Synthesis of enol and vinyl esters catalyzed by an iridium complex

Enol and vinyl esters were successfully synthesized by the use of an iridium complex as a catalyst. The reaction of carboxylic acids with terminal alkynes in the presence of catalytic amounts of [Ir(cod)Cl]₂ and Na₂CO₃ gave the corresponding 1-alkenyl esters. The addition of carboxylic acids to alkynes principally took place in the Markovnikov fashion. In addition, by the use of an Ir complex combined with NaOAc various vinyl esters were prepared through the transvinylation between carboxylic acids and vinyl acetate.     

Copolymerization of ethylene with a homologous series of vinyl esters

The effect of the alkyl group on the relative reactivity of a homologous series of vinyl esters (2) has been studied with ethylene (1) as reference monomer, tert-butyl alcohol as solvent, at 62°C and 35 kg/cm². The experimental method was based on frequent measurement of the monomer feed composition throughout the copolymerization reaction by means of quantitative gas-chromatographic analysis. Highly accurate monomer reactivity ratios were estimated in a statistically justified manner by a nonlinear least-squares method applied to the integrated copolymer equation. The reactivity of the vinyl ester monomers towards an ethylene radical increased with decreasing electron-with-drawing ability of the ester group. All vinyl ester radicals considered turned out to have the same preference for their own monomer over ethylene (constant r₂ = 1.50). Reactivity ratios are discussed in terms of the Q–e scheme and the Taft relation. It appeared that chiefly polar factors contribute to the observed relative reactivity, while probably resonance stabilization only plays a minor part. Steric hindrance seems to impair monomer reactivity, only from vinyl pivalate on. Relative reactivities of the vinyl esters are compared with literature values, where other reference monomers have been used.     

Investigations of vinyl esters of the furan series

The vinyl esters of trans--(2-furyl) acrylic acid, furan-2-carboxylic acid, 5-bromofuran2-carboxylic acid, and 5-nitrofuran-2-carboxylic acid were synthesized by the reaction of the corresponding acids with acetylene and vinyl acetate. Mercuric acetate and boron trifluoride etherate were used as catalysts for the transvinylation of acids of the furan series. The structures of the vinyl esters obtained were proved by IR and PMR spectroscopy. The distribution of the -electron density in the molecules of four of the synthesized vinyl and ethyl esters was studied by means of quantum-chemical calculations by the SCF MO LCAO method (Pople variant) using the Raman and UV absorption spectra.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1443–1447, November, 1972.     

Synthesis of 13C and 2H Labeled Vinyl Pyruvate and Hyperpolarization of Pyruvate

The hyperpolarization of nuclear spins has enabled unique applications in chemistry, biophysics, and particularly metabolic imaging. Parahydrogen-induced polarization (PHIP) offers a fast and cost-efficient way of hyperpolarization. Nevertheless, PHIP lags behind dynamic nuclear polarization (DNP), which is already being evaluated in clinical studies. This shortcoming is mainly due to problems in the synthesis of the corresponding PHIP precursor molecules. The most widely used DNP tracer in clinical studies, particularly for the detection of prostate cancer, is 1-¹³C-pyruvate. The ideal derivative for PHIP is the deuterated vinyl ester because the spin physics allows for 100 % polarization. Unfortunately, there is no efficient synthesis for vinyl esters of β-ketocarboxylic acids in general and pyruvate in particular. Here, we present an efficient new method for the preparation of vinyl esters, including ¹³C labeled, fully deuterated vinyl pyruvate using a palladium-catalyzed procedure. Using 50 % enriched parahydrogen and mild reaction conditions, a ¹³C polarization of 12 % was readily achieved; 36 % are expected with 100 % pH₂. Higher polarization values can be potentially achieved with optimized reaction conditions.     

Kinetic modeling and optimization of operating parameters for transvinylation of lauric acid

The transition metal complex catalyzed transvinylation of carboxylic acid with vinyl acetate monomer is of significant interest to industry. The palladium complex catalyzed transvinylation of lauric acid using vinyl acetate monomer is a reversible reaction. In present article, design of experiments (DOE) statistics is used to study effects of various operating parameters on transvinylation of lauric acid. The kinetic parameters forward and backward rate constants and the thermodynamic parameters such as equilibrium constant and energy of activation of the transvinylation of lauric acid were estimated using the Dynochem model. The optimum operating parameters for the transvinylation of lauric acid were then predicted using the Dynochem model and verified by performing the actual experiments to validate the model. It was found that the experimental results match with the predicted one. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 624–634, 2012     

Reusable rhodium catalyst for the selective transvinylation of sp2-C linked carboxylic acid

The vinyl benzoate derivatives were successfully synthesized by the transvinylation reactions that vinyl group transferred from vinyl acetate to aromatic carboxylic acids with the recoverable catalyst RhCl₃·3H₂O. This catalyst features air stable and tolerance of water, good reusable ability, meanwhile, shows high selectivity for aromatic carboxylic acid in the presence of phenolic hydroxyl. With this method, a variety of vinyl benzoate derivatives can be produced with up to 95% yield.     

