N-Acyl-N-(4-chlorophenyl)-4-nitrobenzenesulfonamides: Highly selective and efficient reagents for acylation of amines in water

Z. Naturforsch. 2015; aop

Sara Ebrahimi, Safoura Saiadi, Simin Dakhilpour, Seyed Nezamoddin Mirsattari

and Ahmad Reza Massah*

N-Acyl-N-(4-chlorophenyl)-4-nitrobenzene-

sulfonamides: highly selective and efficient

reagents for acylation of amines in water

DOI 10.1515/znb-2015-0076

of other functional groups that can be acylated by carbox-

Received April 21, 2015; accepted June 17, 2015

ylic acid anhydrides or chlorides has great practical utility

[4–6]. A variety of reagents has been developed by devis-

ing a leaving group for the above purpose [7]. Acetylation

of amines using a N-methoxydiacetamide [8], N-formylation

using N-formylbenzotriazole [9], trifluoroacetylations with

ethyl trifluoroacetate [10, 11], using N-acetyl-N-acyl-3-amino-

quinazolinones for acetylating of primary amines [12], and

application of (trifluoroacetyl)benzotriazole as trifluoroa-

cetylation reagent [13] are some of the reagents and methods

for chemoselective acylation of amines. Murakami and

coworkers have synthesized N-acyl-N-(pentafluorophenyl)

methanesulfonamides and have used them as chemose-

lective N-acylation reagents [14]. They have shown that

a reagent bearing a bulky leaving group can exhibit suffi-

Abstract:

A variety of N-acyl-N-(4-chlorophenyl)-4-ni-

trobenzenesulfonamides (1a–e) were synthesized in one

pot from 4-chloroaniline under solvent-free conditions and

have been developed as chemoselective N-acylation rea-

gents. Selective protection of primary amines in the pres-

ence of secondary amines, acylation of aliphatic amines in

the presence of aryl amines, and monofunctionalization of

primary-secondary diamines as well as selective N-acyla-

tion of amino alcohols using these reagents are described.

All of the acylation reactions were carried out in water as a

green solvent. High stability and easy preparation of these

acylating reagents are other advantages of this method.

Keywords: green chemistry; N-acyl-N-arylsulfonamide; ciently good chemoselectivity. The low stability of acylating

selective acylation; water.

agents, limited application, and the use of organic solvent

are some of the disadvantages of these methods.

The design of chemical transformations with low

environmental impact is recognized by both industry

and academic research as increasingly important. In this

1 Introduction

Acylation of amines is of enormous interest in organic syn- context, the development of reactions occurring in non-

thesis because it provides a useful and efficient protection toxic solvents is highly desirable [15, 16]. The application

protocol in a multistep synthesis process [1]. Many of chemi- of water as an inexpensive, readily available, and envi-

cal reactions involved in the synthesis of drugs frequently ronmentally benign alternative to organic solvents has

use acylation reactions. Acylation of amines are usually developed into a highly active field of research addressing

done by carboxylic acid anhydrides or chlorides in the pres- current requirements in synthetic chemistry [17–19].

ence of an acid or base catalyst in a suitable organic solvent

In continuation of our research on the acylation reac-

[2, 3]. Selective acylation of amino groups in the presence tions [20–23], we wish to report here the synthesis of a

series of new acylating reagents, which are useful for the

chemoselective acylation of amino groups of compounds

*Corresponding author: Ahmad Reza Massah, Department of

that possess both amino and other groups in water.

Chemistry, Shahreza Branch, Islamic Azad University, Shahreza,

Isfahan 86145-311, Iran; and Razi Chemistry Research Center, Shahreza

Branch, Islamic Azad University, Shahreza, Isfahan 86145-311, Iran,

e-mail: massah@iaush.ac.ir; m assahar@yahoo.com

2 Results and discussion

Sara Ebrahimi, Safoura Sai adi and Simin Dakhilpour: Department

of Chemistry, Shahreza Branch, Islamic Azad University, Shahreza,

Isfahan 86145-311, Iran

2.1 Synthesis of acylating reagents

Seyed Nezamoddin Mirsattari: Department of Chemistry, Shahreza

Branch, Islamic Azad University, Shahreza, Isfahan 86145-311, Iran;

At first, we decided to search for a versatile synthon to

which various acyl groups could be introduced. We chose

and Razi Chemistry Research Center, Shahreza Branch, Islamic Azad

University, Shahreza, Isfahan 86145-311, Iran

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ꢀS. Ebrahimi et al.: New selective and efficient acylating reagents

O

NH₂

1)

O₂N

S

Cl, NaHCO₃

O

S

O

Cl

N

NO₂

O

2) (RCO)₂O, K₂CO₃

R

O

Cl

R = CH₃(1a), n-C₃H₇(1b), n-C₄H₉(1c), n-C₅H₁₁(1d), Ph (1e)

Scheme 1:ꢀSynthesis of N-acyl-N-(4-chlorophenyl)-4-nitrobenzenesulfonamides (1a–e).

to focus on the use of N-(4-chlorophenyl)-4-nitrobenzene- N-benzoyl-N-(4-chlorophenyl)-4-nitrobenzenesulfon-

sulfonamide as a precursor of various N-acylation reagents. amide in 50 % yield after 10 h under solvent-free condi-

This sulfonamide is expected to behave as a bulky leaving tions (Table 1, entry 5, compound 1e). To overcome this

group containing a strongly electron-withdrawing substitu- problem, the reaction was done in acetone as solvent. The

ent on the benzene rings including nitro and chloro groups. procedure consists of the addition of benzoic anhydride

