Cation Clock Reactions for the Determination of Relative Reaction Kinetics in Glycosylation Reactions: Applications to Gluco- and Mannopyranosyl Sulfoxide and Trichloroacetimidate Type Donors

The development of a cation clock method based on the intramolecular Sakurai reaction for probing the concentration dependence of the nucleophile in glycosylation reactions is described. The method is developed for the sulfoxide and trichloroacetimidate glycosylation protocols. The method reveals that O-glycosylation reactions have stronger concentration dependencies than C-glycosylation reactions consistent with a more associative, S(N)2-like character. For the 4,6-O-benzylidene-directed mannosylation reaction a significant difference in concentration dependence is found for the formation of the β- and α-anomers, suggesting a difference in mechanism and a rationale for the optimization of selectivity regardless of the type of donor employed. In the mannose series the cyclization reaction employed as clock results in the formation of cis and trans-fused oxabicyclo[4,4,0]decanes as products with the latter being strongly indicative of the involvement of a conformationally mobile transient glycosyl oxocarbenium ion. With identical protecting group arrays cyclization in the glucopyranose series is more rapid than in the mannopyranose manifold. The potential application of related clock reactions in other carbenium ion-based branches of organic synthesis is considered.

Characteristics of C-, N-DBPs formation from nitrogen-enriched dissolved organic matter in raw water and treated wastewater effluent

The objective of this study is to clarify the relationships between the characteristics of dissolved organic nitrogen (DON) and disinfection by-products (DBPs) formation. Treated wastewater effluents from the Neihu wastewater treatment plant in Taipei City (TN) and source waters from the Tai Lake water treatment plant in Kinmen (KT) were evaluated. These water samples were fractionated to obtain 7 DON isolates with different characteristics. The DON isolates were freeze-dried and re-dissolved to different DON fraction solutions containing 10 mg-C/L of non-purgeable dissolved organic carbon (NPDOC). The DBPs formation potentials (DBPFPs) (trihalomethanes (THMs), haloacetic acids (HAAs), and nitrosamines) of different DON fraction solutions were then assessed with chlorine and monochloramine treatments. After fractionation schemes, mass concentrations of dried DON-enriched isolates ranged from 0.2 to 46.4 mg/L. Both TN effluents and KT raw waters had similar compositions of DON fractions except for the amounts of amphiphilic bases/neutrals (AMPB/N) isolates: hydrophobic acids (HPOA) > hydrophilic acids/neutrals (HPIA/N) > AMPB/N of KT raw waters > hydrophilic bases (HPIB) > amphiphilic acids (AMPA) > hydrophobic bases/neutrals (HPOB/N) > AMPB/N of TN effluents > amino acids (AA). For carbonated DBPs (C-DBPs), AA fraction treated with NaOCl formed the greatest amounts of C-DBPs (up to 1258.2 μg/L of THMs and 1140.6 μg/L of HAAs). For nitrogenated DBPs (N-DBPs), the AMPB/N fraction (DON = 1.4 mg-N/L) treated with NH2Cl was the most important precursor to form N-nitrosodimethylamine (NDMA) and generated up to 9238.0 ng/L of NDMA from KT raw water. Taking both DBP formation and organic composition into account, the HPOA (31.9%-38.4%)/HPIA/N (17.6%-35.7%) fractions and AMPB/N fraction (38.4%-93.9%) were the most important contributors to the overall C-DBPFPs and N-DBPFPs, respectively.

