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Stable isotopes of chlorine have great application potential due to the widespread occurrence of the chlorine anion in water, minerals, living organisms and the environment. In most studies, the chloride ion from the samples is converted to chloromethane, which is then analysed isotopically using a mass spectrometer. In the present study, a new design for a chloromethane preparation line is proposed. In particular, the new chloromethane preparation line uses a new system for injecting iodomethane into the preparation system, as well as ampoules with Teflon valves and the u-shaped freezers. These improvements reduced the preparation time to about 1 h, and also achieved a decent measurement uncertainty of 0.05 permil. [ABSTRACT FROM AUTHOR]

Chlorine has important roles in the Earth's systems. In different forms, it helps balance the charge and osmotic potential of cells, provides energy for microorganisms, mobilizes metals in geologic fluids, alters the salinity of waters, and degrades atmospheric ozone. Despite this importance, there has not been a comprehensive summary of chlorine's geobiology. Here, we unite different areas of recent research to describe a biogeochemical cycle for chlorine. Chlorine enters the biosphere through volcanism and weathering of rocks and is sequestered by subduction and the formation of evaporite sediments from inland seas. In the biosphere, chlorine is converted between solid, dissolved, and gaseous states and in oxidation states ranging from −1 to +7, with the soluble, reduced chloride ion as its most common form. Living organisms and chemical reactions change chlorine's form through oxidation and reduction and the addition and removal of chlorine from organic molecules. Chlorine can be transported through the atmosphere, and the highest oxidation states of chlorine are produced by reactions between sunlight and trace chlorine gases. Partial oxidation of chlorine occurs across the biosphere and creates reactive chlorine species that contribute to the oxidative stress experienced by living cells. A unified view of this chlorine cycle demonstrates connections between chlorine biology, chemistry, and geology that affect life on the Earth. [ABSTRACT FROM AUTHOR]

The selective conversion of methane to high value‐added chemicals under mild conditions is of great significance for the commercially viable and sustainable utilization of methane but remains a formidable challenge. Herein, we report a strategy for efficiently converting methane to acetic acid via CH3Cl as an intermediate. Up to 99.3 % acetic acid and methyl acetate (AA+MA) selectivity was achieved over pyridine‐pretreated MOR (MOR‐8) under moderate conditions of 523 K and 2.0 MPa. Water, conventionally detrimental to carbonylation reaction over zeolite catalysts, was conducive to the production of AA in the current reaction system. In the 100 h continuous test with the MOR‐8 catalyst, the average AA+MA selectivity remained over 98 %. AA was formed by carbonylation of methoxy groups within 8‐membered rings of MOR followed by hydrolysis. This strategy provided an approach for highly efficient utilization of methane to oxygenates under mild reaction conditions. [ABSTRACT FROM AUTHOR]

The selective conversion of methane to high value‐added chemicals under mild conditions is of great significance for the commercially viable and sustainable utilization of methane but remains a formidable challenge. Herein, we report a strategy for efficiently converting methane to acetic acid via CH3Cl as an intermediate. Up to 99.3 % acetic acid and methyl acetate (AA+MA) selectivity was achieved over pyridine‐pretreated MOR (MOR‐8) under moderate conditions of 523 K and 2.0 MPa. Water, conventionally detrimental to carbonylation reaction over zeolite catalysts, was conducive to the production of AA in the current reaction system. In the 100 h continuous test with the MOR‐8 catalyst, the average AA+MA selectivity remained over 98 %. AA was formed by carbonylation of methoxy groups within 8‐membered rings of MOR followed by hydrolysis. This strategy provided an approach for highly efficient utilization of methane to oxygenates under mild reaction conditions. [ABSTRACT FROM AUTHOR]

Background: Chloromethane (CH3Cl) is the most abundant halogenated organic compound in the atmosphere and substantially responsible for the destruction of the stratospheric ozone layer. Since anthropogenic CH3Cl sources have become negligible with the application of the Montreal Protocol (1987), natural sources, such as vegetation and soils, have increased proportionally in the global budget. CH3Cl-degrading methylotrophs occurring in soils might be an important and overlooked sink. Results and conclusions: The objective of our study was to link the biotic CH3Cl sink with the identity of active microorganisms and their biochemical pathways for CH3Cl degradation in a deciduous forest soil. When tested in laboratory microcosms, biological CH3Cl consumption occurred in leaf litter, senescent leaves, and organic and mineral soil horizons. Highest consumption rates, around 2 mmol CH3Cl g−1 dry weight h−1, were measured in organic soil and senescent leaves, suggesting that top soil layers are active (micro-)biological CH3Cl degradation compartments of forest ecosystems. The DNA of these [13C]-CH3Cl-degrading microbial communities was labelled using stable isotope probing (SIP), and the corresponding taxa and their metabolic pathways studied using high-throughput metagenomics sequencing analysis. [13C]-labelled Metagenome-Assembled Genome closely related to the family Beijerinckiaceae may represent a new methylotroph family of Alphaproteobacteria, which is found in metagenome databases of forest soils samples worldwide. Gene markers of the only known pathway for aerobic CH3Cl degradation, via the methyltransferase system encoded by the CH3Cl utilisation genes (cmu), were undetected in the DNA-SIP metagenome data, suggesting that biological CH3Cl sink in this deciduous forest soil operates by a cmu-independent metabolism. [ABSTRACT FROM AUTHOR]

The transformation of methane into high value‐added chemicals such as aromatics provides a more desired approach towards sustainable chemistry but remains a critical challenge due to the low selectivity of aromatics and poor stability. Herein, we first report a coupling reaction of CH3Cl and CO (CCTA) based on methane conversion, which achieves extremely high aromatics selectivity (82.2 %) with the selectivity of BTX up to ca. 60 % over HZSM‐5. The promoting effects have been demonstrated on other zeolites especially 10‐membered rings (10 MR) zeolites. Multiple characterizations show that 2,3‐dimethyl‐2‐cyclopentene‐1‐one (DMCPO) is generated from acetyl groups and olefins. Furthermore, isotopic labeling analysis confirms that CO is inserted into the DMCPO and aromatics rings. A new aromatization mechanism is proposed, including the formation of the above intermediates, which conspicuously weakens the hydrogen transfer reaction, leading to a considerable increase of aromatics selectivity and a dramatic drop in alkanes. [ABSTRACT FROM AUTHOR]

