Physico-chemical aspects of polyethylene processing in an open mixer. Part 23: Mechanisms and kinetics of trans-vinylene group consumption

There are many potential reactions for trans-vinylene groups in oxidizing polyethylene melts. The main possibilities are reactions with peroxy radicals, molecular oxygen, hydroperoxides and peracids. These different reactions can all contribute to the removal of trans-vinylene groups to some extent. This is especially so, for the reactions with hydroperoxides that have been found to be the dominant reactions with vinylidene and vinyl groups in the low temperature range. The reaction with peroxy radicals is thought to be as important relatively as with vinylidene groups. Therefore, the importance of the reaction is decreasing with increasing temperature. However, the most characteristic reaction for trans-vinylene groups can be detected without any doubt only in the advanced stages of processing. It is mechanical stress induced oxygen addition to the double bond. The discussion shows that the reaction should be important from the beginning of processing. The reaction cannot operate with vinyl and vinylidene groups, which are not part of the polyethylene main chain. After oxygen addition to the trans-vinylene group, the “ene” reaction yields an allylic hydroperoxide so that the double bond is not immediately removed. It is acid catalyzed hydroperoxide decomposition that leads to chain scission with aldehyde formation at the new chain ends.     

Reaction of arylenedioxytrihalophosphoranes with acetylenes 11. Electronic effect of the substituent in arylacetylene on the reaction rate

The reactions of 2,2,2-trichlorobenzo-1,3,2-dioxaphosphole and its benzo-substituted derivatives with arylacetylenes containing strong +M-donors and -M-acceptors afford benzo[e]-1,2-oxaphosphinine 2-oxides (phosphacoumarins) in high yields. Studies by the competitive reaction method showed that the reaction rate is sensitive to the electronic nature of the substituent in arylacetylene. Thus, the introduction of +M-donors into the phenyl ring of arylacetylene leads to an increase in the reaction rate, whereas the introduction of -M-acceptors results in its substantial decrease. The molecular and supramolecular structures of selected 2-hydroxyphosphacoumarins and substituted vinylphosphonate, which is generated by the cleavage of the P-heterocycle, were studied by X-ray diffraction.     

New N-substituted sulfinamides of neomenthane series

A reaction of neomenthanethiol with ammonia and N-chlorosuccinimide with subsequent addition of aromatic aldehydes leads to chiral N-arylideneneomenthylsulfenimines, whose oxidation at the sulfur atom gives N-arylideneneomenthylsulfinimines. The reactions of N-arylideneneomenthylsulfinimines with lithium aluminum hydride or Grignard reagents proceed at the imine fragment and lead to the corresponding N-benzylneomenthylsulfinamides.     

Dihydroaromatic compounds in the Diels-Alder reaction—IV : Synthesis of bicyclic ketones

The in situ isomerisation and Diels-Alder reaction with 2-acetoxyacrylonitrile, of 2,5-dihydroanisole, leads to the adducts (1) which may be used as starting point for the synthesis of a number of bicyclo [2,2,2] octenones, bicyclo [3,2,1] octenones and bicyclo [3,2,2] nonenones. Under similar conditions, 2,5-dihydrotoluene reacts via an ene-reaction to produce, after hydrolysis, the acetylcyclohexadiene (27). The base-catalysed equilibration and subsequent Diels-Alder reactions of 2,5-dihydrotoluene have been investigated.     

Dependence of the thermodynamic characteristics of the complexation of alanine-18-crown-6 on the composition of water-ethanol solvent

Standard thermodynamic parameters (Δ_r G○, Δ_r H○, TΔ_r S○) for the complexation reaction of 18-crown-6 ether (18C6) with D,L-alanine (Ala) in mixed water-ethanol (H₂O-EtOH) solvents are calculated from the data of calorimetric titrations performed at T = 298.15 K. It is established that an increase in the concentration of EtOH in mixed solvent leads to a rise in stability and an increase in the exothermicity of [Ala18C6] molecular complex formation; changes in the energetics of reaction upon a change in the solvent composition are determined by changes in the solvation state of 18C6, which is typical of the reactions of molecular complex formation of 18C6 with D,L-alanine and glycine in water-organic solvents.     

