Search results for "Anion"

ChemInform Abstract: Nucleophilic Benzoylation Using Lithiated Methyl Mandelate as a Synthetic Equivalent of the Benzoyl Carbanion. Oxidative Decarbo…

2010

Abstract The synthesis of alkyl aryl ketones using lithiated methyl mandelate as a synthetic equivalent of the benzoyl carbanion is reported (Umpolung). The methodology involves alkylation of methyl mandelate, hydrolysis of the ester group and oxidative decarboxylation of the resulting α-hydroxyacids. The last step is carried out in a catalytic aerobic way using a Co(III) complex in the presence of pivalaldehyde under very mild and advantageous conditions. The procedure is also applied to methyl mandelates substituted on the aromatic ring.

A new access to 2′-amino-substituted vinylindoles as donor-activated heterocyclic dienes and their first diels-alder reactions

1992

Abstract Reactions of the 3-acylindoles 5, 10 , and 15 with α-amino-α′-diphenylphosphinoyl-substituted carbanions gave rise to the 2′-amino-substituted 3− and 2-vinylindoles 7, 12 , and 17 by way of the isolable carbinols 6 , 11 , and 16 . The heterocyclic dienes 7 , 12 , and 17 readily underwent Diels-Alder reactions with N -phenylmaleimide.

Synthesis and thermoresponsive properties of four arm, amphiphilic poly(tert-butyl-glycidylether)-block-polyglycidol stars

2011

Abstract A series of four arm stars with copolymer arms composed of poly(tert-butyl-glycidylether)-b-polyglycidol were prepared using a multi-step process based on anionic ring-opening polymerization. Control of the length of the arms and the number of functional (hydroxyl) reactive groups was achieved by anionic polymerization. Stars with molar masses up to 12200 g/mol were prepared. The amphiphilic character of the star structure was varied using different polyglycidol block lengths. The star structure and molar mass of the obtained stars were characterized by SEC–MALLS and NMR spectroscopy. The temperature behavior of an aqueous solution of the obtained polymers was also investigated. Th…

1980

1974

1978

A newly designed automatically controlled stirred reactor suitable for kinetic measurements of reactions with half lives ≥2s has been applied to follow the anionic polymerization of methyl methacrylate in THF with Na+ as a counter ion in the presence of an excess of NaB(C6H5)4. As initiators were used: benzylsodium reacted with α-methylstyrene (I), fluorenylsodium (II), and 9-methylfluorenylsodium (III). With I the initiation is fast as compared with the polymerization reaction which is first order in monomer concentration. Within the range of −50°C to −100°C an almost unperturbed “living” polymerization is observed. The Arrhenius plot of the rate constants results in a straight line with a…

1984

The decomposition reactions of the lithiated dimer, trimer, and tetramer of methyl methacrylate (MMA) in THF at 25°C were investigated. The decomposition of the lithiated dimer proceeds via depolymerization to lithiated monomer and MMA, addition of MMA to residual lithiated dimer, resulting the trimer (“disproportionation” of the dimer), and subsequent autocondensation of the products. The lithiated trimer almost exclusively undergoes cyclo-autocondensation, whereas for the lithiated tetramer both reactions proceed simultaneously to a remarkable degree. It is shown that the relative rate of autocondensation, which is highly dependent on the degree of polymerization of the oligomer, controls…

Theoretische analyse der bei einem zweiwegwachstumsmechanismus auftretenden molekulargewichtsverteilungen und ihre anwendung auf die anionische polym…

1967

Es werden mittels der Momentmethode die fur einen abbruchfreien Zweiwegwachstumsmechanismus zu erwartenden Molekulargewichtsverteilungen und ihr Zusammenhang mit dem kinetischen Ablauf theoretisch abgeleitet. Die ermittelten Bezichungen werden auf das Polymerisationssystem Styrol in Cumylmethylather mit Cumylnatrium als Initiator angewandt. Durch Einsetzen der vorher experimentell ermittelten kinetischen Daten in die theoretisch abgeleitete Gleichung werden die Molekulargewichtsverteilungen des untersuchten Systems berechnet und mit den experimentell ermittelten verglichen. Die gute Ubereinstimmung zwischen Theorie und Experiment stellt einen schlussigen Beweis fur das Vorliegen eines Zweiw…

Kinetics of Group Transfer Polymerization

1987

The group transfer polymerization (GTP) of methyl methacrylate (MMA) and tert.-butyl methacrylate (TBMA), catalyzed by bifluoride, is of first order with respect to monomer and catalyst concentrations. A slightly negative order with respect to initiator concentration is observed, indicating an inhibitive function of the initiator. Termination reactions occur at lower catalyst concentrations. They are very pronounced for TBMA and result in incomplete conversions. For MMA, at lower catalyst and higher initiator concentrations, induction periods are observed which increase when lowering the temperature. This is related with the formation of active chains. The Arrhenius plots for the propagatio…

Herstellung, charakterisierung und lösungseigenschaften von einheitlichen styrol-α-methylstyrol block-copolymeren

1977

An improved anionic polymerization technique for the preparation of highly uniform styrene/α-methylstyrene linear two-block copolymers is described. Three sets of samples with molecular weights M were prepared under equal experimental conditions, namely polystyrenes (2 · 105 < M < 3 · 106), poly(α-methylstyrene)s (7 · 104 < M < 4 · 106), and block copolymers (2 · 105 < M < 2,5 · 106). Ultracentrifugation in a density-gradient does not show any chemical heterogeneities in the block copolymers. The molecular polydispersity U = Mw/Mn–1 is U = 0,03 or less as estimated from GPC-measurements. The high molecular and chemical homogeneity of the block copolymers and the optical similarity of the tw…