Reaction In D2O Research Articles

Detection and identification of 1-methylethyl and methyl radicals generated by irradiating tea tree (Melaleuca alternifolia) oil with visible light (436 nm) in the presence of flavin mononucleotide and ferrous ion

Here, we determined the electron spin resonance (ESR) spectra of standard reaction mixtures (I) containing 25 μM flavin mononucleotide (FMN), 0.018% tea tree (Melaleuca alternifolia) oil, 1.9 M acetonitrile, 20 mM phosphate buffer (pH 7.4), 0.1 M α-(4-pyridyl-1-oxide)-N-tert-butylnitrone (4-POBN), and 1.0 mM FeSO4(NH4)2SO4 irradiated with 436 nm visible light (7.8 J/cm2). Prominent ESR signals (αN = 1.58 mT and αHβ = 0.26 mT) were detected, suggesting that free radicals form in the standard reaction. In order to know whether singlet oxygen (1O2) is involved in the radical formation or not, ESR measurement was performed for the standard D2O reaction mixture (I) which contained 25 μM FMN, 0.0036% tea tree oil, 1.9 M acetonitrile-d3, 20 mM phosphate buffer (pH 7.4), 0.1 M 4-POBN and 1.0 mM FeSO4 in D2O. The ESR peak height of the standard D2O reaction increased to 169 ± 24% of the control. Thus, 1O2 seems to be involved in the formation of the radicals because D2O increases the lifetime of singlet oxygen. High-performance liquid chromatography-ESR-mass spectrometry analyses detected 1-methylethyl and methyl radicals in the standard reaction. The radicals appear to form through the reaction of ferrous ion with α-terpinene endoperoxide (ascaridole), which generated from the reaction of α-terpinene with 1O2. The 1-methylethyl and methyl radicals may exert a pro-oxidant effect under these conditions.

Role of Methanol Sacrificing Reagent in the Photocatalytic Evolution of Hydrogen

The contribution of methanol (CH3OH) sacrificing reagent to the photocatalytic evolution of H2 from aqueous solutions has been studied by tracing the reaction of D2O over a Cu/S-TiO2 catalyst under...

Reactions of d0 tungsten alkylidyne complexes with O2 or H2O. Formation of an oxo siloxy complex through unusual silyl migrations

(Me3SiCH2)3(Me3SiC≡)W←O=PMe3 (1), an adduct between (Me3SiCH2)3W≡CSiMe3 (2) and O=PMe3, reacts with O2 to give O=W(OSiMe3)(CH2SiMe3)3 (3) and CO2. Reaction of 2 with H2O yields 3 and the trimer [(μ-O)W(CH2SiMe3)2(=O)(THF)]3 (4). In the reaction of D2O with 2, 3-d(n) and methane isotopologues CH2D2, CHD3 and CD4 have been observed.

C–H Activation in Pyridoxal-5′-phosphate Schiff Bases: The Role of the Imine Nitrogen. A Combined Experimental and Computational Study

The origins of C-H activation in pyridoxal-5'-phosphate (PLP) Schiff bases and modulation of reaction specificity in PLP-enzymes are still not completely understood. There are no available studies that compare the reactivity of C4' carbons in ketimine Schiff bases with that of Cα carbons in their aldimine counterparts, which is essential to unravel the mechanisms that govern the evolution of their common carbanionic intermediates. Second-order rate constants for phosphate-catalyzed proton/deuterium exchange reactions in D(2)O of C4' carbons suffer a 10(5)-fold increase due to Schiff base formation (k(B) = 5.3 × 10(1) M(-1) s(-1)) according to NMR measurements. The C4' carbon acidity is also increased to pK(a) = 9.8, which is significantly higher than that of Cα in PLP-aldimines. DFT calculations reveal the role of each heteroatom in modulating the electrophilicity of C4' and Cα carbons. Specifically, the protonation state of pyridine nitrogen is the main factor in determining the absolute carbon acidity in aldimines (pK(a) of Cα varies from ∼14 to ∼23) and ketimines (pK(a) of C4' varies from ∼12 to ∼18), whereas the protonation state of both imine nitrogen and O3' phenol oxygen modulates the relative acidities of Cα and C4' from 1.5 to 7.5 pK(a) units. Our results provide an explanation to the modulation of reaction specificity observed in different PLP-enzymes based on the differences in the protonation state of the cofactor and H-bonding patterns in the active site.

