Wavelength Dependent Photodissociation of OCS via F 31Π Rydberg State:CO(X1Σ+)+S(1D2)Product Channel

The vacuum ultraviolet photodissociation of OCS via the $F$ $3^1\Pi$ Rydberg states was investigated in the range of 134$-$140 nm by means of the time-sliced velocity map ion imaging technique. The images of S($^1$D$_2$) products from the CO($X^1\Sigma^+$)+S($^1$D$_2$) dissociation channel were acquired at five photolysis wavelengths, corresponding to a series of symmetric stretching vibrational excitations in OCS($F$ $3^1\Pi$, $v_1$=0$-$4). The total translational energy distributions, vibrational populations and angular distributions of CO($X^1\Sigma^+$, $v$) coproducts were derived. The analysis of experimental results suggests that the excited OCS molecules dissociate to CO($X^1\Sigma^+$) and S($^1$D$_2$) products via non-adiabatic couplings between the upper $F$ $3^1\Pi$ states and the lower-lying states both in the C$_{\infty \textrm{v}}$ and C$_{\rm{s}}$ symmetry. Furthermore, strong wavelength dependent behavior has been observed: the greatly distinct vibrational populations and angular distributions of CO($X^1\Sigma^+$, $v$) products from the lower ($v_1$=0$-$2) and higher ($v_1$=3, 4) vibrational states of the excited OCS($F$ $3^1\Pi$, $v_1$) demonstrate that very different mechanisms are involved in the dissociation processes. This study provides evidence for the possible contribution of vibronic coupling and the crucial role of vibronic coupling on the vacuum ultraviolet photodissociation dynamics.     

Pyridine- and pyrimidine-2-thiolate complexes of ruthenium

A series of mononuclear ruthenium complexes containing pyridine- and pyrimidine-2-thiolato ligands was prepared and characterized. The new compounds of general formula CpRu(PPh₃)(κ²S,N-SR) (1) (SR = pyridine-2-thiolate (a), pyrimidine-2-thiolate (b)) were prepared directly by reacting the thiolato anions (RS⁻) with CpRu(PPh₃)₂Cl. Complexes 1 readily react with NOBF₄ or CO in THF at room temperature to give [CpRu(PPh₃)(NO)(κ¹S-HSR)][BF₄]₂ (2) and CpRu(PPh₃)(CO)(κ¹S-SR) (3), respectively. The one-pot reaction of CpRu(PPh₃)₂Cl, thiolato anions and bis(diphenylphosphino)ethane (dppe) gave CpRu(dppe)(κ¹S-SR) [dppe: Ph₂PCH₂CH₂PPh₂ (4)]. The complex salts, [CpRu(PPh₃)₂(κ¹S-HSR)]BPh₄ (5) are prepared by mixing CpRu(PPh₃)₂Cl, HSR and NaBPh₄ at room temperature. The structures of CpRu(PPh₃)(κ²S,N-Spy) (1a), [CpRu(PPh₃)(NO)(κ¹S-HSpy)][BF₄]₂ (2a) and CpRu(PPh₃)(CO)(κ¹S-Spy) (3a), (py = C₅H₄N) have been determined.     

Determining factors for high performance silicone rubber microwave absorbing materials

Silicone rubber microwave absorbing materials (RMAMs) based on ferrite as the major absorbent were prepared by the mechanical blending method. The determining factors for the complex permittivity, complex permeability, and reflectivity of RMAM were thoroughly investigated with various samples including different crystal structures of Ba-ferrite (M-type, W-type, and Y-type), the ferrite with doped elements (Ba, Sr), the materials' thickness, the combination ratio of ferrite and carbonyl iron. The effects of surface modification and loading amount of ferrite on the mechanical properties, processing performance, and absorbing property of RMAM were also assessed. The results show that W-type Ba-ferrite based RMAM exhibits better absorbing property at high frequencies (8-18 GHz) than the other two barium ferrites (M-type and Y-type) based ones, and the absorbing property of RMAM based on Sr-ferrite is best. As the thickness of RMAM and the amount of absorbents increase, the absorption peak moves toward low frequency, the absorption frequency bandwidth is narrowed, and the reflectivity first decreases and later increases. The optimum thickness is 1.5-1.7 mm, and the amount of ferrite is 450 parts per hundreds of rubber (phr). Surface modification of the absorbent with silane coupling agent could improve the mechanical properties and processing performance of RMAM. It is concluded that there will be a synergistic effect when carbonyl iron (CI) is used in combination with Sr-ferrite (Sr-W) in an appropriate proportion. When the total volume fraction of absorbents is 51%, the optimum ratio of Cl to Sr-W is 17:34, the absorption frequency bandwidth (<−10 dB) is about 8 GHz, and the absorption area is −99 dB.     

