Melamine Trisulfonic Acid (MTSA): A New Efficient Catalyst for the Chemoselective Methoxymethylation of Alcohols

Melamine trisulfonic acid, which is easily prepared by the reaction of melamine with neat chlorosulfonic acid, is able to efficiently catalyze the chemoselective methoxymethylation of alcohols with dimethoxymethane (DMM). All reactions were performed under mild and completely heterogeneous reaction conditions in good to high yields.     

Pd immobilized on polyamide based on melamine and terephalic acid as an efficient and recyclable catalyst for Suzuki‐Miyaura coupling reaction

A simple synthetic strategy of polyamide was described from melamine and terephalic acid via one‐step polycondensation. PdCl₂ was then immobilized on the polyamide (denoted as Pd/MPA). Melamine and terephalic acid not only acted as monomers but also provided the ligand sites to help the polyamide to coordinate with Pd(II). The Pd/MPA catalyst was characterized by FT‐IR, TGA, SEM, TEM, XPS, N₂ adsorption‐desorption and atomic absorption spectroscopy. The catalyst was used in Suzuki‐Miyaura coupling reaction of various aryl halides, including less reactive chlorobenzene and benzyl chloride, to give the coupling products in moderate to excellent yields. High turnover frequencies (TOF) up to 29400 h^‐1 can be also obtained. In addition, it behaved truly as a heterogeneous catalyst with high reusability after being recycled 6 times and palladium leaching was negligible during the process. This work provides a practical polyamide support to develop heterogeneous palladium catalysts with simple synthetic procedure and low cost.     

NLO polymers based on cellulose diacetate and a cationic chromophore

An attempt has been made to prepare second-order nonlinear optic (NLO) materials based on cellulose diacetate and melamine derivatives. The NLO cationic chromophore, composed of 1,3-dimethyl-2-(4′-N,N-dimethylaminophenyl)-azo-imidazole chloride and small amounts of 1,3-dimethyl-2-(4′-N,N-dimethylaminophenyl)-azo-imidazole methylsulfate, was incorporated into a crosslink network formed from the reaction of cellulose diacetate with trimethylol melamine or hexamethylol melamine. The poled and cured NLO materials exhibited an electro-optic coefficient (r ₁₃) of 1.03 or 1.42 pm/V, respectively, at the laser wavelength 1550 nm and a modulation frequency of 12.7 kHz; the r ₁₃ values decreased to 97% or 86.6%, respectively, of the initial values after 4 days. The laser transmission loss was 0.58 or 0.6 dB, respectively. The crosslinked materials showed better temporal stability than the material of the host/guest system with a doped cationic chromophore. The results of Fourier transform infrared spectroscopy, dielectric relaxation and thermogravimetry analyses proved the formation of a crosslink structure, and the degree of dielectric relaxation was shown to became higher if a crosslinker of too high functionality was used.     

三聚氰胺三聚硫氰酸盐的合成

以三聚氰胺和三聚硫氰酸为原料合成了一种新型含硫三聚氰胺基阻燃剂——三聚氰胺三聚硫氰酸盐(MSA),其结构和热性能经1H NMR,13C NMR,FT-IR,元素分析和TGA表征。确定了合成MSA的最优工艺条件为:去离子水为溶剂,三聚硫氰酸和三聚氰胺摩尔比为1∶1,反应时间为3 h。TGA分析表明:MSA失重5%时,温度为308.8℃,600℃时分解基本完全,残碳率为0.86%。     

高热稳定性三聚氰胺聚磷酸盐的合成

以三聚氰胺和磷酸为原料,以去离子水为溶剂,在杂多酸A催化下,制得改性三聚氰胺磷酸盐(MP);将MP在箱式气氛炉中进行多温度段热缩合反应合成了三聚氰胺聚磷酸盐(MPP),其结构经~(31)P NMR,IR和元素分析表征。通过TG对MPP的热稳定性和成炭性能进行了分析。结果表明:MPP失重1%时温度为372.1℃,失重5%时温度为382.7℃,700℃时残炭率为37.36%。     

