# Preparation, Analytical, IR Spectral, and Thermal Studies of Some New Hydrazinium Carboxylates

Authors: R. Manimekalai; C. R. Sinduja; K. Kalpanadevi
Journal: International Journal of Inorganic Chemistry
 (2012)

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## Abstract

Hydrazinium salts of 2,4-dichlorophenylacetic acid, phenoxyacetic acid, 2,4-dichlorophenoxyacetic acid, diphenylacetic acid, cinnamic acid, and picolinic and nicotinic acids have been prepared by accomplishing neutralization of aqueous hydrazine hydrate with the respective acids. Formation of these hydrazinium salts has been confirmed by analytical, IR spectral, and thermal studies. IR spectra of the salts register N–N stretching frequencies ofN2H5+ ion in the region 963–951 cm−1 and the frequencies of N2H62+ ion in the region 1047–1026 cm−1. Thermal decomposition studies show that the hydrazinium salts undergo melting followed by endothermic decomposition into carbon residue as the endproduct.


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## Body

## 1. Introduction

Hydrazine is the simplest diamine and forms salt with mineral and carboxylic acids [1–5]. The monoprotonated hydrazine, the hydrazinium cation still retains a basic site and hence capable of coordination with various metal ions. However, many hydrazinium complexes reported in the literature contain hydrazinium ion as a mere charge neutralizing species [6, 7]. The complexes containing coordinated hydrazinium ion are used as very good precursor for the preparation of nanoparticles [8] with nearly uniform particle size. Some of these salts are used as flame-retardants [9, 10] and proton conductors [11]. Preparation and thermal behaviour of some salts from few aliphatic acid [12, 13] and aromatic carboxylic acids [14, 15] have been reported. There is no literature citation about hydrazinium salt of aromatic substituted acetic acids, aromatic unsaturated acids, and heteroacids except hydrazinium salt of pyrazine mono and dicarboxylic acids [16, 17]. It is therefore, considered interesting to prepare hydrazinium salt of aromatic-substituted acetic acids.


## 2. Experimental

All the salts reported have been prepared by the neutralization of the respective acids in aqueous medium with hydrazine hydrate (99–100%) in appropriate molar ratios.


### 2.1. Preparation

#### 2.1.1. Hydrazinium Salts of 2,4-Dichlorophenylacetate, Phenoxyacetate, 2,4-Dichlorophenoxyacetate, and Diphenylacetate

These are prepared by mixing hydrazine hydrate and acids in 2 : 3 molar ratio in 50 mL of distilled water. The resulting turbid solution is heated over water bath to obtain clear solution and concentrated to nearly 20 mL. Then it was allowed to crystallize at room temperature. The crystals are filtered off and washed by using benzene and dried in air.


#### 2.1.2. Hydrazinium Cinnamate Hydrate

These are prepared by mixing hydrazine hydrate and diphenylacetic acid or cinnamic acid in 1 : 1 molar ratio in 50 mL of water. The contents of the beaker are heated on water bath. Then the undissolved acid is removed by filtration. The resulting clear solution is concentrated on water bath to 20 mL. Then it is allowed to crystallize at room temperature; they are filtered off, and washed by using alcohol and air dried.


#### 2.1.3. Hydrazinium Picolinate and Hydrazinium Nicotinate

These are prepared by mixing hydrazine hydrate and picolinic acid or nicotinic acid with 1 : 1 molar ratio in 50 mL of distilled water. The resulting clear solution is concentrated on water bath to 20 mL. Then it is allowed to crystallize in a vacuum desiccator over calcium chloride. Salts are separated out after 2 days, filtered, and washed by using ether.


## 2.1. Preparation

### 2.1.1. Hydrazinium Salts of 2,4-Dichlorophenylacetate, Phenoxyacetate, 2,4-Dichlorophenoxyacetate, and Diphenylacetate

These are prepared by mixing hydrazine hydrate and acids in 2 : 3 molar ratio in 50 mL of distilled water. The resulting turbid solution is heated over water bath to obtain clear solution and concentrated to nearly 20 mL. Then it was allowed to crystallize at room temperature. The crystals are filtered off and washed by using benzene and dried in air.


