KHSO4 mediated synthesis, kinetics and mechanistic study of nitration of aromatic compounds in aqueous acetonitrile

Chemical Data Collections 21 (2019) 100222

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Data Article

Hydro peroxides /NaNO2 /KHSO4 mediated synthesis, kinetics and mechanistic study of nitration of aromatic compounds in aqueous acetonitrile Suresh Muppidi a,b, Chinna Rajanna Kamatala a,∗, Sudhakar Chary Voruvala a, Satish Kumar Mukka a a b

Department of Chemistry, Osmania University, Hyderabad 500007 Telangana, India Department of Chemistry, Telangana University, Dichpally, Nizamabad, Telangana, India

a r t i c l e

i n f o

a b s t r a c t

Article history: Received 23 February 2019 Revised 19 April 2019 Accepted 26 April 2019 Available online 26 April 2019

In this study, the authors employed hydrogen peroxide (HP) and tetrabutyl hydrogen peroxide (TBHP) as efficient green reagents for the nitration of aromatic compounds using NaNO2 / KHSO4 . Kinetics of the reactions revealed first order dependence on [Phenol] as well as [hydro peroxide] (i.e. [HP] or [TBHP]) under the conditions [NaNO2] >> [hydro peroxide] and [Phenol]. Introduction of the electron donating groups accelerated the rate, while electron withdrawing groups retarded the rate: m-Me >p-MeO >-H>p-Me > m-OH >≈ p-Br ≈ p-OH>p-Cl. On the other hand, ortho substituted phenols indicated a sequence: o-OH> o-Me> -H. The Hammett’s quantitative structure activity plots (log k versus σ ) deviated from linearity. These deviations were explained due to mesomeric para interaction energy (Gp) parameters arising from the exalted sigma (σ ̅ or σ eff ) values, and Yukawa– Tsuno parameter (r). © 2019 Elsevier B.V. All rights reserved.

Keywords: Synthesis Kinetics Mechanistic study Hydrperoxide reagents Phenols Nitration Structure-reactivity

Specifications table Subject area Compounds Data category Data acquisition format Data type Procedures Data accessibility

Physical organic chemistry, chemical kinetics, reaction mechanism Aromatic compounds Kinetics and spectroscopic Analysis of kinetic and spectroscopic data etc. Experimental Organic synthesis, reaction kinetics, determination of order with respect to [reactants], evaluation of activation parameters, hammett’s structure-activity relationship and related interpretations State if data is with this article or in public repository. If public repository, please explicitly name repository and data identification number and provide a direct URL to data

1. Rationale The nitration of aromatic compounds has come a long way from the era of using “mixed acid,’’ or compositions of the ternary components (HNO3 –H2 O–H2 SO4 ) as catalysts. Hughes, Ingold and Ridd [1,2] revealed that Martinsen (1904) was the first to accomplish definite second-order kinetics for the nitration of aromatic substances in sulphuric acid medium. It is ∗

Corresponding author. E-mail address: [email protected] (C.R. Kamatala).

https://doi.org/10.1016/j.cdc.2019.100222 2405-8300/© 2019 Elsevier B.V. All rights reserved.

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S. Muppidi, C.R. Kamatala and S.C. Voruvala et al. / Chemical Data Collections 21 (2019) 100222

Scheme 1. H2 O2 and TBHP as catalysts for effecient mono nitration of aromatic compounds in presence of KHSO4 /NaNO2 .

