# Oxidative Cleavage ofβ-Keto Sulfones via Nitrous Acid

Authors: Hatem A. Abdel-Aziz
Journal: Journal of Chemistry
 (2014)

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## Abstract

The reaction of nitrous acid with 1-aryl-2-(arylsulfonyl)ethanones3a–e afforded the unexpected arenecarboxylic acids 12a–e, formic acid 14, and benzene/4-toluenesulfinic acid 15a, b through oxidative cleavage reaction. 4-Chlorobenzoic acid (12a), [1,1′-biphenyl]-4-carboxylic acid (12b), 2-naphthoic acid (12c), 2-thiophenecarboxylic acid (12d), and 2-benzofurancarboxylic acid (12e) were isolated in 72%, 62%, 55%, 58%, and 62% yields, respectively. The reported mechanistic pathways proposed the production of 1-aryl-2-(phenyl/tolylsulfonyl)ethane-1,2-dione 7 instead of arenecarboxylic acids 12. A mechanistic pathway to explain the reaction of nitrous acid with 1-aryl-2-(arylsulfonyl)ethanones 3a–e was suggested. In this pathway, the intermediate 1,2-oxazete 10 lost benzene/4-toluenesulfinic acid 15 to produce 1,2-oxazet-3-one 11. Ring cleavage of the latter intermediate afforded the arenecarboxylic acids 12.


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## Body

## 1. Introduction

β-Keto sulfones are versatile synthetic intermediates used for the preparation of diverse classes of organic compounds such as substituted acetylenes, olefins, allenes, vinyles, and pyrans. The chemistry of β-keto sulfones achieved a significant peak of interest during the last decades and nowadays constitutes a whole branch of organosulfur chemistry [1–3]. Although the chemistry of β-keto sulfones has been widely investigated, little has appeared in the literature concerning their oximes. Oximes represent an important class of organic compounds with a wide range of practical applications. Oximes can be synthesized by condensation of an aldehyde or a ketone with hydroxylamine. They can also be obtained from reaction of nitrites with active methylene compounds. The latter reaction producesC-nitroso compounds which usually rearrange to oximino compounds. This reaction has value as a means of introducing an oximino function in a part of molecule that does not have a carbonyl group for direct oximation [4]. The oxidation of oximes with various inorganic acids is a known procedure for the recovery of aldehydes and ketones from their corresponding oximes [5]. This method has been widely utilized and its reaction mechanism has been reported [6]. In this study and in continuation of our interest in chemistry of β-keto sulfones [7–9], we shall deal with the reaction of nitrous acid with β-keto sulfones3 and therefore the probable modes of formation of the corresponding carboxylic acids12.


## 2. Experimental

### 2.1. Chemistry

#### 2.1.1. General

Melting points were determined on a Gallenkamp melting point apparatus and are uncorrected. Infrared (IR) spectra were recorded as KBr disks using the Perkin Elmer FT-IR Spectrum BX apparatus. NMR spectra were scanned in DMSO-d6 on a Bruker NMR spectrometer operating at 500 MHz for 1H and 125 MHz for 13C. Chemical shifts are expressed in δ-values (ppm) relative to TMS as an internal standard. Coupling constants (J) are expressed in Hz. D2O was added to confirm the exchangeable protons. The mass spectra were performed using a Varian MAT CH-5 spectrometer (70 eV).


#### 2.1.2. Synthesis of 1-Aryl-2-arylsulfonyl Ethanones3a–f

These compounds were prepared according to the reported method [10–15].


#### 2.1.3. Synthesis of Oximes4a–f

To a stirred cold solution ofβ-keto sulfones3a–f [10–15] (10 mmol) in glacial acetic acid (20 mL), sulfuric acid (1 mL, 50%) was added. Then cold solution of sodium nitrite (0.7 g, 10 mmol) in water (5 mL) was added dropwise with stirring at such a rate that the temperature remains in the range 0–5°C. Over a period of 30 min, a light blue solution of nitrous acid is produced. The mixture is stirred for extra 1 h at 25°C. The reaction mixture was poured into cold water and the solid product was filtered off, washed with water, and dried. Recrystallization from EtOH afforded4a–f which were used without any further purification in the next step.


