Gas‐phase reaction of Cl with dimethyl sulfide: Temperature and oxygen partial pressure dependence of the rate coefficient

The kinetics of the reaction of Cl atoms with dimethyl sulfide has been investigated using a relative rate technique. Experiments were performed with oxygen partial pressures of 0, 200, and 500 mbar at a total pressure of 1000 mbar (N₂ + O₂) over the temperature range 283–308 K in a 1080 L reactor using long path in situ Fourier transform infrared absorption spectroscopy to monitor the reactants. The 254 nm photolysis of trichloroacetyl chloride was used as the Cl atom source. Three reference hydrocarbons, cyclohexane, n‐butane, and propene were employed. Good agreement was found between the rate coefficients determined using the different reference compounds. The rate coefficients were found to decrease with increasing temperature at constant O₂ pressure and increase moderately with increasing O₂ partial pressure at constant temperature. The temperature dependences of the Cl atom reaction with dimethyl sulfide for the three O₂ partial pressure investigated can be expressed by the simple Arrhenius expressions: k = (4.22 ± 1.78) × 10^?13 exp((1968 ± 379)/T), k = (5.42 ± 1.85) × 10^?13 exp((1946 ± 381)/T), and k = (6.90 ± 2.04) × 10^?13 exp((1912 ± 381)/T). The errors are a combination of the 2σ statistical errors from the kinetic data analysis plus an estimated systematic error that includes the error in the reference hydrocarbon. The mechanistic implications of the results are discussed. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 37: 66–73, 2005     

The 13C and D kinetic isotope effects in the reaction of CH4 with Cl

The kinetic isotope effects in the reaction of methane (CH₄) with Cl atoms are studied in a relative rate experiment at 298 ± 2 K and 1013 ± 10 mbar. The reaction rates of ¹³CH₄, ¹²CH₃D, ¹²CH₂D₂, ¹²CHD₃, and ¹²CD₄ with Cl radicals are measured relative to ¹²CH₄ in a smog chamber using long path FTIR detection. The experimental data are analyzed with a nonlinear least squares spectral fitting method using measured high‐resolution spectra as well as cross sections from the HITRAN database. The relative reaction rates of ¹²CH₄, ¹³CH₄, ¹²CH₃D, ¹²CH₂D₂, ¹²CHD₃, and ¹²CD₄ with Cl are determined as k/k = 1.06 ± 0.01, k/k = 1.47 ± 0.03, k/k = 2.45 ± 0.05, k/k = 4.7 ± 0.1, k/k = 14.7 ± 0.3. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 37: 110–118, 2005     

Kinetics for the gas‐phase reactions of OH radicals with the hydrofluoroethers CH2FCF2OCHF2, CHF2CF2OCH2CF3, CF3CHFCF2OCH2CF3, and CF3CHFCF2OCH2CF2CHF2 at 268–308 K

Rate constants were determined for the reactions of OH radicals with the hydrofluoroethers (HFEs) CH₂FCF₂OCHF₂(k₁), CHF₂CF₂OCH₂CF₃ (k₂), CF₃CHFCF₂OCH₂CF₃(k₃), and CF₃CHFCF₂OCH₂CF₂CHF₂(k₄) by using a relative rate method. OH radicals were prepared by photolysis of ozone at UV wavelengths (>260 nm) in 100 Torr of a HFE–reference–H₂O–O₃–O₂–He gas mixture in a 1‐m³ temperature‐controlled chamber. By using CH₄, CH₃CCl₃, CHF₂Cl, and CF₃CF₂CF₂OCH₃ as the reference compounds, reaction rate constants of OH radicals of k₁ = (1.68) × 10^?12 exp[(?1710 ± 140)/T], k₂ = (1.36) × 10^?12 exp[(?1470 ± 90)/T], k₃ = (1.67) × 10^?12 exp[(?1560 ± 140)/T], and k₄ = (2.39) × 10^?12 exp[(?1560 ± 110)/T] cm³ molecule^?1 s^?1 were obtained at 268–308 K. The errors reported are ± 2 SD, and represent precision only. We estimate that the potential systematic errors associated with uncertainties in the reference rate constants add a further 10% uncertainty to the values of k₁–k₄. The results are discussed in relation to the predictions of Atkinson's structure–activity relationship model. The dominant tropospheric loss process for the HFEs studied here is considered to be by the reaction with the OH radicals, with atmospheric lifetimes of 11.5, 5.9, 6.7, and 4.7 years calculated for CH₂FCF₂OCHF₂, CHF₂CF₂OCH₂CF₃, CF₃CHFCF₂OCH₂CF₃, and CF₃CHFCF₂OCH₂CF₂CHF₂, respectively, by scaling from the lifetime of CH₃CCl₃. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 239–245, 2003     

