final th-5 nitro - shodhgangashodhganga.inflibnet.ac.in/bitstream/10603/4368/13/13...172 1....

170

Chapter 5

Photosensitized reaction of Nitrobenzene

and

Di Nitrobenzene

171

Abstract

Photosensitized reaction of nitrobenzene and di-nitrobenzene derivatives have been

studied with the use of Benzophenone as a sensitizer in aqueous alkaline medium in

visible light. 100W tungsten lamp was used for the irradiation. The strong

electrowithdrawing effect of –NO2 group polarizes the C-H bond. The triplet excited state

of benzophenone abstracts H+ from polarized bond of NB and m-DNB by exciplex

formation. Proton abstraction, Free radical formation of NB and m-DNB and

dimmerization of free radical is observed in the photosensitized reaction. The rate of the

reaction is in order of m-DNB > NB. Photo chemical reaction has not been observed in p-

DNB. The effect of different parameters like pH, concentration of the substrate,

concentration of the sensitizer, light intensity, solvent effect and the rate of the

photochemical reaction have been studied. The quantum efficiency of the product has

been evaluated with the use of potassium ferrioxalate actinometer. The product formation

from the triplet excited state via exciplex formation. The possible products 2, 2’- di nitro

and 2,2’-4,4’ tetra nitro biphenyl were confirmed with the help of U.V.-visible

spectrophotometer and mass spectrometry. The reaction mechanism has been suggested.

172

1. Introduction:

Nitrobenzene and its derivatives like nitrophenol, chloronitrobenzene,

dinitrobenzene are major intermediates in the production of various chemicals and used

in Plastic Industries, Paper Industries, Manufacture of Pesticides, dyes, drugs, Explosives

and wood-preservatives [1].

The nitro aromatic compounds are widely distributed in the environment and are

not bio degradable due to their high solubility and stability in the water. The compounds

are serious environment pollutant and they are highly toxic in trace amount, can affect

central nervous system, skin and eyes irritants, and also carcinogenic effect on living

beings[2-4].

Photochemical degradation of nitro aromatic compounds has been a topic of

growing interest. An extensive work has also been reported on direct irradiation and

photochemical degradation [5-7].

Photochemical reactions like photo-oxidation [8], photo reduction [9,10] and

photo dissociation [11,12] of nitrobenzene have been reported for the destruction of this

toxic compound.

Giridhar Madras M.H. Priya have reported that the photo catalytic degradation of

nitrobenzene and substituted nitrobenzenes with combustion synthesized nano TiO2 and

commercial TiO2 catalyst which suggests the degradation rate higher when substrates

catalyzed with combustion synthesized nano TiO2. [13].

Dulal C. Mukharjee et al. have reported m- dinitrobenzene and acetophenone in

presence of hydroxide ion makes complex and show variation of absorbance with time

[14].

173

Articles have been published on photo catalysis of nitrobenzene, nitro-phenols

and chloro nitrobenzene using TiO2 and ZnO [15,16].

Photochemical degradation has been reported in the literature of nitro phenols

[17] and Nitrobenzene [18] using catalysts for comprehensive study of effect of

substitution in nitrobenzene. Compton et al. have carried out photo- and electrochemical

reduction of m- and p-halo nitrobenzene. [19-21].

The reactivity of nitro aromatic compounds can be affected by electronic nature of

substituents and also by their position in the aromatic ring. Hence, 3-nitrophenol degrades

the slowest among the three nitro phenols which is in accordance with the literature [22]

while the degradation of 4- nitrophenol and 2-nitrophenol are comparabale.

In the present study Aromatic ketone has been used as a photo sensitizer [23-25].

It shows two different type of energy transfer process.

(1) Photo-oxygenation oxygenation

Canonica, S. et. al. have suggested that Aqueous Oxidation of Phenylurea

Herbicides by Triplet Aromatic Ketones via singlet O2 and A laser flash photolysis study

for the reactivity of aromatic amines with triplet 1,8 dihydroxy anthraquinone has been

reported by Y.Pan et. al. [26,27]

(2) Proton abstraction [28] and electron transfer reactions [29].

Teijiro Ichimura et al has reported kinetic study by the quenching the rate of DPA

by triplet benzophenone photo sensitizer. They have also reported that the excitation

energy effect on the reaction with 2- bromo methyl naphthalene [30].

