Thermochemical Processes During the Degradation of Nitroguanidine

Subscriber access provided by AUBURN UNIV AUBURN

A: Environmental, Combustion, and Atmospheric Chemistry; Aerosol Processes, Geochemistry, and Astrochemistry

Thermochemical Processes during the Degradation of Nitroguanidine in Water: A Density Functional Theory Investigation Jing Wang, and Manoj K. Shukla J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/acs.jpca.9b00749 • Publication Date (Web): 22 Feb 2019 Downloaded from http://pubs.acs.org on February 28, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry

Thermochemical Processes during the Degradation of Nitroguanidine in Water: A Density Functional Theory Investigation Jing Wang1, Manoj Shukla2* 1HX5 2Environmental

LLC, Vicksburg, MS 39180, USA

Laboratory, US Army Engineer Research and Development Center Vicksburg, MS 39180, USA

Abstract In the present study, thermochemical mechanisms are proposed for the decomposition of nitroguanidine (NQ) in aqueous solution. Minnesota density functional M06-2X was employed in depicting the pathways for the NQ decomposition with conductor-like polarizable continuum model (CPCM) approach to consider effect of bulk water solution. Followed by the formation of hydroxyguanidine and/or guanidine along with nitrite by eliminating the nitro group from NQ through photolysis, two main degradation steps through thermochemical process were investigated. These thermochemical degradation steps include the formation of cyanamide from hydroxyguanidine and/or guanidine along with ammonia, and the formation of cyanoguanidine from the dimerization of cyanamide. Further degradations of the fragments of cyanamide, cyanoguanidine, guanidine, and hydroxyguandine were also explored. The results show that melamine and urea may exist as degradation fragments while cyanide and nitrosoguanidine are unlikely to form through usual thermochemical processes due to the presence of high energy barriers. Water and hydroxide ions play important roles in the degradation process; in particular, hydroxide ions significantly lower the energy barriers demonstrating that the proposed pathway is energetically viable.

*Corresponding author; email: [email protected]

1 ACS Paragon Plus Environment

The Journal of Physical Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 20

Introduction Nitroguanidine (NQ) is one of the important insensitive munitions compounds that has been used in several munitions formulations.1 NQ degrades in the environment, and cyanamide has been suggested to be the end product of NQ degradation.2 On the other hand, Kaplan et al.3 proposed a mixed biological and chemical degradation mechanism of NQ. In this investigation, NQ was first microbially reduced to nitrosoguanidine after acclimation by the anaerobic sludge microorganisms and then was followed by a chemical degradation of nitrosoguanidine into guanidine, cyanamide, cyanoguanidine, and melamine. Thermal stability of NQ was studied by TG/DSC-MS-FTIR and multivariate non-linear regression under both isothermal and non-isothermal conditions at temperatures of 210 ˚C and 230 ˚C, respectively.4 It was observed that NQ may be decomposed and release some gas products (including N2O, CO, CO2, and NH3, with little amount of NO2 and almost no NO). Simultaneous aerobic degradation was observed after four days of incubation for IMX-101 formulation constituents including 2,4-dinitroanisole (DNAN), 3-nitro-1,2,4-triazol-5-one (NTO), and nitroguanidine (NQ). 5 The degradation products contain nitrourea, 1,2-dihydro-3H-1,2,4-triazol-3-one, and 2,4-dinitrophenol.5 The mechanism of hydrolysis of NQ was theoretically studied at AM1 level.6 The calculated activation energies for the hydrolysis were predicted to be about 278.2 kJ/mol, 330.2 kJ/mol and 213.0 kJ/mol in neutral, acidic and alkaline media, respectively. 6 Guanidine was reported to be a primary degradation product of NQ in the study of the IMX-101 formulation’s photochemical degradation studies.7 Previous experimental studies of NQ photolysis have shown a number of different products, yet the reports are often in disagreement with regard to kinetics and product distribution. 8 Scission of the N—NO2 bond has been proposed as the primary reaction, and evidence exists showing this to be a homolytic cleavage.8 Spin-trapping of NO2 radical provided the proof that ultraviolet (UV) photolysis of RDX, HMX, and NQ (all nitramine explosives) is homolysis decomposition and that the closed shell mechanism was not the pathway. The other product from this initial reaction is shown to be either guanidine or hydroxyguanidine, yet those determinations showed the two products to be indistinguishable by the analytical techniques employed. 8