This sulfonamide was synthesized from 4-chloroaniline and to a mixture of N-(4-chlorophenyl)-4-nitrobenzenesulfon-

4-nitrobenzenesulfonyl chloride in the presence of anhy- amide and K₂CO₃in acetone. By this method, the product

drous NaHCO₃under solvent-free conditions in high yield was obtained in 85 % yield after 4 h in high purity (Table 1,

and purity (Scheme 1) [24]. Then, N-(4-chlorophenyl)-4-ni- entry 6, compound 1e). Also, it should be mentioned that

tro-benzenesulfonamide was reacted with a carboxylic acid these reactions were scalable and all of the N-acyl-N-(4-

anhydride in the presence of anhydrous K₂CO₃under solvent- chlorophenyl)-4-nitrobenzenesulfonamides 1a–e were

free conditions. The reactions were completed very fast and synthesis on 20-mmol scales as well as 2-mmol scales.

the corresponding N-acyl-N-(4-chlorophenyl)-4-nitrobenze-

nesulfonamides1a–ewereobtainedinhighyieldsandpurity.

Also, these N-acyl-N-arylsulfonamides could be prepared in 2.2 Acylation of aromatic and aliphatic

one pot directly from 4-chloroaniline without the need to

isolate N-(4-chlorophenyl)-4-nitro-benzenesulfonamide.

amines

Several structurally varied carboxylic acid anhy- First, to find the best conditions for the acylation of differ-

drides underwent clean and remarkably fast N-acyla- ent amines using these novel acylating reagents, a number

tion reaction (Table 1). The aliphatic anhydride with a of reactions were performed. In our initial study, the

long chain, like hexanoic anhydride (Table 1, entry 4, acylation of p-anisidine with N-acetyl-N-(4-chlorophenyl)-

compound 1d), could be used as effectively as one with 4-nitrobenzenesulfonamide (1a) as a model reaction was

a short chain. Comparison between the aliphatic and carried out in different solvents including water, acetoni-

benzoic anhydride show that aliphatic anhydrides are trile, n-hexane, and also under solvent-free conditions at

more reactive than benzoic anhydride. It was found that different temperatures (Table 2).

the reaction between N-(4-chlorophenyl)-4-nitroben-

It was found that the reaction at room temperature

zenesulfonamide, and benzoic anhydride produces leads to the corresponding product in low yields. So the

reactions were performed at higher temperature (60–

80 °C). The best result was achieved when the reaction

Table 1:ꢀSynthesis of N-acyl-N-(4-chlorophenyl)-4-nitrobenzenesul-

was performed in H₂O and acetonitrile at 80 °C. Based

fonamides 1a–e (Scheme 1).^a

on this, water was selected as the best solvent for further

study because the reaction was completed faster and

the product was obtained in higher yield. Also, water is

a green solvent in comparison with organic solvents. It

should be mentioned that the reaction did not proceed

under solvent-free conditions even after vigorous stirring

for 6 h. The effect of base on the reaction was also studied

in the acylation of p-anisidine in the presence of K₂CO₃,

NaHCO₃, KOH, and also in the absence of base in water at

80 °C. The reaction did not proceed in the absence of base

after 6 h. In the presence of K₂CO₃, NaHCO₃, and KOH, the

Entryꢁ

R

ꢁ

Compoundꢁ

number

Time,ꢁ

min

Yield^b,ꢁ

%

M.p., °C

1

2

3

4

5

6^c

ꢂ

CH₃

C₃H₇

C₄H₉

C₅H₁₁

Ph

ꢂ

1a

1b

1c

1d

1e

ꢂ

95ꢂ

100ꢂ

600ꢂ

240ꢂ

95ꢂ

90ꢂ

50ꢂ

85ꢂ

180–184

183–185

152–154

114–116

134–136

Ph

^aReaction conditions: room temperature, K₂CO₃, solvent-free

conditions. ^bIsolated yields. ^cThe reaction was run in acetone.

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S. Ebrahimi et al.: New selective and efficient acylating reagentsꢃ ꢃ3

Table 2:ꢀAcetylation of p-anisidine with (1a) under different

may be the reason for the lower yield of the obtained

amide. On the basis of these results, K₂CO₃was selected as

a green base for further study.

conditions.^a

Entryꢁ Solvent, mL

ꢁ

Temperature, °C ꢁ Time, min ꢁ Yield, %

To demonstrate the generality and scope of this

method, the acylation of different aliphatic and aromatic

amines was studied using these new acylating reagents in

water. It was observed that both aliphatic and aromatic

amines gave the corresponding amides in good to excel-

lent yield (Tables 3 and 4, compounds 2a–p and 3a–q).

As the results show, in the acylation of aromatic amines,

electronic and steric factors play a significant role in the

reaction. Aromatic amines with electron-donating groups

such as Me and MeO were acylated in a shorter reaction

time, in comparison with aromatic amines containing

electron-withdrawing groups such as Cl (e.g. Table 3,

entries 2 and 4, compounds 2b and 2d). Aromatic amines

with strongly electron-withdrawing group such as NO₂did

not react at all. Also, increasing the steric hindrance at

the ortho position of amino group leads to a substantial

1

ꢂ

–

ꢂ

25

40

60

25

40

60

80

25

80

60

ꢂ

240

360

150

40

ꢂ

0

10

15

0

10

15

75

88

93

20

10

80

20

2

–

3

–

4

Water (5)

Water (2)

Water (1)

5

6

7

8

40

8

40

8

Acetonitrile (5)ꢂ

n-Hexane (5)

Acetonitrile (5)ꢂ

n-Hexane (5)

180

150

9

ꢂ

10

11

ꢂ

^aN-Acetyl-N-(4-chlorophenyl)-4-nitro-benzenesulfonamide (1a)

(0.5 mmol), p-anisidine (1.5 mmol), and K₂CO₃(2 mmol).

corresponding amide was obtained in 95, 80, and 50 % decrease in yield (Table 3, entries 5, 6, and 7, compounds

yield, respectively, after 40 min. When KOH was used as 2e, 2f, and 2g). It is significant to note that the reaction of

base, the acylating reagent hydrolyzed more easily, which secondary amines with acylating reagent did not proceed

Table 3:ꢀAcylation of aromatic amines with different acylating reagents (1a–e) in water^a.

