Demetallation of α, β, γ, δ-tetra(p-sulfophenyl)porphineiron(III) in sulfuric acid-ethanol-water media

The rate of demetallation of α, β, γ,δ-tetra(p-sulfophenyl)porphineiron (III), Fe(TPPS)^3-, was determined in sulfuric acid-ethanol-water media for 8.5-10.65M sulfuric acid at different temperatures. The overall reaction was the conversion of the complex Fe(TPPS)^3- into the diacid species H₄TPPS^2- without other spectrophotometrically important species being formed to an appreciable extent, as shown by three isosbestic points at 418, 462, and 563 nm. The rate was first order in the Fe(TPPS)^3- concentration. The pseudo-first-order rate constants k were exponentially dependent on the sulfuric acid concentration, and log k was linearly dependent on the Hammett acidity function –H₀. The average ΔH? and ΔS? values for five reaction media were 18.4 ± 1.4 kcal/mol and 19 ± 3 cal/°K · mol, respectively. The linear relationship between log k and (-H₀) and the approximately constant values of ΔH? ΔS? over the acid range investigated indicated that the same mechanism of demetallation was operative over this acid range. Because of the dependence of the pseudo-first-order rate constants on the acidity of the medium, the mechanism probably involves the addition of protons to pyrrole N atoms to assist in the breaking of iron (III)-nitrogen bonds.     

K21–δNa2+δIn39 (δ = 2.8): A Cluster-Replacement Clathrate-II Structure with an Alkali Metal M136-Network

K_21–δNa_2+δIn₃₉ with δ = 2.82 was synthesized (melted at 973 K, annealed at 623 K) from the elements in sealed niobium ampoules. The compound forms prismatic crystals with silver metallic lustre and is unstable in air and moisture. The crystal structure of K_21–δNa_2+δIn₃₉ (orthorhombic; space group Pnma, No. 62; a = 17.844(5) Å, b = 17.192(3) Å, c = 25.078(7) Å; Z = 4; Pearson code oP248; δ = 2.82, obtained from the structure refinement) contains eight empty In icosahedra of two types, A (12 exo-bonds) and B (7 exobonds), and four open In₁₅ clusters (15 exo-bonds). The latter are centered by K atoms and belong to C units, which are defined as [K(Na₂M₃In₁₅)] heteroatomic clusters (M = K + Na). The spatial distribution of the In icosahedra A, B and heteroatomic clusters C is that of the atoms in the cubic Laves phase MgCu₂: MgCu₂ ? [K(Na₂M₃In₁₅)][In]₂. All the In_n clusters are interconnected by exo-bonds forming a covalent three-dimensional framework (d(In? In) = 2.832 to 3.301 Å). The remaining alkali metal atoms build up a three-dimensional M₁₃₆ network of the clathrate-II type with (16 + 8) cages, which envelopes the In icosahedra and [K(Na₂M₃In₁₅)] clusters. This structure can be described as a cluster-replacement derivative of the clathrate-II structure: (H₂S)₁₆(CCl₄)₈ · (H₂O)₁₃₆ ? [In]₁₆[K(M₅In₁₅)]₈M₁₃₆, and is one member of a novel hierarchical structure family, based upon cluster-replacement. The bonding as well as the structural relationships to other phases are discussed.     

Ligand Dynamics in the Solid: Lithium‐fluorenide and Lithium‐benzo[b]fluorenide N,N,N′,N′‐Tetramethylethylenediamine (tmeda) Complexes