The resultant NO2 and guanidinyl radicals would be hydrolyzed rapidly to give nitrous acid and 2 ACS Paragon Plus Environment

Page 3 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


hydroxyguanidine or guanidine. Nitrite will go on to photo-oxidize to nitrate9, whereas the hydroxyguanidine and/or guanidine will not be photoactive due to its absorption spectrum not overlapping with the emission from the light source. Cyanamide, the corresponding dimer (cyanoguanidine), and the trimer (melamine) have also been reported or suspected as possible products. 10-12 Since photodegradation of NQ leads to the formation of guanidine and or hydroxyguanidine7,8 and these compounds do not show absorption above 200 nm region (Table S1 in the Supporting Information), this manuscript deals with the further degradation of guanidine/hydroxyguanidine in the water solution using rigorous computational chemistry approaches. Our investigation revealed that further degradation of NQ will be governed by the thermochemical process and cyanamide, cyanoguanidine and urea would be the dominant products. The potential for further degradation of these compounds have also been discussed. Computational Details Minnesota density functional M06-2X13 was applied in exploring the pathways for the NQ decomposition together with the standard 6-311G(d,p) basis set.14,15 Higher level of augmented quadruple Dunning’s correlation consistent basis sets aug-cc-pvqz16 were also adopted in Step 2 for comparison with results at 6-311G(d,p) level. All the studied models have been fully optimized by analytic gradient techniques. The force constants were determined analytically in the analysis of harmonic vibrational frequencies for all of the complexes. An intrinsic reaction coordinate (IRC) analysis was carried out to ensure that each transition state links to the corresponding reactants and products (both as local minima on the potential energy surface). The mechanisms of the thermochemical processes of the decomposition of the corresponding compounds are therefore detailed to every elementary reaction step. The conductor-like polarizable continuum model (CPCM)17,18 was employed to simulate the entire reaction in water solvent (with a dielectric constant of 78.4). The Gaussian-09 package of programs19 was used for all computations.

Results and Discussions 3 ACS Paragon Plus Environment


Page 4 of 20

The present computational investigation involved a thermochemical pathways for the degradation of compounds (guanidine and or hydroxyguanidine) formed during the photodegradation of NQ in water at the room temperature. The degradation scheme of NQ explored here is shown in the Figure 1. Nitroguanidine can have several tautomers, and the most stable tautomer, shown in Figure 2, has been considered for the computational investigation.20,21

Figure 1. Degradation of NQ investigated in the current work.

Figure 2. Structure of NQ 1. Formation of Cyanamide 2.1 Formation of Cyanamide from Guanidine Four different routes were explored for the formation of cyanamide from guanidine in the bulk water solution, as shown in the Figure 3. One step reaction involving an intramolecular proton transfer may lead to the formation 4 ACS Paragon Plus Environment

Page 5 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


of cyanamide from guanidine (Figure 3: Route 1). In this reaction, the hydrogen of the imino group of guanidine is transferred to the nitrogen of one of the amino groups. This will simultaneously cause the cleavage of the N-C bond and release of ammonia gas. However, this step involves a high activation energy (59.6 kcal/mol) and therefore is unlikely to take place. We also considered the role of microhydration and the presence of hydroxide ion on the cyanamide formation in the bulk water. The presence of one water molecule in the reaction path was found to reduce reaction barrier height by about 50% (Figure 3: Route 2). However, addition of a second water molecule does not have significant influence in the transition state reaction barrier height (Figure 3: Route 3). In the single water assisted cyanamide formation, the transition state is characterized by the double proton transfer, and the C-N bond is increased to 1.552 Å (2-2TS in Route 2, Figure 3).

Route 1

Route 2

Route 3

Route 4 5

ACS Paragon Plus Environment


Page 6 of 20

Figure 3. Reaction coordinates for formation of cyanamide from guanidine: Route 1 of mono guanidine decomposition, Route 2 with one water, Route 3 with two water molecules, and Route 4 with one water hydrated hydroxide ion. (zero-point corrected energies were adopted for energy differences in kcal/mol, M06-2X/6311G(d,p) level, CPCM model with water as solvent; energy differences in parenthesis obtained at M06-2X/augcc-pvqz level).

The presence of a hydroxide ion in the monohydrated form in the reaction path was found to significantly reduce the transition barrier height of cyanamide formation (Figure 3: Route 4). The hydrogen of the imino group was attracted by the hydroxide ion and three hydrogen bonds were formed to bind the guanidine and the monohydrated hydroxide ion together as the reactant complex (2-4a in Route 4, Figure 3). It was found that only 14.3 kcal/mol of activation energy would be required for the ammonia and cyanamide to form from guanidine. Therefore, it is expected that the presence of a hydroxide ion would make it viable for the reaction to move forward at room temperature.

