.9 
3.8 

 
0.125 

0.276 
0.396 
0.768 
1.188 
1.42 

 
1.25 

 
3.8 

0.125 
0.25 
0.5 
1 

1.42 
0.726 
0.36 

0.166 

 



 Ammar J. Mohammed /Al-khwarizmi Engineering Journal ,vol.1, no. 1,PP 125-133  (2005)        
                                                                            

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-5

-4

-3

-2

-1

0

1

2

0 10 20 30 40 50 60 70 80 90
Time (min)

I
II
III
IV
V

Ln(At-A∞) 
 

104[Ce4+]/M 
I=5 
II=2.5 
III=1.25 
IV=0.625 
V=0.3125 
 

Ln(At-A∞) 
 
 

-3

-2.5

-2

-1.5

-1

-0.5

0

0 45 90 135 180 225 270 315 360 405

Tim e  (m in)

Figure (1) 

-3
-2.5

-2
-1.5

-1
-0.5

0

0 30 60 90 110 140 170 200 230 260
Time  (m in)

-3
-2.5

-2
-1.5

-1
-0.5

0

0 20 40 60 80 100 120 140 160 180
Time (min)

Ln(At-A∞) 
 
103[Oxalic]/M 
I=2.4 
II=4.8 
III=9.6 
 
 

Ln(At-A∞) 
 

Figure (2) 



 Ammar J. Mohammed /Al-khwarizmi Engineering Journal ,vol.1, no. 1,PP 125-133  (2005)        
                                                                            

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-0.8

-0.6

-0.4
-0.2

0

0.2

0.4

-2.6 -2.4 -2.1 -1.7 -1.4
Log [Oxalic Acid]

log kobs 

S=0.66 

Figure (3) 

-3

-2.5

-2

-1.5

-1

-0.5

0

0 2 4 6 8 10 12 14

Time (min)

Ln(At-A∞) 
 
 

-3
-2.5

-2
-1.5

-1
-0.5

0

0 50 100 150 200 250 300 350
Time  (m in)

Ln(At-A∞) 
 

 [H2SO4]/M 
I=0.25 
II=1 
III=0.5 
 
 

-3
-2.5

-2
-1.5

-1
-0.5

0

0 30 60 90 110 140 170 200
Time (min)

Ln(At-A∞) 
 
 III 

I 

II 

Figure (4) 



 Ammar J. Mohammed /Al-khwarizmi Engineering Journal ,vol.1, no. 1,PP 125-133  (2005)        
                                                                            

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-0.8
-0.6

-0.4
-0.2

0
0.2

0.4

-0.91 -0.61 -0.3 0

S= -1.03 
log kobs 

Figure (5) 
log [H2SO4] 

0

1

2

3

4

25 50 100 205 410

S=0.007 
I=0.546 

1/[Oxalic] 

Figure (6) 

1/ kobs 



 Ammar J. Mohammed /Al-khwarizmi Engineering Journal ,vol.1, no. 1,PP 125-133  (2005)        
                                                                            

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  حركية وميكانيكية اكسدة حامض االوكزاليك بواسطة السيريوم الرباعي
  

  عمار جاسم محمد.د
  جامعة بغداد/وارزميخكلية هندسة ال/قسم هندسة الكيمياء االحيائية

  
  :الخالصة

مت تقنیة االشعة استخد. تم دراسة حركیة ومیكانیكیة اكسدة حامض االوكزالیك في الوسط الحامضي من حامض الكبریتیك              
بینت الدراسة الحركیة ان التفاعل من المرتبة االولى .   nm 320المرئیة لمتابعة التفاعل عند الطول الموجي  - فوق البنفسجیة

  .بالنسبة للسیریوم الرباعي والمرتبة الكسریة بالنسبة لحامض االوكزالیك 
اعل ووجد ان سرعة التفاعل تقل بزیادة تركیز حامض الكبریتیك تم تم دراسة تأثیر تغییر تركیز حامض الكبریتیك على سرعة التف

استخدام الكشوفات العضویة االولیة لتشخیص ناتج االكسدة ووجد ان ناتج التفاعل ھو عبارة عن فقاعات غاز ثاني اوكسید 
  .الكاربون