Application of different advanced oxidation processes for the removal of chloroacetic acids using a planar falling film reactor

Advanced oxidation processes (AOPs) are considered as an effective and promising method for the degradation and mineralization of aqueous recalcitrant organic pollutants. In this study, application of ozonation and various types of AOPs including photocatalysis, Fenton alone and their combinations were investigated and compared for the degradation and mineralization of chloroacetic acids (CAAs) in aqueous solutions, using a planar falling film reactor. CAAs are widely available in water treated by chlorination processes and are resistance against ozonation in the darkness. The results of the present work showed that the plain ozonation was inefficient method for the destruction of the CAAs as only about 2% degradation was observed after 90 min treatment. However, the best results were achieved by ozone in combinations with other oxidation processes. Furthermore, a synergistic effect on the removal rate was observed when these processes were exposed to the UVA light. Among the examined processes, combination of photo-Fenton with ozonation was found to be the fastest one for CAAs degradation. The effects of different parameters such as initial concentration of Fe²⁺, H₂O₂ and CAAs in photo-Fenton combined with ozonation were investigated. The optimum ratio of 0.12 of Fe²⁺/H₂O₂ concentration was found to give the best result for CAAs degradation. The degree of CAAs mineralization, measured by the total organic carbon removal, as well as the effect of falling liquid film flow rate on the removal of CAAs were also studied and discussed.

Ab Initio Molecular Dynamics Simulations of the SN1/SN2 Mechanistic Continuum in Glycosylation Reactions

We report a computational approach to evaluate the reaction mechanisms of glycosylation using ab initio molecular dynamics (AIMD) simulations in explicit solvent. The reaction pathways are simulated via free energy calculations based on metadynamics and trajectory simulations using Born-Oppenheimer molecular dynamics. We applied this approach to investigate the mechanisms of the glycosylation of glucosyl α-trichloroacetimidate with three acceptors (EtOH, i-PrOH, and t-BuOH) in three solvents (ACN, DCM, and MTBE). The reactants and the solvents are treated explicitly using density functional theory. We show that the profile of the free energy surface, the synchronicity of the transition state structure, and the time gap between leaving group dissociation and nucleophile association can be used as three complementary indicators to describe the glycosylation mechanism within the SN1/SN2 continuum for a given reaction. This approach provides a reliable means to rationalize and predict reaction mechanisms and to estimate lifetimes of oxocarbenium intermediates and their dependence on the glycosyl donor, acceptor, and solvent environment.

Palladium-catalyzed α-arylation of 2-chloroacetates and 2-chloroacetamides

A method has been developed for the Pd-catalyzed synthesis of α-(hetero)aryl esters and amides through a Suzuki-Miyaura cross-coupling reaction. This method avoids the use of strong base, does not necessitate inert or low temperature formation of reagents, and does not require the use of a large excess of organometallic reagent. Utilization of organotrifluoroborate salts as nucleophilic partners allows a variety of functional groups and heterocyclic compounds to be tolerated.

Alkylation of Sulfonamides with Trichloroacetimidates under Thermal Conditions

An intermolecular alkylation of sulfonamides with trichloroacetimidates is reported. This transformation does not require an exogenous acid, base, or transition metal catalyst; instead the addition occurs in refluxing toluene without additives. The sulfonamide alkylation partner appears to be only limited by sterics, with unsubstituted sulfonamides providing better yields than more encumbered N-alkyl sulfonamides. The trichloroacetimidate alkylating agent must be a stable cation precursor for the substitution reaction to proceed under these conditions.

Pd-catalyzed alkynylation of 2-chloroacetates and 2-chloroacetamides with potassium alkynyltrifluoroborates

The synthesis of β,γ-alkynyl esters and amides using air-stable potassium alkynyltrifluoroborates as nucleophilic partners in a mild Suzuki-Miyaura cross-coupling reaction has been achieved. Propargyl esters and amides were obtained in high yields using a low catalyst loading, and the substrate scope of the reaction has been significantly improved over previous methods.

Haloacetic acid removal by sequential zero-valent iron reduction and biologically active carbon degradation

An innovative haloacetic acid (HAA) removal process was developed. The process consisted of a zero-valent iron (Fe(0)) column followed by a biologically active carbon (BAC) column that were efficient in degrading tri- and di-HAAs, and mono- and di-HAAs, respectively. The merit of the process was demonstrated by its performance in removing trichloroacetic acid (TCAA). An empty bed contact time of 10 min achieved nearly complete removal of 1.2 μM TCAA and its subsequent products, dichloroacetic acid (DCAA) and monochloroacetic acid (MCAA). HAA removal was a result of chemical dehalogenation and biodegradation rather than physical adsorption. Preliminary kinetic analyses were conducted and the pseudo-first-order rate constants were estimated at ambient conditions for Fe(0) reduction of TCAA and biodegradation of DCAA and MCAA by BAC. This innovative process is highly promising in removing HAAs from drinking water, swimming pool water, and domestic or industrial wastewater.