### 2.1.2. Hydrazinium Cinnamate Hydrate

These are prepared by mixing hydrazine hydrate and diphenylacetic acid or cinnamic acid in 1 : 1 molar ratio in 50 mL of water. The contents of the beaker are heated on water bath. Then the undissolved acid is removed by filtration. The resulting clear solution is concentrated on water bath to 20 mL. Then it is allowed to crystallize at room temperature; they are filtered off, and washed by using alcohol and air dried.


### 2.1.3. Hydrazinium Picolinate and Hydrazinium Nicotinate

These are prepared by mixing hydrazine hydrate and picolinic acid or nicotinic acid with 1 : 1 molar ratio in 50 mL of distilled water. The resulting clear solution is concentrated on water bath to 20 mL. Then it is allowed to crystallize in a vacuum desiccator over calcium chloride. Salts are separated out after 2 days, filtered, and washed by using ether.


## 2.1.1. Hydrazinium Salts of 2,4-Dichlorophenylacetate, Phenoxyacetate, 2,4-Dichlorophenoxyacetate, and Diphenylacetate

These are prepared by mixing hydrazine hydrate and acids in 2 : 3 molar ratio in 50 mL of distilled water. The resulting turbid solution is heated over water bath to obtain clear solution and concentrated to nearly 20 mL. Then it was allowed to crystallize at room temperature. The crystals are filtered off and washed by using benzene and dried in air.


## 2.1.2. Hydrazinium Cinnamate Hydrate

These are prepared by mixing hydrazine hydrate and diphenylacetic acid or cinnamic acid in 1 : 1 molar ratio in 50 mL of water. The contents of the beaker are heated on water bath. Then the undissolved acid is removed by filtration. The resulting clear solution is concentrated on water bath to 20 mL. Then it is allowed to crystallize at room temperature; they are filtered off, and washed by using alcohol and air dried.


## 2.1.3. Hydrazinium Picolinate and Hydrazinium Nicotinate

These are prepared by mixing hydrazine hydrate and picolinic acid or nicotinic acid with 1 : 1 molar ratio in 50 mL of distilled water. The resulting clear solution is concentrated on water bath to 20 mL. Then it is allowed to crystallize in a vacuum desiccator over calcium chloride. Salts are separated out after 2 days, filtered, and washed by using ether.


## 3. Results and Discussion

The analytical data (Table1) of the salts are consistent with the proposed formulae for them.Table 1
Analytical data.
S. no
Compound
Colour
Found (calculated) %
Hydrazine
Carbon
Hydrogen
Nitrogen
1
Hydrazinium 2,4-dichlorophenylacetate hydrate
Light yellow
11.90 (12.95)
37.40 (37.93)
4.50 (4.70)
9.98 (10.97)
2
Hydrazinium phenoxyacetate hydrate
White
16.00 (16.34)
47.20 (47.47)
7.11 (6.92)
13.00 (13.84)
3
Hydrazinium 2,4-dichlorophenoxyacetate hydrate
White
11.21 (12.14)
47.10 (47.04)
4.10 (4.41)
8.80 (8.82)
4
Hydrazinium diphenylacetate hydrate
Light yellow
12.00 (12.55)
63.20 (63.80)
6.20 (6.83)
10.59 (10.63)
5
Hydrazinium cinnamate hydrate
White
17.40 (17.19)
51.00 (51.19)
7.04 (7.02)
14.85 (14.05)
6
Hydrazinium picolinate
Light yellow
12.71 (12.10)
51.29 (51.38)
2.89 (2.85)
9.96 (9.99)
7
Hydrazinium  nicotinate
White
12.83 (12.10)
51.20 (51.38)
2.80 (2.85)
9.95 (9.99)


