Evolution of products during the degradation of polyethylene in a batch reactor

The thermal degradation of two polyethylene samples (LDPE and HDPE) has been carried out in a batch reactor under dynamic conditions. The evolution of products generated after regular intervals of 5 min (temperature increments of approximately 25 °C) has been analyzed. The behaviour of LDPE and HDPE has been compared, and no differences in the quantity and weight fraction of the gaseous products obtained have been found. For both polymers, n-paraffins are the major products at the very beginning of the process, while as the decomposition proceeds 1-olefins are more abundant. The condensed fraction is much larger than the gaseous fraction and its analysis reveals some differences between the behaviour of LDPE and HDPE at the beginning of the degradation process. These differences disappear at higher temperatures where more similar trends are observed. 1-Olefins, n-paraffins, dienes and olefins with wide carbon number distributions are the most important condensed compounds obtained in the thermal degradation of both polyethylenes. The formation of 1-olefins and n-paraffins begins at slightly lower temperatures than for dienes and olefins. On the other hand, as the temperature increases, the amount of low and high molecular weight compounds increases at the expense of intermediate molecular weight products and the former become the most important by the end of the degradation process. This behaviour could be related to the thermal cracking of waxes through secondary reactions.     

A highly regio- and stereoselective synthesis of internal olefins via an elimination of trimethylstannyl group

Internal reaction of secondary alkyltin(IV) compounds having thionium ion gave internal trans olefins with high yield and regio- and stereoselectivity via 1,5- or 1,6-transfer of a hydride β to the trialkylstannyl group.     

From 1,4-diketones to N-vinyl derivatives of 3,3′-bipyrroles and 4,8-dihydropyrrolo[2,3-f]indole in just two preparative steps

Dioximes of hexane-2,5-dione and cyclohexane-1,4-dione react with acetylene in an autoclave (KOH/DMSO, 100 °C, 1 h, initial pressure 14 atm) to give 2,2′-dimethyl-1,1′-divinyl-[3,3′]bipyrrole and 1,5-divinyl-4,8-dihydropyrrolo[2,3-f]indole in 12% and 6% yields, respectively, thus exemplifying a very simple, straightforward route to inaccessible or unknown pyrrolic assemblies.     

Pyrolyses of pentafluorophenyl 2-methylprop-2-enyl ether. Reactions proceeding via internal diels-alder reactions, and the contrasting thermolysis of pentafluorophenyl 2-methylbut-3-en-2-yl ether

The pyrolysis of pentafluorophenyl 2-methylprop-2-enyl ether (XIII) at 310° gave 4-(2-methylprop-2-enyl)-2,3,4,5,6-pentafluoro-2,5-cyclohexadienone (XVI) (46%), while at 410° a mixture of 1-fluorovinyl 2,3,4-trifluoro-5-methylphenyl ketone (XVIII) (30%) and 2,5β,6,7,7aβ-pentafluoro-3aβ-methyl-3aβ,4,5,7a-tetrahydroinden-1-one (XXI) (22%) was formed from the possible internal Diels-Alder adducts (XVII) and (XX) respectively (Scheme 6). Pentafluorophenyl 2-methylbut-3-en-2-yl ether (XVI) decomposed under mild conditions (70°) to give pentafluorophenyl 3-methylbut-2-en-1-yl ether (XXII), pentafluorophenol and 2-methyl-1,3-butadiene possibly via an ion pair intermediate (Scheme 7).     

A convenient methodology for the chemoselective reduction of a wide variety of functionalized alkenes

An efficient method to effect chemoselective reduction of alkenes (including trisubstituted olefins) possessing various sensitive and/or reducible groups such as acetals, allylic alcohols, benzyl ethers, epoxides, esters, halides, nitriles, and sulfones is reported. The reduction is facile at 0 °C in aqueous N,N-dimethylacetamide containing sodium borohydride in the presence of 15 mol % ruthenium(III) chloride. Regioselective reduction of dienes is also feasible if the double bonds are sufficiently different in their structural environment.     

Synthesis and Properties of 1,5-Dimethyltricyclo[3.3.0.02,8]octane- and 1,5-Dimethyltetracyclo[3.3.0.02,804,6]octane Derivatives

The synthesis of 1,5-dimethyltricyclo[3.3.0.0^2,8]octane-3,7-dione ( 2 ), 1,5-dimethyltetracyclo[3.3.0.0^2,80^4,6]-octane-3,7-dione ( 3 ), the corresponding dienes 5 and 6 as well as the mixed enones 13 – 15 is reported. Using He( I ) photoelectron spectroscopy (PE) as a tool, a considerable interaction between the n orbitals on the O-atoms and the σ frame in 2 and 3 as well as of the double bonds in 5 and 6 and the σ frame is found. These interactions are also traced back by the electronic absorption spectra of these compounds. The molecular structures of 2 and 3 have been investigated by X-ray analysis.     