Cl

O

HN

S

NO₂

O

C

O

S

O

H₂O (1–2 mL)

H

Ar NH₂

Ar

N

R

NO₂

R

80 °C

40–480 min

O

Cl

2a–p

R = CH₃(1a), n-C₃H₇(1b), n-C₄H₉(1c), n-C₅H₁₁(1d), Ph (1e)

Entryꢁ

Amines

ꢁ

Product

ꢁ

Compound

number

ꢁ

M.p. (reported [ref.])

ꢁ Time,

min

ꢁ Yield^b,

%

1

ꢂ

Aniline

ꢂ

N-Phenylacetamide

ꢂ

2a

2b

2c

2d

2e

2f

2g

2h

2i

2j

2k

2l

2m

2n

2o

2p

ꢂ

110–112 (114 [25])

ꢂ

180

40

ꢂ

87

95

91

85

55

62

20

10

92

88

85

90

87

80

85

2

4-Methoxyanilineꢂ

N-(4-Methoxyphenyl)acetamide

N-(4-Methylphenyl)acetamide

N-(4-Chlorophenyl)acetamide

N-(2-Methoxyphenyl)acetamide

N-(2-Methylphenyl)acetamide

N-(2-Chlorophenyl)acetamide

N-Ethyl-N-phenylacetamide

N-(4-Methoxyphenyl)butyramide

ꢂ

131–133 (145–147 [4])

3

p-Toluidine

ꢂ

ꢂ 152–154 (149–151 [25])

100

340

280

360

420

480

60

4

4-Chloroaniline

ꢂ

176–178 (178 [4])

88–90 (86–87 [4])

105–108 (109 [25])

89–90 (88–90 [25])

51–53 (50 [26])

82–86 (78–80 [27])

83–86 (83–85 [28])

84–86 (84–86 [29])

152–154 (157 [29])

74–75 (74–76 [30])

68–72 (71–72 [30])

72–74 (74–75 [30])

5

2-Methoxyanilineꢂ

6

o-Toluidine

ꢂ

7

2-Chloroaniline

N-Ethylaniline

8

9

4-Methoxyanilineꢂ

p-Toluidine

10

11

12

13

14

15

16

N-(4-Methoxyphenyl)pentanamideꢂ

N-(4-Methoxyphenyl)hexanamide ꢂ

N-(4-Methoxyphenyl)benzamide

N-(4-Methylphenyl)butyramide

N-(4-Methylphenyl)pentanamide

N-(4-Methylphenyl)hexanamide

N-(4-Methylphenyl)benzamide

60

70

ꢂ

85

ꢂ

110

140

155

ꢂ 154–157 (158–159 [30])

^aReaction conditions: aromatic amine (1.5 mmol), acylating reagent (1a–e) (0.5 mmol), K₂CO₃(2 mmol), H₂O (1–2 mL), 80 °C. ^bIsolated yields.

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4ꢀ ꢀS. Ebrahimi et al.: New selective and efficient acylating reagents

Table 4:ꢀAcylation of aliphatic amines with different acylating reagents (1a–e) in water.^a

Entryꢁ

Amines

ꢁ

Product

ꢁ

Compoundꢁ

Number

M.p. (reported [ref.])

ꢁ Time,

min

ꢁ Yield,^b

%

1

ꢂ

Cyclohexanamine

Hexylamine

ꢂ

N-Cyclohexylacetamide

N-Hexylacetamide

ꢂ

3a

3b

3c

3d

3e

3f

3g

3h

3i

3j

3k

3l

3m

3n

3o

3p

3q

ꢂ

104–106 (101–103 [4])

Oil (106, 20 Torr [31])

56–58 (59–61 [4])

ꢂ

15

12

10

5

10

5

10

6

7

15

5

7

5

ꢂ

80

81

85

89

83

89

84

86

89

86

82

90

95

81

95

92

88

2

3

Benzylamine

N-Benzylacetamide

4

2-Phenylethanamineꢂ

Cyclohexanamine

Benzylamine

Cyclohexanamine

Hexylamine

Benzylamine

Cyclohexanamine

Hexylamine

Benzylamine

2-Phenylethanamineꢂ

Cyclohexanamine

Hexylamine

Benzylamine

2-Phenylethanamineꢂ

N-Phenethylacetamide

N-Cyclohexylbutyramide

N-Benzylbutyramide

N-Cyclohexylpentanamide

N-Hexylpentanamide

N-Benzylpentanamide

N-Cyclohexylhexanamide

N-Hexylhexanamide

N-Benzylhexanamide

N-(2-Phenylethyl)hexanamide ꢂ

N-Cyclohexylbenzamide

N-Hexylbenzamide

N-Benzylbenzamide

N-(2-Phenylethyl)benzamide

152–155 (158–160 [4])

