Synthesis and explosive decomposition of polynitro[60]fullerene

CARBON

6 2 ( 2 0 1 3 ) 4 1 3 –4 2 1

Available at www.sciencedirect.com

journal homepage: www.elsevier.com/locate/carbon

Synthesis and explosive decomposition of polynitro[60]fullerene Franco Cataldo a b c

a,b,* ,

Ornella Ursini c, Giancarlo Angelini

c

Tor Vergata University, Via della Ricerca Scientifica, 00133 Rome, Italy Lupi Chemical Research srl, Via Casilina 1626A, 00133 Rome, Italy Istituto di Metodologie Chimiche, CNR, Via Salaria Km 29,300, Monterotondo Stazione, 00016 Rome, Italy

A R T I C L E I N F O

A B S T R A C T

Article history:

Prolonged treatment of C60 in benzene with very high concentrations of N2O4 leads to a new

Received 22 February 2013

polynitro[60]fullerene whose composition was determined as C60(NO2)14 by thermogravi-

Accepted 12 June 2013

metric analysis. The compound is unstable and deflagrates above 170 C when heated

Available online 20 June 2013

under nitrogen or in air with the release of a considerable amount of heat as observed by the differential thermal analysis and as measured by differential scanning calorimetry. The decomposition steps of C60(NO2)14 were followed by the thermogravimetric analysis coupled with Fourier-transform infrared spectroscopy analytical technique. At the deflagration point C60(NO2)14 releases a mixture of nitrogen oxides: NO2 and NO with minor amounts of N2O. The deflagration leaves a residue of oxidized carbon which by heating releases CO2 and CO and at 700 C is reduced to a carbonaceous matter free from residual oxygenated groups showing also the presence of small amounts (610%) of C60 fullerene.  2013 Elsevier Ltd. All rights reserved.

1.

Introduction

The chemistry of fullerenes has been widely expanded since their discovery at the end of last century [1]. A series of books and reviews [2–9] (cited without the presumption of being exhaustive) testify how deep is our knowledge on the chemical behavior of C60 and C70 and also about their potential applications and impact in very different fields of science. In the current paper we wish to report about a novel fullerene derivative, the tetradecanitro[60]fullerene and about the evidences of its explosive properties. One of the first attempts to produce a nitrofullerene derivative involved the use of nitric acid resulting in the formation of a nitro-oxidized C60 [10]. Instead, the use of NO2 [11] or N2O4 in CS2 [12] as nitrating agent was a successful approach in the synthesis of polynitrofullerene. The synthesis of hexanitrofullerene was achieved using NO2 in benzene solutions of C60 [13–17]. The resulting C60(NO2)6 was used as starting

molecule for the synthesis of other fullerene derivatives taking advantage from the fact that NO2 moieties are very good leaving groups in nitrofullerene. Therefore, arylamino-derivatives of C60 [14,15], fullerenols [16] and other more complex derivatives [17] were prepared using C60(NO2)6 as starting molecule for further synthesis. The interest on nitrofullerenes does not regard only their potential use as precursors for the synthesis of more complex fullerene derivatives but regards also the potential properties as explosives and propellants additives [18] and the relative thermochemical aspects [19–23]. The interest in nitrated fullerene is enforced also by the discovery that another nitrated cage compound: octanitrocubane (ONC) [23–25] which is characterized by a series of unique properties as explosive in terms of high density, favorable oxygen balance, very high detonation velocity and very high detonation pressure which has permitted the classification of ONC as one of the most powerful explosive [24] with a relative effective factor (RE

* Corresponding author at: Tor Vergata University, Via della Ricerca Scientifica, 00133 Rome, Italy. Fax: +39 0694368230. E-mail address: [email protected] (F. Cataldo). 0008-6223/$ - see front matter  2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.carbon.2013.06.026

414

CARBON

6 2 ( 2 0 1 3 ) 4 1 3 –4 2 1

factor) against trinitrotoluene (TNT) of 2.38, which means that 2.38 kg of TNT have the equivalent effect of 1 kg of ONC [25,26].

2.

Experimental

2.1.