now generally accepted that the aromatic nitration occurs through the substitution of hydrogen in the aromatic ring by the nitronium electrophile (NO2 + ). On the basis of the several other investigations [1–3] with possible nitrating agents (X-NO2 ) the ease of nitrating agent to attack the aromatic ring is found proportional to the electron affinity of (X) and the order of increasing nitrating ability came out as: EtONO2 < HONO2 < AcONO2 < NO3 NO2 < ClNO2 < H2 ONO2 +
HNO3 + 2 H2 SO4  NO2 + + H3 O+ + 2 HSO4 − The existence of the nitronium ion species (NO2 + ) has been confirmed from x-ray crystallographic [9,10] and Raman spectroscopic studies [11]. By measuring the intensities of the Raman line, Chedin has also determined the concentration of NO2 + in mixed acid solutions [10]. More definite evidence about the role of NO2 + has come from the work of Hughes, Ingold, and co-workers [11]. Over the years, large numbers of useful methods have been developed for the synthesis of nitroaromatic compounds, because of their key role as important precursors/ intermediates and versatile building blocks in synthetic organic chemistry as well as in the chemical, pharmaceutical and dye industries [12–22]. A perusal of literature further shows that quite a good number of publications appeared in recent years, on the theoretical studies on the nitration of aromatic compounds [23–26]. Over the years, hydrogen peroxide (H2 O2 ) has emerged as an attractive oxidant, which can oxidize organic compounds with an atom efficiency of 47% and with the generation of water as the only theoretical coproduct [27–29]. On the other hand, organic hydro peroxides like tert-butyl hydro peroxide (t-BuOOH or TBHP) and urea-H2 O2 complex were also received notable attention as oxidizing agents in the past several years [30–37]. In continuation of our search for the development of eco-friendly synthetic protocols on nitration of aromatic and heteroaromatic compounds and their kinetic studies [38–47], we have embarked on exploring the use of economically viable and easily available reagents. In this study we have used ecofriendly hydro peroxides (HP) like hydrogen peroxide (H2 O2 ), and tetra butyl hydro peroxide (TBHP) in the presence of NaNO2 and mild (low) concentrations of KHSO4 . The use of (low) concentrations of KHSO4 improves the greenery of the protocol because H+ ions are generated in situ due to the dissociation of HSO4 − by avoiding the used concentrated acid mixture. (Scheme 1). 2. Procedure 2.1. Materials and methods Reagent grade hydro peroxides [HP] (H2 O2 ,t-BuOOH or TBHP) potassium bisulphate (KHSO4 ), sodium nitrite (NaNO2 ) and phenols were obtained from Avra, Aldrich, Merck, or SD-fine chemicals. HPLC grade acetonitrile was used throughout for kinetic studies. Laboratory deionized water was distilled twice over permanganate before use. 2.2. General procedure for synthesis of nitro compounds The constituents of the reaction such as sodium nitrite (12 mmol), aromatic or heteroaromatic compound (10 mmol), KHSO4 (1.0 mmol), hydro peroxide (1 mmol) are mixed with aqueous acetonitrile in a round bottomed. It is continuously stirred at 60 °C till the reaction is completed as ascertained by TLC. Afterwards the resultant reaction mixture is saturated with NaHCO3 and extracted with ethyl acetate (30 mL). The dried extract over Na2 SO4 contained crude product. Further purification by column chromatography using a binary mixture of ethyl acetate and hexane (3:7) afforded pure product. For instance, nitration of phenol using this procedure afforded 2-nitro phenol (70% major proportion), and 4-nitro phenol (20% minor proportion) respectively. Intra molecular hydrogen bonding occurring between o-nitro group and (-OH) hydrogen might cause greater stability and high yields of 2-nitro phenol over 4-nitrophenol. Spectroscopic analysis and physical data of the obtained products confirmed that the products are nitro phenols. 1 HNMR of 2-nitro phenol (300 MHz, CDCl3 ): δ 9.52 (s, 1H, OH), 8.15 (dd, 1H, J = 8.5 Hz, J = 8 Hz), 7.55 (dd, 1H, J = 8 Hz J = 7.5 Hz) 6.95 (d, 1H, J = 8.5 Hz) 8.12 (d, 1H, J = 8 Hz);m/z = 139; Melting Point = 43–48 °C.

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Table 1 Hydro peroxides/NaNO2 /KHSO4 mediated nitration of organic compounds. Entry

Substrate

Product

H 2 O2 R.T (h)

Yield (%)

R.T (h)

Yield (%)

1

Phenol

5

o-Cresol p-Cresol m-Cresol o-Cl Phenol m-Cl Phenol p-Cl Phenol p-Br Phenol p-Nitro Phenol p-Amino Phenol Aniline α -Naphthol β -Naphthol Salicylic acid

70 20 70 75 65 75 75 75 75 75 78 75 80 80 75

5

2 3 4 5 6 7 8 9 10 11 12 13 14

2-NO2 Phenol(major) 4-NO2 Phenol (minor) 2-Me-4-NO2 Phenol 2-NO2 4-Me Phenol 3-Me-4-NO2 Phenol 4-NO2 2-Cl Phenol 4-NO2 3-Cl Phenol 2-NO2 4-Cl Phenol 2-NO2 4-Br Phenol 2, 4-di Nitro Phenol 2-Nitro 4-Amino Phenol 4-Nitro Aniline 2-NO2 -1-Naphthol 1-NO2 -2-Naphthol 2-OH 4-NO2 Benzoic acid

