THERMAL ANALYSIS OF ACYLHYDRAZIDES - …shodhganga.inflibnet.ac.in/bitstream/10603/110663/9/09_chapter 3.pdf · The gaseous combustion ... from the corresponding amide by refluxing

CHAPTER III

THERMAL ANALYSIS OF ACYLHYDRAZIDES

Thermal decomposition studies of six acylhydrazides, viz., benzohydrazide

(BH), 2-hydroxybenzohydrazide (2HBH), 4-hydroxybenzohydrazide (4HBH),

3-nitrobenzohydrazide (3NBH), 4-nitrobenzohydrazide (4NBH) and isonicotino

hydrazide (INH) have been carried out using simultaneous TG-DTA techniques with

a view to compare their thermal behaviour. Thermal decomposition studies of these

six acylhydrazides in presence of urea nitrate (UN) have also been carried out with a

view to study the effect of UN on their thermal behaviour. Apart from the

phenomenological studies of the thermal behaviour of acylhydrazides and their

mixture with UN (5%, w/w), the kinetics and mechanism of their thermal

decomposition reactions have also been studied with a view to get a quantitative

assessment of their thermal behaviour.

Chapter III: Thermal analysis of acylhydrazides

1. Introduction

Carboxylic acid derivatives of hydrazine known as hydrazides are

characterized by -CONHNH2 group. The monoacyl derivatives are known as

primary hydrazides (RCONHNH2) and the N,N'-diacyl derivatives as secondary

hydrazides (RCONHNHCOR) 172. Hydrazides resemble amides in their physical

properties and solubility, but are more resistant to hydrolysis 173. They can be

hydrolysed by heating with acids or alkalies. Acylhydrazides are well known for

their antituberculosis activity and their importance as potential sites for transition

metal complexes52· 125. Alkoxy and hydroxy substituted benzohydrazides have been

tested for their antifungal and tuberculostatic activities9

. 2-Hydroxybenzohydrazide

is a well known antibacterial and antifungal agent. Besides this property it has

analytical and technological importance. 2-Hyclroxybenzohydrazide and its aryl

substituted derivatives are used as anti-oxidants and heat stabilizers for fats, oils and

polymers5 . Benzohydrazide and its derivatives find applications as corros10n

inhibitors20· 21 and optical materials18. Pyridine-4-carboxylic acid hydrazide or

isonicotinohydrazide, the first effective tuberculostat deserves special attention as a

multidentate ligand in coordination complexes 1. Benzohydrazide is reported to boil

with decomposition, and if quickly heated, it boils almost undecomposed 167. This

reveals the effect of heating rate on its thennal behaviour. The gaseous combustion

products of 2-Hydroxybenzohydrazide have been reported to be H2 , CO, CO2, H20,

NH3 and oxides of nitrogen52

in a thennal decomposition study of its transition metal

complexes. Some explosive decomposition character has also been reported for

metal complexes of its nitro derivatives 126.

2. Experimental

Six acylhydrazides, viz., benzohydrazide (BH), 2-hydroxybenzohydrazide

(2HBH), 4-hydroxybenzohydrazide (4HBH), 3-nitrobenzohydrazide (3NBH),

4-nitrobenzohydrazide ( 4NBH) and pyridine-4-carbohydrazide or isonicotino

hydrazide (INH) were used for the present studies. Among these six hydrazides, BH,

2HBH, 4HBH and 3NBH were prepared by method 1158 as described in Chapter II by

66


refluxing corresponding esters with hydrazine hydrate in 1: 1 molar ratio for 1 - 2 h in

a steam bath. The resulting solutions on cooling gave crystals of the respective

hydrazides in good yields. These hydrazides were collected and purified by

recrystallising from absolute alcohol. 4-Nitrobenzohydrazide (4NBH) was prepared

from the corresponding amide by refluxing the amide with hydrazine hydrate in 1 :5

molar ratio in an oil bath at 140-145°C for 3 h159, and then purified and

recrystallised from ethanol. The commercial sample of isonicotinohydrazide

(INH), was purified by recrystallising from ethanol. The recrystallised samples were

dried in vacuo over phosphorus(V) oxide, and these were subjected to simultaneous

TG-DTG-DTA studies using a Mettler Toledo thermal analyzer as described in

Chapter II using a heating rate of 10°C min- 1 in dynamic air and a sample mass of

-3 mg in the temperature region 30 - 600°C in alumina crucibles.

Urea nitrate was prepared by the reaction of urea and concentrated nitric

acid 151, washed with acetone, dried in vacuo and used for the thermal analysis. The

hydrazides were mixed gently with 5% (w/w) urea nitrate in an agate mortar 170 and

dried in vacuo. These binary mixtures were also subjected to non-isothermal

decomposition under the same conditions used for the thermal analysis of

hydrazides.

Melting points of all the six hydrazides were detennined by capillary method,

and these values were compared with those reported in literature167·168

. No sharp

boiling temperatures were detected and all of them decompose with charring on

heating continuously giving no final residue in each case. These melting point

values and the IUP AC names of the hydrazides are given in Table 2.1. Infrared

spectra of the acylhydrazides show peaks corresponding to NH vibrations of the free

NH2 group in the region 3280 - 3010 cm - i and the amide I (the carbonyl absorption

of CO-NH group) frequencies are found in the range 1660-1615cm - 1• The amide II

bands (��stly due to NH bending) appear in the region 1590-1500 cm - 1•

3. Results and discussion

The TG, DTG and DT A curves of the six hydrazides and their mixtures with

67

Chapter///: Thermal analysis of acylhydrazides

urea nitrate, and the Coats-Redfern plots for the various thermal decomposition

reactions studied are presented in Figs 3.1 - 3.6. The TO, DTG and DTA data of the

hydrazides and their mixtures with urea nitrate are given in Tables 3.1 and 3.2, and

the kinetic parameters for the decomposition reactions in Table 3.3 and 3.4. The

effect of urea nitrate on the thennal decomposition reactions of hydrazides is

presented in Table 3.5. These figures and tables are presented at the end of the

chapter.

3.1 Thermal behaviour of acylhydrazides

The salient features of the thermal behaviour of the six acylhydrazides are

discussed under the following sub-headings.

3.1.1 Benzohydrazide

Benzohydrazide ( BH} is stable up to -l 20°C, and thereafter, it undergoes

decomposition in two stages. These two decomposition stages are denoted by the

DTG peaks at 225 and 269°C, and the corresponding endothermic DT A peaks at 229

and 270°C (vide Fig 3. l a). Apart from the two OTA peaks, there is an additional

endothermic DT A peak at l l 5°C, which does not have any corresponding DTG peak

and mass change in the TG curve. This additional DT A peak indicates that the

sample melts at l l 5°C prior to its decomposition, and the reported melting point of

BH is l l 3-115°C 168

. The first decomposition stage is the major event, which occurs

in the temperature region 120 - 240°C with a peak height of 0.68 mg min- 1 at 225°C

indicating that the sample losses the maximum mass at that temperature. The mass

loss observed for the first decomposition stage is 89.2%. The second decomposition

stage is a minor event occurring in the temperature region 240 - 280°C, which

follows the first decomposition stage without any stability region between these

stages. The DTG peak height for the second decomposition stage is 0.12 mg min- 1 at

269°C with a mass loss of 10.8%. The total mass loss for the complete

decomposition of BH is I 00.0%, and there is no residue left behind after -280°C in

conformity with the final TG plateau after this temperature. The first decomposition

stage is the actual d�composition of the sample, and the second decomposition stage

68

Chapter Ill: Thermal analysis of acylhydrazides

is the removal of any solid decomposition product formed in the first decomposition

stage. Therefore, the decomposition reaction of the sample can be represented by the

following equation.