Improved Catalytic Activity of Ruthenium–Arene Complexes in the Reduction of NAD+

A series of neutral Ru II half-sandwich complexes of the type ((η 6 -arene)Ru(N,N')Cl) where the arene is para-cymene (p-cym), hexamethylbenzene (hmb), biphenyl (bip), or benzene (bn) and N,Nis N-(2-aminoethyl)-4-(trifluoromethyl)benzenesulfonamide (TfEn), N-(2- aminoethyl)-4-toluenesulfonamide (TsEn), or N-(2-aminoethyl)- methylenesulfonamide (MsEn) were synthesized and characterized. X-ray crystal structures of ((p-cym)Ru(MsEn)Cl) (1), ((hmb)Ru(TsEn)Cl) (5), ((hmb)Ru(TfEn)Cl) (6), ((bip)Ru(MsEn)Cl) (7), and ((bip)Ru(TsEn)Cl) (8) have been determined. The complexes can regioselectively catalyze the transfer hydrogenation of NAD + to give 1,4-NADH in the presence of formate. The turnover frequencies (TOF) when the arene is varied decrease in the order bn > bip > p-cym > hmb for complexes with the same N,N' chelating ligand. The TOF decreased with variation in the N,Nchelating ligand in the order TfEn > TsEn > MsEn for a given arene. ((bn)Ru(TfEn)Cl) (12) was the most active, with a TOF of 10.4 h �1 . The effects of NAD + and formate concentration on the reaction rates were determined for ((p-cym)Ru(TsEn)Cl) (2). Isotope studies implicated the formation of ((arene)Ru(N,N')(H)) as the rate-limiting step. The coordination of formate and subsequent CO2 elimination to generate the hydride were modeled computationally by density functional theory (DFT). CO2 elimination occurs via a two-step process with the coordinated formate first twisting to present its hydrogen toward the metal center. The computed barriers for CO2 release for arene = benzene follow the order MsEn > TsEn > TfEn, and for the MsEn system the barrier followed bn < hmb, both consistent with the observed rates. The effect of methanol on transfer hydrogenation rates in aqueous solution was investigated. A study of pH dependence of the reaction in D2O gave the optimum pH* as 7.2 with a TOF of 1.58 h �1 for 2. The series of compounds reported here show an improvement in the catalytic activity by an order of magnitude compared to the ethylenediamine analogues.

Measurement of astrophysical S factors and electron screening potentials for d(d, n)3He reaction In ZrD2, TiD2, D2O, and CD2 targets in the ultralow energy region using plasma accelerators

The paper is devoted to study electron screening effect influence on the rate of d(d, n)3He reaction in the ultralow deuteron collision energy range in the deuterated polyethylene (CD2), frozen heavy water (D2O) and deuterated metals (ZrD2 and TiD2). The ZrD2 and TiD2 targets were fabricated via magnetron sputtering of titanium and zirconium in gas (deuterium) environment. The experiments have been carried out using high-current plasma pulsed accelerator with forming of inverse Z pinch (HCEIRAS, Russia) and pulsed Hall plasma accelerator (NPI at TPU, Russia). The detection of neutrons with energy of 2.5MeV from dd reaction was done with plastic scintillation spectrometers. As a result of the experiments the energy dependences of astrophysical S factor for the dd reaction in the deuteron collision energy range of 2–7 keV and the values of the electron screening potential Ue of interacting deuterons have been measured for the indicated above target: Ue(CD2) ⩽ 40 eV; Ue(D2O) ⩽ 26 eV; Ue(ZrD2) = 157 ± 43 eV; Ue(TiD2) = 125±34 eV. The value of astrophysical S factor, corresponding to the deuteron collision energy equal to zero, in the experiments with D2O target is found: Sb(0) = 58.6 ± 3.6 keV b. The paper compares our results with other available published experimental and calculated data.