Materials and equipment

Fullerene C60 was a high purity grade (99.9%) from MTR Ltd. Company, USA. Benzene, concentrated nitric acid (>65%) and copper turnings were obtained from Sigma–Aldrich, USA. Thermogravimetric analysis was made on a Linseis apparatus model L81 + DTA at a heating rate of 10 C/min under N2 flow of 20 L/h or under a air flow of 40 L/h. Differential scanning calorimetry (DSC) was performed on a Mettler-Toledo DSC-1 Star System using heating rates of 10 C/min or 20 C/min (see Section 3) under a nitrogen or air flow of 5 L/ h. The DSC on polynitrofullerene samples were performed under N2 flow using stainless steel hermetically sealed medium pressure crucibles on samples size of 5–9 mg instead, the DSC under air flow were made using opened stainless steel crucibles. The FT-IR spectra of polynitrofullerenes and their decomposition products were recorded on a Nicolet 6700 spectrometer from Thermo-Scientific with samples embedded in KBr pellets.

2.2.

Synthesis of polynitro[60]fullerene

C60 fullerene (114 mg) was mixed with 110 ml of benzene and sonicated for 3 h in a stoppered conical flask in an ultrasonic bath. The resulting solution was transferred in a gas washing bottle and then an abundant stream of NO2 was passed into the solution which was cooled externally at +10 C. Nitrogen dioxide was produced in a separate apparatus by dropping concentrated nitric acid 64% over abundant copper turnings. NO2 was dried over anhydrous calcium chloride prior to bubbling into the benzene solution of C60 as suggested in Ref. [11,13]. Because of the large amount of NO2 employed and the low temperature adopted, a brown mixture of benzene and N2O4 was obtained and left stoppered at 10 C for 24 h. Afterwards the benzene/N2O4 solution was found with a darkgreen color with an abundant red precipitate. The benzene/ N2O4 was decanted and the red precipitate was dried at room temperature in vacuum. On drying it turned its color from red to orange-red. The yield of the collected precipitate was 122 mg. The distillation of the benzene/N2O4 yielded other 58 mg of nitrofullerene.

2.3. Synthesis of polynitro[60]fullerene with pre-saturated benzene/N2O4 mixture About 90 ml of benzene recovered from the previous batch were treated with NO2 until a brown solution was obtained. Then, C60 fullerene (104 mg) was added to the solution which was sonicated for 30 min in an ultrasonic bath. The C60 dissolution was rapid and complete. The solution appeared reddish. The reaction mixture kept at +10 C was saturated with dry NO2 until it has assumed a dark-green color. After 24 h on standing at +10 C the mixture showed a red precipitate at the bottom while the benzene solution remained dark-

green. The red precipitate was collected by decantation and dried in vacuum to yield 104 mg. Other 50 mg of polynitrofullerene were collected by distillation of the benzene/N2O4 under reduced pressure.

3.

Results and discussion

3.1.

Aspects of the synthesis of polynitrofullerene

Nitrogen dioxide (NO2) and its dimer dinitrogen tetroxide (N2O4) are well known nitrating agents either used alone or dissolved in organic solvents [27–30]. NO2 is prevalent in the gas phase and it is used in gas phase nitration reactions [27]. Instead the dimer N2O4 is prevalent in liquid phase and in organic solvents where it is highly soluble and forms also charge-transfer complexes [26–30]. When N2O4 is dissolved in CS2 and reacted with C60 yields on average a tetranitro derivative [2]. However, it is more convenient to use benzene as reaction solvent in the nitration of C60 with N2O4 since the reaction mixture of N2O4/CS2 may be dangerous to handle. Instead, benzene does not undergo nitration reaction with N2O4 at ambient and sub-ambient temperature while there is the formation of a charge-transfer complex between benzene and N2O4 where the former acts as a charge donor [28,29]. The complex is described as an equimolar ratio of benzene/N2O4 with a melting point at 7 C [28]. The dissociation constant of the reaction N2O4 ! 2NO2 is reported to be 3.2 · 105 mol/ L in liquid N2O4 against 1.4 · 105 mol/L when N2O4 is dissolved in benzene in a wide molar ratio range with solvent [29]. This implies that the nitration mechanism of the substrate C60 is the same both in liquid N2O4 or in benzene solution and is due the free radical attack of the NO2 radicals to the fullerene double bonds. Some authors [11,13–16] have studied the gradual nitration of C60 and shown that the nitration stops at the hexanitro[60]fullerene derivative after a very long contact time between the benzene/N2O4 and the fullerene substrate. However, none of the mentioned authors have used very high concentration of N2O4 in benzene as we have done and none of the authors reported the spontaneous precipitation of the polynitrofullerene from the benzene solution on standing, as we observed. Consequently, our synthetic approach has lead to the production of highly nitrated fullerene C60.

