Kinetics and mechanism of acid hydrolysis of peroxyketals

The kinetics of hydrolysis of aliphatic ketone di-tert-butylperoxyketals R¹R²C=O, R¹, R²=CH₃, CH₃; CH₃, C₂H₅; CH₃, n-C₃H₇; CH₃, n-C₆H₁₃; CH₃, i-C₅H₁₀; CH₃, i-C₄H₉; C₂H₅, i-C₃H₇; n-C₄H₉, n-C₄H₉; CH₃, C₆H₅-CH₂, in dioxane in the presence of H₂SO₄ were investigated by IR spectroscopy. It was found that the reaction is reversible and takes place according to the equation R¹R²C· (OOC(CH₃)₃)₂ + H₂O;_H+ R¹R²C=O + 2HOOC(CH₃)₃. The proposed mechanism of hydrolysis includes the fast, quasiequilibrium formation of protonated peroxyketal and subsequent formation of the alkylperoxycarbenium ion. A three-parameter correlation equation is proposed for describing the initial rates of hydrolysis of R¹R²C(oo-t-Bu)₂ peroxyketals.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2501–2506, November, 1990.     

Structure and Stability of Quaternary Ammonium Interhalides: Experimental and Quantum-Chemical Study

The electronic structure of a series of ammonium interhalides [R¹R²R³R⁴N]XI₂, where R¹ = CH₃, C₂H₅, C₃H₇, F, H; R² = R³ = R⁴ = CH₃, H; X = Cl, Br, I, was studied by ab initio calculations (RHF/3-21G, RHF/HW, MP2/HW). The thermodynamic stability of these compounds correlates with the strength of the hydrogen bond N-H···X and three-center interhalide bond X-I-I. Calculations confirmed that, in polar solvents, these compounds preferably decompose to [R¹R²R³R⁴N]⁺ and XI₂ ^- (with subsequent decomposition of the anion), and in nonpolar solvents, to the neutral species [R¹R²R³R⁴N]X and I2. The calculation results were compared to the experimental data obtained by single crystal X-ray diffraction, ¹H NMR spectroscopy, and spectrophotometry.     

Mechanism of the controlled hydrolysis of (NPCl2)2NSOCl: Crystal and molecular structure of [KC12H24O6]+[NHPO2NPCl2NSOCl]−

The reaction mechanism of controlled hydrolysis of the inorganic ring system (NPCl₂)₂NSOCl in the presence of KCl and 18-crown-6 has been revised and is explained from steric constraints rather than from electronic considerations. The X-ray structure of one of the hydrolysis products, [KC₁₂H₂₄O₆]⁺-[NHPO₂NPCl₂NSOCl]⁻, shows a dimeric structure of two centrosymmetrically related formula units kept together by hydrogen bridges and K … O coordination. Crystals are monoclinic, space group C2/c with a = 25.698(5), b = 8.223(2), c = 23.665(4) Å, β = 106.03(1)°, V = 4806(2) ų, and Z = 8. The final R and R_w values are 0.048 and 0.044, respectively.     

A mechanistic study of the photochemistry of tricarbonyl(1-aza-1,3-butadiene)iron complexes [Fe(CO)3(R′NCHCHCHPh)] in CH4 matrices at 10 K and in solution at 293 K

The photochemistry has been studied of the complexes [Fe(CO)₃(R¹, Ph-ABD)] (R¹,Ph-ABD represents R¹NCHCHCHPh; 1R¹,4Ph-1-aza-1,3-butadiene) both in a CH₄ matrix at 10 K and in solution at 293 K. Matrix photolysis of [Fe(CO)₃(i-Pr,Ph-ABD)] causes breaking of the ironolefin bond with formation of the 16-electron species [Fe(CO)₃(]gs-N-i-Pr,Ph-ABD)]. In solution the R¹Ph-ABD ligand is replaced photochemically by other R¹,Ph-ABD molecules and by R-DAB (R-DAB = 1,4-diaza-1,3-butadiene; RNCHCHNR). Photolysis in the presence of PR₃ results in the formation of [Fe(CO)₂(R¹,Ph-ABD)(PR₃)], [Fe(CO)₃(PR₃)₂] and [Fe(CO)₄(PR₃)]. The relative amounts of these photoproduct depend on the PR₃ concentration, on the R¹,Ph-ADB ligand used, and on the polarity of the solvent. A mechanism is proposed in which the product of the matrix photolysis is assumed to be the primary photoproduct of the photosubstitution reactions.     