We also performed a higher level of calculation (M06-2X/aug-cc-pvqz) for all the four above routes. It was revealed that results at M06-2X/6-311G(d,p) level are comparable with those obtained at M06-2X/aug-cc-pvqz level. This suggests that the consideration of the 6-311G(d,p) basis set is reasonable and was adopted for the entire pathways in the present study.

2.2 Formation of Cyanamide from Hydroxyguanidine The formation of cyanamide from hydroxyguanidine appears to be a major two-step process (Figure 4). These steps correspond to two consecutive proton transfers from the amino hydrogens to the nitrogen of the hydroxyl imine site. This will lead to the scission of the C-NH2OH bond in the second step (Figure 4: Route 5). It was found that the hydrogen of the hydroxide group from the product of step 1 (2-5b) rotates easily to form the reactant of step 2 (2-5c). However, these steps involve high energy barriers of 44.7 and 60.0 kcal/mol for the first and 6 ACS Paragon Plus Environment

Page 7 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


second steps respectively. The presence of one water molecule in the proton transfer reaction paths (Figure 4: Route 6) significantly reduces the activation energy barriers, and they are predicted to be 15.6 and 28.2 kcal/mol for the first and second steps, respectively. The further reduction among barrier heights was revealed when two water molecules were involved in the proton transfer reaction paths. Consequently, the activation energy for the first and second steps was predicted to be 10 and 24.5 kcal/mol, respectively (Figure 4: Route 7). The presence of hydroxide ion considered in the monohydrated form also significantly reduced the barrier height for formation of cyanamide; the activation barrier was predicted to be only 12.3 kcal/mol (Figure 4: Route 8).

Route 5: Step 1

Route 5: Step 2

Route 6: Step 1

Route 6: Step 2



Route 7: Step 1

Page 8 of 20

Route 7: Step 2

Route 8: Step 2 Figure 4. Reaction coordinates for the hydrolysis of hydroxyguanidine: Route 5 of mono hydroxyguanidine decomposition, Route 6 with one water, Route 7 with two water molecules, and Route 8 with one water hydrated hydroxide ion. (zero-point corrected energies were adopted for energy differences in kcal/mol, M06-2X/6311G(d,p) level, CPCM model with water as solvent) 2. Formation of Cyanoguanidine from Cyanamides. Cyanoguanidine can be obtained from the dimerization of cyanamide molecules in the bulk water solution as depicted in the Figure 5. In the initial reactant configuration, the amino group of one monomer interacts with the carbon atom of the second monomer. The transition state is characterized by the formation of 4-membered ring structure (Figure 5: Route 9). While the product is about 23.7 kcal/mol more stable than the reactant, the transition state barrier height is predicted to be 61.9 kcal/mol and thus unlikelihood of the possibility of this reaction at the room temperature. 8 ACS Paragon Plus Environment

Page 9 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Route 9

Route 10 Figure 5. Reaction coordinated for formation of cyanoguanidine from cyanamide: Route 9 with two cyanamides, Route 10 with assistance of one water hydrated hydroxide ion (zero-point corrected energies were adopted for energy differences in kcal/mol, bond lengths in Å, M06-2X/6-311G(d,p) level, CPCM model with water as solvent) When considering the reaction assisted by one water hydrated hydroxide ion, the energy barrier was lowered for the dimerization process. Through hydrogen bonding interactions, a near attacking reactant compound was stabilized as shown in 3-2a (Route 10 in Figure 5). In this reactant, the amino group of the first cyanamide forms a hydrogen bond with the nitrogen of the second cyanamide (with atomic distance of 1.787 Å for N2H…N11). 9 ACS Paragon Plus Environment


Page 10 of 20

Furthermore, the hydroxide ion forms two hydrogen bonds with the two cyanamide molecules with atomic distances of 1.824 Å and 2.029 Å. The water was attached to the hydroxide ion with one hydrogen bond by an interatomic distance of 1.839 Å. The transition state structure is characterized by the structure that the atomic distance between C1 and N22 was shortened to 1.853 Å (3-2TS). The activation barrier is predicted to be 20.1 kcal/mol. The product of cyanamide bounded with the hydrated hydroxide ion 3-2b (Figure 5) is about 11 kcal/mol more stable in energy than the reactant.

