Clustering of HClO4 with Bronsted (H2SO4, HClO4, HNO3) and Lewis acids BX3 (X = H, F, Cl, Br, OH) : a DFT study

HClO4 is an important catalyst in organic chemistry, and also acts as a reservoir or sink species in atmospheric chlorine chemistry. In this study, we computationally investigate the interactions of Bronsted (H2SO4, HClO4, HNO3) and Lewis acids (BH3, BF3, BCl3, BBr3, B(OH)(3)) with HClO4 using the omega B97xD method and the aug-cc-pVDZ basis set. Different isomers of clusters with up to 4 molecules (tetramer) were optimized, and the most stable structures were determined. The enthalpies, Delta H, and Gibbs free energies, Delta G, of cluster formation were calculated in the gas phase at 298 K. Atoms in molecules (AIM) calculations find B-O bond critical points only in the (BH3)(n)HClO4 clusters, while formation of other clusters was based on hydrogen bonding interactions. (H2SO4)HClO4 and (B(OH)(3))HClO4, with formation enthalpies of -14.1 and -12.0 kcal mol(-1), were the most stable, and (BCl3)HClO4 with a formation enthalpy of -2.9 kcal mol(-1), was the least stable cluster among the dimers. Clustering of the Lewis and Bronsted acids with HClO4 enhanced its acidity, so that clustering of four HClO4 molecules and formation of (HClO4)(4) increases the acidity of HClO4 by about 35 kcal mol(-1). The most acidic dimer cluster found in the study was (BBr3)HClO4, with Delta H-acid of 275 kcal mol(-1); 26 kcal mol(-1) stronger than that of the HClO4 monomer.Peer reviewe

Clustering of H2SO4 with BX3 (X = H, F, Cl, Br, CN, OH) compounds creates strong acids and superacids

The interaction of H2SO4 with boron compounds including BH3, BF3, BCl3, BBr3, B(CN)(3) and B(OH)(3) was studied computationally using the omega B97xD density functional. All the BX3 compounds except B(OH)(3) bind to H2SO4 via both SOH center dot center dot center dot X hydrogen bonds, and interactions between the B atoms and the S=O oxygen atoms. B(OH)(3) interacts with H2SO4 solely through hydrogen bonds. B(CN)(3) and BCl3 exhibit the strongest and weakest interactions with H2SO4, respectively. Natural bond orbital (NBO) analysis shows that the relative weakness of the H2SO4- BCl3 interaction may be due to pi-bonding between the B and Cl atoms, and the occupation of the p(z) orbital of the B atom. The strong electron withdrawing groups CN in B(CN)(3) intensify electron deficiency of B atom and promote its tendency to capture electrons of oxygen atom of O=S group. Atoms in molecules (AIM) calculations show bond critical points (BCP) between the X groups of BX3 and the hydrogen atoms of H2SO4 for all cases except X = OH. Enthalpies and Gibbs free energies of deprotonation in the gas phase (Delta H-acid, Delta G(acid)) were calculated for (BX3)H2SO4 and (BX3)(2)H2SO4 complexes. These data revealed that clustering of BX3 with H2SO4 enhances the acidity of H2SO4 by about 9-58 kcal mol(-1). The (B(CN)(3))(2)H2SO4 cluster had Delta H-acid and Delta G(acid) values of 255.0 and 246.7 kcal mol(-1), respectively, and is the strongest Bronsted acids among the (BX3)(2)H2SO4 clusters.Peer reviewe

Effect of Hydration on the Kinetics of Proton-Bound Dimer Formation: Experimental and Theoretical Study

A kinetic study was performed on the proton-bound dimer formation of cyclopentanone, cyclohexanone, and cycloheptanone at atmospheric pressure with ion mobility spectrometry (IMS) at the temperature range of 30 to 70 °C. Measured rate constants were in the range of 9.5 × 10^–11 to 4.5 × 10^–10 cm³ s^–1. Rate constants were also calculated using average dipole orientation (ADO) theory employing density functional theory (DFT). Calculated rate constants were in the range of 1.0–5.5 × 10^–9 cm³ s^–1. The difference between experimental and calculated rate constants was interpreted based on the hydration of the protonated monomers so that water molecules were replaced with a neutral monomer molecule in the process of dimer formation. This process requires activation energy for the formation of dimer and consequently reduces the rate constants. To verify our hypothesis, an effective rate constant (<i>k</i>_eff) was introduced, which accounted for the energetically activated water–monomer replacement in the dimer formation reactions. A good agreement was observed between the experimental rate constants and calculated <i>k</i>_eff, confirming the validity of the proposed model in explaining the kinetics of dimer formation in atmospheric pressure

Effect of the Number of Methyl Groups on the Cation Affinity of Oxygen, Nitrogen, and Phosphorus Sites of Lewis Bases

The effect of number of CH₃ groups (<i>n</i>) on the cation (H⁺, Li⁺, Na⁺, Al⁺, CH₃⁺) affinity, polarizability, and dipole moment of 14 simple molecules was investigated. Linear correlations were observed between the polarizabilities and the number of methyl groups. The variations of the cation affinities and dipole moments with the number of methyl groups (<i>n</i>) were not linear, and a quadratic function was proposed for obtaining a good fit of the experimental data. Also, because the proton affinities (PA), lithium cation affinities (LCA), sodium cation affinities (SCA), aluminum cation affinity (AlCA), and methyl cation affinity (MCA) varied quadratically with polarizabilities (α), a formula of the form [cation affinities] = <i>a</i> + <i>b</i>α + <i>c</i>α² was proposed. After correction of the PAs, LCAs, SCAs, AlCA, and MCA for the dipole/charge interaction (<i>E</i>_μ), linear relationships were observed between the corrected cation affinities and <i>n</i> or α. The contribution of <i>E</i>_μ to PA and MCA was small (less than 20%), and its contribution to LCA and SCA was large (>50%). The electrostatic contribution to AlCA was considerable (20–50%); however, it was smaller than the electrostatic contribution to LCA and SCA

Ion Mobility Spectrometry of Heavy Metals

A simple, fast, and inexpensive method was developed for detecting heavy metals via the ion mobility spectrometry (IMS) in the negative mode. In this method, Cl⁻ ion produced by the thermal ionization of NaCl is employed as the dopant or the ionizing reagent to ionize heavy metals. In practice, a solution of mixed heavy metals and NaCl salts was directly deposited on a Nichrome filament and electrically heated to vaporize the salts. This produced the IMS spectra of several heavy-metal salts, including CdCl₂, ZnSO₄, NiCl₂, HgSO₄, HgCl₂, PbI₂, and Pb­(Ac)₂. For each heavy metal (M), one or two major peaks were observed, which were attributed to M·Cl^– or [M·NaCl]­Cl^–complexes. The method proved to be useful for the analysis of mixed heavy metals. The absolute detection limits measured for ZnSO₄ and HgSO₄ were 0.1 and 0.05 μg, respectively