2–Butoxyethanol and benzyl alcohol reactions with the nitrate radical: Rate coefficients and gas‐phase products

The bimolecular rate coefficients k and k were measured using the relative rate technique at (297 ± 3) K and 1 atmosphere total pressure. Values of (2.7 ± 0.7) and (4.0 ± 1.0) × 10^?15 cm³ molecule^?1 s^?1 were observed for k and k, respectively. In addition, the products of 2‐butoxyethanol + NO₃^? and benzyl alcohol + NO₃^? gas‐phase reactions were investigated. Derivatizing agents O‐(2,3,4,5,6‐pentafluorobenzyl)hydroxylamine and N, O‐bis (trimethylsilyl)trifluoroacetamide and gas chromatography mass spectrometry (GC/MS) were used to identify the reaction products. For 2‐butoxyethanol + NO₃^? reaction: hydroxyacetaldehyde, 3‐hydroxypropanal, 4‐hydroxybutanal, butoxyacetaldehyde, and 4‐(2‐oxoethoxy)butan‐2‐yl nitrate were the derivatized products observed. For the benzyl alcohol + NO₃^? reaction: benzaldehyde ((C₆H₅)C(?O)H) was the only derivatized product observed. Negative chemical ionization was used to identify the following nitrate products: [(2‐butoxyethoxy)(oxido)amino]oxidanide and benzyl nitrate, for 2‐butoxyethanol + NO₃^? and benzyl alcohol + NO₃^?, respectively. The elucidation of these products was facilitated by mass spectrometry of the derivatized reaction products coupled with a plausible 2‐butoxyethanol or benzyl alcohol + NO₃^? reaction mechanisms based on previously published volatile organic compound + NO₃^? gas‐phase mechanisms. © 2012 Wiley Periodicals, Inc.

1 This article is a U.S. Government work and, as such, is in the public domain of the United States of America.

© 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 778–788, 2012     

Peculiar kinetics of the complex formation in the iron(III)–sulfate system

The results of comprehensive equilibrium and kinetic studies of the iron(III)–sulfate system in aqueous solutions at I = 1.0 M (NaClO₄), in the concentration ranges of T = 0.15–0.3 mM, and at pH 0.7–2.5 are presented. The iron(III)–containing species detected are FeOH²⁺ (=FeH_?1), (FeOH) (=Fe₂H_?2), FeSO, and Fe(SO₄) with formation constants of log β = ?2.84, log β = ?2.88, log β = 2.32, and log β = 3.83. The formation rate constants of the stepwise formation of the sulfate complexes are k_1a = 4.4 × 10³ M^?1 s^?1 for the ${\rm Fe}^{3+} + {\rm SO}_4^{2-}\,\stackrel{k_{1a}}{\rightleftharpoons}\, {\rm FeSO}_4^+The results of comprehensive equilibrium and kinetic studies of the iron(III)–sulfate system in aqueous solutions at I = 1.0 M (NaClO₄), in the concentration ranges of T = 0.15–0.3 mM, and at pH 0.7–2.5 are presented. The iron(III)–containing species detected are FeOH²⁺ (=FeH_?1), (FeOH) (=Fe₂H_?2), FeSO, and Fe(SO₄) with formation constants of log β = ?2.84, log β = ?2.88, log β = 2.32, and log β = 3.83. The formation rate constants of the stepwise formation of the sulfate complexes are k_1a = 4.4 × 10³ M^?1 s^?1 for the ${\rm Fe}^{3+} + {\rm SO}_4^{2-}\,\stackrel{k_{1a}}{\rightleftharpoons}\, {\rm FeSO}_4^+$ step and k₂ = 1.1 × 10³ M^?1 s^?1 for the ${\rm FeSO}_4^+ + {\rm SO}_4^{2-} \stackrel{k_2}{\rightleftharpoons}\, {\rm Fe}({\rm SO}_4)_2^-$ step. The mono‐sulfate complex is also formed in the ${\rm Fe}({\rm OH})^{2+} + {\rm SO}_4^{2-} \stackrel{k_{1b}}{\longrightarrow} {\rm FeSO}_4^+$ reaction with the k_1b = 2.7 × 10⁵ M^?1 s^?1 rate constant. The most surprising result is, however, that the 2 FeSO? Fe³⁺ + Fe(SO₄) equilibrium is established well before the system as a whole reaches its equilibrium state, and the main path of the formation of Fe(SO₄) is the above fast (on the stopped flow scale) equilibrium process. The use and advantages of our recently elaborated programs for the evaluation of equilibrium and kinetic experiments are briefly outlined. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 114–124, 2008     