3.2. Determination of the composition polynitrofullerene and discovery of its explosiveness

of

To assess the chemical composition of the polynitro[60]fullerene prepared as detailed in Section 2 we have used the thermogravimetric analysis both under nitrogen flow and under air flow. The TGA curves obtained are shown in Fig. 1. Both TGA curves show a sudden and explosive decomposition of the polynitro[60]fullerene suggested by the vertical lines parallel to the ordinate axis which show an extremely rapid and complete weight loss which is not accompanied by further weight loss at higher temperatures. The sudden and rapid weight loss corresponds to a deflagration process of the polynitro[60]fullerene with the onset occurring at 171 C under N2 and at 176 C under air (see Fig. 1). The sudden weight loss in

CARBON

6 2 (2 0 1 3) 4 1 3–42 1

415

Fig. 1 – Thermogravimetric analysis (TGA) of tetradecanitro[60]fullerene recorded at a heating rate of 10 C/min under nitrogen flow and air flow. The decomposition onset of the former sample under N2 occurs at slightly lower temperature than the sample tested in air flow. The total weight loss of 47.3% corresponds to the theoretical value of 47.2% which can be calculated for C60(NO2)14. the TGA corresponds to the strong exothermal peaks observed in the differential thermal analysis (DTA) recorded simultaneously with TGA (Fig. 2). In the DTA the peaks of the deflagration process occur at 175 C under N2 and at 185 C in air flow. The total weight loss after the deflagration of the polynitro[60]fullerene samples is 47.3% for the sample heated under N2 and 46.2% for the sample heated under air flow. Both these values are almost coincident to the theoretical value of 47.2% which can be calculated for C60(NO2)14, the tetradecanitro[60]fullerene which is the composition of the polynitro[60]fullerene prepared in the present work.

Neither the explosive decomposition of polynitrofullerene nor a so high level of nitration of C60 has ever been reported in literature till now suggesting that our new synthetic approach has been fecund.

3.3. Infrared spectroscopy of polynitro[60]fullerene and of the carbon residue collected after the deflagration The FT-IR spectrum of the polynitro[60]fullerene prepared in the present work and having the elemental composition C60(NO2)14 displays an infrared spectrum dominated by the asymmetric and symmetric NO2 vibrations at about 1570

Fig. 2 – Differential thermal analysis (DTA) signal recorded simultaneously with the TGA measurement of the previous figure on tetradecanitro[60]fullerene samples under N2 flow and under air flow. In both cases two strong exothermal transitions respectively at 175 C and 183 C were observed corresponding to the deflagration of the tetradecanitro[60]fullerene.

416

CARBON

6 2 ( 2 0 1 3 ) 4 1 3 –4 2 1

and 1330 cm1 respectively (see Fig. 3). These bands were also observed in other nitro[60]fullerenes with lower content of nitro groups [11–15]. In the C–N stretching region of the nitrogroups [31], the main infrared absorption band at about 805 cm1 is accompanied by a series of sub-bands. The NO2 deformation vibrations which include the scissoring, wagging and rocking of the NO2 group occurs in the spectrum at low wavenumbers [31] and in particular the peak at about 685 cm1 in Fig. 3 can be assigned to the NO2 wagging mode [31]. The weak peaks at 561 and 543 cm1 shown in Fig. 3 are attributable to the NO2 group rocking [31]. When C60(NO2)14 is heated under nitrogen, it deflagrates at 175 C as shown by the TGA and DTA (Figs. 1 and 2 respectively). The decomposition leaves a residue of carbonaceous matter in the TGA crucible. In Fig. 4 are reported the infrared spectra of a series of carbonaceous samples obtained from the thermal decomposition of C60(NO2)14 under nitrogen flow and heated till 210 C, 300 C, 400 C, 500 C, 650 C and 700 C and then cooled down to room temperature under nitrogen flow. The FTIR spectra of the carbonaceous matter obtained from C60(NO2)14 from 210 C to 400 C show a broad ketone band with two peaks at 1775 and 1735 cm1 accompanied by the a,b-unsaturated ketone band stretching at 1617 cm1 having approximately the same intensity of the ketone band. At 500 C the broad ketone band shifted at 1774 and 1720 cm1 and has the same intensity as the a,b-unsaturated ketone band at 1617 cm1. At 650 C the ketone band appears much weaker and shifted at 1711 cm1 while the a,b-unsaturated