### 3.1. Infrared Spectra

The important IR bands of the salts are listed in Table2.Table 2
IR spectral data (cm−1).
S. no
Compound
υ
OH of water/acid
υ
N – H
υ
asymm
(OCO)
υ
sym
(OCO)
υ
N – N
1
Hydrazinium 2,4-dichlorophenylacetate hydrate
—
3276
1590
1380
958
3257
1030
2
Hydrazinium phenoxyacetate hydrate
—
3443(b)
1589
1375
959
1541
1338
1026
1047
3
Hydrazinium 2,4-dichlorophenoxyacetate hydrate
3330(s)
3172
1577
1390
951
3072
1569
1328
4
Hydrazinium diphenylacetate hydrate
3346(s)
3276
1596
1375
963
3331(s)
3245
1527
1340
5
Hydrazinium cinnamate hydrate
3332(b)
3251
1558
1386
953
3236
1521
1338
6
Hydrazinium picolinate
—
3276
1583
1385
1043
3213
1560
1331
7
Hydrazinium  nicotinate
—
3265
1598
1386
1029
3246
1544
1323The IR spectra of the hydrated salts display absorption bands in the region of 3346–3330 cm−1 due to O–H stretching of water molecule. In hydrazinium 2,4-dichlorophenoxyacetate hydrate and hydrazinium phenoxyacetate, the band due to O–H stretching frequency overlaps with the band due to N–H stretching frequency. The bands in the region of 1390–1323 cm−1 and 1598–1521 cm−1 for these salts correspond to symmetric and asymmetric stretching frequencies of the carboxylate ions. The N–N stretching frequencies of N2H5+ ion appear in the range of 963–951 cm−1 [1, 11, 12] and the N–N stretching frequencies of N2H62+ ion show bands in the region of 1043–1029 cm−1.


### 3.2. Thermal Analysis

See Table3.Table 3
TG-DTA data.
S. no
Compound
DTA peak temp. (°C)
Thermogravimetry (TG)
Decomposition product
Temp. range °C
Mass loss (%)
Obsd
Cald
1
99 (+)
25–133
5.18
6.49
Dehydration
Hydrazinium 2,4-dichlorophenylacetate hydrate
211 (+)
133–286
79.43
81.54
Decomposition to formic acid
269 (−)
305 (−)
286–329
90.38
90.91
Decomposition to carbon residue
2
99 (+)
25–90
—
—
Melting
Hydrazinium phenoxyacetate hydrate
149 (−)
90–234
50.41
53.51
Decomposition leads to phenol
265 (−)
327 (−)
234–344
97.6
—
Decomposition to carbon residue
3
170 (+)
103–225
18.21
18.39
Dehydration and dehydrazination
Hydrazinium 2,4-dichlorophenoxyacetate hydrate
285 (−)
225–528
96
—
Complete decomposition  to carbon residue
488 (−)
4
106 (+)
25–86
1
—
Removal  of moisture
Hydrazinium diphenylacetate hydrate
186 (−)
86–354
81.51
82.53
Dehydration and dehydrazination leads to formic acid
233 (−)
484 (−)
354–483
97
—
Complete decomposition to carbon residue
5
92 (+)
25–102
9.67
9.03
Dehydration dehydrazination
Hydrazinium cinnamate hydrate
150 (+)
102–150
25.04
26.13
289 (−)
150–481
98.41
—
Decomposition to carbon residue
458 (−)
6
121 (+)
25–99
—
—
Removal of moisture
Hydrazinium picolinate
155 (−)
99–218
87.70
—
Decomposition to carbon residue
191 (+)
7
Hydrazinium  nicotinate
117 (+)
25–127
3.69
—
Removal of moisture
183 (−)
127–304
90.20
Decomposition to carbon residue
282 (+)


#### 3.2.1. Hydrazinium 2,4-Dichlorophenylacetate Hydrate (Scheme1)

Scheme 1The thermogram of this salt indicates that the decomposition of the salt takes place in three steps. In the first step, dehydration takes place with endothermic peak at 99°C. In the second step the carboxylate intermediate decomposes to formic acid with endothermic peak at 211°C and an exothermic peak at 269°C. Finally, it decomposes to carbon residue at 305°C.


