Journal of Scientific & Industrial Research

Vol. 591July 2000, pp 575-582

Studies on Energetic Compounds- Part Nineteen: Preparation and Thermolysis of N-Methylanilinium and N,N-Dimethylanilinium

Nitrates and Perchlorates

Gurdip Singh*, lnder Pal Singh Kapoor and Smiju Jacob

Department of Chemistry, DDU G@rakhpur University, Gorakhpur 273 009, India

Received : 24 May 1999; accepted : 24 April 2000

Nitrates and perchlorates salts of N-methylaniline and N,N-dimethylaniline have been prepared and characterised. Thermal and explosive characteristi cs of these salts are studied by TG, DSC, DTA, DTG and ignition del ay measurements. Although the kinetics of thermolysis of these salts were evaluated by fitting TG data in nine mechanism-based kinetic model s but the parabolic law gives the best fits. Slow thermolysis involves proton transfer and rapid thermolysis leads to ignition to yield gaseous products.

Introduction

As a part of research programme on high energetic compounds 1

-11 (HEC) and keeping in view

their technological use in pyrotechnics, explosives and solid propellants, the preparation and thermolysis of N­methylanilinium and N,N-dimethylanilinium nitrates and perchlorates are reported. Although several perchlorates and nitrates of ring substituted arylamjnes are known 1

·7 but studies on salts of N-methyl substi­

tuted arylarrunes are not yet available in literature.

Experimental Procedure

Materials

N-Methylaniline (E-Merck), N,N-dimethyl-aniline (BDH), Cone. nitric acid (AR, Qualigens), perchloric acid (E-Merck), silica gel G (TLC grade, Qualigens), nitron (CDH) were used as received.

Preparation and Characterisation of Nitrates and Perch/orates

N-Methylanilinium and N,N-dimethylanilinium nitrates and perchlorates were prepared by the reaction

*Author for correspondence

+

...--20_'Yo_. H_N-'0''--7) OH,N(CH,)NO,

I 0 -5°C l\JJ

6'' I 20% HCIO,

RT

N- MAN

+ -, o·~'" N- MAP

Scheme 1

+ HN(CH3) 2NO,

A ( 20% HNO,

l\JJ 0 - 5°C I

""."~ - 6'' HN(CH3) 2CIO, 0 20%:~10,

N,N- DMAP

of 20 per cent HN03 with N-methyl and N,N­dimethylaniline (1:1), respectively, at 0-5°C (Scheme l). N-methylanilinium and N,N-dimethylanilinium perchlorates were prepared by reacting 20 per cent HCI04 with N-methyl and N,N-dimethylaniline ( 1: 1 ), respectively, at room temperature (Scheme 1 ). The mixture was concentrated at 60°C under rotatory vacuum evaporator (JSGW). It was cooled to obtain crystalline solids. All the four salts were recrystalised from absolute alcohol, crystals were vacuum dried and purity was checked by TLC. Moreover, these salts were characterised by gravimetric (using nitron

12 13 . reagent) and IR spectra. Their structures and physical properties are presented in Table I.

576 J SCf IND RES VOL 59 JULY 2000

T able I - Physical parame te rs, TLC and ana lytical data (using nitron reagent) and spectral d ata on N-methyl ani linium and

N,N-dimethylanilinium nitrates and perc hlorates

Compound Mol. formu la Colour M.P. TLC Rf. Analyti cal data FflR

(oC) Eluent# Spot (g.) (in KBR)

colour Experimential

(Theoreti cal)

N-methylanilinium C1HwN20 J Brownish 60 a:b Grey 0.81 0.2210 343 1 s, 2380s (N-H).

nitrate (N-MAN) needles ( II ::l) (0.2206) 2900s(CHJ), 875s(C-N).