A highly uniform lamination micromixer with wedge shaped inlet channels for time resolved infrared spectroscopy

We present a horizontal multi-lamination micromixer with specially wedge shaped vertical fluid inlets for fast and highly uniform fluid mixing in the low millisecond range. The four-layer laminar flow is created by a fluidic distribution network, reducing the amount of fluid connectors to the macroscopic world to two. All the geometries of the channel inlets and the distribution network were optimized for low flow rates and hence for low sample consumption using CFD simulations. The device materials applied feature low absorption in the mid-infrared (wavelength 3--10 μm) allowing to use this device for time resolved infrared spectroscopy. The micromixer itself can be built by silicon micromachining techniques without the need of complicated fabrication steps. Due to a transparent calcium fluoride cover optical measurements are possible as well which were used to characterize the device. Mixing times in the range of 1 ms with optical color measurements of aqueous solutions and with time resolved infrared measurement of the proton exchange reaction of H2O and D2O are achieved.

Unusual products observed in gas-phase WxOy−+H2O and D2O reactions

Addition of H(2)O and D(2)O to small tungsten suboxide cluster anions W(x)O(y)(-) (x = 1-4; y < or = 3x) was studied using mass spectrometric measurements from a high-pressure fast flow reactor. Within the WO(y)(-) mass manifold, which also includes WO(4)H(-), product masses correspond to the addition of one to three H(2)O or D(2)O molecules. Within the W(2)O(y)(-) cluster series, product distributions suggest that sequential oxidation W(2)O(y)(-) + H(2)O/D(2)O --> W(2)O(y+1)(-) + H(2)/D(2) occurs for y < 5, while for W(2)O(5)(-), W(2)O(6)H(2)(-)/W(2)O(6)D(2)(-) is primarily produced. W(2)O(6)(-) does not appear reactive. For the W(3)O(y)(-) cluster series, sequential oxidation with H(2) and D(2) production occurs for y < 6, while W(3)O(6)(-) and W(3)O(7)(-) produce W(3)O(7)H(2)(-)/W(3)O(7)D(2)(-) and W(3)O(8)H(2)(-)/W(3)O(8)D(2)(-), respectively. Lower mass resolution in the W(4)O(y)(-) mass range prevents definitive product assignments, but intensity patterns suggest that sequential oxidation with H(2)/D(2) evolution occurs for y < 6, while W(4)O(y+1)H(2)(-)/W(4)O(y+1)D(2)(-) products result from addition to W(4)O(6)(-) and W(4)O(7)(-). Based on bond energy arguments, the H(2)/D(2) loss reaction is energetically favored if the new O-W(x)O(y)(-) bond energy is greater than 5.1 eV. The relative magnitude of the rate constants for sequential oxidation and H(2)O/D(2)O addition for the x = 2 series was determined. There are no discernable differences in rate constants for reactions with H(2)O or D(2)O, suggesting that the H(2) and D(2) loss from the lower-oxide/hydroxide intermediates is very fast relative to the addition of H(2)O or D(2)O.

Acceleration of the Substrate Cα Deprotonation by an Analogue of the Second Substrate Palmitoyl-CoA in Serine Palmitoyltransferase

