Synthesis and Characterization of Novel CarbonâNitrogen Materials

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Chapter 17

Synthesis and Characterization of Novel Carbon—Nitrogen Materials by Thermolysis of Monomers and Dimers of 4,5-Dicyanoimidazole Eric C. Coad and Paul G. Rasmussen

1

Department of Chemistry, University of Michigan, Ann Arbor, MI 48109-1055 Our preparation of materials with high nitrogen and no hydrogen content is an effort to obtain thermally stable materials with low flammability. The thermolysis of 2-chloro-4,5-dicyanoimidazole and 2-(2-chloro-4,5-dicyano1-imidazolyl)-4,5-dicyanoimidazole functionalized with -H, and -I as leaving groups at the 1-position were examined. Thermolysis of the 2-chloro-4,5-dicyanoimidazole derivatives between 100-290°C were found to yield Tris(imidazo)[1,2-a:1,2-c:1,2-e]-1,3,5-triazine-2,3,5,6,8,9-hexacarbonitrile (HTT) with (C N ) composition. Thermolysis of HTT at 490500°C resulted in a carbon-nitrogen material with C/N = 1.020, while the thermolysis of HTT at 1070°C resulted in a carbonaceous material. The examination of the thermal properties of H T T and its thermal decomposition products demonstrate bulk thermal stability to 350°C. The thermolysis of the 2-(2-chloro-4,5-dicyano-1-imidazolyl)-4,5-dicyanoimidazole derivatives and their products are under further investigation. 5

4

3

Examples of heterocyclic polymers or materials which exhibit enhanced thermal stability include semi-ladder type polymers such as polyimides, polybenzimides, polybenzimidazoles, polybenzothiazoles, polybenzoxazoles, polyoxadiazoles, and polytriazoles; and ladder type polymers such as polyimidazopyrrolones, polyquinoxalines, and polyquinizarines. In these systems, theflammabilityis repressed by increasing the carbon to hydrogen ratio, while the thermal stability is enhanced by fusing heteroaromatic ring systems together in both the semi-ladder and ladder type polymers. The Oxygen Index (OI) value provides a relative measure of theflammabilityof a substance, where the OI value is equal to 100 times the ratio of oxygen to the total amount of gas in the atmosphere required to sustain combustion. Comparison of the OI values to the weight % of nitrogen in the selected nitrogen containing materials in Table I indicate that theflammabilitygoes down (OI value goes up) as the weight % of nitrogen increases. It is also evident in Table I that some of the other nitrogen containing polymers (Nomex, Kapton, and polybenzimidazole) have high OI values. The comparison of OI values of selected polymers to their carbon/hydrogen ratio in Table Π indicates to a rough approximation that as the carbon/hydrogen ratio goes up (hydrogen content decreases) theflammabilitygoes down (OI values go up). 1

2

3

1

Corresponding author 0097-6156/95/0599-0256512.00/0 © 1995 American Chemical Society In Fire and Polymers II; Nelson, G.; ACS Symposium Series; American Chemical Society: Washington, DC, 1995.

17.

COAD & RASMUSSEN

Novel Carbon-Nitrogen Materials

257

Table I: Oxygen Index data of selected nitrogen containing polymeric materials


Polymeric Material

Nitrogen Content (wt %) 4.5-5.2

Polyurethane foam Polyacrylonitrile Nylon-6,6 12.4 Wool 16-17 Silk 18-19 Aromatic polyamide(Nomex) Polyimide(Kapton, Dupont) Polybenzimidazole Source: Data are taken from ref. 2.

OI 16.5 18 24.0 25.2 >27 28.5 36.5 41.5

This report will compare the thermal stabilities of Iris(imidazo)[l,2-a:l,2-c: l,2-e]-13,5-lriazine-2,3,5,6,8,9-liexacarbonitrile or Hexacarbonitrile Iris(imidazo) Iriazine (HTT) and thermolysis products from HTT to the thermal stabilities of thermolysis products from 2-(2-chloro-4,5-dicyano-l-imidazolyl)-4,5-dicyanoimidazole (4). Table Π: Comparison of Oxygen Index data to the Carbon / Hydrogen Ratios of selected polymeric materials Polymeric Material

Carbon/Hydrogen Ratio 0.50 0.& Ô.5Ô 1.00 1.14 1.21 1.5Ô 1.58 ό.&ι 1.5Ô 1.00

Polyacetal Polymethyl methacrylate Polyethylene Polystyrene Polycarbonate Polyarylate Polyethersulphone PEEK PVC* PPS PVDC* PTFE * These polymers contain halogen atoms. Source: Data from ref. 3.