ketone band is now replaced by an aromatic band at 1575 cm1. At 700 C the ketone band is completely removed remaining only the aromatic band at 1586 cm1. These data show very clearly that the decomposition of polynitrofullerene produces an highly oxidized carbonaceous matter resembling polymeric fullerene oxide, the heavy oxidized carbon obtained by prolonged ozonization of C60 [32–34]. The assignments of the ketone band at 1775 cm1 observed up to 500 C were discussed in previous works [33,34] and are due to acid anhydride group (–CO–O–CO–), to lactones and to four-membered cyclic ketone while the band at 1720 cm1 is due to regular ketone or aldehyde group [31]. Fig. 4 shows also two weak features at 551 and 525 cm1 in the sample prepared at 300 C. Such features become slightly stronger in the samples obtained at higher temperature than 300 C and at 650–700 C the two bands are clearly located at 576 and 528 cm1 and consequently must be attributed to C60. This implies that C60(NO2)14 decomposes to amorphous and oxidized carbon resembling polymeric fullerene oxide but also back to C60 fullerene especially at higher temperature (i.e. >650 C) when the oxygenated functional groups are removed. From the infrared spectrum of Fig. 4 recorded on the carbonaceous matter obtained at 700 C, the C60 fullerene fraction can be estimated 610% of the total carbon. The carbonaceous matter obtained at 700 C shows also the aromatic out-of plane bending modes respectively at 878 cm1 due to isolated C–H in a polycyclic aromatic structure, 823 cm1 due to two adjacent aromatic C–H groups

1.4 364-37 Nitro[60]fullerene 1.2 1.0

Abs

1330 0.8 0.6

805

0.4 1266

1115

0.2

1036

978

561

851 736

1566

-0.0 0.7

683

786 764

543 524

403-37 Nitro[60]fullerene

0.6

Abs

0.5

1332

0.4 822

0.3

802

685

788

1118

0.2

1034

761

0.1 0.0 2600

1570 2400

2200

2000

1800

1600

1400

1200

1000

800

600

Wavenumbers (cm-1)

Fig. 3 – FT-IR spectra of tetradecanitro[60]fullerene having the elemental composition of C60(NO2)14 as determined by the TGA. The infrared spectrum of the sample prepared as detailed in Section 2.2 (spectrum at the top of the figure) is practically identical to that prepared as reported in Section 2.3 (spectrum at the bottom of the figure).

CARBON

1.0 382-37 Nitro[60]fullerene heated 210°C N2 Abs

417

6 2 (2 0 1 3) 4 1 3–42 1

1735 1776 1617

1345

1067

0.5

Abs

0.0 1.0 *403-37 Nitro[60]fullerene heated 300°C N2 1774 1735 1619

0.5

1386

1223 928

751 697

551 525

Abs

1.0 411-37 Nitro[60]fullerene heated 400°C N2 1777 1614 1732 0.5 2337

1230 925

765

2226

698

547 528

1.0 *410-37 Nitro[60]fullerene heated 500°C N2 Abs

1384

1853

1240

1774 1720 1614

911

0.5

764

709

545 528

2336 2225 1.0 *364-37 Nitro[60]fullerene heated 650°C N2

1575

1439

Abs

1221 1711

768

576 525

883

0.5

1.0 *364-37 Nitro[60]fullerene heated 700°C N2 Abs

1586

1429

1282 878

0.5

823

576 757 528

2500

2000

1500

1000

500

Wavenumbers (cm-1)

Fig. 4 – FT-IR spectra of C60(NO2)14 decomposed by deflagration under nitrogen at the following temperatures (from top to bottom): 210 C, 300 C, 400 C, 500 C, 650 C and 700 C.

and 757 cm1 due to four adjacent aromatic C–H groups [31]. This fact suggests that the removal of oxygenated groups from the carbonaceous matter obtained from C60(NO2)14 leads to polycyclic aromatic moieties necessarily formed from the fullerene cage breakdown although a small fraction of C60(NO2)14 is transformed back to C60.

