Methyl Isobutyrate Research Articles

Photoaddition Reactions of Silyl Ketene Acetals with Aromatic Carbonyl Compounds: A New Procedure for β‐Hydroxyester Synthesis.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Active control of site specificity in ion desorption by core excitation

Active control of site-specific photon stimulated ion desorption (PSID) following core excitation was examined by changing the molecular environment and the direction of the electric field vector of the incidence light in the three different molecular systems, poly-methylmethacrylate (PMMA) thin film, methyl ester terminated self-assembled monolayer (MHDA-SAM), and condensed methyl isobutyrate (MIB) molecule. In PMMA and MHDA-SAM, the site-selective resonant excitation causes site-specific PSID, and the site specificity of MHDA-SAM is more enhanced than that of PMMA, while there is no specific desorption in MIB. These variations were explained with the change of molecular environment. Moreover, PSID of CH n + ( n=1–3) ions observed at the σ *(O–CH 3)←C1s(OCH 3) excitation of MHDA-SAM exhibits significant dependence on the incidence angle of the light.

Photoaddition Reactions of Silyl Ketene Acetals with Aromatic Carbonyl Compounds: A New Procedure for ?-Hydroxyester Synthesis

Photochemical reactions of aromatic carbonyl compounds with silyl ketene acetals have been explored. Irradiation of acetonitrile or benzene solutions containing aryl aldehydes or ketones in the presence of silyl ketene acetals is observed to promo te formation of <TEX>${\beta}-hydroxyester$</TEX>, 2,2-dioxyoxetane and 3,3-dioxyoxetane products. The ratios of these photoproducts, which arise by competitive single electron transfer (SET) and classical Paterno-Buchi mechanistic pathways, is found to be dependent on the degree of methyl-substitution on the vinyl moieties of the ketene acetals in a manner which reflects expected alkyl substituent effects on the oxidation potentials of these electron rich donors. An analysis of the product distribution arising by irradiation of a solution containing butyrophenone (6) and the silyl ketene acetal 9, derived from methyl isobutyrate, provides an estimate of the rate constants for the competitive Norrish type Ⅱ, SET and Paterno-Buchi processes occuring. Finally, sequences involving silyl ketene acetal-aryl aldehyde or ketone photoaddition followed by 2,2-dioxyoxetane hydrolysis represent useful procedures for Claisen-condensation type, <TEX>${\beta}-hydroxyester$</TEX> synthesis.

Homogeneous oxidation of methyl isobutyrate with oxygen catalysed by metal complexes: polyoxometalates versus metalloporphyrins and metallophthalocyanines

Two types of homogeneous oxidation of methyl isobutyrate (MIB) with O 2 catalysed by transition metal complexes aiming at methyl α-hydroxyisobutyrate (MHIB) have been studied: (1) low-temperature (30–50 °C, 1 bar O 2) co-oxidation with isobutyraldehyde (IBA); (2) high-temperature (100–140 °C, 10 bar O 2) direct oxidation. As the catalysts, Keggin-type polyoxometalates (PMo 12− n V n O 40; n=1–3) and (PW 11MO 39; M=Ni(II), Co(II), Cu(II), Fe(III), and Ru(III)) as well as metalloporphyrins and metallophthalocyanines of Co(II), Ni(II), Cu(II), Fe(II, III), Mn(III), and Ru(III) have been used. The complexes of Fe(II, III), Co(II), and Ru(III) have been found to be the most active catalysts. The co-oxidation occurs with a fairly good efficiency, allowing up to 0.55 mol MIB to be converted per 1 mol IBA reacted at 50 °C and a molar ratio [MIB]:[IBA]=5:1. About a half of IBA is non-productively consumed to isobutyric acid (IBAcid; up to 95% yield) and acetone. MIB appears to be mainly converted to methyl α-hydroperoxyisobutyrate (MHPIB), the maximum selectivity to MHIB being only 15%. The high-temperature direct oxidation of MIB is found to be more efficient providing 24% selectivity to MHIB at 19% MIB conversion (120 °C). The drawback to this route is the formation of a large amount of IBAcid (39–59% selectivity) and acetone (25–46%). All three types of complexes studied perform quite similarly as the catalysts for these reactions. The important result is that in the low-temperature co-oxidation, the complexes with organic ligands (porphyrins and phthalocyanines) are more active than the corresponding polyoxometalates, whereas the opposite is observed in the high-temperature oxidation. This is in agreement with the views on polyoxometalates as robust, oxidation-resistant analogs of metal complexes with macrocyclic ligands.

