Alkyl Methyl Research Articles

Molecular Energetics of Alkyl Pyrrolecarboxylates: Calorimetric and Computational Study

The pyrrole subunit plays an important role in material science as the building block of polypyrroles, an important representative class of conducting polymers, which found widely applications in the area of new materials due to their chemical, thermal, and electrical properties associated with their easiness and low cost of production, making them especially promising for commercial applications. The energetic characterization of this kind of molecules provides information concerning stability, reactivity, and biodegrability of chemical compounds in environment being, for example, helpful in choosing the most adequate method for their elimination by converting the waste into harmless compounds or even decreasing the production of toxic substances in industrial processes. This work reports a combination of calorimetric and computational determinations of several alkyl pyrrolecarboxylates (alkyl = methyl or ethyl) whose main purpose is the calculation of their standard (p° = 0.1 MPa) molar enthalpies of formation, in the gaseous phase, at T = 298.15 K. Experimentally, for methyl 1-pyrrolecarboxylate (M1PC), methyl 2-pyrrolecarboxylate (M2PC), and ethyl 2-pyrrolecarboxylate (E2PC), these values were derived from the standard (p° = 0.1 MPa) molar enthalpies of formation, in the condensed phase, ΔfHm° (cr,l), at T = 298.15 K, obtained by static bomb combustion calorimetry, and from the standard molar enthalpies of phase transition, Δcr,l(g)Hm°, at T = 298.15 K, determined by high-temperature Calvet microcalorimetry. Standard ab initio molecular calculations, at the G3(MP2)//B3LYP level, were performed, and the standard enthalpies of formation of these three compounds were estimated. A very good agreement between the calculated and the experimental data was obtained. Thereby, we have extended these calculations to other alkyl pyrrolecarboxylates, namely, ethyl 1-pyrrolecarboxylate (E1PC), methyl 3-pyrrolecarboxylate (M3PC), and ethyl 3-pyrrolecarboxylate (E3PC), whose study was not performed experimentally. The computational analysis, at the B3LYP/6-31G(d) level of theory, of the six molecules allowed a detailed inspection and a better knowledge about their molecular structure and geometrical parameters.

Reaction Pathways for the Thermal Decomposition of Methyl Butanoate

In recent years, biodiesel fuels, consisting of long-chain alkyl (methyl, ethyl, propyl) esters, have emerged as viable alternatives to petroleum-based fuels. From a combustion chemistry standpoint, there is great interest in developing accurate reaction models for these new molecules that can be used to predict their behaviors in various regimes. In this paper, we report a detailed study of the unimolecular decomposition pathways of methyl butanoate (MB), a short-chain ester that contains the basic chemical structure of biodiesel fuels. Using ab initio/DFT methods, we identified five homolytic fissions of C-C and C-O bonds and five hydrogen transfer reactions. Rate constants were determined using the G3B3 theory coupled with both variational transition state theory and Rice-Ramsperger-Kassel-Marcus/master equation simulations with hindered rotation corrections. Branching ratios in the temperature range 1500-2200 K indicate that the main pathway for thermal decomposition of MB is the reaction CH3CH2CH2C(═O)OCH3 → C2H5 + CH2C(═O)OCH3. The results, in terms of reaction pathways and rate constants, can be used for future development of mechanisms for long alkyl-chain esters.

Synthesis and antibacterial activity of 4,4′-(aryl or alkyl methylene)-bis(1H-pyrazol-5-ol) derivatives

A rapid, improved, and environmentally benign synthesis of 4,4′-aryl or alkyl methylene-bis(1H-pyrazol-5-ols) has been accomplished by tandem Knoevenagel–Michael reaction of 1-aryl-3-alkyl-1H-pyrazol-5-ol with various aldehydes catalyzed by ammonium acetate. All the synthesized compounds 3a–v were evaluated in vitro for their antibacterial activity against Pseudomonas aeruginosa, Xanthomonas protophormiae, Bacillus licheniformis, and Staphylococcus aureus. Among the tested compounds, compounds with trifluromethyl group show excellent antibacterial activity.