Studies on the Stereoselectivity of the Preparation of α,β-UNSATURATED ESTERS FROM α-Lithio-α-Silyl Esters

The reaction o f the lithium enolate o f a-trimethylsilyl esters with aldehydes and ketones has been shown to be an excellent entry into a, B-unsaturated esters as a result of the facile elimination o f the B-oxidosilane intermediate produced in the initial step of the reaction. (eq. 1) More recently it was shown that the bromomagnesium enolate o f trimethylsilyl acetates a1 lowed for the highly stereoselective preparation of (E) a, B-unsaturated esters via the isolable B-hydroxy-a-silyl ester, which was treated with BF₃0Et₂ to effect a trans elimination of the elements of trimethylsilanol⁵ (eq. 2) If this elimination were carried out with base, however, the stereoselectivity is much lower.     

Preparation of Functionalized Esters of Carboxylic Acids

The synthesis of simple esters (methyl, ethyl, etc.) of carboxylic acids is generally a trivial synthetic transformation due to the great variety of mehtods available (CH₂N₂, MeOH-H⁺,Me₂SO₄-Base, copper salts-alkylhalides¹, and CaO with alkylhalides²). However, what was sought in this laboratory were methods for preparation of functionalized esters. Specifically, Investigations are underway to develop methods for intra molecular transfer or intramolecular reaction of the functionalized (“R”) portion of the carboxylic acid ester (as illustrated below).     

Rate constant and a detailed error analysis for C2H3 + H reaction

The production and reactions of vinyl radicals and hydrogen atoms from the photolysis of vinyl iodide (C₂H₃I) at 193 nm have been examined employing laser photolysis coupled to kinetic-absorption spectroscopic and gas chromatographic product analysis techniques. The time history of vinyl radicals in the presence of hydrogen atoms was monitored using the 1,3-butadiene (the vinyl radical combination product) absorption at 210 nm. By employing kinetic modeling procedures a rate constant of 1.8 × 10^?10 cm² molecule^?1 s^?1 for the reaction C₂H₃ + H has been determined at 298 K and 27 KPa (200 torr) pressure. A detailed error analysis for determination of the C₂H₃ + H reaction rate constant, the initial C₂H₃ and H concentrations are performed. A combined uncertainty of ±0.43 × 10^?10 cm² molecule^?1 s^?1 for the above measured rate constant has been evaluated by combining the contribution of the random errors and the systematic errors (biases) due to uncertainties of each known parameter used in the modeling. © 1995 John Wiley & Sons, Inc.     

The Reaction of Phosphoryl Chlorides with Enamines - A New Approach to β-Ketophosphonates

Abstract

Several approaches are available for the preparation of β-ketophosphonate esters. A Michaelis-Arbuzov approach using the reaction of an α-halo ketone with a trialkyl phosphite may in certain instances be controlled to favor the preparation of the target materials. However, an alternative pathway leading to the formation of vinyl phosphate esters often predominates. (This reaction system has recently been reviewed by Borowitz and Borowitz.¹) An alternative approach is that developed in recent years by Wiemer, et al.² involving the rearrangement of vinyl phosphate esters to the β-ketophosphonates.     

N-Vinylformamide – Building Block for Novel Polymer Structures

Abstract

N-Vinylformamide (NVF, N-ethenylformamide) is a precursor to amide and amine functional polymers and to other monomers, oligomers, and functional polymers. NVF shows attractive physical and toxicological properties and high reactivity, both in polymerization and in subsequent hydrolysis to cationic and reactive amine functional polymers or oligomers. NVF radical polymerization readily yields water soluble homopolymers with molecular weights from 10⁴ to >10⁶. Copolymerizability is similar to other vinyl amides. Unexpectedly, NVF will also undergo cationic oligomerization. Hydrolysis of polymers and copolymers with base or acid is facile, although reactions with neighboring groups (e.g., with coacrylate ester groups to give lactams) complicate copolymer hydrolysis.

