Elimination Of HCl Research Articles

Controlling (E/Z)-Stereoselectivity of -NHC=O Chlorination: Mechanism Principles for Wide Scope Applications.

Organic halogen compounds are cornerstones of applied chemical sciences. Halogen substitution is a smart molecular design strategy adopted to influence reactivity, membrane permeability and receptor interaction. Chiral bioreceptors may restrict the stereochemical requirements in the halo-ligand design. Straightforward (but expensive) catalyzed stereospecific halogenation has been reported. Historically, PCl5 served access to uncatalyzed stereoselective chlorination although the stereochemical outcomes were influenced by steric parameters. Nonetheless, stereochemical investigation of PCl5 reaction mechanism with carbamoyl (RCONHX) compounds has never been addressed. Herein, we provide the first comprehensive stereochemical mechanistic explanation outlining halogenation of carbamoyl compounds with PCl5; the key regioselectivity-limiting nitrilimine intermediate (8-Z.HCl); how substitution pattern influences regioselectivity; why oxadiazole byproduct (P1) is encountered; stereo-electronic factors influencing the hydrazonoyl chloride (P2) production; and discovery of two stereoselectivity-limiting parallel mechanisms (stepwise and concerted) of elimination of HCl and POCl3. DFT calculations, synthetic methodology optimization, X-ray evidence and experimental reaction kinetics study evidence all supported the suggested mechanism proposal (Scheme 2). Finally, we provide mechanism-inspired future recommendations for directing the reaction stereoselectivity toward elusive and stereochemically inaccessible (E)-bis-hydrazonoyl chlorides along with potentially pivotal applications of both (E/Z)-stereoisomers especially in medicinal chemistry and protein modification.

An experimental and mechanism study on the pyrolysis of sulfur mustard

Experimental studies on the pyrolysis of sulfur mustard (HD) were conducted from 673 to 1473 K using Py-GC/MS combined with two separate columns. The HD pyrolysis rate exceeded 99 % at a pyrolysis time of approximately 2 seconds above 1073 K. The pyrolysis products of HD mainly include ethylene, vinyl chloride, carbon disulfide, thiophene, hydrogen chloride and hydrogen sulfide. The main reaction mechanism of HD pyrolysis was investigated using quantum chemistry methods combined with the TST/VTST theory. At 673 K, the initial reaction pathway of HD primarily involves an intramolecular HCl elimination and the cleavage of the C-S bond. The radical reactions will dominate the pyrolysis of HD once radical pool is formed. The reaction pathways of the important radical intermediates were analyzed, and the formation mechanisms of the main pyrolysis products were investigated. Theoretically, the high-pressure limit rate constants for the major reactions were calculated. This study contributes to a deeper understanding of the HD pyrolysis mechanism and provides a theoretical and data foundation for the destruction of HD.

Kinetics of Plasticized Poly(vinyl chloride) Thermal Degradation, Induction, Autocatalysis, Glass Transition, Diffusion

AbstractKinetics of non‐oxidative thermal degradation of poly(vinyl chloride) (PVC) plasticized with di(2‐ethylhexyl)phthalate and epoxidized linseed oil (ELO) were studied using differential scanning calorimetry. PVC thermal degradation autocatalyzed by forming HCl is delayed in the presence of acid scavenging ELO. Direct HCl elimination rates during steady state degradation (induction period) were almost independent on ELO concentration, with rate constants ranging from ≈3.2×10−6 s−1 at 463 K to ≈7.0×10−5 s−1 at 503 K. Activation energy of HCl elimination increased with glass transition temperature (Tg) increase from 136.0 kJ mol−1 at Tg=260.3 K to 141.9 kJ mol−1at Tg=274.2 K. Diffusion coefficients of HCl diffusion in plasticized PVC deduced using Williams‐Landel‐Ferry equation were of the order of 10−4 cm2 sec−1. Calculated activation energy of HCl diffusion in plasticized PVC was ≈30 kJ mol−1. The rate constants of PVC autocatalytic degradation were derived from the experimental data (for the 1st time) using Šesták‐Berggren approach and ranged from 3.2×10−2 sec−1 at 503 K to 4.4×10−3 sec−1 at 463 K. Autocatalysis activation energies ranged from 70.4 kJ mol−1 to 85.1 kJ mol−1 and increased with increase of glass transition temperature. It was established that PVC degradation kinetics was not controlled by HCl diffusion. Compensation effect was observed for initial and catalyzed PVC degradation.