The transformation of methane into high value‐added chemicals such as aromatics provides a more desired approach towards sustainable chemistry but remains a critical challenge due to the low selectivity of aromatics and poor stability. Herein, we first report a coupling reaction of CH3Cl and CO (CCTA) based on methane conversion, which achieves extremely high aromatics selectivity (82.2 %) with the selectivity of BTX up to ca. 60 % over HZSM‐5. The promoting effects have been demonstrated on other zeolites especially 10‐membered rings (10 MR) zeolites. Multiple characterizations show that 2,3‐dimethyl‐2‐cyclopentene‐1‐one (DMCPO) is generated from acetyl groups and olefins. Furthermore, isotopic labeling analysis confirms that CO is inserted into the DMCPO and aromatics rings. A new aromatization mechanism is proposed, including the formation of the above intermediates, which conspicuously weakens the hydrogen transfer reaction, leading to a considerable increase of aromatics selectivity and a dramatic drop in alkanes. [ABSTRACT FROM AUTHOR]

We report the tunable conversion of chloromethane to olefins and aromatics using different metal-promoted zeolites as catalysts. Despite SAPO-34 was industrially used as catalysts for methanol to olefins reaction (MTO), the SAPO-34 based zeolites exhibited low activity and short lifetime when using chloromethane as the feed. Higher chloromethane conversion and longer catalyst lifetime were found on H-ZSM-5. The activity and product distribution can be improved by optimizing the reaction temperature and space velocity. Impregnating the H-ZSM-5 zeolite with 1 wt% and 5 wt% metal oxide as promoters significantly enhanced the conversion efficiency and altered the product distribution. The highest aromatics selectivity (38%) was obtained on the H-ZSM-5 zeolite promoted by 5 wt% Ni, whereas on 5 wt% Mg and 5 wt% Mn promoted H-ZSM-5, the aromatics selectivity is merely 5%. Therefore, different modified H-ZSM-5 could be used to convert chloromethane to either aromatics or olefin-heavy products. It was found that the aromatics yield is strongly correlated to the acidity of the H-ZSM-5 zeolite. [ABSTRACT FROM AUTHOR]

This work presents a comprehensive kinetic modeling study of the pyrolysis and oxidation of chloromethane. Theoretical calculations were performed for the decomposition reaction CH3Cl + M = CH3 + Cl + M and for a set of relevant H‐abstraction reactions (CH3Cl + R, R = Cl, Ḣ, ȮH, HȮ2, O2, Ö, ĊH3, Ċ2H3, Ċ2H5; CH4 + Cl, C2H6 + Cl, C2H4 + Cl, C2H2 + Cl). Comparison with previous experimental or theoretical determinations, when available, proved the appropriateness of the adopted protocols and the accuracy of the calculated rate constants. Previously developed subsets for CH3Cl and HCl/Cl2 were updated with the theoretical rate constants and combined with the CRECK C1–C3 mechanism, yielding a kinetic mechanism consisting of 143 species and 2347 reactions. The validation was performed through comparison with all the pyrolysis and oxidation measurements available for pure CH3Cl and its mixtures with CH4, H2, and CO/H2O. The kinetic discussion highlights the role of key reaction steps that have been theoretically investigated in this work and in previous efforts and sheds light on additional reaction pathways needing better assessments. [ABSTRACT FROM AUTHOR]

In this paper, a series of Al−Ti mixed oxides with different Al/Ti ratios are prepared by a simple sol‐gel method and they are used as active catalysts for selective dechlorination of dichloromethane to chloromethane. The Al−Ti mixed oxide catalyst with the same molar ratio of Al and Ti shows the highest activity in dechlorination of dichloromethane. The strong and abundant Lewis acid sites in the Al−Ti mixed oxides formed along with Al−O−Ti bondings are responsible for the high catalytic activity toward the selective dechlorination reaction in this work. From a kinetic study, the activation energy of this reaction over the optimum Al−Ti mixed oxide catalyst appears to be 59.4 kJ mol−1 based on Langmuir‐Hinshelwood model. The improved catalytic performance suggests that the Al−Ti mixed oxide could be used as the effective catalyst for the highly selective dechlorination of dichloromethane to chloromethane. [ABSTRACT FROM AUTHOR]

Chloromethane is an important reagent for methylations in the process industry. However, as a gas suspected of causing cancer, it is rarely used at laboratory scale. Therefore, a setup is presented here for studies in a laboratory under safe and reproducible conditions. The use of a microreactor guarantees high heat transfer rates and a low holdup of the reagent. As a proof‐of‐concept, the reaction of chloromethane with the secondary amine morpholine in aqueous solution is investigated. By applying elevated pressures, a liquid‐liquid system with enhanced solubility of chloromethane in the aqueous phase is accessible. [ABSTRACT FROM AUTHOR]

Ro-vibrational spectra of the ν 3 and ν 6 bands of chloromethane ( CH 3 Cl) were recorded in the 650–1130 cm − 1 range using a Fourier transform spectrometer at the AILES beamline of the SOLEIL synchrotron facility. Two isotopologues ( CH 3 35 Cl and CH 3 37 Cl) have been analyzed with the tensorial formalism developed in Dijon and a total of 6753 lines were assigned. We derived 23 tensorial parameters for the lines positions (4 for the ground state, 6 for ν 3 , and 13 for ν 6), and 7 for the lines intensities (4 for ν 3 , 3 for ν 6). From those parameters and self-broadening coefficients found in the literature, we simulated spectra of both isotopologues. The derived parameters were converted in the Watson formalism to be compared with a previous study. Using these results, we set up a new database of calculated chloromethane spectral lines (ChMeCaSDa). • High-resolution infrared spectroscopy of two bands of chloromethane. • Analysis of two isotopologues of chloromethane in the tensorial formalism. • Fit of the tensorial parameters for line positions and intensities. • Simulation of the spectra. • New database of calculated spectral lines (ChMeCaSDa). [ABSTRACT FROM AUTHOR]