796s(N-C), 1384s(NOJ-)

N,N-dimethylan ilinium CsH12N20 J Yellowish 78 a:b Brown 0.82 0.1004 3430b,2443s(N-H).

nitrate (N,N-DMAP) -brown (10:3) (0.10 19) 286 1 s(CH3 ), 899s(C-N).

fl at 827 ( -C), 1382s(N0J-)

N-methylanilinium C7H111NClO• Grt!enish 62 a:b:c Greenish- 0.82 0.3718 3400b ,2393s(N-H),

perchlorate (N-MAP) needles (5:7: I) black (0.3956) 2886b(CHJ), 1287s(C-N),

974s(N-C), 629.9s(CI0d

N,N-dimethylani linium CsH12NClO• Greenish- 7 1 a:b:c Brownish 0.83 0.0902 3440g, 2444s(N-H),

perchlorate black (3.5:8.5: I) (0 093 1) 2860b(CHJ), 995s, 693s (N-C),

(N,N-DMAP) fl at 899s(C-N), 630s(Cl0d

#a= chloroform, b= carbon tetrachloride, c= methanol; locating reagent -iodi ne

- ----0.8

[©J-i~j NOJ 0 .8

[ @r~~~]c•O• O.G O.G ~

0.4 N-MAN 0.4

• 0. 2 0 .2 •

t 0 ~

0.8 [ CH3] [ CH3] ©J-+:_H NO"J cgr-~~H CI04 O.G -------CH3 CH3

O,l .. N,N-DMAN 0.4 N7 N-DMAP •E I

2f.6°C 0 .2 0.2

0 240 300 3GO 420 48 180 240 300 3 6 0 4 20 480

Temperature ,°C -Fi gure I -Non-i sothermal T G of N-MAN, N,N-DMAN, N-MAP and N,N-DMAP

Thermal Decomposition Studies on Nitrates and Perchlorates

Thermal decomposition of N-methylanilinium and N,N-dimethyl-anilinium nitrates and perch lorates was carried out using following techniques .

Non-isothermal TG

TG studies on nitrates and perch lorates (wt 30 mg, l00-200 mesh) were undertaken in static air at a heating rate of 5°C/min using indigenous ly fabricated TG apparatus

14 fitted with temperature indicator cum

controller (Model CT 808T Century) and bucket type

SINGH eta/.: STUDIES ON ENERGETIC COMPOUNDS 577

platinum cmcible (h = I em and diam = l em). Per cent decomposed (a) vs temperature (0 C) plot is given in Figure I . The overall decomposition temperature are given in Table 2.

Isothermal TG

ls6thermal TG analysis of N-methylanilinium and N,N-dimethylani linium nitrates and perchlorates were carried out in static air using the same apparatus as mentioned above and 30 mg of the sample (I 00-200 mesh) at appropriate temperatures 135°C, 150°C, J65°C, 175°C for nitrates and 175°C, 190°C, 200°C, 220°C for perch I orates. Per cent decomposition (a) verses time (min) plot are shown in Figure 2 .

. 40

N - MAN

•- 13 S ° C ~-1 so•c 0-1 GS°C

t ><- 17 S°C

"6 13 1 0

.so

. 4 0

.30

N,N"-DMAN •-13S °C "' - 150° C o - 1 GSOC >< - 17S°C

20 30 40 so

12

GO

Differential Scanning Calorimetry ( DSC)

DSC thermograms on these nitrates and perchlorates were obtained on a Mettler TA 4000 in nitrogen atmosphere (flow rate 40 cm3/min) . Weighed samples (Sartorius-Werke Type 2405 electro balance, Germany) were sealed with sample sealer. A pin hole was made at the top of the lid so that the product gases could escape during decomposition. The sample and the reference pans were positioned at the centre of the holder cells and were covered with aluminium domes. The thermograms (Figure 3) were recorded at a heating rate of l 0°C/min using Hewlett Packard 7475A plotter. DSC endothermic and exothermic peaks are given in Table 2.

.2S

• N-MA P

• - 17 S°C ... - 1 90 °C 0 -200°C ><-220° C

tG 20

--G>-

.1 s

• _, 0 N,N··-DMAP •-17s~c ... - 190 ° C o- 200°C ><- 220°C

4 8 12 1 G 20

Time (min.)-

Figure 2 - Isothermal TG of N- MAN , N,N- DMAN , N-M AP and N,N-DMAP

Table 2 - Thermal analytica l data on N-meth ylanilinium and N,N-dimethylanilinium nitrates and perchlorates

TG DSC DTA DTG

Compound O veall Endothermi c L'> ll Exot hermic L'>H Peak Peak decomposition (OC) (Jig) (OC) (J/g) temperatu re temperature