#### 3.2.2. Hydrazinium Phenoxyacetate Hydrate (Scheme2)

Scheme 2This undergoes decomposition in three steps. In the first step, compound undergoes melt with endothermic peak at 99°C. Then the compound decomposes to phenol with exothermic peak at 149°C and 265°C. Finally, at 327°C it decomposes to carbon residue.


#### 3.2.3. Hydrazinium 2,4-Dichlorophenoxyacetate Hydrate (Scheme3)

Scheme 3The thermogram of this salt indicates that the decomposition of the salt takes place in two steps. In the first step, both dehydration and dehydrazination occur simultaneously showing a sharp endotherm at 170°C. In the second step, the acid intermediate decomposes exothermally at 285°C and 488°C to carbon residue.


#### 3.2.4. Hydrazinium Diphenylacetate Hydrate (Scheme4)

Scheme 4This undergoes decomposition in three steps. First step shows an endothermic peak at 106°C corresponding to the removal of moisture. In the second step, both dehydration and dehydrazination occur simultaneously showing two exothermic peaks at 186°C and 233°C to form formic acid. In the final step, formic acid completely decomposes to carbon residue.


#### 3.2.5. Hydrazinium Cinnamate Hydrate (Scheme5)

Scheme 5This compound also undergoes three steps of decomposition. First step shows an endothermic peak at 92°C corresponding to liberation of water molecule. Second step shows on endothermic peak at 150°C due to the elimination of one molecule of hydrazine. In the third step, complete decomposition to carbon residue takes place.


#### 3.2.6. Hydrazinium Picolinate and Nicotinate (Scheme6)

Scheme 6Both compounds undergo two step decomposition. First step is the removal of moisture with endothermic peaks at 121°C and 117°C, respectively. In the second step, the compound completely decomposes to carbon residue.TG-DTA curves of some compounds are given (Figures1, 2, 3, 4, and 5) as representative examples.Figure 1
Hydrazinium phenoxyacetate hydrate.Figure 2
Hydrazinium 2,4-dichlorophenoxyacetate hydrate.Figure 3
Hydrazinium diphenylacetate hydrate.Figure 4
Hydrazinium cinnamate hydrate.Figure 5
Hydrazinium picolinate.


## 3.1. Infrared Spectra

The important IR bands of the salts are listed in Table2.Table 2
IR spectral data (cm−1).
S. no
Compound
υ
OH of water/acid
υ
N – H
υ
asymm
(OCO)
υ
sym
(OCO)
υ
N – N
1
Hydrazinium 2,4-dichlorophenylacetate hydrate
—
3276
1590
1380
958
3257
1030
2
Hydrazinium phenoxyacetate hydrate
—
3443(b)
1589
1375
959
1541
1338
1026
1047
3
Hydrazinium 2,4-dichlorophenoxyacetate hydrate
3330(s)
3172
1577
1390
951
3072
1569
1328
4
Hydrazinium diphenylacetate hydrate
3346(s)
3276
1596
1375
963
3331(s)
3245
1527
1340
5
Hydrazinium cinnamate hydrate
3332(b)
3251
1558
1386
953
3236
1521
1338
6
Hydrazinium picolinate
—
3276
1583
1385
1043
3213
1560
1331
7
Hydrazinium  nicotinate
—
3265
1598
1386
1029
3246
1544
1323The IR spectra of the hydrated salts display absorption bands in the region of 3346–3330 cm−1 due to O–H stretching of water molecule. In hydrazinium 2,4-dichlorophenoxyacetate hydrate and hydrazinium phenoxyacetate, the band due to O–H stretching frequency overlaps with the band due to N–H stretching frequency. The bands in the region of 1390–1323 cm−1 and 1598–1521 cm−1 for these salts correspond to symmetric and asymmetric stretching frequencies of the carboxylate ions. The N–N stretching frequencies of N2H5+ ion appear in the range of 963–951 cm−1 [1, 11, 12] and the N–N stretching frequencies of N2H62+ ion show bands in the region of 1043–1029 cm−1.