Abstract Methyl Chloride (MeCl; Chloromethane) is a high production volume chemical (>1000 t/a) and is used as an industrial solvent. Based on cardiac lesions reported in developmental toxicity studies in mice, but not in rats, manufacturers decided to classify MeCl as a developmental toxicant, cat. 2. Recently, the European Chemical Agency required a developmental toxicity study in a non-rodent species. No developmental toxicity was observed in rabbits in the recently completed, GLP, OECD 414 guideline study. In view of the absence of cardiac effects in rats and rabbits, the purpose of this review is to consider whether the cardiac effects reported in mice should be considered real effects and, if so, their potential for relevance to humans. This paper provides substantive new evidence with data from a third species and shows that an evaluation of the integrated scientific evidence indicates the reported developmental cardiac effects in mice, if not an artifact, are unlikely to be relevant to humans. As such the classification of MeCl for developmental toxicity was reconsidered. Highlights • Cardiac lesions were reported in fetal mice following exposure to high concentrations of MeCl but were not replicated. • These lesions, viz. reduced number of papillary muscles, were reported in fetal mice but not in fetal rats or rabbits. • The normal anatomy and variability in appearance of tiny papillary muscles in the fetal mouse heart complicate evaluation. • Number, length, and shape of cardiac papillary muscles are reported to be variable in humans. • Integrated evidence indicates these cardiac effects in fetal mice, if not an artifact, are unlikely to be relevant to humans. [ABSTRACT FROM AUTHOR]

Abstract H-ZSM-35 with 2D channel intersections has been first found to be an effective catalyst over chloromethane transformation into propylene. Fluoride treatment is further introduced to improve the catalytic performance. With a proper concentration of fluoride treatment, the selectivity and yield of propylene can be enhanced significantly while a high propylene/ethylene ratio is achieved. Detailed characterizations demonstrate that dealumination caused by fluoride treatment results in a reduction in acidic sites, which is responsible for the improvement of catalytic performance. Graphical abstract Unlabelled Image Highlights • H-ZSM-35 is an effective catalyst for the conversion of chloromethane to propylene. • Fluoride treatment can enhance the catalytic performance of H-ZSM-35 significantly. • Fluoride treatment result in desilication and dealuminization to the framework. • The strong Brønsted acidic sites are reduced by the fluoride treatment. • Catalytic activity is improved by the suppression of hydrogen-transfer reactions. [ABSTRACT FROM AUTHOR]

Chloromethane (CH 3 Cl) is the most abundant halogenated trace gas in the atmosphere. It plays an important role in natural stratospheric ozone destruction. Current estimates of the global CH 3 Cl budget are approximate. The strength of the CH 3 Cl global sink by microbial degradation in soils and plants is under discussion. Some plants, particularly ferns, have been identified as substantial emitters of CH 3 Cl. Their ability to degrade CH 3 Cl remains uncertain. In this study, we investigated the potential of leaves from 3 abundant ferns ( Osmunda regalis , Cyathea cooperi , Dryopteris filix-mas ) to produce and degrade CH 3 Cl by measuring their production and consumption rates and their stable carbon and hydrogen isotope signatures. Investigated ferns are able to degrade CH 3 Cl at rates from 2.1 to 17 and 0.3 to 0.9 μg g dw −1 day − 1 for C. cooperi and D. filix-mas respectively, depending on CH 3 Cl supplementation and temperature. The stable carbon isotope enrichment factor of remaining CH 3 Cl was −39 ± 13‰, whereas negligible isotope fractionation was observed for hydrogen (−8 ± 19‰). In contrast, O. regalis did not consume CH 3 Cl, but produced it at rates ranging from 0.6 to 128 μg g dw −1 day − 1 , with stable isotope values of −97 ± 8‰ for carbon and −202 ± 10‰ for hydrogen, respectively. Even though the 3 ferns showed clearly different formation and consumption patterns, their leaf-associated bacterial diversity was not notably different. Moreover, we did not detect genes associated with the only known chloromethane utilization pathway “ cmu ” in the microbial phyllosphere of the investigated ferns. Our study suggests that still unknown CH 3 Cl biodegradation processes on plants play an important role in global cycling of atmospheric CH 3 Cl. [ABSTRACT FROM AUTHOR]

This article presents the first empirical experimental data on the skin absorption of methyl chloride gas using an in vitro technique and human skin. Methyl chloride is a commonly used industrial agent that is known to be an inhalational hazard but is also reported to be absorbed through human skin in amounts that contribute substantially to systemic intoxication. As a result, is has been assigned a skin notation by the ACGIH. Other than predictive models, there is a general paucity of experimental data on the skin absorption of methyl chloride and therefore a distinct lack of empirical evidence in the open literature to support the assignment of a skin notation for this chemical. This study found that methyl chloride permeates through human epidermis when exposed at high atmospheric concentrations within relatively short timeframes. Therefore, providing important initial empirical evidence in support of the assignment of a skin notation. [ABSTRACT FROM AUTHOR]

Chloromethane (CH 3 Cl) and dichloromethane (CH 2 Cl 2 ) are known to have both natural and anthropogenic sources to the atmosphere. From recent studies it is known that tropical and sub tropical plants are primary sources of CH 3 Cl in the atmosphere. In order to quantify the biogenic emissions of CH 3 Cl and CH 2 Cl 2 from mangroves, field measurement were conducted in a tropical mangrove forest on the coast of Brazil. To the best of our knowledge these field measurements were the first of its kind conducted in the tropical mangrove ecosystem of Braganca. A mesoscale atmospheric model, MEsoscale TRAnsport and fluid (Stream) model (METRAS), was used to simulate passive tracers concentrations and to study the dependency of concentrations on type of emission function and meteorology. Model simulated concentrations were normalized using the observed field data. With the help of the mesoscale model results and the observed data the mangrove emissions were estimated at the local scale. By using this bottom-up approach the global emissions of CH 3 Cl and CH 2 Cl 2 from mangroves were quantified. The emission range obtained with different emission functions and different meteorology are 4–7 Gg yr −1 for CH 3 Cl and 1–2 Gg yr 2 for CH 2 Cl 2 . Based on the present study the mangroves contribute 0.3 percent of CH 2 Cl 2 and 0.2 percent of CH 3 Cl in the global emission budget. This study corroborates the study by Manley et al. (2007) which estimated that mangroves produce 0.3 percent of CH 3 Cl in the global emission budget. Although they contribute a small percentage in the global budget, their long lifetime enables them to contribute to the destruction of ozone in the stratosphere. From the detailed analyses of the model results it can be concluded that meteorology has a larger influence on the variability of concentrations than the temporal variability of the emission function. [ABSTRACT FROM AUTHOR]