174

S. Jockusch et al have reported that Photo-induced energy and electron transfer

processes between ketone triplet state and organic dyes (methylene blue, thiopyrinine,

safranine and phenosafranine) [31].

Koji Yamada et. al. have reported that Nitrile-forming radical elimination

reactions of 1-naphthaldehyde O-(4-substituted benzoyl) oximes activated by triplet

benzophenone [32].

Electron/proton transfer reaction of sensitizer:

R.G.Brinson and et.al have reported the proton abstraction and electron transfer

photo reaction by anthraquinone [33].R.E.Galian et.al. have reported that the

intramolecular electron transfer between tyrosin and trytophan photo sensitized by

aromatic ketone[34].Xichen Cai et. al. have suggested mechanism of Sensitized reaction

by benzophenone in the triplet excited state [35].

Santi Nonell et al. have reported that aromatic ketones as standards for singlet

molecular Oxygen photosensitization [36].

In the present work, Benzophenone has been used as a photo sensitizer. The

photosensitized reaction of Nitrobenzene and m-dinitrobenzene has been studied in the

visible light using a 100 W tungsten lamp for the irradiation. Strong electro withdrawing

effect of –NO2 group polarizes the C-H bond of benzene ring which forms unstable

exciplex with triplet excited state of benzophenone. The Proton abstraction from benzene

nucleolus, Free radical formation of NB and m-DNB takes place and dimerization is

observed in the photosensitized product formation.

175

The rate of the reaction has been calculated with the use of change in the

absorbance at the λmax of the substrate with time. The effect of the different parameters

like pH, concentration of the sensitizer, concentration of the substrate, effect of the

solvent and the intensity of the light on the rate of the photosensitized reaction have been

studied and the reaction conditions have been established. The rate of the reaction has

also been studied in anaerobic condition.

The quantum efficiency of the photosensitized reaction has been evaluated using

potassium ferrioxalate actinometer. The effect of the substrate concentration on quantum

efficiency has been studied to evaluate the different excited state of the substrate

molecule.

The λmax and molar absorptivity of the photo product has been evaluated and

compared with the pure sample. The photo products are identified with the use of mass

spectrometry and compared with the standard sample of di nitro biphenyl. The reaction-

mechanism of the photosensitized reaction has been suggested.

176

2. RESULTS

2.1 Spectral Characteristics

The spectra of the substrate molecules and benzophenone solutions were recorded

in the acidic and alkaline medium in the range of 200-350 nm. The spectra of

nitrobenzene and m-dinitrobenzene show λmax at 225nm and 228nm in acidic medium.

Nitrobenzene and m-dinitrobenzene with benzophenone do not show change in the

spectrum on the exposure to visible light. The spectrum of the exposed reaction mixture

between 2 to 6 pH remains same as the control solution this suggests that the photo

reaction does not take place in the acidic medium.

The absorbance bands of nitrobenzene and m-dinitrobenzene show λmax of π -

π* transition at 266nm and 242 nm respectively in the aqueous alkaline medium between

the pH range of 8-12. The alkaline solution of nitrobenzene and m-dinitrobenzene with

benzophenone shows spectral changes with time when exposed to visible light. This

suggests that a photochemical reaction occur only in the deprotonated species. The

spectra of nitrobenzene and m-dinitrobenzene were recorded in the spectral range of 200-

350 nm under the experimental conditions against the reagent blank.

The spectrum of NB and m-DNB with benzophenone shows that the π - π* bands

of nitrobenzene at 266 nm is blue shifted to 255 nm (Fig. 1), and m-dinitrobenzene at 242

nm is red shifted to 254 nm with increased absorptivity (Fig. 2) when exposed to visible

light. The new absorption bands appear at 255nm and 254nm for NB and m-DNB

respectively corresponding to photo reaction product. The exposed solution of p-

dinitrobenzene with benzophenone in the aqueous alkaline medium does not show

spectral change on the exposure to visible radiation (Fig. 3).

177

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

200 250 300

Wavelength (nm)

Abs

orba

nce

0 min30 min60 min90 min120 min

Fig 1. Spectral changes of NB with time.

Substrate:[NB] = 3×10-5 M,

Sensitizer:[B.P.] = 5 ×10-5 M,

Light intensity=11.18 x 10-8 E/s, pH= 11.