68 20 70 75 65 75 75 75 75 70 75 70 80 75 75

5 5 5 6 6 6 6 7 7 5 4 5 6

TBHP

5 5 5 6 6 6 6 8 7 5 4 5 7

2.3. Kinetic method of following the reaction In kinetic studies, requisite amounts of aqueous hydro peroxide (H2 O2 or TBHP) and NaNO2 solutions were pippetted out in a reaction flask. Another reaction flask contained phenol (prepared in acetonitrile) along with requisite amounts of KHSO4 , acetonitrile and water. Total solvent in each set was equal to 5% (V/V). Both these flasks were thermostated in a constant temperature bath at a desired temperature for about twenty minutes to attain thermal equilibrium. To initiate the reaction both the sets of solutions were mixed thoroughly. Progress of the reaction kinetics was followed spectrophotometrically at 405 nm, because most of the nitro phenols absorb around 400 nm. Absorbance (or optical density-OD) values recorded at known time intervals were reproducible with an accuracy of ±3% error. Absorbance at a given time is defined as (At ), while the absorbance at infinite time (at the end of the reaction) is considered as A∞ , and A0 , the absorbance (if any) before the on-take of reaction. Thus (A∞ - At ) is proportional to (a-x), the concentration of reactant at any given time while (A∞ - A0 ) is proportional to initial concentration of the reactant (a). This method is almost identical to the one reported recently in our earlier publications [46].

3. Data, value and validation 3.1. Chemistry 3.1.1. Hydro peroxides /NaNO2 /KHSO4 mediated nitration of organic compounds The data presented in Table 1 clearly show that hydro peroxides/NaNO2/KHSO4 mixtures mediate the nitration of aromatic compounds. Obtained results herein revealed that, phenol and p-bromophenol gave corresponding nitration products in good yields, while the conversion of p-aminophenol to 2-nitro-4-aminophenol required longer reaction time. Observed slower reactivity in the nitration of para-aminophenol could be probably attributed to a reduced electron density at the reaction site because more activating amino (-NH2 ) group might be protonated by the (H+ ) ions generated in situ by the dissociation of bisulfate ion (HSO4 − ), which converts active amino group to a deactivating (−NH3 + ) group. Structural variation in the hydro peroxy compound (from H2 O2 to TBHP) did not affect much either in the reaction times or (%) yields of products. In both the cases, reactions afforded to give fairly good yields.

3.1.2. Salient features of the kinetic study We used requisite amounts of phenol, hydro peroxides (HP) (H2 O2 or TBHP), NaNO2 , and KHSO4 in (5%) aqueous acetonitrile media in the present kinetic study. In these studies, concentration of NaNO2 is taken in large excess over [HP]0 ([NaNO2 ]0 >>[HP]0 ) in aqueous acetonitrile/KHSO4 medium, so that in situ generated [NO2 + ] is equal to [HP]0 . Initial concentration of an additive (phenol, hydro peroxides (HP) (H2 O2 or TBHP), NaNO2 , and KHSO4 ) in the reaction is represented by [–]0 . For instance, initial concentration of NaNO2 is represented by [NaNO2 ]0 . (i) First order kinetics with respect to [HP] was determined from linear plots of ln [(A∞ - A0 )/ (A∞ - At )] vs time passing through origin (Figs. 1 and 2), in accordance with the following equation, under pseudo first order conditions ([Phenol]0 ≈ [NaNO2 ]0 >>[HP]0 )



 ( A∞ − A0 ) ln = k t (A∞ − At )

(1)

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Fig. 1. First order plot for H2 O2 / NaNO2 mediated nitration of phenols 103 [Phenol] = 5.0 mol/dm3 ; 104 [H2 02 ] = 5.0 mol/dm3 ; 103 [NaNO2 ] = 5.0 mol/dm3 ; [KHSO4 ] = 0.010 mol/dm3 ; MeCN(% V/V) = 5.0; Temperature = 303K.

Fig. 2. First order plot for TBHP/ NaNO2 mediated nitration of phenols 103 [Phenol] = 5.0 mol/dm3 ; 104 [H2 02 ] = 5.0 mol/dm3 ; 103 [NaNO2 ] = 5.0 mol/dm3 ; [KHSO4 ] = 0.010 mol/dm3 ; MeCN(% V/V) = 5.0; Temperature = 303 K.