Synthesis and Diels-Alder reactions of α-fluoro- and α-trifluoromethylacrylonitriles

A novel synthetic method for the preparation of α-fluoro- and the still unknown α-trifluoromethylacrylonitriles is elaborated. The reaction of α-fluorovinylbromides and α-trifluoromethylvinylbromides with CuCN leads to the title compounds in good to high yields. While the α-fluoroacrylonitriles were isolated as mixture of Z/E-isomers, the α-trifluoromethylacrylonitriles were obtained as pure Z-isomers. The α-trifluoromethylacrylonitriles are shown to be excellent dienophiles for Diels-Alder reactions.     

Synthesis of fluorinated 1,2,4-oxadiazin-6-ones through ANRORC rearrangement of 1,2,4-oxadiazoles

The reaction of 3-ethoxycarbonyl-5-perfluoroalkyl-1,2,4-oxadiazoles with hydroxylamines has been investigated, evidencing the possibility of competitive reaction paths. Nucleophilic addition of hydroxylamine to the electrophilic C(5) of the 1,2,4-oxadiazole ring, followed by ring-opening and ring-closure with enlargement, leads to high yield and in very mild experimental conditions to the formation of 5-hydroxyamino-3-perfluoroalkyl-6H-1,2,4-oxadiazin-6-ones, one of these presenting water gelation ability. In turn, reactions with N-methylhydroxylamine lead the exclusive formation of 4-perfluoroacylamino-2-methyl-2H-1,2,5-oxadiazol-3-ones through the well known Boulton-Katritzky rearrangement.     

Polarography of complex compounds in the absence of large excess of the complexing agent

A general expression for the current—voltage characteristic was derived which is valid for all degrees of reversibilities and ligand concentrations, taking into account quantitatively the effect of complex formation on the polarographic curves. When the reaction is reversible the current—voltage characteristic and half-wave potential are independent of the reaction mechanism. For quasi-reversible electron-transfer reactions both the reaction mechanism and the stability constants may be established. When the reaction is irreversible, quantitative investigation of the changes of (E_1/2^′)_irr with concentrations of complexing ligands leads to the composition of the activated complex. However, except in special cases independent information is necessary to determine stability constants. The theory of the polarographic reduction of metal ions in the absence of large excess of the complexing agent was tested experimentally. In the case of the Bi-NTA complex reduction, the electrode reaction was found to be quasi-reversible and the equations of the theoretical section to be applicable.     

Cyclobutene derivatives from addition of α-halogeno electrophilic olefins to ynamines

Reaction of α-chloro- and α-bromoacrylonitrile, α-chloro- and α-bromoacrylic esters with diethylaminomethylacethylene and diethylaminophenylacetylene leads to cyclobutene derivatives of type 3 in high yields. Reaction of E- and Z-α-bromocrotononitrile takes place in a stereospecific way. A mechanistic scheme for a reaction sequence of cycloaddition and subsequent allylic isomerization is formulated on the basis of stereochemical and kinetic data. The halogen substituents of the cyclobutene derivatives are stereospecifically displaced by the OH or the OEt groups in solvolytic reactions, with retention of configuration. Methylenecyclobutene derivatives are obtained from the 3-methylcyclobutenes by elimination of hydrogen halide with potassium t-butoxide. Hydrolysis of the enamine function of the cyclobutenes leads to the corresponding cyclobutanones. The configurations of four pairs of cis-trans isomeric cyclobutenes have been established by ¹H- and ¹³C-NMR spectroscopy.     

The solvent effect on the reaction constants of tert-butyl radical addition to 2-substituted allyl chlorides

The ρ values of free radical S_H2′ reactions have been determined in various solvents. The correlation of Hammett ρ with Taft's π* gives a W value of 0.70. The W value is a measure of susceptibility of the reaction constant to change in solvent polarity. However, the W value is 2.64 in the dissociation reactions of substituted benzoic acids. The free radical reactions are less susceptible to the solvent effect than ionic reactions and this could be rationalized in terms of the partial charge formed in the transition state of free radical reaction is less than that of heterolytic reaction. The ρ values in S_H2′ reactions might not reflect truly the partial charge separation at transition state, however, it might be a measure of the susceptibility of the reaction to the electronic effect of the substituents.     