Facile Access to Chiral Alcohols with Pharmaceutical Relevance Using a Ketoreductase Newly Mined from Pichia guilliermondii

Chiral secondary alcohols with additional functional groups are frequently required as important and valuable synthons for pharmaceuticals, agricultural and other fine chemicals. With the advantages of environmentally benign reaction conditions, broad reaction scope, and high stereoselectivity, biocatalytic reduction of prochiral ketones offers significant potential in the synthesis of optically active alcohols. A CmCR homologous carbonyl reductase from Pichia guilliermondii NRRL Y‐324 was successfully overexpressed. Substrate profile characterization revealed its broad substrate specificity, covering aryl ketones, aliphatic ketones and ketoesters. Furthermore, a variety of ketone substrates were asymmetrically reduced by the purified enzyme with an additionally NADPH regeneration system. The reduction system exhibited excellent enantioselectivity (>99% ee) in the reduction of all the aromatic ketones and ketoesters, except for 2‐bromoacetophenone (93.5% ee). Semi‐preparative reduction of six ketones was achieved with high enantioselectivity (>99% ee) and isolation yields (>80%) within 12 h. This study provides a useful guidance for further application of this enzyme in the asymmetric synthesis of chiral alcohol enantiomers.     

New Applications of Solid Silica Chloride (SiO 2 -Cl) in Organic Synthesis. Efficient Preparation of Diacetals of 2,2-Bis(Hydroxymethyl)-1,3-propanediol from Different Substrates and Their Transthioacetalization Reactions. Efficient Regeneration of Carbonyl Compounds from Acetals and Acylals

A new application of solid silica chloride, an easily available and efficient catalyst for the preparation of diacetal of 2,2-bis-(hydroxymethyl)-1,3-propanediol from aldehydes, acetals, acylals, and oximes, is described. Transthioacetalization of diacetals of 2,2-bis-(hydroxymethyl)-1,3-propanediol into their corresponding 1,3-dithianes and 1,3-dithiolanes in the presence of silica chloride is presented. Efficient regeneration of carbonyl compounds from their corresponding acetals, ketals, diacetals, and acylals in the presence of this catalyst also is described.     

Regeneration of Carbonyl Compounds from Phenylhydrazones Under Microwave Irradiation

An environmentally benign, efficient, and mild methodology for the cleavage of phenylhydrazones using potassium ferrate under microwave irradiation in solvent-free conditions is described.     

Efficient Method for Thioacetalization of Carbonyl Compounds in the Presence of a Catalytic Amount of Benzyltriphenylphosphonium Tribromide (BTPTB) under Solvent-Free Conditions

A variety of carbonyl compounds have been successfully converted to the corresponding thioacetal derivatives in good to excellent yields on reaction of carbonyl compounds with 1,2-ethanedithiole, 1,3-propanedithiol, and ethylthiol in the presence of a catalytic amount of benzyltriphenylphosphonium tribromide (BTPTB) under solvent-free conditions. Some of the major advantages of this method are mild reaction conditions, high efficiency, and the compatibility with other reported methods. In addition, no bromination occurs at the double bond or α to the keto position or even in the aromatic ring under these experimental conditions.     

Deprotection Chemistry Mediated by ZrOCl2 · 8H2O: An Efficient,Mild, and Green Method for the Conversion of Oximes to Carbonyl Compounds in Aqueous Acetone

Abstract

Less-toxic, moisture-stable, inexpensive, and ecofriendly zirconium oxychloride octahydrate (ZrOCl₂ · 8H₂O) in aqueous acetone (1:1) mediates the conversion of oximes to carbonyl compounds in moderate to good yields. This green methodology is applicable to both aldoximes and ketoximes with tolerance to >C?C<, -NO₂, -OH, and -Cl groups. The reaction and workup are simple.

Sulfamic Acid as a Cost‐Effective and Recyclable Catalyst for Protection of Carbonyls to Acetals and Ketals Under Mild Conditions

Abstract

An efficient H₂NSO₃H‐catalyzed protection of various carbonyl compounds at room temperature was investigated. The features of mild conditions, cost‐efficient catalyst, simple workup, and the recyclability of the catalyst were represented in this process.