ÔI 15 17 17 18 26 34 34-38 35 23-43 44-53 60 90

The synthesis of HTT (3) with (CsN4)3 composition is accomplished by thermolysis of compounds 1-2 (Scheme l ) . In an effort to prepare polymeric materials (Scheme 2), compound (4) was synthesized (Schemes 3-4). TGA data for compounds 4-5 (Figure 8) demonstrate the analogous thermal transitions found for compounds 2-3 (Figure 2-3). Further work is underway to characterize the products from the thermolysis reactions in Scheme 2. 4

In Fire and Polymers II; Nelson, G.; ACS Symposium Series; American Chemical Society: Washington, DC, 1995.

258

FIRE AND POLYMERS II

Scheme 1 c

/

Thermolysis under Nitrogen^ -XCI *

l

u 1-2


1

A

A

y

n c

"^N^N*CCN ^ >N NVN

Thermolysis Temperature 1: X=H, 200-220°C 2: X=l, 220-240°C

M

NC

C

N

Scheme 2 CI .

v

\=J

• 4: X=H 5: X=l

X

we N

C

N

CN C

Thermolysis under Nitrogen^

-XCI

Carbon

Nitrogen

Materials

N

Experimental. General Procedures. Melting points were recorded on a Mel-Temp apparatus and are uncorrected. Infrared spectra were recorded on a Nicolet 5-DX FTIR spectrophotometer. C NMR (75 MHz) were recorded on a Bruker AM-300 spectrophotometer. Elemental analyses were done at the University of Michigan on a Perkin-Elmer 2400 CHN analyzer or done by Oneida Research Services, Inc., Whitesboro, NY. TGA were recorded on a Perkin-Elmer Series 7 Thermal Analysis System with a heating rate of 5°C/minute, under N2 or air. l-methyl-2-bromo-4,5dicyanoimidazole (6) was prepared as in reference 5. HTT (3) and thermolysis products from HTT were prepared as in reference 6. l-methyl-2-fluoro-4,5-dicyanoimidazole (7). A reaction mixture comprised of 20.0 g (0.094 mol) of 6, 13.68 g (0.236 mol) of spray-dried KF, a catalytic amount of 18-crown-6 ether, and 25 mL of diglyme were heated at reflux overnight. The liquid was decanted and the salt was washed with acetone. The decanted liquid and acetone washes were combined. The acetone and diglyme were removed under reduced pressure. The resulting brown oil was vacuum distilled twice with Bp 95110°C at 0.02-0.03 mm producing 50.0 g (89%) of 7 as a clear oil which crystallized upon standing. The white solid 7 displays the following properties: TLC EtOAc R 0.64; Mp 46-48°C; IR(KBr): 2243, 1595, 1512, 1411, 1174 cm" ; UV-vis(CH CN) ληιαχ(ε) 250(12120); *H NMR (300.1 MHz, C D C I 3 , ppm) δ 1 3

1

f

3

3.73(s, 3H); ^ C NMR (75.5 MHz, CDCI3, ppm) δ 150.0(d, 7 = 252.1 Hz), 117.3(d, J = 12.7 Hz), 110.7, 110.4(d, J = 3.9 Hz), 107.0, 31.4; MS (E/I) m/z (relative intensity) 151 (M+l, 8), 150 (M+, 100%), 149 (20), 135 (2), 122 (5), 109 (5); HRMS (EI with DCI probe) m/z calcd. for C 6 H 3 N 4 F 150.0342, obsd. 150.0338; Anal, calcd for C 6 H 3 N 4 F : C, 48.02; H, 2.00; N, 37.32. Found: C, 47.96; H, 1.85; N, 37.15. l-methyl-2-(2-amino-4,5-dicyano-l-imidazolyl)-4,5-dicyanoimidazole (9). A reaction mixture comprised of 40.0 g (.267 mol) of 7, 68.4 g (.400 mol) of 8, a catalytic amount of 18-crown-6 ether, and 400 mL of C H 3 C N were heated for 8 h at 50°C. The C H 3 C N was removed under vacuum. The resulting solid was dissolved in EtOAc and was extracted with 10% N H 4 O H . The solvent was removed under


17.