3. Formation of Urea through Hydrolysis of Cyanamide Urea can be obtained through the hydrolysis of cyanamide following two steps process. The first step involves the addition of one water molecule to cyanamide followed by an intramolecular proton transfer in the second step (Figure 6, Route 11). The energy barriers for these steps are calculated to be 56.7 kcal/mol and 28.5 kcal/mol, respectively; the first step being the rate-determining step. When additional water molecules were considered, the second step involving the proton transfer was predicted to be almost barrierless. The energy barriers for the first step was lowered to 35.6 kcal/mol and 34.1 kcal/mol with the consideration of assistance with one and two water molecules, respectively. Moreover, this barrier height was further lowered to 31.0 kcal/mol when monohydrated hydroxide ion was considered (Figure 6, Route 14). Although, the energy barriers were lowered by more than 20 kcal/mol with the help of water and hydroxide ion, it is unlikely that this reaction would proceed at the room temperature. Thus, urea is likely to form under elevated temperature.


Page 11 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Route 11: Step 1

Route 11: Step 2

Route 12: Step 1

Route 12: Step 2

Route 13: Step 1

Route 13: Step 2



Page 12 of 20

Route 14: Step 1 Figure 6. Reaction coordinate for formation of urea from cyanamide and water: Route 11 as hydrolysis of cyanamide with water, Route 12 as reaction of Route 11 with assistance of one water molecule, Route 13 as reaction of Route 11 with assistance of two water molecules, and Route 14 as reaction of Route 11 with assistance of monohydrated hydroxide ion (zero-point corrected energies were adopted for energy differences in kcal/mol, M06-2X/6-311G(d,p) level, CPCM model with water as solvent)

4. Formation of Melamine from Cyanoguanidine and Guanidine Melamine can be formed through cyanoguanidine when catalyzed by potassium hydroxide. 10-12,21 It may also be formed through dimerization of cyanoguanidine and guanidine. Four steps: addition of guanidine to cyanoguanidine, proton transfer, six-member ring closure, and deamination were considered for this reaction. Guanidine and cyanoguanidine would form a complex as the first step through hydrogen bonds with distances of 2.063 Å (5-1A in Route 15, Figure 7). The nitrogen from guanidine attacks the carbon on cyanoguanidine forming transition state 5-1TS1; the transition state energy barrier is estimated to be around 10 kcal/mol for this step. In the following step, a proton transfer between two nitrogens would lead to 5-1TS2 with transition state barrier of about 33 kcal/mol. The intermediate 5-1C will then proceed to form a six-member ring leading to intermediate 51D. The energy barrier for the ring closure is about 12.4 kcal/mol. Through a proton transfer between the nitrogen of the six-member ring and one amino group of the neighboring carbon and overcoming the 31.6 kcal/mol energy 12 ACS Paragon Plus Environment

Page 13 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


barrier, intermediate 5-1D is deaminated to release ammonia from the ring and form melamine. It can be noticed that step 2 of proton transfer and step 4 of deamination are the rate-determing steps, whose energy barriers are over 30 kcal/mol. Route 16 in Figure 7 demonstrates the reaction with participation of one water molecule, and four steps are involved in this route also. The first step of addition and the third step of ring closure have comparable energy barriers as the corresponding steps in Route 15 (9.2 kcal/mol vs 9.9 kcal/mol, and 13.6 kcal/mol vs 12.4 kcal/mol). However, for step 2 of the proton transfer and step 4 of deamination, the energy barriers were significantly lowered to 8.9 kcal/mol and 15.6 kcal/mol, respectively. This reveals that the last step of deamination is the ratedetermining step and energetically viable. It also implies that water plays a more important role when proton transfer is involved. This illustrates that melamine may be formed when both cyanoguanidine and guanidine exist in the aqueous solution.