DFT study of the effect of sigma-ligands on the structure of ester enolates in THF, as models of the active center in the anionic polymerization of methyl methacrylate.

A Density Functional Theory (DFT) study was carried out on structures of the lithium ester enolate of methyl isobutyrate (MIB-Li) in THF solution, in the presence of TMEDA, dimethoxyethane (DME), crown ether 12-crown-4, and cryptand-2,1,1, as electron donor ligands (sigma-ligands). Both specific solvation with THF and/or ligand molecules and nonspecific solvation by the solvent continuum were taken into account. The possibility of ligand-separated ion pair formation was analyzed for each of the ligands, including THF alone. In most cases peripherally solvated dimers are the most stable species. Only in the presence of cryptand-2,1,1 was a ligand-separated triple ion pair, (MIB-Li-MIB)(-)(THF)(2),Li(2,1,1)(1)(+), shown to be comparable in stability to the THF-solvated dimer, (MIB-Li)(2)(THF)(4). These results are in agreement with experimental NMR data on the structure of MIB-Li in the presence of DME, 12-crown-4, and cryptand-2,1,1. An upfield shift of the (13)C NMR signal of the alpha-carbon of MIB-Li observed in the presence of cryptand-2,1,1, originally attributed to a ligand-separated monomer, MIB(-),Li(2,1,1)(+), was well reproduced by Hartree--Fock calculated NMR shifts for the predicted ligand-separated triple ion pair.

Mechanism of ion desorption reaction of PMMA thin film induced by core excitation

Abstract Auger electron spectra of PMMA (poly-methylmethacrylate) which show remarkable site-specific ion desorption are calculated using ab initio molecular orbital (MO) calculation and compared with the results of Auger electron-photoion coincidence experiments. Methyl isobutyrate and its trimer are used as model molecules of PMMA. The calculation is based on the single configuration state function and limited configuration interaction methods, and Auger transition probabilities are estimated by overlap between core and valence MOs. The calculated normal Auger spectra obtained on specific atoms reproduce well the experimental resonant Auger spectra for both the carbon and oxygen sites. The careful analysis of the calculated Auger spectra indicates that the desorption of CHn+ ions is strongly concerned with the Auger final states which have holes in the O–CH3 bonding orbitals.

Styrene/potassium persulfate/water systems: effects of hydrophilic comonomers and solvent additives on the nucleation mechanism and the particle size

Emulsifier-free emulsion polymerizations based on styrene/potassium persulfate/water (St/kps/H 2O) in the presence of a relatively hydrophilic comonomer, such as vinyl acetate (VAc) or methyl methacrylate (MMA), or the nonpolar solvent, such as ethyl acetate (EAc) or methyl isobutyrate (MIB) having structural similarity with VAc and MMA respectively, or the polar solvent such as glycerin or acetone etc., have been carried out. From the gel permeation chromatograph (GPC) analysis of polymers obtained in the presence of VAc or MMA comonomer, or even MIB or EAc nonpolar solvent, the presence of oligomers having the molecule weight of 1000 at the early stage of polymerization suggests a micellar nucleation mechanism. From the study for effects of additives on the rate of polymerization, we found that all curves for the conversion versus time showed concave upward at about the conversion of 45% but level off at about 80%. Moreover, when the polar or nonpolar solvent was used as an additive, a controllable particle size of monodisperse microspheres with the ranges 270–750 nm could be expected. Besides, the particle size of monodisperse microspheres was decreased with increasing of the addition amount of the polar solvent. Monosize polystyrene microspheres with smaller particle sizes can be obtained by adding of the polar solvent; on contrary, microspheres with larger particle sizes can be generated by a limited addition amount of the nonpolar solvent.

Penetrant diffusion in poly(methyl methacrylate) near Tg: dependence on temperature and polymer weight fraction

Forced Rayleigh scattering was employed to measure diffusion coefficients for a ternary system comprising camphorquinone or diacetyl in poly(methyl methacrylate) with methyl isobutyrate as the diluent. Measurements were made at polymer weight fractions, w p, over the range 0.78–0.90 and temperature 25–50°C for camphorquinone (which spans the glass transition regime), and at w p=0.9 and 0.95 and at room temperature for diacetyl. Results for camphorquinone show a strong temperature dependence, with diffusion coefficients changing as much as two orders of magnitude between 25 and 50°C, and showing high activation energies for diffusion≈125 kJ mol −1. No sharp change in the activation energy for diffusion was observed as the glass transition is crossed. The pre-exponential factor for the diffusion coefficient decreased dramatically through the glass transition. The diffusion coefficients of small penetrants in glassy polymers appear strongly dependent on the molecular size.