OcoNHNH2

3.1.2 2-Hydroxybenzohydrazide

2-Hydroxybenzohydrazide (2HBH) is stable up to -150°C, and then it

decomposes in two stages, which are denoted by the DTG peaks at 233 and 309°C,

and the corresponding endothennic DTA peaks at 238 and 311 °C (vide Fig. 3.2a).

There is an additional endothennic DT A peak l 49°C, which does not have any

corresponding DTG peak and no mass change in the TG curve. This additional DT A

peak corresponds to melting of the sample prior to its decomposition48 · 168 . The melt

then decomposes in two stages, the first stage being the major decomposition stage.

The first decomposition stage occurs in the temperature region 150 - 250°C with a

mass loss of 86.1 % and the maximum decomposition rate of 0.68 mg min- 1 at 233°C.

The second decomposition stage is a minor event occurring in the temperature region

250 - 320°C with a mass loss of 13.9% and the maximum decomposition rate of 0.16

mg min· 1 at 311 °C. As in the case of BH, both the decomposition stages are

continuous without any plateau between the two stages. The total mass loss obtained

is 100.0%, and no residue is left behind after -320°C. Thus, 2HBH decomposes in

two stages to give gase;ous products as per the equation given below.

OH

Q-coNHNH,

3.1.3 4-Hydroxybenzohydrazide

4-Hydroxybenzohydrazide (4HBH) is stable up to -240°C, and then it

undergoes decomposition in three stages as indicated by the DTG peaks at 275, 365

and 569°C, and the corresponding DTA peaks at 267, 373 and 566°C. The first two

69


DT A peaks are endothermic, while the third one is exothermic in nature due to

oxidative decomposition in that stage. As the first DT A peak at 267°C is very sharp

unlike the other two DT A peaks, it is attributed to melting along with decomposition

of the sample (the reported m.p. is 267°C). The first decomposition stage occurs in

the temperature region 240 - 330°C with a mass loss of 48.8% and the DTG peak

height of 0.27 mg min- 1 at 275°C. The second decomposition stage takes place in the

temperature region 330 - 420°C with a mass loss of 20.3% and the DTG peak height

of 0.15 mg min- 1 at 365°C. The third and final decomposition stage occurs in the


of 0.13 mg min- 1 at 569°C. The total mass loss for the complete decomposition of

4HBH is found to be l 00.0%, and no residue is obtained after -580°C. No stability

regions are observed in between the three decomposition stages. On the basis of the

above observation and discussion, 4HBH decomposes to give gaseous products as

per the equation given below.

HO�CONHNH2

3.1.4 3-Nitrobenzohydrazide

3-Nitrobenzohydrazide (3NBH) is stable up to -l 70°

C, and thereafter, it

undergoes decomposition in three stages, which are denoted by the DTG peaks at

263, 334 and 552°C, and the corresponding exothermic DTA peaks at 249, 334 and

540°C (vide Fig 3.4a). The compound melts at l 53°C before decomposition as

indicated by the additional endothermic DT A peak at this temperature. The first

decomposition stage takes place in the temperature region 170 - 300°C with a mass

loss of 48.2% and the DTG peak height of 0.24 mg min- 1 at 263°C. The second

decomposition occurs in the temperature region 300 - 400°C with a mass loss of

30.7% and the DTG peak height of 0.26 mg min- 1 at 334°C. The third


loss of 19.2% and the DTG peak height of 0.06 mg min- 1• The total mass loss

obtained for the complete decomposition of the sample is 98.1 %, and no final

70


decomposition residue is obtained after 590°C. The TG curve does not give any

plateau in between the three decomposition stages. The decomposition of 3NBH

may be represented by the following equation.

02N

b-CONHNH2

3.1.5 4-Nitrobenzohydrazide

?CO2 + N2 + N02 + 7/2 H20

4-Nitrobenzohydrazide ( 4NBH) is stable up to -l 90°C (vide Fig.3.5a). The

decomposition takes place in two stages as indicated by the DTG peak,; at 277 and

592°C, and the corresponding exothermic DTA peaks at 280 and 594°C (vide Fig

3.5a). The compound melts at 221 °C before decomposition as indicated by the

endothermic DTA peak at this temperature (the reported m.p. is 2 l 8°C 168). The first


loss of 54.9% and the DTG peak height of 0.22 mg min- 1 at 277°C. The second

decomposition stage is not completed within the temperature region studied (up to

-600°C), which occurs in the temperature region from 390 to above 600°C with a

mass loss of 37.4% and the DTG peak height of 0.20 mg min- 1 at 592°C. There is no

plateau between the two decomposition stages as the TG curve shows gradual mass

loss between the two stages. The total mass loss recorded is only 92.3% due to

incomplete decomposition within the temperature region studied. Traces of

carbonaceous matter are left behind as residue. The thermal decomposition reaction

of 4NBH may be represented by the equation given below.

3.1.6 Isonicotinohydrazide

?CO2 + N2 + N02 + 7/2 H20

Isonicotinohydrazide is pyridine-4-carbohydrazide popularly known as

71


'isoniazid' (INH). This is stable up to -170°C, and thereafter, it undergoes

decomposition in two stages, which are denoted by the DTG peaks at 249 and 307°C,

and the corresponding endothermic DTA peaks at 255 and 310°C (vide Fig 3.6a).

The additional endothermic DT A peak observed at 170°C, which does not have any

corresponding DTG peak, is attributed to melting of the sample prior to

decomposition. The first decomposition stage occurs in the temperature region 170 -

270°C with a mass loss of 71.3% and the DTG peak height of 0.46 mg min- 1 at

249°C. The second decomposition stage takes place in the temperature region 270 -

320°C with a mass loss of 26.2% and the DTG peak height of 0. 24 mg min- 1 at

307°C. The second decomposition stage is the continuation of the first stage, and

there is no stability region between the two stages. The total mass loss obtained for

the complete decomposition of INH is 97 .5%, and there is no residue obtained after

-320°C. The decomposition reaction of lNH can be represented by the following

equation.

� \

N \_----CONHNH> 'L_

-

Among the six acylhydrazides studied, four of them, viz., benzohydrazide

(BH), 2-hydroxybenzohydrazide (2HBH}, 4-nitrobenzohydrazide ( 4NBH) and

isonicotinohydrazide (INH) decompose in two stages, while the remaining two, viz.,

4-hydroxybenzohydrazide (4HBH) and 3-nitrobenzohydrazide (3NBH) decompose

in three stages. A comparison of the decomposition parameters for the first stage

decomposition of these hydrazides are summarized in Table 3.6. All the six

acylhydrazides decompose completely to give gaseous products. and hence, no

residue is left behind in each case. 4-Hydroxybenzohydrazide has the highest

thermal stability (-240°C), ,vhile benzohydrazide is the least stable (-l 20°C) among

the six. The thermal stability order of the six acylhydrazides is as given below.

4NBH (190°C)

> 3NBH(170°C)

= INH >

(l 70°C) 2HBH >

( 150°C) BH

(120°C)

The above stability order can he justified as discussed below. In hydrazine

the repulsion between the lone pairs of electrons on the N atoms destabilize the N-N

Tl


bond1 . Substituents on N can, therefore, alter the N-N bond scission. Electron

releasing groups favour N-N cleavage, while electron attracting groups strengthen

the N-N bond. In acylhydrazides, the C=O group imparts some stability to N-N bond

due to decrease in lone pair-lone pair repulsion compared to hydrazine.

I .. RC =NH-NH2

This, in tum, can be influenced by the nature of R in hydrazide derivatives.

Substituted benzoyl derivatives have greater stability than the unsubstituted

benzohydrazide (BH). Substitution at the para or meta position ( 4HBH, 4NRH and

3NBH) brings about greater stability than the substitution at the ortho position

(2HBH), where steric factor also operates.