Cyclopolymerization Initiated by Peroxydisulfate Ion and Metal Ion Catalysis

The kinetics of cyclopolymerization of N,N' -methylenebisacrylamide (MBA) was carried out using peroxydisulfate ion as initiator. The rate of polymerization, R_p, was found to be proportional to [M] and [S₂O₈ ^2-]^1/2 for the uncatalyzed system. A cyclopolymerization mechanism was found to fit the experimental results. The k₂₁/k_t ^1/2 value for MBA polymerization was evaluated. Evidence in favor of the cyclopolymerization mechanism is provided. The addition of Ag ion enhances R_p.     

Dihydrogen Generation from Amine/Boranes: Synthesis,FT‐ICR,and Computational Studies

A Fourier transform ion cyclotron resonance spectrometry (FT‐ICR) study of the gas‐phase protonation of ammonia‐borane and sixteen amine/boranes R¹R²R³N? BH₃ (including six compounds synthesized for the first time) has shown that, without exception, the protonation of amine/boranes leads to the formation of dihydrogen. The structural effects on the experimental energetic thresholds of this reaction were determined experimentally. The most likely intermediate and the observed final species (besides H₂) are R¹R²R³N? BH₄⁺ and R¹R²R³N? BH₂⁺, respectively. Isotopic substitution allowed the reaction mechanism to be ascertained. Computational analyses ([MP2/6‐311+G(d,p)] level) of the thermodynamic stabilities of the R¹R²R³N? BH₃ adducts, the acidities of the proton sources required for dihydrogen formation, and the structural effects on these processes were performed. It was further found that the family of R¹R²R³N? BH₄⁺ ions is characterized by a three‐center, two‐electron bond between B and a loosely bound H₂ molecule. Unexpected features of some R¹R²R³N? BH₄⁺ ions were found. This information allowed the properties of amine/boranes most suitable for dihydrogen generation and storage to be determined.     

Theoretical studies on QSAR and mechanism of 2‐indolinone derivatives as tubulin inhibitors

The theoretical studies on three‐dimensional quantitative structure activity relationship (3D‐QSAR) and action mechanism of a series of 2‐indolinone derivatives as tubulin inhibitors against human breast cancer cell line MDA‐MB‐231 have been carried out. The established 3D‐QSAR model from the comparative molecular field analysis (CoMFA) shows not only significant statistical quality but also predictive ability, with high correlation coefficient (R² = 0.986) and cross‐validation coefficient (q² = 0.683). In particular, the appropriate binding orientations and conformations of these 2‐indolinone derivatives interacting with tubulin are located by docking study, and it is very interesting to find that the plot of the energy scores of these compounds in DOCK versus the corresponding experimental pIC₅₀ values exhibits a considerable linear correlation. Therefore, the inhibition mechanism that 2‐indolinone derivatives were regarded as tubulin inhibitors can be theoretically confirmed. Based on such an inhibition mechanism along with 3D‐QSAR results, some important factors improving the activities of these compounds were discussed in detail. These factors can be summarized as follows: the H atom adopted as substituent R₁, the substituent R₂ with higher electropositivity and smaller bulk, the substituents R₄–R₆ (on the phenyl ring) with higher electropositivity and larger bulk, and so on. These results can offer useful theoretical references for understanding the action mechanism, designing more potent inhibitors, and predicting their activities prior to synthesis. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Molecular mechanics of peroxides. I. Parametrization and conformational analysis of linear compounds

A force field has been developed for use in MM2 calculations of geometric and energy data for linear peroxides R₁? O? O? R₂ and tested in some of them (R₁, R₂ = H, Me, Et, Prⁱ, Bu^t). The field obtained yield results that agree considerably better with experimental and ab initio data than those afforded by the only set of estimated parameters hitherto available.     

The Formation of Phosphacycloheptatrienes in Ring Enlargement Reaction

Abstract

The forrmation of substituted phosphacycloheptatrienes in ring expansion reaction(s) is describzd. From thc: reac-tion of 3,4-dimethyl-l-phenyl-3-phospholene-l-oxide(1,R¹ = c₆H₅, R₂=R₃ = CH₃) with dichlorocarbene under liquid-liquid phase transfer circumstances not the expected adduct but the appropriate phoshacycloheptatrisne (4, R_l, R₂,R₃ as above) was prepared. The formation of this product can be explained assuming two ring expansions effected by two series of dichlorocarbene addition and cyclopropane ring opening. In the similar reaction of the methoxy-phospholenc derivative (1, R¹=CH₃O, R² = R³ = CH3 four other products are also formed beside the phosphacyclohcptatriene. Again phosphacycloheptatrienes (4) are formed as the result of dichlorocarbene addition to the regioisoners of dihidrophosphorins (2) obtained from the phospholene-dichlorocarbene adducts by thermolysis. The same product can be derived from each regioisomeric pair.     

