Methyl Bond Research Articles

Effects of Chemical Curing Temperature and Time on the Properties of Liquefied Wood based As-cured Precursors and Carbon Fibers

Liquefied wood based as-cured precursors and carbon fibers prepared by different chemical curing processes were carried out to investigate the effects of curing temperature and time on the thermostability and microstructure of liquefied wood based precursors, the tensile strength of carbon fibers as well. The primary fibers can be converted into precursors with high performance by directly heating at target curing temperature. With the temperature and duration increasing, the numbers of methylene bonds in precursors increased, resulting in the enhancement of cross-linkages among molecular chains and then the improvement of thermostability of precursors. Carbon fibers prepared from as-cured precursors (curing temperature 95 oC, curing time 3h) had the minimum value of the average interlayer spacing (d002), it also showed the highest tensile strength, almost 800 MPa, which can be classified as fibers of general grade.

Reductive functionalization of 3d metal–methyl complexes: The greater importance of ligand than metal

Selective oxidation of methane, which is the primary component of natural gas, to methanol, as a more easily transportable liquid, using organometallic catalysis, has become more important recently due to the abundance of domestic natural gas. In this regard, reductive functionalization (RF) of methyl ligands in [M(diimine)2(CH3)(Cl)] complexes, where M is a 3d metal with oxidation state of 2+ has been studied computationally using density functional techniques. The metal ions chosen for study were VII (d3) through CuII (d9) in the 3d row of the periodic table to assess changes in RF energetics as a function of d orbital occupation. A SN2 mechanism for the nucleophilic attack of hydroxide on the metal–methyl bond, resulting in the formation of methanol, was studied. Similar highly exergonic pathways with very low energy SN2 barriers were observed for the proposed RF mechanism for all the studied complexes. Changes in spin state occurred through the RF pathway for most of the metals studied. To modulate RF pathways closer to thermoneutral for catalytic purposes, a future challenge, paradoxically, requires finding a way to strengthen the metal–carbon bond. Furthermore, the DFT calculations suggest that for 3d metals, ligand properties will be of greater importance than metal identity in identifying suitable catalysts for alkane hydroxylation in which reductive functionalization is used to form the C–O bond.

Tribology and oxidation studies of fatty acid sulfide derivatives synthesized via thiol‐ene “Click” additions

The synthesis of sulfide derivatives via thiol‐ene addition reactions of methyl oleate and methyl 10‐ undecenoate as substrates is reported. The substrate fatty acids contained a terminal double bond in methyl 10‐undecenoate and an internal double bond in methyl oleate. Thiol‐ene addition of unsaturated fatty acid ester derivatives with hydroxy and amine functionality on the fatty acids was carried out under thermal conditions. The synthesized products were characterized by 1H, 13C NMR, FT‐IR, and GC‐MS analysis and evaluated for their antioxidant, extreme pressure (EP), and antiwear (AW) properties in base oil namely, epoxy jatropha fatty acid n‐butyl esters (EJB). Synthesized products exhibited comparable antioxidant efficacy to butylated hydroxyl toluene (BHT). All four synthesized sulfide derivatives significantly enhanced the weld point of the base oil EJB and exhibited comparable performance to TCP (tricresyl phosphate) at 1 wt% level. Methyl 9(10)‐(2‐hydroxyethylthio) octadecanoate at 0.5% concentration exhibited considerable improvement in the wear scar of base oil from 0.834 to 0.422 mm. The synthesized sulfide derivatives have potential as multifunctional additives for biolubricant basestocks.Practical applications: Synthesis of multifunctional additives via thiol‐ene addition under thermal conditions. The prepared sulfide derivatives were found to exhibit good antioxidant, antiwear, and extreme pressure additives. The synthesized additives exhibited comparable performance to commercial additives. The products are potential biobased alternatives for commercial additives.Sulfide derivatives as multifunctional additives.

Direct Annulation of Hydrazides to 1,3,4-Oxadiazoles via Oxidative C(CO)-C(Methyl) Bond Cleavage of Methyl Ketones.

A new strategy for the synthesis of 1,3,4-oxadiazoles was established through direct annulation of hydrazides with methyl ketones. It was found that the use of K2CO3 as a base achieves an unexpected and highly efficient C-C bond cleavage. This reaction is proposed to go through oxidative cleavage of Csp(3)-H bonds, followed by cyclization and deacylation.