3.2 Thermal behaviour of urea nitrate

Ammonium nitrate (AN) is considered as one of the important propellant

oxidizers like ammonium perchlorate (AP). But AP is an air pollutant as it gives out

a large amount of hydrogen chloride gas in the exhaust. Moreover, AN is highly

hygroscopic and undergoes crystal phase transition around 32°C resulting in

undesirable dimensional changes at the operation temperature leading to crack

formation 150. However, urea nitrate (UN) containing 34.13% nitrogen is reported to

have a negative enthalpy cf fonnation (-134 kcal mor 1) 151, whereas the enthalpies of

formation of AN and AP are -87 kcal mor' and-70 kcal mor 1 , respectively150. But

UN can be easily prepared and is quite stable with low friction and shock

sensitivity154 . It melts with decomposition at l 52°C, and is considered as an

explosive compound151 · 152.

Thermal decomposition study of urea nitrate using TG and OT A techniques

suggests the probability of the existence of NH4NCO.HN03 in equilibrium with urea

nitrate at high temperature, which expels the weak acid HOCN151.

73


The NH4N03 formed melts and then decomposes to N20 and H20.

A fast thermolysis study also supports the formation of NH4N03 by suggesting two

different pathways for its thermal decomposition as 152,

(Path I)

(Path II)

Path I represents an endothennic, low temperature channel, and Path II represents an

exothennic and high temperature channel. The products fonned, NH3 and HNCO

may combine to fonn NH4NCO. Since no oxygen is released in any of the stages of

its decomposition, it is seldom used as an oxidizer for fuels 1• But because of its

explosive nature, the effect of UN on the thermal behaviour of hydrazides has been

undertaken for investigation. Moreover, the intermediate formation of NH4N03

(AN) in its thermal decomposition eliminates the disadvantages of the hygroscopic

nature of AN.

Thermal decomposition studies of UN have been carried out using TG-DT A

techniques and the kinetics of the decomposition reaction has been done, which are

given in Appendices I and II. The compound is stable up to - l 40°C, and then it

decomposes in three stages as denoted by the OTG peaks at 161, 242 and 293 °C, and

the corresponding OT A peaks at 163, 242 and 295°C. The first decomposition stage

occurs in the temperature region 140 - l 70°C with mass loss of 39 .8% and DTG peak

height of 0.92 mg min-1 at 161 °C. The OTA peak corresponding to the first

decomposition stage is very peculiar in that there is an endothermic peak at l 57°C,

which is followed by an exothennic peak at I 63°C. The second decomposition stage

is endothennic, while the third decomposition stage is exothermic in nature. These

two decomposition stages occur in the temperature regions I 70 - 260°C and 260 -

300°C respectively with the corresponding mass losses of 54.9% and 5.3% and the

OTG peak heights of 0.38 mg min-1 and 0.05 mg min-1at 242 and 293°C. The total

74


mass loss for the decomposition of UN is 100.0% indicating complete decomposition

into gaseous products. The results obtained in the present studies are in agreement

with those reported earlier151•

The activation parameters for the thermal decomposition reaction of UN

indicate a high value of energy of activation (330.9 kJmor1) for the thermal

decomposition of urea nitrate (Appendix II). This accounts for the high stability of

urea nitrate. If activated it decomposes owing to greater decomposition tendency as

indicated by the high values of pre-exponential factor (2.6x 1038) and entropy of

activation (487.5 JKmor1 ). This property of UN has been exploited in the thermal

decomposition of hydrazides by mixing them with UN.

3.3 Thermal behaviour of acylhydrazides in presence of urea nitrate

Binary mixtures of acylhydrazides and urea nitrate (5% w/w) have been

studied using simultaneous TG-DT A techniques with a view to study the effect of

urea nitrate on the thermal behaviour of acylhydrazides. The TG, DTG and DT A

curves of these six binary mixtures are presented in Figs 3 .1 c - 3 .6c. The changes in

the TG, DTG and DTA curves caused by 5% UN are summarized in Tables 3.5-3.6.

In all the cases, the decomposition products are expected to be CO2, N2, H20 and

oxides of nitrogen such as NO, N02 or N20. The salient feature of the thermal

behaviour of the binary mixtures of acylhydrazides and urea nitrate (UN) are

discussed under the following sub-headings.

3.3.1 Benzohydrazide-UN mixture

Benzohydrazide in presence of UN (5% w/w) is stable up to -120°C, and

then it decomposes in two stages, which are denoted by the DTG peaks at 187 and

243°C, and the corresponding endothermic DTA peaks at 190 and 240°C (vide Fig

3.lc). The sample melts at 108°C prior to decomposition as indicated by the

additional endothermic DT A peak at this temperature. The first decomposition stage

takes place in the temperature region 120 - 220°C with a mass loss of 75.0% and the

DTG peak height of 0.46 mg min- 1 at I 78°C. The second decomposition stage

occurs in the temperature region 220 - 290°C with a mass loss of 25.0% and the

75


DTG peak height of 0.22 mg min-1

at 243°C. Both the decomposition stages are

continuous without any stability region between them, and the total mass loss is

100.0% confirming that no residue is left behind. There is appreciable changes in

the TG, DTG and DT A curves of both pure BH and BH in presence of UN, although

the decomposition takes place in both the samples in two stages and the stability of

the sample remains the same at -120°C ( vide Table 3 .5). The DTG and DT A peak

temperatures are lowered for the sample mixed with UN. The melting point of BH is

lowered by 7°C with the addition of 5% (w/w) UN. The mass loss for the first

decomposition stage is diminished from 89.2% to 75.0% in the presence of UN (vide

Table 3.6). It is observed that the decomposition of BH is enhanced appreciably by

UN compared to pure BH. The decomposition reaction of BH in presence UN is

represented by the following equation.

3.3.2 2-Hydroxybenzohydrazide-UN mixture

2-Hydroxybenzohydrazide (2HBH) when mixed with UN (5% w/w) is stable

up to -150°C, and thereafter, it decomposes in two stages as denoted by the DTG

peaks at 223 and 320°C, and the corresponding endothermic OT A peaks at 189 and

321 °C (vide Fig 3.2c). The additional endothennic OTA peak at l 39°C corresponds

to melting of the sample prior to decomposition. The first decompo:;ition stage

occurs in the temperature region 150 - 250°C with a mass loss of 49.1 % and the

DTG peak height of 0.35 mg min-1 at 223°C. The second decomposition stage takes

place in the temperature region 250 - 330°C with a mass loss of 50.9% and the DTG

peak height of 0.80 mg min-1 at 320°C. There is no TG plateau between the two

decomposition stages, and the total mass loss . obtained for the complete

decomposition of 2HBH is 100.0%. There are distinct changes in the TG, DTG and

DTA curves of2HBH with the addition of UN and in the absence of UN, although in

both the cases the decomposition takes place in two stages (vide Table 3.5). The

melting point of the sample is lowered from 149°C to l 39°C with the addition of 5%

{w/w) UN. Also, the OTG and OTA peak temperatures are shifted to lower

76


temperatures due to UN. However, the stability of the sample remains unchanged at

-150°C even in the presence of UN. Thus, UN enhances the decomposition of the

sample as in the case of BH. The thermal decomposition reaction of 2HBH in

presence of UN can be represented by the following equation.