Reactions of Diazo Compounds with Alkenes Catalysed by [RuCl(cod)(Cp)]: Effect of the Substituents in the Formation of Cyclopropanation or Metathesis Products

The reaction of diazo compounds with alkenes catalysed by complex [RuCl(cod)(Cp)] (cod=1,5‐cyclooctadiene, Cp=cyclopentadienyl) has been studied. The catalytic cycle involves in the first step the decomposition of the diazo derivative to afford the reactive [RuCl(Cp){?C(R¹)R²}] intermediate and a mechanism is proposed for this step based on a kinetic study of the simple coupling reaction of ethyl diazoacetate. The evolution of the Ru–carbene intermediate in the presence of alkenes depends on the nature of the substituents at both the diazo N₂?C(R¹)R² (R¹, R²=Ph, H; Ph, CO₂Me; Ph, Ph; C(R¹)R²=fluorene) and the olefin substrates R³(H)C?C(H)R⁴ (R³, R⁴=CO₂Et, CO₂Et; Ph, Ph; Ph, Me; Ph, H; Me, Br; Me, CN; Ph, CN; H, CN; CN, CN). A remarkable reactivity of the complex was recorded, especially towards unstable aryldiazo compounds and electron‐poor olefins. The results obtained indicate that either cyclopropanation or metathesis products can be formed: the first products are favoured by the presence of a cyano substituent at the double bond and the second ones by a phenyl.     

13C NMR spectra of 2,3-dihydro-1H-benzo[b]azepines: Differentiation of diastereomers

The ¹³C NMR spectra of 23 2,3-dihydro-1H-benzo[b]azepines, including nine pairs of diastereomers separated by chromatography, [(2R*, 3R^*) and (2R^*), 3S^*)] are hereby assigned and discussed. The relative configurations of the diastereomers were assigned by two methods. The first, based on the chemical shifts of the asymmetric carbons C-2 and C-3 (with regression analysis), shows that the values for (R^*, R^*) are approximately 1 ppm lower than those for (R^*, S^*) diastereomers. The second method uses the chemical shifts, δ₃, of the R₃(CH₃) substituents. When these δ₃ values are compared by means of the δ₃-δ_m difference (δ_m is the mean value obtained from compounds where R₂=H), the difference is always negative for (R^*, R^*) and positive for (R^*, S^*). This is attributed to a γ-gauche effect between R₂ and R₃ in the case of (R^*, R^*) diastereomers (R₂ and R₃ are cis). The results corroborate those already obtained by ¹H NMR [J(23)(R^*, R^*)<J(23)(R^*, S^*)] and are a confirmation of the results of a radiocrystallographic examination carried out on two nitrogen acetylated diastereomers.     

Alkane loss from collisionally activated alkylmethyleneimmonium ions

The collision-induced dissociation (CID) spectra of five alkylmethyleneimmonium ions (H₂C-N⁺R¹R², (a) R¹ = R² = C₂H₅, (b) R¹ = n-C₃H₇, R² = H, (c) R¹ = n-C₃H₇, R² = CH₃, (d) R¹ = n-C₃H₇, R² = C₂H₅, (e) R¹ = R² = n-C₃H₇) are reported and discussed in terms of the mechanism of alkane loss. The most abundant alkane losses result from 2-azaallylic bond cleavages within R¹ and R² leading to daughter ions of m/z 84. Ion d (R¹ = n-C₃H₇, R² = C₂H₅) was chosen for a deuterium-labelling study because it exhibited methane loss nearly free from interferences with other fragmentations. The methane lost consists to a great extent (95%) of the methyl moiety of R². Whereas the methyl moiety obviously stays intact during the fragmentation process, the hydrogen additionally needed originates from all positions of R¹ and the double-bonded methylene in an approximately random distribution, suggesting extensive hydrogen migrations preceding the transfer step.     