Biologically active carbon filtration for haloacetic acid removal from swimming pool water

A biologically activate carbon (BAC) filter was continuously operated on site for the treatment of haloacetic acids (HAAs) in an outdoor swimming pool at an average empty bed contact time (EBCT) of 5.8 min. Results showed that BAC filtration was a viable technology for direct removal of HAAs from the pool water with a nominal efficiency of 57.7% by the filter while the chlorine residuals were 1.71 ± 0.90 mg/L during the study. THMs and TOC were not removed and thus were not considered as indicators of the effectiveness of BAC filtration. Increased EBCT in the range of 4.5 and 6.4 min led to improved HAA removal performance, which could be best fit by a logarithmic regression model. BAC filtration also affected the HAA speciation by removing more dichloroacetic acid (DCAA) than trichloroacetic acid (TCAA), resulting in a lower ratio of DCAA/TCAA in the filtered effluent. However, the observation of an overall constant ratio could be attributable to a complex formation and degradation mechanism occurring in swimming pools.

Peptide bonds affect the formation of haloacetamides, an emerging class of N-DBPs in drinking water: free amino acids versus oligopeptides

Haloacetamides (HAcAms), an emerging class of nitrogenous disinfection by-products (N-DBPs) of health concern, have been frequently identified in drinking waters. It has long been appreciated that free amino acids (AAs), accounting for a small fraction of the dissolved organic nitrogen (DON) pool, can form dichloroacetamide (DCAcAm) during chlorination. However, the information regarding the impacts of combined AAs, which contribute to the greatest identifiable DON portion in natural waters, is limited. In this study, we compared the formation of HAcAms from free AAs (tyrosine [Tyr] and alanine [Ala]) and combined AAs (Tyr-Ala, Ala-Tyr, Tyr-Tyr-Tyr, Ala-Ala-Ala), and found that HAcAm formation from the chlorination of AAs in combined forms (oligopeptides) significantly exhibited a different pattern with HAcAm formation from free AAs. Due to the presence of peptide bonds in tripeptides, Tyr-Tyr-Tyr and Ala-Ala-Ala produced trichloroacetamide (TCAcAm) in which free AAs was unable to form TCAcAm during chlorination. Moreover, peptide bond in tripeptides formed more tri-HAcAms than di-HAcAms in the presence of bromide. Therefore, the peptide bond may be an important indicator to predict the formation of specific N-DBPs in chlorination. The increased use of algal- and wastewater-impacted water as drinking water sources will increase health concerns over exposure to HAcAms in drinking water.

Insight into changes during coagulation in NOM reactivity for trihalomethanes and haloacetic acids formation

Natural organic matter (NOM) in raw water can contribute in many ways to the poor quality of drinking water, including the formation of disinfection byproducts such as trihalomethanes (THM) and haloacetic acids (HAA) during disinfection. This paper investigates the role of individual NOM fractions on changes in THM and HAA formation during coagulation with iron chloride (FeCl3) and a combination of polyaluminium chloride and iron chloride (FeCl3/PACl). The dissolved organic carbon (DOC) in the raw water and after coagulation was fractionated into four fractions, based on their hydrophobicity. Fractionation showed that most of the DOC (68%) in the raw water comes from the fulvic acid fraction, yielding 41% of the total THM precursors and 21% of the total HAA precursors. Both coagulants remove the humic acid fraction, but result in different changes to the reactivity of the remaining NOM fractions towards THM and HAA formation, indicating that coagulation occurs by different pathways, depending upon the type of coagulant used. In particular, significant changes in the reactivities of the hydrophilic acidic and non-acidic fractions were observed.