The dynamic behavior of the N,N,N′,N′‐tetramethylethylenediamine (tmeda) ligand has been studied in solid lithium‐fluorenide(tmeda) ( 3 ) and lithium‐benzo[b]fluorenide(tmeda) ( 4 ) using CP/MAS solid‐state ¹³C‐ and ¹⁵N‐NMR spectroscopy. It is shown that, in the ground state, the tmeda ligand is oriented parallel to the long molecular axis of the fluorenide and benzo[b]fluorenide systems. At low temperature (<250 K), the ¹³C‐NMR spectrum exhibits two MeN signals. A dynamic process, assigned to a 180° rotation of the five‐membered metallacycle (π‐flip), leads at elevated temperatures to coalescence of these signals. Line‐shape calculations yield ΔH^?=42.7 kJ mol^?1, ΔS^?=?5.3 J mol^?1 K^?1, and =44.3 kJ mol^?1 for 3 , and ΔH^?=36.8 kJ mol^?1, ΔS^?=?17.7 J mol^?1 K^?1, and =42.1 kJ mol^?1 for 4 , respectively. A second dynamic process, assigned to ring inversion of the tmeda ligand, was detected from the temperature dependence of T_1ρ, the ¹³C spin‐lattice relaxation time in the rotating frame, and led to ΔH^?=24.8 kJ mol^?1, ΔS^?=?49.2 J mol^?1 K^?1, and =39.5 kJ mol^?1 for 3 , and ΔH^?=18.2 kJ mol^?1, ΔS^?=?65.3 J mol^?1 K^?1, and =37.7 kJ mol^?1 for 4 , respectively. For (D₁₂)‐ 3 , the rotation of the CD₃ groups has also been studied, and a barrier E_a of 14.1 kJ mol^?1 was found.     

Collision-induced emission of O2(b1Σ → a1Δg) in the gas phase

In flow tube studies of the quenching of O₂(b¹Σ), broad band emission of O₂(b):M collision complexes was found to appear under the discrete rotational lines of the 0–0 band of the b¹Σ → a¹Δ_g electric quadrupole transition at higher oxygen pressures and on addition of foreign gases. Bimolecular rate constants for the collision-induced emission processes have been derived from the ratio of the intensities of the discrete lines and the continuum as well as from low-resolution measurements of the relative intensities of the b → a and b → X bands as a function of O₂ and added gas pressure. They range from ≈10^?21 cm³ s^?1 for He to ≈4 × 10^?19 cm³ s^?1 for PCl₃ vapor.     

Low temperature 13C NMR study of 1-(3-pentyloxyphenylcarbamoyloxy)-2-dialkyl- aminocyclohexanes

Cyclohexane and piperidine ring reversal in 1-(3-pentyloxyphenylcarbamoyloxy)-2-dialkylaminocyclohexanes was investigated by ¹³C NMR. An unusually low conformational energy ΔG = 0.59 kJ mol^?1 and activation parameters ΔG^≠₂₁₈ = 43.8 ± 0.4 kJ mol^?1, ΔH^≠ = 48.9 ± 2.5 kJ mol^?1 and ΔS^≠ = 23 ± 9 J mol^?1 K^?1 were found for the diequatorial to diaxial transition of the cyclohexane ring in the trans-pyrrolidinyl derivative. In the trans-piperidinyl derivative, ΔG₂₂₂ = 44.7 ± 0.5 KJ mol^?1, ΔH^≠ = 55.7 ± 6.3 kJ mol^?1 and ΔS^≠ = 51 ± 21 J mol^?1 K^?1 was found for the piperidine ring reversal from the non-equivalence of the α-carbons.     

The Crystal and Molecular Structure of 3-Oxo-17β-acetoxy-Δ4-14α-methyl-8α, 9β, 10α, 13α-estrene

The crystal and molecular structure of 3-oxo-17β-acetoxy-Δ⁴-14α-methyl-8α, 9β, 10α, 13α-estrene, C₂₁H₃₀O₃, has been determined by X-ray diffraction analysis. The crystals belong to the orthorhombic space group P2₁2₁2₁, with the cell dimensions a = 12.093 Å, b = 19.667 Å, c = 7.746 Å; Z = 4. Intensity data were collected at room temperature with an automatic four-circle diffractometer. The structure was solved by direct methods and the parameters were refined by least-squares analysis. All the hydrogen atoms were included in the refinement. The final R value was 0.038 for 1413 observed reflections. The conformation of ring A is intermediate between a half-chair and a 1, 2-diplanar form. The hydrogens at C(9) and C(10) are anti, the B/C ring junction is trans, and rings B and C adopt chair conformations. Ring D is cis fused and is halfway between C₂ and C_s forms.     