Reaction of NVF at the unusually acidic NH group allows reaction with isocyanates to give vinylacylureas or Michael addition to acrylates to give a family of new N-vinylformamidopropionate esters. These esters in turn react with functional amines to generate new families of divinyl, vinyl/alcohol functional, or vinyl/amino functional comonomers. Applications for NVF and its derived monomers and polymers appear numerous, in particular in radiation cure coatings, based on their good physical and toxicological properties.     

Synthesis of gibberellins A8 and A56 from gibberellin A3

A mixture of gibberellin A₃ derivatives with 1(10)-ene-2β,3β-diol and 1(10)-ene-2α,3β-diol (2:5) groups, readily obtained from gibberellin A₃, has been used for a new and simple synthesis of gibberellin A₈ and its esters. The hydrolysis of GA₃ and the iodolactonization of a mixture of the 2-epimers was carried out in aqueous solution in a single flask, as also was a synthesis of GA₅₆ from GA₃ by a method that we have modified. The mixture of 1β-iodides of GA₈ and GA₅₆ was separated by chromatography on SiO₂ in the form of methyl or p-bromophenacyl esters which were then deiodinated and the methyl or p-bromphenacyl ester of GA₈ was isolated. Free GA₈ was obtained by the dephenylation of the latter ester. By two-dimensional NMR spectroscopy we succeeded in assigning all the signals in the¹³C and¹H NMR spectra of the methyl esters of GA₈ and GA₅₆. In an attempt to obtain GA₅ methyl ester by the action of trimethylchlorosilane/sodium iodide on the 2α,3β-diol system in GA₅₆ methyl ester, the 8,13-epimer of the latter was formed, the structure of its molecule being established from the results of X-ray structural analysis.     

Calcium ion selective membrane electrode

The calcium salts of the mono- and diesters of [4-(1,1,3,3-tetramethylbutyl)phenyl phosphoric acid] have been prepared, and the individual esters as well as mixtures of the esters have been used with several varieties of polyvinyl chloride to construct macro membrane electrodes selective to calcium ions. These electrodes have been calibrated by using solutions of CaCl₂ and Ca ion buffers. The mixed ester electrodes showed Nernstian response in the concentration range 10^-1 to 10^-7M; the diester electrodes showed Nernstian response down to 7.9 x 10^-8M. The detection limit of the mixed ester electrode was 10^-8M, whereas that of the diester electrode was 7.9 x 10^-9M. Contrary to these results, the monoester electrodes showed unsatisfactory behavior. The responses of both the mixed ester and diester electrodes to calcium ions were not affected by the presence of sodium, potassium, or other divalent ions. Only ferric and lanthanum ions showed interferences with the electrode response to calcium ions. p]The electrode response was independent of pH in the approximate range 5–8 at a CaCl₂ concentration of 10^-4M. As the Ca ion concentration was increased, the range of pH independence widened to approximately 4–8. The dynamic response time constant of the mixed ester electrode was in the range 0.7–1.5 sec, whereas that of the diester electrode was in the range 0.5–0.75 sec.     

Characterization of long-chain carboxylic esters with CH3OBOCH 3 + in a small fourier-transform ion cyclotron resonance mass spectrometer

The usefulness of CH₃OBOCH ₃ ⁺ as a chemical ionization reagent was examined by allowing the ion to react with carboxylic esters of various chain lengths in a small Fourier-transform ion cyclotron resonance mass spectrometer equipped with a permanent magnet. CH₃OBOCH ₃ ⁺ is a strong electrophile and readily abstracts an oxygen-containing group from the carboxylic esters. Long-chain esters exclusively lose the alkoxide moiety to give the acylium ion. The same reaction was observed for saturated, unsaturated, branched and cyclic esters. In each case, the acylium ion reacts further with a neutral ester molecule by proton transfer to yield the protonated ester as a secondary product. This remarkably simple product distribution reveals the molecular weight of the ester, the chain length of its acid moiety, and the degree of unsaturation in the acid and alcohol moieties.     

Synthesis of a novel ferrocene derivative having flame-retardant and smoke-suppressant properties

Reaction of ferrocene with chlorendic anhydride (1,4,5,6,7,7-hexachloro-5-norbornene-2,3-dicarboxylic acid anhydride) under Friedel–Crafts reaction conditions affords a new monosubstituted dervative of ferrocene which has significant flameretardant and smoke-suppressant properties when incorporated into poly(vinyl chloride) (PVC). The monocarboxylic acid from the above reaction undergoes smooth methylation with diazomethane to give the corresponding methyl ester. ¹H and ¹³C NMR spectra of these compounds have been compared with those obtained from similar compounds, namely β-ferrocenoylpropanoic acid and its methyl ester. Distant asymmetric centres in the chlorendic anhydride substituent markedly affect the proton spectra of the ferrocene derivative.     