ChemInform Abstract: Direct Arylation of C(sp3)—H Bonds in Aliphatic Amides with Diaryliodonium Salts in the Presence of a Nickel Catalyst.

The Ni(II)-catalyzed direct arylation of C(sp3)–H (methyl and methylene) bonds in aliphatic amides containing an 8-aminoquinoline moiety as the directing group with diaryliodonium salts as coupling electrophiles is described. A wide variety of functional groups are tolerated in the reaction. The reaction represents the first example of the Ni-catalyzed direct arylation of C(sp3)–H bonds with diaryliodonium salts.

Experimental Study on Effects of Mechanical Properties of Lytag Concrete

Pyrolysis behavior of a new kind of polybenzoxazine with aldehyde groups was investigated by pyrolysis gas chromatography-mass spectroscopy (PyGC-MS) at the temperatures ranging from 450°C to 750°C. It was found from the pyrolysis chromatograms that the type and amount of its pyrolysates obviously change with pyrolysis temperature due to various pyrolysis behaviors at different temperatures. From the structures and relative contents of the pyrolysates, the pyrolysis mechanism of the polybenzoxazine was described as follows: the initial degradation reactions occurred mainly at the Cmethylene-N bond, followed by the Cphenyl-C methylene bonds.

Study on Pyrolysis Behavior of Polybenzoxazine by PyGC-MS

Pyrolysis behavior of a new kind of polybenzoxazine with aldehyde groups was investigated by pyrolysis gas chromatography-mass spectroscopy (PyGC-MS) at the temperatures ranging from 450°C to 750°C. It was found from the pyrolysis chromatograms that the type and amount of its pyrolysates obviously change with pyrolysis temperature due to various pyrolysis behaviors at different temperatures. From the structures and relative contents of the pyrolysates, the pyrolysis mechanism of the polybenzoxazine was described as follows: the initial degradation reactions occurred mainly at the Cmethylene-N bond, followed by the Cphenyl-C methylene bonds.

DFT Virtual Screening Identifies Rhodium–Amidinate Complexes As Potential Homogeneous Catalysts for Methane-to-Methanol Oxidation

In the search for new organometallic catalysts for low-temperature selective conversion of CH_4 to CH_3OH, we apply quantum mechanical virtual screening to select the optimum combination of ligand and solvent on rhodium to achieve low barriers for CH_4 activation and functionalization to recommend for experimental validation. Here, we considered Rh because its lower electronegativity compared with Pt and Pd may allow it to avoid poisoning by coordinating media. We report quantum mechanical predictions (including implicit and explicit solvation) of the mechanisms for Rh^(III)(NN) and Rh^(III)(NN^F) complexes [where (NN) = bis(N-phenyl)benzylamidinate and (NN^F) = bis(N-pentafluorophenyl)pentafluorobenzylamidinate] to catalytically activate and functionalize methane using trifluoroacetic acid (TFAH) or water as a solvent. In particular, we designed the (NN^F) ligand as a more electrophilic analogue to the (NN) ligand, and our results predict the lowest transition state barrier (ΔG‡ = 27.6 kcal/mol) for methane activation in TFAH from a pool of four different classes of ligands. To close the catalytic cycle, the functionalization of methylrhodium intermediates was also investigated, involving carbon–oxygen bond formation via S_N2 attack by solvent, or S_R2 attack by a vanadium oxo. Activation barriers for the functionalization of methylrhodium intermediates via nucleophilic attack are lower when the solvent is water, but CH_4 activation barriers are higher. In addition, we have found a correlation between CH_4 activation barriers and rhodium–methyl bond energies that allow us to predict the activation transition state energies for future ligands, as well.

Reductive Functionalization of a Rhodium(III)–Methyl Bond in Acidic Media: Key Step in the Electrophilic Functionalization of Methane

The reductive functionalization of RhIII–Me bonds in acids is a key step for RhI/III-based catalysts for methane functionalization. Heating electronic-rich [tBu3terpy]Rh(Me)(Cl)I (1; tBu3terpy = 4,4′,4″-tri-tert-butylterpyridine) in H2O, AcOD, or trifluoroacetic acid (HTFA) released a stoichiometric amount of methane. With use of a less donating ligand, [(NO2)3terpy]Rh(Me)(Cl)I (2; (NO2)3terpy = 4,4′,4″-trinitroterpyridine), a mixture of CH4 and CH3X (X = Cl, TFA, OAc, OH) was obtained. The selectivity between MeX and CH4 was found to be dependent on the halide present (I– or Cl–). In a key experiment with the removal of one halide from 2, {[(NO2)3terpy]Rh(Me)Cl}{BF4} (3) was completely protonated in acidic solvent. DFT calculations were employed to investigate the mechanism of reductive functionalization and protonation.