3.4. TGA-FTIR of the gases released polynitro[60]fullerene thermal decomposition

by

The aspect of the decomposition of hexanitrofullerene yielding oxidized carbon was examined by other authors [32] who have proposed also a mechanism explaining the formation of oxidized carbon residue. In this section using the TGA-FTIR analytical tool (under nitrogen flow) we have analyzed the gaseous products released by C60(NO2)14 during the thermal decomposition. In Fig. 5 is reported the infrared spectrum of the gaseous products released by C60(NO2)14 at 170 C, a temperature corresponding to the onset of the deflagration. Three gaseuos products were identified: nitric oxide (NO), nitrogen dioxide (NO2) and even dinitrogen monoxide (N2O). These gases are firmly identified through the Omnic library of our spectrometer and in Fig. 5 are shown also the reference spectra of these three gases. The decomposition of nitrocompounds normally produces a mixture of nitrogen oxides. This has been found in a previous work with TGA-FTIR dedi-

cated to the thermal decomposition of nitro-polyisoprene [35] and reported also in other reference works [36]. Fig. 6 shows the temporal evolution of the nitrogen oxides NO2 and NO as function of the temperature of the C60(NO2)14 and the values in the ordinate of the graph are reported as Ln[(Abs)t/(Abs)0] where (Abs)t is the area measured below the peak at 1626 cm1 for NO2 and below the peak at 1903 cm1 for NO at any temperature t while (Abs)0 is the area below the mentioned peak at the temperature when the evolution of a given gas starts. Of course, being each TGA-FTIR experiment conducted at a heating rate of 10 C/min, the temperature scale in abscissa can be converted into a time scale. Fig. 6 shows that the production of NO2 and NO starts already at 60 C and the amount of the evolved gases grows with temperature. At 100 C NO2 reaches a first maximum and then peaks again at the deflagration temperature of C60(NO2)14 between 170 C and 180 C. Instead NO shows a plateau between 100 C and 140 C and then it the largest amount is released again at the deflagration temperature between 170 C and 180 C. The trend of N2O is not shown in Fig. 6 because it is produced exclusively between 170 C and 180 C, during the deflagration and in considerably smaller amounts than the other nitrogen oxides. Particularly interesting is the production of NO from the decomposition of C60(NO2)14. It has been suggested [32] that the nitrogroup of a generic nitrofullerene once is released by thermal treatment as NO2 it reacts with

418

CARBON

6 2 ( 2 0 1 3 ) 4 1 3 –4 2 1

410-37 Nitro[60]fullerene 170°C

1629 1600

Abs

0.04 1902 0.02

18751851

2209 2236

-0.00 1.0 Nitrogen dioxide NO2

Abs

1628

1600

0.5

1.0 Nitric oxide NO

Abs

1906

1875

0.5

1842

Abs

1.0 Dinitrogen monoxide N2O

0.5

2237

2213

2200

2000

1800

1600

1400

Wavenumbers (cm-1)

Fig. 5 – FTIR spectrum of the gaseous products released by C60(NO2)14 at the decomposition temperature of 170–180 C (spectrum at the top of the figure). The 2nd, 3rd and 4th spectra from top are reference spectra taken from the Omnic library.

Fig. 6 – Amount of gases NO2 and NO produced from the thermal decomposition of C60(NO2)14 as measured through the TGAFTIR analysis. The area below the peak at 1626 cm1 for NO2 and below the peak at 1903 cm1 for NO was measured with the Ominc software of the infrared spectrometer and reported as Ln[(Abs)t/(Abs)0] in the ordinate of the graph.

the surface of the fullerene cage forming a labile nitrito-adduct which, on further heating decomposes to NO leaving an oxygen atom in the oxidized carbon network: C  NO2 ! C þ NO2 ! C  ONO ! C  O þ NO

ð1Þ

After the deflagration of C60(NO2)14 the release of nitrogen oxides drops to zero but continuous heating of the residual carbonaceous matter reveals the release of CO2 and CO. Also

these two gases were revealed by the TGA-FTIR analytical technique and identified through the Ominc library of our spectrometer. Fig. 6 shows that the emission of CO2 reaches its maximum immediately after the deflagration of the sample, when the carbonaceous residue is brought at about 200 C. Afterwards the CO2 release drops to a certain level and from 250 C stabilizes and remains constant. On the other hand, the release of CO starts as well after the deflagration,

CARBON

6 2 (2 0 1 3) 4 1 3–42 1

419

3.5. DSC of polynitro[60]fullerene and determination of the heat of decomposition

Fig. 7 – Amount of gases CO2 (circles) and CO (squares) produced from the thermal decomposition of C60(NO2)14 as measured through the TGA-FTIR analysis. The area below the peaks at 2363 and 2335 cm1 for CO2 and 2172 and 2115 cm1 for CO was measured with the Ominc software of the infrared spectrometer and reported as Ln[(Abs)t/(Abs)0] in the ordinate of the graph.