02 -�>- 8C02 + N2 + N20 + NH3 + 5H20

3.3.3 4-Hydroxybenzohydrazide-UN mixture

4-Hydroxybenzohydrazide(4HBH) in presence of UN (5% w/w) is thermally

stable up to -150°C. Then it decomposes in two stages as denoted by the DTG

peaks at 305 and 547°C, with the corresponding endothermic DTA peak at 293°C

and exothermic DT A peak at 54 7°C ( vide Fig.3 .3c ). The additional endothennic

DT A peak at 250°C indicates melting of the sample along with decomposition. The

first decomposition stage occurs in the temperature region 150 - 430°C with a mass

loss of 55.2% and the DTG peak height of 0.16 mg min-' at 305°C. The second


loss of 43.4% and the DTG peak height of 0.17 mg min-' at 547°C. There is no

stability region between the two decomposition stages. The total mass loss is 98.6%,

and there is no residue left behind after -590°C. There are marked changes in the

TG, DTG and DT A curves of 4HBH with the addition of UN compared to those of

pure 4HBH. The stability of the sample is dropped from 240°C to l 50°C, and the

DTG and DTA peaks are lowered very much with the addition of UN (vide Table

3.5). The melting point of the sample is reduced from 267°C to 250°C in presence of

UN. Here also, UN reduces the stability of the sample. The decomposition reaction

of 4HBH-UN mixture can be represented by the following equation.

02 C6H4(0H) CONHNH2 + NH2CONH2.HN03 - ->- 8C02 + N2 + N20 + NH3 + 5H20

3.3.4 3-Nitrobenzohydrazide-UN mixture

On mixing with UN (5% w/w) 3NBH is stable up to -170°C, and then it

decomposes in three stages. These three decomposition stages as denoted by DTG

peaks at 239, 330 and 574°C, and the corresponding exothermic DTA peaks at 237,

77

Chapter 111: Thermal analysis of acylhydrazides

329 and 577°C (vide Fig 3.4c). The first decomposition stage occurs m the

temperature region 170 - 300°C with a mass loss of 33.1 % and the DTG peak height

of 0.15mg min- 1 at 239°C. The second decomposition stage takes place in the


of 0.31mg min- 1 at 330°C. The third decomposition stage occurs in the temperature

region 400 - 590°C with a mass loss of 22.4% and the DTG peak height of 0.09 mg

min- 1 at 574°C. All the three decomposition stages are parts of a continuous

decomposition process as there are no stability regions between these decomposition

stages. Although there is no change in the stability of 3NBH with the addition of

UN, there are marked changes in the TG, OTG and OTA curves in comparison

with those of pure 3NBH. The OTG and OT A peaks are lowered in presence of

UN. The melting point of the sample is reduced from 153 to 142°C with the addition

of UN. These changes show that 3NBH is destabilized by UN as in the cases of the

previous samples studied. On the basis of the data available, the 3NBH-UN mixture

is decomposed completely to give gaseous products as per the following equation.

02 C6H4(N02) CONHNH2 + NH2CONH2.HN03 ---> 8C02 + N2 + N02 + N20

+ NH3 + 9/2H20

3.3.5 4-Nitrobenzohydrazide-UN mixture

4-Nitrobenzohydrazide mixed with UN (5% w/w) shows thennal stability up

to -170°

C, and then it decomposes in three stages ( vide Fig. 3 .Sc). These three

decomposition stages are indicated by the OTG peaks at 232, 308 and 589°C, and the

corresponding exothermic OT A peaks at 236, 310 and 591 °C. The first

decomposition stage occurs in the temperature region 170 - 280°C with a mass loss

of 16.8% and the OTG peak height of 0.11 mg min- 1 at 232°C. The second


loss of 22.6% and the OTG peak height of 0.09 mg min- 1 at 308°C. The third

decomposition stage is the major decomposition stage, which occurs in the

temperature region 400 - 600°C with a mass loss of 55.8% and the OTG peak height

of 0.31 mg min-1 at 589°C. The decomposition is over at -600

°

C, and the total mass

loss obtained is 95.2% leaving no decomposition residue. The additional

78


endothermic DT A peak at 199°C is attributed to melting of the sample. The stability

of 4NBH is reduced from 190 to 170°C with the addition of UN. Similarly, the

melting point of the sample is reduced from 221 to 199°C in presence of added UN.

Moreover, the DTG and DT A peaks are also lowered for the sample mixed with UN

compared to those of pure sample. On the basis of the thermal decomposition data

obtained the decomposition of the mixture of 4NBH and UN can be represented by

the following equation.

3.3.6 Isonicotinohydrazide-UN mixture

8C02 + N2 + N02 + N20

+ NH3 + 9/2H20

Isonicotinohydrazide (INH) mixed with UN (5% w/w) is stable up to

-160°C. Then it decomposes in two stages as denoted by the OTG peaks at 243 and

309°C, and the corresponding exothennic OT A peak at 250°C and endothermic DT A

peak at 307°C (vide Fig 3.6c). The first decomposition stage occurs in the


of 0.25 mg min- 1 at 243°C. The second decomposition s�age is noted in the

temperature region 270 - 340°C with a mass loss of 49.6% and the OTG peak height

of 0.37 mg min- 1 at 309°C. There is no stability region between the two

decomposition stages as in the case of pure INH. The additional endothennic OT A

peak observed at 165°C indicates melting of INH along with decomposition. Total

mass loss obtained is I 00.0% indicating that both INH and UN decompose

completely to give gaseous products without any residue left behind. There are

marked changes in the TG, OTG and OTA curves of INH with the addition of UN

compared to those of pure INH. The stability of INH is decreased from 170 to

160°C, an.d ,the melting point is lowered from 170 to 165°C with the addition of UN.

The DTG and DT A peaks are also lowered for the sample mixed with UN compared

to those of the pure sample. The decomposition reaction of the sample can be

represented by the following equation.

79


02 -�-� 7C02 + N2 + NO+ N20

+ NH3 + 9/2H20

Thennal stabilities of all the six acylhydrazides are lowered with the addition

of 5% (w/w) urea nitrate, and their melting points are also lowered in comparison

with those of the pure samples. The highest stability of 4-hydroxybenzohydrazide

(-240°C) is very much lowered to I 50°C with the addition of urea nitrate, and the

stability of benzohydrazide (-l 20°C) remains the same even in presence of urea

nitrate. More over, the DTG and OT A peaks are shifted to lower temperatures for all

the six acylhydrazides mixed with urea nitrate. However, the decomposition stages

remain the same for the pure sample and the respective mixture with urea nitrate.

Urea nitrate acts as an initiator for the thennal decomposition of acylhydrazides, and

the reaction is more exothennic than in the cases of the pure samples. On the basis

of the plateau in TG and DTG peak temperature, the following stability order is

found for the six acylhydrazides in presence of urea nitrate.

3NBH (170°C)

4NBH (170°C)

> INH(160°C)

3.4 Kinetics and mechanism

> 4HBH(l 50°C)

= 2HBH (150°C)

> BH(120°C)

The kinetics and mechanism of thennal decomposition reactions of

acylhydrazides and their mixtures with urea nitrate (5% w/w) have been studied, and

the results of these studies are discussed under the following sub-headings.

3.4.1 Kinetics of thermal decomposition of acylhydrazides

The kinetic parameters for the thermal decomposition reactions of all the six

acylhydrazides have been evaluated using the Coats-Redfern equation�2 as well as

the mechanistic equations proposed by Satava87 (vide Table 3.3). The Coats-Redfern

plots for the decomposition reactions of acylhydrazides are presented in Figs 3.1 b -

3.6b. The values of order parameter for the various decomposition stages of the six

acylhydrazides are in the range 1.0 - 2.0 with fractional orders in some of the

decomposition stages. The values of activation energy for the first decomposition

80


stages fall in the range 164 - 288 kJ mor 1 with the lowest value (164.0 kJ mor 1)

for benzohydrazide and the highest value for 4-nitrobenzohydrazide. The values of

activation energy for the second decomposition stages are in the range 274 - 544 kJ

mor 1 with the lowest value (274.7 kJ mor 1) for isonicotinohydrazide and the highest

value (543.5 kJ mor 1) for 4-nitrobenzohydrazide. Among the six acylhydrazides

studied, only two of them, viz., 4-hydroxybenzohydrazide and 3-nitrobenzohydrazide

have third decomposition stages, for which the values of activation energy are 898.1

kJ mor' and 462.8 kJ mor', respectively.