PNPP Cleavage Catalyzed by Schiff Base Mn(III) Complexes Containing Polyether Side Chains in CTAB Micellar Solutions

Two Schiff base Mn(III) complexes containing polyether side chain were synthesized and characterized. The catalytic hydrolysis of p‐nitrophenyl picolinate (PNPP) by the two complexes in the buffered CTAB micellar solution in the pH range of 6.60–8.20 was investigated kinetically in this study. The influences of acidity, temperature, and structure of complex on the catalytic cleavage of PNPP were also studied. The mechanism of PNPP hydrolysis catalyzed by Schiff base manganese(III) complexes in CTAB micellar solution was proposed. The relative kinetic and thermodynamic parameters were determined. Comparied with the pseudo‐first‐order rate constant (k ₀) of PNPP spontaneous hydrolysis in water, the pseudo‐first‐order rate constants (k _obsd) of PNPP catalytic hydrolysis are 1.93×10³ fold for MnL¹ ₂Cl and 1.06×10³ fold for MnL² ₂Cl in CTAB micellar solution at pH=7.00, T=25°C, and [S]=2.0×10^?4mol · dm^?3, respectively. Furthermore, comparing the k _obsd of PNPP catalytic hydrolysis by metallomicelles with that of PNPP hydrolysis catalyzed only by metal complexes or CTAB micelle at the above‐mentioned condition, metallomicelles of MnL₂(L=L¹, L²) Cl/CTAB exhibit notable catalytic activities for promoting PNPP hydrolysis, and MnL¹ ₂Cl/CTAB system is superior in promoting cleavage of PNPP relative to MnL² ₂Cl/CTAB system under the same experimental conditions. The results indicate that the rate of PNPP catalytic cleavage is influenced by the structures of the two complexes, the acidity of reaction systems, and the solubilization of PNPP in CTAB micelles.     

The synthesis of the insect pheromone (2S,3R,7R)-3,7-dimethyltridec-2-yl acetate from racemic 3,4-dimethyl-γ-butyrolactone by diastereoselective chiral resolution

The insect pheromone (2S,3R,7R)-3,7-dimethyltridec-2-yl acetate 1-Ac was prepared from diastereomerically enriched (2S¹,3R¹,7R)-1, which in turn was obtained by the coupling of racemic 3,4-dimethyl-γ-butyrolactone with (7S)-2-methyloctyllithium, followed by a Wolff–Kishner reduction of the resulting ketone. Conversion of (2S¹,3R¹,7R)-1 to the corresponding alkyl hydrogen phthalate and diastereomer salt formation with (S)-PhCHMeNH₂ provided after several crystallizations individual diastereomer, which was later transformed into target 1-Ac after hydrolysis and acylation.     

Optical energy storage properties of Sr<Subscript>2</Subscript>MgSi<Subscript>2</Subscript>O<Subscript>7</Subscript>:Eu<Superscript>2+</Superscript>,R<Superscript>3+</Superscript> persistent luminescence materials

The details of the mechanism of persistent luminescence were probed by investigating the trap level structure of Sr₂MgSi₂O₇:Eu²⁺,R³⁺ materials (R: Y, La-Lu, excluding Pm and Eu) with thermoluminescence (TL) measurements and Density Functional Theory (DFT) calculations. The TL results indicated that the shallowest traps for each Sr₂MgSi₂O₇:Eu²⁺,R³⁺ material above room temperature were always ca. 0.7 eV corresponding to a strong TL maximum at ca. 90 °C. This main trap energy was only slightly modified by the different co-dopants, which, in contrast, had a significant effect on the depths of the deeper traps. The combined results of the trap level energies obtained from the experimental data and DFT calculations suggest that the main trap responsible for the persistent luminescence of the Sr₂MgSi₂O₇:Eu²⁺,R³⁺ materials is created by charge compensation lattice defects, identified tentatively as oxygen vacancies, induced by the R³⁺ co-dopants.     

Improved water resistance of SrAl2O4: Eu2+, Dy3+ phosphor directly achieved in a water-containing medium

In this paper, a heterogeneous precipitation method utilizing urea hydrolysis was adopted to coat a SiO₂ layer on the surface of SrAl₂O₄:Eu²⁺, Dy³⁺ long persistence phosphors. To avoid phosphor hydrolysis in a water-containing coating medium, the hydrolysis and polymerization reactions of tetraethyl orthosilicate (TEOS) were concerned and carried out. The crystal phases, surface morphologies, hydrolysis stability and water resistance on afterglow properties of coated phosphors were investigated. Scanning electron microscopy, energy dispersive spectrum analysis, transmission electron microscope and Fourier transform infrared spectrum results confirmed that a continuous, uniform and compact SiO₂ coating layer was successfully obtained on the phosphors surface. A theoretical coating amount of 5% or higher was found to be good for hydrolysis stability. Photoluminescence results revealed the coated phosphors showed much better water resistance on afterglow properties than the uncoated phosphor. We also discussed and proposed the hydrolysis restriction mechanism of SrAl₂O₄:Eu²⁺, Dy³⁺ in the water-containing coating medium.     