Features of switchable multicomponent heterocyclizations of salicylic aldehydes and 5-aminopyrazoles with pyruvic acids and antimicrobial activity of the reaction products

Three-component reactions of 5-aminopyrazoles and salicylic aldehydes with pyruvic acids were studied. The method of tuning of the selectivity of the heterocyclizations allowing to change its direction by variation of the reaction parameters was worked out. The treatment involving pyruvic acid can be selectively directed to the formation to either 3-aryl-10,11-dihydro-4,10-methano-pyrazolo[4,3-c][1,5]benzoxazocine-4-carboxylic acids or 3,6-diarylpyrazolo[3,4-b]pyridine-4-carboxylic acids, while the reaction involving arylpyruvic acid leads only to 7-hydroxy-2,5,6-triaryl-4,5,6,7-tetrahydro-pyrazolo[1,5-a]pyrimidine-7-carboxylic acids. Antimicrobial activity of the compounds obtained was also studied: Gram-positive bacteria (Bacillus subtilis and Staphylococcus aureus) were found sensitive to the substances tested, however, only in the highest concentration.     

Isomerization in the reaction of (aminoalkyl)trialkoxysilanes with carboxylic acid anhydrides

The products of the reactions of monofunctional (3-aminopropyl)triethoxysilane and (3-aminopropyl)trimethoxysilane and bifunctional [3-N-(2-aminoethyl)aminopropyl]trimethoxysilane with acetic and maleic anhydrides in CCl₄ at varied reagent molar ratios are studied by ¹H and ¹³C NMR spectroscopy. It is shown that the reaction of [3-N-(2-aminoethyl)aminopropyl]trimethoxysilane with the above anhydrides leads to formation of diamides as mixtures of cisoid and transoid rotamers about both amide bonds. The reactions with monofunctional (aminopropyl)trialkoxysilanes give individual isomers.     

Isoconversional kinetic analysis of stoichiometric and off-stoichiometric epoxy-amine cures

The curing reaction of stoichiometric and off-stoichiometric diglycidyl ether of bisphenol A (DGEBA) and 1,3-phenylene diamine (m-PDA) mixtures was studied by differential scanning calorimetry, thermogravimetric analysis and rheological measurements. In order to highlight the side reactions such as etherification and homopolymerization, the neat DGEBA and DGEBA/DMBA (N,N-dimethylbenzylamine) mixture were examined. The classical model-fitting and the advanced isoconversional methods were used to determine the activation energy of the different reactions. The advanced isoconversional method leads to a good agreement between isothermal, nonisothermal and rheological results. The effective activation energies of primary amine epoxy reaction, etherification and homopolymerization were estimated to about 55-60, 104 and 170 kJ mol⁻¹, respectively.     

Reactions of ethyl triphenylphosphoranylideneacetate with fluorinated β-ketoaldehyde derivatives

The reactions of fluorinated β-ketoaldehyde derivatives: β-alkoxyvinyl polyfluoroalkyl ketones 1 and fluorinated β-ketoacetals 2 with ethyl triphenylphosphoranylideneacetate 3 are described. In the case of ketones 1 the result of the reaction is a mixture of products: fluorinated alkoxydienes 5 (Wittig reaction product) and polyfluoroacyl vinyl ylides 7 (Michael addition product). The reaction with fluorinated β-ketoacetals 2 leads to a mixture of E- and Z-isomers of polyfluoroalkyl acrylates 8 and 9, respectively. The influence of the nature of fluorinated substituent and solvent or other factors on the outcome of the reactions are discussed.     