178

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

200 250 300 350

Wavelength (nm)

Abs

orba

nce

0 min20 min40 min60 min80 min

Fig 2. Spectral changes of m-DNB with time.

Substrate:[m-DNB] = 5×10-5 M,



179

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

200 250 300

Wavelength (nm)

Abs

orba

nce

0 min90 min

Fig. 3 Spectral change of p-DNB with time.

Substrate:[p-DNB] = 4 ×10-5 M,



180

2.2 Product study:

The products of NB and m-DNB were identified by comparison of their UV

spectrum with authentic standards by U.V-visible spectrophotometer. The spectrum of

the exposed solution of NB and m-DNB is matched with the spectrum of di nitro

biphenyl

The λmax and the molar absorptivity of the photo product of the NB and m-DNB

in aqueous alkaline solution has been evaluated and compared with the standard sample

by U.V.Spectrophtometer under experimental condition. The molar absorptivity of the

substrate and product has been calculated by measuring the absorbance of a number of

known concentration solutions of di nitro biphenyl (Table 1) in the experimental

condition. The absorbance at λmax 255nm and 254nm for NB and m-DNB respectively

has been found higher than the molar absorptivity of the substrates NB and m-DNB.

The reaction product was isolated by extracting the exposed solution 4 times with

5 ml acetonitrile solvent. The Acetonitrile was collected and evaporated to dryness and

the product was dissolved in 5ml methanol. The methanolic solution of the product was

used for the mass spectrometry.

The mass spectrum of the isolated product shows three mains peak. The peak at:

m/z = 245(M+1, 100./.) which is the base peak also corresponds to [m+1]+ protonated

molecular ion. The second and third are observed at m/z = 199 and m/z = 154

corresponding to loss of –NO2 moiety.

The photo product of NB and m-DNB show same λmax (255+ 1) and molar

absorptivity suggesting that only one photo product is formed in each reaction.

181

Table 1. Experimental value of λmax and molar absorptivity of NB and DNB.

Copounds Experimental

λ max

ε value Product

λ max

Calculated

ε value of

product

NB 232 6800 255 16000

m-DNB 266 5900 254 16380

p-DNB 264 7650 - -

Nitro biphenyl 256 16800 - 16150

182

Mass Spectra of the Di nitro biphenyl

183

2.3 The rate of the reaction

The change in the absorbance of the reaction mixture has been measured with

different time intervals; which increased and became constant indicating the completion

of the reaction. The absorbance increased at 255nm for nitrobenzene and 254nm for m-

di-nitrobenzene. The change of the absorbance with different time has been used to

calculate the rate constant for the reaction of corresponding NB and m-DNB.

A plot of 2 + log (OD) (optical density) vs. time has been plotted and was found

to be a straight line with a positive slope which indicates that the reaction follows first

order reaction kinetics.(Fig 4). The rates of the photo sensitized reaction for NB and m-

DNB have been calculated (Table 2).

The rate constant of the reaction has been determined using the following

expression:

Rate constant = 2.303 x slope

184

Table 2.

Rate of photo sensitized reaction of NB and m-DNB.

Compounds

Rate of reaction

( k x 103) min-1

NB 7.3

m-DNB 9.94

p-DNB -

Substrate:[NB] = 5×10-5 M, [m-DNB.] = 6×10-5 M,

Sensitizer : [B.P.] = 5×10-5 M, Light intensity=11.18 x 10-8 E/s, pH= 11.

185

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

0 50 100 150 200

Time (min)

2+ lo

g (O

.D.)

NBm-DNB

Fig 4. Typical Run

Rate of reaction (k× 103) min-1

Substrate: :[NB] = 3×10-5 M, [m-DNB] = 5×10-5 M,


Light intensity=11.18 x 10-8 E/s, pH=11.

186

3. The effect of the variables on the rate of the photo reaction of NB and m-DNB has

been studied:

3.1 Effect of pH:

The photo sensitizer effect of benzophenone on NB and m-DNB has not been

observed in the acidic and neutral medium. The rate constant of the photosensitized

reaction has been calculated for nitrobenzene- and m-DNB between pH 8-12. It has been

observed that the rate of the reaction increases as pH increases (Fig.5) and becomes

constant after pH 11. So the pH 11 of the solution was maintained for the subsequent

study.