#### 2.1.4. The Reaction of Nitrous Acid withβ-Keto Sulfones3a–e

To a stirred cold solution ofβ-keto sulfones3a–e (10 mmol) or oximes4a–e (10 mmol) in glacial acetic acid (30 mL), sulfuric acid (5 mL, 50%) was added. Then cold solution of sodium nitrite (2.1 g, 30 mmol) in water (10 mL) was added dropwise with stirring at such a rate that the temperature remains in the range 0–5°C. Over a period of 30 min, a light blue solution of nitrous acid is produced. The mixture is stirred for extra 48 h at 25°C. The solid that precipitated was collected, washed with water, and dried. Recrystallization from EtOH afforded the corresponding carboxylic acids12a–e in 55–72% yield. Formic acid (14) and benzene/4-toluenesulfinic acid15 were detected in filtrate using chromatographic analyses. 4-Chlorobenzoic acid (12a) was isolated in 65% yield by the reaction of 1-(4-chlorophenyl)-2-[(4-methylphenyl)sulfonyl]ethanone (3f) instead of3a.(1) 4-Chlorobenzoic Acid (
12a
). This acid was prepared from 1-(4-chlorophenyl)-2-(phenylsulfonyl)ethanone (3a) [10] in 65% yield (1.02 g). 1-(4-Chlorophenyl)-2-[(4-methylphenyl)sulfonyl]ethanone (3f) [11] afforded 1.13 g (72% yield) of 4-chlorobenzoic acid (12a); m.p. 238–240°C (Let. m.p. 238–241°C) [16]; 1H NMR δ 7.57 (d,J = 8.5 Hz, 2H, ArHs), 7.95 (d,J = 8.5 Hz, 2H, ArHs), 13.20 (s, D2O exchangeable, 1H, OH); 13C NMR δ 128.69 (C3 and C5), 129.72 (C1), 131.10 (C2 and C6), 137.70 (C4), 166.45 (C=O); MS (EI)m/z 156 [M+], 157 [M++1], 158 [M++2].(2) [1,1
′
-Biphenyl]-4-carboxylic Acid (
12b
). This acid was prepared from 1-(1,1′-biphenyl-4-yl)-2-(phenylsulfonyl)ethanone (3b) [12] in 62% yield (1.23 g); m.p. 225–227°C (Let. m.p. 220–225°C) [17]; 1H NMR δ 7.43 (t,J = 7.5 Hz, 1H, ArH), 7.51 (t,J = 7.5 Hz, 2H, ArHs), 7.75 (d,J = 7.5 Hz, 2H, ArHs), 7.79 (d,J = 8.5 Hz, 2H, ArHs), 8.03 (d,J = 8.5 Hz, 2H, ArHs), 13.00 (s, D2O exchangeable, 1H, OH); 13C NMR δ 126.70 (C3 and C5), 126.91 (C2 and C6), 128.20 (C4 and C4′), 129.04 (C3′ and C5′), 129.90 (C2′ and C6′), 139.07 (C1′), 144.0 (C1), 167.26 (C=O); MS (EI)m/z 198 [M+].(3) 2-Naphthoic Acid (
12c
). This acid was prepared from 2-[(4-methylphenyl)sulfonyl]-1-(2-naphthalenyl)ethanone (3c) [13] in 55% yield (0.95 g); m.p. 186–188°C (Let. m.p. 185–187°C) [18]; 1H NMR δ 7.60–7.68 (m, 2H, ArHs), 7.98–8.03 (m, 3H, ArHs), 8.21 (d,J = 8.0 Hz, 1H, ArH), 8.62 (s, 1H, ArH), 13.11 (s, D2O exchangeable, 1H, OH); 13C NMR δ 125.25 (C3), 126.69 (C2), 127.60 (C7), 128.01 (C5), 128.14 (C4), 128.63 (C6), 129.20 (C8), 130.34 (C1), 132.14 (C8a), 134.80 (C4a), 167.56 (C=O); MS (EI)m/z 172 [M+].(4) 2-Thiophenecarboxylic Acid (
12d
). This acid was prepared from 2-[(4-methylphenyl)sulfonyl]-1-(2-thienyl)ethanone (3d) [14] in 58% yield (0.74 g); m.p. 124–126°C (Let. m.p. 125–127°C) [19]; 1H NMR δ 7.19 (dd,J = 3.5, 4.8 Hz, 1H, H4), 7.727 (dd,J = 0.7, 3.5 Hz, 1H, H5), 7.91 (dd,J = 0.7, 4.8 Hz, 1H, H3), 13.23 (s, D2O exchangeable, 1H, OH); 13C NMR δ 135.20 (C2), 133.79 (C3), 128.82 (C4), 133.81 (C5), 163.51 (C=O); MS (EI)m/z 128 [M+].(5) 2-Benzofurancarboxylic Acid (
12e
). This acid was synthesized from 1-(2-benzofuranyl)-2-(phenylsulfonyl)ethanone (3e) [15] in 52% yield (0.84 g); m.p. 193–195°C (Let. m.p. 193–196°C) [20]; 1H NMR δ 7.38 (t,J = 7.5 Hz, 1H, H5), 7.53 (t,J = 7.5 Hz, 1H, H4), 7.71–7.77 (m, 2H, H3+H4), 7.83 (d,J = 7.5 Hz, 1H, H6), 13.80 (s, D2O exchangeable, 1H, OH); 13C NMR δ 114.35 (C8), 115.82 (C3), 123.00 (C4), 123.91 (C5), 127.04 (C6), 127.84 (C3a), 146.02 (C2), 154.95 (C8a), 160.02 (C=O); MS (EI)m/z 162 [M+].