Synthesis and Structural Studies of Three Uracil Derivatives, Methyl 3-(2,4-dioxo-3,4-dihydropyrimidin-1(2H)-yl)propanate, Methyl 3-(5-Nitro-2,4-dioxo-3,4-dihydropyrimidin-1(2H)-yl)propanoate and Ethyl 3-(5-Nitro-2,4-dioxo-3,4-dihydropyrimidin-1 (2H)-yl)propanoate

Three uracil derivatives of methyl 3-(2,4-dioxo-3,4-dihydropyrimidin-1(2H)-yl)propanoate (I), methyl 3-(5-nitro-2,4-dioxo-3,4-dihydropyrimidin-1(2H)-yl)propanoate (II) and ethyl 3-(5-nitro-2,4-dioxo-3,4-dihydropyrimidin-1(2H)-yl)propanoate (III) have been prepared through one pot synthesis and examined by X-ray crystallography, FT-IR and NMR spectroscopy. Compound I, C8H10N2O4, is monoclinic with space group P 21/c and cell constants a = 11.4437(12), b = 11.7980(13), c = 6.9496(7) A, β = 103.180(2)°, V = 913.57(17) A3, and Z = 4. Compound II, C8H9N3O6, crystallizes in the monoclinic P 21 space group with cell constants a = 8.0342(14), b = 5.7155(10), c = 11.572(2) A, β = 105.200(3)°, V = 512.79(16) A3, and Z = 2. Compound III, C9H11N3O6, is Orthorhombic with space group P 212121 and cell constants a = 5.7560(16), b = 8.032(2), c = 25.302(7) A, β = 90°, V = 1169.8(6) A3, and Z = 4. The supramolecular architectures of the three compounds involve N–H···O hydrogen bond. The supramolecular architectures of the three compounds involve N–H···O hydrogen bond. Depiction of packing and showing the N–H···O hydrogen bond in methyl 3-(2,4-dioxo-3,4-dihydropyrimidin-1(2H)-yl)propanoate Depiction of packing and showing the N–H···O hydrogen bond in methyl 3-(5-nitro-2,4-dioxo-3,4-dihydropyrimidin-1(2H)-yl)propanoate Depiction of packing and showing the N–H···O hydrogen bond in ethyl 3-(5-nitro-2,4-dioxo-3,4-dihydropyrimidin-1(2H)-yl)propanoate.

Oxygen insertion into metal carbon bonds: formation of methylperoxo Pd(II) and Pt(II) complexes via photogenerated dinuclear intermediates.

Platinum(II) and palladium(II) complexes [M(CH3)(L)]SbF6 with substituted terpyridine ligands L undergo light-driven oxygen insertion reactions into metal methyl bonds resulting in methylperoxo complexes [M(OOCH3)(L)]SbF6. The oxygen insertion reactions occur readily for complexes with methyl ligands that are activated due to steric interaction with substituents (NH2, NHMe or CH3) at the 6,6″-positions on the terpyridine ligand. All complexes exhibit attractive intermolecular π···π or M···M interactions in the solid state and in solution, which lead to excited triplet dinuclear M-M complexes upon irradiation. A mechanism is proposed whereby a dinuclear intermediate is generated upon irradiation that has a weakened M-C bond in the excited state, resulting in the observed oxygen insertion reactions.

Oxygen Atom Insertion into Iron(II) Phenyl and Methyl Bonds: A Key Step for Catalytic Hydrocarbon Functionalization

Oxy-functionalization of metal–alkyl and −aryl bonds is a key step in potential hydrocarbon oxidation catalysis. However, well-defined examples of M–R to ROH conversion are rare, especially for first-row transition metals. Cp*Fe(CO)(NCMe)Ph reacts with oxygen or hydrogen peroxide to produce benzoic acid. Removing CO from the Cp*Fe(L)(L′)Ph framework allows simple oxygen atom insertion into the Fe–Ph bond. Cp*Fe(P(OCH2)3CEt)2Ph reacts with Me3NO in THF to produce PhOH in high yield when Brønsted acids are added. Studies show that light promotes P(OCH2)3CEt dissociation from Cp*Fe(P(OCH2)3CEt)2Ph, which facilitates the conversion to PhOH. The methyl analogue Cp*Fe[P(OCH2)3CEt]2Me reacts with oxidants to produce MeOH.