The values of pre-exponential factor for the various decomposition stages of

the six acylhydrazides are in the range 10 15 - 1054

, with the lowest value

(2.8xl0 15 s- 1) for the first decomposition stage of benzohydrazide and thf. highest

value (9 .2x l 054 s- 1) for the third decomposition stage of 4-hydroxybenzohydrazide.

The values of entropy of activation are all positive indicating that the activated

complexes are "less ordered" than the reactants, and hence, the reaction is "faster"

than normal. The lowest value of entropy of activation (46.7 JK mor 1) is obtained

for the first decomposition stage of benzohydrazide and the highest value (798.6 JK

mor 1) is obtained for the third decomposition stage of 4-hydroxybenzohydrazide.

The correlation coefficients are very close to unity for all the decomposition stages

of the six acylhydrazides studied.

The mechanisms of all the decomposition stages have been elucidated, and it

is found that all the reactions have the same mechanism of random nucleation with

one nucleus on each particle. The kinetic parameters have also been evaluated using

the Mampel equation (vide Table 3.3). The values of these kinetic parameters are

comparable with those calculated using the Coats-Redfern equation.

3.4.2 Kinetics of thermal decomposition of acylhydrazide-UN mixtures

The kinetic parameters for the decomposition reactions of the mixtures of

acylhydrazides and urea nitrate have been evaluated using the Coats-Redfern

equation as well as the mechanistic equation proposed by Satava (vide Table 3.4).

The Coats-Redfern plots for these decomposition reactions are depicted in Fig.3.l d -

81


3.6d. The values of order parameter are in the range 1.0 - 2.0 with fractional values

in many cases. The values of activation energy are in the range 14 7 - 618 kJ mor 1

with the lowest value (1 47. 1 kJ mor 1 ) for the first decomposition stage of

benzohydrazide-UN mixture and the highest value (61 7. 4 kJ mor 1) for th� third

decomposition stage of 4-nitrobenzohydrazide-UN mixture. The values of pre

exponential factor are in the range 1014 -1044 with the lowest value (3. 9x l014 s- 1) for

the first decomposition stage of isonicotinohydrazide-UN mixture and the highest

value (8. lx 1044 s- 1) for the second decomposition stage of 2-hydroxybenzohydrazide

UN mixture. The values of entropy of activation are positive in all the decomposition

reactions of all the six samples studied. The lowest value of entropy of activation

(29.9 JK mor 1) is observed for the first decomposition stage of isonicotinohydrazide

UN mixture, and the highest value of entropy of activation (609.1 JK mor 1) is for the

second decomposition stage of 2-hydroxybenzohydrazide-UN mixture. The values

of correlation coefficient are very close to unity for all the decomposition reactions

of the six mixtures. All the decomposition reactions of the samples follow the

mechanism of random nucleation with one nucleus on each particle obeying the

Mampel equation. The kinetic parameters evaluated using the Mampel equation are

comparable with those calculated using the Coats-Redfern equation.

4. Summary and conclusion

Six acylhydrazides, viz., benzohydrazide (BH), 2-hydroxybenzohydrazide

(2HBH), 4-hydroxybenzohydrazide (4HBH}, 3-nitrobenzohydrazide (3NBH),

4-nitrobenzohydrazide ( 4NBH) and pyridine-4-carbohydrazide or isonicotino

hydrazide (INH), and their binary mixtures with urea nitrate (5% w/w) have been

studied using simultaneous TG-DTG-DTA techniques with a view to compare their

thermal behaviour and to study the effect of urea nitrate (UN) on the thermal stability

of these six acylhydrazides.

Among the six acylhydrazides studied, four of them, viz., benzohydrazide

(BH), 2-hydroxybenzohydrazide (2HBH), 4-nitrobenzohydrazide ( 4NBH) and

isonicotinohydrazide (INH) decompose in two stages, while the remaining two, viz.,

4-hydroxybenzohydrazide (4HBH) and 3-nitrobenzohydrazide (3NBH) decompose

82


in three stages. All the six acylhydrazides decompose completely to give gaseous

products, and hence, no residue is left behind in each case. 4-Hydroxybenzo

hydrazide has the highest thermal stability (-240°C), while benzohydrazide is the

least stable (-l 20°C) among these hydrazides. The thermal stability order of the six

acylhydrazides is as given below.

4HBH (240°C)

> 4NBH(190°C)

> 3NBH(170°C)

INH

(l 70°C)

> 2HBH >

(150°C)

BH

(120°C)

The above stability order can be justified as discussed below. In hydrazine

the repulsion between the lone pairs of electrons on the N atoms destabilize the N-N

bond 1• Substituents on N can, therefore, alter the N-N bond scission. Electron

releasing groups favour N-N cleavage, while electron attracting groups strengthen

the N-N bond. In acylhydrazides, the C=O group imparts some stability to N-N bond

due to decrease in lone pair-lone pair repulsion compared to hydrazine.

I .. -c --� RC =NH-NH2

This, in tum, can be influenced by the nature of R in hydrazide derivatives.

Substituted benzoyl derivatives have greater stability than the unsubstituted

benzohydrazide (BH). Substitution at the para or meta position (4HBH, 4NBH and

3NBH) brings about greater stability than the substitution at the ortho position

(2HBH), where steric factor also operates.

Thennal stabilities of all the six acylhydrazides are lowered with the addition

of 5% (w/w) urea nitrate, and their melting points are also lowered in comparison

with those of the pure samples. The highest stability of 4-hydroxybenzohydrazide

(-240°C) is very much lowered to l 50°C with the addition of urea nitrate, and the

stability of benzohydrazide (- l 20°C) remains the same even in presence of urea

nitrate. More over, the DTG and OT A peaks are shifted to lower temperatures for all

the six acylhydrazides mixed with urea nitrate. However, the decomposition stages

remain the same for the pure sample and the respective mixture with urea nitrate.

83


Urea nitrate acts as an initiator for the thermal decomposition of acylhydrazides, and

the reaction is more exothermic than in the cases of the pure samples. On the basis

of the plateaus in TG and DTG peak temperatures, the following stability order is

found for the six acylhydrazides in presence of urea nitrate.

3NBH (l 70°C)

4NBH (l 70°C)

> INH > (160°C)

4HBH (150°C)

2HBH (150°C)

> BH(120°C)

The kinetics and mechanism of thennal decomposition reactions of

acylhydrazides and their mixtures with urea nitrate (5% w/w) have also been studied.

The kinetic parameters for the thennal decomposition reactions of all the six

acylhydrazides have been evaluated using the Coats-Redfern equation82 as well as

the mechanistic equations proposed by Satava87 (vide Table 3.3). The Coats-Redfern

plots for the decomposition reactions of acylhydrazides are presented in Figs 3. lc -

3.6c. The values of order parameter for the various decomposition stages of the six

acylhydrazides are in the range 1.0 - 2.0 with fractional orders in some of the

decomposition stages. The values of activation energy for the first decomposition

stages fall in the range 164 - 288 kJ mor' with the lowest value ( 164.0 kJ mor') for

benzohydrazide and the highest value for 4-nitrobenzohydrazide. The values of

activation energy for the second decomposition stages are in the range 274 -544 kJ

mor' with the lowest value (274.7 kJ mor') for isonicotinohydrazide and the highest

value (543.5 kJ mor') for 4-nitrobenzohydrazide. Among the six acylhydrazides

studied, only two of them, viz., 4-hydroxybenzohydrazide and 3-nitrobenzohydrazide

have third decomposition stages, for which the values of activation energy are 898.1

kJ mor' and 462.8 kJ mor' respectively.