Study of Biodiesel Production from Sunflower Oil Using Non Usual Basic Polymeric Resin as Catalyst

Biodiesel is defined as a long-chain mono alkyl (methyl, ethyl or propyl) ester of fatty acids obtained from renewable sources by transesterification reaction using an acid or base. In this work, a basic resin, Amberlyst A26, was used to produce methyl sunflower biodiesel. The iodine value, corrosion to copper, oxidative stability, specific mass, water content, acid value, cloud point and ester composition were evaluated. The heterogeneous catalyst was also characterized to verify its efficiency and its ability to be reused. We used the following analytical techniques: scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-rays fluorescence (XRF) and differential scanning calorimetry (DSC). The results showed that the characteristics of biodiesel made from sunflower oil using resin A26 as a catalyst are in accordance with Brazilian biodiesel regulations, except the oxidative stability. The techniques used to characterize the resin showed that it is possible to reuse the resin after regeneration.

On the mechanism of activation of copper-catalyzed atom transfer radical polymerization

The mechanism of activation of atom transfer radical polymerization (ATRP) has been analyzed by investigating the kinetics of dissociative electron transfer (ET) to alkyl halides (RX) in acetonitrile. Using a series of alkyl halides, including both bromides and chlorides, the rate constants of ET (kET) to RX by electrogenerated aromatic radical anions (A−) acting as outer-sphere donors have been measured and analyzed according to the current theories of dissociative ET. This has shown that the kinetic data fit very well the “sticky” dissociative ET model with the formation of a weak adduct held together by electrostatic interactions. The rate constants of activation, kact, of some alkyl halides, namely chloroacetonitrile, methyl 2-bromopropionate and ethyl chloroacetate, by [CuIL]+ (L=tris(2-dimethylaminoethyl)amine, tris(2-pyridylmethyl)amine, 1,1,4,7,7-pentamethyldiethylenetriamine) have also been measured in the same experimental conditions. Comparisons of the measured kact values with those predicted assuming an outer-sphere ET for the complexes have shown that activation by Cu(I) is 7–10 orders of magnitude faster than required by outer-sphere ET. Therefore, the mechanism of RX activation by Cu(I) complexes used as catalysts in ATRP occurs by an inner-sphere ET or more appropriately by a halogen atom abstraction.

Reversible-Deactivation Radical Polymerization in the Presence of Metallic Copper. Activation of Alkyl Halides by Cu0

The rate coefficients for activation (ka0app) of two alkyl halides, methyl 2-bromopropionate, MBrP, and Br-capped poly(methyl acrylate), by Cu0 were determined under various conditions. The value of ka0app was studied in two solvents, dimethyl sulfoxide (DMSO) and acetonitrile (MeCN), and their mixtures with methyl acrylate (MA), using tris[2-(dimethylamino)ethyl]amine (Me6TREN) and tris(2-pyridylmethyl)amine (TPMA) as ligands. The experiments showed that the rate of activation increased with the surface area of Cu0 but was typically not affected by the ratio of ligand to initiator, if a sufficient amount of ligand was present. The choice of solvent and presence of monomer/polymer had a small influence on ka0app. The activation rate coefficient of MBrP was ka0app= 1.8 × 10–4 cm s–1 with Me6TREN as the ligand in DMSO at 25 °C while the activation rate coefficient of Br-capped poly(methyl acrylate) by Cu0 was slightly lower, ka0app = 1.0 × 10–4 cm s–1, as measured in a polymerization of MA in MA/DMSO = 1/1 ...

ChemInform Abstract: Birch Reductive Alkylation of Methyl m‐(Hydroxymethyl)benzoate Derivatives and the Behavior of o‐ and p‐(Hydroxymethyl)benzoates under Reductive Alkylation Conditions.

AbstractTitle reaction of methyl m‐(hydroxymethyl)benzoate derivatives using lithium in ammonia/THF in the presence of tert‐butyl alcohol, is achieved without loss of benzylic oxygen substituents.