## 2.1. Chemistry

### 2.1.1. General

Melting points were determined on a Gallenkamp melting point apparatus and are uncorrected. Infrared (IR) spectra were recorded as KBr disks using the Perkin Elmer FT-IR Spectrum BX apparatus. NMR spectra were scanned in DMSO-d6 on a Bruker NMR spectrometer operating at 500 MHz for 1H and 125 MHz for 13C. Chemical shifts are expressed in δ-values (ppm) relative to TMS as an internal standard. Coupling constants (J) are expressed in Hz. D2O was added to confirm the exchangeable protons. The mass spectra were performed using a Varian MAT CH-5 spectrometer (70 eV).


### 2.1.2. Synthesis of 1-Aryl-2-arylsulfonyl Ethanones3a–f

These compounds were prepared according to the reported method [10–15].


### 2.1.3. Synthesis of Oximes4a–f

To a stirred cold solution ofβ-keto sulfones3a–f [10–15] (10 mmol) in glacial acetic acid (20 mL), sulfuric acid (1 mL, 50%) was added. Then cold solution of sodium nitrite (0.7 g, 10 mmol) in water (5 mL) was added dropwise with stirring at such a rate that the temperature remains in the range 0–5°C. Over a period of 30 min, a light blue solution of nitrous acid is produced. The mixture is stirred for extra 1 h at 25°C. The reaction mixture was poured into cold water and the solid product was filtered off, washed with water, and dried. Recrystallization from EtOH afforded4a–f which were used without any further purification in the next step.