Serine palmitoyltransferase (SPT) is a key enzyme of sphingolipid biosynthesis and catalyzes the pyridoxal 5'-phosphate (PLP)-dependent decarboxylative condensation reaction of l-serine with palmitoyl-CoA to generate 3-ketodihydrosphingosine. The binding of l-serine alone to SPT leads to the formation of the external aldimine but does not produce a detectable amount of the quinonoid intermediate. However, the further addition of S-(2-oxoheptadecyl)-CoA, a nonreactive analogue of palmitoyl-CoA, caused the apparent accumulation of the quinonoid. NMR studies showed that the hydrogen-deuterium exchange at Calpha of l-serine is very slow in the SPT-l-serine external aldimine complex, but the rate is 100-fold increased by the addition of S-(2-oxoheptadecyl)-CoA, showing a remarkable substrate synergism in SPT. In addition, the observation that the nonreactive palmitoyl-CoA facilitated alpha-deprotonation indicates that the alpha-deprotonation takes place before the Claisen-type C-C bond formation, which is consistent with the accepted mechanism of the alpha-oxamine synthase subfamily enzymes. Structural modeling of both the SPT-l-serine external aldimine complex and SPT-l-serine-palmitoyl-CoA ternary complex suggests a mechanism in which the binding of palmitoyl-CoA to SPT induced a conformation change in the PLP-l-serine external aldimine so that the Calpha-H bond of l-serine becomes perpendicular to the plane of the PLP-pyridine ring and is favorable for the alpha-deprotonation. The model also proposed that the two alternative hydrogen bonding interactions of His(159) with l-serine and palmitoyl-CoA play an important role in the conformational change of the external aldimine. This is the unique mechanism of SPT that prevents the formation of the reactive intermediate before the binding of the second substrate.

Chemistry and Stereochemistry of the Interaction of the Water-Soluble Phosphine [HO(CH2)3]3P with Cinnamaldehyde in Aqueous Media

To learn more about the bleaching action of pulps by (hydroxymethyl)phosphines, cinnamaldehyde was reacted with tris(3-hydroxypropyl)phosphine, [HO(CH2)3]3P (THPP), in aqueous solution at room temperature under argon. Self-condensation of the aldehyde into two isomeric products, 2-benzyl-5-phenyl-pent-2,4-dienal and 5-phenyl-2-(phenylmethylene)-4-pentenal, is observed; this implies initial nucleophilic attack of the phosphine at the beta-carbon of the alpha,beta-unsaturated aldehyde. Reaction in D2O gives the same products in which all but the phenyl and CHO protons are replaced by deuterons. NMR studies are consistent with carbanion formation and subsequent condensation of two phosphonium-containing aldehyde moieties to generate the products with concomitant elimination of phosphine oxide. In D2O in the presence of HCl, THPP reversibly attacks the aldehyde-C atom to form the (alpha-hydroxy)phosphonium derivative [PhCH=C(H)CH(OD)PR3]Cl (where R=(CH2)3OD), which slowly converts into the deuterated bisphosphonium salt [R3PCH(Ph)CD(H)CH(OD)PR3]Cl2 via the deuterated monophosphonium salt [R3PCH(Ph)CD(H)CHO]Cl. The phosphonium intermediates and phosphonium products in this chemistry, although having up to three chiral carbon centers, are formed with high stereoselectivity just in enantiomeric forms. In acetone-H2O (1:1 v/v), a cross-condensation of cinnamaldehyde with acetone to give 6-phenyl-3,5-hexadien-2-one is promoted by THPP via generation of OH-.

Solvent Isotope Effects in Reactions of Human Medium-Chain Acyl-CoA Dehydrogenase Active Site Mutants