ZnGa2O4 Nanorod Arrays Decorated with Ag Nanoparticles as Surface‐Enhanced Raman‐Scattering Substrates for Melamine Detection

The availability of sensitive, reproducible, and stable substrates is critically important for surface‐enhanced Raman spectroscopy (SERS)‐based applications, but it presently remains a challenge. In this work, well‐aligned zinc gallate (ZnGa₂O₄) nanorod arrays grown on a Si substrate by chemical vapor deposition were used as templates to fabricate SERS substrates by deposition of Ag nanoparticles onto the ZnGa₂O₄ nanorod surfaces. The coverage of the Ag nanoparticles on the ZnGa₂O₄ nanorod surfaces was easily controlled by varying the amount of AgNO₃. SERS measurements showed that the number density of Ag nanoparticles on the ZnGa₂O₄ nanorod surfaces had a great effect on SERS activity. The SERS signals collected by point‐to‐point and SERS mapping images showed that as‐prepared SERS substrates exhibited good spatial uniformity and reproducibility. Detection of melamine molecules at low concentrations (1.0×10^?7 M ) was used as an example to show the possible application of such a substrate. In addition, the effect of benzoic acid on the detection of melamine was also investigated. It was found that the SERS signal intensity of melamine decreased greatly as the concentration of benzoic acid was increased.     

N,N-二甲基羟胺与HNO2的反应动力学

分别在高氯酸和硝酸介质中研究了N,N-二甲基羟胺(DMHAN)与HNO₂的反应动力学,通过考察溶液酸度、还原剂浓度、离子强度和温度等因素对反应过程的影响,获得高氯酸介质中反应动力学速率方程为-d[HNO₂]/dt=k[DMHAN][HNO₂],在18.5 ℃,离子强度μ=0.73 mol/L时,反应速率常数k=(12.8±1.0) mol/(L·min),反应活化能Ea=41.5 kJ/mol。 在硝酸介质中DMHAN与HNO₂的反应比较复杂,硝酸浓度较高时,硝酸将参与反应重新生成HNO₂,且硝酸浓度越大,HNO₂的生成速度越快,HNO₂与DMHAN的反应是自催化氧化的。 对DMHAN与HNO₂的反应产物进行了分析,并推导了硝酸体系中DMHAN与HNO₂的反应机理。     

Synthesis of a new schiff base oxovanadium complex with melamine and 2‐hydroxynaphtaldehyde on modified magnetic nanoparticles as catalyst for allyl alcohols and olefins epoxidation

A new magnetically recoverable nanocatalyst designated as Fe₃O₄@SiO₂@PTMS@Mel‐Naph‐VOcomplex was synthesize by covalent binding of a Schiff base ligand derived from melamine and 2‐hydroxy1naphtaldehyde on the surface of silica coated iron oxide magnetic nanoparticles followed by complexation with VO (acac)₂. Characterization of the prepared nanocatalyst was accomplished with FT‐IR, XRD, SEM, HRTEM, VSM and atomic absorption techniques. It was found that the epoxidation of geraniol, trans‐2‐hexen‐1‐ol, 1‐octen‐3‐ol, norbornene, and cyclooctene is highly selective, affording quantitative yields of the corresponding epoxides with tert‐butyl hydroperoxide (TBHP) using Fe₃O₄@SiO₂@Mel‐Naph‐VOcomplex as catalyst. High reaction yields, short reaction times, simple experimental and work up procedure, catalyst stability and excellent reusability even after five‐cycles of usage in the case of geraniol are some advantages of this research.     

InBr3 catalyzed three-component reactions of an aryldiazoacetate,an alcohol,and a carbonyl compound

InBr₃ promoted three-component reactions of an aryldiazoacetate, an alcohol, and an electron deficient carbonyl compound gave α,β-dihydroxyl acid derivatives in good yield with high diastereoselectivity. The reaction is proposed through a protic oxonium ylide trapping process. The reaction mechanism for the formation of the protic oxonium ylide via Lewis acid InBr₃ catalyzed diazo decomposition is suggested through a vinyl cationic intermediate.     