66–68 (66–67 [32])

5

ꢂ

6

42–44 (41–44 [33])

7

54–56 (68 [32])

8

Oil (164–166, 13 Torr [34])

50–52 (49–52 [35])

9

10

11

12

13

14

15

16

17

72–74 (72–73 [34])

Oil (168–170, 13 Torr [34])

56–58 (54–55 [36])

40–42 (38–41 [34])

147–149 (149.5 [32])

40–42 (46–47 [37])

ꢂ

35

7

15

30

106–108 (106–108 [35])

115–117 (119–120 [38])

^aReaction conditions: aliphatic amines (0.75 mmol), acylating reagent (1a–e) (0.5 mmol), K₂CO₃(1 mmol), H₂O (1 mL), 80 °C. ^bIsolated yields.

considerably under similar conditions even after 480 min, 5a–g), several aliphatic and aromatic amino alcohols and

which may be due to unfavorable steric and electronic diamines were acylated with different acylating reagents

effects on nitrogen (Table 3, entry 8, compound 2h). Also, in water, and the corresponding amides were obtained in

the results showed that increased steric hindrance on high to excellent yield (74–98 %). The N-acylation of amino

the acylating reagents leads to increased reaction time phenols was achieved in moderate to good yield, whereas

and decreased yield of product (Table 3, entries 9–16, hydroxyl groups remained unaffected under the reaction

compounds 2i–p).

conditions (Table 5, entries 1–6, compounds 4a–f). Also,

Then, the change of the substrate from aryl amines to the results show that the amino alcohols were acylated

alkyl amines was studied. As it was shown in Table 4 (com- faster than amino phenols and the corresponding amides

pounds 3a–q), all of the used primary aliphatic amines were obtained in higher yield. Selective monoacyla-

were reacted with different acylating reagents in short tion of aromatic diamines in water using these acylating

reaction time (3–35 min), and the corresponding amides reagents was also studied. The reaction of 1,4-benzen-

were obtained in high to excellent yield (80–95 %).

ediamine with N-acetyl-N-(4-chlorophenyl)-4-nitroben-

zene-sulfonamide lead to N-(4-aminophenyl)acetamide

in 86 % yield (Table 5, entry 7, compound 5a), and there

was no diacylated product in the reaction mixture. Then,

acylation of N-phenyl-ethylenediamine as an aliphatic-

aromatic diamine was studied. The acylation reaction

2.3 Chemoselective acylation of amino

alcohols and diamines

During the course of this study, we have shown the che- occurred selectively on the aliphatic amino group, and

moselectivity of this method for the acylation of amino N-(2-(phenylamino)ethyl)-amides were obtained in 87–90

alcohols and diamines using these acylating reagents in % yield (Table 5, entries 8 and 9, compounds 5b and c).

water. As it is shown in Table 5 (compounds 4a–f and Finally, aliphatic diamines were acylated with this

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ꢃ5

S. Ebrahimi et al.: New selective and efficient acylating reagentsꢃ

Table 5:ꢀAcylation of diamines and amino alcohols or amino phenols with different acylating reagents (1a–e) in water.^b

Cl

O

S

O

N S

O

R

H₂N

n XH

HX

NH

K₂CO₃

n

R

Cl

NH

NO₂

O

H₂O, 80 °C

O

Ar XH

HX Ar NH

X = N, NH, O

4a–f

5a–h

R = CH₃(1a), n-C₃H₇(1b), n-C₄H₉(1c), n-C₅H₁₁(1d), Ph (1e)

Entryꢁ Diamine or amino alcohol ꢁ Product

ꢁ Compound numberꢁ

M.p. (reported [ref.])ꢁ Time, minꢁ Yield,^a%

NH₂

H

N

1

2

3

ꢂ

ꢂ 4a

ꢂ 4b

ꢂ 4c

ꢂ

62–64 (56–58 [39])ꢂ

57–59 (56–58 [39])ꢂ

58–60 (60–63 [39])ꢂ

25ꢂ

20ꢂ

97

98

92

HO

Ph

HO

O

HO

NH₂

HO

N

H

Ph

OH

H

N

NH₂

Ph

O

NH₂

OH

4

5

6

ꢂ

ꢂ 4d

ꢂ 4e

ꢂ 4f

ꢂ

208–210 (207–209 [4])ꢂ

84–86 (81 [40])ꢂ

30ꢂ

120ꢂ

180ꢂ

86

65

H

N

OH

CH₃

H

N

CH₂CH₂CH₃

76–78 (74 [40])ꢂ

H

N

CH₂CH₂CH₂CH₂CH₃

O

H

7

ꢂ

ꢂ 5a

ꢂ 5b

ꢂ 155–157 (164–165 [41])ꢂ

ꢂ 124–126 (123–124 [42])ꢂ

120ꢂ

40ꢂ

86

H₂N

NH₂

H₂N

N

C

CH₃

HN CH₂CH₂

O

NH₂

8^c

90

HN CH₂CH₂NH

C

Ph

HN CH₂CH₂

O

C

NH₂

9^c

ꢂ

ꢂ 5c

ꢂ

109–112ꢂ

10ꢂ

87

HN CH₂CH₂NH

(CH

₂)₃CH₃

O

10 ꢂ H₂N–(CH₂)₄–NH₂

ꢂ

ꢂ 5d

ꢂ 5e

ꢂ 5f

ꢂ 172–174 (175–176 [43])ꢂ

ꢂ 158–162 (164–165 [44])ꢂ

ꢂ 258–260 (256–257 [45])ꢂ

15ꢂ

10ꢂ

30ꢂ

74

75

78

H

Ph

N

Ph

H

O

11 ꢂ H₂N–(CH₂)₆–NH₂

H

N

Ph

N

H

O

NH₂

O

C

12

13

ꢂ

H

N

Ph

NH₂

N

H

C

O

H

O

ꢂ

ꢂ 5g

ꢂ 140–142 (135–136 [46])ꢂ

15ꢂ

77

H

N

H₂N

NH₂

Ph

N

H

Ph

H

^aIsolated yields after purification. ^bReaction conditions: diamines or amino alcohols (0.5 mmol), acylating reagent (1a–e) (0.5 mmol), K₂CO₃