Halocarbons play an important role in combustion and stratospheric chemistry and have been an active subject of many studies for a long time. The six reaction channels, between CH 3 Cl and CN, have been investigated at CCSD(T)/aug-cc-pVTZ//CASSCF(11,10)/6-311++g(2df,p) level of theory. Only two channels dominate noticeably in the temperature range of 298–1000 K. The calculated values of the rate constants to different temperatures are in good agreement with the available experiment data. This reaction has a rate constant of k = 3.50 × 10−10 T − 0. 5 exp(−7.50 kJ mol−1/RT) over the range 298–1000 K. [Display omitted] • CCSD(T)//CASSCF(11,10) studies on the reaction kinetics of CN radical with chloromethane. • PESs for six reaction channels are evaluated at CASSCF(11,10)/6-311++g(2df,p) high level of theory. • Two channels dominate noticeably in the temperature range of 298–1000 K. • The MESMER package has been employed to evaluate the theoretical rate coefficients. [ABSTRACT FROM AUTHOR]

The introduction of small amounts of oxygen inhibits the photoinduced ignition of chloromethane-chlorine mixtures. This is accompanied by an increase in the induction period and a decrease in the degree of heating of the reaction mixture. After the consumption of the entire inhibitor, the photochlorination reaction takes place again in the thermal explosion regime but with a lower degree of heating. In the dependence of the mixture temperature on the oxygen concentration, criticality is not pronounced. With an increasing concentration of oxygen, its effect on the induction period weakens. [ABSTRACT FROM AUTHOR]

By means of in situ FTIR and ex situ 13 C NMR studies, the initial periods of the chloromethane-to-olefins (CTO) reaction over SAPO-34 were probed in order to investigate the activation period of the reaction and to elucidate the formation of the catalyst active site. A methylated benzene species has been observed to form during the initial activation period of the reaction, and a direct positive correlation was constructed between the formation of this species and the catalytic activity. The data thus indicate that these methylated benzene species contribute to the formation of active sites within SAPO-34 for the CTO reaction. This is the first known report identifying a direct semi-quantitative correlation between the catalyst activity and growth of a methylated benzene active species, during the activation period of the chloromethane to olefins reaction. The findings here in correspond well to those reported for the methanol to olefins reaction, suggesting that a similar ‘hydrocarbon pool’ mechanism may be responsible for the formation of light olefins in CTO chemistry as well. [ABSTRACT FROM AUTHOR]

Methyl chloride and methyl bromide (CH 3 Cl and CH 3 Br) are the largest natural sources of chlorine and bromine, respectively, to the stratosphere, where they contribute to ozone depletion. We report the anthropogenic production of CH 3 Cl and CH 3 Br during breadbaking, and suggest this production is an abiotic process involving the methyl ester functional groups in pectin and lignin structural polymers of plant cells. Wide variations in baking styles allow only rough estimates of this flux of methyl halides on a global basis. A simple model suggests that CH 3 Br emissions from breadbaking likely peaked circa 1990 at approximately 200 tonnes per year (about 0.3% of industrial production), prior to restrictions on the dough conditioner potassium bromate. In contrast, CH 3 Cl emissions from breadbaking may be of similar magnitude as acknowledged present-day CH 3 Cl industrial emissions. Because the mechanisms involve functional groups and compounds widely found in plant materials, this type of methyl halide production may occur in other cooking techniques as well. [ABSTRACT FROM AUTHOR]

Thermal decomposition of polyvinylchloride (PVC)–wood and wood component mixtures were examined under slow and fast heating by pyrolysis–gas chromatography/mass spectrometry (Py–GC/MS) and thermogravimetry/mass spectrometry(TG/MS) techniques in order to clarify the chemical interaction of biomass materials and PVC during thermal decomposition. A hardwood and a softwood (beech and pine), their lignin and two types of cellulose (Avicel and Whatman) were chosen as natural polymer components. Comparing the gaseous and liquid pyrolysis products of pure samples to those of mixtures it was found that considerably lower amount of several reactive compounds have been produced when the biomass sample was mixed with PVC. On the other hand significant amount of chloromethane appeared in the pyrolysate of wood and lignin samples mixed with PVC under fast and slow pyrolysis conditions as well, but only in traces of chlorinated organic compounds were detected from cellulose mixtures. It was concluded that the methoxy groups at phenolic rings in lignin are the methyl source of chloromethane formation, and this reaction consumed most of the HCl evolved from PVC. [ABSTRACT FROM AUTHOR]

A series of M/ZSM-5 (M = Co, Fe, Ce, and Mn) catalysts with different molar ratios of SiO 2 /Al 2 O 3 (30, 107) was prepared via a traditional wetness impregnation, and further characterized by XRD, BET, H 2 -TPR, NH 3 -TPD, and XPS as well as activity test for the catalytic combustion of chloromethane. Characteristic structure of ZSM-5 is basically maintained even after impregnating the various metallic components. Catalytic activities achieving under an atmosphere of 1500 ppm CH 3 Cl, 10% O 2 , and GHSV of 15,000 h −1 of the investigated catalysts follow a trend of Co/ZSM-5-30, Ce/ZSM-5-30 > Co/ZSM-5-107, Ce/ZSM-5-107, Fe/ZSM-5-30, Mn/ZSM-5-30 > Mn/ZSM-5-107, Fe/ZSM-5-107 > H-ZSM-5-30 > H-ZSM-5-107. The binary Co/ZSM-5-30 and Ce/ZSM-5-30 show the satisfactory conversions of CH 3 Cl (87% and 95%) associated with a low yield of CO (9.6% and 16%) at 400 °C, owing to the excellent redox properties (determined by the chemical nature of the loaded metallic components) and strong acidic properties (modified by Al isomorphic substitution) of the as-prepared zeolitic catalysts. [ABSTRACT FROM AUTHOR]

Zinc-modified alumina catalysts for methyl chloride synthesis were prepared with varying zinc loadings: from 2.4 to 21.1 wt%. The influence of the zinc loading, zinc precursor and the pH of the impregnation on the physico-chemical properties of the catalyst, and on the catalyst activity and selectivity for methyl chloride (MeCl) synthesis was investigated. The prepared catalysts were thoroughly characterized by FTIR, TEM, physisorption and EDX. On the alumina surface, both molecular and bulk zinc species are created upon zinc loading. The surface area of the catalyst decreases steadily with zinc loading. Bulk zinc species dominate on the catalyst starting at a zinc loading of 9.4 wt% and the amount of Lewis acid sites (LAS) decreases. A shift in the acid site type takes place upon zinc modification. Sites assigned to stronger LAS are eliminated while zinc-based weaker acid sites started to predominate. The shift in acidity increases the selectivity and activity of methyl chloride synthesis, which was demonstrated in a series of experiments in a laboratory-scale fixed bed reactor. [ABSTRACT FROM AUTHOR]