Chiral photochromic 2-(N-acyl-N-arylaminomethylene)benzo[b]thiophen-3(2H)-ones

Photochromic 2-(N-acyl-N-arylaminomethylene)benzo[b]thiophen-3(2H)-ones containing ortho-substituents in the N-phenyl ring were studied by X-ray diffraction analysis and ¹H NMR spectroscopy. It was established that these compounds have stable chiral structures due to hindered rotation of the phenyl ring around the C—N bond. The energy barrier to racemization evaluated by dynamic NMR spectroscopy is G ^# _{428 K} = 98 kJ mol^–1.     

Reactions of [NiIII(cyclam)] with aqueous sulfur dioxide: Exhibition of a deuterium isotope effect and catalysis by chloride and bromide

One unit of S(IV) (SO₂ or SHO₃^?) is oxidized per 2 units of [Ni^III(cyclam)] species to obtain sulfate. Kinetic analyses have been done by varying the acidities (0.013 ? [H⁺] ? 1.0 M) and halide concentrations (0.000 ? [X^?] ? 0.012 M; X=Cl and Br) at constant ionic strength (μ = 1.0 M). The rate law that incorporates the [X^?] and [H⁺] dependence is ?d[Ni^III]_T/dt=2k[Ni^III]_T[S(IV)]_T where 2k={k_a[H⁺] + k_bK + kK′_X[H⁺] [X^?] + kK′_XK[X^?]} {[H⁺] + K}^?1 {1 + K′_X[X^?]}^?1, here k_a=87 ± 7 M^?1 s^?1, k_b=(2.5 ± 0.5)×10³ M^?1 s^?1 and pK = 1.8 ± 0.2. Rate constants k_a and k_b are attributed to the reactions of [Ni^III(cyclam) (H₂O)₂]³⁺ with SO₂ and SHO₃^?, respectively. Monohalo species apparent equilibrium constants K′_Cl=(1600 ± 400) M^?1 and K′_Br=(190 ± 20) M^?1 and rate constants k=80 ± 8 M^?1 s^?1 and k = 140 ± 15 M^?1 s^?1 are ascribed to the protonated pathway, involving the [Ni^III(cyclam) (H₂O)X]²⁺ and SO_2(aq) reaction pairs. The other two rate constants of k=(5 ± 1)×10³ M^?1 s^?1 and k=(3.1 ± 0.5)×10⁴ M^?1 s^?1, refer to the deprotonated pathway and are assigned to the [Ni^III(cyclam) (H₂O)X]²⁺ /SHO₃^? redox couple. A deuterium H₂O / D₂O isotope effect of 2.1–2.8 can be attributed partially to an equilibrium isotope effect at low acidity though a small kinetic isotope (2.5 ± 0.5) effect is evident for the dihydrogen sulfito pathway, k_a. The kinetic isotope effect and the absence of sulfite radical scavenging effects are explained by a mechanism entailing migration of a hydride from sulfur to the Ni^III center to produce a Ni^III—H species, which rapidly comproportionates, and S(VI). © 1993 John Wiley & Sons, Inc.     

Synthese von diastereo- und enantio-selektiv deuterierten β,ε-, β,β-, β,γ- und γ,γ-Carotinen