Fig. 3. Plots of (k’) vs [Sub] in H2 O2 /NaNO2 mediated nitration reactions of phenols 104 [H2 O2 ] = 5.0 mol/dm3; 103 [NaNO2 ] = 5.0 mol/dm3 ;[KHSO4 ] = 0.010 mol/dm3 ; MeCN(% V/V) = 5.0; Temperature = 303 K.

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Fig. 4. Plots of (k’) vs [Sub] in TBHP/NaNO2 mediated nitration reactions of phenols 104 [TBHP] = 5.0 mol/dm3; 103 [NaNO2 ] = 5.0 mol/dm3 ;103 [KHSO4 ] = 0.010 mol/dm3 ; MeCN(% V/V) = 5.0; Temperature = 303 K.

Fig. 5. Second order plot for H2 O2 /NaNO2 mediated nitration reaction of phenol at 303 K 104 [Phenol] = 104 [H2 O2 ] = 5.0 mol/dm3 ; MeCN(% V/V) = 5.0; 103 [NaNO2 ] = 103 [KHSO4 ] = 5.0 mol/dm3 ;.

Fig. 6. Second order plot for H2 O2 /NaNO2 mediated nitration reaction of p-Cresol at 303 K 104 [p-Cresol] = 5.0 mol/dm3 ; 104 [H2 O2 ] = 5.0 mol/dm3 ; 103 [NaNO2 ] = 103 [KHSO4 ] = 5.0 mol/dm3 ; MeCN(% V/V).

(ii) Pseudo first order rate constants increased with an increase in the first power of phenol concentration ([Phenol]). Accordingly, the plots of (k’) vs [Phenol] (Figs. 3 and 4), were linear passing through origin, which confirms first order in [Phenol] (iii) Under pseudo second order conditions ([NaNO2 ]0 >> [HP]0 = [Phenol]0 ), and at constant [bisulphate], plots of (1/ (A∞ - At )) vs time have been found linear with a positive gradient and definite intercept on ordinate (vertical axis) indicating pseudo second order kinetics (Figs. 5–8) according to the following expression:

1

( A∞ − At )

=

k

(ε )

(t ) +

1

( A∞ − A0 )

(Where ε = [Reagent]0 /(A∞ − A0 )

6

S. Muppidi, C.R. Kamatala and S.C. Voruvala et al. / Chemical Data Collections 21 (2019) 100222

Fig. 7. Second order plot for TBHP/NaNO2 mediated nitration reactions p-Cresol 104 [p-Cresol] = 5.0 mol/dm3 ; 104 [TBHP] = 5.0 mol/dm3 ; 103 [NaNO2 ] = 5.0 mol/dm3 ; 103 [KHSO4 ] = 5.0 mol/dm3 ; MeCN(% V/V) = 5.0; Temperature = 303 K.

Fig. 8. Second order plot for TBHP/NaNO2 mediated nitration reaction of p–chloro phenol 104 [p–chloro phenol] = 5.0 mol/dm3 ; 104 [TBHP] = 5.0 mol/dm3 ; 103 [NaNO2 ] = 5.0 mol/dm3 ;103 [KHSO4 ] = 5.0 mol/dm3 ; ture = 303 K.

MeCN(%

V/V) = 5.0;

Tempera-

Proper substitution of (ε ) into the above equation leads to

1

( A∞ − At )

=

k[Reagent]0 1 (t ) + ( A∞ − A0 ) ( A∞ − A0 )

(2)

In Eq. (2), [Reagent]0 = [NO2 + ]0 = [HP]0, because nitronium ion (NO2 + ) electrophile is generated in situ due the oxidation of NaNO2 by hydro peroxide (HP or TBHP) under conditions ([NaNO2 ]0 >> [HP]0 . Thus [NO2 + ]0 could equal to [HP]0. 3.1.3. Test for the detection of free radical species Addition of freshly prepared acrylamide or deareated acrylonitrile to the reaction mixture (containing hydro peroxide reagents (H2 O2 and / or TBHP) and other constituents like phenol, NaNO2 , and KHSO4 ) under nitrogen atmosphere did not affect the rate of reaction or initiated/induced polymerization of added olefinic monomers even after 24 h under reflux conditions. This observation may indicate the absence of free radical intermediates during the course of present reaction. 3.1.4. Effect of variation of [additives] on the rate of nitration Kinetic experiments were conducted to know the effect of other additives/ reactants on pseudo first order rate constants (k’) in H2 O2 / NaNO2 mediated as well as TBHP/NaNO2 mediated nitration reactions by taking phenol as a specific example. Observed results are compiled Table 2. The data revealed that (k’) values were not altered to any significant extent. 3.1.5. Temperature effect on the rate of nitration The free energy of activation (࢞G# ) at various temperatures is calculated for second order rate constant (k) using Eyring’s theory of reaction rates [48,49]. We have also evaluated enthalpy and entropies of activation (࢞H# and ࢞S# ) from the slope and intercept values of the Gibbs – Helmholtz plot ࢞G# vs temperature (T) as shown in Figs. 9 and 10. Evaluated activation parameters are compiled in Table 3. Negative entropy of activation (−࢞S#) probably suggests greater solvation and/or cyclic transition state before yielding products.