(oC) (OC) (oC ) N-MA 44-253 59 63.7 202.2 1102. 3 66,212 208

,N-DMAN 78-464 7 9. 5 8 5. 5 187.7 1067 . 1 148 142

N-MAP 48-345 6 3 . 3 145.8 255.3 3973.2 83.4 , 230.8 224

N,N-DMAP 84-2 12* 72.6 I 6 . 7 244 .2 3308.3 86.3, 239 232

*Explosion temperature

57&

10

'5

0

"'g UJ

1'5

100

N-MAN

200 300

N,N -OMAN

1 SCI IND RES VOL 59 JULY 2000

400

a

~

4

2

-------I •'c 500 100

/ 1'5

10

. 5

s'oo 0

Temperat ure: , C --

N-MAP

200 300 400

N,N-DMAP

300 400

Figure 3- DSC thermograms of N-MAN, N,N-DMAN, N-MAP and N,N-DMAP

~

__ __._ 500 •c

-----

/ soo ·c

Fig. 4- Simultaneous TG, DTA-DTG thermograms of N-MAN, N,N-DMAN , N-MAP and N,N-DM AP

Simultaneous TGA-DTA-DTG Toledo TGNSDT A 851 (Switzertand) in nitrogen atmosphere (flow rate 50 cm3/mjn). Weiged empty sample pan (Alumina crucible, size 70111) tared (zeroed), then weight of the sample along with the

Simultaneous TGA-DT A-DTG thennograms on nitrates and perchlorates were obtained on a Mettler

SINGH eta/.: STUDIES ON ENERGETIC COMPOUNDS 579

Table 3- Ign iti on delay (tid),ignition temperature (IT), activation energy for ignition (E*), oxygen balance(OB) and velocity of detonation

Compound

N-MAN

N,N-DMAN

N-MAP

N.N-DMAP

t N

~

225°C

DNI

DNI

DNI

DNI

0.080

0.

0 .030

0.020

for N-methylanilinium and N,N-dimethylanilinium nitrates and perchlorates

250°C 275°C 300°C

128±3 87±2 70±1 .3

125±2 61.3±2 .9 55±3.3

DNI 114±6 .6 82.3± 1.5

DNI 96.3± 3 73.6± 2.4

B 12

tid (sec) at

325°C 350°C

56.3±1.1 46±0.6

44.6±0.6 43± 1.1

63 .6±1. 1 54.3±2.2

59 .3±1.5 49± 1.3

N-MAN 0.010

a

0,010

N,N-DMAN

o.roo

O.OOG

0.004

16

375°C 400°C

37.3±1. 1 3 1.6±1.1

39.3±0.6 36± 1.3

42± 1. 3 35 .3± 1.1

39±0.6 34±1

2

Time ( minJ -

IT

425°C (35 s)

26.3±0.9 382

33± 1.3 400

29.3±0.4 394

28±0.3 389

B

E* OB

(KJmol- 1)

25 .8 -72.7

13 .4 -76.0

27.7 -65 .2

25.4 -69.2

10

'<• • '

Figure 5 - Kineti c analysis or N-MAN . N,N-D !IAN, N-MAP and N,N-DMAP by paraboli c law

Ignition Delay and Ignition Temperature Measurements

VOD

(m/scc)

6 124

60 1-1

6377

62-12

cruc ible is observed by the inbuilt microbalance. The weight of the sample is displayed in the monitor of the computer continuously along with the temperature. The thermograms (Figure 4) were recorded at a heating rate of I5°C/min and peak temperatures from DT A and DTG plots are given in Table 2 . .

Twenty milligram of the sample was taken in an ignition tube (h = 5 em and diam = 0.4 em) and the time between the insertion of the sample tube in the

580 1 SCI !NO RES VOL 59 "J ULY 2000

tube furnace and appearance of the smoky fl ame was taken to be the ignition delay and data are given in Table 3. The activation energy (Table 3) for ignition was calculated using the following Eq (I ) (ref. 15-16) and plots are given in Figure 5.

l ict == B exp (E*IR7) ... (I)

where t;ct is the ignition delay, B is a constant, Tis absolute temperature and E* is the activation energy for ignition. The ignition temperature (/7) at 35 seconds was noted and data are reported in Table 3.