To measure the amount of heat of decomposition released by C60(NO2)14 a differential scanning calorimetric (DSC) measurement was recorded as shown in Fig. 8. The DSC trace shows three main exothermal transitions: first of all a minor exothermal peak at 98 C can be observed followed by the deflagration peak at 190 C with the onset at 160 C, thus in a temperature range completely in line with that measured in the DTA of Fig. 2. After the deflagration peak there is another broad exothermal transition with a peak at 247 C. From the TGA-FTIR we know that above the 210 C C60(NO2)14 is completely decomposed into an oxidized carbon which releases only CO2 and CO. Consequently, the real decomposition enthalpy of C60(NO2)14 should be calculated using only the first two transitions at 98 C and 190 C. The integration of these two peaks corresponds to a total released heat of 434 J/g which, multiplied by the molecular weight of C60(NO2)14 (1364.74 Da) corresponds to a decomposition enthalpy DHr = 592.3 kJ/mol. Assuming that the decomposition reaction of C60(NO2)14 is essentially of the following type: C60 ðNO2 Þ14 ! 60Camorphous þ 14NO2

reaches a plateau from 250 C to 340 C and then grows again at higher temperatures. Of course the production of CO2 and CO should be considered in the frame of the discussion of the previous Section 3.3 where it was shown that the oxidized carbon produced from the deflagration gradually loses its oxygenated groups with the increase of the temperature becoming completely free from oxygenated groups at 700 C (see Fig. 4). Therefore, the release of CO2 and CO as reported in Fig. 7 is a consequence of the carbonization process.

ð2Þ

Then, it is possible to calculate the free enthalpy of formation as follows: DHr ¼ 14DHNO2  DHnitro½60fullerene

ð3Þ

592:3 ¼ 14ð33:2Þ  DHnitro½60fullerene

ð4Þ

DHnitro½60fullerene ¼ þ1057 kJ=mol

ð5Þ

This value of free enthalpy of formation of C60(NO2)14 is considerably lower than the value predicted by Richard and Ball who expected theoretically DHnitro[60]fullerene = +4617 kJ/

Fig. 8 – DSC trace of C60(NO2)14 recorded at a heating rate of 10 C/min under N2 flow in a sealed stainless steel crucible. The integral heat of decomposition is 2017 J/g.

420

CARBON

6 2 ( 2 0 1 3 ) 4 1 3 –4 2 1

Table 1 – Thermodynamic parameters of tetradeca[60]fullerene and octanitrocubane.

Tetradeca[60]fullerene up to 200 C Tetradeca[60]fullerene DSC integration Octanitrocubane Ref. [24,37]

Decomposition enthalpy (J/g)

Decomposition enthalpy (kJ/mol)

Free energy of formation (kJ/mol)

434 2017 7489

592 2752 3475

1051 3217 594

mol [22]. The complete integration of all the exothermal transitions of the DSC trace including also those occurring at temperatures higher than 210 C leads to total decomposition enthalpy of 2017 J/g. In this value we are integrating all the phenomena that from C60(NO2)14 lead to amorphous carbon and multiplying by the molecular weight of C60(NO2)14 we get a decomposition enthalpy (DHr) of 2752.7 kJ/mol. Substituting this value in Eqs. (3) and (4) it leads to a free enthalpy of formation of C60(NO2)14: DHnitro½60fullerene ¼ þ3217:5 kJ=mol

ð6Þ

a value considerably closer to the theoretical value predicted by Richard and Ball [22] (DHnitro[60]fullerene = +4617 kJ/mol) [22] and more reasonable than the former value of +1057 kJ/mol. In Table 1 are summarized the key parameters of tetradeca[60]fullerene in terms of the decomposition enthalpy as measured by the DSC up to 200 C or integrated on the entire DSC curve up to 500 C and the resulting free energy of formation calculated according to reaction (2). These values are compared with the decomposition enthalpy of octanitrocubane as reported in Ref. [24,37]. Octanitrocubane is by far a more energetic material than tetradeca[60]fullerene releasing 3.71 times more energy per gram than the latter. The decomposition reaction of octanitrocubane is admitted to occur under the conventional form [24,37]: C8 ðNO2 Þ8 ! 8CO2 þ 4N2

ð7Þ

a decomposition path which is completely different from that we have observed for tetradeca[60]fullerene reported in Eq. (2).