### 2.1.4. The Reaction of Nitrous Acid withβ-Keto Sulfones3a–e

To a stirred cold solution ofβ-keto sulfones3a–e (10 mmol) or oximes4a–e (10 mmol) in glacial acetic acid (30 mL), sulfuric acid (5 mL, 50%) was added. Then cold solution of sodium nitrite (2.1 g, 30 mmol) in water (10 mL) was added dropwise with stirring at such a rate that the temperature remains in the range 0–5°C. Over a period of 30 min, a light blue solution of nitrous acid is produced. The mixture is stirred for extra 48 h at 25°C. The solid that precipitated was collected, washed with water, and dried. Recrystallization from EtOH afforded the corresponding carboxylic acids12a–e in 55–72% yield. Formic acid (14) and benzene/4-toluenesulfinic acid15 were detected in filtrate using chromatographic analyses. 4-Chlorobenzoic acid (12a) was isolated in 65% yield by the reaction of 1-(4-chlorophenyl)-2-[(4-methylphenyl)sulfonyl]ethanone (3f) instead of3a.(1) 4-Chlorobenzoic Acid (
12a
). This acid was prepared from 1-(4-chlorophenyl)-2-(phenylsulfonyl)ethanone (3a) [10] in 65% yield (1.02 g). 1-(4-Chlorophenyl)-2-[(4-methylphenyl)sulfonyl]ethanone (3f) [11] afforded 1.13 g (72% yield) of 4-chlorobenzoic acid (12a); m.p. 238–240°C (Let. m.p. 238–241°C) [16]; 1H NMR δ 7.57 (d,J = 8.5 Hz, 2H, ArHs), 7.95 (d,J = 8.5 Hz, 2H, ArHs), 13.20 (s, D2O exchangeable, 1H, OH); 13C NMR δ 128.69 (C3 and C5), 129.72 (C1), 131.10 (C2 and C6), 137.70 (C4), 166.45 (C=O); MS (EI)m/z 156 [M+], 157 [M++1], 158 [M++2].(2) [1,1
′
-Biphenyl]-4-carboxylic Acid (
12b
). This acid was prepared from 1-(1,1′-biphenyl-4-yl)-2-(phenylsulfonyl)ethanone (3b) [12] in 62% yield (1.23 g); m.p. 225–227°C (Let. m.p. 220–225°C) [17]; 1H NMR δ 7.43 (t,J = 7.5 Hz, 1H, ArH), 7.51 (t,J = 7.5 Hz, 2H, ArHs), 7.75 (d,J = 7.5 Hz, 2H, ArHs), 7.79 (d,J = 8.5 Hz, 2H, ArHs), 8.03 (d,J = 8.5 Hz, 2H, ArHs), 13.00 (s, D2O exchangeable, 1H, OH); 13C NMR δ 126.70 (C3 and C5), 126.91 (C2 and C6), 128.20 (C4 and C4′), 129.04 (C3′ and C5′), 129.90 (C2′ and C6′), 139.07 (C1′), 144.0 (C1), 167.26 (C=O); MS (EI)m/z 198 [M+].(3) 2-Naphthoic Acid (
12c
). This acid was prepared from 2-[(4-methylphenyl)sulfonyl]-1-(2-naphthalenyl)ethanone (3c) [13] in 55% yield (0.95 g); m.p. 186–188°C (Let. m.p. 185–187°C) [18]; 1H NMR δ 7.60–7.68 (m, 2H, ArHs), 7.98–8.03 (m, 3H, ArHs), 8.21 (d,J = 8.0 Hz, 1H, ArH), 8.62 (s, 1H, ArH), 13.11 (s, D2O exchangeable, 1H, OH); 13C NMR δ 125.25 (C3), 126.69 (C2), 127.60 (C7), 128.01 (C5), 128.14 (C4), 128.63 (C6), 129.20 (C8), 130.34 (C1), 132.14 (C8a), 134.80 (C4a), 167.56 (C=O); MS (EI)m/z 172 [M+].(4) 2-Thiophenecarboxylic Acid (
12d
). This acid was prepared from 2-[(4-methylphenyl)sulfonyl]-1-(2-thienyl)ethanone (3d) [14] in 58% yield (0.74 g); m.p. 124–126°C (Let. m.p. 125–127°C) [19]; 1H NMR δ 7.19 (dd,J = 3.5, 4.8 Hz, 1H, H4), 7.727 (dd,J = 0.7, 3.5 Hz, 1H, H5), 7.91 (dd,J = 0.7, 4.8 Hz, 1H, H3), 13.23 (s, D2O exchangeable, 1H, OH); 13C NMR δ 135.20 (C2), 133.79 (C3), 128.82 (C4), 133.81 (C5), 163.51 (C=O); MS (EI)m/z 128 [M+].(5) 2-Benzofurancarboxylic Acid (
12e
). This acid was synthesized from 1-(2-benzofuranyl)-2-(phenylsulfonyl)ethanone (3e) [15] in 52% yield (0.84 g); m.p. 193–195°C (Let. m.p. 193–196°C) [20]; 1H NMR δ 7.38 (t,J = 7.5 Hz, 1H, H5), 7.53 (t,J = 7.5 Hz, 1H, H4), 7.71–7.77 (m, 2H, H3+H4), 7.83 (d,J = 7.5 Hz, 1H, H6), 13.80 (s, D2O exchangeable, 1H, OH); 13C NMR δ 114.35 (C8), 115.82 (C3), 123.00 (C4), 123.91 (C5), 127.04 (C6), 127.84 (C3a), 146.02 (C2), 154.95 (C8a), 160.02 (C=O); MS (EI)m/z 162 [M+].


