Moscow State University, Russia
Faculty of physics and International Laser Center
RAMAN AND ATR FTIR SPECTROSCOPY
IN THE STUDY OF CHEMICAL REACTION RATES
I.A. Balakhnina, N.N. Brandt, A.Yu. Chikishev, A.A. Mankova, I.G. Shpachenko
How to measure reaction rate?
Reaction rate = Rate of changes in reagent (product) concentration
Optical methods
Disadvantages
PHOTOMETRY
Overlapping absorption bands
POLARIMETRY
Optically active substrate or product
FLUORIMETRY
Overlapping absorption bands and
concentrational limitations
Universal method is unavailable
Task:
Experimentally prove the applicability of vibrational
spectroscopy in the measurements of chemical reaction rates
Reaction of alkaline hydrolysis of ethyl acetate:
Raman spectroscopy of the components

 CH 3COOK  C2 H 5OH
KOH  CH 3COOC2 H 5 
k1
k1
** *
Reaction
Approximation
CH3COOK
KOH
CH3COOC2H5
Frequency
сm-1
Component
637
852
880
929
1345
1413
CH3COOC2H5
CH3COOC2H5
C2H5OH
CH3COOK
CH3COOK
CH3COOK
1453
CH3COOC2H5
, C2H5OH
1736
CH3COOC2H5
C2H5OH
600
700
800
900
1000 1100 1200 1300 1400 1500 1600 1700 1800
-1
см
Raman spectrum of the reaction and its approximation with linear combination of Raman spectra of the
components: ethyl acetate (CH3COOC2H5), ethanol (C2H5OH) , potassium acetate (CH3COOK), and KOH.
Intensity kinetics
900
1000
1100
1200
1300
1400
1500
1600
Raman intensity
Интенсивность КР, отн.ед.
Processing of Raman data series
1700
*
0
200
400
600
800
Time, s
900
1000
1100
1200
1300
, см
A  B 
C  D
 A t 0  a,  B t 0  b  a
k
1400
1500
1600
1700
-1
C  

b e
kt  a b 

1
b kt  a b 
e
1
a
Reaction rate
1000
Effect of background subtraction and scaling
Raman band area
y t  

B e
b  a  kt
b b a kt
e
1
a
2,0
2,0
1,8
1,8
--
Error
-- Value
-1,5E-5
Chi-Sqr
1,6
1,4
K
0,09
0,003
B
0,259
0,002
C
1,756
0,003
1,6
1,4
1,2
1,2
1,0
1,0
0
200
400
600
Time, s
800
 C
1
1000
0
Value
Error
Chi-Sqr
6E-5
K
0,09
0,003
B
0,519
0,005
C
1,513
0,006
200
400
600
Time, s
800
1000
Temperature dependence of reaction rates
T = 42 °С
T = 31 °С
T = 22 °С
*
k, М-1с-1
T = 22 °C
840
860
880
900
920
940
-1
cm
Raman spectra of the reaction mixture (hydrolysis
of ethyl acetate), measured at 14-2110 s from the
beginning of reaction at a temperature of 22 °C
0
200
400
22°С
42°С
0,048±0,004
0,28±0,02
600
800
1000 1200 1400
Time, s
Time dependence of the integral Raman
intensity of the band at 880 cm-1
measured at different temperatures
An increase in temperature leads to an increase in reaction rate
Reaction rate and activation energy
Arrhenius equation : k  Ae
This work
Kuheli Das et al., 2011
Schneider et al., 2005
Tsujikawa et al., 1966
Jensen et al., 1951
Amis et al., 1950
Smith et al., 1939
Terry et al., 1927
Warder, 1881
Approximation
0,30
0,25
0,20
-1 -1
k, М s
  Ea


RT 

0,15
А – const
Еа – activation energy
R – gas constant
Т – temperature
0,10
0,05
0,00
15
20
25
30
35
40
45
Т, °С
Reaction rates of ethyl acetate hydrolysis at different temperatures
Reaction rate and activation energy
-0,5
-1,0
k  Ae
  Ea