Water-Soluble Mono- and Dimethyl N-Heterocyclic Carbene Platinum(II) Complexes: Synthesis and Reactivity

A family of water-soluble dimethyl complexes of formula cis-[PtMe2(dmso)(NHC·Na)] (2), in which NHC is an anionic N-heterocyclic carbene bearing a sulfonatopropyl chain on one of the nitrogen atoms and a sulfonatopropyl (a), methyl (b), mesityl (c), or 2,6-diisopropylphenyl group (d) on the other, have been prepared. The hydrolytic stability of the Pt–C bonds in these complexes under different neutral, alkaline, and acidic aqueous conditions has also been studied. Complexes 2 were found to be quite stable at room temperature in water under neutral or alkaline conditions. Degradation occurred at higher temperatures but involved C sp3–H activation and C–C reductive elimination processes in addition to Pt–Me bond hydrolysis. Hydrolytic cleavage of the platinum–methyl bonds was favored by good nucleophiles. Thus, the addition of KCN to an aqueous solution of 2 resulted in formation of the monomethyl complexes K[PtMe(CN)2(NHC·Na)] (9), whereas the dimethyl complexes K[PtMe2(CNR)(NHC·Na)] (10) were formed with the isocyanide CNCH2COOK. The addition of stoichiometric amounts of protic acids to aqueous solutions of 2 resulted in the clean cleavage of one or both platinum(II)–methyl bonds. Thus, the reaction of 2 with HCl afforded the complexes [PtClMe(dmso)(NHC·Na)] (3) and [PtCl2(dmso)(NHC·Na)] (4), whereas [PtMe(OH2)(dmso)(NHC)] (5) and [Pt(OH2)2(dmso)(NHC)][BF4] (7) were obtained upon treatment with HBF4. The crystal structure of 9a is remarkable in light of the longitudinal channels around 6 Å in diameter internally decorated with Pt–Me bonds.

Direct arylation of C(sp3)-H bonds in aliphatic amides with diaryliodonium salts in the presence of a nickel catalyst.

The Ni(II)-catalyzed direct arylation of C(sp(3))-H (methyl and methylene) bonds in aliphatic amides containing an 8-aminoquinoline moiety as the directing group with diaryliodonium salts as coupling electrophiles is described. A wide variety of functional groups are tolerated in the reaction. The reaction represents the first example of the Ni-catalyzed direct arylation of C(sp(3))-H bonds with diaryliodonium salts.

Influence of porosity and methyl doping inside silica network: An electron diffraction and DFTB analysis

The continuous scaling of transistor size towards deep submicron level demands an inevitable replacement of SiO2 with a low-k dielectric material. Doping of methyl groups in SiO2 network reduces the dielectric constant by replacing oxygen atoms bonded with silicon and creating a lower polarizable silicon methyl bond in the network. Further reduction in dielectric constant is possible by introducing porosity in the dense low-k network. The detailed knowledge about atomic structure of such low-k materials is a must for understanding their electronic and optical properties. In this study, electron diffraction and (density functional based tight binding) DFTB calculations are used to investigate the structure of dense and porous low-k dielectric materials. The radial distribution function (RDF) obtained from electron diffraction technique contains information about the short-range order present in the material. Bond lengths and bond angles determined from RDF indicate a significant modification occurring in the SiO2 network after doping with methyl groups. The local density of the materials is also derived from radial distribution function. It depends on the number and distances of nearest neighbors and was found to be decreased in these low-k materials compared with amorphous SiO2.

ChemInform Abstract: Nickel‐Catalyzed Direct Arylation of C(sp3)—H Bonds in Aliphatic Amides via Bidentate‐Chelation Assistance.