Per cent Oxygen Balance and Velocity of Detonation

The per cent oxygen balance (OB) was calculated by the Eq (2) suggested by Martin and Yallop 17 and data are given in Table 3.

OB = [( z - 2x- y/2) I 00] In ... (2)

where x, y, z are the respective number of atoms of carbon, hydrogen and oxygen and n is the total number of atoms in then molecule. Furthermore, the velocity of detonation (VOD) was calculated by the relation (3) and data are reported in Table 3.

VOD = 8578 + 33 .74 (OB) .. . (3)

Results and Discussions

It is evident from TG curvt'.o.: (in static air) presented in Figure I that N-MAN, NN-DMAN and N­MAP show weight loss (a) up to 60-70 per cent except N,N-DMAP, which explode at 266 °C. Scheme 2 represents that all these salts, except N,N-DMAP undergo thermolysis which involves N-H bond heterolysis (proton transfer) 1

-7 via an activated complex

to form parent amine and acid molecule in condensed phase. The latter then undergo oxidation-reduction rer., tions to yield gaseous products and carbonaceous residue is obtained (Scheme 2) . Rapid thermolysis involves the breaking of C-N bond to re lease methylamine and dimethylamine molecules from corresponding nitrate and perchlorate salts. Weight loses observed in TG curves and endothermic peaks of DSC, DT A & DTG (Table 2) corresponds to the removal of amine molecules. Moreover, Co-TLC with authentic samples confirmed the evolution of amine as vapours. Ion pairs formed undergo 0-N/0-CI homolytic cleavages to produce free radicals, which propagate to cause ignition forming ga-eous products.

The kinetics of thermal decomposition of these salts were evaluated using nine mechanism based kinetic models 14-

16. Out of the nine-kinetic models

tested, on ly the parabolic law (01) equation was found to fit the TG data (Figure 6). The rate constants (k), activation energy (Ea) and corre lation coeffici ents (r) are reported in Table 4. The value of activation energies for N-methyl substituted salts were higher

+

{C01NO_,--__...,,.,.,S'=Io""w~ ~ t h cnnoly:-;is

Soli d P hase (I)

[<c··ot~ .l .... ... t: .. No,J =.N~·#"~bo~n~d= (C?; ---- he1e rolvsis ~

<> '-:::-Co:-'-nd-:-e.,.,-n ..,.,~ph:--~-cc ---' Ac civ.ate d com p lex o-S-o 6

•HNO, Oxidal io'n - red uc t ion

r e .:. c ti o n s

~ 0 -N b ond ~ V h omoly•;• ~

+

(CH,),;:;I-fNO,- - on 0 N_o,_-_ _ _, 6 -(CH,),NH h c<cmly.,, . ion pn;r

So~;)h~•c~ [ (C*H. ~ NO~ em•oy•~ v J -=~N~-H~bo~n~d:=<cA ·•l iN. o ,

...,. h e te ro l vsi.'l ~

. Acl ivll. te d conl plc,..

>-->..c.:~,;.,s~;:';-·c;:-;:Ra':-:;p,--id-;>- 0 c •_o c_• ---~· t-hcnn o ly sU.

- C-N bond

(CH6 10 o - (C H ,),NH h e tcmly> ;, Jo n ptlir _

Sol id Pht"~se ( I V)

C nnd e n !icd piuuc

(CH :a)NH

N - H bond

h e tero lysis 6 +HCIOo

0 - C IOl

6 ==~=:: ,,,.~ hnmoly!':i~ ~

I g nitio n

OxidAtio n - n: dueti<•n

reac1inn~1

0xjti8 ti o n- re duct ion

rea c tio n s

l Ignition CO..-C02+H~O

-----;>- :g::~:: :i ~~~~'"~:~ I CAr b on

Schcrnc 2 - Schcntatic representation oC N - Methylaniliniurn and N,.N - Dirnethylaniliniurn Nitrnt.es un&.J Per .. chloratcs .