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Table 2 Effect of variation of [additives] on pseudo first order rate constants (k’) in H2 O2, TBHP/NaNO2 mediated nitration reactions of phenol 103 [phenol] = 5.0 mol/dm3 ; MeCN (% V/V) = 5.0; Temperature = 298 K. 104 [HP] (mol/ dm3 )

103 [NaNO2 ] (mol/ dm3 )

[KHSO4 ] (mol/ dm3 )

103 k’/min H2 O2

TBHP

5.00 5.00 5.00 5.00 5.00 5.00 5.00 5.00 5.00 5.00 5.00 10.0 15.0 20.0

5.00 5.00 5.00 5.00 5.00 5.00 1.00 2.00 4.00 8.00 10.0 20.0 20.0 20.0

0.005 0.010 0.015 0.020 0.025 0.050 0.010 0.010 0.010 0.010 0.010 0.010 0.010 0.010

2.80 2.85 2.78 2.89 2.92 2.82 2.96 2.77 2.90 2.95 2.86 2.81 2.85 2.95

1.70 1.85 1.90 1.75 1.88 1.77 1.65 1.72 1.67 1.62 1.65 1.82 1.84 1.72

Fig. 9. Gibbs–Helmholtz plot for H2 O2 /NaNO2 mediated nitration reactions.

Fig. 10. Gibbs–Helmholtz plot for TBHP /NaNO2 mediated nitration reactions.

3.2. Kinetic results and discussion 3.2.1. Reactive species and mechanism of nitration in HP/NaNO2 mediated nitration of aromatic compounds The present nitration study is taken up with economically viable reagents like hydro peroxides (HP) like hydrogen peroxide (H2 O2 ), and/or tetra butyl hydro peroxide (TBHP) in the presence of large excess of NaNO2 over hydro peroxide under and mild (low) concentrations of KHSO4 . In an extensive review Koppenol revealed that the reaction of hydrogen peroxide (H2 O2 ) with nitrite (NO2 − ) affords peroxynitrite (or peroxonitrite with the formula ONOO− [28], which is an unstable

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Table 3 Activation parameters for hydro peroxide /NaNO2 mediated nitration reactions. Substrate

H2 O2 -NaNO2 system

Phenol

p-Cresol

p-chloroPhenol

p-bromoPhenol

p-methoxy Phenol

m-Cresol

Resorcinol

m–chloro Phenol

o-Cresol

Catechol

o-chloroPhenol

TBHP-NaNO2 system =

Temp (K)

K (dm /mol/s)

࢞G ࢞H (kJ/ mol)

303 308 318 323 303 308 318 323 303 308 318 323 303 308 318 323 303 308 318 323 303 308 318 323 303 308 318 323 303 308 318 323 303 308 318 323 303 76.0 308 318 323 303 308 318 323

0.56 0.76 1.14 1.40 1.10 1.64 2.64 3.34 0.66 0.80 0.84 0.94 1.76 2.28 3.54 4.16 2.30 2.76 2.94 3.10 2.46 3.66 6.38 8.48 2.06 2.42 2.66 2.96 0.14 0.16 0.18 0.20 0.86 1.10 2.00 2.60 4.70

75.7 76.2 77.7 78.4 74.0 74.2 75.5 76.1 75.3 76.1 78.5 79.5 72.8 73.4 74.7 75.5 72.2 72.9 75.2 76.3 72.0 72.2 73.2 73.6 72.4 73.3 75.4 76.4 79.2 80.2 82.6 83.6 74.6 75.3 76.2 76.8 70.4

6.22 8.46 10.98 0.80 0.98 1.38 1.58

70.8 72.4 72.9 74.8 75.6 77.2 78.1

3

=

−࢞S

33.8

138

41.2

108

9.67

217

32.58

133

8.06

211

46.7

83.2

10.7

203

11.0

225

43.2

104

30.0

133

25.1

164

=

(J/Kmol)