Glu376, the base involved in substrate alphaH+ abstraction at the active center of medium-chain acyl-CoA dehydrogenase (MCAD), has been mutated to Gln and Gly. The mutants are active; however, their rates of dehydrogenation are lowered by approximately 5 orders of magnitude. Binding of the substrate octanoyl-CoA to Glu376Gln-MCAD involves (at least) two steps. The ensuing dehydrogenation reaction that corresponds to reduction of the flavin cofactor also occurs in two phases. These are interpreted to consist of a first, reversible step, followed by a slower, practically irreversible one. For Glu376Gln-MCAD, the log of the rates of dehydrogenation increases linearly with pH (slope = 1) in the pH range of 6-10, suggesting HO- as a reactant. The rates of the same reactions in D2O have the same pD profile and reflect a solvent kinetic isotope effect (SKIE) of approximately 8.5. Glu376Gln+Glu99Gly-MCAD (studied to assess the role of Glu99 also present at the bottom of the active center cavity) has activities and activity profiles similar to those of Glu376Gln-MCAD. This excludes Glu99 as the active center base for Glu376Gln-MCAD catalysis. Proton inventories for the two phases of the dehydrogenation reaction were investigated at 4 and 25 degrees C. The inventories at 25 degrees C reflect a SKIE of approximately 4.5; the profiles are "bowl-shaped", in which a transition-state contribution predominates. The profiles for the 4 degrees C reaction are very unusual. That for the first phase can be analyzed on a two-step model with one step (80% rate-limiting) having a conformational reorganization with an isotope effect of 90-100, from small isotope effects at many protein sites, and the other step (20% rate-limiting) having an inverse isotope effect of ca. 2, characteristic of the reaction of hydroxide ion as a base. For the second phase, only a contribution from many protein sites with a KIE of approximately 4.5 is observed. The results are compatible with a very rigid active site framework that must undergo rearrangements for dehydrogenation to take place, and specifically to allow access of HO-, the reactant that must neutralize the H+ abstracted from the alphaC-H substrate. The large isotope effects are attributed to the changes in state of several H-bonds that occur during the process.

Reactive Quenching of OH A 2Σ+ in Collisions with Molecular Deuterium via Nonadiabatic Passage through a Conical Intersection

The D and H atom products from collisional quenching of OH A 2Σ+ (v = 0) by D2 have been examined through Doppler spectroscopy using two-photon (2 2S ← ← 1 2S) laser-induced fluorescence. A bimodal Doppler profile is observed for the D atoms, indicating that two different velocity distributions result from the OH A 2Σ+ + D2 → D + HOD reaction. Nearly 40% of the products are H atoms produced in the OH A 2Σ+ + D2 → H + D2O reaction with a single Gaussian profile. The two components of the D atom kinetic energy distribution are characterized by translational temperatures of approximately 1200 and 10 000 K and on average account for 4% and 30% of the available energy. The H atom products accommodate about 37% of the available energy and are described by a 13 000 K temperature. The translational energy distributions of the H/D atom products are attributed to two dynamical pathways through the strong nonadiabatic coupling region at the HO−D2 conical intersection. The narrow “cold” distribution of D atoms arises from an abstraction reaction in a direct passage through the conical intersection region. The broad statistical distribution observed for both D and H atom products suggests that the HO−D2 collision pair lives long enough on the excited-state surface for energy to randomize before evolving through the conical intersection that leads to products.

First-principles theory for the H + H2O, D2O reactions.

A full quantum dynamical study of the reactions of a hydrogen atom with water, on an accurate ab initio potential energy surface, is reported. The theoretical results are compared with available experimental data for the exchange and abstraction reactions in H + D2O and H + H2O. Clear agreement between theory and experiment is revealed for available thermal rate coefficients and the effects of vibrational excitation of the reactants. The excellent agreement between experiment and theory on integral cross sections for the exchange reaction is unprecedented beyond atom-diatom reactions. However, the experimental cross sections for abstraction are larger than the theoretical values by more than a factor of 10. Further experiments are required to resolve this.

Paraoxon and parathion hydrolysis by aqueous molybdenocene dichloride (Cp2MoCl2): first reported pesticide hydrolysis by an organometallic complex.