The photo effect of Benzophenone is sensitive to OH¯ ion concentration of the

solution therefore the increase in OH¯ ion concentration increases the sensitivity of the

sensitizer, which shows higher proton abstract of benzophenone [37]. Similar effect of

OH¯ ion concentration has been observed in the present study. The rate of the reaction is

in order m-DNB> NB.

3.2 Effect of the concentration of the Sensitizer:

The effect of the different concentrations of benzophenone on the rate of the

photosensitized reaction has been studied. The rate constant was determined for

nitrobenzene and m-DNB by using the different concentrations of benzophenone in the

range of 0.2 x 10-4–1.0 x 10-4 M. (Fig.6). The rate of the reaction remains constant for the

range of the sensitizer. The rate of the reaction slightly decreases by increasing the

concentration of the sensitizer. It appears that as the sensitizer concentration increases the

deactivation of the excited molecule by intermolecular collision takes place.

187

3.3 Effect of the concentration of the substrate:

The effect of the different initial concentrations of NB and m-DNB on the rate of

the reaction has been studied in the range of (0.4 – 1.0) x 10-4 M. The rate of the reaction

remains constant with increase in the concentration range of the substrate. The rate of the

reaction is independent of the initial concentration of the substrate (Fig. 7).

The half-time reaction is also calculated at different concentration of the substrate

and t1/2 value is constant over the above range of the concentration. This suggests that the

photochemical reaction is of first order. (Table 3).

188

Table 3. τ½ of the photosensitized reaction.

τ½ x 103 Concentration of

substrate (C) x

104 M NB m-DNB

0.4 0.094 0.07

0.5 0.094 0.07

0.6 0.094 0.07

0.8 0.094 0.07

1.0 0.094 0.07


Sensitizer: [B.P] = 5×10-5 M


189

0

2

4

6

8

10

12

0 2 4 6 8 10 12 14

pH

Rat

e of

Rea

ctio

n (k

x 1

03 )min

-1

NBm-DNB

Fig.5 Effect of pH.

Rate of reaction (k× 103) min-1

Substrate: :[NB] = 3×10-5 M, [m-DNB] = 5×10-5 M,


Light intensity=11.18 x 10-8 E/s,

190

0

2

4

6

8

10

12

0 2 4 6 8 10

Concentration of Sensitizer [S] x 105 M

Rat

e of

Rea

ctio

n (k

x 1

03 ) min

-1NBm-DNB

Fig 6. Effect of Concentration of Sensitizer.

Substrate: [NB] = 3×10-5 M, [m-DNB] = 5×10-5 M,


Rate of reaction (k× 103) min-1, Concentration of Sensitizer [B.P.] ×105 M

191

0

2

4

6

8

10

12

0 2 4 6 8

Concentration of Substrate [C] x 105 M

Rat

e of

Rea

ctio

n (k

x103 ) m

in -1

NBm-DNB

Fig.7 Effect of Concentration of Substrates.

Sensitizer: [B.P.] = 5 ×10-5, Light intensity=11.18 x 10-8 E/s, pH= 11.

Rate of reaction (k× 103) min-1, Concentration of Substrate [C] × 105 M

192

3.4 Effect of the light intensity:

The increase of the light intensity [Einstein / second (E /s)] shows positive effect and the

rate of the photo chemical reaction increases as the light intensity increases. The number

of the excited molecules of the sensitizer increases with higher light intensity as the

number of photons increases and correspondingly the rate of the reaction increases (Table

4). A linear relationship has been observed between the light intensity and the rate of the

reaction.

Table 4. Effect of light intensity.

Rate of reaction ( k x 103) min-1 Intensity of light

I x 108 E/S

NB m-DNB

4.85 0.78 0.90

6.87 1.03 1.15

11.18 7.3 9.94


Sensitiser:[B.P.] = 5 ×10-5 M , pH= 11.

193

3.5 Effect of the solvent:

The effect of the solvent on photo sensitized reaction of nitrobenzene and m-DNB

was studied by changing the medium from aqueous alkaline to methanolic alkaline. The

spectrum of Nitrobenzene and m-DNB shows absorbance bands at 266nm and 242 nm

correspond to π - π* transition in the alkaline methanolic medium.