(1 mmol for diamines and 3 mmol for amino alcohols or amino phenols), H₂O (1–2 mL), 80 °C. ^cReaction conditions: diamines (0.75 mmol),

acylating reagent (1a–e) (0.5 mmol), K₂CO₃(1 mmol), H₂O (1–2 mL), 80 °C.

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6ꢀ ꢀS. Ebrahimi et al.: New selective and efficient acylating reagents

method. As it is shown in Table 5, primary diamines such amines with electron-withdrawing group is possible with

as 1,6-hexanediamine and 1,2-cyclohexanediamine were this method.

acylated completely, and the diamides were obtained

To investigate the reason for these chemoselectiv-

(Table 5, entries 11, 12, compounds 5e, 5f). Interestingly, ity, the structure of synthesized acylating reagents were

acylation of N¹-(2-aminoethyl)ethane-1,2-diamine contain- studied by density functional theory (DFT) calculations

ing both primary and secondary aliphatic amine with [47] using the program gaussian 98 [48]. The geom-

N-benzoyl-N-(4-chlorophenyl)-4-nitrobenzenesulfona- etries of the acylating reagents were optimized using

mide occurred only on the primary amino group, and the the DFT/B3LYP theory and a 6-31G (d,p) basis set. Vibra-

corresponding diamine was obtained in 77 % yield after tional frequency calculations were used to characterize

15 min (Table 5, entry 13, compound 5g).

all stationary points as minima (the number of imagi-

The results of selective acylation of diamines and nary frequencies [NIMAG] ꢀ=ꢀ 0). The calculated vibra-

amino alcohols encouraged us to consider the selectivity tional frequencies were found to be in good agreement

of acylation of different amines in the presence of phenols with the experimentally recorded values. Figure 1 shows

and alcohols. Several reactions were carried out, and sur- the optimized molecular structure of N-butyryl-N-(4-

prisingly, excellent selectivity was found (Scheme 2). For chlorophenyl)-4-nitrobenzenesulfonamide (1b) as an

example, aromatic amines such as aniline can be con- example, with its molecular structure belonging to

verted into amide in the presence of phenol or aliphatic point group symmetry C₁. The structural information

alcohol like 1-hexanol. Meanwhile, aliphatic amines were for this compound is listed in Table 6. As this structure

acylated selectively in the presence of aromatic amines. shows, the 4-chlorophenyl group is placed almost per-

Also, the selective acylation of aromatic amines with pendicular to the plane of carbonyl and provides high

electron-donating substituent in the presence of aromatic steric bulkiness around this group. These results are

supported by the experimental observations. Increasing

the steric hindrance around the carbonyl group leads to

O

an increase in acylation reaction time and a decrease

NH₂

HN

CH₃

of the product yield especially for poor and bulky

nucleophiles.

2

K CO

mmol

2

3

OH

4

H O,

80 °C

2

Acylating reagent: 1a

Only product

O

2.4 Stability and reusability of acylating

reagents

NH₂

OH

HN

CH₃

2

K CO

mmol

The special property of these new acylating reagents is

their enormous stability. These compound can be stored

in a bottle for a long time without any decomposition.

As mentioned earlier, these reagents were used for

2

3

H O,

80 °C

2

Acylating reagent: 1a

Only product

O

NH₂

HN CH₃

HN

CH₃

2

K CO

mmol

2

3

H O,

80 °C

2

OCH₃

20 %

Acylating reagent: 1a

80 %

O

NH₂

HN

CH₃

NH₂

2

K CO

mmol

2

3

H O,

80 °C

2

NO₂

Acylating reagent: 1a

OCH₃

Only product

OCH₃

Scheme 2:ꢀChemoselective acylation of amine and alcohol or

phenol in the presence of K₂CO₃in water at 80 °C.

Fig. 1:ꢀThe optimized structure of N-butyryl-N-(4-chlorophenyl)-

4-nitrobenzenesulfonamide (1b).

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S. Ebrahimi et al.: New selective and efficient acylating reagentsꢃ

ꢃ7

Table 6:ꢀBond lengths (Å), angles (deg), and dihedral angles (deg) of N-butyryl-N-(4-chlorophenyl)-4-nitrobenzenesulfonamide (1b) as

obtained by DFT calculations.