## 2.1.1. General

Melting points were determined on a Gallenkamp melting point apparatus and are uncorrected. Infrared (IR) spectra were recorded as KBr disks using the Perkin Elmer FT-IR Spectrum BX apparatus. NMR spectra were scanned in DMSO-d6 on a Bruker NMR spectrometer operating at 500 MHz for 1H and 125 MHz for 13C. Chemical shifts are expressed in δ-values (ppm) relative to TMS as an internal standard. Coupling constants (J) are expressed in Hz. D2O was added to confirm the exchangeable protons. The mass spectra were performed using a Varian MAT CH-5 spectrometer (70 eV).


## 2.1.2. Synthesis of 1-Aryl-2-arylsulfonyl Ethanones3a–f

These compounds were prepared according to the reported method [10–15].


## 2.1.3. Synthesis of Oximes4a–f

To a stirred cold solution ofβ-keto sulfones3a–f [10–15] (10 mmol) in glacial acetic acid (20 mL), sulfuric acid (1 mL, 50%) was added. Then cold solution of sodium nitrite (0.7 g, 10 mmol) in water (5 mL) was added dropwise with stirring at such a rate that the temperature remains in the range 0–5°C. Over a period of 30 min, a light blue solution of nitrous acid is produced. The mixture is stirred for extra 1 h at 25°C. The reaction mixture was poured into cold water and the solid product was filtered off, washed with water, and dried. Recrystallization from EtOH afforded4a–f which were used without any further purification in the next step.