Nitrobenzene and m-DNB do not give photo reaction with benzophenone when

exposed to visible light in the alkaline methanolic solution. The methanol acts as free

radical scavenger and the photo chemical reaction follows the path of free radical

formation in the product formation.[38-40]

3.6 Study in the anaerobic condition:

The study was carried out to see the effect of the oxygen concentration on the rate

of the reaction. A purified nitrogen gas was passed through the solution to remove the

dissolved oxygen of the solution. The maximum deoxygenated reaction mixture of

Nitrobenzene and m-DNB with benzophenone was exposed to the visible light for

definite period of time. The rate of the reaction was calculated which remains the same in

the absence of oxygen. This result suggests that singlet oxygen does not participate in the

photosensitized reaction. The production of oxygen in different solvent and the kinetic

study has also been reported [41].(Table 5)

194

Table 5.

Rate of photo sensitized reaction of NB and m-DNB.

Rate of reaction ( k x 103) min-1

Compounds Aerobic Anaerobic

NB 7.3 7.3

m-DNB 9.95 9.94


Sensitizer:[B.P.] = 5 ×10-5 M , Light intensity=11.18 x 10-8 E/s, pH= 11.

195

3.7 (φ) Value:

The quantum efficiency of the photo chemical reaction was determined by using

potassium ferrioxalate as an actinometer at different initial concentration of the

nitrobenzene and m-DNB. The φ– values were calculated for the nitrobenzene and m-

DNB at different initial concentration.

The plot of φ– value and the initial concentration of the substrate show a linear

relation ship with positive slope for nitrobenzene and m-DNB. This suggests that the φ

value of the photo chemical reaction is dependent on the initial concentration of the

substrates. (Fig.-8).

The plot of the inverse of the quantum efficiency versus inverse of the

concentration of the substrate is also linear with positive slope with curve [42] this

suggests that exciplex decomposes to make radical of the substrate in the triplet excited

state and the product formation is via triplet excited state (Fig.-9).

The φvalue was calculated in deoxygenated solution which is same as oxygenated

solution which suggests that singlet oxygen does not participate in the photosensitized

reaction (Table 6). The φ values in the aqueous alkaline are in the order of m-DNB >

NB.

196

Table 6.

Quantum efficiency (Ø) of NB and m-DNB.

Quantum efficiency(Ø)

Compounds Aerobic Anaerobic

NB 0.043 0.043

m-DNB 0.592 0.0592


Sensitizer:[B.P.] = 5 ×10-5 M , , Light intensity=11.18 x 10-8 E/s, pH= 11.

197

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0 2 4 6

Concentration of Substrate [C] x105M

Qua

ntum

Effi

cien

cy

NBm-DNB

Fig 8. Quantum Efficiency (φ) VS Concentration of Substrate [C]

Substrates: [NB] = 3×10-5 M, [m-DNB] = 5×10-5 M,

Sensitizer: [B.P.] = 5 ×10-5,


198

0

5

10

15

20

25

30

0 0.2 0.4 0.6 0.8 1 1.2

Inverse of concentration of substrate (1/[C])

Inve

rse

of q

uant

um e

ffici

ency

m-DNB

NB

Fig 9. Inverse of the Quantum Efficiency 1/(φ) VS

Inverse of the Concentration of Substrate 1/[C]

Substrates: [NB] = 3×10-5 M, [m-DNB] = 5×10-5 M,

Sensitizer: [B.P.] = 5 ×10-5,


199

4. Discussion:

The absorbance at λmax 255nm and 254nm for NB and m-DNB respectively and

calculated molar absorptivity suggests that a common product is formed after

photoreaction.

The Mass spectra of isolated reaction product suggest that the di nitro biphenyl is

the photo product. m/z = 245(M+1, 100./.) which is the base peak also corresponds to

[m+1]+ protonated molecular ion. The molecular ion shows mass loss corresponding to

44 suggesting loss of –NO2 group and a peak at m/z = 199 and m/z = 154.

The λmax and the molar absorptivity and the peak in the mass spectrum at m/z =

154 suggest that the photo product can be a di nitro bi phenyl.

The spectrum of the reaction mixture of NB and m-DNB with B.P in aqueous

alkaline solution shows changes in the spectrum on exposure to visible light. The

absorbance at 242nm and 266nm decreases and a new band appear at 254nmand 255nm

for NB and m-DNB respectively corresponding to the photo product on exposure to

visible light. The photo product formation takes place by breaking of the exciplex formed

between excited state of B.P. with NB and m-DNB in the aqueous alkaline medium on

exposure to visible light.