Chloromethane, accounting for approximately 16% of the tropospheric chlorine, is mainly coming from natural sources. However anthropogenic activities, such as combustion of biomass may contribute significantly as well. The present study focuses on the thermal solid state reaction between pectin, an important constituent of biomass, and chloride ions as found in alkali metal chlorides. The formation of chloromethane is evident with the amount formed being linear with respect to chloride if pectin is in great excess. Thus the reaction is explained as a pseudo first order SN2 reaction between the chloride ion and the methyl ester moiety in pectin. It is suggested that the polymeric nature of pectin plays an active role by an enhanced transport of halides along the carbohydrate chain. Optimal reaction temperature is around 210 °C. At higher temperatures the yield of chloromethane decreases due to a thermal decomposition of the pectin. The possible influence of the type of cation is discussed. [ABSTRACT FROM AUTHOR]

Hierarchical SAPO-34 molecular sieve was successfully synthesized by hydrothermal crystallization method with cetyltrimethyl ammonium bromide as mesoporous generating agent. The influence of different addition amounts of CTAB on the crystalline structures, morphology features, textural properties and acidity of hierarchical SAPO-34 catalysts were characterized by XRD, SEM, BET and NH-TPD techniques. The results exhibit that the crystal size, mesoporous structure and the total acid amounts of hierarchical SAPO-34 are affected greatly by the molar ratio of CTAB/AlO. The selectivity of light olefins (ethane and propylene) can achieve 80 % for all SAPO-34 samples tested in the conversion of chloromethane to light olefins. Compared with the conventional SAPO-34, the hierarchical SAPO-34 samples show better catalytic stability and less carbon deposit in this conversion due to the reduction in total acid sites and the increasing mesopore volume. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Highlights: [•] We present data-driven AFs for human kinetic variability for 3 organic solvents. [•] The AFs are derived by population PBPK modeling. [•] We explore effects of age, gender and various workplace conditions. [•] For most groups and conditions our AFs are below 2.2. [•] For certain occupational exposure scenarios the AFs are up to 5.0. [Copyright &y& Elsevier]

Keywords: Aromatics; Carbon Monoxide; Chloromethane; HZSM-5; Methane Conversion EN Aromatics Carbon Monoxide Chloromethane HZSM-5 Methane Conversion 1 1 1 03/16/22 20220321 NES 220321 B The coupling of CH SB 3 sb Cl with CO b over H-zeolites is an efficient reaction strategy for the transformation of methane into aromatics, which ensures the sustainable development of natural gas in an environmental pathway. Aromatics, Carbon Monoxide, Chloromethane, HZSM-5, Methane Conversion Inside Back Cover: Highly Enhanced Aromatics Selectivity by Coupling of Chloromethane and Carbon Monoxide over H-ZSM-5 (Angew. [Extracted from the article]

Innenrücktitelbild: Highly Enhanced Aromatics Selectivity by Coupling of Chloromethane and Carbon Monoxide over H-ZSM-5 (Angew. Keywords: Aromatics; Carbon Monoxide; Chloromethane; HZSM-5; Methane Conversion EN Aromatics Carbon Monoxide Chloromethane HZSM-5 Methane Conversion 1 1 1 03/16/22 20220321 NES 220321 B Die Kupplung von CH SB 3 sb Cl mit CO b über H-Zeolithen ist eine effiziente Reaktion für die Umwandlung von Methan in Aromaten, die die nachhaltige Entwicklung von Erdgas auf einem umweltfreundlichen Weg gewährleistet. Methane Conversion, Aromatics, Carbon Monoxide, Chloromethane, HZSM-5. [Extracted from the article]

The transformation of methane into high value‐added chemicals such as aromatics provides a more desired approach towards sustainable chemistry but remains a critical challenge due to the low selectivity of aromatics and poor stability. Herein, we first report a coupling reaction of CH3Cl and CO (CCTA) based on methane conversion, which achieves extremely high aromatics selectivity (82.2 %) with the selectivity of BTX up to ca. 60 % over HZSM‐5. The promoting effects have been demonstrated on other zeolites especially 10‐membered rings (10 MR) zeolites. Multiple characterizations show that 2,3‐dimethyl‐2‐cyclopentene‐1‐one (DMCPO) is generated from acetyl groups and olefins. Furthermore, isotopic labeling analysis confirms that CO is inserted into the DMCPO and aromatics rings. A new aromatization mechanism is proposed, including the formation of the above intermediates, which conspicuously weakens the hydrogen transfer reaction, leading to a considerable increase of aromatics selectivity and a dramatic drop in alkanes. [ABSTRACT FROM AUTHOR]

Abstract: Stable isotope techniques are increasingly applied to study atmospheric budgets of methyl halides. Here we use compound specific thermal conversion isotope ratio mass spectrometry to measure the stable hydrogen isotope values of methyl chloride () released thermally from dried leaves of halophyte plants collected from different geographical locations. We developed an automated purification and pre-concentration unit to enable measurement of from samples (100 ml) when mixing ratios were as low as 1 ppmv. Even though this is considerably higher than normal atmospheric mixing ratios this unit enabled measurement of the δ2H values of CH3Cl released during heating of samples at temperatures ranging from 30 to 300 °C. No substantial changes of values were observed over this temperature range. However, the values of all plants examined were strongly depleted (−178 ± 34‰) relative to the δ2H values of their modelled meteoric water, but differ only by 1–50‰ from those observed for their methoxyl groups. Our results indicate that plant methoxyl groups are an important precursor of the methyl group for CH3Cl thermally emitted from lyophilised and homogenized dry halophyte leaves. Furthermore, the thermal reaction producing CH3Cl did not show a substantial kinetic hydrogen isotope fractionation between CH3Cl and precursor methoxyl groups over the temperature range investigated. Moreover, we found a moderate linear correlation (R 2 = 0.37) for the relationship between values released from halophytes and the δ2H values of modelled precipitation at their geographical locations. As CH3Cl emissions from terrestrial vegetation, including senescent and dry plants and biomass burning, are considered to provide a substantial fraction of the global emissions our findings are important when establishing a global hydrogen isotope model for atmospheric CH3Cl. [Copyright &y& Elsevier]