Structural, vibrational and theoretical studies of anilinium trichloroacetate: new hydrogen bonded molecular crystal with nonlinear optical properties

In this work, we report a combined experimental and theoretical study on molecular structure, vibrational spectra and NBO analysis of the potential nonlinear optical (NLO) material anilinium trichloroacetate. The FT-IR and FT-Raman spectra of the compound have been recorded together between 4000-80 cm(-1) and 3600-80 cm(-1) regions, respectively. The compound crystallizes in the noncentrosymmetric space group of monoclinic system. The optimized molecular structure, vibrational wavenumbers, IR intensities and Raman activities have been calculated by using density functional method (B3LYP) with 6-311++G(d,p) as higher basis set. The obtained vibrational wavenumbers and optimized geometric parameters were seen to be in good agreement with the experimental data. DSC measurements on powder samples do not indicate clearly on the occurrence of phase transitions in the temperature 113-293 K. The Kurtz and Perry powder reflection technique appeared to be very effective in studies of second-order nonlinear optical properties of the molecule. The non-linear optical properties are also addressed theoretically. The predicted NLO properties of the title compound are much greater than ones of urea. In addition, DFT calculations of the title compound, molecular electrostatic potential, frontier orbitals and thermodynamic properties were also performed at 6-311++G(d,p) level of theory. For title crystal the SHG efficiency was estimated by Kurtz-Perry method to be d(eff)=0.70 d(eff) (KDP).

Unusual complex formation and chemical reaction of haloacetate anion on the exterior surface of cucurbit[6]uril in the gas phase

Noncovalent interactions of cucurbit[6]uril (CB[6]) with haloacetate and halide anions are investigated in the gas phase using electrospray ionization ion mobility mass spectrometry. Strong noncovalent interactions of monoiodoacetate, monobromoacetate, monochloroacetate, dichloroacetate, and trichloroacetate on the exterior surface of CB[6] are observed in the negative mode electrospray ionization mass spectra. The strong binding energy of the complex allows intramolecular S(N)2 reaction of haloacetate, which yields externally bound CB[6]-halide complex, by collisional activation. Utilizing ion mobility technique, structures of exteriorly bound CB[6] complexes of haloacetate and halide anions are confirmed. Theoretically determined low energy structures using density functional theory (DFT) further support results from ion mobility studies. The DFT calculation reveals that the binding energy and conformation of haloacetate on the CB[6] surface affect the efficiency of the intramolecular S(N)2 reaction of haloacetate, which correlate well with the experimental observation.

Pd-catalyzed cross-coupling of potassium alkenyltrifluoroborates with 2-chloroacetates and 2-chloroacetamides

A protocol for the stereocontrolled synthesis of (E)- and (Z)-β,γ-unsaturated esters and amides is reported. 2-Chloroacetates as well as secondary and tertiary 2-chloroacetamides were successfully employed as electrophiles in the Suzuki-Miyaura cross-coupling reaction with potassium (E)- and (Z)-alkenyltrifluoroborates, affording the corresponding products in high yield.

Existence of a robust haloacid transport system in a Burkholderia species bacterium

Bacterium Burkholderia sp. MBA4 can utilize haloacids as the sole carbon and energy source for growth. We have previously reported that a haloacid operon, encoding for a dehalogenase (Deh4a) and an associated permease (Deh4p), was responsible for the transformation and uptake of haloacids in MBA4. A disruption of deh4p in MBA4 caused a decrease in monochloroacetate (MCA) uptake, confirming its role as a haloacid transporter. However, this disruptant retained 68% of its MCA-uptake activity indicating the possibility of an alternative system. In this study, we report the identification of a second MCA-inducible haloacid transporter (Dehp2) in MBA4. Its function was confirmed by gene disruption and heterologous expression in Escherichia coli. A dehp2(-) mutant has 30% less, and an E. coli expressing Dehp2 has 40% more, of wildtype MCA-uptake activity. Quantitative RT-PCR illustrated that the minor loss of MCA-uptake activity in single disruptants of deh4p and dehp2 was partly due to a compensatory expression of the alternative gene. Competition assay and kinetics study revealed that Deh4p has a higher affinity for MCA while Dehp2 prefers chloropropionate. A deh4p(-)dehp2(-) double mutant retained 36% of MCA-uptake activity, indicating a robustness of the haloacid uptake systems. The MCA uptake activities mediated by Deh4p, Dehp2 and the uncharacterized system were completely abolished by protonophore carbonyl cyanide 3-chlorophenylhydrazone, suggesting that transmembrane electrochemical gradient is the driving force for MCA uptake.

