Pavel Čefelín

Polymer-supported dimethyl sulfoxide as phase-transfer catalyst

SummaryCrosslinked polystyrenes with pendant -CH2SOCH3 grouping are efficient phase-transfer catalysts in liquid-liquid reactions of 1-bromooctane with several inorganic nucleophiles. Direct introduction of -CH2SOCH3 grouping into polystyrene by the reaction of a halogenated polystyrene with methylsulfinyl-methylsodium is described.

Solid-phase cosolvents. A polymer analog of N-methyl-2-pyrrolidone based on crosslinked polystyrene

Abstract Polymer analogs of N-methyl-2-pyrrolidone were prepared by reacting crosslinked polystyrene with N-hydroxymethyl-2-pyrrolidone. These polymers are effective catalysts of nucleophilic substitution reactions carried out under liquid-solid (L-S) and liquid-solid-liquid conditions.

Poly(styrylmethylthiol) as an efficient debrominating reagent of 1,2-dibromides

Abstract Dibromides are readily debrominated by means of poly(styrylmethyl thiolate) with formation of the respective olefins. The polymeric reagent with a high content of sulphhydryl groups can be easily prepared from chloromethylated polystyrene; it extends possibilities of protection-deprotection reactions of the double bond.

The co-operative effect in the activation of the phenoxide anion with oligo(oxyethylenes) containing quaternary ammonium groups

An unusual increase in activity accompanying the catalysis of a model substitution reaction between sodium phenoxide and 1-bromo-octane with oligo(oxyethylenes), linear or bound to the polymer, was observed after the introduction of quaternary ammonium groups as terminal groups into the oligo(oxyethylene) chain.

Pseudocrown ethers based on polyphosphazene as effective catalysts of nucleophilic substitution reactions

SummaryPolymer pseudocrownethers based on polyphosphazene are active catalysts of nucleophilic substitution reactions. With respect to the catalytic activity, polyphosphazene is a more suitable carrier of oligo(oxyethylenes) than poly(styrene-co-divinylbenzene). With increasing length of oligo(oxyethylene) branches the catalytic activity of polymers increases. The favorable effect of the content of pseudocrownether structures is particularly visible in polymers having a longer oligo(oxyethylene) chain in those reactions in which the polymer acts as a solid cosolvent. The catalysts preserve their activity also if reused.

Conformational structure of ϵ-caprolactam and its methyl derivatives

Abstract A series of caprolactams (caprolactam, N-methylcaprolactam, the α-, β-, γ-, δ- and ϵ-methylcaprolactams and α, α-dimethylcaprolactam) have been prepared. Their IR and NMR spectra were measured in various media and the temperature dependence of these spectra was analysed. In all these compounds, only the chair form of the ring was observed. All C-mono-methyl derivatives exhibited a strong preference for the equatorial position of the methyl substituent.

Polymer-supported aza-15-crown-5 as effective catalyst for phase-transfer reactions

SummaryImmobilized aza-15-crown-5 were prepared by the reaction of chloromethylated polystyrene resin with N-(2-hydroxyethyl)-aza-15-crown-5. These polymer-supported crowns were very effective catalysts of nucleophilic substitution reactions carried out under the conditions of the two-phase (L-S) or three-phase (L-S-L) catalysis.

Polymer reagents: preparation of polymer esters of thiocarboxylic acids based on crosslinked polystyrene

SummaryThe process of acylation of polymer thiols based on microporous poly (styrene-co-divinylbenzene) (crosslinking agent content 1–2%) with carboxylic acids was investigated depending of the degree of functionalization, on the crosslinking of the polymer carrier and on the structure of acids. In the presence of dicyclohexylcarbodiimide and 4-dimethylaminopyridine the acylation reactions can be conducted to high degrees of the transformation of SH groups already at room temperature. The extent of such refunctionalization reactions depends neither on the degree of functionalization of the starting polymer thiol nor on the structure of the acids. Reactions of polymer esters of thiocarboxylic acids with primary, secondary and tertiary alcohols activated with mercury (II) trifluoroacetate lead to low ester yields.

The kinetics of acid hydrolysis of polymeric ketone acetals

The kinetics of acid hydrolysis of poly[(2,2-dimethyl-1,3-dioxolane-4-yl)methyl methacrylate] and of its copolymers with methyl methacrylate in homogeneous phase was investigated by means of mass spectrometry using perdeuterated acetone as the internal standard. It was found that under conditions of a pseudomonomolecular reaction the homopolymer is capable of an acceleration process with respect to the splitting-off of acetone according to the content of the syndiotactic dyads. The respective rate constants K0 and K1 were calculated. Characterization of the steric situation by means of models of polymeric ketonacetals and the absence of acceleration in the case of copolymers even containing only a small amount of methyl methacrylate units lead to the conclusion that the reported phenomenon is due to steric effects combined with a neighbouring group effect.