## 3.2. Thermal Analysis

See Table3.Table 3
TG-DTA data.
S. no
Compound
DTA peak temp. (°C)
Thermogravimetry (TG)
Decomposition product
Temp. range °C
Mass loss (%)
Obsd
Cald
1
99 (+)
25–133
5.18
6.49
Dehydration
Hydrazinium 2,4-dichlorophenylacetate hydrate
211 (+)
133–286
79.43
81.54
Decomposition to formic acid
269 (−)
305 (−)
286–329
90.38
90.91
Decomposition to carbon residue
2
99 (+)
25–90
—
—
Melting
Hydrazinium phenoxyacetate hydrate
149 (−)
90–234
50.41
53.51
Decomposition leads to phenol
265 (−)
327 (−)
234–344
97.6
—
Decomposition to carbon residue
3
170 (+)
103–225
18.21
18.39
Dehydration and dehydrazination
Hydrazinium 2,4-dichlorophenoxyacetate hydrate
285 (−)
225–528
96
—
Complete decomposition  to carbon residue
488 (−)
4
106 (+)
25–86
1
—
Removal  of moisture
Hydrazinium diphenylacetate hydrate
186 (−)
86–354
81.51
82.53
Dehydration and dehydrazination leads to formic acid
233 (−)
484 (−)
354–483
97
—
Complete decomposition to carbon residue
5
92 (+)
25–102
9.67
9.03
Dehydration dehydrazination
Hydrazinium cinnamate hydrate
150 (+)
102–150
25.04
26.13
289 (−)
150–481
98.41
—
Decomposition to carbon residue
458 (−)
6
121 (+)
25–99
—
—
Removal of moisture
Hydrazinium picolinate
155 (−)
99–218
87.70
—
Decomposition to carbon residue
191 (+)
7
Hydrazinium  nicotinate
117 (+)
25–127
3.69
—
Removal of moisture
183 (−)
127–304
90.20
Decomposition to carbon residue
282 (+)


### 3.2.1. Hydrazinium 2,4-Dichlorophenylacetate Hydrate (Scheme1)

Scheme 1The thermogram of this salt indicates that the decomposition of the salt takes place in three steps. In the first step, dehydration takes place with endothermic peak at 99°C. In the second step the carboxylate intermediate decomposes to formic acid with endothermic peak at 211°C and an exothermic peak at 269°C. Finally, it decomposes to carbon residue at 305°C.


### 3.2.2. Hydrazinium Phenoxyacetate Hydrate (Scheme2)

Scheme 2This undergoes decomposition in three steps. In the first step, compound undergoes melt with endothermic peak at 99°C. Then the compound decomposes to phenol with exothermic peak at 149°C and 265°C. Finally, at 327°C it decomposes to carbon residue.


### 3.2.3. Hydrazinium 2,4-Dichlorophenoxyacetate Hydrate (Scheme3)

Scheme 3The thermogram of this salt indicates that the decomposition of the salt takes place in two steps. In the first step, both dehydration and dehydrazination occur simultaneously showing a sharp endotherm at 170°C. In the second step, the acid intermediate decomposes exothermally at 285°C and 488°C to carbon residue.


### 3.2.4. Hydrazinium Diphenylacetate Hydrate (Scheme4)

Scheme 4This undergoes decomposition in three steps. First step shows an endothermic peak at 106°C corresponding to the removal of moisture. In the second step, both dehydration and dehydrazination occur simultaneously showing two exothermic peaks at 186°C and 233°C to form formic acid. In the final step, formic acid completely decomposes to carbon residue.


### 3.2.5. Hydrazinium Cinnamate Hydrate (Scheme5)

Scheme 5This compound also undergoes three steps of decomposition. First step shows an endothermic peak at 92°C corresponding to liberation of water molecule. Second step shows on endothermic peak at 150°C due to the elimination of one molecule of hydrazine. In the third step, complete decomposition to carbon residue takes place.