Synthesis of α,α-disubstituted amino acids based on tandem reaction of dehydroamino acid derivatives

The formation of all-substituted sp³-hybridized carbon-center was investigated via tandem reaction of dehydroamino acid derivatives. The diethylzinc-promoted reaction of dehydroamino acid derivatives with acid anhydride or π-allyl palladium complex proceeded smoothly to afford α,α-disubstituted amino acids via a radical and anionic carbon-carbon bond-forming processes. The tandem reductive reaction of N-phthaloyl dehydroalanine also proceeded effectively by using Bu₃SnH and Pd(PPh₃)₄.     

三聚氰胺甲醛树脂合成—盐酸的催化作用及对产物稳定性的影响

三聚氰胺 (MA)在含有HCl的水溶液中与甲醛 (FA)进行羟甲基化反应。HCl与MA以等摩尔比结合 ,在反应过程中逐渐析出 ,至反应完毕仍保留半结合量。氢离子浓度对三聚氰胺甲醛树脂 (MF)溶液的稳定性有重要的影响     

酸功能化-温控型三元杂多酸离子液体的合成、表征及其酯催化性能

采用酸化-乙醚萃取法制备了不同钒取代数目的 Keggin结构的磷钨钒杂多酸,并进一步通过离子交换法合成了磺酸功能化的杂多酸离子液体催化剂,采用核磁、元素分析、红外、紫外、X射线衍射、热重-差示扫描、电位滴定等分析手段对所得样品进行了表征,考察了所得样品对氯乙酸和正戊醇的酯化反应性能和重复使用性能。结果表明,所制备的杂多酸离子液体是一种具有温度响应特性的无定型结构化合物,仍保留Keggin结构和较高的酸强度,该催化剂在反应温度下与反应物形成一相,而反应结束温度降低后,催化剂和产物又形成两相,通过简单的倾倒法就可以快速分离催化剂和反应产物。与杂多酸以及未磺酸化的杂多酸离子液体相比,磺酸功能化的杂多酸离子液体具有更高的酯催化活性。在优化的反应条件下,[PyPS]4PW11VO40(PyPS为1-(3-磺酸基)丙基吡啶)对氯乙酸的转化率可达到97.6%,重复使用4次后转化率为91.9%,而催化剂的结构未有明显变化。     

Synthese von N-Di(alk-, ar-)oxyphosphoryl-tri(alk-, ar-)-oxyphosphazenen, (RO)2P(O)?NP(OR)3, durch P?N-Bindungsknüpfung

Synthesis of N-Di(alk-, ar-)oxyphosphoryl-tri(alk-, ar-)oxyphosphazenes, (RO)₂P(O)? N?P(OR)₃, by P? N-Bond Formation The title compounds can be prepared from di- and triesters of phosphorous acid, sodium azide, and carbon tetrachloride in a single step procedure and in high yields. Due to the combination of the Atherton-Todd and the Staudinger reaction toxic phosphoric acid ester azides are formed only in situ and their concentration is kept very small. As by-products trichloromethane phosphonic acid esters, (RO)₂P(O)CCl₃, esters of phosphoric acid and condensed phosphoric acids as well as N-alkylimidodiphosphoric acid esters, [(RO)₂P(O)]₂NR, are formed. Their formation can be avoided or reduced by choosing suitable reaction conditions. The mechanism of the reaction is discussed.     

Effect of microheterogeneous environments of CTAB,Triton X-100, and Tween 20 on the oxidative degradation of d-fructose by nanoparticles of MnO2