Abstract: Construction of accurate lineshape models for chlorosubstituted hydrocarbons is challenging. In this account the problem has been investigated thoroughly for the chloromethane series, CH4−n Cl n , n =1–4, using high-resolution experimental data and extensive theoretical calculations. The Contraction following ionization is a key parameter for a quantitative description of the vibrational excitation for all four molecules. We determine this quantity accurately for the title molecules and also propose approximate approaches that may applied to larger molecules. Having developed accurate vibrational lineshape models as well as reliable estimates of the instrumental broadening in each case, the carbon 1s hole lifetime broadening is determined from a fit to the experimental spectrum for each molecule. The resulting values for the lifetime broadening are 88±5meV for CH3Cl, 80±5meV for CH2Cl2, 74±5meV for CHCl3 and 62±5meV for CCl4. The lifetime widths decrease systematically with the number of chlorine substituents and correlate excellently with the valence occupancy of the core-ionized carbon. This indicates that the one-center model for Auger decay of the core hole is valid for the present series of molecules. [Copyright &y& Elsevier]

Abstract: Mesoporous γ-alumina, mp-γ-Al2O3, possessing surface area around 385m2/g and total pore volume of 2.0cm3/g was prepared via template-free sol–gel synthesis. The catalytic activity of the prepared alumina for the conversion of chloromethane to dimethyl ether, DME, in the presence of water or methanol was studied in the temperature range of 170–450°C employing FTIR spectroscopy. In the absence of water and methanol, the fresh surface of mp-γ-Al2O3 showed 100% conversion of chloromethane to DME at temperatures between 250 and 350°C. However, rapid deactivation of the catalyst resulted in a sharp decrease in the conversion to <5% within a few minutes of reaction. The catalytic activity was noticeably enhanced by adding water vapor to the gas feed resulting in higher conversions to DME and methanol. The catalytic activity and DME selectivity were further enhanced in the presence of methanol instead of water. In the temperature range of 200–300°C, complete conversions were obtained at the beginning of reactions before they declined to values between 31 and 45% depending on the reaction temperature. It was proposed that the surface hydroxyl groups are the active sites where chloromethane molecules dissociatively adsorb forming adsorbed methoxy ion intermediates. The adsorption of molecular methanol regenerates the surface hydroxyl groups and enhances the formation of adsorbed methoxy ions on the surface which react further with chloromethane or methanol molecules to produce more DME. [Copyright &y& Elsevier]

Abstract: Temperate woodland ecosystems are believed to be both a source and sink for atmospheric methyl bromide and methyl chloride. To separate the gross production and consumption fluxes in this ecosystem, we applied a stable isotope tracer technique in field and laboratory-based experiments. Flux measurements were conducted in a California oak-savanna woodland ecosystem at several intervals throughout the day during the wet and dry seasons to observe the diurnal and seasonal variability of fluxes. While gross production was small and variable, gross consumption showed a clear difference between seasons, with much larger rates during the wet season and negligible rates during the dry season. Laboratory incubations confirmed that fluxes were strongly affected by soil moisture. Consumption rates of methyl bromide, however, are less than half of the previous estimates of temperate woodland soil uptake rates during the growing season. Nevertheless, woodlands cover a significant portion of the world''s land surface area and may still be an important component of the soil sink for these methyl halides. [Copyright &y& Elsevier]

Abstract: The catalytic hydrolysis of chloromethane to methanol and dimethyl ether was studied over metal-exchanged zeolite Y (NaY, KY, CsY, MgY, CuY and FeY). All catalysts showed higher conversions than the blank reaction in the temperature range between 453 and 673K. Methanol was the major product on all catalysts, with selectivity ranging from 76 to 95%. Dimethyl ether (DME) was the other major product formed with selectivity of 5–7% over alkaline cation-exchanged zeolite Y and 10–24% over the zeolites exchanged with polyvalent cations. The higher selectivity to DME over MgY, CuY and FeY is associated with the presence of stronger acid sites with respect to NaY. Theoretical calculations indicated that a mechanistic pathway involving methanolysis of an adsorbed methoxy group may account for the formation of dimethyl ether on alkaline cation-exchanged zeolites. [Copyright &y& Elsevier]

Abstract: This paper presents results of new microwave studies of two chloromethane isotopologues 12CH3 35Cl and 12CH3 37Cl. The microwave spectra were obtained using the Prague millimeter wave semiconductor spectrometer with an estimated uncertainty of individual well-developed (well-separated, not saturated with low noise) lines about 5kHz. The spectra were measured at different pressures and a pressure dependence of the molecular parameters was studied. The measurable pressure dependence was found only for the B constant. Moreover, our new data were merged with top quality data previously published and an additional set of the precise ground state molecular parameters B, DJ , DJK , HJJ , HJK ,, HKJ , eQq, and CN was derived for both the isotopologues. [Copyright &y& Elsevier]

The Arctic tundra has been shown to be a potentially significant regional sink for methyl chloride (CH3Cl) and methyl bromide (CH3Br), although prior field studies were spatially and temporally limited, and did not include gross flux measurements. Here we compare net and gross CH3Cl and CH3Br fluxes in the northern coastal plain and continental interior. As expected, both regions were net sinks for CH3Cl and CH3Br. Gross uptake rates (−793 nmol CH3Cl m−2 day−1 and −20.3 nmol CH3Br m−2 day−1) were 20–240% greater than net fluxes, suggesting that the Arctic is an even greater sink than previously believed. Hydrology was the principal regulator of methyl halide flux, with an overall trend towards increasing methyl halide uptake with decreasing soil moisture. Water table depth was one of the best predictors of net and gross uptake, with uptake increasing proportionately with water table depth. In drier areas, gross uptake was very high, averaging −1201 nmol CH3Cl m−2 day−1 and −34.9 nmol CH3Br m−2 day−1; in flooded areas, gross uptake was significantly lower, averaging −61 nmol CH3Cl m−2 day−1 and −2.3 nmol CH3Br m−2 day−1. Net and gross uptake was greater in the continental interior than in the northern coastal plain, presumably due to drier inland conditions. Within certain microtopographic features (low- and high-centered polygons), uptake rates were positively correlated with soil temperature, indicating that temperature played a secondary role in methyl halide uptake. Incubations suggested that the inverse relationship between water content and methyl halide uptake was the result of mass... [ABSTRACT FROM AUTHOR]