EXCESS MOLAR ENTHALPIES OF THE TERNARY SYSTEMS (ACETONITRILE+METHYL ISOBUTYRATE +TOLUENE) AND (PROPIONITRILE+METHYL ISOBUTYRATE+ETHYLBENZENE) AT 298.15 K

Excess molar enthalpies were measured at 298.15 K with a flow calorimeter built in our laboratory for the two ternary systems (acetonitrile+methyl isobutyrate+toluene) and (propionitrile+methylisobutyrate+ethylbenzene). Experimental data were nicely predicted by some empirical andsemi empirical procedures, exception made for UNIFAC group contribution method. The latter equation proved unsatisfactory for all mixtures containing methyl isobutyrate. The first ternary set proved a good model system to simulate mixing enthalpies reported in the literature for mixtures of poly(styrene-co-acrylonitrile) with polymethylmethacrylate.

Intramolecular homolytic displacements. Part 29: induced decompositions of 4,5-ethylenic peroxyketals

Thermolysis of a free radical initiator in solutions of hydrogen donor solvents such as cyclohexane, 1,4-dioxane and methyl isobutyrate, generated radicals by hydrogen abstraction of the solvent that were capable of adding to the unsaturated bond of 4,5-ethylenic peroxyketals. The adduct radical obtained led to 2-alkoxytetrahydrofuran by an SHi on the O–O bond.

Gas phase reactions of VO + with methyl methacrylates as studied by fourier transform ion cyclotron resonance mass spectrometry

Direct laser ablation of pressed vanadium pentoxide (V 2O 5) powder in the reaction cell of a Fourier transform ion cyclotron resonance (FTICR) mass spectrometer produces VO + as the only reproducible cation. This ion was reacted with methyl isobutyrate, methyl methacrylate, and methyl methacrylate dimer. Gas phase ion/molecule chemistry reveals that the complexity of the product distribution increases with the number of electron rich sites on the reagent molecule. Two sets of ion products are observed: (a) protonated reagent molecule and its corresponding stable fragment, formed by loss of CH 4O, and (b) products containing VO, formed by addition of whole reagent molecules and associated fragments. Products formed are a result of both consecutive and parallel reactions. Collision-induced dissociation (CID) experiments reveal that VO-whole molecule bonds are of a noncovalent nature.

Measurements of Primary Radical Concentrations Generated by Pulsed Laser Photolysis Using Fluorescence Detection

Details of a novel technique for direct real-time measurement of the primary radical concentrations generated in pulsed laser photolysis (PLP) experiments are presented. The method takes advantage of the large increase in fluorescence quantum yield that occurs when a nitroxide containing a suitable fluorophore couples with a carbon-centered radical. The technique is applied to PLP experiments which involve photolysis of azobisisobutyronitrile (AIBN) or azobis(methyl isobutyrate) (AIBMe) in the presence of 4-(1-naphthoyloxy)-2,2,6,6-tetramethylpiperidine-1-oxyl (NTEMPO). In these experiments, the method is shown to be capable of reliably measuring transient radical concentrations of less than 10-7 M. Various side reactions that might complicate the technique are considered and shown not to be of significance. The concentration of radicals generated per pulse is shown to have a linear dependence on [AIBN], [AIBMe], and laser energy per pulse (and is shown to be independent of [NTEMPO]) over a wide range of ...

Plasma dissociation reaction kinetics. II. Precursors related to methyl methacrylate: Methyl crotonate, methyl isobutyrate, ethyl methacrylate, and vinyl acetate

The methodology described in the previous article was utilized to study the plasma chemistry of precursors related to methyl methacrylate (MMA). This article discusses the plasma chemistry of methyl crotonate (MC), methyl isobutyrate (MIB), ethyl methacrylate (EMA), vinyl acetate (VA), isopropanol (IA), and methanol. The monomer structure was found to have strong effects on the dissociation chemistry and product formation. For α,β-unsaturated esters and VA, intramolecular rearrangement (the C—O bond cleavage reaction) and decarboxylations are two efficient dissociation pathways. The intramolecular rearrangement reaction yields a pair of ketene and aldehyde neutrals. Decarboxylations produce CO, CO2, and a number of radicals that subsequently stabilize to form neutrals. For example, the secondary propyl radicals generated from MMA and EMA decarboxylations form propylene and allene neutrals while the primary propyl radicals generated from MC decarboxylations form propylene and acetylene. The other monomers studied, such as MIB and IA, cannot dissociate via this intramolecular rearrangement mechanism. As a result, they decompose much slower in the plasma. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 17–27, 1999