Synthesis of Diastereo- and Enantioselectively Deuterated β,ε-, β,β-, β,γ- and γ,γ-Carotenes We describe the synthesis of (1′R, 6′S)-[16′, 16′, 16′-²H₃]-β, εcarotene, (1R, 1′R)-[16, 16, 16, 16′, 16′, 16′-²H₆]-β, β-carotene, (1′R, 6′S)-[16′, 16′, 16′-²H₃]-γ, γ-carotene and (1R, 1′R, 6S, 6′S)-[16, 16, 16, 16′, 16′, 16′-²H₆]-γ, γ-carotene by a multistep degradation of (4R, 5S, 10S)-[18, 18, 18-²H₃]-didehydroabietane to optically active deuterated β-, ε- and γ-C₁₁-endgroups and subsequent building up according to schemes \documentclass{article}\pagestyle{empty}\begin{document}${\rm C}_{11} \to {\rm C}_{14}^{C_{\mathop {26}\limits_ \to }} \to {\rm C}_{40} $\end{document} and C₁₁ → C₁₄; C₁₄+C₁₂+C₁₄→C₄₀. NMR.- and chiroptical data allow the identification of the geminal methyl groups in all these compounds. The optical activity of all-(E)-[²H₆]-β,β-carotene, which is solely due to the isotopically different substituent not directly attached to the chiral centres, is demonstrated by a significant CD.-effect at low temperature. Therefore, if an enzymatic cyclization of [17, 17, 17, 17′, 17′, 17′-²H₆]lycopine can be achieved, the steric course of the cyclization step would be derivable from NMR.- and CD.-spectra with very small samples of the isolated cyclic carotenes. A general scheme for the possible course of the cyclization steps is presented.     

Yields of O2(b1Σ) from reactions of HO2

A discharge-flow apparatus with resonance fluorescence and chemiluminescence detection has been used to monitor O₂(b ¹σ) production from several reactions of the HO₂ radical at 300 K and 1-torr total pressure. O₂(b), HO₂, and OH were observed when F atoms were added to H₂O₂ in the gas phase. Signal strengths of O₂(b) were proportional to initial concentrations of H₂O₂ and HO₂. These observations were analyzed by using a simple three step mechanism and a more complete computer simulation with 22 reaction steps. The results indicate that the F + HO₂ reaction yields O₂(b) with an efficiency of (3.6 ± 1.4) × 10^?3. By monitoring [O₂(b)] and [HO₂] upon addition of an excess second reactant to HO₂, O₂(b) yields from the reactions of HO₂ with O, Cl, D, H, and OH were found to be <1 × 10^?2, <5 × 10^?4, <2 × 10^?3, <8 × 10^?3, and <1 × 10^?3, respectively. Yields of O₂(b) from the HO₂ ± HO₂ reaction were found to be less than 3 × 10^?2.     

(M)‐ and (P)‐8‐[(1S,2R)‐2‐hydroxy‐1‐methyl‐2‐phenylethyl]‐8‐methyl‐8,9‐dihydro‐7H‐dinaphth[2,1‐c:1′,2′‐e]azepinium bromide solvates

The title compounds are diastereoisomers with antipodean axial chirality. The M isomer crystallizes as a (1/3) acetone solvate, C₃₂H₃₀NO⁺·Br^?·3C₃H₆O, while the P isomer crystallizes as a (1/1) di­chloro­methane solvate, C₃₂H₃₀NO⁺·Br^?·CH₂Cl₂. In each structure, O—H?Br hydrogen bonds link the cations and anions to give ion pairs. The seven‐membered azepinium ring adopts the usual twisted‐boat conformation and its ring strain causes a slight curvature of the plane of each naphthyl ring.     

Studies in nickel(IV) chemistry. Kinetics of electron transfer from dimethyl sulfoxide to oxohydroxonickel(IV) in aqueous acid medium