A kinetic study of the gas‐phase reactions of OIO with NO,NO2, and Cl2

The kinetics of iodine dioxide (OIO) reactions with nitric oxide (NO), nitrogen dioxide (NO₂), and molecular chlorine (Cl₂) are studied in the gas‐phase by cavity ring‐down spectroscopy. The absorption spectrum of OIO is monitored after the laser photodissociation, 266 or 355 nm, of the gaseous mixture, CH₂I₂/O₂/N₂, which generates OIO through a series of reactions. The second‐order rate constant of the reaction OIO + NO is determined to be (4.8 ± 0.9) × 10^?12 cm³ molecule^?1 s^?1 under 30 Torr of N₂ diluent at 298 K. We have also measured upper limits for the second‐order rate constants of OIO with NO₂ and Cl₂ to be k < 6 × 10^?14 cm³ molecule^?1 s^?1 and k < 8 × 10^?13 cm³ molecule^?1 s^?1, respectively. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 688–693, 2007     

The mechanism of O(3P) atom reaction with ethylene and other simple olefins

Reactions of oxygen atoms with ethylene, propene, and 2-butene were studied at room temperature under discharge flow conditions by resonance fluorescence spectroscopy of O and H atoms at pressures of 0.08 to 12 torr. The measured total rate constants of these reactions are K = (7.8 ± 0.6)·10^?13cm³s^?1,K = (4.3 ± 0.4) ± 10^?12 cm³ s^?1, K = (1.4 ± 0.4) · 10^?11 cm³ s^?1. The branching ratios of H atom elimination channels were measured for reactions of O atoms with ethylene and propene. No H-atom elimination was found for the reaction of O-atoms with 2-butene. A redistribution of reaction O + C₂ channels with pressure was found. A mechanism of the O + C₂ reaction was proposed and the possibility of its application to other olefins is discussed. On the basis of mechanism the pressure dependence of the total rate constant for reaction O + C₂ was predicted and experimentally confirmed in the pressure range 0.08–1.46 torr.     

Rate constants for the gas‐phase reactions of nitrate radicals with geraniol,citronellol, and dihydromyrcenol

Terpenes and terpene alcohols are prevalent compounds found in a wide variety of consumer products including soaps, flavorings, perfumes, and air fresheners used in the indoor environment. Knowing the reaction rate of these chemicals with the nitrate radical is an important factor in determining their fate indoors. In this study, the bimolecular rate constants of k (16.6 ± 4.2) × 10^?12, k (12.1 ± 3) × 10^?12, and k (2.3 ± 0.6) × 10^?14 cm³ molecule^?1 s^?1 were measured using the relative rate technique for the reaction of the nitrate radical (NO₃?) with 2,6‐dimethyl‐2,6‐octadien‐8‐ol (geraniol), 3,7‐dimethyl‐6‐octen‐1‐ol (citronellol), and 2,6‐dimethyl‐7‐octen‐2‐ol (dihydromyrcenol) at (297 ± 3) K and 1 atmosphere total pressure. Using the geraniol, citronellol, or dihydromyrcenol + NO₃? rate constants reported here, pseudo‐first‐order rate lifetimes (k′) of 1.5, 1.1, and 0.002 h^?1 were determined, respectively. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 669–675, 2010     