Computational study of topological effects on intramolecular electron transfer in mixed-valence compounds

The constrained density functional theory (CDFT) was used to investigate the topological effects on intramolecular electron transfer processes that have been reported in previous experimental work [Inorg. Chem., 1997, 36 (22), pp 5037–5049]. The computation mainly focused on three isomers of diferrocenylbenzenes (ortho, para, and meta) and 5-substituted derivatives of m-diferrocencylbenzenes with R = NH₂, Cl, CH₃, CN, NO₂, NeCH₃)₃³⁺, and N₂⁺. The influence of a third group R′ (R′ = NH₂ and N₂⁺) was introduced to the ortho and para isomers. The calculations were compared with the experimental results. The relation between the substituted functional groups and the effectiveness of intramolecular electron transfer was discussed on the basis of CDFT computational results.     

Surface properties and structure of organofluorosilicon polymers based on organotrialkoxysilanes R<Superscript>F</Superscript>OCH<Subscript>2</Subscript>Si(OR<Superscript>F</Superscript>)<Subscript>3</Subscript>

The hydrolysis of trifunctional alkoxysilanes R^FOCH₂ Si(OR^F)₃, where R^F = CH₂CF₃, CH₂CF₂CF₃, CH₂CF₂CF₂CF₃, or CH₂CF₂CF₂CF₂CF₃, during the action of atmospheric moisture in the presence of 3-aminopropyltriethoxysilane under mild conditions yields new ladderlike polysiloxanes. Their structure is studied via ¹H NMR spectroscopy, GPC, TGA, and AFM. Polymer coatings prepared on their basis are found to be low-energy and hydrophobic. The total surface energy and polarity of the surface of polysiloxane films decrease, while their hydrophobicity increases with lengthening of the fluoroorganic substituent at the silicon atom.     

Relationships between the acidity of the Z and E isomers of N-Nitroso-N-alkyl-α-amino acids and their conformations

The acidity constants of both Z and E conformational isomers of five N-nitroso-N-alkyl-α-amino acids, ON? N(R₁)? CH(R₂)? COOH, are determined by the observation of selected pH titrated ¹H NMR signals. For two glycine derivatives (1, R₁?CH₃, R₂?H, ON? Sar; 2, R₁?C₂H₅, R₂?H, ON? EtGly) and two alanine derivatives (3, R₁?CH₃, R₂?CH₃, ON? MeAla; 4, R₁?C₂H₅, R₂?CH₃, ON? EtAla) the E isomers appear to be stronger acids than the Z while for the third alanine derivative (5, R₁?n-C₃H₇, R₂?CH₃, ON? PrAla) the opposite is observed. These results, also including anisotropy effects associated with the N? NO group, are discussed in terms of conformations. A 7-membered ring conformation with an ? NO…HOOC? intramolecular hydrogen bond is proposed to be statistically important in the Z isomers of 1, 2, 3 and, to a lesser extent, 4.     

A Series of [Mn6] Complexes with Terminal Functional Groups

A series of [Mn₆O₂(R¹OH)₄(sao)₆(R²COO)₂] complexes with terminal functional groups ( 1 : R¹ = CH₃, R² = HO‐C₆H₄, 2 : R¹ = C₂H₅, R² = H₂N‐C₆H₄, 3 : R¹ = CH₃, R² = Cl‐C₆H₄, 4 : R¹ = CH₃, R² = CH₃S‐C₆H₄, 5 : R¹ = CH₃, R² = I‐C₆H₄, 6 : R¹ = CH₃, R² = pymSCH₂, 7 : R¹ = CH₃, R² = ortho‐pyr‐SCH₃, 8 : R¹ = C₂H₅, R² = (CH₃)₃OOCNHCH₂C₆H₄; sao = doubly deprotonated salicylaldoxime ligand, pym = pyrimidyl, pyr = pyridyl) have been obtained in a reaction of a ligand R²C₆H₄COOH, salicylaldoxime, manganese(II) perchlorate and [NEt₄](OH) in methanol or a 1:1 mixture of ethanol and dichloromethane. In this report, structural aspects as well as preliminary studies of magnetic and thermal properties are presented. Compounds 1 , 3 , 6 , 8 exhibit an antiferromagnetic coupling of the Mn²⁺ ions, whereas 4 and 7 show ferromagnetic interactions. The title compounds may act as starting materials for further derivatization addressing the functional groups.