Sodium Hypochlorite Pentahydrate as a Chlorinating Reagent: Application to the Tandem Conversion of β,γ-Unsaturated Carboxylic Acids to α,β-Unsaturated Lactones

Sodium hypochlorite pentahydrate (NaClO·5H2O, 1) has recently been employed in organic synthesis as an oxidant for alcohols, sulfides, glycols, etc. In most of these reactions, however, reagent 1 functions just as a simple oxidant, and the variations of the reactions have not been well explored. In this study, we report another useful and fascinating reaction, in which reagent 1 functions as a green chlorinating reagent toward β,γ-unsaturated carboxylic acid (2). When substrate 2 was stirred at room temperature with 1 (2 eq) in acetonitrile for 1 h, α,β-unsaturated lactone (3) was obtained in moderate yields (up to 62%). The same reaction proceeded in various organic and aqueous solvents as well. When excess reagent 1 was employed, lactone 3 was further oxidized to the corresponding epoxide (4) for some cases. The conversion is initiated by electrophilic attack of HOCl to the C=C bond of 2 to generate a chloronium ion intermediate, which is cyclized to β-chlorolactone (5) and then 3 through the elimination of HCl. The usefulness of 1 as a chlorinating reagent was further demonstrated in the electrophilic substitution of activated aromatic compounds.

Adducts of Lewis acidic stibanes with phosphane chalcogenides.

Starting from ClSbRF2 (RF = C2F5, 3,5-(CF3)2C6H3) and H(E)P(tBu)2 (E = O, S), we prepared the oxy- and sulphanediyl-bridged adducts RF2Sb(Cl)-E-(H)P(tBu)2, which are stable against the elimination of HCl. The different electron-withdrawing substituents and chalcogen bridging units influence the size of the Sb-E-P angle. ClSb(C2F5)2 and nBu3SnH react to give HSb(C2F5)2, which seems to interact weakly with H(O)P(tBu)2 in solution as observed via NMR. All products were characterised by NMR spectroscopy and all the stable ones were additionally characterised by X-ray diffraction and elemental analyses.

Facile Access to Cationic Methylstannylenes and Silylenes Stabilized by E-Pt Bonding and their Methyl Group Transfer Reactivity.

We describe a family of cationic methylstannylene and chloro- and azidosilylene organoplatinum(II) complexes supported by a neutral, binucleating ligand. Methylstannylenes MeSn:+ are stabilized by coordination to PtII and are formed by facile Me group transfer from dimethyl or monomethyl PtII complexes, in the latter case triggered by concomitant B-H, Si-H, and H2 bond activation that involves hydride transfer from Sn to Pt. A cationic chlorosilylene complex was obtained by formal HCl elimination and Cl- removal from HSiCl3 under ambient conditions. The computational studies show that stabilization of cationic methylstannylenes and cationic silylenes is achieved through weak coordination to a neutral N-donor ligand binding pocket. The analysis of the electronic potentials, as well as the Laplacian of electron density, also reveals the differences in the character of Pt-Si vs. Pt-Sn bonding. We demonstrate the importance of a ligand-supported binuclear Pt/tetrel core and weak coordination to facilitate access to tetrylium-ylidene Pt complexes, and a transmetalation approach to the synthesis of MeSnII :+ derivatives.

Synthesis of α‐Branched Enones via Chloroacylation of Terminal Alkenes

AbstractHere, we show the conversion of unactivated alkenes into α‐branched enones via regioselective chloroacylation with acyl chlorides. The method relies upon the initial in situ generation of chlorine radicals directly from the acyl chloride precursor under cooperative nickel/photoredox catalysis. Subsequent HCl elimination provides enones and α,β‐unsaturated esters that are not accessible via the conventional acylation approaches that provide the other, linear constitutional isomer.

Synthesis of α-Branched Enones via Chloroacylation of Terminal Alkenes.