The values of pre-exponential factor for the various decomposition stages of

the six acylhydrazides are in the range 10 15 - 1054

, with the lowest value

(2.8xl0 15 s- 1) for the first decomposition stage of benzohydrazide and the highest

value (9.2xl054 s- 1) for the third decomposition stage of 4-hydroxybenzohydrazide.

The values of entropy of activation are all positive indicating that the activated

complexes are "less ordered" than the reactants, and hence, the reaction is "faster"

than normal. The lowest value of entropy of activation (46.7 JK mor') is obtained

for the first decomposition stage of benzohydrazide and the highest value

84


(798.6 JK mor 1) is obtained for the third decomposition stage of 4-hydroxybenzo

hydrazide. The mechanisms of all the decomposition stages have been elucidated,

and it is found that all the reactions have the same mechanism of random nucleation

with one nucleus on each particle. The kinetic parameters evaluated using the

Mampel equation (vide Table 3.3) are comparable with those calculated using the

Coats-Redfern equation.

The kinetic parameters for the decomposition reactions of the mixtures of

acylhydrazide and urea nitrate have been evaluated using the Coats-Redfern equation

as well as the mechanistic equation proposed by Satava (vide Table 3.4). The Coats

Redfern plots for these decomposition reactions are depicted in Fig.3 .1 d - 3 .6d. The

values of order parameter are in the range 1.0 - 2.0 with fractional values i11 many

cases. The values of activation energy are in the range 14 7 - 618 k:J mor 1 with the

lowest value (147.1 kJ mor1) for the first decomposition stage of benzohydrazide

UN mixture and the highest value (617.4 kJ mor 1) for the third decomposition stage

of 4-nitrobenzohydrazide-UN mixture. The values of pre-exponential factor are in

the range 10 14 -1044

with the lowest value (3.9x1014

s-1) for the first decomposition

stage of isonicotinohydrazide-UN mixture and the highest value (8.lx1044 s- 1) for the

second decomposition stage of 2-hydroxybenzohydrazide-UN mixture. The values of

entropy of activation are positive in all the decomposition reactions of all the six

samples studied. The lowest value of entropy of activation (29.9 JK mor 1) is

observed for the first decomposition stage of isonicotinohydrazide-UN mixture, and

the highest value of entropy of activation (609.1 JK mor1) is for the second

decomposition stage of 2-hydroxybenzohydrazide-UN mixture. All the

decomposition reactions of the samples follow the mechanism of random nucleation

with one nucleus on each particle obeying the Mampel equation. The kinetic

parameters evaluated using the Mampel equation are comparable with those

calculated using the Coats-Redfern equation.- �

85

..


mgmui1

ii,�':".:.·:.··,:.·.:.:.·.:.t� ... "·1·•11,

,,,, ·�·\.,,,, , .. ·--··-·-···----------------·---•·O.

115

', .... \ .:

'\ r, : \ \ : '-,/

, , 1 2 a

\ \ : ,� \ \ I

\ \ :

\ \ j I I I \ \ I I I I

\ \:

•O. I

@•O, I

-•-3

..... I i'\ \: �---·--···�,-----···· , i. ·v

... ,

'··,.,., 2" ···, , ....... - ..... __

... , .. , .......................... .

•c

•I

. .. ., ·-- ....

T empm.ture (Cle)

Fia,3.la TG-DTG-DTA curves ofBH

.....

....

•• UI a.• Z.11

"exo

{ff

iil .. ..

.

a.•

,.� ,.� 4-lf·

. M•


.. "II'.;.,." .... --- ... : • • ...... � ·� • • •• •. . • • • -- • - .•• - - • - -�g ��

l

..... - ... ;

\\ ....

\ \\

\ \ .....

. • l ., :

i ·� :

/ I I

. . elm

dt

&•

---........._ � , , •, -----.., �i ' •• ,-:,2'.rv1·�-----------------#---f

I: I \ I· \ : ',o

��8 ; \1"1.. V

�

! \,I I •, 2,&I) � m: ·, G \ \ A \ I \ I

I • . .\.,. \ _. . :

·�· ......... 18?

,- : I I • I I r J 11 --, y-,r-;-.........-,-,-1 •

·i

... -�-

n ao. '"" z,., .t5II Jct · ,1n ;:,c. ·'c

Temperature (°C)

Fig. 3.lc TG- DTG-DTA curves ofBH-UN

-10

-14

Smgell

1.5 2.0

(11T)x1G3

-]ig. 3.ld C.R plot for the thermal decomposition of BH-UN

87

"exo

{ff

.,


,,. •+h•·u"'•·•.- . •• •,-.

--- ... --- ........... ,, ............ •, ", ',

\ \

\ \ ' '. \

• • • P' • ,. .. *

1•�. I t t \.

\ � I :

....

�--��-------��-;t�-

0-;

Aexo

8T

f :1 l.U

' \ I I \ l I ' \ i

I • t

' \: \ ... , ' :. I

Il .,. ' I '

� . .. 1' • 233

311

········ '''''• ' ...... -

... s

i -• ....

. . . . . . ..... � ...... ·O. I:

··-

•···1 ··,�·--r··T··-r,--y-,,-1�1 ,.. ,u :t•o

; I • I I I r.,.,--...,..,...,.......... .. ' ' . r,�·-.---··,· . ' .... ; 111 :l4Mt J!Ja 4M ••• 1"• UII

Temperature c0c)

Fig. 3.2a TG� DTG-DTA curves of2HBH

-12lllgtll

·1'4

·1& ...... ----.....-----.,------------,

1.5 2.5

Fig. 3.2b C.R plot for the thermal decomposition of 2HBH

88

l·


-"!, ............. .: :.!-·.:.: ::· ... .. , ···.,.. ... ,\ . ' .

", ... \ . ·.' ·. l ' \

/ ....... , .... , ' ' ' I I I

I I I

' •. ' ' \ �' .. , \ ), 2ii'·· .•.

' I I I

I

\1 ·�

I I

If._ I '·'b .• th I 't (/ r C

,• • • - ... - ... • .. - • - • • • _, - - - - - ...... CL

' . I • I

-----------::--:-r-..,,...' "exo..0,4 .. ,

� QT

-a�

ll .. · .. ,, ... . , .. ..... . ·•••�- •• ., •• , •· ........ ,.,.��••>''tD,, . .. �u,u.._, ... 'I

320

rr"T"T ....... ...,.....,...,......,..T'T-.-,-r-,r-r-.,...,..-r-T-r-r-r,n--,r-r..-rT'T.,.-;-,-,,...·.,....,.,......,··� ....... �....+ ......... ...,...,.+ 00 HO Sta 41/f. •t

1

i

I S6 no

Temperature (CC)

Fig. 3.lc TG-DTG-DTA curves oflHBH-UN

.... ,

-12.... 1,

-14'

·11-t-��--�--�---.-�----�...---��--.

u 2.0

(11T)X1a3 2.5

Fig.3.ld C.R plot for the thermal decomposition oflHBH-UN

89


'

\

\ I I

I

I ,

\· 2?5

. , . . . .' .... '

. ·., \ '

' .

'' ' ' ' '

-7\'·.··�5.. ·t, .

• 3?3

. ·1 mg min

,...-...................... ....,. ....... � ......... ,...,...,....,.., . • ,,...,...,-,-...--"T"T".......-y-.-,-�..,...,......-,,-,-,--..-,-.,......,.�....-.-+-�

b� I ot l'SO 2H H4 Jo. s ..

-10

-11

-12

N

I;_ -13 .s. Q

.S -14

-15

Fig. 3.3a TG - DTG - DTA curves of 4HBH

...

.1e..L---..:..-----r-----.-----:r2.0=------

1» 1J

(1fl')X1<>3

Fig. 3.3b C.R plot for the thermal decomposition of 4HBH

90


... ::-.:·�·�· ....................... . •-• n••• ...... ..

