Prediction of heat of formation for exo-Dicyclopentadiene

https://doi.org/10.1016/j.jlp.2016.10.015Get rights and content

Highlights

  • Computational chemistry methods were applied to predict the heat of formation for dicyclopentadiene.

  • The enthalpy difference between two dicyclopentadiene isomers was determined.

  • Homodesmotic reaction was constructed per the hierarchy.

  • The predicted thermochemical data could be used for future thermal runaway studies.

Abstract

Dicyclopentadiene (DCPD) is an organic compound with two structural isomers, the exo and endo isomers. There have been several thermal runaway accidents related to this hazardous compound. It is well known that heat of formation is one of the most important parameters to investigate thermal runaway reactions. The heat of formation for the endo isomer has been characterized via computational and experimental studies. However, there is no thorough computational or experimental study on the heat of formation for the exo isomer. In this work, computational chemistry methods with homodesmotic reaction schemes were proposed to predict the heat of formation for the exo isomer. First, the computational methodology was validated by comparing predicted results of the endo isomer with its existing experimental value (42.2 ± 0.6 kcal/mol). The results from high level ab-initio, density functional theory, and composite methods were shown in a good agreement with the experimental value. The same methodology was then applied to predict the heat of formation for the exo isomer. The energy difference of heat of formation between two isomers was estimated at 0.7 ± 0.1 kcal/mol based on various computational methods. Therefore, combining the experimental and computational data, the predicted heat of formation for the exo isomer is 41.5 ± 0.6 kcal/mol. This work could provide reliable thermochemical data for inherently safer design of any processes involving DCPD.

Introduction

Dicyclopentadiene (DCPD) is an organic compound with the chemical formula being C10H12. It was obtained primarily from steam cracking of naphtha or crude feed in the C5 stream. There has been a strong interest in the polymerization of DCPD via the ring opening metathesis polymerization (ROMP) using metallic catalysts (Hayano et al., 2006) due to its unique properties and new applications including self-healing polymers (Mauldin et al., 2007) and cryogenic storage (Toplosky and Walsh, 2006). There are two structural isomers: the endo and the exo isomer (Fig. 1). The endo isomer has been a subject of many computational (Feng et al., 2012, Guner et al., 2003) and experimental studies (Hayano and Tsunogae, 2005, Liu et al., 1999, Burcat and Dvinyaninov, 1997). To the best of our knowledge, there has never been a thorough computational study on the exo isomer. The exo isomer is preferred over the endo isomer in the ring opening metathesis polymerization due to its kinetics and the exothermic nature of the process (Davidson et al., 1996), which has also attracted lots of attention as a potential high density fuel (Krishnamachary et al., 2014).

Despite its valuable applications, there have been questions of its safety issue (Herndon and Manion, 1968). Previous experiments in the dimerization of cyclopentadiene (CPD) (Ende et al., 2007) showed that the dimerization of CPD was highly exothermic which ruptured the test cell. Herndon et al. (Herndon et al., 1967) showed experimentally that the dimer decomposed to CPD before forming the endo isomer thus indicating that the exo isomer cannot change its conformation to endo directly. Harkness et al. studied the kinetics of CPD to endo-DCPD using spectroscopy (Harkness et al., 1937). Recently, Guner et al. (Guner et al., 2003) benchmarked the reaction energy of CPD to endo-DCPD as part of a proposed set of pericyclic reactions for benchmarking new computational methods. A computational study on DCPD was conducted by Jamróz et al. (Jamróz et al., 2003) and the geometries of the 14 possible isomers were calculated and compared with available experimental values using the B3PW91 functional.

DCPD has been involved in a catastrophic incident of a plant manufacturing synthetic resins. The incident at Nevcin Polymers in Netherlands on July 2nd, 1992 resulted in 3 fatalities and a large scale destruction of the city due to a thermal runaway initiated by charging wrong amounts of DCPD mixture into a reactor. The recommended preparation of exo-DCPD took place at more than 150 °C in an Argon atmosphere (Nelson and Kuo, 1975), but the product is often not pure enough to characterize the compound using conventional calorimetry. Many researchers reported novel methods to convert the endo isomer to the exo isomer (Zhang et al., 2007) in order to prepare fuels and polymers. However, due to its reactivity the normal characterization of exo-DCPD and measurement of its heat of formation at standard conditions is challenging.

Computational chemistry has been extensively applied to compare the reaction pathways (Wang et al., 2009a, Wang et al., 2009b, Wang et al., 2010) and estimate the heat of formation or heat of reaction for runaway reactions in our previous studies (Saraf et al., 2003, Wang et al., 2009a, Wang et al., 2009b, Wang et al., 2010, Wang and Mannan, 2010). The heat of formation is an important data for safe design of chemical process and characterizing the thermodynamics of the compound and kinetic pathways. Given the considerable industrial interest in the ring opening metathesis polymerization of exo-DCPD (Henna and Larock, 2009, Rule and Moore, 2002, Mol, 2004) and obtaining high accurate heat of formation to model fuel combustion processes (Chung et al., 1999), we are presenting a thorough computational investigation using quantum mechanical methods to reliably estimate the heat of formation for exo-DCPD at 298.15 K and 1 atm.

Section snippets

Computational methods

A variety of methods were used in this work including semi-empirical (AM1) (Dewar et al., 1985), post-SCF methods (MP2, MP3, MP4, CCSD, CCSD(T)) (Møller and Plesset, 1934, Pople et al., 1976, Krishnan and Pople, 1978, Purvis and Bartlett, 1982, Pople et al., 1987), density functional theory (B3LYP, M06-2X, M06-HF, M06-L) (Becke, 1993, Zhao and Truhlar, 2006, Zhao and Truhlar, 2008), double-hybrid density functionals (B2PLYP, mPW2PLYP) (Grimme, 2006, Schwabe and Grimme, 2006) and composite

Results and discussion

The initial calculations were performed for all the schemes and the results were provided in Table 2. Four homodesmotic reaction schemes with varying degrees of conservation of the ringed species on the either side of the reaction were investigated to gauge the quality of results as shown in Fig. 4. The results were tested using 4 different levels of theories: ab initio SPE, DFT methods with and without Grimme's corrections, double hybrid density functionals with and without Grimme's

Conclusions

This study used HD-4 reaction schemes and a variety of computational methods with varying levels of complexity to predict the heat of formation for the exo isomer. The results of the endo isomer were in a good agreement with the existing experimental value, which validated the methodology of these computational models. The heat of formation results for the exo isomer should be accurate enough by applying the same computational models. The heat of formation for the exo isomer was determined as

Acknowledgements

We thank the Texas A&M Supercomputing Facility for the computing time and the Laboratory for Molecular Simulations (LMS) in the Department of Chemistry for software, computing time and support. We thank Dr. Lisa Perez and Dr. Steven Wheeler for their helps in molecular modeling, useful discussions and interpreting the results.

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