Temp(K)

k(dm3 /mol/s)

࢞G= ࢞H= (kJ/ mol)

−࢞S= (J/Kmol)

303 308 318 323 303 308 318 323 303 308 318 323 303 308 318 323 303 308 318 323 303 308 318 323 303 308 318 323 308 313 318 323 303 308 318 323 303

0.34 0.48 0.80 1.00 2.50 3.06 5.20 6.80 0.18 0.28 0.66 0.98 0.28 0.42 0.88 1.28 2.62 2.98 3.58 3.94 2.36 3.56 6.60 9.06 1.80 2.40 2.82 2.98 0.26 0.42 0.64 0.98 1.30 1.76 2.10 2.42 3.14

77.0 77.4 78.6 79.3 72.0 72.6 73.7 74.2 78.6 78.8 79.2 79.4 77.4 77.7 78.4 78.6 71.8 72.7 74.7 75.6 72.1 72.3 73.0 73.4 72.8 73.3 75.3 76.4 79.0 79.0 79.2 79.4 73.6 74.1 76.1 76.9 71.4

40.8

119

38.6

110

66.5

39.8

58.9

61.2

13.7

191

51.2

68.7

16.3

186

70.2

28.4

20.4

175

308 318 323 303 308 318 323

4.46 8.34 10.98 0.72 0.94 1.62 2.22

71.7 72.4 72.9 75.1 75.7 76.8 77.2

48.3

43.0

106

structural isomer of nitrate (NO3 − ).

H2 O2 + NO− 2 → OONO + H2 O Peroxynitrite is reported an efficient oxidant and nitrating agent, which is relatively stable in alkaline solutions (pH > 12, half-life time t1/ 2 ≥ 105 s), whereas at physiological pH, peroxynitrous acid (pKa = 6.8) rapidly isomerizes/decomposes to nitrate (NO3 − ) with t1/ 2 = 10 s at 1 °C [19,29,35,37] or 0.53 s at 25 °C. On the basis of this discussion, nitration through the peroxy nitrite could be ruled out, and nitration through insitu formation of nitronium (NO2 + ) is more likely. Mechanism of nitration could be explained through the following sequence of reaction steps: Kd

−2 + HSO− 4  H + SO4 K1

H+ +NO− 2  HNO2 K2

HNO2 + ROOH  HNO3 + ROH

(1) (2) (3)

S. Muppidi, C.R. Kamatala and S.C. Voruvala et al. / Chemical Data Collections 21 (2019) 100222 K3

HNO3 + H+  NO+ 2 + H2 O

9

(4)

Slow(k1 )

NO2 + + R − C6 H4 − X → R − C6 H3 − X − ( NO2 ) + H+

(5)

Rate-law for these mechanistic steps could be derived using equilibria (1–4 and step 5),

Rate = -d[R-C6 H4 -X]/dt = k1 [NO2 + ][R-C6 H4 -X]

(6)

From step (4)

[NO2 + ] = K3 [HNO3 ][H+ ]

(7)

But from step (3) in situ produced [HNO3 ] could be evaluated as,

[HNO3 ] = K2 [HNO2 ][ROOH]/[ROH]

(8)

Substituting for [HNO3 ] from Eq. (8) into Eq. (7), [NO2 + ] could be given as,

[NO2 + ] = K2 K3 [HNO2 ][ROOH][H+ ]/ [ROH]

(9)

From step (2), it could be shown that

[HNO2 ] = K1 [H+ ][NO2 − ]

(10)

Substitution for [HNO2 ] from Eq. (10) into Eq. (9), [NO2 + ] reduced to,

[NO2 + ] = K1 K2 K3 [NO2 − ][ROOH][H+ ]2 / [ROH]

(11)

From Eq. (1), dissociated proton (H+ ) comes out as, [H+ ] = Kd [HSO4 − ]/ [SO4 −2 ]. Substution for [H+ ] in Eq. (11), [NO2 + ] takes the form

[NO2 + ] = (K1 K2 K3 [NO2 − ]t [ROOH]t (Kd [HSO4 − ]/ [SO4 −2 ])2 / [ROH] Upon further simplification, the active species [NO2 + ] could be written as,





NO+ 2 =

   2 (Kd )2 K1 K2 K3 NO−2 t [ROOH]t HSO−4  −2 2

(12)

[ROH] SO4

Substitution of active species [NO2 + ] from Eq. (12) into Eq. (6), rate law comes out as,