One-pot protection-glycosylation reactions for synthesis of lipid II analogues

(2,6-Dichloro-4-methoxyphenyl)(2,4-dichlorophenyl)methyl trichloroacetimidate (3) and its polymer-supported reagent 4 can be successfully applied to a one-pot protection-glycosylation reaction to form the disaccharide derivative 7 d for the synthesis of lipid II analogues. The temporary protecting group or linker at the C-6 position and N-Troc protecting group of 7 d can be cleaved simultaneously through a reductive condition. Overall yields of syntheses of lipid II (1) and neryl-lipid II N(ε)-dansylthiourea are significantly improved by using the described methods.

X-ray diffraction, vibrational and quantum chemical investigations of 2-methyl-4-nitroanilinium trichloroacetate trichloroacetic acid

The structural investigations of the molecular complex of 2-methyl-4-nitroaniline with trichloroacetic acid, namely 2-methyl-4-nitroanilinium trichloroacetate trichloroacetic acid (C(11)H(10)Cl(6)N(2)O(6)) have been performed by means of single crystal and powder X-ray diffraction method. The complex was formed with accompanying proton transfer from trichloroacetic acid molecule to 2-methyl-4-nitroaniline. The studied crystal is built up of singly protonated 2-methyl-4-nitroanilinium cations, trichloroacetate anions and neutral trichloroacetic acid molecules. The crystals are monoclinic, space group P2(1)/c, with a=14.947Å, b=6.432Å, c=19.609Å and Z=4. The vibrational assignments and analysis of 2-methyl-4-nitroanilinium trichloroacetate trichloroacetic acid have also been performed by FTIR, FT-Raman and far-infrared spectral studies. More support on the experimental findings were added from the quantum chemical studies performed with DFT (B3LYP) method using 6-31G, cc-pVDZ, 6-31G and 6-31++G basis sets. The structural parameters, energies, thermodynamic parameters and the NBO charges of 2M4NATCA were also determined by the DFT methods.

Assessing the role of trichloroacetyl-containing compounds in the natural formation of chloroform using stable carbon isotopes analysis

Chloroform (CHCl(3)) is an environmental contaminant widely distributed around world, as well as a natural compound formed in various aquatic and terrestrial environments. However, the chemical mechanisms leading to the natural formation of chloroform in soils are not completely understood. To assess the role of trichloroacetyl-containing compound (TCAc) in the natural formation of chloroform in forest soils, carbon stable isotope analyses of chloroform and TCAc in field samples and chlorination experiments were carried out. The isotope analysis of field samples have revealed that the δ(13)C value of natural chloroform (δ(13)C(mean)=-25.8‰) is in the same range as the natural organic matter (δ(13)C(mean)=-27.7‰), whereas trichloromethyl groups of TCAc are much more enriched in (13)C (δ(13)C(mean)=-9.8‰). A similar relationship was also observed for TCAc and chloroform produced by chlorination of natural organic matter with NaOCl. The strong depletion of (13)C in chloroform relative to TCAc can be explained by carbon isotope fractionation during TCAc hydrolysis. As shown using a mathematical model, when steady state between formation of TCAc and hydrolysis is reached, the isotope ratio of chloroform is expected to correspond to isotope composition of NOM while TCAc should be enriched in (13)C by about 18.3‰, which is in good agreement with field observations. Hence this study suggests that TCAc are likely precursors of chloroform and at the same time explains why natural chloroform has a similar isotope composition as NOM despite large carbon isotope fractionation during its release.