The reduction and hydrolysis of some 7,7-diethylpyrazolo[1,2-a]-pyridazine-6,8(7H)dione derivatives

The chemistry of several of the Diels-Alder adducts formed by the reaction of 4,4-diethylpyrazoline-3,5-dione ( 1 ) with conjugated dienes was studied with respect to reduction (hydride and catalytic) and reaction with base. Reaction of the 2,3-dimethyl-1,3-butadiene adduct with lithium aluminum hydride followed by hydrogenation gave 1,3,5,6,7,8-hexahydro-cis-endo-6,7-dimethyl-2,2-diethylpyrazolo[1,2-a]pyridazine ( 11 ). Attempted conversion of this compound to 3,3-diethyl-cis-7,8-dimethyl-1,5-diazacyclononane ( 12 ) gave instead a compound which has been tentatively identified as N-(2,3-dimethyl-4-aminobutyl)-2-ethyl-2-methylbutanaldimine ( 14 ). Lithium aluminum hydride reduction of 4,4-diethylpyrazolidine-3,5-dione ( 22 ) or the adducts formed from 1 and cyclopentadiene or 1,3-cyclohexadiene gave good yields of 4,4-diethylpyrazolidine ( 21 ). This later reduction gave a new and efficient synthetic route to the pyrazolidine ring system. Lithium aluminum hydride reduction of 5,6,7,8-tetrahydro-5,8-ethano-2,2-diethylpyrazolo[1,2-a]pyridazine-1,3(2H)dione ( 26 ) followed by hydrogenolysis led to a high yield of 4,4-diethyl-2,6-diazabicyclo[5.2.2]undecane ( 28 ) which is the first reported example of this ring system. Reaction of several of the adducts with ethanolic potassium hydroxide resulted in the opening of the five-membered ring.     

(NHC)NiH‐Catalyzed Intermolecular Regio‐ and Diastereoselective Cross‐Hydroalkenylation of Endocyclic Dienes with α‐Olefins

Highly selective cross‐hydroalkenylations of endocyclic 1,3‐dienes at the least substituted site with α‐olefins were achieved with a set of neutral (NHC)Ni^IIH(OTf) catalysts and cationic Ni^II catalysts with a novel NHC ligand. Under heteroatom assistance, skipped dienes were obtained in good yields, often from equal amounts of the two substrates and at a catalyst loading of 2–5 mol %. Rare 4,3‐product selectivity (i.e., with the H atom at C4 and the alkenyl group at C3 of the diene) was observed, which is different from the selectivity of known dimerizations of α‐olefins with both acyclic Co and Fe systems. The influence of the various substituents on the NHC, 1,3‐diene, and α‐olefin on the chemo‐, regio‐, and diastereoselectivity was studied. High levels of chirality transfer were observed with chiral cyclohexadiene derivatives.     

CuI/Dabco as a highly active catalytic system for the Heck-type reaction

An efficient catalytic system using CuI/Dabco (triethylenediamine) for the Heck-type cross-coupling reaction was developed. In the presence of 10 mol % of CuI and 20 mol % of Dabco, the coupling of various aromatic iodides and 1-((Z)-2-bromovinyl)benzene with olefins was carried out efficiently and selectively to afford the corresponding internal olefins in moderate to good yields.     

Synthesis and unusual beckmann fragmentation reaction of syn-3-Methoxy-6α,17β-Dihydroxyestra-1,3,5(10)-trien-7-one oxime

Sodium borohydride reduction of anti-3-methoxy-17β-hydroxyestra-1,3,5(10)-trien-6,7-dione 7-oxime (4a) afforded syn-3-methoxy-6α,17β-dihydroxyestra-1,3,5(10)-trien-7-one oxime (5), which in thionyl chloride at −18 °C undenvent Beckmann fragmentation reaction to the unexpected 3-methoxy-6-oxo-17β-hydroxy-6.7-secoestra-1.3.5(10)-trien-7-nitrile (6). A mechanism of this fragmentation process was proposed.     