RT 

 ln k  ln A 
Ea 1
R T
-2,0 0,30
-2,5 0,25
-3,0
0,20
k, М-1s-1
-1 -1
ln(k), ln(M s )
-1,5
-3,5
0,15
This work
Kuheli Das et al., 2011
Schneider et al., 2005
Tsujikawa et al., 1966
Jensen et al., 1951
Amis et al., 1950
Smith et al., 1939
Terry et al., 1927
Warder, 1881
Approximation
0,10
-4,0
3,0
0,05
3,1
3,2
3,3
3
1/T*10 , 1/K
3,4
3,5
Reaction rates of alkaline hydrolysis of ethyl
acetate determined using different spectral lines
Time dependences of Raman intensity of the
bands at 880, 929, and 852 сm-1 at a
temperature of 25 °C and their approximations
-1
852 сm
-1
880 сm
840
860
880
900
920
-1
940
929 сm
-1
сm
Raman spectra of the reaction of ethyl acetate
hydrolysis, measured at 20-600 seconds from the
beginning of reaction at a temperature of 25 °C
Mean value of the reaction rate is
0
100
200
300
Time, s
k = 0,088 ± 0,006 M-1s-1
400
500
600
Raman spectroscopy of spontaneous
and enzymatic hydrolysis
14°С
pH 7,8
Raman spectra of the reaction of enzymatic
hydrolysis of 2,4-dinitrophenylacetate (DNPA)
in the presence of chymotrypsin, measured at
100 s - 260 min from the beginning of reaction
*
Enzymatic hydrolysis:
800
900
1000 1100 1200 1300 1400
-1
Raman intensity at 1318 cm
-1
сm
Enzymatic reaction
k1
k2

 ES 
E  S 
E  P

k1

 P 
P

S
t

K

ln
1

   0


M
S
  0 
Spontaneous hydrolysis:
kh
S 
P
Spontaneous reaction
 P    S 0 1  e k t 
h
0
100
200
Time, s
300
400
KM = (39,55±0,01)10-4 M
kh = (1,26±0,01)10-5 s-1
S – substrate; E – enzyme; P – product; ES – enzyme-substrate complex
ATR FTIR geometry
Evanescent wave
4,0
d
Penetration depth d, m
3,5
3,0
Incident IR light
ATR crystal
(diamond)
Reflected IR light
2,5
2,0
d
1,5

2 n12 sin 2   n22
1,0
0,5
0,0
400
800
1200 1600 2000 2400 2800 3200 3600 4000
Wavenumbers, cm
-1
Reaction of alkaline hydrolysis of ethyl acetate:
ATR FTIR spectroscopy of the components
k1

 CH 3COOK  C2 H 5OH
KOH  CH 3COOC2 H 5 

k1
900
1000
1100
1200
1300
1400
1500
Frequency
сm-1
Component
1022
CH3COOK
1050
CH3COOC2H5
C2H5OH
1265
CH3COOC2H5
CH3COOK
1380
EtOAc
1414
CH3COOK
1553
CH3COOK
1600
-1
Wave number, сm
ATR FTIR spectrum of the reaction mixture at 17 s and the spectra of the components:
ethyl acetate (CH3COOC2H5), ethanol (C2H5OH) , potassium acetate (CH3COOK), and KOH
-1
Reaction rates: ATR FTIR spectroscopy
1100
1200
1300
1400
1500
1600
Wave number, сm
ATR FTIR spectra of the reaction of ethyl acetate
hydrolysis, measured at 13-300 s from the
beginning of reaction at a temperature of 27,4 °C
Raman
T, °C
k103, М-1с-1
T, °C
k103, М-1с-1
1,6
1,4
1,2
1,0
0,8
800
1000 1200 1400 1600 1800 2000
-1
Wave number, сm
0
-1
ATR FTIR
Penetration depth, m
Raman intensity at 1265 cm
*
1000
1,8
50
100
150
200
250
Time, s
Time dependence of the area under the band at
1265cm-1 measured at 27.4 °C and its approximation
25,6
25,6
27,4
27,8
490±10 540±10 830±10 480±10
25
27,4
89±8
94±8
ATR FTIR time-dependence: liquid-in-liquid solution
*
ATR-FTIR absorbance
1,2
1045 cm
0,8
Benzoic ether
-1
*
*
Ethanol
* *
0,4
*
*
Benzoic ether
in ethanol (3 M)
*
**
0,0
0,08
1000
Concentration
changes are
obvious
1200
1400
1600
Solvent
evaporation?
Solution (200 s) - solution (5 s)
 OD
0,04
0,00
Benzoic ether (200 s) - benzoic ether (5 s)
-0,04
-0,08
Molar ratio:
Ethanol / Benzoic ether = 5
1000
Ethanol (200 s) - ethanol (5 s)
1200
1400
, cm
-1
1600
Interaction
with ATR
crystal
surface?
10
 OD, *10
-3
ATR-FTIR absorbance, *10
-2
ATR FTIR time-dependence: solid-in-liquid solution
200 mM 2,4-dinitrophenyl acetate
(DNPA) in acetonitrile
*
*
Molar ratio:
Acetonitrile / DNPA = 100
*
5
*
0
800
*
*
1000
*
*
Acetonitrile
*
1200
*
1400
1600
1400
1600
5
0
DNPA (200 s) - DNPA (5 s)
-5
Acetonitrile (200 s) - acetonitrile (5 s)
800
1000
1200
, cm
-1
In case of reaction: product increasing rate = reagent decreasing rate
Reaction rates: ATR FTIR spectroscopy
3,6
0,24
-1
ATR-FTIR OD
ATR-FTIR integral OD
1552 cm
0,18
-1
1265 cm
0,12
0,06
3,3
1000
1200
1400
-1
, cm
1600
Potassium acetate