Route 15



Page 14 of 20

Route 16

Figure 7. Reaction coordinated for formation of melamine from cyanoguanidine and guanidine without water (Route 15) and with one water molecule (Route 16) (zero-point corrected energies were adopted for energy differences in kcal/mol, M06-2X/6-311G(d,p) level, CPCM model with water as solvent)

5. Other Possible Degradation Products with Suitable Experimental Conditions 5.1 Formation of Cyanide from Cyanoguanidine It is not expected that cyanoguanidine can release cyanide and produce a hydroxyguanidine in water solution in the presence of hydroxide ion at room temperature, since computed energy barriers were estimated to be as high as 97.5 kcal/mol (Route 17 in Figure 8). Moreover, we also investigated the presence of hydroxyl radical on the formation of cyanide. We investigated that hydroxyl radical can attack the nitrogen of cyanoguanidine forming an intermediate 6-2B through the transition state 6-2TS1 as shown in Route 18 (Figure 8). The transition barrier for this step was computed to be around 45 kcal/mol. The intermediate 6-2B will then easily eliminate cyanide and produce hydroxyguanidine with an energy barrier around 3.5 kcal/mol. From the pathway of Route 18, it can be noted that the intermediate of 6-2B has very short lifetime and the product 6-2C is over 40 kcal/mol less stable 14 ACS Paragon Plus Environment

Page 15 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


than the reactant 6-2A. Hence the formation of cyanide from cyanoguanidine by hydroxyl radical is very difficult to proceed and the reverse reaction will be much more favored.

Route 17

Route 18

Figure 8. Reaction coordinates for formation of cyanide from cyanoguanidine. Route 17 is cyanoguanidine reacts with monohydrated hydroxide ion; Route 18 is cyanoguanidine reacts with hydroxyl radical. (zeropoint corrected energies were adopted for energy differences in kcal/mol, M06-2X/6-311G(d,p) level, CPCM model with water as solvent)

5.2 Formation of Nitrosoguanidine through Hydrolysis of Hydroxyguanidine Hydrolysis of hydroxyguanidine may lead to form nitrosoguanidine as shown in Figure 9. There are two major steps which require overcoming energy barriers of 93 kcal/mol and 7.1 kcal/mol, respectively. The energy barrier for step 1 in Route 18 is obviously too high for this reaction to take place at room temperature in water solution.



Route 18: Step 1

Page 16 of 20

Route 18: Step 2

Figure 9. Reaction coordinated for formation of nitrosoguanidine from hydroxyguanidine. (zero-point corrected energies were adopted for energy differences in kcal/mol, M06-2X/6-311G(d,p) level, CPCM model with water as solvent) Conclusions The post degradation pathway for the photolysis intermediates of NQ includes formation of cyanamide from guanidine or hydroxyguanidine, and formation of cyanoguanidine from cyanamides. The influence of microhydration, hydrated hydroxide ion and hydroxyl radical were also considered in these reactions. Our calculations show that both water and hydroxide ion and or hydroxyl radical would significantly lower the activation energy for degradation of NQ. Hydroxide has been found to be more efficient catalyst for degradation process of NQ. Further possible degradation products are also investigated. Our results demonstrate that degradation intermediates and final products may include guanidine, hydroxyguanidine, nitrite, cyanamide, ammonia, cyanoguanidine, urea, ammonia, and melamine, which were reported by some experiments3,8,10-12,22. However, nitrosoguanidine and cyanide would not form under normal condition due to the corresponding high energy barriers. The proposed pathways combining the mixed photolysis and hydrolysis processes are energetically viable for the degradation of NQ in water at room temperature. Acknowledgements


Page 17 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


The use of trade, product, or firm names in this report is for descriptive purposes only and does not imply endorsement by the U.S. Government. The tests described and the resulting data presented herein, unless otherwise noted, were obtained from research conducted under the Environmental Quality Technology Program of the United States Army Corps of Engineers and the Environmental Security Technology Certification Program of the Department of Defense by the USAERDC. Permission was granted by the Chief of Engineers to publish this information. The findings of this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents. Supporting Information The Supporting Information is available free of charge on the ACS Publications website which includes the first four excitation properties of nitroguanidine, guanidine and hydroxyguanidine at TDDFT/M06-2X/6-311G(d,p) level in CPCM (water as solvent), and the complete citation of reference 19. References 1.

Taylor, S.; Dontsova, K.; Walsh, M. Insensitive Munitions Formulations: Their Dissolution and Fate in Soils in Energetic Materials: From Cradle to Grave, Shukla, M.; Boddu, V.; Steevens, J.; Reddy, D.; Leszczynski, J. (Eds.), 2017, Springer+Business Media B.V, Dordrecht, Heidelberg, London, New York (In Press).