Here, we show the conversion of unactivated alkenes into α-branched enones via regioselective chloroacylation with acyl chlorides. The method relies upon the initial in situ generation of chlorine radicals directly from the acyl chloride precursor under cooperative nickel/photoredox catalysis. Subsequent HCl elimination provides enones and α,β-unsaturated esters that are not accessible via the conventional acylation approaches that provide the other, linear constitutional isomer.

An alkali-enhanced subcritical water treatment strategy of short-chain chlorinated paraffins: Dechlorination and hydrocarbons recovery

As persistent organic pollutants, short-chain chlorinated paraffins (SCCPs) have attracted wide attention in the field of environmental health risk and hazardous waste management. Efficient dechlorination of high content of SCCPs in plastic waste is the committed step for its detoxification and safety treatment. In this study, a high-efficiency and low-temperature process for dechlorination and hydrocarbons recovery from typical SCCPs (52#SCCPs) by subcritical water (SubCW) with alkali enhancer was developed. The introduction of alkali enhancer in the SubCW process had significantly enhanced effect on the dechlorination of 52#SCCPs, and the order of the enhanced effect of alkali enhancer for the dechlorination was NaOH > Na2CO3 > NaHCO3 > NH3·H2O > KOH. The dechlorination behaviors of 52#SCCPs in the NaOH-enhanced SubCW process were studied systematically under different conditions including temperature, residence time, alkali concentration, and volume ratio. The results showed that high-efficiency dechlorination (100 %) of 52#SCCPs could be achieved by the NaOH-enhanced SubCW process at low temperature for a short time (250 °C, 5 min). All of the chlorine released from the molecular chain of 52#SCCPs was transferred to the aqueous phase in the form of inorganic chlorine. The continuous HCl elimination reaction was the primary dechlorination mechanism for 52#SCCPs in the NaOH-enhanced SubCW process. After the dechlorination of 52#SCCPs, high value-added hydrocarbons such as 2,4-hexadiyne (31.74 %) could be obtained. The alkali-enhanced SubCW process proposed in this study is believed to be an environmentally friendly and high-efficiency method for dechlorination/detoxification and resource recovery of SCCPs.

Synthesis of tetrazoles through a domino reaction: A molecular electron density theory study of energetics, selectivities, and molecular mechanistic aspects

This study corresponds to a molecular electron density theory (MEDT) investigation to shed light on the energetics, selectivities, and molecular mechanistic aspects of an experimental domino reaction. Theoretical evidences at the M06–2X/6-31G(d) level indicates that this domino reaction includes three different successive steps and is initialized by a stepwise HCl elimination from precursor chlorohydrazone NPCH to yield nitrile imine NI-2. A subsequent stepwise and highly regioselective [3 + 2] cycloaddition (32CA) reaction of NI-2 toward tetramethylguanidine TMG-3 affords corresponding formal [3 + 2] cycloadduct CA-1 as the sole product. Finally, a stepwise HNMe2 elimination experienced by CA-1 leads to amino triazole ATA as an aromatic five-membered target product. Computed rate constants reveal that the HCl elimination step should be considered as the bottleneck of this domino reaction. However, a topological analysis of electron localization function (ELF) of NI-2 demonstrates a zwitterionic type (zw-type) 32 C A reaction is expected between NI-2 and TMG-3. This 32CA reaction also displays an almost noticeable polar character arising from moderate electrophilicity and strong nucleophilicity of NI-2 and TMG-3, respectively. The regioselectivity of 32CA reaction can be explained via analysis of Parr functions values calculated at the reactive sites of reagents. The molecular mechanism of the 32CA reaction was explored through portraying bond forming/breaking patterns involved in this polar, stepwise, and zw-type reaction by means of the ELF analysis. Indeed, formation of both C–N single bonds along the first and second steps takes place through coupling of the corresponding pseudoradical centers.

Reverse Regioselectivity in the Ultrasound‐Promoted Synthesis of 1,3,4‐Tri‐Substituted Pyrazoles via [3+2] Cycloaddition of Hydrazonoyl Chlorides with β‐Nitrostyrenes

AbstractHydrazonoyl chlorides react with β‐nitrostyrenes in ethanol under the clean action of ultrasonic irradiation. The reaction proceeds at room temperature via 1,3‐dipolar cycloadditions of in situ generated nitrile imine with β‐nitrostyrenes with concurrent elimination of HCl and HNO2 to afford 1,3,4‐trisubstituted pyrazoles with good to high yields and excellent regioselectivity in a short time.