The kinetics of the reaction F + H2 → HF + H. A critical review of literature data

Published experimental studies concerning the determination of rate constants for the reaction F + H₂ → HF + H are reviewed critically and conclusions are presented as to the most accurate results available. Based on these results, the recommended Arrhenius expression for the temperature range 190–376 K is k = (1.1 ± 0.1) × 10⁻¹⁰ exp |-(450 ± 50)/T| cm³ molecule⁻¹ s⁻¹, and the recommended value for the rate constant at 298 K is k = (2.43 ± 0.15) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. The recommended Arrhenius expression for the reaction F + D₂ → DF + D, for the same temperature range, based on the recommended expression for k and accurate results for the kinetic isotope effect k/k is k = (1.06 ± 0.12) × 10^×10 exp |-(635 ± 55)/T|cm³ molecule⁻¹ s⁻¹, and the recommended value for 298 K is k = (1.25 ± 0.10) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 67–71, 1997.     

Kinetics and mechanism of the oxidation of some carboxylates by a nickel (III) oxime-imine complex

The kinetics of the oxidation of formate, oxalate, and malonate by |Ni^III(L¹)|²⁺ (where HL¹ = 15-amino-3-methyl-4,7,10,13-tetraazapentadec-3-en-2-one oxime) were carried out over the regions pH 3.0–5.75, 2.80–5.50, and 2.50–7.58, respectively, at constant ionic strength and temperature 40°C. All the reactions are overall second-order with first-order on both the oxidant and reductant. A general rate law is given as - d/dt|Ni^III(L¹)²⁺| = k_obs|Ni^III(L¹)²⁺| = (k_d + nk_s |R|)|Ni^III(L¹)²⁺|, where k_d is the auto-decomposition rate constant of the complex, k_s is the electron transfer rate constant, n is the stoichiometric factor, and R is either formate, oxalate, or malonate. The reactivity of all the reacting species of the reductants in solution were evaluated choosing suitable pH regions. The reactivity orders are: k_HCOOH > k; k > k > k, and k > k < k for the oxidation of formate, oxalate, and malonate, respectively, and these trends were explained considering the effect of hydrogen bonded adduct formation and thermodynamic potential. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 225–230, 1997.     

Reactivity of dpph• in the oxidation of catechol and catechin

A kinetic study of the reduction of pyrocatechol and catechin by dpph^? radical has been carried out in various ratios of CH₃OH/H₂O mixed solvent at pH 5.5–7.5, μ = 0.10 M [(n‐Bu)₄N]ClO₄, and T = 25°C. The rate constants of oxidation in aqueous solvent, k, were obtained from the extrapolation of the linear plots of the specific rate constants k vs. % H₂O plots at each pH value. A linear relationship between k and 1/[H⁺] was observed for both flavonoids with k = k₁K_a1/[H⁺], where K_a1 was the first acid dissociation constant on the catechol ring and k₁ is the rate constant of the oxidation of the mononegative species HX^?. The values of k₁ obtained from the slopes of the plots are (8.2 ± 0.2) × 10⁵ and (6.1 ± 0.1) × 10⁵ M^?1 s^?1 for pyrocatechol and catechin, respectively. The analysis of the reaction on the basis of Marcus theory for an outer‐sphere electron transfer reaction yielded a value of 3.7 × 10³ M^?1 s^?1 for the self‐exchange rate constant of dpph^?/dpphH couple. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 147–153, 2011     

The N(4S) + N2O(X̃1∑) reaction

The title reaction, which is spin‐forbidden for N₂(X¹∑) + NO(X²Π) production, has been studied from 960 to 1130 K in a high‐temperature photochemistry reactor. No reaction could be observed, indicating k < 1 × 10^?15 cm³ molecule^?1 s^?1. It is concluded that there is no significant contribution from the spin‐allowed exothermic path leading to N₂(X¹∑) + NO(a⁴Π). © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 387–389, 2001     