COAD & RASMUSSEN


259

vacuum and the solid was recrystallized from CH3CN/H2O producing 56.99g (84%) of compound 9. The white solid 9 displays the following properties: TLC EtOAc R 0.62; Mp 288-290°C; IR(KBr): 3364, 3424, 3171, 2248, 2230, 1643, 1579, 1525, 1487, 1453, 1421, 1408, 1320, 1255 cm-1; *H NMR (200.1 MHz, (CD ) SO, ppm) δ 7.71 (s, 2H), 3.75 (s, 3H); NMR (50.3 MHz, (CD ) SO; ppm) δ 153.1, 136.2, 123.3, 119.4, 115.7, 112.1, 111.3, 108.5, 107.7, 106.9, 34.0; MS (EI with DCI probe) m/z (relative intensity) 265 (5.6), 264 (45.2), 263 (M+, 100.0), 262 (5.6), 236 (10.1), 222 (11.8), 184 (10.5), 158 (29.3), 132 (43.6); HRMS (EI/w DCI probe) m/z (M+) calcd. for C11H5N9 263.0668, obsd 263.0650. 1- methyl-2-(2-chloro4,5-dicyano-l-irrudazolyl)-4,5-dicyanoimidazole(10). A reaction mixture comprised of 10.0 g (.038 mol) of 9 were dissolved in 120 mL of cone. HCI. The mixture was cooled to 0°C, and 90 mL of H2O were added followed by 3.28 g (.048 mol) of NaN0 in 20 mL of H 0 . The mixture was maintained at 0-5°C for 4 h and was allowed to warm to room temperature overnight The product was extracted with EtOAc. The solvent was removed under vacuum. The yellow product was a mixture of hydrolysis products from 10 with the following mass data: MS (EI with DCI probe) m/z (relative intensity) 320 (1.9), H £ (5.6), 302 (14.7), 2ÛÛ (35.1), 284 (11.3), 2S2 (12.5), 267 (2.1), 266 (18.9), 265 (68.3), 257 (5.2), 238 (7.1), 221 (16.7), 210 (14.5), 195 (6.3), 183 (10.1); HRMS (EI/w DCI probe) m/z (M+) calcd. for C n H N 0 3 5 c i 318.0380, obsd 318.0378, calcd. for C n H N 0 3 5 c i 300.0275, obsd 300.0265, calcd. for CiiH N 35ci 282.0169, obsd 282.0166, calcd. for C n H N 0 265.0586, obsd 265.0577. The above product mixture (9.65 g) was refluxed without purification with 12.1 g (.079 mol) of POCl , 14.5 g (.250 mol) of NaCl in 145 mL CH CN for 5 h. The solvent and POCl were removed under vacuum and the product was purified by column chromatography using EtOAc. The EtOAc was removed under vacuum and 10 was dried at 110°C. The white solid 10 displays the following properties: IR(KBr): 2964, 2246, 1522, 1493, 1456, 1311, 1292, 1021 cm" ; *H NMR (360.1 MHz, (CD ) CO, ppm) δ 4.01(s, 3H); 13c NMR (50.3 MHz, ( C D ^ C O ; ppm) δ 139.9, 135.5, 124.5, 121.2, 117.7, 116.5, 111.4, 110.9, 107.8, 106.9, 35.1; MS (EI) m/z (relative intensity) 285 (7.9), 284 (35.6), 283 (19.3), 282 (100.0), 281 (4.8), 247 (8.1), 232 (6.8), 230 (15.8), 221 (64.6); HRMS (EI/w DCI probe) m/z (M+) calcd. for CnH N 35ci 282.0169, obsd 282.0178. 2- (2-chloro-4,5-dicyano- 1-imidazoly l)-4,5-dicyanoimidazole(4). A reaction mixture comprised of 10.0 g (.038 mol) of 10,3.20 g (.076 mol) of LiCl, and 30 mL of DMAC were heated for 4 h at 165°C resulting in the formation of the lithium salt of 4. The solvent was removed under vacuum and the lithium salt of 4 was boiled in CHC1 to remove trace DMAC. The lithium salt of 4 was dissolved in 10% HCI and extracted with EtOAc. The EtOAc was removed under vacuum and 4 was dried at 110°C. The off-white solid 4 displays the following properties: IR(KBr): 2242, 1617, 1566, 1527, 1458, 1450, 1424, 1381, 1326, 1302, 1148 enr ; HRMS (EI/w DCI probe) m/z (M+) calcd. for C n H N 5 c l 268.0013, obsd 268.0009. f


3

2

3

2

2

7

5

8

2

8

3

5

3

2

8

8

3

3

1

3

2

3

8

3

1

3

3

8

Results and Discussion. Thermolysis of compound 1 to HTT at 200-220°C suffers from sublimation yielding an incomplete reaction. Thermolysis of compound 2 at 220-240°C yields complete reaction to HTT. The TGA of 2 (Figure 1) shows a weight loss of 50% by 243°C which corresponds to loss of ICI and the formation of HTT. The weight losses of 11% between 243-456°C, and 6% between 456-606°C correspond to the loss of (CN)2> N , and to the formation of carbon-nitrogen(C-N) materials. Heating to 900°C yields complete weight loss. 2