Degradation of Polyvinyl Chloride by Sequential Dehydrochlorination and Olefin Metathesis.

Polyvinyl chloride (PVC) is a problematic waste plastic with limited options for recycling or upcycling. Herein, we demonstrate preliminary results in breaking down the long carbon chains of PVC into oligomers and small organic molecules. First, treatment with a substoichiometric amount of alkali base effects elimination of HCl to form a salt and creates regions of conjugated carbon-carbon double bonds, as determined by 1H NMR and UV-Vis spectroscopy. Olefin cross metathesis with an added partner alkene then cleaves carbon-carbon double bonds of the polymer backbone. Addition of allyl alcohol to the dehydrochlorination step introduces allyloxy groups by substitution of allylic chlorides. Subsequent metathesis of the pendant allyloxy groups provides a reactive terminal alkene to promote insertion of the metathesis catalyst onto the olefins in the all-carbon backbone. The products obtained are a mixture of PVC oligomers with greatly reduced molecular weights and a small-molecule diene corresponding to the substituents of the added alkene, as evidenced by 1H and DOSY NMR and GPC . This mild procedure provides a proof of concept towards harvesting carbon resources from PVC waste.

Degradation and dechlorination of trichloroacetic acid induced by an in situ 222 nm KrCl* excimer radiation

Since the coronavirus disease 2019 (COVID-19) pandemic epidemic, the excessive usage of chlorinated disinfectants raised the substantial risks of disinfection by-products (DBPs) exposure. While several technologies may remove the typical carcinogenic DBPs, trichloroacetic acid (TCAA), their application for continuous treatment is limited due to their complexity and expensive or hazardous inputs. In this study, degradation and dechlorination of TCAA induced by an in situ 222 nm KrCl* excimer radiation as well as role of oxygen in the reaction pathway were investigated. Quantum chemical calculation methods were used to help predict the reaction mechanism. Experimental results showed that UV irradiance increased with increasing input power and decreased when the input power exceeded 60 W. Decomposition and dechlorination were simultaneously achieved, where around 78% of TCAA (0.62 mM) can be eliminated and 78% dechlorination within 200 min. Dissolved oxygen showed little effect on the TCAA degradation but greatly boosted the dechlorination as it can additionally generate hydroxyl radical (•OH) in the reaction process. Computational results showed that under 222 nm irradiation, TCAA was excited from S0 to S1 state and then decayed by internal crossing process to T1 state, and a reaction without potential energy barrier followed, resulting in the breaking of C–Cl bond and finally returning to S0 state. Subsequent C–Cl bond cleavage occurred by a barrierless •OH insertion and HCl elimination (27.9 kcal/mol). Finally, the •OH attacked (14.6 kcal/mol) the intermediate byproducts, leading to complete dechlorination and decomposition. The KrCl* excimer radiation has obvious advantages in terms of energy efficiency compared to other competitive methods. These results provide insight into the mechanisms of TCAA dechlorination and decomposition under KrCl* excimer radiation, as well as important information for guiding research toward direct and indirect photolysis of halogenated DBPs.

Microstructural insight into the thermal decomposition of MgCl2·6H2O examined by in-situ high-temperature X-ray powder diffraction

A sequential thermal conversion of MgCl2·6H2O, including dehydration, hydrolysis and decomposition, was studied in terms of microstructure using in-situ high-temperature X-ray diffraction. The dehydration is occurred serially from room temperature to 208 ​°C that resulted in ∼48% weight loss. A decrease in unit cell volume is more prominent during dehydration until the monohydrate formed. The volume of monohydrate is slightly increased upon monoclinic to orthorhombic conversion. A gradual decrease in crystallite size is observed during the entire period of dehydration, resulting from lattice distortions upon ongoing lattice vibrations. The dehydration is also accounted for increased lattice strain. The hydrolysis of monohydrate produced magnesium chloride hydroxide, which is partly crystalline in nature. The magnesium chloride hydroxide increased its crystallinity upon further heating and decomposed to stable MgO at 458 ​°C. The hydrolysis and decomposition, both are occurred by the elimination of HCl that resulted in ∼28% weight loss. The MgO is formed under increased crystallite size and decreased lattice strain. The unit cells of MgO are packed tightly, minimizing the influence of ongoing lattice vibrations. At elevated temperatures, major steps that are involved in lattice stabilization are the elimination of water and HCl followed by rearrangement to minimize unfavorable interactions.