1,5-Benzoheteroazepines through eco-friendly general condensation reactions

Condensation reactions of o-phenylenediamine and 2 equiv of acetone produce biaryl-substituted 1,5-benzodiazepines. The synthetic protocol shows general applicability since similar reaction of o-phenylenediamines, o-aminophenol, and o-aminothiophenol with ketones or chalcones leads to formation of functionalized 1,5-benzoheteroazepines in good to excellent yields. The synthetic protocol fulfills many green-chemical requirements using simple MW-assistance to promote the activation of ketones and the eco-compatible Er(III) triflate as activator of chalcones.     

Organoboranes for synthesis : Reaction of organoboranes with representative organic azides. A general stereospecific synthesis of secondary amines and N-substituted aziridines

Reaction of trialkylboranes with organic azides in refluxing xylene, followed by hydrolysis, leads to good yields of secondary amines. This reaction is highly dependent on the steric effects around both boron and the azide moiety. The reaction becomes much slower when the steric bulk of one of the reagents is increased and fails when both are hindered. The dialkylchloroboranes are more reactive than trialkylboranes and provide better yields of the desired secondary amines with a11 azides tested. The alkyldichloroboranes react with organic azides at temperatures between room temperature and 60°C and produce excellent yields of secondary amines. Furthermore, the stereochemistry of the original carbon-boron bond is retained. The mechanism of these reactions is discussed and the reaction applied to the synthesis of N-alkyl- and N-arylaziridines.     

Understanding the mechanisms of [3+2] cycloaddition reactions. The pseudoradical versus the zwitterionic mechanism

Analysis of 12 three-atom-components (TACs) participating in [3+2] cycloaddition (32CA) reactions towards ethylene and acetylene allows establishing good correlations between the pseudodiradical character, the hardness η, and the nucleophilicity N index of the TAC with the feasibility of these non-polar reaction. These results allow the introduction of the pr index, which comprises the two aforementioned DFT reactivity indices. The increase of the pr index for an allylic-type TAC goes accompanied by a linear decrease of the activation enthalpy of the reaction. The present study makes it possible to establish a useful classification of 32CA reactions into zw-type reactions involving TACs with a high zwitterionic character, and pr-type reactions involving TACs with a high pseudodiradical character.     

Functionalized fluorenes via dicationic electrophiles

Dicationic fluorenyl cations are shown to react with nitriles to provide amide-functionalized fluorenes. A similar reaction with alcohols gives ether derivatives. The chemistry is initiated by the reactions of N-heterocyclic ketones in a superacidic solution. This leads to cyclizations involving 2-biphenyl groups and formation of the reactive fluorenyl cations.     

Factors determining the reactivity of the bromine atom toward haloalkanes

Experimental data concerning reactions of the bromine atoms with haloalkanes and carbonyl compounds (25 reactions) have been analyzed within the intersecting parabolas model. The following factors have an effect on the activation energy of these reactions: enthalpy of reaction, triplet repulsion, electronegativity of reaction center atoms, dipole–dipole and multidipole interactions of the reaction center with polar groups, and the interaction of π electrons with electrons of the reaction center. The increments characterizing the contribution from each factor to the activation energy of the reaction have been calculated. The increment ΔEμ, which characterizes the dipole–dipole interaction in the transition state, and the dipole moment of the polar group (μ) are correlated by the following empirical equation: ln(ΔE _μ/Σμ) = ?0.14 + 0.47(ΔE _μ/Σμ) ? 0.024(ΔE _μ/Σμ)².     

Polyhalogenated heterocyclic compounds: Part 52. [1] Macrocycles from 3,5-dichloro-2,4,6-trifluoropyridine

Model studies show that displacement of fluorine, rather than chlorine, occurs upon reaction of 3,5-dichloro-2,4,6-trifluoropyridine with sodium methoxide and phenoxide. Subsequent hydro-dechlorination can be achieved by reaction with lithium aluminium hydride whereas reaction of sodium in iso-propanol leads to formation of the tri-iso-propoxy pyridine derivative, via nucleophilic substitution of the methoxy group, rather than the dechlorinated products. Macrocycles can be synthesised by reactions of appropriate difunctional oxygen nucleophiles with 3,5-dichloro-2,4,6-trifluoropyridine, one of which was characterised by X-ray crystallography.