260


The TGA of HTT (Figure 2) shows weight losses of 21% by 489°C, and 51% between 518-765°C which correspond to loss of (CN)2, N , and to the formation of C-N materials. Heating to 900°C yields complete weight loss. Comparison of Figures 1 and 2 show that the thermal transitions of HTT are also represented in Figure 1. Thermolysis of HTT at 490-500°C resulted in a C-N material (Scheme 3) giving an elemental analysis with weight percentages of 46.4% carbon and 45.5% nitrogen with average C/N = 1.020. The C-N material's IR data indicated a change in the nitrile stretch from 2252 cnr to 2221 cnr , as well as significant broadening of IR absorptions. The TGA of the C-N material (Figure 3) shows a weight loss of 49% between 446-733°C and 41% between 733-883°C. Comparison of Figures 2 and 3 show that the weight loss of 21% at 489°C present in the TGA of HTT is absent in Figure 3 indicating complete decomposition of the HTT starting material into a C-N material. The thermolysis of HTT at 1070°C resulted in a carbonaceous material (Scheme 3) giving an elemental analysis with weight percentages of 91.6% carbon and 0.9% nitrogen. The carbonaceous material's IR data indicated the disappearance of the nitrile stretch. The TGA of the carbonaceous material (Figure 4) shows a weight loss of 61% between 443-877°C. Comparison of Figures 2 and 4 show that the weight loss of 21% at 489°C present in the TGA of HTT is absent in Figure 4 indicating complete decomposition of the H T T starting material into a carbonaceous material. The examination of the thermal properties of HTT and its thermal decomposition products demonstrate bulk thermal stability to 350°C. In addition, these materials do not burn or melt when exposed to higher temperatures. 2


1

1

Scheme 3 Carbon Nitrogen 490-500°C 1070°C ^Carbonaceous HTT under N ,15 days* Material Material * under N ,1-2 hr. 2

2

Examination of isothermal properties of HTT, the C - N material and the carbonaceous material at 400°C under nitrogen (Figure 5) indicate a 3.4% wt. loss per h. for HTT, a 2.7% wt. loss per h. for the C-N material, and a 4.5% wt. loss per h. for the carbonaceous material. The isothermal properties of HTT, the C-N material and the carbonaceous material at 400°C under air (Figure 6) indicate a 7.3% wt. loss per h. for HTT, a 3.6% wt loss per h. for the C-N material, and a 8.1% wt. loss per h. for the carbonaceous material. In an effort to prepare a polymeric material, 2-(2-chloro-4,5-dicyano-limidazolyl)-4,5-dicyanoimidazole (4) was synthesized (Schemes 4-5). Transhalogenation of 6 with potassium fluoride in diglyme and a catalytic amount of 18-crown-6 ether yields 7. Preparation of 9 takes advantage of the good leaving group characteristics of fluorine to make 7 an ideal candidate for a nucleophilic Scheme 4 NC B

NC' 6

CH

3

r

KF (spray-dried) NC Cat. 18-crown-6 ether Diglyme ^ NC

89%

7 CH

3



17.

Τ

261


COAD & RASMUSSEN

1

1

1

1

1

—ι

f

100 200 300 400 500 600 700 800 900 Temperature (°C) Figure 1. TGA of l-iodo-2-chloro-4,5-dicyanoiniidazole (2) under nitrogen.

100 200 300 400 500 600 700 800 900 Temperature (°C) Figure 2. TGA of HTT (3) under nitrogen and air.




100 200 300

400 500 600 700 800 900 Temperature (°C)

Figure 3. TGA of Carbon Nitrogen Material from HTT under nitrogen and air.



17.

COAD & RASMUSSEN

80 J 25

50


263

I 75 100 125 150 175 200 225 250 Time (min.)

Figure 5. Isothermal TGA of HTT, Carbon Nitrogen Material from HTT, and Carbonaceous Material from HTT at 400°C under nitrogen.

Figure 6. Isothermal TGA of HTT, Carbon Nitrogen Material from HTT, and Carbonaceous Material from HTT at 400°C under air.


264

FIRE A N D POLYMERS II

Scheme 5 ^ - τ τ Ά Ή y.