We report the first case of an organometallic complex that effectively hydrolyzes the organophosphate pesticides parathion and paraoxon. The complex is the water-soluble compound bis(eta 5-cyclopentadienyl)molybdenum(IV) dichloride (1), which hydrolyzes parathion to produce ethanol and deethyl parathion in a biphasic reaction in D2O. Rate accelerations were 130 and 10(5) at pH 7 and 3, respectively. Paraoxon is readily hydrolyzed by 1 to yield p-nitrophenol and diethyl phosphate with rate accelerations of 2300 and 27 at pH 7 and 3, respectively. Kinetic data for paraoxon hydrolysis by 1 are consistent with a process that involves intermolecular (delta S++ = -49 +/- 10 eu) hydroxide attack on the phosphate triester in which the aquated 1 serves as a coordinated Lewis acid that activates the organophosphate. Interestingly parathion hydrolysis by 1 occurs via nucleophilic attack at the alpha-carbon of the phosphorothioate pesticide that involves C-O bond cleavage. These parathion results represent one of the few cases of this type of unusual hydrolytic chemistry and the first case of an organometallic complex that accelerates organophosphate pesticide hydrolysis.

Temperature Dependence and Kinetics of the Scrambling Reaction of H2O and D2O Mixture Determined by Microscopic ATR/FT-IR/DSC System

In order to investigate the thermodynamics of the scrambling reaction of H2O and D2O mixture, the activation energy associated with the rate of HOD formation in the H2O-D2O reaction at lower or higher temperature under gentle mixing was studied. A microscopic attenuated total reflection (ATR)/Fourier transform infrared (FT-IR) spectroscopy, combined with differential scanning calorimetry (DSC), was used to investigate this scrambling reaction of H2O and D2O. The result indicates that the HOD formation may be supposed to be one dimer of H2O reacting with one trimer of D2O. A biphasic Arrhenius plot with an inflection point at about 11°C was obtained. The activation energy of HOD formation was 2.83 kcal/mole above 11°C, which was consistent with the consecutive hydrogen-bond disruption model. But, in the range of 4-11°C, its activation energy of HOD formation was 21.98 kcal/mole, which was contrary to the consecutive hydrogen-bond disruption model. The decreased deformation of stronger cluster structure and the special properties of D2O at lower temperature might be responsible for the higher activation energy. The inflection temperature at 11°C was critical to change the density and length scale of hydrogen bond of D2O. This study suggests that the HOD formation may be easily used as a probe for thermodynamic explanation of H2O-D2O reaction by using a newly developed microscopic ATR/FT-IR/DSC system.

Kinetic Solvent Isotope Effect: A Simple, Multipurpose Physical Chemistry Experiment

The spontaneous hydrolysis of acetic anhydride in H2O and D2O is a convenient undergraduate physical chemistry experiment that is used to teach practical kinetics, and to demonstrate the kinetic solvent isotope effect. The reaction is monitored by UV-Vis spectroscopy (disappearance of acetic anhydride) by employing a new approach, namely, by measuring the absorbance difference between cuvettes containing the reaction in H2O (reference beam) and D2O (sample beam) in a double-beam spectrophotometer. This technique allows determination of rate constants in both solvents, kH2O and kD2O, respectively, from a single kinetic run by using commercial curve fitting programs. Advantages of the differential absorbance method are instrument time saving, and introduction of the students to the application of curve fitting. To test the quality of the calculated rate constants, the students determine kH2O by conductance measurement, and compare results of both methods. The use of two experiments to study the reaction illustrates the variety of experimental techniques that can be employed for rate measurements.

Identification of enzyme-substrate and enzyme-product complexes in the catalytic mechanism of glucoamylase from Aspergillus awamori.