The Ni-catalyzed, direct arylation of C(sp3)–H (methyl and methylene) bonds in aliphatic amides containing an 8-aminoquinoline moiety as a bidentate directing group with aryl halides is described. Deuterium-labeling experiments indicate that the C–H bond cleavage step is fast and reversible. Various nickel complexes including both Ni(II) and Ni(0) show a high catalytic activity. The results of a series of mechanistic experiments indicate that the catalytic reaction does not proceed through a Ni(0)/Ni(II) catalytic cycle, but probably through a Ni(II)/Ni(IV) catalytic cycle.

The effects of solvents on the chemical decomposition of foamed phenol resin in high-temperature conditions

In this study, thermosetting resin such as foamed phenol resin (FPR) powder was solubilized and decomposed into their monomeric and oligomeric compounds in high temperature fluids. Solvents play important roles as stable physical medium at high temperature and reactive chemical reagents to accelerate decomposition reaction of the thermosetting resin. The decomposition of FPR into their monomers occurred by cleaving methylene bond of the resin selectively via the ionic reaction. The effects of solvent which has a hydroxyl group and methylene carbon atoms (high affinity with FPR) on the solubilization of FPR were confirmed by the reaction in high-temperature m-cresol and straight-chain alcohols. More than 90 % of FPR was solubilized in the reaction in m-cresol and 1-heptanol at 350 °C for 2 h suggesting the presence of the solubilization route other than methylene chain scission.

Performances of larch (larix gmelini) tannin modified urea–formaldehyde (TUF) resin and plywood bonded by TUF resin

ABSTRACTTannin from larch (Larix gmelini) bark extracts, as a natural renewable resource, was used to prepare tannin–urea–formaldehyde (TUF) resin. The chemical structures of larch tannin and TUF resin were characterized by matrix‐assisted laser desorption/ionization‐time of flight mass spectrometry and 13C nuclear magnetic resonance. The thermal behaviors of TUF resin were evaluated by differential scanning calorimetry (DSC) and thermomechanical analysis (TMA). The performances of TUF resin were investigated by measuring the bond strength and formaldehyde emission of its bonded plywood. It was clearly shown that larch tannin is mainly composed of prodelphinidin repeating units. Phenolic groups were introduced into TUF resin mainly linked by methylene bond. Larch tannin has an adverse effect on the resin curing. However, it promoted the rigidity and flexibility of the glued system and upgraded the properties of plywood. Therefore, larch tannin could be applied in the modification of urea–formaldehyde resin. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41064.

Effect of formaldehyde/phenol ratio (F/P) on the properties of phenolic resins and foams synthesized at room temperature

Six types of phenolic foaming resins were synthesized at room temperature with different formaldehyde/phenol (F/P) ratios in this study. The effects of F/P ratios on physicochemical characteristics and foaming properties of the resulting resins were analyzed based on viscosity, solids content, hydroxymethyl index, residual monomer content, molecular structure of the foaming resin, flame retardancy, and foam compression strength measurements. The results of the present study indicated that viscosity and solids content of the foaming resins increased with an increase in F/P; the hydroxymethyl index of the resin first increased and then decreased with an increase in F/P, reaching its maximum at F/P = 1.6; the trimer, tetramer, and pentamer contents of the resins increased with an increase in F/P. Nuclear magnetic resonance (13C NMR) spectral analysis indicated that the presence of para/para‐methylene, para‐hydroxymethyl, and ortho‐hydroxymethyl groups in the resin gradually increased with an increase in F/P; the proportions of ortho/ortho‐ and ortho/para‐methylene bonds of the resin increased as F/P was increased. The increase in F/P was demonstrated to be conducive to improving the compression strength, thermal stability, and flame retardancy of the phenolic foam and reducing its peak heat release rate and total smoke release. The morphology of phenolic foams show that the closed cell content in the PF foam increases with the F/P ratio until it reaches a ratio of 1.6. Furthermore, the cell size becomes more uniform. POLYM. COMPOS., 36:1531–1540, 2015. © 2014 Society of Plastics Engineers

ChemInform Abstract: Chemoselective Oxidative C(CO)—C(Methyl) Bond Cleavage of Methyl Ketones to Aldehydes Catalyzed by CuI with Molecular Oxygen.

AbstractA wide range of aromatic methyl ketones as well as aliphatic methyl ketones are subjected to the copper‐catalyzed oxidative cleavage of the C(CO)‐C(CH3) bond to yield the corresponding aldehydes.The oxidation terminates at the aldehyde stage and can be considered as an unprecedented dehydrogenation of saturated aliphatics.