Bond lengths

N1–O2

Cl22–C19ꢂ

S10–O11 ꢂ

N13–C14 ꢂ

C14–O15 ꢂ

C31–C34 ꢂ

C31–H33 ꢂ

ꢁ

Angles

ꢁ

Dihedral angles

ꢂ

1.22ꢂ

1.75ꢂ

1.46ꢂ

1.40ꢂ

1.21ꢂ

1.53ꢂ

1.09ꢂ

O2–N1–O3

ꢂ

124.9ꢂ

121.5ꢂ

120.5ꢂ

123.1ꢂ

112.8ꢂ

113.7ꢂ

ꢂ

O11–S10–N13–C14ꢂ

–179.8

151.9

–177.0

O11–S10–O12ꢂ

N13–C14–O15ꢂ

O15–C14–C31ꢂ

C14–C31–C34 ꢂ

C31–C34–C37 ꢂ

ꢂ

O12–S10–C7–C8

ꢂ

C16–N13–C14–O15ꢂ

ꢂ

the acylation of amines in alkaline hot water. So, the 4.1 General procedure for the synthesis of

stability of these compounds was examined in water

N-acyl-N-(4-chlorophenyl)-4-nitroben-

at 80 °C in the presence of K₂CO₃. It is interesting that

zene sulfomamides (1a–d)

after 6 h, ꢀ<ꢀ10 % of hydrolysis products were separated.

Meanwhile, after acylation reaction, N-(4-chlorophenyl)- 4-Chloroaniline (2 mmol, 0.255 g) and anhydrous NaHCO₃

4-nitrobenzenesulfonamide can be separated from the (1 g) were ground together into a fine powder, and 4-nitro-

reaction mixture almost completely and reused for the benzenesulfonyl chloride (2 mmol, 0.442 g) was added

synthesis of the N-acyl-N-(4-chlorophenyl)-4-nitrobenze- under vigorous stirring at room temperature. The progress

nesulfonamides 1a–e.

of the reaction was followed by TLC until the conversion of

amine was completed. The product showed one spot on TLC

and was used in the second step without isolation. Carbox-

ylic acid anhydrides (10 mmol of acetic anhydride, 4 mmol

of butyric anhydride, 5 mmol of pentanoic anhydride and

hexanoic anhydride) and anhydrous K₂CO₃(1 g) were added,

and the mixture was stirred vigorously at room temperature.

The reaction was monitored by TLC. Upon completion of the

reaction, water was added and the mixture was stirred for a

few minutes. After filtration, washing with additional water

and drying, the corresponding N-acyl-N-(4-chlorophenyl)-

4-nitrobenzenesulfonamide (compounds 1a–d) was

obtained in 90–95 % yield with high purity and was used

for the acylation reaction without purification.

3 Conclusion

In conclusion, an efficient approach was introduced for

the synthesis of a series of new acylating reagents under

solvent-free conditions. The chemoselective acylation

of amino groups in diamines, amino alcohols, amino

phenols, and also in the mixture of amine and alcohol or

phenol in the presence of K₂CO₃as a green base in water

as an environmental friendly solvent was easily achieved

by these new acylating agents. These acylating reagents

are highly stable even in water at 80 °C. High yields of the

products, simple experimental procedures, and the use of

water as a green solvent are the other main advantages of 4.1.1 N-(4-Chlorophenyl)-4-nitrobenzenesulfonamide

this method.

M.p. 180–184 °C. – IR (film): ν ꢀ=ꢀ 3269 (N–H), 1527, 1348, 1333

(SO₂), 1306, 1160 (SO₂), 561 (C–N) cm⁻¹. – ¹H NMR (400 MHz,

CDCl₃): δ ꢀ=ꢀ 6.65 (s, 1 H, NH), 7.06 (d, J ꢀ=ꢀ 8.8 Hz, 2 H, Ar-H⁸),

4 Experimental section

7.26–7.32 (m, 2 H, Ar-H⁷), 7.95 (d, J ꢀ=ꢀ 8.8 Hz, 2 H, Ar-H⁶), 8.30

(d, J ꢀ=ꢀ 8.8 Hz, 2 H, Ar-H⁵). – ¹³C NMR (100 MHz, CDCl₃): δ ꢀ=ꢀ

All chemicals were purchased from Merck and Fluka. Infra-

123.9 (C-8), 124.4 (C-7), 128.5 (C-6), 129.8 (C-5), 132.3 (C–Cl),

red spectra were recorded on a Perkin-Elmer V IR spectro-

133.8 (C–NH), 144.3 (C–SO₂), 150.3 (C–NO₂).

photometer. ¹H NMR and ¹³C NMR spectra were recorded on

a Bruker (400 MHz) FT spectrometer in CDCl₃and [D or d]

DMSO. Chemical shifts δ are given in parts per million and 4.1.2 N-Acetyl-N-(4-chlorophenyl)-4-nitrobenzene-

coupling constants J in hertz. Column chromatography

was performed using silica gel 60 (230–400 mesh). All

sulfonamide (1a)

reactions were conducted open to the atmosphere, and the M.p. 183–185 °C. – R_f(film): ν ꢀ=ꢀ 3139, 1719 (Cꢀ=ꢀO), 1535,

yields refer to isolated products.

1352 (SO₂), 1166 (SO₂), 553 (C–N) cm⁻¹. – ¹H NMR (400 MHz,

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8ꢀ ꢀS. Ebrahimi et al.: New selective and efficient acylating reagents

CDCl₃): δ ꢀ=ꢀ 1.92 (s, 3 H, CH₃), 7.23–7.30 (m, 2 H, Ar-H⁶), 7.53 Ar-H⁸). – ¹³C NMR (100 MHz, CDCl₃): δ ꢀ=ꢀ 13.7 (C-14), 22.2

(d, J ꢀ=ꢀ 8.8 Hz, 2 H, Ar-H⁸), 8.25 (d, J ꢀ=ꢀ 8.8 Hz, 2 H, Ar-H⁷), (C-13), 23.8 (C-12), 30.8 (C-11), 36.7 (C-10), 124.0 (C-9), 130.4

8.42 (d, J ꢀ=ꢀ 8.8 Hz, 2 H, Ar-H⁹). – ¹³C NMR (100 MHz, CDCl₃): (C-8), 130.6 (C-7), 131.1 (C-6), 134.0 (C–Cl), 136.8 (C–N),

δ ꢀ=ꢀ 24.9 (C-10), 124.0 (C-9), 130.5 (C-8), 130.6 (C-7), 131.0 144.4 (C–SO₂), 150.7 (C–NO₂), 172.9 (Cꢀ=ꢀO). – C₁₈H₁₉ClN₂O₅S:

(C-6), 134.5 (C–Cl), 136.9 (C–N), 144.2 (C–SO₂), 150.8 (C– calcd. C 52.62, H 4.66, N 6.82; found C 52.51, H 4.49, N 6.80.