Intermediates in the catalytic mechanism of Aspergillus awamori glucoamylase (GA) were identified by studying pre-steady-state and steady-state kinetics of the wild-type GA/maltose and Trp120 -->Phe GA/maltotriose reactions in H2O and D2O. Pre-steady-state fluorescence signal analysis was carried out to ascertain the relative intrinsic fluorescence of the enzyme intermediates. A three-step minimal pathway for oligosaccharide hydrolysis represented by E + Gx (k1) reversible (k-1) EGX (k2)reversible(k-2) EP (kcat)--> E + P is proposed. The first step, represented by the association constant K1 (k1/k-1), depicts the fast formation of enzyme-substrate complex and is the primary factor in fluorescence quenching. A 2.7-fold increase in K1 with D2O as solvent is observed with both enzymes due to the cumulative effect of deuterium on complex hydrogen bonding at the active site. The second step further quenches the enzyme fluorescence and is identified as the hydrolytic step, forming an enzyme-product complex. Both k2 and k-2 values show similar 2-fold decreases in D2O for both enzymes, consistent with the microscopic reversibility of the hydrolytic reaction. The solvent isotopic effect on the hydrolytic step is likely due to either abstraction of an exchangeable proton from the general acid Glu179 or directed addition of water to the oxocarbonium ion intermediate by the general base Glu400. No significant isotope effect was observed on the steady-state kcat value for wild-type GA with maltose, indicating a ronhydrolytic step as rate-limiting. The third step, a posthydrolytic rate-determining step, is the product release as evident from steady-state kinetics with wild-type and Trp120-->Phe GAs using alpha-D-glucosyl fluoride.

Synthesis of cyclophosphamide‐4,4,5,5‐d4

Abstract3‐Hydroxypropionitrile was subjected to a base‐catalyzed exchange reaction in D2O which provided 2,2‐dideuterio‐3‐deuteroxypropionitrile (DOCH2CD2CN) in 70% yield. Reduction of the nitrile with LiAlD4 gave 3‐amino‐2,2,3,3‐tetradeuteriopropan‐1‐o1 (HOCH2CD2CD2NH2) in a crude yield of 71%. Reaction of this intermediate with N,N‐bis(2‐chloroethyl)phosphoramidic dichloride [Cl2P(O)N(CH2CH2Cl)2] followed by the combination of those chromatography fractions which contained only pure material gave cyclophosphamide‐4,4,5,5‐d4 as a white oil in 13% yield. A portion of this oil was converted to the monohydrate by the addition of water (1.1 equivalents) and crystallization from ether/petroleum ether (62% yield). For the hydrate, MS analyses gave an average mole percent enrichment (with average deviation over 5 determinations) of 89.1 ± 0.5% d4.

The mechanism of hydrolysis of 2-hydroxyethanesulfonyl chloride: the intermediacy of 1,2-oxathietane 2,2-dioxide (β-sultone)

The hydrolysis of 2-hydroxyethanesulfonyl chloride (1) has been investigated with the aid of kinetic and product analysis studies. The results are quantitatively consistent with the mechanism of hydrolysis shown in Scheme 1, the chief features of which are (a) formation of β-sultone (2) and its rapid further reaction (the major pathway), together with (b) a minor direct hydrolysis route. The kinetics of both the β β-sultone formation and the direct hydrolysis shows two terms, one first order in 1 alone, and the other first order in hydroxide as well; the rates of the first- and second-order reactions are lowered by added sodium chloride. It is suggested (a) that the unimolecular β-sultone formation involves 1 in a complex with water (as in 9) and that the water acts as a general base in the cyclization to 2, and (b) the hydroxide-promoted reaction proceeds by cyclization of the conjugate base of 1 (i.e., 10). The unimolecular direct hydrolysis is regarded as a conventional hydrolysis of a sulfonyl chloride with attack of the water with general base assistance from a second water molecule. The hydroxide-promoted direct reaction in D2O leads to no uptake of deuterium, showing that the reaction does not go by way of the sulfene, and a reaction by way of a six-membered cyclic transition state is tentatively proposed. Evidence is presented that the chloride ion rate suppression is not primarily due to reaction of β-sultone with Cl− to give back 1; the possible origins of the effect are discussed. Keywords: sulfonyl chlorides, 2-hydroxyethanesulfonyl chloride, β-sultone, kinetics of sulfonyl chloride hydrolysis, mechanisms of sulfonyl chloride hydrolysis.

ChemInform Abstract: X‐Ray Photoelectron Study of the Reaction of O2, NO, N2O, and D2O with Gadolinium.

AbstractAt 300 K, O2, NO, N2O, and D2O are found to adsorb dissociatively on a polycrystalline gadolinium foil.