The kinetics of decomposition of “oxohydroxonickel(IV)” [Ni(IV)] with concomitant intramolecular electron transfer to produce hexaaquanickel(II) and dioxygen in aqueous acid solutions show pseudo-first-order dissappearance of the Ni(IV). The pseudo-first-order rate constants for the acid decomposition (k_ad) satisfy where K_MH and k_d refer to the equilibrium protonation constant and the decomposition constant of the protonated species of the Ni(IV) respectively. The values of K_MH and k_d in aqueous medium at 45°C and μ = 2.0M are 25.5 ± 1M^?1 and (1.7 ± 0.1) × 10^?5 s^?1, respectively. The kinetics of the intermolecular electron transfer from dimethyl sulfoxide (DMSO) to the Ni(IV), producing Ni(H₂O)₆²⁺ and dimethyl sulfone as products, have been investigated by monitoring the formation of Ni(H₂O)₆²⁺. The pseudo-first-order rate constants for the electron transfer k_obs are linearly dependent on [DMSO]₀ or [H⁺], attaining limiting values at higher relative [DMSO]₀ or [H⁺], in accordance with where K_1c and K_2c represent the formation constants of the precursors involving DMSO and the unprotonated and one-protonated Ni(IV) species, respectively, and k_1x and k_2x are the corresponding decomposition rate constants of the precursors. The values of K_2c and k_2x are (2.3 ± 0.1) × 10⁴M^?1 and 19 ± 1 s^?1, respectively, at 45°C and μ = 1.0M. Results are interpreted in terms of probable mechanisms involving (1) a rate-determining decomposition of the protonated Ni(IV) followed by rapid product formation steps, and (2) precursor complex formation between DMSO and the unprotonated or the protonated species of the Ni(IV) followed by rate-determining decomposition with electron transfer.     

EPR-Einkristalluntersuchungen System Fe(NO)(Et2dsc)2/In(Et2dsc)3 (Et2dsc = Diethyldiselenocarbamat). Kristall- und Molekülstruktur von Tris(diethyldiselenocarbamato)indium(III), In(Et2dsc)3

Single Crystal Electron Paramagnetic Resonance Study on the System Fe(NO)(Et₂dsc)₂/In(Et₂dsc)₃ (Et₂dsc = diethyldiselenocarbamate). Crystal and Molecular Structure of Tris(diethyldiselenocarbamato)indium(III), In^III(Et₂dsc)₃ A single-crystal EPR study (T = 295 K) of Bis(diethyldiselenocarbamato)nitrosyliron(I) incorporated in Tris(diethyldiselenocarbamato)indium(III) is reported. The tensors g an A^N have rhombic symmetry with g₁ = 2.048, g₂ = 2.058, g₃ = 2.062 and A = 9.2 · 10^?4 cm^?1, A = 10.0 · 10^?4 cm^?1, A = 11.3 · 10^?4 cm^?1. The A values are discussed in terms of spin density distribution. The x-ray crystallographic data of In^III(Et₂dsc)₃ (space group P2₁/c, a = 6.731(3) Å, b = 18.05(9) Å, c = 20.914(10) Å, α = 90.02(2)°, β = 93.74(2)° and γ = 90.01(2)°) are given.     

Well‐defined polyolefin/poly(ε‐caprolactone) diblock copolymers: New synthetic strategy and application

A new synthetic strategy, the combination of living polymerization of ylides and ring‐opening polymerization (ROP), was successfully used to obtain well‐defined polymethylene‐b‐poly(ε‐caprolactone) (PM‐b‐PCL) diblock copolymers. Two hydroxyl‐terminated polymethylenes (PM‐OH, M_n= 1800 g mol^?1 (PDI = 1.18) and M_n = 6400 g mol^?1 (PDI = 1.14)) were prepared using living polymerization of dimethylsulfoxonium methylides. Then, such polymers were successfully transformed to PM‐b‐PCL diblock copolymers by using stannous octoate as a catalyst for ROP of ε‐caprolactone. The GPC traces and ¹H NMR of PM‐b‐PCL diblock copolymers indicated the successful extension of PCL segment (M_n of PM‐b‐PCL = 5200–10,300 g mol^?1; PDI = 1.06–1.13). The thermal properties of the double crystalline diblock copolymers were investigated by differential scanning calorimetry (DSC). The results indicated that the incorporation of crystalline segments of PCL chain effectively influence the crystalline process of PM segments. The low‐density polyethylene (LDPE)/PCL and LDPE/polycarbonate (PC) blends were prepared using PM‐b‐PCL as compatibilizer, respectively. The scanning electron microscopy (SEM) observation on the cryofractured surface of such blend polymers indicates that the PM‐b‐PCL diblock copolymers are effective compatibilizers for LDPE/PCL and LDPE/PC blends. Porous films were fabricated via the breath‐figure method using different concentration of PM‐b‐PCL diblock copolymers in CH₂Cl₂ under a static humid condition. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Cyclic Tribismuthide as a Piano Stool Complex Ligand – Synthesis and Crystal Structure of (η3‐Bi3)M(CO)33– (M = Cr,Mo)