4.

Summary

This study has shown that under certain experimental circumstances a highly nitrated C60 fullerene is obtained which is insoluble in benzene and precipitates from the solution. The TGA analysis has shown that the polynitro[60]fullerene has a elemental composition of the type C60(NO2)14 and the TGA in combination with the DTA have shown that it decomposes exothermally above 170 C with a considerably release of heat, a process which can be refereed as deflagration. The FTIR analysis of the carbonaceous product formed after the deflagration and heated from 200 C to 650 C has revealed which consists of oxidized carbon rich in different types of oxygenated groups and resembling polymeric fullerene oxide. At 700 C the carbonaceous matter appears completely free from oxygenated groups and shows also the signature of C60 fullerene which is present in low amounts 610% in the carbon matrix. C60(NO2)14 was also analyzed through the TGA-FTIR analytical technique and it was found that the deflagration occurs with the release of a mixture of nitrogen oxides: NO2,

NO and smaller amounts of N2O. After the deflagration, when the release of nitrogen oxide mixture is stopped, only CO2 and CO are released. The former in higher amounts at lower temperature while the latter becomes more abundant at higher temperatures. The DSC analysis of C60(NO2)14 in sealed crucibles has permitted us to measure the decomposition enthalpy of this compound. The decomposition enthalpy including the deflagration point (up to 210 C) corresponds to 434 J/g or DHr = 592.3 kJ/mol. If instead the entire DSC exotherm is integrated as shown in Fig. 8, then the decomposition exotherm involves the release of 2017 J/g which corresponds to decomposition enthalpy DHr = 2752.7 kJ/mol. The decomposition enthalpy of tetradeca[60]fullerene is by far lower than that of octanitrocubane. From these values the free energy of formation of C60(NO2)14 has been calculated and compared with a theoretical value.

R E F E R E N C E S

[1] Kroto HW, Allaf AW, Balm SP. C60 buckminsterfullerene. Chem Rev 1991;91:1213–35. [2] Taylor R. Lecture notes on fullerene chemistry. A handbook for chemists. London: Imperial College Press; 1999. [3] Birkett PR. Fullerene chemistry. Annu Rep Prog Chem Sect A Inorg Chem 1999;95:431–51. [4] Hirsch A, Brettreich M. Fullerenes. Chemistry and reactions. Weinheim: Wiley-VCH; 2005. [5] Nierengarten JF, Martin N, Fowler P, editors. Chime des fullerenes – fullerene chemistry. Comptes Rendus Chimie 2006;9:859–1116. [6] Troshin PA, Lyubovskaya RN. Organic chemistry of fullerenes: the major reactions, types of fullerene derivatives and prospects for practical use. Russ Chem Rev 2008;77:323–69. [7] Cataldo F, Da Ros T. Medicinal chemistry and pharmacological potential of fullerenes and carbon nanotubes. Dordrecht: Springer; 2008. [8] Cataldo F, Iglesias-Groth S. Fulleranes: the hydrogenated fullerenes. Dordrecht: Springer; 2010. [9] Darwish AD. Fullerenes. Annu Rep Prog Chem Sect A Inorg Chem 2010;106:356–75. [10] Hamwi A, Marchand V. Oxidized fullerene derivatives containing hydroxyl, nitro and fluorine groups. Fullerene Sci Technol 1996;4:835–51. [11] Chiang LY, Bhonsle JB, Wang L, Shu SF, Chang TM, Hwu JR. Efficient one-flask synthesis of water-soluble [60]fullerenols. Tetrahedron 1996;52:4936–72. [12] Cataldo F. Preparation of polynitrofullerene by the action of dinitrogen tetroxide on C60. Fullerene Sci Technol 1997;5:257–65. [13] Anantharaj V, Bhonsle J, Canteenwala T, Chiang LY. Synthesis and characterization of nitrated [60]fullerene derivatives. J Chem Soc Perkin Trans 1999;1:31–6.