Arrhenius parameters for the gas‐phase reactions of O3 with two butenes and two methyl‐substituted butenes over the temperature range of 295–351 K

Gas‐phase reactions of ozone with two butenes (1‐butene and isobutene) and two methyl‐substituted butenes (2‐methyl‐1‐butene and 3‐methyl‐1‐butene) have been studied in an indoor chamber at 295–351 K. The O₃ concentrations were monitored by Model 49C‐Ozone analyzer. The butene concentrations were measured by gas chromatography–flame ionization detector. The Arrhenius expressions of k=3.50×10^?15e^{(?1756±84)/T} cm³ molecule^?1 s^?1, k=3.39×10^?15e^{(?1697±52)/T} cm³ molecule^?1 s^?1, k=6.18×10^?15e^{?(1822±80)/T} cm³ molecule^?1 s^?1, and k=7.24×10^?14e^{?(2741±139)/T} cm³ molecule^?1 s^?1 were obtained for the ozonolysis reactions of 1‐butene, isobutene, 2‐methyl‐1‐butene, and 3‐methyl‐1‐butene, respectively. Both the reaction rate constant and activation energy obtained in this work are in good agreement with those reported by using different techniques in the literature. © 2011 Wiley Peiodicals, Inc. Int J Chem Kinet 43: 238–246, 2011     

Rate constants for some reactions of free radicals with haloacetates in aqueous solution

The kinetics of the acqueous-phase reactions of the free radicals ·OH, ·Cl, and SO· with the halogenated acetates, CH₂FCOO^?, CHF₂COO^?, CF₃COO^?, and with CH₂ClCOO^?, CHCl₂COO^?, CCl₃COO^? were investigated. Generally, the reactivity decreases with increasing halogen substitution and is in the order k(·OH) > k(SO·) > k(·Cl), but there is no general relation between the effect on reactivity of chlorine and fluorine substitution. © 1995 John Wiley & Sons, Inc.     

Recommendations for measuring second-order rate constants and kinetic solvent isotope effects on acid-catalyzed reactions

Kinetic solvent isotope effects (KSIE) were measured for the hydrolyses of acetals of benzaldehydes in aqueous solutions covering the pH (pD) range of 1–6. For p-methoxybenzaldehyde diethyl acetal, k/k = 1.8–3.1, depending on the procedure used to calculate the KSIE and on the pH (pD) range used as the basis for k(k). It is shown that this variation is an experimental artifact, and is a characteristic of KSIE measurements in general. It is recommended that k be calculated from a least-squares fit of data to the equation k_obs = k[L⁺], and that the KSIE be reported as k/k. The limitation remains, however, that the KSIE measured for a variety of substances over quite different pH (pD) ranges may not be comparable to more than ?20%. The source of these observations is discussed in terms of small changes in the activity coefficient ratios (a specific salt effect), including the solvent isotope effect on the activity coefficient ratio [eq. (3)].     

Chemical actinometry at 147.0 nm

Hexafluoroacetone (HFA) and O₂ were photolyzed at 147.0 nm to investigate their use in chemical actinometry. The products, CO for the former and O₃ in the latter case, were monitored. For accurate comparison, both of these substances were irradiated by a single light source with two identical reaction cells at 180° to each other. The light intensities I were measured under the same integrated as well as instantaneous photon flux based on ? and ?_CO (quantum yield) as 2 and 1, respectively. Optimum conditions for maximum product yield were 5.0 torr HFA pressure and an O₂ flow rate of 200 ml/min at 1 atm pressure for a 20-minute photolysis period. For light intensity variations between 1.09 × 10¹⁴ and 2.10 × 10¹⁵ photons absorbed/sec, the ratio I/I_HFA was found to be unity. Calibration with the commonly used N₂O actinometer for a ? value of 1.41 showed that I/I_HFA and I/I are unity. Both HFA and O₂ are suitable chemical actinometers at 147.0 nm with ?_CO and ? of 1 and 2, respectively. The light intensity determination in the first case involves the measurement of only one product which is noncondensible at 77°K, whereas wet analysis for O₃, the only product, in the second actinometer is necessary. Both of these determinations are quite simple and are preferable over product analysis in N₂O actiometry, wherein N₂ separation from other noncondensibles at 77°K is required.     