The influence of the pH on the photo sensitized reaction has been investigated,

considering that pH of the medium affect the photo chemical reaction. The plot of the rate

of the reaction and pH effect suggest that the reaction takes place only in the alkaline

solution. The protonated form of the benzophenone does not form an exciplex with

polarized C-H bond of NB and m-DNB in the acidic solution.

200

The pH effect study on the rate of the reaction suggests that only deprotonated

species of benzophenone undergo photo sensitized reaction with NB and m-DNB in the

pH range 8 to 12.The rate constant of the photosensitized reaction has been calculated. It

has been observed that the rate of the reaction increases as pH increases and becomes

constant after pH 11.

The photo effect of Benzophenone is sensitive to OH¯ ion concentration of the

solution therefore the increase in OH¯ ion concentration increases the sensitivity of the

sensitizer, which shows the rate of the proton abstraction of the triplet excited state

benzophenone is higher [37]. Similar effect of OH¯ ion concentration has been observed

in the present study. The rate of the reaction is in order m-DNB> NB.

A similar experiment was carried out using methanol as a solvent. The

photochemical reaction does not take place in the alkaline methanolic solution. The

spectral profile of the reaction mixture remains the same as the control solution. It

appears that the methanol acts as free radical scavenger and stops the product formation.

It suggests that the formation of the photo product of the substrate involves a Radical

reaction.

The rate of the reaction in the anaerobic condition remains the same as in the

aerobic condition both in aqueous and methanolic alkaline solution. The singlet state of

the oxygen does not participate in the photo reaction and oxidation photo- products are

not formed by oxidation of the substrates.

The rate of the reaction of m-DNB is faster than the NB. The number of electron

withdrawing –NO2 group in benzene ring plays an important role in the kinetic study in

201

the photo reaction. The presence of two electron withdrawing group in DNB shows

increased polarization of C-H bond which results in increased the rate of the reaction.

The two nitro group of p-DNB are symmetrical by placed and show same

electron-density. The p-DNB does not allow the polarization of C-H bond of the benzene

ring. The Proton of the benzene ring can not make an exciplex with the excited state of

benzophenone. The p-DNB does not undergo photo sensitized reaction.

. The quantum yield of NB and m-DNB shows similar effect and the φ value are

in order of m-DNB>NB>P-DNB. The plot of inverse of the quantum efficiency versus

inverse of the concentration of the substrate shows positive slope with curve this suggests

that the exciplex decomposes to make radical of the substrate in the triplet excited state.

The product formation takes place from the triplet excited via exciplex formation.

202

5. Mechanism:

BP gives two types of reaction like proton abstraction and oxidation [25-28.The

photo reaction of benzophenone is specific suggest the proton abstraction by long lived

triplet excited state of BP is observed.

(1) The photo sensitizer absorbs energy from visible radiation and goes to singlet

excited state which undergoes ISC to form triplet excited state.

(2) Triplet excited state of benzophenone is more basic than the ground state which

transfers the energy to the acceptor molecule.

(3) The electron withdrawing group –NO2 Polarizes C-H bond of molecules NB and m-

DNB and triplet excited benzophenone forms a DA exciplex.

(4) The DA exciplex breaks down and free radical of molecules is produced.

The Triplets excited state free radical dimerizes to form biphenyl nitro-derivatives

as a product.

The photo sensitizer BP absorbs energy from the visible light and goes to singlet

excited state which undergoes ISC to form triplet excited state which is more basic. The

NB and m-DNB have strong electron withdrawing group which polarizes C-H bond of

the benzene ring. The plot of φ vs. [C] is linear with positive slope suggesting formation

of an exciplex between B.P. and NB and m-DNB.

The plot of 1/φ vs. 1/[C] is curved which suggests the product formation from

triplet excited state via exciplex. This suggested that proton abstraction takes place from

the substrate molecules by excited state of BP. The exciplex is unstable and a proton is

203

transferred to benzophenone produce a free radical of NB and m-DNB which di merizes

to produce di nitro biphenyl.

Photo catalytic degradation of NB has been reported that the unshared pair of

electrons on the nitrogen atom bound to the ring is also affected [3]. H. Mohan et al. have

reported electron and proton transfer process observed in benzophenone [43,44]. Free

radical of NB and m-DNB in the triplet excited state is produced which dimerizes and the

nitro derivatives of biphenyl are observed.