J.o

,.,

'

'

�, '

.....................

\

I \ '

··· ....... · ....

.

-..... _______ ,

Fig. 3.3c TG - D TG - D TA curves of 4HBH - UN

-10

....

\ -16

1.0 -- ...

2.0

Fig. 3.3d C.R plot for the thermal decomposition of 4HBH - UN

91

liT

..J5

..~

Chapter III: Thermal analysis ofacylhydrazides

. -1mg mm

'0.'.,,~ --- "

,- "I ~

I 'I

I,,334:,

~

I ~\,, , \ I· , ,

\, I ••• 1.'1· I • I· ,· , I I153 • · I "' .• · • 'I• · • ....• I I I .•.••.••. -020[];l] · , I• I

\ I I I '" " ..........---- DTG . I , , .........- ............... ,..' I I-DTA 2'3 I I

\ ,~ . .,..:

334

.,. ,.j I I • • • i , i ·I , I' j , I I • /100 ISO Z.. ~so "00 m +00 .110 ",00

dmdt

o

-3

"exo

AT

Fig.3.4a TG - DTG - DTA curves of3NBH

-12

.....

1.8

(11T)x1o'1.1

.....

Fig.3.4b C.R plot for the thermal decomposition of 3NBH

92


Temperature (CC)

Fig.3.4c IG - DIG - DIA curves of3NBH- UN

·10

·12

III

Slagel

2.0

(11T)x1031.5

.181----....----,..------.-----...--- ... 1.0

Fig.3.4d C.R plot for the thermal decomposition of3NBH - UN

93

, ..

,. '

-10


1.0

Ii I; I I I lH

Fig. 3.5a

\ I 221 I I

I I I I I I I '

\ I

I t \ I \ J

. , ... ,Z??

Temper a.ture (OC)

TG - DTG - DTA curves of 4NBH

.....

.....

1.5 2.0

(11T)x1e>3

Fig. 3.5b C.R plot for the thermal decomposition of 4NBH

94

"exo

• .iT,


Aexo

.c..mgmin-

1 I0.00 .:n 591

-0. ZS

....... TG

---- DTG-DTA

1$.:loouo100

t.o

2.•'till 1-------.....g5 1~'~

a.,

Fig.3.5c IG - DIG - DIA curves of4NBH-UN

-12

..."

u(1fT)x103

2.0 2.5

Fig.3.5d C.R plot for the thermal decomposition of 4NBH - UN

95

Chapter Ill: Thennal analysis of acylhydrazi.des

t15

' . , r , r ' / I ,

I I

-"• • 0,,,••••,.,.,,,,, ___ ,,,,0.0,0 •••-•�•••••••••-·•-••••H• ••

- -

·«.

t t

-(1...1 r

.t ..

·ci.s:j

C.R plot for the thermal clecamposition. of INH

96

·. I

e=x:

t!r

.a.J I 1

--4

·j"t:

Cltrapkr Ill: 11t~rmdlmmlysis rq(idiCylhj>JNzMes.- - ~ ..

•

'.'It

•• t

'. ,

·o.t

......., .."

....... TO==== DiO_orA

III ft\U\"._ __ :10 So .. Ill" .",

~...•II

•IIIIIII

I,.....,,\ :" 1\ t. .. ... 31" ,

,', I

'. \, II \ I• \ I, ...'. ~'. ."," .' ~~~ , ", ~.,/ ••'II·'J~'1'UItHI:'I"."'.""'~

SG'

166

"~'=;:'~::::-'.~'"''''''... '.... ,,~''.\\

" \\\

\\

'.0

'"s. ..

~.o

•. 0

Fig.3.6c TG - DTG - DTA curves ofINH = UN

·10

811gt1

·12

N

~f

·14

.....

u.'.~+------------.....-----1.1

(1fT)x1oJ

Fig.3.6d C.R plot for the thermal decomposition ofINH· 1m

97

T<.J-DTG-DTA data of the thermal decomposition of acylhydrazidesI °

.l.aOle j • .l

* exothermic change

(Heating Rate= lOoC min' , Sample mass - 3 mg, Temp. range 30-600 C)

Compound Plateau Decom- DTGoeak DTA neak massin TG position temp. width height temp. width loss Tentative phenomenon( 0c) Stage ( 0c) ( DC) m2min'I ( 0c) (%)BH Up to 120 - - - 115(m) 115-125 - melting- I 225 120-240 0.68 229 210-240 89.2 decompositionII 269 240-280 0.12 270 260-275 10.8 oxidative decompositionAfter 280

t Up to 150 - - - 149(m) 145-165 - melting followed by2HBH - I 233 150-250 0.68 238 190-250 86.1 decompositionII 309 250-320 0.16 311 295-320 13.9 decompositionAfter320

Up to 2404HBH - I 275 240-330 0.27 267(m,d) 265-295 48.8 melting with decomposition- II 365 330-420 0.15 373 370-390 20.3 decomposition- III 569 420-580 0.13 566* 535-600 29.9 oxidative decompositionAfter 580

Up to 170 - - - 153(m) 150-170 - melting3NBH - I 263 170-300 0.24 249* 240-260 48.2 decomposition- II 334 300-400 0.26 334* 330-350 30.7 oxidative decompositionIII 552 400-590 0.06 540* 490-590 19.2 oxidation of residual carbonAfter 590Up to 190 - - - 221(m) 215-240 - melting

4NBHI 277 190-390 0.22 280* 270-300 54.9 decomposition

-- II 592 390-600 0.20 594* 530-600 37.4 oxidation continuing

Up to 170 - - - 170(m) 165-185 - meltingINH

I 249 170-270 0.46 255 250-265 71.3 decomposition-- II 307 . 270-320 0.24 310 305-315 26.2 decompositionAfter 320

Table 3.2 TG-DTG-DTA data of the thermal decomposition of acylhydrazide-UN mixtures(Heating rate = 10°C min'l, Sample mass -3 mg, Temp. range 30-600°C)

• exothermIC change

Plateau Decomposi DTG peak DTA peak massCompound in TG -tion Stage temp. width height temp. width loss Tentative phenomenon

+UN (DC) tc) (DC) (ml!min· l) (DC) (DC) (%)

Up to 120 - - - 108(m) 100-110 - meltingBU - I 187 120-220 0.46 190 180-200 75.0 decomposition

- II 243 220-290 0.22 240 235-250 25.0 decompositionAfter 290Up to 150 - - - 139(m) 130-150 - melting2UBU - 1 223 150-250 0.35 189& 185-200 49.1 decomposition

II 320 250-330 0.80 321 310-330 50.9 decompositionAfter 330Up to 150 - - - 250(m,d) 240-260 - Melting with decomposition

4UBU 1 305 150-430 0.16 293 290-300 55.2 decomposition- II 547 430-590 0.17 547* 530-570 43.4 oxidative decomposition

After 590

Up to 170 - - - 142(m) 140-155 - Melting with decomposition- I 239 170-300 0.15 237* 230-245 33.1 decomposition

3NBU - II 330 300-400 0.31 329* 320-340 41.9 oxidative decompositionIII 574 400-590 0.09 577* 560-590 22.4 oxidative decomposition

After 590Up to 170 - - - 199(m) 190-210 - Melting with decomposition

- I 232 170-280 0.11 236* 225-245 16.8 decompositionII 308 280-400 0.09 310* 295-325 22.6 oxidative decomposition4NBUIII 589 400-600 0.31 591* 570-590 55.8 oxidation continuing

After 600Up to 160 - - - 165(m) 150-170 - melting

- I 243 160-270 0.25 250* 245-255 50.4 decompositionINU - II 309 270-340 0.37 307 300-310 49.6 decomposition

After 340

oo

Table 3.3

Compound

BB

2HBH

0 4HBH

3NBH

4NBH

INH

Kinetic parameters for the thermal decomposition of acylhydrazides

Decomposi-tion Stage n

I 1.0

II 1.0

I 1.5

II 1.0

I 2.0

II 2.0

III* 2.0

I* 2.0

II* 1.5

III* 2.0

I* 2.0

II* 1.8

I 1.6

II 1.0

Non-mechanistic( Coats-Redfern) Equation

E

(kJmol"1)

164.0

309.5

170.7

303.5

237.9

373.7

898.1

244.8

344.4

462.8

287.8

543.5

194.2

274.7

A (s-1)

2.8xl01'

6.4X ]O.!X

l.2x I 0 10

3.8x!o.!>

3.0x!O.:u

3.4x IO""

9.2x I 0'4

9.7x!O"j

9.8xI0· 1

9. lx 10-'

3. I xi 0.:,

2.8xl0' 1

7.9xl0 17

1.lxlO"j

AS Corr.