Rate = -d[R-C6 H4 -X]/dt = k(Kd )2 K1 K2 K3 [NO2 − ]t [ROOH]t [HSO4 − ]2 [R-C6 H4 -X]/ [ROH][SO4 −2 ]2 Above rate equation is in agreement with the observed kinetic results viz, first order in [Substrate] (i.e., R-C6 H4 -X), and [ROOH]t (hydro peroxide). Since [NO2 − ]>>[ROOH] and [KHSO4 ], it is understood that order in [active NO2 + species] is also one. Bisulfate term ([HSO4 − ]) appeared in the numerator of the rate law (13) is negated by (SO4 −2 ) terms in the denominator, suggesting the observed negligible (HSO4 − ) effect on rate of the reaction. Thus, at constant (HSO4 − ) concentration, and known excess that rate law reduces to,

Rate = -d[R-C6 H4 -X]/dt = k [NO2 + ] [R-C6 H4 -X] (where [NO2 + ] = (Kd )2 K1 K2 K3 [NO2 − ]t [ROOH]t [HSO4 − ]2 / [SO4 −2 ]2 [ROH] The kinetic results obtained in the present study together with the foregoing discussions substantiate a plausible mechanism for the nitration of the aromatic compounds as shown in Scheme 2.

10

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Scheme 2. Hydrperoxides triggered mechanism of nitration of aromatic compounds.

3.2.2. Quantitative structure and reactivity study The kinetic data pertaining to the hydro peroxide mediated nitration of phenols revealed that the reaction is sensitive to the structural variation of phenol with the introduction of electron donating (EDG) or electron withdrawing groups (EWG). We have tried to correlate the rate data into Hammett’s quantitative structure and reactivity relationship [50,51].

log (k ) = log (k0 ) ± σ ρ Accordingly the log(k) vs σ (the Hammett’s substituent constant) [50] should be a straight line graph with either a positive or negative slope (ρ ; Hammett’s Rho) depending on the nature of substituent. But the Hammett’s plots of log(k) vs σ deviated from linearity with very low correlation coefficient (R2 ) and negative slope value with (ρ < 0), which can be seen from the representative plots in Figs. 11(a) and 12(a). However, the plots between the logarithmized rate constants and the effective Hammett constants (σ eff ) gave extraordinarily good correlation (R2 = 1.0) as shown in Figs. 11(b) and 12(b). The observed deviations from linearity may attribute to the cumulative effects arising either from inductive, resonance and steric effects, or the mesomeric para interaction energy (Gp) parameters, and effective sigma (σ ̅ or σ eff ) values, as suggested by Brown, Okamoto, van Bekkum, Webster and others [51–54].

(σ¯ or σeff ) = (log k − logk0 )/ρm where “ρ m ” is the modified reaction constant obtained for the Hammett’s plot after removing the scattered points from the of log(k) vs σ shown in Hammett’s plots given in Figs. 11(a) and 12 (a).

−Gp = 2.3RTρm (σ¯ − σ ) The Gp value indicates a less pronounced electron-withdrawing effect between the substituent and the reaction centre in the transition state. The Yukawa–Tsuno equation [53,54] is one the best modifications to the Hammett equation, which quantified the role of enhanced resonance effects on the reactivity of meta- and para-substituted aromatic compounds. This equation explained enhanced resonance effects in electrophilic reactions of para- and meta-substituted organic compounds, by introducing a new term (r) to the original Hammett relation, as shown the following sets of Yukawa–Tsuno equations:

log k = log k0 + ρ [σ + r (σ + − σ )] log k = log k0 + ρ [σ − − σ ] where kX and k0 represent the rate constants for an X-substituted and unsubstituted compound, respectively; ρ represents the Hammett reaction constant; σ represents the Hammett substituent constant; σ + and σ − represent the Hammett substituent constants for reactions in which positive or negative charge is built up at the reactive center, respectively; and (r) represents the Yukawa–Tsuno parameter [54]. This term provides a measure of the extent of resonance stabilization for a reactive structure that builds up charge (positive) in its transition state. When (r) = 0, the resonance effects for a particular compound in the reaction are almost similar to those of the unsubstituted reference compound in a reaction. However, when (r) > 0, the reaction understudy is more sensitive to resonance effects than the standard, and when (r) < 0, the reaction is less sensitive to resonance effects. Incidentally the observed enhanced resonance parameter herein, is equal to unity [(r) = 1] for all the systems (Tables 4 and 5), which is greater than “zero (0)” as cited by Yukawa and Tsuno [54]. This value probably indicates that both the hydro peroxides (H2 O2 and TBHP) follow a similar type of mechanism in “hydro peroxides /NaNO2 /KHSO4 ” mediated nitration of aromatic compounds in aqueous acetonitrile medium. However, Yukawa and Tsuno equation did not take into account the effects of various solvents on organic reactions.