Vanadium oxide anion cluster reactions with methyl isobutyrate and methyl methacrylate monomer and dimer: a study by FT/ICR mass spectrometry

Laser ablation of vanadium pentoxide (V 2O 5) powder produces VO 3 −, V 2O 5 −, V 3O 7 −, V 3O 8 −, and V 4O 10 − cluster ions which have subsequently been reacted with methyl isobutyrate, methyl methacrylate monomer and its dimer in the ion cell region of a Fourier transform ion cyclotron resonance mass spectrometer. Gas phase ion/molecule chemistry has revealed that reactivity decreases with increased mass of the vanadium oxide cluster anions. VO 3 −, V 2O 5 −, and V 3O 7 − ions react with the three reagents, methyl isobutyrate, methyl methacrylate and its dimer, respectively, either by addition of a whole reagent molecule or an associated fragment. All products formed are a result of parallel processes. V 4O 10 − undergoes no reaction for reaction times of up to 500 s, while V 3O 8 − adds a water molecule. Although the ions possess a net negative charge, the reactive site toward electron rich reagents such as methyl isobutyrate, methyl methacrylate and its dimer is the under-coordinated vanadium atom. This observation is supported by the lack of reactivity toward the studied reagents by those anions (V 3O 8 − and V 4O 10 −) whose most likely stable structures contain fully coordinated vanadium atoms.

The hydroxyl radical reaction rate constant and products of methyl isobutyrate

The relative rate technique has been used to measure the rate coefficient for the reaction of the hydroxyl radical (OH) with methyl isobutyrate (MIB, (CH3)2 CHC(O)OCH3) to be (1.7 ± 0.4) × 10−12cm3molecule−1s−1 at 297 ± 3 K and 1 atmosphere total pressure. To more clearly define MIB's atmospheric degradation mechanism, the products of the OH + MIB reaction were also determined. The observed products and their yields were: acetone (97 ± 1%, (CH3)2C(O)) and methyl pyruvate (MP, 3.3 ± 0.3%, CH3C(O)C(O)OCH3). The products' formation pathways are discussed in light of current understanding of the atmospheric chemistry of oxygenated organic compounds. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 551–557, 1999

The hydroxyl radical reaction rate constant and products of methyl isobutyrate

The relative rate technique has been used to measure the rate coefficient for the reaction of the hydroxyl radical (OH) with methyl isobutyrate (MIB, (CH3)2 CHC(O)OCH3) to be (1.7 ± 0.4) × 10−12cm3molecule−1s−1 at 297 ± 3 K and 1 atmosphere total pressure. To more clearly define MIB's atmospheric degradation mechanism, the products of the OH + MIB reaction were also determined. The observed products and their yields were: acetone (97 ± 1%, (CH3)2C(O)) and methyl pyruvate (MP, 3.3 ± 0.3%, CH3C(O)C(O)OCH3). The products' formation pathways are discussed in light of current understanding of the atmospheric chemistry of oxygenated organic compounds. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 551–557, 1999

Measurement of Diffusion Coefficients of Oligomeric Penetrants in Rubbery Polymer Matrixes

The diffusion coefficients of oligomeric radicals in monomer-polymer systems have a major influence on properties such as polymerization rates and molecular weight distributions. The present work reports the results of an extensive set of studies of diffusion coefficients of rubbery ternary systems comprising polymer, diluent, and oligomer, determined by pulsed-field-gradient NMR, at 25 and 40 degrees C. Oligomers of methyl methacrylate (MMA) and of butyl methacrylate (BMA) were synthesized by using a catalytic cobalt chain transfer agent to produce macromonomers with a terminal double bond. Where necessary, these were fractionated by preparative GPC to obtain samples ranging from dimeric to decameric; typical polydispersities were 1.08. Pulsed-field gradient NMR is facilitated by being able to monitor the proton NMR of the CH2 hydrogens on the double bond. Matrixes used were high molecular weight polyMMA and polyBMA, the weight fraction of polymer (w(p)) being varied by adding appropriate amounts of diluent (the saturated equivalents of MMA and BMA, viz., methyl isobutyrate and butyl isobutyrate). Above c* (the concentration at which chains start to overlap), all data for diffusion coefficients Di of an oligomer of degree of polymerization i could be fitted with acceptable accuracy by D-1(w(p))/D-i(w(p)) = i(0.664+2.02wp), for both BMA and MMA oligomers in both MMA and BMA matrixes; the same relation also fits earlier data on styrene oligomers in polystyrene. If more accurate scaling parameters are obtained experimentally for smaller oligomers, these can be used to predict data for higher oligomers with even better reliability. For MMA monomer in pMMA, where free-volume parameters are available, the predicted dependences of monomer diffusion coefficient on w(p) and temperature are in accord with experiment.