(JK1mo1" 1

) Coeff.

(r)

46.7 0.9994

301.6 0.9999

75.1 0.9994

239.3 0.9999

142.1 0.9994

314.1 0.9962

798.6 0.9973

190.3 0.9999

284.9 0.9999

281.8 0.9999

237.9 0.0999

348.3 0.9993

93.1 0.9993

190.6 0.9998

Mechanistic Equation( Model-Fl)

E A (s-1) AS (kJmol"1) (JK

1mor1

)

164.0 2.8x!O" 46.7

309.5 6.4x IO.;� 301.6

151.4 8.2x!Ou 17.0

303.5 3.8xIO·' 239.3

166.0 2.5xl015 6.4

249.0 5.6xl0 1' 107.7

673.9 4.4x!O�u 524.4

190.1 l .5xl011 79.1

289.4 l .2x I O"j 190.7

376.4 1.4x 10-- 170.5

201.8 l.Ox!0 11 75. 6

438.6 5.9x!O"� 220.5

164.7 5.lxl014 31.9

274.7 l. lxlO.:J 190.6

E= energy of activation, A= pre exponential factor, AS = entropy of activation, n= order parameter,* exothermic stage

Corr. Coeff.

(r) (J

0.9939

0.9999

0.9984 ::::::�

0.9999

0.9948

0.9970

0.9893

::-3

s::i.......

� t,j

0.9986

0.9987

E:;·

� s::i

0.9986

0.9973

0.9997 t,j

0.9978

0.9998

0 N

Table 3.4

Compound +UN

BH

2HBH

4HBH

3NBH

4NBH

INH

Kinetic parameters for the thermal decomposition of acylhydrazide-UN mixtures

Non-mechanistic (Coats-Redfern) Equation Mechanistic Equation( model-Fl) Decomposi-tion Stage n E A (s"1) AS Corr. E A AS Corr.

(kJmof1) (JK"1mor0 Coeff. (kJmol"1) (s-1) (JK1mor1) Coeff.

(r) ( r)

I 1.5 147.1 1.2x 10 15 40.4 0.9993 141.5 3.2xl0 14 29.11 0.9989

II 2.0 186.7 5.7x 1016 71.3 0.9994 182.5 9.3xl0 14 37.1 0.9981

I* 1.6 164.5 7.3xl015 54.5 0.9995 140.9 l.3x l Ou 2.2 0.9984

II 1.5 526.8 8.lxl044 609.1 0.9999 475.6 1.8xl04U 520.2 0.9996

I 1.0 218.3 6. 8xl017 90.9 0.9999 218.3 6. 8x10" 90.9 0.9999 ·-

II* 1.5 398.8 3.6xl0.;3 197.6 0.9994 336.9 2.6xl0 19 118.4 0.9974

I* 2.0 247.5 I.IX 1023 191.7 0.9994 170.8 l.OxlO" 38.1 0.9938

II* 1.7 368. 5 l .7xl030 328.1 0.9999 279.4 l .8x lo-- 175.1 0.9974

III* 1.5 585.6 2.3xl034 404.4 0.9999 495.8 4.5xl0"" 294. 9 0.9989

I* 1.4 170.9 8.5xl0 15 55. 7 0.9997 147.8 2.4xJO U 6.69 0.9988

II* 1.7 234.5 3.7xl01� 105.0 0.9999 180. 6 4.lxJOu IO.I 0.9977

III* 2.0 617.4 J.9x I 036 441.0 0.9999 482.5 4.9xl0�1 276.5 0.9978

I* 1.7 160.4 3.9xl0 14 29.9 0.9992 176.3 2.2x10'0 63.5 0.9970

II 2.0 281.8 I. 9x I 0�4 213.8 0.9999 213.7 4.6xl0" 87.7 0.9987

E= energy of activation, A= pre exponential factor, AS= entropy of activation, n= order parameter, *exothermic stage

()

-§ �

��

Cl

Cl :::: Cl

r:;·

Cl

:::::: � � Ei

c..,

0 l..,.)

Table3.5 Effect of 5% UN in the TG, DTG and DTA data for the first sage decomposition

of acylhydrazides

, ,

t Upper limit of initial Melting temp. DTG peak temp. DT A peak temp. DTG peak height TG plateau (Tm) (0C) (Ts) (0C) ("C) (mgmin·1)

Sample Ti(0C)

pure mixture pure mixture pure mixture pure mixture pure mixture

120 120 115 108 225 187 229 190 0.68 0.46 BB

2HBH 150 150 149 139 233 223 238 189 0.68 0.35

4HBH 240 150 267(d) 250 275 305 267 250 0.27 0.16

3NBH 170 170 153 142 263 239 249* 237* 0.24 0.15

4NBH 190 170 221 199 277 232 280* 236* 0.22 0.11

INH 170 160 170 165 249 243 255 250* 0.46 0.25

* exothermic change

a >§ � ;::::�

�

s:::i -

s:::i :::: s:::i

'?"' ;;;· �

� s:'..e §-

"'

�

Table 3.6 Comparison of the thermal decomposition parameters for the first stage decomposition of

acylhydrazides (values for UN mixtures are given in parenthesis)

parameter BH 2HBH 4HBH 3NBH 4NBH INH

225 233 275 263 277 249 Ts(0C) ( 187) (223) (260)* (239) (232) (243)

-

maximum rate 0.68 0.68 0.27 0.24 0.22 0.46 (mg min-1

) (0.46) (0.35) (0.16) (0.15) (0.11) (0.25)

0/o mass loss 89.2 86.1 48.8 48.2 54.9 71.3 (75.0) (49.1) (55.2) (33.1) (16.8) (50.4)

E(k.Jmor1) 164.0 170.7 237.9 244.8 287.8 194.2 (147.1) (164.1) (218.3) (247.5) (170.9) (160.4)

A (s-1) 2.8x10 15 l.2xl0 16 3.0xl020 9.7xl023 3. lx1025 7.9xl0 17

(1.2x 10 15) (7.3xl 015) (6.8x10 17) ( 1.1 X 1023) 8.5xl0 15) (3.9xl0 14)

AS 46.7 75.1 I 142.1 190.3 237.9 93.1 (JK

1mor1) (40.4) (54.5) I

(90.9) {191.7) (55. 7) (29.9)

*minor peak, E activation energy, A pre-exponential factor, AS entropy of activation

Q -§ &' t::::�::a ni

t:i

t:i :::s�

1;:;·

� � s:� � �

c.,

3D Optimized structu res of acylhydrazides

2HBH

3NBH

4HBH

4NBH

c N 0 H

•••

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THERMAL ANALYSIS OF ACYLHYDRAZIDES - …shodhganga.inflibnet.ac.in/bitstream/10603/110663/9/09_chapter 3.pdf · The gaseous combustion ... from the corresponding amide by refluxing