Polyfluorocycloalkenes. Part XIV.[1] A novel hydrolysis of decafluorocyclohepta-1,4-diene. Crystal structure of 2H, 4H-hexafluoro-1,5-dimethoxy-8-oxabicyclo(3,2,1)octan-3-one

Decafluorocyclohepta-1,4-diene and fuming sulphuric acid at 100° gave a bright yellow solution which was decolourised on dilution with water to give 2H,4H-hexafluoro-1,5-dihydroxy-8-oxabicyclo(3,2,1)octan-3-one. This was methylated with diazomethane in ether to give 2H,4H-hexafluoro-1,5-dimethoxy-8-oxabicyclo(3,2,1)octan-3-one and 2H-hexafluoro-1,3,5-trimethoxy-8-oxabicyclo(3,2,1)oct-3-ene. The crystal and molecular structure of the former compound was determined by a single crystal X-ray analysis from three-dimensional counter data.     

Unprecedented Selectivity of Ruthenium Iodide Benzylidenes in Olefin Metathesis Reactions

The development of selective olefin metathesis catalysts is crucial to achieving new synthetic pathways. Herein, we show that cis‐diiodo/sulfur‐chelated ruthenium benzylidenes do not react with strained cycloalkenes and internal olefins, but can effectively catalyze metathesis reactions of terminal dienes. Surprisingly, internal olefins may partake in olefin metathesis reactions once the ruthenium methylidene intermediate has been generated. This unexpected behavior allows the facile formation of strained cis‐cyclooctene by the RCM reaction of 1,9‐undecadiene. Moreover, cis‐1,4‐polybutadiene may be transformed into small cyclic molecules, including its smallest precursor, 1,5‐cyclooctadiene, by the use of this novel sequence. Norbornenes, including the reactive dicyclopentadiene (DCPD), remain unscathed even in the presence of terminal olefin substrates as they are too bulky to approach the diiodo ruthenium methylidene. The experimental results are accompanied by thorough DFT calculations.     

Effect of reaction conditions on product distribution from the co-pyrolysis of α-amino acids with glucose

The effect of reaction conditions on product distribution from the co-pyrolysis of amino acids with glucose was studied. Three different amino acids, proline, tryptophan and asparagine, were studied. Some experiments were also conducted with aspartic acid, glutamic acid and glutamine. Equimolar binary mixtures of each amino acid and glucose were pyrolyzed at 300 °C to obtain low temperature char (LTC) and low temperature tar (LTT). The LTC in each case was then pyrolyzed further at 625 °C to obtain high temperature char (HTC) and high temperature tar (HTT). In a few experiments, the LTT and HTT were also pyrolyzed at 870 °C (secondary cracking) to obtain the final tars (LTFT and HTFT, respectively) and study the formation of polycyclic aromatic compounds (PACs) via secondary reactions. Experiments were also conducted at different amino acid/glucose molar ratio or at a temperature of 200 °C. All the experiments were performed in an inert atmosphere. The extent of interaction between the amino acids and glucose was determined by comparing the observed results to that calculated from the separate pyrolyses of amino acids and glucose. At 200 °C, the co-pyrolysis led to lower LTC yields relative to the calculated yields. At 300 and 625 °C the yields of LTC and HTC were mostly higher whereas those of LTT and HTT were lower than the calculated yields, except for asparagine and aspartic acid where the observed and calculated LTC yields were comparable. Although proline formed no char in the absence of glucose, it gave a significant amount of nitrogen-containing char when co-pyrolyzed with glucose. The pyrolysis tars contained a number of nitrogenous products not observed from the pyrolysis of amino acids alone. After the secondary cracking, the product changed from mainly single-ring heterocycles to PACs and, in some cases, PAHs.     

Microwave-assisted regioselective olefinations of cyclic mono- and di-ketones with a stabilized phosphorus ylide

A number of cyclic mono- and di-ketones underwent regioselective olefination with (carbethoxyethylidene)triphenylphospharane under controlled microwave heating. The Wittig reaction of 4-substituted cyclohexanones or 1,2- and 1,4-cyclohexanediones with the ylide at 190 °C for 20 min in MeCN afforded the exocyclic olefins in >94:6 isomer ratios. On the other hand, the same reactions carried out at 230 °C for 20 min in the presence of 20 mol % DBU furnished the endocyclic olefins in >83:17 isomer ratios. The base-mediated isomerization of the exocyclic olefins into the endocyclic isomers was primarily driven by thermodynamic stability of the products and the effect of ring structures on deconjugation was examined.     