S. Muppidi, C.R. Kamatala and S.C. Voruvala et al. / Chemical Data Collections 21 (2019) 100222

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Fig. 11. (a) Hammett’s plots in H2 O2 system. (b) Hammett’s plots in H2 O2 system with modified sigma values (σ eff ).

Table 4 Effective Hammett’s constants and mesomeric para interaction energy (Gp) parameters (H2 O2 ). Temp

Substituent

Effective sigma (σ ̅ or σ eff )

Hammett’s sigma (σ )

(Gp) kJ/mol

(r)

303K

p-Cl p-Br p-OMe m-OH m-Me p-Cl p-Br p-OMe m-OH m-Me p-Cl p-Br p-OMe m-OH m-Me p-Cl p-Br p-OMe m-OH m-Me

−0.043 −0.302 −0.373 −0.344 −0.391 −0.012 −0.258 −0.302 −0.272 −0.369 0.061 −0.228 −0.190 −0.170 −0.346 0.076 −0.208 −0.152 −0.143 −0.344

0.23 0.43 −0.27 0.12 −0.07 0.23 0.43 −0.27 0.12 −0.07 0.23 0.43 −0.27 0.12 −0.07 0.23 0.43 −0.27 0.12 −0.07

2.61 6.99 0.98 4.43 3.06 2.64 7.51 0.35 4.28 3.26 2.22 8.66 −1.05 3.82 3.63 2.16 8.97 −1.66 3.70 3.85

1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00

308K

318K

323K

12

S. Muppidi, C.R. Kamatala and S.C. Voruvala et al. / Chemical Data Collections 21 (2019) 100222

Fig. 12. (a) Hammett’s plots in TBHP system. (b) Hammett’s plots in TBHP system with modified sigma values (σ eff ).

Table 5 Exalted Hammett’s constants and mesomeric para interaction energy (Gp) parameters (TBHP). Temp

Substituent

Effective sigma (σ ̅ or σ eff )

Hammett’s sigma (σ )

(Gp) kJ/mol

(r)

303K

p-Me p-Br p-OMe m-OH m-Me p-Me p-Br p-OMe m-OH m-Cl m-Me p-Me p-Br p-OMe m-OH m-Cl m-Me p-Me p-Br p-OMe m-OH m-Cl m-Me

−0.722 0.070 −0.739 −0.603 −0.701 −0.791 0.057 −0.780 −0.687 0.262 −0.856 −2.24 −0.114 −1.79 −1.51 0.267 −2.52 −21.9 −2.82 −15.7 −12.5 0.231 −25.2

−0.17 0.43 −0.27 0.12 −0.07 −0.17 0.43 −0.27 0.12 0.37 −0.07 −0.17 0.43 −0.27 0.12 0.37 −0.07 −0.17 0.43 −0.27 0.12 0.37 −0.07

3.84 2.50 3.26 5.03 4.39 3.72 2.24 3.06 4.84 0.65 4.71 4.57 1.20 3.36 3.60 0.23 5.42 5.11 0.76 3.62 2.96 0.033 5.90

1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00

308K

318K

323K

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4. Conclusions In summary, the authors have investigated the use of hydrogen peroxide and tetra butyl hydrogen peroxide (TBHP) as efficient green reagents for the nitration of aromatic compounds (Phenols) using NaNO2 / KHSO4 . The reaction followed second order kinetics with first order dependence on [Hydro peroxide] and [Phenol], under the conditions [NaNO2 ] >>[HP], [Phenol], [HSO4 − ]. A closer look into the kinetic data revealed that the reaction is sensitive to the structural variation of substituted phenols, but could not be quantitatively correlated with Hammett’s equation. The deviations could attribute to the mesomeric para interaction energy (Gp) parameters, and exalted sigma (σ ̅ or σ eff ) values, as suggested by Brown, Okamoto, van Bekkum, Webster and others. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] [36] [37] [38] [39] [40] [41] [42] [43] [44] [45] [46] [47] [48] [49] [50] [51] [52] [53] [54]

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