Formation of haloacetonitriles and haloacetamides during chlorination of pure culture bacteria

The increasing reuse of organic nitrogen-rich wastewater raises concerns regarding the formation of nitrogenous disinfection by-products (N-DBPs), such as haloacetonitriles and haloacetamides. Previous research mainly focused on N-DBPs formation from dissolved organic matter in wastewater. In this study, dichloroacetonitrile (DCAN) and dichloroacetamide (DCAcAm) formation from particles in the secondary effluents of a domestic wastewater treatment plant during chlorination was assessed to account for 26-46% of the total formation. As part of particles in wastewater, bacterial cells enriched in organic nitrogen are considered a potential source for the formation of N-DBPs during chlorination. The formation of DCAN, DCAcAm and trichloroacetamide (TCAcAm) during the chlorination of a Gram-negative bacterium of Escherichia coli (E. coli) and a Gram-positive bacterium of Enterococcus faecalis (E. faecalis) were then evaluated. Compared with dissolved organic matter in the secondary effluent, bacterial cells formed more DCAN, DCAcAm and TCAcAm during chlorination. E. faecalis formed more DCAN, but less DCAcAm and TCAcAm than E. coli did under most chlorination conditions. Moreover, the effects of contact time, chlorine dose, pH value and ammonia nitrogen concentration on the N-DBPs formation from the two bacterial suspensions were investigated. Under the chlorination conditions in this study, DCAN formation from the bacterial suspensions initially increased and then decreased, while TCAcAm formation increased with increasing contact time and chlorine dose. DCAcAm formation from the bacterial suspensions increased with the prolonged contact time, and increased and then decreased with increasing chlorine dose. DCAN, DCAcAm and TCAcAm formation was favored under neutral pH condition, but was reduced with the addition of ammonia during the chlorination of the two bacterial suspensions.

The interaction between nitrobenzene and Microcystis aeruginosa and its potential to impact water quality

The potential water quality problems caused by the interaction between nitrobezene (NB) and Microcystis aeruginosa was investigated by studying the growth inhibition, the haloacetic acids formation potential (HAAFP) and the secretion of microcystin-LR (MC-LR). The results showed that NB can inhibit the growth of M. aeruginosa, and the value of EC50 increased with the increase of initial algal density. Although NB can hardly react with chlorine to form HAAs, the presence of NB can enhance the HAAFP productivity. The secretion of the intracellular MC-LR is constant under the steady experimental conditions. However, the presence of NB can reduce the MC-LR productivity of M. aeruginosa. Overall, the increased disinfection risk caused by the interaction has more important effect on the safety of drinking water quality than the benefit of the decreased MC-LR productivity, and should be serious considered when the water contained NB and M. aeruginosa is used as drinking water source.

Promoter free allylation of trichloroacetimidates with allyltributylstannanes under thermal conditions to access the common 1,1'-diarylbutyl pharmacophore

1,1'-Diarylbutyl groups are a common pharmacophore found in many biologically active small molecules. To access these systems under mild conditions, the reaction of diarylmethyl trichloroacetimidates with allyltributylstannanes was explored. Simply heating allyltributylstannane with the trichloroacetimidate resulted in substitution of the imidate with an allyl group. Unlike other methods used to access these systems, no strong base, transition metal catalyst, Brønsted acid or Lewis acid promoter was required to affect the transformation. Conversions are best with electron rich benzylic trichloroacetimidate systems, where excellent yields are achieved just by refluxing the reactants together in nitromethane.

Dialkylation of Indoles with Trichloroacetimidates to Access 3,3-Disubstituted Indolenines

2-Substituted indoles may be directly transformed to 3,3-dialkyl indolenines with trichloroacetimidate electrophiles and the Lewis acid TMSOTf. These reactions provide rapid access to complex indolenines which are present in a variety of complex natural products and medicinally relevant small molecule structures. This method provides an alternative to the use of transition metal catalysis. The indolenines are readily transformed into spiroindoline systems which are privileged scaffolds in medicinal chemistry.