Abstract: SAPO-34 and MeAPSO-34s (Mee) molecular sieves have been synthesized and used as catalysts for chloromethane transformation to light olefins. The influences created by metal incorporation are characterized with XRD, XRF, SEM, NMR, TG and H2-TPR. The synthesized MeAPSO-34s have the same CHA topology structure, while metal incorporation gives rise to the increase of unit cell parameter and crystalline particle size. The coexistence of metal species in the synthesis starting gel has effect on the Si substitution into AlPO framework. Co, Mn or Fe incorporation generates a negligible difference on the chemical shift in 31P and 27Al MAS NMR. 29Si MAS NMR study has demonstrated that metal incorporation favors the Si island formation, predicting the stronger acidity. The reducibility of metal species in the synthesized MeAPSO-34s has been investigated by H2-TPR with the comparison of metal-impregnated SAPO-34. Two weight losses in TG analysis from template decomposition in diluted oxygen suggest different chemical location of template molecules in the molecular sieves. For MeAPSO-34, more template removal occurrence at high temperature range indicates stronger template-framework interaction and stronger acidity than SAPO-34 after calcinations. All the SAPO-34 and MeAPSO-34 molecular sieves are very active and selective catalyst for light olefins production. Metal incorporation improves the catalyst life and favors the ethylene and propylene generation. These catalytic properties enhancements are possibly related to the mechanism of chloromethane conversion with deposited coke species as reaction center. [Copyright &y& Elsevier]

Abstract: The effects of chloromethane (CH3Cl) addition on soot inception in methane–air and ethylene–air counterflow diffusion flames were investigated by varying the concentrations of chloromethane and nitrogen in the fuel stream. Experiments showed a monotonic increase in the critical sooting stretch rate for methane–air flames when methane was replaced by chloromethane, while ethylene and chloromethane flames exhibited a larger sooting tendency than flames under comparable conditions and burning either ethylene or chloromethane alone. For the conditions investigated, the critical sooting stretch rates of methane–chloromethane–nitrogen flames were shown to be primarily a function of the chloromethane loading in the fuel stream. The structure of these flames was modeled using detailed chemistry and transport. Modeling results suggested that the enhancement of soot formation in ethylene–chloromethane flames may be a combined result of increased concentrations of C2 species and chlorinated C1 radicals (CH2Cl and CHCl). A large rate of the reactions among these species may be the first steps in the molecular growth processes, which leads to the inception of soot particles. [Copyright &y& Elsevier]

Granular graphite is a potential electrode material for the electrochemical remediation of refractory chlorinated organic compounds such as trichloroethylene (TCE). However, the use of granular graphite can complicate the experimental results. On one hand, up to 99% of TCE was removed and up to 75% was eliminated during TCE dechlorination; on the other hand, the chloride yield was extremely low—less than half of the amount of chlorine was recovered, and a carcinogenic, namely chloromethane (CM) was formed. These perplexing results were investigated, through experiments and theoretical analysis, to determine the true extent of dechlorination. Analysis of TCE adsorption results indicated that, in a dechlorination experiment, the adsorbed amount, which varies with the rate of decrease of the concentration of TCE in the solution, were between 7 and 25% of the initial amount of TCE. Results of the dechlorination of carbonstable isotope TCE confirmed that CM was not a product of dechlorination; in fact, it was a product of an electrode reaction of chloride in the acetate ammonium electrolyte. Extremely low yield of chloride was caused by its reaction with acetate in forming CM and by the reactions at the graphite anode; preventing these chloride-consuming reactions, by using a platinum anode and a potassium nitrate electrolyte, increased chloride yield and chlorine recovery significantly. Based on these findings, the percentage of TCE dechlorinated using a granular-graphite electrode was estimated in a range between 60 and 85%. [ABSTRACT FROM AUTHOR]

SAPO-34s with low and high Si content were synthesized and characterized by XRD, XRF, NMR, FTIR and TG-DSC. Different Si content generated no apparent difference in XRD patterns and 31P and 27Al MAS NMR spectra. The Si coordination states studied by 29Si MAS NMR predicted the acidity difference caused by Si incorporation. The absorbance of bridge hydroxyls in FTIR spectra also showed the amount of active sites differed with Si content. Both of the two samples were employed as catalysts in the transformation of chloromethane to light olefins and proved to be very selective catalysts for light olefins production. The influences of Si content on chloromethane conversion and product selectivity were investigated in details. Coke amount and coke species were determined by TG-DSC and FTIR. Coke formation was related to the Si content of SAPO-34 and corresponded to the catalytic performance. [ABSTRACT FROM AUTHOR]

Abstract: Methyl chloride (MeCl) and methyl bromide (MeBr) were converted to hydrocarbons over a H-SAPO-34 catalyst in a fixed-bed reactor at atmospheric total pressure. The feed rate (WHSV, equivalent to the mass of methanol) was in the range of 0.8–7.7 h−1, and the reaction temperature was varied from 300 to 450 °C. Comparative experiments were performed using methanol (MeOH). An induction period was observed for all reactants. The induction period may be overcome by adding a small amount of propene to the reactor before admission of the methyl halide feed. MeCl and MeBr were converted to the same extent under identical reaction conditions, whereas the methanol conversion was more than one order of magnitude greater than the methyl halide conversion. Product selectivities were similar for all reactants. Partial pressure variations of MeCl (0.1 vs. 1.0 bar pressure) indicated a first-order reaction rate in MeCl at 350–450 °C. Rapid catalyst deactivation was observed for all reactants at and above 350 °C. Repeated reaction–regeneration cycles using 1 bar of MeCl at 450 °C led to a loss of initial activity only, whereas the subsequent activity and product distribution with time on stream were identical for cycles 2–5. No structural changes in the catalyst were observed by X-ray diffraction after the regeneration tests. [Copyright &y& Elsevier]

Abstract: In this work, the effect of isotopes on vibrational frequencies of chloroform and chloromethane has been studied using different computational quantum chemistry methods. It was found that for our calculations, the results of the B3LYP method are comparable or even better than the more expensive MP2 method. By scaling the computed vibrational frequencies, it is possible to obtain the isotope effects very similar to the experimental data. The obtained results in this work show that it is possible to use a simple procedure to find a transition structure and to calculate vibrational frequencies, then study the kinetic isotope effects for the environmentally important processes. In this work, the reduced isotopic partition function ratios and the equilibrium constants for isotope exchange of chloroform and chloromethane has been calculated. [Copyright &y& Elsevier]