CARBON

6 2 (2 0 1 3) 4 1 3–42 1

[14] Anantharaj V, Wang LY, Canteenwala T, Chiang LY. Synthesis of starburst hexa-oligoanilinated C60 using hexanitro[60]fullerene as a precursor. J Chem Soc Perkin Trans 1999;1:3357–66. [15] Anantharaj V, Wang LY, Chiang LY. Phenylamine analogous adducts of C60. Fullerene Sci Technol 1999;7:493–504. [16] Troshin PA, Astakhova AS, Lyubovskaya R. Synthesis of fullerenols from halofullerenes. Fullerenes Nanot Carbon Nanostruct 2005;13:331–43. [17] Franco JU, Ell JR, Hilton AK, Hammons JC, Olmstead MM. C60Cl6, C60Br8 and C60(NO2)6 as selective tools in organic synthesis. Fullerenes Nanot Carbon Nanostruct 2009;17:349–60. [18] Wang N. Review on the nitration of [60]fullerene. Propellants Explos Pyrotech 2001;26:109–11. [19] Slanina Z, Sugiki T, Zhao X, Lee S-L, Chiang LY, Osawa E. C60(NO2)2: quantum-chemical evaluations of structure, energetics, and vibrational spectra. Fullerene Sci Technol 2000;8:351–867. [20] Slanina Z, Zhao X, Chiang LY, Osawa E. Biologically active fullerene derivatives: computations of structures, energetics, and vibrations of C60(OH)x and C60(NO2)y. Int J Quantum Chem 1999;74:343–9. [21] Slanina Z, Iida S, Zhao X, Chiang LY, Adamowicz L, Osawa E. Computation of hexa-nitrated and hexa-anilinated fullerenes. Synthetic Met 2001;121:1101–2. [22] Richard RM, Ball DW. Enthalpies of formation of nitrobuckminsterfullerenes: extrapolation to C60(NO2)60. J Mol Struct Theochem 2008;858:85–7. [23] Peko¨z R, Erkoc¸ S. Structural and thermochemical properties, and energetics of C8(NO2)8 and C20(NO2)4n (n = 0–4). Comput Mater Sci 2009;46:849–53. [24] Eaton PA, Gilardi RL, Zhang MX. Polynitrocubanes: advanced high-density, high-energy materials. Adv Mater 2000;12:1143–8. [25] Kubota N. Propellants and explosives. Weinheim: WileyVCH; 2007.

421

[26] Cooper PW. Explosives engineering. Weinheim: Wiley-VCH; 1996. [27] Gray P, Yoffe AD. The reactivity and structure of nitrogen dioxide. Chem Rev 1955;55:1069–154. [28] Waddington TC. Non-aqueous solvents. London: Thomas Nelson; 1969. [29] Miaskiewicz MK, Kecki Z. EPR study of the dinitrogen tetroxide dissociation in organic solvents. J Sol Chem 1985;14:665–73. [30] Shiri M, Zolfigol MA, Kruger HG, Tanbakouchian Z. Advances in the application of N2O4/NO2 in organic reactions. Tetrahedron 2010;66:9077–106. [31] Lin-Vien D, Colthup NB, Fateley WG, Grasselli JG. The handbook of infrared and raman characteristic frequencies of organic molecules. Academic Press; 1991 [chapter 11]. [32] Zhai R-S, Das A, Hsu C-K, Han C-C, Canteenwala T, Chiang LY, et al. Polymeric fullerene oxide films produced by decomposition of hexanitro[60]fullerene. Carbon 2004;42:395–403. [33] Cataldo F, Heymann D. A study of polymeric products formed by C60 and C70 fullerene ozonation. Polym Degrad Stabil 2000;70:237–43. [34] Cataldo F. Polymeric fullerene oxide (fullerene ozopolymers) produced by prolonged ozonation of C60 and C70 fullerenes. Carbon 2002;40:1457–67. [35] Cataldo F, Ursini O, Cherubini C, Rocchi S. Synthesis of cisand trans-polyisoprene adduct with nitrogen dioxide (NO2/ N2O4 mixture) and a study of the thermal stability of the adduct. Polym Degrad Stabil 2012;97:1090–100. [36] Hatakeyama T, Liu Z. Handbook of thermal analysis. Chichester: John Wiley & Sons; 1998. p. 337–77. [37] Sikder AK, Sikder N. A review of advanced high performance, insensitive and thermally stable energetic materials emerging from military and space applications. J Hazard Mater 2004;A112:1–15.