2. Spanggord, R. J.; Chou, T.-W.; Mill, T.; Haag, W.; Lau, W. Environmental Fate of Nitroguanidine, Diethyleneglycol Dinitrate, and Hexachloroethane Smoke. 1987. 3. Kaplan, D.L.; Cornell, J. H.; Kaplan, A. M. Decomposition of Nitroguanidine Environ. Sci. Technol., 1982, 16, 488-492. 4. Li, Y.; Cheng, Y. Investigation on the thermal stability of nitroguanidine by TG/DSC-MS-FTIR and multivariate non-linear regression J. Therm. Anal. Calorim. 2010, 100. 949-953. 5. Richard, T.; Weidhaas, J. Biodegradation of IMX-101 explosive formulation constituents: 2,4Dinitroanisole (DNAN), 3-nitro-1,2,4-triazol-5-one (NTO), and nitroguanidine J. Hazardous materials 2014, 180, 372-379.



Page 18 of 20

6. Xiao, H. M.; Li, Y. M.; Li, Y. F., Theoretical studies on the mechanism of hydrolysis of nitroguanidine by AMI method. Propellants Explosives Pyrotechnics 1998, 23 (1), 23-27. 7. Halasz, A.; Hawari, J.; Perreault, N. N., New Insights into the Photochemical Degradation of the Insensitive Munition Formulation IMX-101 in Water. Environ. Sci. Technol. 2018, 52, 589-596. 8. Pace, M. D.; Holmes, B. S. Spin trapping of .NO2 radicals produced by uv photolysis of RDX, HMX, and nitroguanidine." Journal of Magnetic Resonance 1969, 52, 143-146. 9. Mack, J.; Bolton, J. R. Photochemistry of nitrite and nitrate in aqueous solution: a review. Journal of Photochemistry and Photobiology A: Chemistry 1999, 128, 1-13. 10. Burrows, E. P., et al. Chromatographic trace analysis of guanidine, substituted guanidines and striazines in water. Journal of Chromatography A 1984, 294, 494-498. 11. Haag, W. R., et al. Aquatic environmental fate of nitroguanidine. Environmental Toxicology and Chemistry 1990, 9, 1359-1367. 12. Spanggord, R. J., et al. Environmental Fate of Nitroguanidine, Diethyleneglycol Dinitrate, and Hexachloroethane Smoke, 1987, SRI International: 67. 13. Zhao, Y.; Truhlar, D. G. The M06 suite of density functionals for main group thermochemistry, thermochemical kinetics, noncovalent interactions, excited states, and transition elements: two new functionals and systematic testing of four M06-class functionals and 12 other functionals Theor. Chem. Acc., 2008, 120, 215-241. 14. McLean, A. D.; Chandler, G. S. Contract Gaussian-basis sets for molecular calculations. 1. 2nd row atoms, Z=11-18 J. Chem. Phys., 1980, 72, 5639-5648. 15. Raghavachari, K.; Binkley, J. S.; Seger, R.; Pople, J. A. Self-Consistent Molecular Orbital Methods. 20. Basis set for correlated wave-functions J. Chem. Phys., 1980, 72, 650-654.


Page 19 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


16. D. E. Woon, T. H. Dunning Jr. Gaussian-basis sets for use in correlated molecular calculations. 3. The atoms aluminum through argon J. Chem. Phys. 1993, 98, 1358-1371. 17. Barone, V.; Cossi, M. Quantum calculation of molecular energies and energy gradients in solution by a conductor solvent model. J. Phys. Chem. A 1998, 102, 1995-2001. 18. Cossi, M.; Rega, N.; Scalmani, G.; Barone, V. Energies, structures, and electronic properties o molecules in solution with the C-PCM solvation model J. Comp. Chem. 2003, 24, 669-681. 19. Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A. et al. Gaussian 09, Revision D.01; Wallingford, CT, 2009. 20. Bulusu, S.; Dudley, R. L.; Autera, J. R. Structure of nitroguanidine: nitroamine or nitroimine? New NMR evidence from nitrogen-15 labeled sample and nitrogen-15 spin coupling constants Magnetic Resonance in Chemistry. 1987, 25 (3): 234–238. 21. Murmann, R. K.; Glaser, R.; Barnes, C. L. Structures of nitroso- and nitroguanidine x - ray crystallography and computational analysis. Journal of Chemical Crystallography. 2005, 35 (4): 317–325. 22. Kawasaki, A.; Ogata, Y. Kinetics of the formation of melamine from dicyandiamide. Tetrahedron, 1966, 22, 1267-1274.

Table of Content




Page 20 of 20

Thermochemical Processes During the Degradation of Nitroguanidine

Recommend Documents