NO₂), 169.9 (Cꢀ=ꢀO). –C₁₄H₁₁ClN₂O₅S: calcd. C 47.40, H 3.13, N

7.90; found C 47.21, H 3.05, N 8.01.

4.2 Synthesis of N-benzoyl-N-(4-chloro-

phenyl)-4-nitrobenzenesulfonamide (1e)

4.1.3 N-Butyryl-N-(4-chlorophenyl)-4-nitrobenzene-

sulfonamide (1b)

4-Chloroaniline (2 mmol, 0.255 g) and anhydrous NaHCO₃

(1 g) were ground together into a fine powder, and

M.p. 152–154 °C. – R_f(film): ν ꢀ=ꢀ 3103, 1723 (Cꢀ=ꢀO), 1535, 4-nitrobenzenesulfonyl chloride (2 mmol, 0.442 g) was

1374 (SO₂), 1146, 1185 (SO), 567 (C–N) cm⁻¹. – ¹H NMR (400 added under vigorous stirring at room temperature. The

MHz, CDCl₃): δ ꢀ=ꢀ 0.81 (t, J ꢀ=ꢀ 7.2 Hz, 3 H, CH₃), 1.56 (sext, progress of the reaction was followed by TLC until the

J ꢀ=ꢀ 7.2 Hz, 2 H, CH₂¹¹), 2.02 (t, J ꢀ=ꢀ 7.2 Hz, 2 H, CH₂¹⁰), 7.24 (d, conversion of amine was completed. The product showed

J ꢀ=ꢀ 8.4 Hz, 2 H, Ar-H⁶), 7.53 (d, J ꢀ=ꢀ 8.4 Hz, 2 H, Ar-H⁹), 8.26 one spot on TLC and was used in the second step without

(d, J ꢀ=ꢀ 8.4 Hz, 2 H, Ar-H⁷), 8.42 (d, J ꢀ=ꢀ 8.4 Hz, 2 H, Ar-H⁸). isolation. Benzoic anhydride (2 mmol, 0.452 g), anhydrous

– ¹³C NMR (100 MHz, CDCl₃): δ ꢀ=ꢀ 13.3 (C-12), 17.6 (C-11), 38.5 K₂CO₃(1 g), and acetone (10 mL) were added to the mixture

(C-10), 124.0 (C-9), 130.4 (C-8), 130.6 (C-7), 131.2 (C-6), 134.0 and stirred at room temperature. Upon completion of the

(C–Cl), 136.8 (C–N), 144.4 (C–SO₂), 150.7 (C–NO₂), 172.7 reaction, as it was shown by TLC, the solvent was evapo-

(Cꢀ=ꢀO). – C₁₆H₁₅ClN₂O₅S: calcd. C 50.20, H 3.95, N 7.32; found rated, water was added, and the mixture was stirred for

C 50.31, H 3.85, N 7.41.

a few minutes. After filtration, washing with additional

water, and drying, N-benzoyl-N-(4-chlorophenyl)-4-ni-

trobenzenesulfonamide (1e) was obtained in 85 % yield

with high purity and was used for the acylation reaction

without any purification. M.p. 206–208 °C. – R_f(film):

4.1.4 N-(4-Chlorophenyl)-N-pentanoyl-4-nitrobenzene-

sulfonamide (1c)

ν ꢀ=ꢀ 3108, 1702 (Cꢀ=ꢀO), 1533, 1372 (SO₂), 1176 (SO₂), 577

M.p. 144–146 °C. – R_f(film): ν ꢀ=ꢀ 3099, 1713 (Cꢀ=ꢀO), 1531, 1376 (C–N) cm⁻¹. – H NMR (400 MHz, CDCl₃): δ ꢀ=ꢀ 7.11 (d, J ꢀ=ꢀ

(SO₂), 1186, 1159 (SO₂), 572 (C–N) cm⁻¹. – ¹H NMR (400 MHz, 8.4 Hz, 2 H, Ar-H⁸), 7.25 (d, J ꢀ=ꢀ 7.6 Hz, 2 H, Ar-H⁹), 7.28–7.35

CDCl₃): δ ꢀ=ꢀ 0.80 (t, J ꢀ=ꢀ 6.8 Hz, 3 H, CH₃), 1.16–1.24 (m, 2 H, (m, 3 H, H^solvent, Ar-H¹¹), 7.40 (t, J ꢀ=ꢀ 7.6 Hz, 1 H, Ar-H⁶), 7.48 (d,

CH₂¹²), 1.46 (quint, J ꢀ=ꢀ 6.8 Hz, 2 H, CH₂¹¹), 2.04 (t, J ꢀ=ꢀ 6.8 J ꢀ=ꢀ 7.6 Hz, 2 H, Ar-H¹⁰), 8.15 (d, J ꢀ=ꢀ 8.8 Hz, 2 H, Ar-H¹²), 8.40