ChemInform Abstract: Bismuth‐Catalyzed Addition of Silyl Nucleophiles to Carbonyl Compounds and Imines

AbstractReview: 159 refs.

Palladium-Catalyzed Direct α-Arylation of Methyl Sulfones with Aryl Bromides

A direct and efficient approach for palladium-catalyzed arylation of aryl and alkyl methyl sulfones with aryl bromides has been developed. The catalytic system affords arylated sulfones in good to excellent yields (73-90%).

ChemInform Abstract: Iridium‐Catalyzed Enantioselective Allylic Alkylation of Methyl 2‐(4‐Nitrophenylsulfonyl)acetate and Subsequent Transformations.

AbstractThe reaction of 4‐nosylacetate with allyl carbonates proceeds with poor diastereoselectivity and epimerization at the α‐position of the carbonyl group.

An efficient metal-free synthesis of organic disulfides from thiocyanates using poly-ionic resin hydroxide in aqueous medium

An efficient and metal-free method is described for the preparation of organic disulfides from alkyl and acyl methyl thiocyanates in the presence of poly-ionic resin hydroxide in aqueous medium. Further extension of this protocol has been tested using two different organyl thiocyanates to prepare unsymmetrical disulfides.

Palladium-Catalyzed Direct Arylation of Methyl Sulfoxides with Aryl Halides

The palladium-catalyzed α-arylation of unactivated sulfoxides has been developed. The weakly acidic α-protons of sulfoxides are reversibly deprotonated by LiOtBu, and a palladium phosphine complex facilitates the arylation. A variety of aryl methyl sulfoxides were coupled with aryl bromides. More challenging coupling partners, such as alkyl methyl sulfoxides (including dimethyl sulfoxide) and aryl chlorides proved to be suitable under the optimized conditions. This method was utilized to synthesize bioactive benzyl sulfoxide intermediates.

Stereoselective Synthesis of Multiple Stereocenters by Using a Double Aldol Reaction

The reaction of alkyl methyl ketones with aromatic aldehydes under the conditions shown affords dihydroxyketones with high stereoselectivity.

Stereoselective Synthesis of Multiple Stereocenters by Using a Double Aldol Reaction

Triple play: The title reaction of an alkyl methyl ketone and two aldehydes using chiral (S)-binapo as a Lewis base catalyst allows access to 1,5-dihydroxy-3-pentanone derivatives with multiple chiral centers in good yields with high diastereo- and enantioselectivities in a single operation (see scheme).

Discovery of an iridacycle catalyst with improved reactivity and enantioselectivity in the hydrogenation of dialkyl ketimines

Catalytically active iridacycles are formed by cyclometalation of acetophenone imines with Ir–PHOX complexes under hydrogen atmosphere. These complexes show unusually high reactivity and enantioselectivity in the hydrogenation of alkyl methyl ketimines. The structure of the cyclometalated imine has a strong effect on the conversion and enantiomeric excess.

Ion-selective electrodes with solid contact for heavy metals determination

Potentiometric properties of ion-selective electrodes with solid contact for lead, cadmium and zinc determination were investigated. The ionic liquids (ILs) alkyl methyl imidazolium chlorides are used as lipophilic ionic additive to the membrane phase and as transducer media. The basic analytical parameters of the studied electrodes, such as the slope characteristic, the detection limit, response time, lifetime, selectivity coefficients against various inorganic cations as well as the dependence of the electrodes potential on pH were determined. The obtained electrode are characterized by good analytical parameters: theoretical characteristic slope, low detection limit, short response time and very long lifetime. The electrodes was successfully applied to the direct determination of lead, cadmium and zinc ions in waste water samples. The results obtained indicate that the electrodes provide a good alternative for the determination of these heavy metals in real samples.