## 2.1.4. The Reaction of Nitrous Acid withβ-Keto Sulfones3a–e

To a stirred cold solution ofβ-keto sulfones3a–e (10 mmol) or oximes4a–e (10 mmol) in glacial acetic acid (30 mL), sulfuric acid (5 mL, 50%) was added. Then cold solution of sodium nitrite (2.1 g, 30 mmol) in water (10 mL) was added dropwise with stirring at such a rate that the temperature remains in the range 0–5°C. Over a period of 30 min, a light blue solution of nitrous acid is produced. The mixture is stirred for extra 48 h at 25°C. The solid that precipitated was collected, washed with water, and dried. Recrystallization from EtOH afforded the corresponding carboxylic acids12a–e in 55–72% yield. Formic acid (14) and benzene/4-toluenesulfinic acid15 were detected in filtrate using chromatographic analyses. 4-Chlorobenzoic acid (12a) was isolated in 65% yield by the reaction of 1-(4-chlorophenyl)-2-[(4-methylphenyl)sulfonyl]ethanone (3f) instead of3a.(1) 4-Chlorobenzoic Acid (
12a
). This acid was prepared from 1-(4-chlorophenyl)-2-(phenylsulfonyl)ethanone (3a) [10] in 65% yield (1.02 g). 1-(4-Chlorophenyl)-2-[(4-methylphenyl)sulfonyl]ethanone (3f) [11] afforded 1.13 g (72% yield) of 4-chlorobenzoic acid (12a); m.p. 238–240°C (Let. m.p. 238–241°C) [16]; 1H NMR δ 7.57 (d,J = 8.5 Hz, 2H, ArHs), 7.95 (d,J = 8.5 Hz, 2H, ArHs), 13.20 (s, D2O exchangeable, 1H, OH); 13C NMR δ 128.69 (C3 and C5), 129.72 (C1), 131.10 (C2 and C6), 137.70 (C4), 166.45 (C=O); MS (EI)m/z 156 [M+], 157 [M++1], 158 [M++2].(2) [1,1
′
-Biphenyl]-4-carboxylic Acid (
12b
). This acid was prepared from 1-(1,1′-biphenyl-4-yl)-2-(phenylsulfonyl)ethanone (3b) [12] in 62% yield (1.23 g); m.p. 225–227°C (Let. m.p. 220–225°C) [17]; 1H NMR δ 7.43 (t,J = 7.5 Hz, 1H, ArH), 7.51 (t,J = 7.5 Hz, 2H, ArHs), 7.75 (d,J = 7.5 Hz, 2H, ArHs), 7.79 (d,J = 8.5 Hz, 2H, ArHs), 8.03 (d,J = 8.5 Hz, 2H, ArHs), 13.00 (s, D2O exchangeable, 1H, OH); 13C NMR δ 126.70 (C3 and C5), 126.91 (C2 and C6), 128.20 (C4 and C4′), 129.04 (C3′ and C5′), 129.90 (C2′ and C6′), 139.07 (C1′), 144.0 (C1), 167.26 (C=O); MS (EI)m/z 198 [M+].(3) 2-Naphthoic Acid (
12c
). This acid was prepared from 2-[(4-methylphenyl)sulfonyl]-1-(2-naphthalenyl)ethanone (3c) [13] in 55% yield (0.95 g); m.p. 186–188°C (Let. m.p. 185–187°C) [18]; 1H NMR δ 7.60–7.68 (m, 2H, ArHs), 7.98–8.03 (m, 3H, ArHs), 8.21 (d,J = 8.0 Hz, 1H, ArH), 8.62 (s, 1H, ArH), 13.11 (s, D2O exchangeable, 1H, OH); 13C NMR δ 125.25 (C3), 126.69 (C2), 127.60 (C7), 128.01 (C5), 128.14 (C4), 128.63 (C6), 129.20 (C8), 130.34 (C1), 132.14 (C8a), 134.80 (C4a), 167.56 (C=O); MS (EI)m/z 172 [M+].(4) 2-Thiophenecarboxylic Acid (
12d
). This acid was prepared from 2-[(4-methylphenyl)sulfonyl]-1-(2-thienyl)ethanone (3d) [14] in 58% yield (0.74 g); m.p. 124–126°C (Let. m.p. 125–127°C) [19]; 1H NMR δ 7.19 (dd,J = 3.5, 4.8 Hz, 1H, H4), 7.727 (dd,J = 0.7, 3.5 Hz, 1H, H5), 7.91 (dd,J = 0.7, 4.8 Hz, 1H, H3), 13.23 (s, D2O exchangeable, 1H, OH); 13C NMR δ 135.20 (C2), 133.79 (C3), 128.82 (C4), 133.81 (C5), 163.51 (C=O); MS (EI)m/z 128 [M+].(5) 2-Benzofurancarboxylic Acid (
12e
). This acid was synthesized from 1-(2-benzofuranyl)-2-(phenylsulfonyl)ethanone (3e) [15] in 52% yield (0.84 g); m.p. 193–195°C (Let. m.p. 193–196°C) [20]; 1H NMR δ 7.38 (t,J = 7.5 Hz, 1H, H5), 7.53 (t,J = 7.5 Hz, 1H, H4), 7.71–7.77 (m, 2H, H3+H4), 7.83 (d,J = 7.5 Hz, 1H, H6), 13.80 (s, D2O exchangeable, 1H, OH); 13C NMR δ 114.35 (C8), 115.82 (C3), 123.00 (C4), 123.91 (C5), 127.04 (C6), 127.84 (C3a), 146.02 (C2), 154.95 (C8a), 160.02 (C=O); MS (EI)m/z 162 [M+].