The reaction does not take place in the presence of methanol which shows

scavenging effect of the free radical.

Scheme

S + hv → 1S*

1S* ISC 3S*

3S* + NB → [NB---S]*3

Exciplex

[NB---S]*3 → NB. + S.---H

Proton transfer

NB. + NB. → NB—BN

Dimer of the Substrate

O O

O

NO2

NO2 NO2

O2N NO2

NO2

NO2

NO2

+

H +

+

. .

*3*1

*3

*1

hv

ISC

O

O

O

Exiplex

H +

O

Exiplex

.

204

6. Conclusion:

Photo sensitizer absorbs energy from visible light and goes to triplet excited state.

Nitrobenzene and m-DNB undergo photosensitized reaction in the presence of

benzophenone in alkaline medium in the visible light. The spectral profile of the exposed

solution suggest that the product of the reaction is di nitro biphenyl and tetra nitro

biphenyl for NB and m-DNB but p-DNB does not undergo photosensitized reaction

under similar experimental condition. Proton abstraction, free radical is observed and

triplet excited state of free radical of NB and m-DNB dimerize to give product. The rate

of the reaction is dependent on pH, and light intensity but is independent of the initial

concentration of the substrate and concentration of the sensitizer. The rate of the reaction

follows the order m-DNB > NB > p- DNB show the position of -NO2 group played an

important role. The φ– value of NB and m-DNB shows similar effect. Photochemical

reaction does not take place in the alkaline methanolic solution.

205

References:

[1].W.M.Schackleford, D.M.Cline, L.Faas, G.Kurth,Anal.Chim.Acta,146,(1983),15-27.

[2].R.I.Adkins Nitrobenzene and nitro toluene, in K. Orthmer, “Encyclopedia of chemical

technologiy”, 4th Eds., Wiley-Interscience, New York, 1994, 133-154.

[3].S. Contreras, M. Rodriguez, E. Chamarro and S. Esplugas, J. Photochem. Photobiol.

A: Chemistry, 142, (2001), 79.

[4].T. S. S. Dikshith, “Safety evaluation of environmental chemicals”, New Age

International (P) Limited, New Delhi, India, (1996) page: 2.

[5].E. Browning, “Toxicity of metabolism of industrial solvents”, Elsevier Publishing

Col., Amsterdam, London, (1965).

[6].H. Tomioka, K. Ueda, H. Ohi and Y. Izawa, Chem. Lett., 8, (1986), 1359.

[7]..A. Schmidt and W. Butte, Chemosphere, 38(6), (1999), 1293

[8].E. Lipczynska-Kochany, Chemosphere, 22(5-6), (1991), 529.

[9].A. Akata and M. D. Gurol, Chem. Oxid. 2, (1994), 140.

[10].N. Levy and M. D. Cohen, Mol. Photochem., 8(2), (1977), 155.

[11]. K. Sundarajan, V. Ramakrishnan and J. C. Kuriacose, Indian J. Chem., Sec. B,

23B(11), (1984), 1068.

[12]. D. B. Galloway, J. A. Bartz, L. G. Huey and F. F. Crim, J. Chem. Phys., 98(3),

(1993), 2107.

[13].M.H. Priya and Giridhar Madras*,J.Photochem. Photobiol. A: Chemistry 178,

(2006),1-7.

[14].Dulal C. Mukharjee, A.K. Mukharjee,p.Pal, B.Mandal,and K.Ray,

J.Indian.Chem.Soc., 81, (2004), 1093-1096.

206

[15].R.Dillert, M.Brandt, L. Fornefett, U. Siebers, D.Bahnemann, Chemosphere,.30,

(1995),2333.

[16].M.S.Dieckmann, K.A. Gray, Wat. Res. 30,(1996),1169.

[17]. N.San, A. Hatipoglu, G. Kocturk, Z. Cmar. J.Photochem. Photobiol. A: Chemistry

146, (2002), 189.

[18].F.S.G. Einschlag, J. Lopez, L.Carlos, A.I. Capparelli, A.M.Braun, E.Olivors,

Environ. Sci. Tech. 36, (2002), 3936.