Synthesis of Pyridine-SF4-Alkynes via Light-Promoted Radical Coupling of Pyridine-SF4-Chlorides and EBX Reagents

Abstract Pyridine-tetrafluoro-λ6-sulfanyl-alkynes have emerged as building blocks for synthesizing linearly-linked pyridine-heterocycles. They are prepared via a two-step procedure comprising the radical addition of pyridine-tetrafluoro-λ6-sulfanyl-chlorides and alkynes and subsequent base-promoted elimination of HCl. Herein we developed a straightforward alternative synthesis via the radical coupling of pyridine-tetrafluoro-λ6-sulfanyl-chlorides with ethynylbenziodoxolone reagents under LED irradiation.

Flash pyrolysis mechanism of trimethylchlorosilane

The thermal decomposition mechanism of trimethylchlorosilane at temperatures up to 1400 K was investigated using flash pyrolysis microreactor coupled with vacuum ultraviolet (118.2 nm) photoionization time-of-flight mass spectrometry. The main initiation reaction of the parent molecule was identified to be HCl molecular elimination producing Me2Si=CH2, and its onset temperature was estimated to be around 1210 K. The methyl loss channel was also observed at an onset temperature of ∼1280 K. Other possible initiation pathways such as chlorine atom loss and methane molecular elimination were considered to be insignificant. Quantum chemistry calculations at the UCCSD(T)/cc-pVTZ//UM05–2X/aug-cc-pVDZ level of theory were performed to study the energetics of the possible initiation pathways. The theoretical calculations revealed that the HCl elimination channel via a van der Waals intermediate was the most energetically favored pathway among all the initiation channels, in agreement with the experimental observations. Transition state theory (TST) and variational transition state theory (VTST) calculations were employed to calculate unimolecular dissociation rate constants of the initiation reactions at elevated temperatures. The results supported the experimental observations and reaction energetics calculations that the HCl molecular elimination reaction was the most prominent initiation reaction and the CH3 loss channel was a significant initiation reaction channel. Secondary reactions of the initial products were identified, and the possible mechanisms were proposed.

Selective Photodetoxification of a Sulfur Mustard Simulant Using Plasmonic Aluminum Nanoparticles.

Plasmonic nanostructures have attracted increasing interest in the fields of photochemistry and photocatalysis for their ability to enhance reactivity and tune reaction selectivity, a benefit of their strong interactions with light and their multiple energy decay mechanisms. Here we introduce the use of earth-abundant plasmonic aluminum nanoparticles as a promising renewable detoxifier of the sulfur mustard simulant 2-chloroethylethylsulfide through gas phase photodecomposition. Analysis of the decomposition products indicates that C-S bond breaking is facilitated under illumination, while C-Cl breaking and HCl elimination are favored under thermocatalytic (dark) conditions. This difference in reaction pathways illuminates the potential of plasmonic nanoparticles to tailor reaction selectivity toward less hazardous products in the detoxification of chemical warfare agents. Moreover, the photocatalytic activity of the Al nanoparticles can be regenerated almost completely after the reaction concludes through a simple surface treatment.

Investigation of Hydrothermal Aging on Polyvinyl Chloride (PVC) Used in Medium Voltage Cables