### 3.2.6. Hydrazinium Picolinate and Nicotinate (Scheme6)

Scheme 6Both compounds undergo two step decomposition. First step is the removal of moisture with endothermic peaks at 121°C and 117°C, respectively. In the second step, the compound completely decomposes to carbon residue.TG-DTA curves of some compounds are given (Figures1, 2, 3, 4, and 5) as representative examples.Figure 1
Hydrazinium phenoxyacetate hydrate.Figure 2
Hydrazinium 2,4-dichlorophenoxyacetate hydrate.Figure 3
Hydrazinium diphenylacetate hydrate.Figure 4
Hydrazinium cinnamate hydrate.Figure 5
Hydrazinium picolinate.


## 3.2.1. Hydrazinium 2,4-Dichlorophenylacetate Hydrate (Scheme1)

Scheme 1The thermogram of this salt indicates that the decomposition of the salt takes place in three steps. In the first step, dehydration takes place with endothermic peak at 99°C. In the second step the carboxylate intermediate decomposes to formic acid with endothermic peak at 211°C and an exothermic peak at 269°C. Finally, it decomposes to carbon residue at 305°C.


## 3.2.2. Hydrazinium Phenoxyacetate Hydrate (Scheme2)

Scheme 2This undergoes decomposition in three steps. In the first step, compound undergoes melt with endothermic peak at 99°C. Then the compound decomposes to phenol with exothermic peak at 149°C and 265°C. Finally, at 327°C it decomposes to carbon residue.


## 3.2.3. Hydrazinium 2,4-Dichlorophenoxyacetate Hydrate (Scheme3)

Scheme 3The thermogram of this salt indicates that the decomposition of the salt takes place in two steps. In the first step, both dehydration and dehydrazination occur simultaneously showing a sharp endotherm at 170°C. In the second step, the acid intermediate decomposes exothermally at 285°C and 488°C to carbon residue.


## 3.2.4. Hydrazinium Diphenylacetate Hydrate (Scheme4)

Scheme 4This undergoes decomposition in three steps. First step shows an endothermic peak at 106°C corresponding to the removal of moisture. In the second step, both dehydration and dehydrazination occur simultaneously showing two exothermic peaks at 186°C and 233°C to form formic acid. In the final step, formic acid completely decomposes to carbon residue.


## 3.2.5. Hydrazinium Cinnamate Hydrate (Scheme5)

Scheme 5This compound also undergoes three steps of decomposition. First step shows an endothermic peak at 92°C corresponding to liberation of water molecule. Second step shows on endothermic peak at 150°C due to the elimination of one molecule of hydrazine. In the third step, complete decomposition to carbon residue takes place.


## 3.2.6. Hydrazinium Picolinate and Nicotinate (Scheme6)

Scheme 6Both compounds undergo two step decomposition. First step is the removal of moisture with endothermic peaks at 121°C and 117°C, respectively. In the second step, the compound completely decomposes to carbon residue.TG-DTA curves of some compounds are given (Figures1, 2, 3, 4, and 5) as representative examples.Figure 1
Hydrazinium phenoxyacetate hydrate.Figure 2
Hydrazinium 2,4-dichlorophenoxyacetate hydrate.Figure 3
Hydrazinium diphenylacetate hydrate.Figure 4
Hydrazinium cinnamate hydrate.Figure 5
Hydrazinium picolinate.


## 4. Conclusions

2,4-dichlorophenylacetic acid, phenoxyacetic acid, 2,4-dichlorophenoxyacetic acid, diphenylacetic acid, and cinnamic acid formed as hydrazinium(+1) salts, whereas picolinic and nicotinic acid formed as hydrazinium(+2) salts.All compounds undergo two- or three-step exothermic or endothermic decomposition through various intermediates and decompose completely to carbon residue as the final product.



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*Source: 624374-2012-11-05.xml*