First principles computational study on hydrolysis of water-reactive chemicals phosphorus trichloride and oxychloride (PCl3 and POCl3)

15th June 2018

Hyunwook Jung, Joonhee Kang, Hoje Chun, Byungchan Han

Department of Chemical and Biomolecular Engineering, Yonsei University, 03722, Seoul, Republic of Korea Motivation

PCl3 0 POCl3 0 (Phosphorus Trichloride) 4 2 (Phosphorus Oxychloride) 3 2 ₩ ₩ • Chemical Properties • Chemical Properties - Colorless Liquid - Colorless Liquid - Density: 1.576g g/cm3 - Density: 1.576g g/cm3 - Vapour pressure: 100mmHg - Vapour pressure: 100mmHg

• Common Uses • Common Uses

Pesticides Flame Retardant N-type Dopant Solar Cell

Chelating Agent Plastic Additives IC Optical Fiber

 World production of PCl3 & POCl3 exceeds more than 1/3 million tons annually  They are essential chemicals in industry because of their versatile uses 2 Y. Segall et al. Chem. Res. Toxicol. 2003, 16, 350-356 Motivation

Chemical disasters from unexpected reaction

AZF Disaster (France) Tianjin Explosion (China) Death: 30 Deaths: 173

Cause: NH4NO3 Cause: NaCN, NH4NO3, …

2 Dec. 1984 27 Sep. 2012

21 Sep. 2001 12 Aug. 2015

Bhopal Disaster (India) Gumi HF leakage Death: at least 3787 (Korea) Cause: Methyl isocyanate Deaths: 5 Cause: HF

 Yet, reaction database is far from completeness, which hinders safe control of

chemical accident 3 Motivation

REACH Regulations in EU (Registration, Evaluation, Authorization, and Restriction of Chemicals)

Experiments, Animal testing Physicochemical, Conventional approach Toxicological, Ecotoxicological Properties Computer Simulation, Ab-initio calculation

Alternative approach

Measurement methods of required physicochemical properties Experiment Ab-initio Calculation Reliable but, Not realistic in time, cost, Fast, low cost, and very safe. feasibility, and safety

4 Carlos Nieto-Draghi et al. 2015. Chem. Rev. 115 (24) 13093-13164 Outline

1. Motivation

2. Model Systems and Computational Details

3. Results and Discussion - Water-catalyzed hydrolysis - Structural analysis - Solvent effect by water and charge analysis - Potential energy surface profile

4. Summary

5. Acknowledgement 5 Model Systems and Computational Details

Grotthuss Mechanism; three-fold role of water

Reactant

H2O water Solvent

Catalyst

PCl3 Model Systems

Calculated using: Gaussian09 B3LYP 6-31+g(d,p)

6 Water-Catalyzed Hydrolysis

Free energy diagram

PCl3(g) + 3H2O(g) → H3PO3(g) + 3HCl(g) POCl3(g) + 3H2O(g) → H3PO4(g) + 3HCl(g)

Table 1. Reaction heat for each steps of the hydrolysis and experimental data (in parenthesis)

PCl3 POCl3 1st step -5.88 -8.85 2nd step -0.19 -9.84 3rd step -3.98 -8.34 Tautomerization -3.67 - ΔH -13.73 (-15.44) -27.03 (-24.1) 7 H. Jung et al. Journal of Hazardous Materials 341 (2018) 457-463 Structural Analysis

Torsional angle as key-descriptor of kinetics

CCPCl 90°

See-saw jh1

CC 180°

Trigonal bipyramidal Table 2. Torsional angle around central Phosphorus in the transition states

Torsional PCl3 Torsional POCl3 Step Angle High ∆‡ Low ∆‡ Angle High ∆‡ Low ∆‡ st 1 Cl1Cl2PCl3 150.26˚ 91.63˚ Cl1Cl2PO 157.87˚ 177.57˚ nd 2 Cl1Cl2PO 148.70˚ 91.16˚ O1ClPO2 151.06˚ 167.66˚ rd 3 ClO1PO2 146.33˚ 79.07˚ ClO1PO2 150.96˚ 151.89˚ ° ° 8 H. Jung et al. Journal of Hazardous Materials 341 (2018) 457-463 Slide 8 jh1 sp3 -> sp3d state로 전환된다는 내용을 좀더 잘 표현할 필요가 있음. jung hyunwook; 12/6/2018 Solvent Effect by Water: Charge Analysis

Charge Density Distribution

 Hybridization shift(sp3→sp3d) is qualitatively confirmed

9 H. Jung et al. Journal of Hazardous Materials 341 (2018) 457-463 Potential Energy Surface Profile

‡ ‡ ‡

PCl3+n·H2O POCl3+n·H2O

PCl2(OH)+HCl POCl2(OH)+HCl

 Typical gas phase SN2 reaction has double-well PES profile (PCl3)

 POCl3 has triple-well PES profile; Due to additional coordination by

double bonded Oxygen 10 H. Jung et al. Journal of Hazardous Materials 341 (2018) 457-463 Summary

 Adjacent water molecules play key role as a catalyst toward hydrolysis reaction via proton transfer.  Torsional angle around phosphorus atom is key-descriptor of the kinetics.  Hybridization of phosphorus is shifted from sp3 to sp3d at transition state.  Activated complex with charge separation was more stabilized by water.

 PCl3 and POCl3 have different potential energy profile due to different coordination around phosphorus.

11 H. Jung et al. Journal of Hazardous Materials 341 (2018) 457-463 Acknowledgement

This work was supported by • The Korea Ministry of Environment (MOE) as “the Chemical Accident Prevention Technology Development Project” • Global Frontier Program through the Global Frontier Hybrid Interface Materials (GFHIM) (2013- M3A6B1078882) • The Defense Industry Technology Center (DITC) for financial support from contract No.UC15000ID

12 Thank you for your attention!!

Contact Info. Hyunwook Jung Email: [email protected] Phone: +82-10-2780-2396

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