The kinetics of the oxidative degradation of d -fructose by nanoparticles of MnO₂ has been studied in dilute sulfuric acid medium and also in the presence of surfactants of cetyl trimethyl ammonium bromide (CTAB), Triton X-100 (TX-100), and Tween 20. Amorphous nanoparticles of MnO₂ in the form of spherical particulates of size 50–200 nm, as detected by a transmission electron microscope, have been found to exist, supported on two-dimensional gum acacia sheets. The reaction is first order in MnO₂ but complex order with respect to fructose and H⁺. The reaction is inhibited due to adsorption of reaction products on the surface of MnO₂ nanoparticles. The reaction takes place through an intermediate complex formation between β-d -fructopyranose and protonated MnO₂. A one-step two-electron transfer reaction ultimately leads to the formation of an aldonic acid and formic acid. The entropy of activation plays the key role for the reaction in the absence of surfactants. In the surfactant-mediated reaction, partitioning of both the reactants takes place between the aqueous and micellar pseudophases and reaction occurs following Berezin's model. Binding of fructose with the surfactants in the Stern/palisade layer takes place through the ion–dipole interaction and H-bonding while protonated MnO₂ remains at the outer side of the Stern/palisade layer within the micelle. Both the enthalpy and entropy changes associated with the fructose–water interaction, fructose–micelle interaction, and micelle–water interaction finally control the fructose–micelle binding.     

Rate constants for the reactions of methylvinyl ketone,methacrolein, methacrylic acid,and acrylic acid with ozone

Rate constants for the reaction of ozone with methylvinyl ketone (H₂C(DOUBLEBOND)CHC(O)CH₃), methacrolein (H₂C(DOUBLEBOND)C(CH₃)CHO), methacrylic acid (H₂C(DOUBLEBOND)C(CH₃)C(O)OH), and acrylic acid (H₂C(DOUBLEBOND)CHC(O)OH) were measured at room temperature (296±2 K) in the presence of a sufficient amount of cyclohexane to scavenge OH-radicals. Results from pseudo-first-order experiments in the presence of excess ozone were found not to be consistent with relative rate measurements. It appeared that the formation of the so-called Criegee-intermediates leads to an enhanced decrease in the concentration of the two organic acids investigated. It is shown that the presence of formic acid, which is known to react efficiently with Criegee-intermediates, diminishes the observed removal rate of the organic acids. The rate constant for the reaction of ozone with the unsaturated carbonyl compounds methylvinyl ketone and methacrolein was found not to be influenced by the addition of formic acid. Rate constants for the reaction of ozone determined in the presence of excess formic acid are (in cm³ molecule⁻¹ s⁻¹): methylvinyl ketone (5.4±0.6)×10⁻¹⁸; methacrolein (1.3±0.14)×10⁻¹⁸; methacrylic acid (4.1±0.4)×10⁻¹⁸; and acrylic acid (0.65±0.13)×10⁻¹⁸. Results are found to be consistent with the Criegee mechanism of the gas-phase ozonolysis. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 769–776, 1998     

Synthesis of Metal Chalcogenide Semiconductors by Thermal Decomposition of Organosulfur and Organoselenium Compounds

Metal chalcogenides – because of their excellent optical and electrical properties – are important semiconductor materials for optical devices, such as solar cells, sensors, and photocatalysts. The challenges associated with metal chalcogenides are the complexity of the conventional synthesis methods and the stringent synthesis conditions. In this study, the synthesis conditions were simplified in a solvent-free synthesis method using cadmium precursor, thiourea and selenium to synthesize metal chalcogenides, such as CdS and CdSe, which have particularly suitable band gaps for the optical devices. CdS_xSe_1-x solid solution was successfully synthesized under molten thiourea as the reactive reaction medium at relatively low temperatures, even at 180 °C, with residual melamine derivatives in the solid phase. The luminescence properties of CdS_xSe_1-x and the products in the gas and solid phases were investigated. Optimization of the synthesis conditions for solid solutions of CdS_xSe_1-x and the role of organic compounds in the formation of metal chalcogenides are discussed.     