[19].R. G. Compton, R. A. W. Dryfe, J. C. Eklund, S. D. Stephen and J. Hirst, J. Chem.

Soc. Perkin Trans 2, 8, (1995), 1673.

[20]. R. G. Compton, R. A. W. Dryfe and A. C. Fisher, J. Chem. Soc. Perkin Trans. 2,

(1994), 1581.

[21]. R. G. Compton, R. A. W. Dryfe and A. C. Fisher, J. Electroanal. Chem. 361,

(1993), 275.

[22]. K.Tanaka, W.Luesaiwong, T.Hisanaga, J. Mol.Catal. A : Chem., 122,(1997), 67.

[23]. J.M.Pena, N.S. Allen, M.Edge, C.M Liauw, I. Roberts and B. Valange, Polymer

Degradation and stability.,70, (2000) 437-454.

[24]. C.H. Tung, L.P.Zhang and Y. Li., Macromolecules, 31, (1998), 8794-8801.

[25].Y.Kawamura, R.TaKayama, M. Nishiuchi and M.Tsukayama., Tetrahedron letters,

41,( 2000), 8101-8106.

[26].S.Canonica*,B.Hellrung,P.Muller and J.Wirz., Environ.Sci.Tech.. 40(21), (2006),

6636-6641.

207

[27].Y.Pan, Y.Fu, S.Liu, H.Yu, Y.Gao , Q.Guo and S.Yu* J.Phys.Chem.A 110,(2006),

7316-7322.

[28]. Alan J. Post and Harry Morrison*. J. Am. Chem. Soc.; 117(29), (1995), 7812-7813.

[29].J.M.Matxain, Klefah A.K. Musa and L.A.Erikssion*, J.Med.Chem. 50(8),

(2007),1735-1743.

[30].T.Suzuki, M.Nagano, S.Watanabe and T.Ichimura., J.Photochem. Photobiol. A:

Chemistry 136, (2000), 7-13.

[31]. S. Jockusch, H.-J. Timpe, W. schnabel and N. J. Turro, J. Phys. Chem., A. 101(4),

(1997), 440.

[32]. K.Yamada, M.Sato, K. Tanaka, A. Wakabayashi, T. Igarashi, T. Sakurai, Journal

of Photochemistry and Photobiology A: Chemistry, 183(1-2), (2006), 205-211

[33]. R.G.Brinson and P.B.Jones, J.Photochem.PhotoBio. C 175 (2-3) ,(2005), 118-124.

[34].R.E.Galian, Pastor perez L., M.A. Miranda, J.Perez-pgieto, J.Am.Chem.Soc. 127,

(2005), 255-269.

[35]. X.Cai, M. Hara, K. Kawai, S. Tojo, T. Majima, Chem. Phy. Lett., 371, (2003), 68-

73.

[36].C.Marti, O.Jurgens, O.Cuenca, M.Casals and S.Nonell. J.Photochem. Photobiol. A:

Chemistry 97, (1996), 11-18.

[37].K. K. Rohatgi-Mukherjee, “Fundamentals of photochemistry”, 3rd Eds., New age

international (P) limited, New Delhi, India, (1997),

[38].S.K.Dogra.*, J.Photochem. Photobiol. A: Chemistry 172(2), (2005), 207-213.

[39].M.K. Nayak and S.K.Dogra.*, J.Photochem. Photobiol. A: Chemistry171(3), (2005),

281-290.

208

[40].Lemp, E., N. Pizarro, M. V. Encinas and A. L. Zanocco, Phys. Chem. Chem. Phys.

3,(2001), 5222–5225.

[41].Eduardo Silva.a ,Constanza De Landea a, Ana Maria Edwards a and Eduardo Lissi b

J.Photochem. Photobiol. B: Biolog., 55(2-3),( 2000), 196-200.

[42].P. K. Freeman, Jung-Suk Jang and N. Ramnath, J. Org. Chem. 56, (1991), 6072.

[43].H.Mohan, O.Brede and J.P.Mittal. J.Photochem. Photobiol. A: Chemistry 140,

(2001),191-197.

[44].H.Mohan, O.Brede and J.P.Mittal. J.Photochem. Photobiol. A: Chemistry 124,

(1999), 119-125.

final th-5 nitro - shodhgangashodhganga.inflibnet.ac.in/bitstream/10603/4368/13/13...172 1....

Documents