Comparison of Volatile Compounds from Chungkuk-Jang and Itohiki-Natto.

Volatile compounds from two South-East Asian fermented soybean foods, Chungkuk-jang (CKJ) and Itohiki-natto (natto), were analysed by gas chromatography-mass spectrometry (GC-MS), gas chromatography (GC), and GC-sniffing. A total of 112 compounds were identified. A large amount of ethanol was detected from CKJ, while acetone and methyl isobutyrate were major components of natto. The characteristic odor compounds of CKJ were some ethyl esters of short chain fatty acids, diallyl disulfide, and several natto-like odor compounds were identified as ammonia, 2,5-dimethylpyrazine, and 2-methylbutanoic acid.

Mean-Square Electric Dipole Moment of Oligo- and Poly(methyl methacrylate)s in Dilute Solution

The mean-square electric dipole moment 〈μ2〉 was determined for 12 samples of atactic (a-) oligo- and poly(methyl methacrylate)s (PMMA), each with the fraction of racemic diads fr = 0.79, in the range of the weight-average degree of polymerization xw from 3 to 1.19 × 103 and for 11 samples of isotactic (i-) PMMA and its oligomers, each with fr ≃ 0.01, in the range of xw from 3 to 5.88 × 102, both in benzene at 30.0 °C. The determination was also made for a syndiotactic (s-) PMMA sample with fr = 0.92 and xw = 3.76 × 102 and for methyl isobutyrate in the same solvent condition. For both a- and i-PMMAs, the ratio 〈μ2〉/xw as a function of xw decreases monotonically with increasing xw for xw ≲ 20 and then approaches its asymptotic value (〈μ2〉/xw)∞, i.e., 1.927 and 2.126 D2 for a- and i-PMMAs, respectively, indicating that the excluded-volume effect on 〈μ2〉 is negligibly small if any. From a comparison of these values of (〈μ2〉/xw)∞ along with that of 〈μ2〉/xw obtained for the s-PMMA sample, it is found that (〈μ2...

Comparison of chemical analysis of residual monomer in a chemical-cured dental acrylic material to an FTIR method

Objective The purpose of this work was to perform quantitative analysis of residual monomer in chemical-cured acrylic using an infrared spectroscopic method and to compare it to an accepted form of quantitative chemical analysis. Identical samples of acrylic were analyzed and compared using Fourier transform infrared (FTIR) spectroscopy with multiple standard additions vs. “wet” chemical analysis of bromination followed by titration. Methods Two 6 g disks from a single mix of cold-cured acrylic (Lang Dental Mfg. Co., Inc.) were prepared and cured in room air for 1 hr using a ratio of 12 g of powder to 8 mL of liquid. One of the cold-cured acrylic disks was dissolved in glacial acetic acid and analyzed according to the “wet” technique described by Smith and Bains (Smith and Bains,1956). The other disk was dissolved in methyl isobutyrate (MIBT). Five aliquots, zero plus four incremental additions of pure methyl methacrylate (MMA), were prepared from the MIBT solution. Absorption spectra were collected for all five aliquots. The data were plotted with the ratio of the mass of methyl methacrylate added to the mass of aliquot of MIBT solution as the independent variable, and the absorption, corrected for dilution, as the dependent variable. Least squares fit of the data yielded the slope and intercept. The ratio of intercept to slope divided by the weight fraction of the acrylic disk dissolved in MIBT yielded the concentration of methyl methacrylate in the disk. Results The plot of absorbance as a function of mass ratio of MMA added to MIBT solution was linear over the concentration range covered (r = 0.999). Analysis of the spectroscopic data revealed a concentration of residual C=C double bonds of 0.32 ± 0.01 mol/kg. “Wet” chemical analysis of the acrylic yielded a concentration of residual C=C double bonds of 0.288 ± 0.003 mol/kg. There was significant difference (students Mest, 99% confidence level) between the two techniques with respect to the amount of residual monomer calculated. Significance The multiple standard additions technique works well for the quantitative analysis of small amounts of residual double bonds in the poly(methyl methacrylate) chemical-cured acrylic polymer system, eliminating the need for an internal standard or external calibration.