Mechanism and kinetics of halogenated compound removal by metallic iron: Transport in solution, diffusion and reduction within corrosion films

A detailed kinetic model comprised of mass transport (k_tra), pore diffusion (k_dif), adsorption and reduction reaction (k_rea), was developed to quantitatively evaluate the effect of corrosion films on the removal rate (k_obs) of halogenated compounds by metallic iron. Different corrosion conditions were controlled by adjusting the iron aging time (0 or 1 yr) and dissolved oxygen concentration (0-7.09 mg/L DO). The k_obs values for bromate, mono-, di- and tri-chloroacetic acids (BrO₃^-, MCAA, DCAA and TCAA) were 0.41-7.06, 0-0.16, 0.01-0.53, 0.10-0.73 h^-1, with k_tra values at 13.32, 12.12, 11.04 and 10.20 h^-1, k_dif values at 0.42-5.82, 0.36-5.04, 0.30-4.50, 0.30-3.90 h^-1, and k_rea values at 14.94-421.18, 0-0.19, 0.01-1.30, 0.10-3.98 h^-1, respectively. The variation of k_obs value with reaction conditions depended on the reactant species, while those of k_tra, k_dif and k_rea values were irrelevant to the species. The effects of corrosion films on k_dif and k_rea values were responsible for the variation of k_obs value for halogenated compounds. For a mass-transfer-limited halogenated compound such as BrO₃^-, an often-neglected k_dif value primarily determined its k_obs value when pore diffusion was the rate-limiting step of its removal. In addition, the value of k_dif might influence product composition during a consecutive dechlorination, such as for TCAA and DCAA. For a reaction-controlled compound such as MCAA, an increased k_rea value was achieved under low oxic conditions, which was favorable to improve its k_obs value. The proposed model has a potential in predicting the removal rate of halogenated compounds by metallic iron under various conditions.

Organocatalyzed O-glycosylation of glycosyl trichloroacetimidates donors: l-prolinethioamide as brønsted acid catalyst

In this study, we present the utilization of l-proline-derived thioamide small organic molecules as an effective organocatalyst for the O-glycosylation of various glycosyl trichloroacetimidate donors, eliminating the need for any cocatalysts or additives. The catalytic process achieves high yields with a wide array of alcohol and sugar nucleophiles, demonstrating a broad substrate scope and operational simplicity under mild reaction conditions. Preliminary mechanistic investigations indicate that l-prolinethioamide facilitates the glycosylation reaction via Brønsted acid/base catalysis, involving the formation of a catalyst-acceptor adduct.

Trichloroacetyl chloride, CCl3COCl, as an alternative Cl atom precursor for laboratory use and determination of Cl atom rate coefficients for n-CH2[double bond, length as m-dash]CH(CH2)xCN (x = 3-4)

An investigation of CCl3COCl was conducted with the purpose of using the compound as an alternative Cl atom precursor in laboratory settings. CCl3COCl can be used with or without O2 as a source of Cl atoms and photolysis studies in air and N2 diluent displayed COCl2 and CO as being the major photolysis products. Relative rate studies were performed to determine the Cl atom rate coefficients for reaction with CH3Cl and C2H2 and the results were in agreement with literature values. Cl atom rate coefficients for reaction with n-CH2[double bond, length as m-dash]CH(CH2)3CN and n-CH2[double bond, length as m-dash]CH(CH2)4CN were determined as (2.95 ± 0.58) × 10-10 and (3.73 ± 0.60) × 10-10 cm3 molecule-1 s-1, respectively. CCl3COCl requires UV-C irradiation, so not all molecules are feasible for use in e.g. relative rate studies. Furthermore, it is recommended to perform experiments with O2 present, as this minimizes IR feature disturbance from product formation.