Hz, 2 H, CH₂¹⁰), 7.24 (d, J ꢀ=ꢀ 8.0 Hz, 2 H, Ar-H⁶), 7.53 (d, J ꢀ=ꢀ (d, J ꢀ=ꢀ 8.8 Hz, 2 H, Ar-H¹³). – ¹³C NMR (100 MHz, CDCl₃):

8.0 Hz, 2 H, Ar-H⁹), 8.25 (d, J ꢀ=ꢀ 8.0 Hz, 2 H, Ar-H⁷), 8.41 (d, δ ꢀ=ꢀ 123.9 (C-13), 128.4 (C-12), 129.7 (C-11), 129.8 (C-10), 130.8

J ꢀ=ꢀ 8.0 Hz, 2 H, Ar-H⁸). – ¹³C NMR (100 MHz, CDCl₃): δ ꢀ=ꢀ 13.6 (C-9), 131.1 (C-8), 132.3 (C–Cl), 132.7 (C-6), 135.40 (C-5),

(C-13), 21.8 (C-12), 26.1 (C-11), 36.4 (C-10), 124.0 (C-9), 130.4 135.8 (C–N), 143.4 (C–SO₂), 150.7 (C–NO₂), 169.7 (Cꢀ=ꢀO).

(C-8), 130.6 (C-7), 131.1 (C-6), 134.0 (C–Cl), 136.8 (C–N), – C₁₉H₁₃ClN₂O₅S: calcd. C 54.75, H 3.14, N 6.72; found

144.4 (C–SO₂), 150.7 (C–NO₂), 172.8 (Cꢀ=ꢀO). – C₁₇H₁₇ClN₂O₅S: C 54.61, H 3.25, N 6.65.

1

calcd. C 51.45, H 4.32, N 7.06; found C 51.31, H 4.45, N 7.11.

4.2.1 General procedure for the acylation of aromatic

4.1.5 N-(4-Chlorophenyl)-N-hexanoyl-4-nitrobenzene-

and aliphatic amines

sulfonamide (1d)

A mixture of the acylating reagents 1a–e (0.5 mmol), aryl

M.p. 134–136 °C. – R_f(film): ν ꢀ=ꢀ 3103, 1723 (Cꢀ=ꢀO), 1534, 1374 amine (1.5 mmol), or alkyl amine (0.75 mmol) and K₂CO₃

(SO₂), 1185, 1146 (SO₂), 567 (C–N) cm⁻¹. – ¹H NMR (400 MHz, (2 mmol for aromatic amines and 1 mmol for aliphatic

CDCl₃): δ ꢀ=ꢀ 0.83 (t, J ꢀ=ꢀ 7.2 Hz, 3 H, CH₃), 1.1–1.26 (m, 4 H, amines) was stirred in H₂O (1–2 mL) at 80 °C for the appro-

2 ꢀ×ꢀ CH₂^12,13), 1.47–1.63 (m, 2 H, CH₂¹¹), 2.03 (t, J ꢀ=ꢀ 7.6 Hz, 2 H, priate period of time. After completion of the reaction

CH₂¹⁰), 7.24 (dd, J₁ꢀ=ꢀ 6.4 Hz, J₂ꢀ=ꢀ 3.2 Hz, 2 H, Ar-H⁶), 7.53 (dd, as indicated by TLC, the reaction mixture was acidified

J₁ꢀ=ꢀ 6.4 Hz, J₂ꢀ=ꢀ 3.2 Hz, 2 H, Ar-H⁹), 8.26 (dd, J₁ꢀ=ꢀ 5.2 Hz, J₂ꢀ=ꢀ with 5 % HCl and extracted with EtOAc (50 mL) and water

2.0 Hz, 2 H, Ar-H⁷), 8.42 (dd, J₁ꢀ=ꢀ 5.2 Hz, J₂ꢀ=ꢀ 2.0 Hz, 2 H, (10 mL). The combined organic layer was concentrated

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in vacuo and purified by column chromatography on Acknowledgments: We appreciate financial support

silica gel to afford the pure product (compounds 2a–p and of Shahreza Branch, Islamic Azad University (IAUSH)

3a–q).

Research Council.

4.2.2 General procedure for the acylation of diamines,

amino alcohols, and amino phenols

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3.76 (m, 3 H, CH₂, NH), 6.66–6.72 (m, 3 H, Ar-H⁹, NHCO),

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1

1603, 1647, 1512, 1259, 749, 692 cm⁻¹. – H NMR (400 MHz,

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8

6

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7

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(C-10), 27.8 (C-9), 36.5 (C-8), 39.0 (C–NHCO), 44.2 (C–NH),

112.8 (C-5), 117.8 (C-4), 129.3 (C-3), 147.8 (C-2), 174.0 (Cꢀ=ꢀO).

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Sara Ebrahimi, Safoura Saiadi, Simin

Dakhilpour, Seyed Nezamoddin

Mirsattari and Ahmad Reza Massah

N-Acyl-N-(4-chlorophenyl)-4-nitroben-

zenesulfonamides: highly selective

and efficient reagents for acylation of

amines in water

DOI 10.1515/znb-2015-0076

Z. Naturforsch. 2015; x(x)b: xxx–xxx

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N-Acyl-N-(4-chlorophenyl)-4-nitrobenzenesulfonamides: Highly selective and efficient reagents for acylation of amines in water

DOI: 10.1515/znb-2015-0076

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