The simple solvent-free synthesis of 1H-quinazoline-2,4-diones using supercritical carbon dioxide and catalytic amount of base

Only supercritical carbon dioxide (scCO₂) as a reactant and a solvent, and catalytic amount of base (DBU (1,8-diazabicyclo[5.4.0]undec-7-ene), DBN (1,5-diazabicyclo[4.3.0]non-5-ene), Dabco^® (1,4-diazabicyclo[2.2.2]octane), and triethylamine) afforded 1H-quinazoline-2,4-diones in good to excellent yields from 2-aminobenzonitriles. 6,7-Dimethoxy-1H-quinazoline-2,4-dione, which is a key intermediate of medicines (Prazosin, Bunazosin, and Doxazosin) was synthesized successfully in a 97% yield, using 0.1 equiv of DBU under scCO₂ (10 MPa) at 80 °C.     

PTC and organic bases–LiCl assisted alkylation of imidazolidinone–glycine iminic derivatives for the asymmetric synthesis of α-amino acids

Iminic derivatives of (4R,5S)-1,5-dimethyl-4-phenylimidazolidin-2-one and glycine 4 have been highly diastereoselectively alkylated with activated alkyl halides or electrophilic olefins either under PTC conditions or in the presence of the strong organic bases DBU or BEMP at −20°C in the presence of LiCl. Hydrolysis of the alkylated imino imides gave (S)-α-amino acids with recovery of the imidazolidinone chiral auxiliary.     

Conjugate addition of aromatic amines to ethenetricarboxylates

The conjugate addition of amines is considered to be a useful reaction in synthetic organic chemistry. The reaction of reactive electrophilic olefins, ethenetricarboxylates, and aromatic amines with and without catalytic Lewis acids such as ZnCl₂ and ZnBr₂ at room temperature gave amine adducts in high yields. The products were converted to α-amino acid, dl-aspartic acid derivatives. Using Lewis acids such as Sc(OTf)₃ and Zn(OTf)₂ at higher temperature (40-80 °C), the reaction of ethenetricarboxylates and N-methylaniline gave an aromatic substitution product. A catalytic enantioselective conjugate addition using a chiral Lewis acid was also investigated. For example, the reaction of 1,1-diethyl 2-tert-butyl ethenetricarboxylate with N-methylaniline in the presence of chiral bisoxazoline-Cu(II) complex in THF at −20 °C for 17 h gave an amine adduct in 91% yield and 78% ee. On the other hand, the reaction with aniline and primary aniline derivatives gave adducts with almost no ee%.     

Surface tension of water at 100°C

The surface tensions of water samples of various degrees of purity were measured at 100°C using the Wilhelmy slide method. The purest water, obtained by constant redistillation and overflowing of the distillate surface assayed at 60.22 dyn/cm which may be compared with 58.74 dyn/cm (σ = 5.994 mg/mm) reported in the literature. Samples of distilled water of lesser purity gave values between σ = 59.48 dyn/cm and σ = 60.16 dyn/cm. It is concluded that the accepted value at 100°C for water should be increased by 2.5%.     

Chemical reaction in chromatographic columns : Dehydrogenation of ethane over cadmium-exchanged zeolite 4A

Pulsed-flow techniques were used to detect considerable differences in the heats of adsorption of ethane and ethylene on various cadmium-exchanged zeolites 4A at temperatures up to 500°C. Higher values (about 10.0 kcal/mole) were observed for ethylene than for ethane (5.0 kcal/mole) at 300–400°C. Experimental verification is provided pertaining to the dehydrogenation of ethane in a gas chromatographic reactor. By appropriate choice of the reaction conditions, conversions up to 80% per pass could easily be obtained at temperatures (400–500°C) at which the thermodynamic equilibrium for a diluted ethane stream (Pc⁺₂ = 0.01-0.1 P_tot.) would not permit more than 25%.     

Perfluoroalkylated eight- and nine-membered benzoheterocycles from F-2-methyl-2-pentene

The reactions of $\text{F}$-2-methyl-2-pentene (1) with several $\text{ortho}$- difunctional benzenes afforded eight- and nine-membered benzoheterocyclic compounds carrying perfluoroalkyl groups. Salicylic acid, salicylaldehyde, and their methyl or chloro derivatives reacted in triethylamine-acetonitrile system giving perfluoroalkylated 2H,6H-1,5-benzodioxocin-2,6-dione (8) and 4H,6H-1,5-benzodioxocin (9) compounds respectively, while phthalyl alcohol and o-hydroxyphenethyl alcohol in triethylamine-diethyl ether system gave perfluoroalkylated 1H,3H,7H-2,6- and 4H,6H,7H-1,5-benzodioxonin compounds, (10) and (11). o-Aminobenzyl alcohol and (1) in diethyl ether afforded a perfluoroalkylated benzoxazocinobenzoxazocinone compound (15).