The reactions between K₅Bi₄, [(C₆H₆)Cr(CO)₃] or [(C₇H₈)Mo(CO)₃], and [2.2.2]crypt in liquid ammonia yielded the compounds [K([2.2.2]crypt)]₃(η³‐Bi₃)M(CO)₃ · 10NH₃ (M = Cr, Mo), which crystallize isostructurally in P2₁/n. Both contain an 18 valence electron piano‐stool complex with a η³‐coordinated Bi₃‐ring ligand. The Bi–Bi distances range from 2.9560(5) to 2.9867(3) Å and are slightly shorter than known Bi–Bi single bonds but longer than Bi–Bi double bonds. The newly found compounds complete the family of similar complexes with E₃‐ring ligands (E = P‐Bi).     

β,β‐(1,4‐Dithiino)subporphyrin Dimers Capturing Fullerenes with Large Association Constants

β,β‐(1,4‐Dithiino)subporphyrin dimers 7‐syn and 7‐anti were synthesized by the nucleophilic aromatic substitution reaction of 2‐bromo‐3‐(4‐methoxyphenylsulfonyl)subporphyrin 4 with 2,3‐dimercaptosubporphyrin 5 under basic conditions followed by axial arylation. Additions of C₆₀ or C₇₀ to a dilute solution of 7‐anti (ca. 10^?6 m ) in toluene did not cause appreciable UV/Vis spectral changes, while similar additions to a concentrated solution (ca. 10^?3 m ) resulted in precipitation of complexes. In contrast, dimer 7‐syn captured C₆₀ and C₇₀ in different complexation stoichiometries in toluene; a 1:1 manner and a 2:1 manner, respectively, with large association constants; K_a=(1.9±0.2)×10⁶ m ^?1 for C₆₀@ 7‐syn , and K₁=(1.6±0.5)×10⁶ and K₂=(1.8±0.9)×10⁵ m ^?1 for C₇₀@( 7‐syn )₂. These association constants are the largest for fullerenes‐capture by bowl‐shaped molecules reported so far. The structures of C₆₀@ 7‐anti , C₇₀@ 7‐anti , C₆₀@ 7‐syn , and C₇₀@ 7‐syn have been determined by single‐crystal X‐ray diffraction analysis.     

Kinetics and mechanism of the aquation of pentaaqua (trichloroacetato-O)-chromium(2+) ion

The kinetics of the aquation of (H₂O)₅Cr(O₂CCCl₃)²⁺ have been examined at 35–55°C and 1.00M ionic strength with [H⁺] = 0.01?1.00M. The reaction follows the rate equation -d ln [Cr_total]/dt = (a[H⁺]^?1 + b + c[H⁺])/(1 + d[H⁺]), where [Cr_total] is the stoichiometric concentration of the complex. At 45°C a = (1.41 ± 0.03) × 10^?7M/s, b = (1.66 ± 0.02) × 10^?5 s^?1, c = (7.0 ± 0.8) × 10^?5M^?1·S^?1 and d = 2.3 ± 0.3M^?1. Two mechanisms consistent with this rate law are discussed, with evidence being presented in favor of an ester hydrolysis mechanism involving steady-state intermediates. Equilibrium and activation parameters were determined.     