N

8 K

3


NH N C

N C

^ ' V _ JI / I 9

CH

M

VNH

2

3

NC^tf

+

CH

Cat. 18-Crown-6 ether CH CN

^ * " A

{j

F

N C - ^ I /

7

C

50-70°C

+

84%

2

^/ W . . 11 ) Cone. HCI, H 0, NaN0 ,0-5°C, 4 h \ / 2) O-RT. 12 h. Isolate Product Mixture^ F={ 3) POCI , NaCI, CH CN, Δχ, 5 h w

2

W N C

C

Cl

3

3

2

3

N

CI

10

CH

N C

Cl

C

N

4

3

i

N

C

C

N

aromatic substitution reaction using 8 as a nucleophile. The amino group of compound 9 is diazotized and decomposed forming a mixture of compound 10, and its hydrolysis products, and a small amount of the corresponding imidazolone dimer. The imidazolone dimer and hydrolysis products are converted to 10 using P O C I 3 . Dealkylation of 10 is accomplished using LiCl and DMAC yielding compound 4. The thermal properties of compound 11 were investigated to model the effect of 1,2-connectivity between 4,5-dicyanoimidazole rings. The TGA of 11 under nitrogen (Figure 7) shows weight losses of 7% by 560°C, and 70% between 560900°C, while the TGA data under air shows weight losses of 4% by 300°C, 25% between 300-600°C, and 68% between 600-750°C. The results from the model compound demonstrate strong thermal stability to 500°C under both air and nitrogen. H

T V N

I

A

N

NC

CN

Compound 11 Preliminary TGA data for compounds 4-5 demonstrate the analogous thermal transitions found for compound 2. The TGA of 4 (Figure 8) shows a weight loss of 14% between 95-270°C which may correspond to loss of HCI, and a weight loss of 14% between 270-480°C which may correspond to the loss of (CN)2, and N2. Heating to 900°C yields complete weight loss. The TGA of 5 (Figure 8) shows a weight loss of 44% between 95-325°C which may correspond to loss of ICI, and a weight loss of 9% between 325-545°C which may correspond to the loss of (CN)2, and N2. Heating to 900°C yields complete



17.

COAD & RASMUSSEN


100 200 300

400 500 600 700 800 900 Temperature (°C)

Figure 7. TGA of Compound 11 under nitrogen and air.

100 200 300

400 500 600 700 800 900 Temperature (°C)

Figure 8. TGA of Compounds 4 and 5 under nitrogen.


265

266

FIRE AND P O L Y M E R S II


weight loss. Further work is underway to characterize the products from these thermolysis reactions. Conclusions. The thermolyses the 2-cMoro-4,5-dicyanoimidazole derivatives between 100290°C were found to yield Iris(imidazo)[l,2-a:l,2-c:l,2-e]-l,3,5-iriazine-2,3,5,6, 8,9-liexacarbonitrile (HTT) with (CsN^ composition. Thermolysis of HTT at 490-500°C resulted in a carbon-nitrogen material with C/N = 1.020, while the thermolysis of HTT at 1070°C resulted in a carbonaceous material. Examination of the thermal properties of H T T and its thermal decomposition products demonstrated bulk thermal stability to 350°C. The thermolysis of the 2-(2-chloro4,5-dicyano-l-imidazolyl)-4,5-dicyanoimidazole derivatives and their products are under further investigation. References. 1. Rossbach, V.; Oberlein, G., in Handbook of Polymer Synthesis, Ed. by Kricheldorf, H.R., pp.1197-1280, Marcel Dekker, INC, New York, 1992. 2. Cullis, C.F; Hirschler, M.M. The Combustion of Organic Polymers, pp.49, 5354, 254-255, Oxford University Press, New York, 1981. 3. Brydson, J.A., in Developments in Plastics Technology-4, Ed. by Whelan, Α.; Goff, J.P., pp. 178-179, Elsevier Science Publishers Ltd., New York, 1989. 4. (a) Coad, E.C.; Apen, P.G.; Rasmussen, P.G. J. Am. Chem. Soc., 1994, 116, 391; (b) Coad, E.C. Ph.D. Thesis, University of Michigan 1994. 5. Apen, P.G.; Rasmussen, P.G. Heterocycles, 1989, 29, 1325. 6. (a) Coad, E.C.; Rasmussen, P.G. Proceedings of the ACS Division of Polymeric Materials: Science and Engineering, 1993, 69, 321; (b) Coad, E.C. Ph.D. Thesis, University of Michigan 1994. RECEIVED January 11, 1995


Synthesis and Characterization of Novel CarbonâNitrogen Materials

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