Optimization and oxidative stability of biodiesel production from rice bran oil

Biorefinery approach is introduced for the biodiesel production by utilizing low cost raw material, such as rice bran oil (RBO). The valorization of RBO was carried out by homogeneous transesterification process using response surface methodology (RSM) based on a two-variable central composition design (CCD). The process variables, temperature and catalyst concentration were found to have significant influence on biodiesel yield. The optimum combination derived via RSM for high ester yield (99.4%) was found to be 0.75% wt catalyst concentration at a reaction temperature of 45 °C. As biodiesel chemically is a long-chain alkyl methyl esters, its long-term fuel properties have become of great concern to the fuel industry. In order to determine the effects of long storage on oxidation stability, RBO biodiesel sample was stored for 24 months and the different physical–chemical properties were checked with respect to time. The results show that the acid value (AV), peroxide value (PV), and viscosity (ν) increased while the iodine value (IV) decreased. Based on results, correlations were obtained in terms of AV, IV, PV and ν as a function of time. Those correlations can be used to predict how long time biodiesel can safely be stored. AV, IV and PV of the biodiesel sample which was stored were within the limits in European biodiesel specifications (EN 14214).

Birch Reductive Alkylation of Methylm-(Hydroxymethyl)benzoate Derivatives and the Behavior ofo- andp-(Hydroxymethyl)benzoates under Reductive Alkylation Conditions

Birch reductive alkylation of methyl m-(hydroxymethyl)benzoate derivatives, using lithium in ammonia-tetrahydrofuran in the presence of tert-butyl alcohol, can be achieved without significant loss of benzylic oxygen substituents. Similar treatment of o- and p-(hydroxymethyl)benzoate derivatives results largely in loss of benzylic oxygen substituents. The results are rationalized by computations describing electron density patterns in the putative radical anion intermediate involved in these reactions.

Measurements and Correlations of the Isobaric Vapor–Liquid Equilibria of Binary Mixtures and Excess Properties for Mixtures Containing an Alkyl (Methyl, Ethyl) Butanoate with an Alkane (Heptane, Nonane) at 101.3 kPa

In this work, the measurements of the isobaric vapor–liquid equilibrium (VLE) data at 101.32 kPa and the excess molar volumes (vE), obtained at 10 K intervals of temperature in the range (288.15 to 328.15) K, for four binary systems comprised of methyl or ethyl butanoate with two alkanes (heptane and nonane) are presented. The vE are positive for the four mixtures, and their variation with temperature presents a thermal coefficient (∂vE/∂T)p > 0, and the behavior of these systems is interpreted. Experimental VLE data (p,T,x,y), obtained in a small capacity ebulliometer, present a positive consistency according to the method of Fredenslund. The methyl butanoate + heptane system presents a minimum boiling-temperature azeotrope with the following coordinates at the working pressure: (x1,az = 0.404; Taz = 367.65 K). Measurements of (T,pio) are also shown for all of the compounds and were determined using the same equilibrium equipment. Experimental data are correlated with an appropriate polynomial model prop...

Enantioselective Metalation of N,N‐Diisopropylferrocenecarboxamide and Methyl Ferrocenecarboxylate Using Lithium‐Metal Chiral Bases

AbstractEnantioselective deprotonative metalations of substituted ferrocenes using mixed lithium‐metal bases are described. Using N,N‐diisopropylferrocenecarboxamide as substrate, magnesium, iron, cobalt, zinc, and cadmium were tested as metals in bis[(S)‐1‐phenylethyl]amido‐based combinations; after interception of the metalated species with iodine, very high enantiomeric excess (96 %) but low yield was obtained with cobalt, whereas zinc and cadmium only gave 27 and 30 % ee, respectively, but in excellent yields. The small alkyl groups methyl and ethyl were identified as particularly suitable in the reaction using the putative dialkyl bis[(S)‐1‐phenylethyl]amido‐based lithium and dilithium zincates. The dimethyl dilithium zincate was selected for a study of dependency on the temperature, reaction time, and amount of base. Increased enantioselectivities with temperature, reaction time, and amount of base were noted (ee = 86 % at 0 °C after 2 h, 2 equiv. of base). The best result using methyl ferrocenecarboxylate as substrate was observed without alkyl ligand.