Abstract: HSAPO-34 molecular sieve was employed in chloromethane conversion and showed high performance in activity and selectivity in production of light olefins. Our detailed IR investigation allowed the identification of the active sites and the adsorbed species and demonstrated that the conversion started from 350°C with alkoxy group as the intermediate. The fixed-bed catalytic testing evidenced that in the range of 350–500°C, 70–80% of chloromethane was transferred to ethylene, propylene and butenes. Increasing reaction temperature favors the conversion and enhances the yield of lighter olefins. A very important reversible phenomenon, the breaking of Alh name="sbnd" />P bonds upon adsorption of HCl, a main product of reaction to generate a large amount of P and the recovery of Alh name="sbnd" />P upon removal of HCl was revealed. [Copyright &y& Elsevier]

Abstract: Ab initio calculations have been performed for both H-atom and Cl-atom abstraction reactions by the hydroxyl radical. Geometry optimization and vibrational frequencies analysis were performed for reactants, transition state and products at the MP2(full)/cc-pVTZ level of theory. On the basis of the ab initio data, the rate constants have been deduced over a wide temperature range, 200–2000 K, using conventional transition state theory, including Wigner tunneling correction and the hindered rotor approximation. Calculated transition state rate constants with Wigner tunneling correction are in good agreement with experimental results. The tunneling contribution becomes important at ambient temperatures, resulting in the exhibited non-Arrhenius behavior of the rate constant. [Copyright &y& Elsevier]

Abstract: The conversion of chloromethane to light olefins, like ethene and propene, was studied over ZSM-5 catalysts at 698K. For HZSM-5, the selectivity to olefins increased for higher Si/Al ratio and was interpreted in terms of reducing hydrogen transfer, as the sites become more isolated. The exchange of Zn2+ cation increased the activity and selectivity to light olefins. Theoretical calculations using a MT6 cluster (T=Si or Al and M is an alkaline cation) showed that the activation energy for the formation of an adsorbed methoxide from chloromethane increases in the alkaline metal series, with Li+ showing the lowest and Cs+ the higher barrier. The calculations also indicated that the metal–chloride interaction plays an important role in the reaction. [Copyright &y& Elsevier]

Compound-specific stable isotope analysis (CSIA) using gas chromatography-isotope ratio mass spectrometry (GC/IRMS) has developed into a mature analytical method in many application areas over the last decade. This is in particular true for carbon isotope analysis, whereas measurements of the other elements amenable to CSIA (hydrogen, nitrogen, oxygen) are much less routine. In environmental sciences, successful applications to date include (i) the allocation of contaminant sources on a local, regional, and global scale, (ii) the identification and quantification of (bio)transformation reactions on scales ranging from batch experiments to contaminated field sites, and (iii) the characterization of elementary reaction mechanisms that govern product formation. These three application areas are discussed in detail. The investigated spectrum of compounds comprises mainly n-alkanes, monoaromatics such as benzene and toluene, methyl tert-butyl ether (MTBE), polycyclic aromatic hydrocarbons (PAHs), and chlorinated hydrocarbons such as tetrachloromethane, trichloroethylene, and polychlorinated biphenyls (PCBs). Future research directions are primarily set by the state of the art in analytical instrumentation and method development. Approaches to utilize HPLC separation in CSIA, the enhancement of sensitivity of CSIA to allow field investigations in the µg L-1 range, and the development of methods for CSIA of other elements are reviewed. Furthermore, an alternative scheme to evaluate isotope data is outlined that would enable estimates of position-specific kinetic isotope effects and, thus, allow one to extract mechanistic chemical and biochemical information. [ABSTRACT FROM AUTHOR]

The Bro¨nsted acidity of a series of protonated zeolites with different structures and Si/Al ratios such as HY (Si/Al=2.4), H(Na)EMT (3.6), HMOR (9.5), HZSM-5 (21.7) and HBeta (12.5) have been studied at room temperature and at various temperatures by means of in situ FT-IR spectroscopy using chloromethane as probe molecule. CH3Cl was found to interact by its negatively charged chlorine atom with the polarised hydrogen atoms of hydroxyls of zeolites through hydrogen bonding, causing the red-shift of the hydroxyls vibration. The extent of the red-shift supplies important information on the strength of Bro¨nsted acidity of zeolites which ranks in the order: HBeta>HMOR&ap;HZSM-5>H(Na)EMT≥HY. The study made at various temperatures revealed that the interaction of chloromethane with hydroxyls of zeolites was dependent on the temperature, reflecting the strength and the heterogeneity of acidic hydroxyls of zeolites. This temperature-dependent study confirms also the acid strength ranking obtained on the basis of the extent of the red-shift. The direct conversion of CH3Cl was carried out in the temperature range of 200–500 °C. The intrinsic activity of the five investigated zeolites has been compared with and was found to vary in the sense as acid strength. The selectivity of products of chloromethane conversion was also correlated with the Bro¨nsted acid strength of the zeolites. [Copyright &y& Elsevier]

EPR spectroscopy was chosen to investigate the ligand exchange reactions between copper(II) bis(dithiocarbamate), Cu(dtc)2, and copper(II) salts which proceeds with the formation of mixed-ligand complexes of the type Cu(dtc)X, where X=Cl, NO3, ClO4. Large concentrations of 1:1 mixed-ligand complexes of this type are obtained as indicated by the EPR spectra of acetone, CHCl3/EtOH, CHCl3/i-PrOH, CCl4/EtOH and CCl4/i-PrOH, solutions of Cu(dtc)2 and the appropriate copper(II) salt CuCl2, Cu(NO3)2 or Cu(ClO4)2. Double integration of Cu(dtc)2 EPR signals obtained at temperatures between 240 and 310 K affords the calculation of the equilibrium constant (K) of the reaction: Cu(dtc)2+CuX2⇌2 Cu(dtc)X in all solvents as a function of T. From the values of K the stability constant β of the mixed-ligand complexes has been derived. The error associated with the calculated stability constant is ±10%. Thermodynamic parameters (ΔH0, ΔG0 and ΔS0) are determined from the temperature dependence of K as measured by EPR spectroscopy. [ABSTRACT FROM AUTHOR]