## 3. Results and Discussion

β-Keto sulfones3a–e were synthesized by the reaction of 2-bromo-1-arylethanone1a–e with the appropriate sodium arylsulfinate2a,b according to the reported method [10–15]. Treatment of β-keto sulfones3a–e with sodium nitrite, in acetic acid containing sulfuric acid, afforded the corresponding carboxylic acids12a–e in addition to formic acid (14) and benzene/4-toluenesulfinic acid15a,b (Figure 1).Figure 1
The reaction of nitrous acid withβ-keto sulfones3a–e.Interestingly, it was found that this method provides the possibility to prepare carboxylic acids through the formation of oximes4a–e as intermediates followed by the oxidative cleavage process of C–C bond by nitrous acid under the application of mild reaction conditions. In general, normal ketones are not oxidized except under extremely hard conditions and give several products [21].4-Chlorobenzoic acid (12a), [1,1′-biphenyl]-4-carboxylic acid (12b), 2-naphthoic acid (12c), 2-thiophenecarboxylic acid (12d), and 2-benzofurancarboxylic acid (12e) were isolated in 72%, 62%, 55%, 58%, and 62% yields, respectively, by the reaction of β-keto sulfones3a–e with excess nitrous acid at 0–5°C. 4-Chlorobenzoic acid (12a) was isolated in 65% yield by the reaction of 1-(4-chlorophenyl)-2-[(4-methylphenyl)sulfonyl]ethanone (3f) instead of3a. The structures of carboxylic acids12a–e are assigned on the basis of their spectral data and physical constants which are identical with those described for authentic samples of12a–e obtained commercially [16–20]. For example, 1H NMR of acids12a–e revealed the D2O exchangeable signal of carboxylic OH in the region δ 13.0–13.8 whereas their 13C NMR showed the signal due to the carbon of carbonyl function in the region δ 160.2–167.56. 1H NMR of12a showed the AB system ofPara substituted benzene ring at δ 7.57 and 7.95 as two doublets withJ = 8.5 Hz, whereas the 1H NMR of15d revealed three doublets of doublets (dd) signals at δ 7.19 (J = 3.5, 4.8 Hz), 7.727 (J = 0.7, 3.5 Hz), and 7.91 (J = 0.7, 4.8 Hz) for H4, H5, and H3 of thiophene moiety, respectively.Mechanistic explanation has been reported for the reaction of nitrous acid and nitrosonium ion NO+ with oximes by Kliegman and Barnes [6]. They proposed two mechanistic pathways using 15N nitrous acid to determine the reaction products. The intermediate product of the reaction of nitrous acid with oxime4 is the iminoxyl cation5 which can react in one of these two pathways A or B (Figure 2).Figure 2
The reported mechanistic pathwaysA and B [6] for the reaction of nitrous acid with oximes suggested the formation of sulfonyl-diketone7 during the reaction of nitrous acid with oxime4. The proposed mechanistic pathway of the reaction of nitrous acid with β-keto sulfones3 through intermediate 1,2-oxazete10, pathwayC.The nitrosating agent nitrous acid is formedin situ by the action of acetic or mineral acid on sodium nitrite and a further reaction takes place to give the nitrosonium ion NO+ (Figure 2). The reported mechanistic pathways through hydrolysis of iminoxyl cation5 to give hydroxy precursor6 (pathwayA) or through nitrosation of5 to give intermediate8 and then 1,2,3-oxadiazete9 (pathwayB) proposed the production of 1-aryl-2-(phenyl/tolylsulfonyl)ethane-1,2-dione7 instead of arenecarboxylic acids12 (Figure 2).These results stimulate our interest to offer a mechanistic pathway (pathwayC) to explain the formation of acids12 as main reaction products through oxidative cleavage of β-keto sulfone oximes4, keeping in mind the formation of formic acid (14) and benzene/4-toluenesulfinic acid15 (Figure 2). In this pathway, hydroxy precursor6 cyclized to give the intermediate 1,2-oxazete10 which lost benzene/4-toluenesulfinic acid15 to produce 1,2-oxazet-3-one11. Ring cleavage of the latter intermediate afforded the arenecarboxylic acids12 and di-anion13 [6] which reacted with water to give formic acid (14).


## 4. Conclusion

In conclusion, we studied the reaction of nitrous acid withβ-keto sulfones3a–e, and we also proposed a mechanistic pathway to explain the formation of unexpected carboxylic acids12a–e through the oxidative cleavage reaction.



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