The atmospheric oxidation of ethyl formate and ethyl acetate over a range of temperatures and oxygen partial pressures

The Cl‐atom‐initiated oxidation of two esters, ethyl formate [HC(O)OCH₂CH₃] and ethyl acetate [CH₃C(O)OCH₂CH₃], has been studied at pressures close to 1 atm as a function of temperature (249–325 K) and O₂ partial pressure (50–700 Torr), using an environmental chamber technique. In both cases, Cl‐atom attack at the CH₂ group is most important, leading in part to the formation of radicals of the type RC(O)OCH(O^?)CH₃ [R = H, CH₃]. The atmospheric fate of these radicals involves competition between reaction with O₂ to produce an anhydride compound, RC(O)OC(O)CH₃, and the so‐called α‐ester rearrangement that produces an organic acid, RC(O)OH, and an acetyl radical, CH₃C(O). For both species studied, the α‐ester rearrangement is found to dominate in air at 1 atm and 298 K. Barriers to the rearrangement of 7.7 ± 1.5 and 8.4 ± 1.5 kcal/mole are estimated for CH₃C(O)OCH(O^?)CH₃ and HC(O)OCH(O^?)CH₃, respectively, leading to increased occurrence of the O₂ reaction at reduced temperature. The data are combined with those obtained from similar studies of other simple esters to provide a correlation between the rate of occurrence of the α‐ester rearrangement and the structure of the reacting radical. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 397–413, 2010     

TiCl4 promoted menthyl ester chiral auxiliary mediated synthesis of chiral syn-β-amino esters and applications of a representative syn-β-amino ester

β-Amino esters were obtained in up to 78% yield with 72:28–96:4 diastereomeric ratios by the reaction of the chiral titanium enolate of menthyl esters, prepared using the TiCl₄/Et₃N reagent system with prochiral imines. A representative syn-β-amino ester derivative has been used for the resolution of racemic mandelic acid to obtain a sample with >99% ee in a single step. A representative syn-β-amino ester was converted to the corresponding N-deprotected amino ester using the Pd–C/HCOOH reagent system, and then to the corresponding β-amino acid using the glacial CH₃COOH/HCl reagent system, and to the corresponding β-lactam derivative with partial epimerization by the reaction using C₂H₅MgBr.     

Regioselective and Stereoselective Addition of Tetrazole Derivatives to Electron‐poor Acetylenic Esters in the Presence of Triphenylphosphine

Protonation of the highly reactive 1:1 intermediates produced in the reaction between triphenylphosphine and acetylenic esters by tetrazole derivatives leads to the formation of vinyltriphenylphosphonium salts. The cation of these salts undergoes an addition reaction with the counter anion in CH₂Cl₂ at room temperature to yield the corresponding stabilized phosphorus ylides. Elimination of triphenylphosphine from the stabilized phosphorus ylides leads to the corresponding electron‐poor N‐vinyl tetrazoles in fairly high yields. Structures of N‐vinyl tetrazoles were determined by IR, ¹H NMR, ¹³C NMR and single crystal X‐ray structure analyses. The reaction is fairly regioselective and stereoselective.     

Living cationic polymerization of ethyl 2-(vinyloxy)ethoxyacetate: A vinyl ether with an ether and an ester function in the pendant

Ethyl 2-(vinyloxy)ethoxyacetate ( 4 ; CH₂?CH? OCH₂CH₂OCH₂? COOC₂H₅), a vinyl ether having both carboxylic acid ester and oxyethylene unit in its pendant, afforded well-defined living polymers when polymerized by the hydrogen iodide/iodine (HI/I₂) initiating system in toluene at ?40°C. The polymers possessed a narrow molecular weight distribution (M _w/M _n ≤ 1.15), and their molecular weight (M _n) increased proportionally to monomer conversion or the molar ratio of the monomer to hydrogen iodide. The polymer molecular weight also increased upon addition of a fresh feed of the monomer to a completely polymerized reaction mixture. Polymers of high molecular weights (M _n > 5 × 10⁵) and broad molecular weight distributions were obtained by BF₃OEt₂ in toluene at ?40°C. Polymerization rate of 4 with HI/I₂ is ca. 100 times greater than that of the corresponding alkyl vinyl ether, and thus 4 was found to be one of the most reactive vinyl ethers thus far studied. Alkaline hydrolysis of the pendant ester groups of the polymers gave a vinyl ether-based polymeric carboxylic acid 6 with a narrow molecular weight distribution.