Search results for "transesterification"

Assessing the MALDI-TOF MS sample preparation procedure to analyze the influence of thermo-oxidative ageing and thermo-mechanical degradation on poly…

2011

[EN] Multiple processing by means of successive injection cycles was used to simulate the thermo-mechanical degradation effects on the oligomeric distribution of PLA under mechanical recycling. Likewise, an accelerated thermal ageing over PLA glass transition was performed in order to simulate its service life. MALDI-TOF MS was used for the analysis and the sample preparation procedure was assessed by means of a statistical Design of Experiments (DoE). The quality effects in use for the analysis were signal-to-noise ratio and Resolution. Different matrixes, analyte/matrix proportions and the use of NaTFA as cationization agent were considered. A deep inspection of the statistical results pr…

Syntheses, X-ray structures, and physicochemical properties of phenoxo-bridged dinuclear nickel(II) complexes: kinetics of transesterification of 2-h…

2009

Four dinuclear nickel(II) complexes [Ni(II)(2)(L(1))(O(2)CMe)(2)(H(2)O)(2)][PF(6)].MeOH.3H(2)O (1), [Ni(II)(2)(L(1))(O(2)CMe)(2)(NCS)] (2), [Ni(II)(2)(L(2))(O(2)CMe)(2)(MeOH)(H(2)O)][ClO(4)] (3), and [Ni(II)(2)(L(2))(O(2)CMe)(2)(MeOH)(H(2)O)][BPh(4)].3MeOH.H(2)O (4) have been synthesized [HL(1): 2,6-bis[N-methyl-N-(2-pyridylethyl)amino]-4-methylphenol; HL(2): 2,6-bis[3-(pyridin-2-yl)pyrazol-1-ylmethyl]-4-methylphenol]. Complexes 1, 3, and 4 are new while complex 2 was reported previously by Fenton and co-workers (the structure of 2 was presented but no physicochemical properties of this complex were reported; in this work such studies have been completed). X-ray crystallographic analyses of…

THERMO-CATALYTIC PROCESSES FOR BIOFUEL PRODUCTION

2017

A novel phosphorus–carbon bond formation by ring opening with diethyl phosphite of oxazolines derived from serine

2004

Abstract A new reaction of oxazolines derived from serine with diethyl phosphite leading to ring opening products with P–C bond formation is reported. This reaction, which proceeds under neutral conditions and without the use of any halogenated intermediate, results in a mixture of racemic α- and β-phosphono alanines in an approximate 1:2 ratio, with isolated yields up to 77%. The mechanism involves the rearrangement of the oxazoline into the corresponding α-benzamido acrylate, followed by addition of the diethyl phosphite to the double bond. Since no significant transesterification is observed, this method constitutes a simple route for α- and β-phosphono amino acids bearing suitable prote…

DUAL APPLICATION OF DIVALENT ION-ANCHORED CATALYST: BIODIESEL SYNTHESIS AND PHOTOCATALYTIC DEGRADATION OF CARBAMAZEPINE

2019

Improving lipase activity in solvent-free media by interfacial activation-based molecular bioimprinting

1997

Abstract Nine lipases of mammalian, fungal and bacterial origin and two different model reactions, direct esterification and transesterification (alcoholysis), have been used to probe the potential in solvent-free media of the recently reported strategy of interfacial activation-based molecular (bio)imprinting (IAMI) [Mingarro et al., Proc. Natl. Acad. Sci. USA , 92 (1995) 3308]. The results demonstrate that the imprinting treatment permits nonaqueous rate accelerations which are lipase-dependent and span in some cases up to higher than two orders of magnitude. For several lipases, the method allows conversion yields after short reaction times (in either of the model reactions assayed) whic…

Neutron Scattering of Poly(ethylene terephthalate)

1986

Through the use of deuterium labeling, small angle neutron scattering (SANS) has been found to be an extremely effective tool for elucidating the structure of polymer molecules in the condensed matter state. In this study, the molecular morphology of poly(ethylene terephthalate) (PET) has been determined under four different conditions: (1) in the glassy state, (2) in the semicrystalline state, (3) after cold-drawing, and (4) after undergoing partial transesterification.

The Catalytic Mechanism of Carboxylesterases: A Computational Study

2014

The catalytic mechanism of carboxylesterases (CEs, EC 3.1.1.1) is explored by computational means. CEs hydrolyze ester, amide, and carbamate bonds found in xenobiotics and endobiotics. They can also perform transesterification, a reaction important, for instance, in cholesterol homeostasis. The catalytic mechanisms with three different substrates (ester, thioester, and amide) have been established at the M06-2X/6-311++G**//B3LYP/6-31G* level of theory. It was found that the reactions proceed through a mechanism involving four steps instead of two as is generally proposed: (i) nucleophilic attack of serine to the substrate, forming the first tetrahedral intermediate, (ii) formation of the ac…

Selective Formal Transesterification of Fluorinated 2-(Trimethylsilyl)ethyl α-Imino Esters Mediated by TBAF

2008

The scope of the transesterification reaction between beta-fluorinated alpha-imino esters and various electrophiles in the presence of TBAF as fluorine source is described. The reaction is highly selective for alkyl iodides, bromides, and mesylates, while alkyl chlorides react at a significantly slower rate and tosylates do not react under the reaction conditions. This methodology represents a simple and useful alternative for the preparation of a wide variety of fluorinated alpha-imino esters.

1978

Synthesis and characterization of polymeric derivatives of the folic acid antagonist, Methotrexate, N-[4-(N-methyl-2,4-diamino-6-pteridinylmethylamino)benzoyl] glutamic acid (1a), a widely used antitumor agent, are described. Derivatives of poly(L-lysine), poly(iminoethylene), poly(vinyl alcohol), and carboxymethylcellulose with various contents (3–15 mole-%) of substituted repeating units were prepared by polymer-analogous amidation and transesterification of the dimethyl ester of 1a and with N-[2-(N-methylmorpholinio)ethyl]carbodiimide p-toluenesulfonate as coupling reagent. By nucleophilic addition reactions of the pteridinyl amino groups under mild conditions, 1a was bound without cross…