This investigation deals with the effect of hydrothermal aging on the electrical insulating properties of polyvinyl chloride used in medium voltage cables. The evolution of dielectric properties (dielectric loss factor, dielectric constant, dielectric strength and volume resistivity) as a function of aging time and temperature has been studied. After that, the mechanical characteristics (elongation at break and tensile strength) were also determined. Physico-chemical analysis was performed to highlight the structural changes induced by hydrothermal aging. Infrared spectroscopy using the Fourier transform (ATR-FTIR) and thermogravimetric analysis (TGA-DTA) have been performed. The results obtained show that the loss factor and dielectric constant increase gradually with the increase of temperature, while the volume resistivity decreases. At 100℃, the general shape of the curves giving the evolution of dielectric properties as a function of aging time shows that both loss factor and dielectric constant increase while those of volume resistivity and dielectric strength decrease. In the case of 80℃, the loss factor decreases slightly and the dielectric constant remains almost constant with aging time, whereas the volume resistivity and dielectric strength increase. The activation energy varies with aging time. The impact of hydrothermal aging on the properties of the material has been established in this study. At the beginning of aging, the degradation is mainly due to the elimination of molecular HCl. At more advanced stages of aging, the degradation is attributed to the elimination of HCl and double bonds formation followed by a change in color. Other consequences of the degradation like crosslinking and swelling of the samples are also noticed.

Green emitting β$\ubeta$‐SiAlON:Eu2+ phosphors derived from chemically modified perhydropolysilazanes

AbstractWe report the first synthesis of β‐SiAlON:Eu2+ phosphors from single‐source precursors, perhydropolysilazane (PHPS), chemically modified with Al(OCH(CH3)2)3, and EuCl2. The reactions occurring during the precursor synthesis and the subsequent thermal conversion of polymeric precursors into β‐SiAlON:Eu2+ phosphors have been studied by a complementary set of analytical techniques, including infrared spectroscopy, gas chromatography–mass spectrometry, thermogravimetry–mass spectrometry, X‐ray diffraction (XRD), photoluminescence spectroscopy, and scanning electron microscopy. It has been clearly established that Al(OCH(CH3)2)3 immediately reacted with PHPS to afford N–Al bonds at room temperature, whereas N–Eu bond formation was suggested to proceed above 600°C accompanied by the elimination of HCl up to 1000°C in flowing N2. The subsequent 1800°C‐heat treatment for 1 h under an N2 gas pressure at 980 kPa allowed converting the single‐source precursors into fine‐grained β‐SiAlON:Eu2+ phosphors. XRD analysis revealed that the Al/Si of .09 was the critical atomic ratio in the precursor synthesis to afford single‐phase β‐SiAlON (z = .55). Moreover, Eu2+‐doping was found to efficiently reduce the carbon impurity in the host β‐SiAlON. The polymer‐derived β‐SiAlON:Eu2+ phosphors exhibited green emission under excitation at 460 nm and achieved the highest green emission intensity at the critical dopant Eu2+ concentration at 1.48 at%.

Transformation mechanisms of acetaldehyde and its substituted aldehydes into the corresponding nitriles and (N-chloro)amides during chloramination: A computational study.

As an alternative disinfectant to free chlorine, monochloramine reduces the formation of regulated disinfection byproducts (DBPs); however, it also contributes to the formation of highly toxic nitrogenous DBPs (N-DBPs), especially through the aldehyde pathway. The current understanding of aldehyde pathway mechanisms is limited. In this study, the transformation pathways of acetaldehyde and its substituted aldehydes into the corresponding nitriles and (N-chloro)amides during chloramination were investigated using quantum chemical calculations. Consistent with previous studies, 1-chloroamino alcohol first forms in the chloramination of aldehydes and then undergoes competitive dehydration and HCl elimination branch reactions to generate the nitrile and (N-chloro)amide, respectively. Iminol was found to be a key intermediate for (N-chloro)amide formation. Moreover, the results indicated that acetaldehydes substituted with electron-donating groups (EDGs) and electron-withdrawing groups (EWGs) are beneficial to the formation of the respective nitriles and N-chloro-amides, while those substituted with conjugated groups (CGs) are favourable for both. Based upon the above results, in addition to acetaldehyde, other aldehydes, such as propionaldehyde, glycolaldehyde, 3-butenal, and phenylacetaldehyde, which are the α-H of acetaldehydes substituted with -CH3, -OH, -CH=CH2, and -C6H5 groups, respectively, are potential precursors of toxic nitriles and (N-chloro)amides during chloramination. Thus, more attention should be given to these aldehydes. The findings of this work are helpful for further understanding the aldehyde pathway mechanisms and predicting potential precursors of toxic nitriles and (N-chloro)amides during chloramination.