Beiträge zur Kristallchemie und zum thermischen Verhalten von wasserfreien Phosphaten. XXXIII [1] In2P2O7, ein Indium(I)‐diphosphato‐indat(III) und In4(P2O7)3 — Darstellung,Kristallisation und Kristallstrukturen

Contributions on Crystal Chemistry and Thermal Behaviour of Anhydrous Phosphates. XXXIII [1] In₂P₂O₇ an Indium(I)‐diphosphatoindate(III), and In₄(P₂O₇)₃ — Synthesis, Crystallization, and Crystal Structure Solid state reactions via the gas phase lead to the new mixed‐valence indium(I, III)‐diphosphate In₂P₂O₇. Colourless single crystals of In₂P₂O₇ have been grown by isothermal heating of stoichiometric amounts of InPO₄ and InP (800 °C; 7d) using iodine as mineralizer. The structure of In₂P₂O₇ [P2₁/c, a = 7.550(1) Å, b = 10.412(1) Å, c = 8.461(2) Å, b = 105.82(1)°, 2813 independent reflections, 101 parameter, R1 = 0.031, wR2 = 0.078] is the first example for an In⁺ cation in pure oxygen coordination. Observed distances d(In^I‐O) are exceptionally long (d_min(In^I‐O) = 2.82 Å) and support assumption of mainly s‐character for the lone‐pair at the In⁺ ion. Single crystals of In₄(P₂O₇)₃ were grown by chemical vapour transport experiments in a temperature gradient (1000 → 900 °C) using P/I mixtures as transport agent. In contrast to the isostructural diphosphates M₄(P₂O₇)₃ (M = V, Cr, Fe) monoclinic instead of orthorhombic symmetry has been found for In₄(P₂O₇)₃ [P2₁/a, a = 13.248(3) Å, b = 9.758(1) Å, c = 13.442(2) Å, b = 108.94(1)°, 7221 independent reflexes, 281 parameter, R1 = 0.027, wR2 = 0.067].     

TI(III) oxidation of alkenes and alkynes and Ru(III) catalysis in the oxidation of alkenes: A kinetic and mechanistic study

The oxidation of trans-stilbene, phenylacetylene, and diphenylacetylene by Tl(OAc)₃ in aqueous acetic acid medium in the presence of HClO₄ follows the rate law in [H⁺] of 0.1–1.0M, the [H⁺] dependence below 0.1M being marginal. The reactions are strongly dielectric dependent. The order of reactivity among the substrates is styrene > phenylacetylene and trans-stilbene > diphenylacetylene. A mechanism involving the oxythallation adduct by the Tl⁺(OAc)₂ species has been discussed. The use of Ru(III) as a homogeneous catalyst brings a change in the kinetic orders for trans-stilbene, the rate law being The formation constants K for the Ru(III)–alkene π complex at 40, 50, and 60°C are 90.14M^?1, 105.2M^?1, and 127.7M^?1, respectively. Interestingly the oxidation of phenylacetylene and diphenylacetylene does not undergo catalysis by Ru(III). The mechanism involving the metal–arene π complex is discussed.     

Inorganic reactions of iodine(III) in acidic solutions and free energy of iodous acid formation

An analysis of the former works devoted to the reactions of I(III) in acidic nonbuffered solutions gives new thermodynamic and kinetic information. At low iodide concentrations, the rate law of the reaction IO + I^? + 2H⁺ ? IO₂H + IOH is k_+B [IO][I^?][H⁺]² – k_?B [IO₂H][IOH] with k_+B = 4.5 × 10³ M^?3s^?1 and k_?B = 240 M^?1s^?1 at 25°C and zero ionic strength. The rate law of the reaction IO₂H + I^? + H⁺ ? 2IOH is k_+C [IO₂H][I^?][H⁺] – k_?C [IOH]² with k_+C = 1.9 × 10¹⁰ M^?2s^?1 and k_?C = 25 M^?1s^?1. These values lead to a Gibbs free energy of IO₂H formation of ?95 kJ mol^?1. The pK_a of iodous acid should be about 6, leading to a Gibbs free energy of IO formation of about ?61 kJ mol^?1. Estimations of the four rate constants at 50°C give, respectively, 1.2 × 10⁴ M^?3s^?1, 590 M^?1s^?1, 2 × 10⁹ M^?2s^?1, and 20 M^?1 s^?1. Mechanisms of these reactions involving the protonation IO₂H + H⁺ ? IO₂H and an explanation of the decrease of the last two rate constants when the temperature increases, are proposed. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 647–652, 2008