 CH 3COOK  C2 H 5OH
KOH  CH 3COOC2 H 5 
k1
Ethyl acetate
k1
3,0
0
50
100
Time, s
150
200
Reaction rates: ATR FTIR spectroscopy
Pure ethyl acetate
19
18
1
1264, 1300,
1359, 1393,
2800-3100 cm-1
unchanged
ATR-FTIR OD
ATR-FTIR integral OD
20
607, 634, 785,
847, 916, 938,
1097, 1115,
1373 cm-1 –
intensity
1
1045, 1238 cm-1
(skeletal) –
intensity and
width
17
0
600
0
800
1000
-1
, cm
50
1200
14003000 0
1200
100
Time, s
1250
150
1300
200
Ethyl acetate ordering (crystallization) on diamond surface
Conclusions

Raman spectroscopy makes it possible to locally measure the rates of
chemical processes (including enzymatic) in experiments with liquids
and solids in the absence of specific requirements to reagents
(substrates)

Raman measurements make it possible to determine rate constants
using variations in intensities of several spectral bands, so that the
accuracy of calculations can be increased

In the case of ATR FTIR measurements, the phase transition of liquids
into quasi-crystalline state on the surface of ATR crystal is possible
(even for diamond)
Взаимодействие гомогенных растворов с алмазом
0.10
0.7
Оптическая плотность
Оптическая плотность
0.6
0.05
0.5
0.4
0.3
0.2
0.1
0.0
1000
1000
1500
Волновое число, см
-1
1200
1400
Волновое число, см
1600
-1
ИК спектры 2,1 М этилового эфира бензойной
ИК спектры 190 мМ раствора 2,4-динитрофенил
кислоты (этилбензоата) в этиловом спирте из
ацетата в ацетонитриле из серии, измеренные через
серии, измеренные через 15(черная кривая), 100
3(черная кривая), 100 (красная кривая) и 200 секунд (синяя
(красная кривая) и 200 секунд (синяя кривая) после
кривая) после начала измерений на кристалле НПВО.
начала измерений на кристалле НПВО.
Оптическая плотность
0.4
0.3
0.2
0.1
0.0
800
1000
1200
1400
1600
1800 2800
3000
Волновое число, см
-1
3200
3400
3600
3800
ИК спектры фосфатного буфера из серии,
измеренные через 3 (черная кривая), 100
(красная кривая) и 200 секунд (синяя кривая)
после начала измерений на кристалле НПВО.
Все спектры совпадают.
ATR FTIR spectroscopy of spontaneous
and enzymatic hydrolysis
k1

 CH 3COOK  C2 H 5OH
KOH  CH3COOC 2H5 

IR absorption at 1380 cm
-1
k1
*
1.0
5
Four reaction kinetics at 1380 см-1
4
3
2
1
0
100
200
300
400
500
600
Time, s
1000
1100
1200
1300
-1
1400
0.8
ATR FTIR spectra of spontaneous
reaction of 100 mM ethyl acetate
hydrolysis, measured at 11-600 s
from the beginning of reaction at
the temperature of 23,5 °C
Оптическая плотность
Wave number, сm
0.6 FTIR spectra of ethyl acetate
ATR
measured at 3, 100, and 200 s after
the beginning of reaction
0.4
0.2
0.0
600
800
1000
1200
1400