Kinetics and mechanisms of substitution reactions with sulfur-containing nucleophiles in aqueous acid solutions. I—rates of reactions of some tetrahalopalladate (II) anions with thiourea and selenourea

The activation energy parameters for the reaction of PdX (X=Cl^?, Br^?) in aqueous halide acid solution with thiourea (tu) and selenourea (seu) have been determined. High rates of reaction parallel low enthalpies and appreciable negative entropy of activation. The rate law in each case simplifies to k_obs=k[L] where L=tu or seu, and only ligand-dependent rate constants are observed at 25°C. The ligand-dependent rate constants for the first identifiable step in the PdCl + X system is (9.1±0.1) × 10³ M^?1 sec^?1 and (4.5±0.1) × 10⁴ M^?1 sec^?1 for X=tu and seu, respectively, while for the PdBr + X system it is (2.0±0.1) × 10⁴ M^?1 sec^?1 and (9.0±0.1) × 10⁴ M^?1 sec^?1 for X=tu and seu, respectively.     

Competitive study of the reactions Br + RFI → IBr + RF and determination of bond dissociation energies D(RF−I) where RF = CF3, C2F5, n-;C3F7, i-C3F7, and n-C4F9

The overall photobromination reactions have been studied using a competitive technique. Relative Arrhenius parameters were obtained for the rate-determining step These were placed on an absolute basis using previous-absolute values of A and E for R_FI=CF₃I. The activation energies were used to calculate bond dissociation energies D(R? I) with the following results:

Reactions of Cl2P3/2: Absolute rate constants for reaction with H2, CH4, C2H6, CH2Cl2, C2Cl4, and c?C6H12

The absolute rate constants have been measured for several gas-phase chlorine atom-molecule reactions at 25°C by resonance fluorescence. These reactions and their corresponding rate constants in units of cm³ mole^?1 sec^?1 are: The effects of varying the substrate pressure, total pressure, light intensity and chlorine-atom source on the value of the bimolecular rate constants have been investigated for all these reactions. Conditions under which no competing side reaction occurs were established and the reported rate constants were measured under these conditions. For reactions (2), (5), (6), (7), and 8, there is a discrepancy of a factor of two between the rate constants measured in this work and values in the literature; it is suggested that this is due to an error in the previously measured value of k/k upon which the relative measurements in the literature ultimately depend.     

Kinetics of the solvolysis of [Co(3Rpy)4Cl2]+ ions (R = Me or Et) in water and in water + methanol mixtures

Rates of solvolysis of ions [Co(3Rpy)₄Cl₂]⁺ with R = Me and Et have been measured over a range of temperatures for a series of water-rich water + methanol mixtures to investigate the effect of changes in solvent structure on the solvolysis of complexes presenting a largely hydrophobic surface to the solvent. The variation of the enthalpies and entropies of activation with solvent composition has been determined. A free energy cycle relating the free energy of activation in water to that in water + methanol is applied using free energies of transfer of individual ionic species from water into water + methanol. Data for the free energy of transfer of chloride ions ΔG(Cl^?) from both the spectrophotometric solvent sorting method and the TATB method for separating ΔG(salt) into ΔG(i) for individual ions are used: irrespective of the source of ΔG(Cl^?), in general, ?ΔG(Co(Rpy)₄Cl²⁺) > ?ΔG(Co(Rpy)₄Cl₂⁺), where Rpy = py, 4Mepy, 4Etpy, 3Etpy, and 3Mepy, showing that changes in solvent structure in water-rich water + methanol mixtures generally stabilize the cation in the transition state more than the cation in the initial state for this type of complex ion. A similar result is found when the free energy cycle is applied to the solvolysis of the dichloro (2,2′,2″-triaminotriethylamine)cobalt(III) ion. The introduction of a Me or Et group on the pyridine ring in [Co(Rpy)₄Cl₂]⁺ has little influence on the difference {ΔG(Co(Rpy)₄Cl²⁺)?ΔG(Co(Rpy)₄Cl₂⁺)} in water + methanol with the mol fraction of methanol < 0.20.