Quantum-chemical study of the Lewis acid influence on the cycloaddition of benzonitrile oxide to acetonitrile, propyne and propene

Quantum chemical methods (MP2 and B3LYP) together with a topological analysis of the charge density have been used to study the BH₃- or BF₃-mediated reaction of benzonitrile oxide with acetonitrile, propyne and propene. In the reaction with propene or propyne, addition of Lewis acids has only little influence on the outcome of the reactions. The cycloaddition of nitrile oxides with nitriles, however, is generally promoted by strong Lewis acids. When the Lewis acid coordination takes place at the nitrile oxide the reactant is activated and the product binds weakly to the Lewis acid so that the reaction is expected to be catalytic. In the case of coordination to the nitrile the reaction is Lewis acid mediated. Here the reactant is not much influenced by addition of Lewis acid, but the transition state and the product are stabilised and consequently such processes require a stoichiometric amount of Lewis acid and form a stable Lewis acid-product complex.It has also been demonstrated that the different activation routes for these reactions involve different reaction mechanisms. Whereas the reaction of a Lewis acid coordinated nitrile oxide is of ‘inverse electron demand’, the Lewis acid coordinated nitrile reacts through a ‘normal electron demand’ cycloaddition.     

Metal complexes in organic chemistry,by R.P. Hougton. : Cambridge University Press,Cambridge - London - New York - Melbourne, 1979, vii + 308 pages, £21.00 (hard cover); £7.50 (paperback).

The reaction of acetic acid with (Ph₃P)₂Pt(dma) (dma = dimethylacetylene dicarboxylate), in the presence of triphenylphosphine, proceeds by addition of triphenylphosphonium acetate across the acetylenic triple bond, rather than by oxidative addition of the acid to platinum.     

Synthesis and Characterization of S-Triazine Cored Tripodal Keto-oxime and Its Trinuclear Complexes

2,4,6-Tris(4-hydroxybenzimino)-1,3,5-triazine (II) has been synthesized by the reaction of 1 equiv. melamine (I) and 3 equiv. 4-hydroxybenzaldehyde and characterized by means of elemental analysis, ¹H NMR, Fourier transform–infrared spectroscopy, and liquid chromatography–mass spectrometry (LC-MS). 2,4,6-tris(4-(2-phenyl-2-keto-hydroxyiminoyloxy)benzimino)-1,3,5-triazine L (III) has been synthesized by the reaction of 1 equiv. II and 3 equiv. chloroisonitrozoacetophenone and characterized by means of the same methods. Four novel trinuclear Fe(III) and Cr(III) complexes involving tetradentate Schiff bases N,N′-bis(salicylidene)ethylenediamine-(salenH₂) or bis(salicylidene)-o-phenylenediamine-(salophen H₂) with L (III) have been synthesized and characterized by means of elemental analysis, Fourier transform–infrared spectroscopy, LC-MS (ESI⁺), and thermal analyses. The metal ratios of the prepared complexes have been determined using atomic absorption spectroscopy. The aim of the present study is to synthesize novel tridirectional-trinuclear systems and to present their effects on magnetic behavior of [salen or salophenFe(III)/Cr(III)] capped complexes. The complexes have also been characterized as low-spin distorted octahedral Fe(III) and as distorted octahedral Cr(III) bridged by keton-oxime group.     

Synthesis of α,β- and β-Unsaturated Acids and Hydroxy Acids by Tandem Oxidation,Epoxidation, and Hydrolysis/Hydrogenation of Bioethanol Derivatives

We report a reaction platform for the synthesis of three different high-value specialty chemical building blocks starting from bio-ethanol, which might have an important impact in the implementation of biorefineries. First, oxidative dehydrogenation of ethanol to acetaldehyde generates an aldehyde-containing stream active for the production of C₄ aldehydes via base-catalyzed aldol-condensation. Then, the resulting C₄ adduct is selectively converted into crotonic acid via catalytic aerobic oxidation (62 % yield). Using a sequential epoxidation and hydrogenation of crotonic acid leads to 29 % yield of β-hydroxy acid (3-hydroxybutanoic acid). By controlling the pH of the reaction media, it is possible to hydrolyze the oxirane moiety leading to 21 % yield of α,β-dihydroxy acid (2,3-dihydroxybutanoic acid). Crotonic acid, 3-hydroxybutanoic acid, and 2,3-dihydroxybutanoic acid are archetypal specialty chemicals used in the synthesis of polyvinyl-co-unsaturated acids resins, pharmaceutics, and bio-degradable/ -compatible polymers, respectively.