SINGH et al.: STUDIES ON ENERGETIC COMPOUNDS 581

Table 4- Rate constant( k ), correlation coefficient ( r) and activation energy ( Ea) for thermal decomposition of N-methylanilinium and N,N-dimethylanilinium nitrates and perchlorates

Compound Parabolic law (o:2) equ ation rate constant (k x I 0-3.min-l ) Ea

N-MAN

N,N-DMAN

N-MAP

N,N-DMAP

2 .06

1 .98

1 .82

, . 66

1 . '58

l . SO

1 . 4 2

37.06 (408)

1.16 (408)

0.85 (448)

0.84 (448)

• - N~ N -OMAN

,. - N-MAN • - N.N'- OMAP • - N - MAP

16.97 (423)

1.80 (423)

1.35 (463)

1.26 (463)

.001 54 .00162 -00 1 7

' Yr ( '"'K)--

(oK)

Figure 6- Plots of log tid vs lff(°K) for N-MAN, N,N-DMAN, N-MAP and N,N-DMAP

10.92 (438)

4.21 (438)

2.09 (473 )

2.00 (473)

than the N,N-dimethyl derivatives. This may be due to the strong steric hindrance of methyl groups though they have strong inductive effect.

Although these salts are stable at room temperature and ignite when subjected to a sudden high temperature (>225 oc for nitrates and >250 oc for perchlorates). Therefore, it was of interest to undertake rapid thermolysis ( ignition delay studies) of these salts. However not much difference was observed 111

ignition temperatures.

Oxygen balance and VOD (Table 3) of perchlorates are high which indicates that they are more prone to ignition than nitrates. A linear relationships were obtained when £ * and YOD plotted against Td (Figure 7) .

It can be concluded that thermolysis involves competitive decomposition reaction paths. The proton transfer seems to control the decomposition of these salts and free radicals are predomjnantly involved in thermal reactions induced by heat energy.

o400

~ 13

' E 6200

0

!: 6100

5.97 (448)

6.50 (448)

4.09 (493 )

3.43 (493)

N-MAN

•

bCOO N1 N:- OMAN

'a E ~

" .-"'

28

21.

20

" \2

• N-MAN

N,N'-OMAN

0.99 12 68.4

0.9735 48.6

0.9978 62.2

0.9962 57.4

N-MAP

N- MAP

N,N-OMAP

190 200 210 22 0 230 21.0 25 0 260 270

Td(C)trom osc -

Figure 7- Plots of E* and VOD vs Td (°C )

Acknowledgements

Authors are thankful to Head, Chemjstry Department, DDU Gorakhpur University, Gorakhpur for providing laboratory facilities; RSIC, Nagpur for IR and DSC data and ISRO, Banglore and DST, New Delhi for financial assistance.

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2 Singh G & Kapoor I P S, Combust Flam e, 92 ( 1993) 283 . 3 Singh G, Kapoor I P S & Mannan S M, Combust Fla111e, 97

( 1994) 355. 4 Singh G, Kapoor I P S & Mannan S M, Thennochi111 Acta,

262 ( 1995) 117. 5 Singh G. Kapoor I P S & Mann an S M, .I Ener Mater. 13

( 1995) 141.

582 J SCI IND RES VOL 59 JULY 2000

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Mater, 16( 1) (1998) 31; 16(2) ( 1998) 101. I 0 Singh G, Kapoor I P S, Mannan S M & Tiwari S K, J

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T L, Combust Flame, (Accepted for publication)(2000). 12 Bassett J, Denney R C, Jaffery G H & Mandham J, Vogel's

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14 Singh G & Singh R R, Res lnd, 23 (l 9n) 92.

15 Semenov N, Chemical Kinetics and Chain ReactiollS (Clarendon Press, Oxford) 1935, Chap. 18.

16 Freeman E S & Gardon S, J Phys Chem, 66 (1962) 2646.

17 Martin A R & Yallop H J , Trans Faraday Soc, 54 ( 1958) 257.

18 Satwa V, Thennochim Acta, 2 ( 1971) 423.

19 Sharp J H, Brindley G W & Achar B N N, JAm Ceram Soc, 49 (1966) 379.

~ ·') Masuda Y, Iwata K, Ito R & Ito Y, J Phys Chem, 91 ( 1987) 6543.