Iminium Salts in Solid‐State Syntheses Giving 100% Yield

Numerous reaction types in the field of iminium salts are performed in the gas‐solid and solid‐solid techniques in order to reach 100% yield. The stoichiometric runs are waste‐free and do not require costly workup. Frequently, iminium salts were avoided, as acid catalysis was dispensable. Thioureas and α‐halogenated ketones give a variety of 2‐aminothiazoles via thiuronium salts in quantitative yield. A new intramolecular solid‐state thermal condensation is reported. Enaminoketones are synthesized quantitatively from anilines and 1,3‐diketones without catalysis and those can be used for quantitative solid‐state 4‐cascade reactions. Solid paraformaldehyde is used to produce methylene imines and internally trapped methylene iminium salts. Benzoylhydrazones are produced again without catalysis in the solid state. Vacuum and ball‐mill techniques are particularly useful in the production of highly sensitive iminium salts. Hexahydro‐1,3,5‐triazines cyclorevert upon exposure to HCl gas to give solid arylmethylene iminium chlorides as new versatile reagents. These are used in arylaminomethylations of β‐naphthol and of themselves to give Troeger's bases in 3‐cascades. More direct are 4‐cascade Troeger's base syntheses by dissolving hexahydro‐1,3,5‐triaryltriazines in trifluoroacetic acid. Alkylations of imines with trimethyloxonium tetrafluoroborate and triphenylmethyl cation give highly sensitive quaternary iminium salts in the ball‐mill. The products are characterized by spectroscopic techniques and density functional theory (DFT) calculations at the B3LYP 6‐31G* level. Molecular movements in the crystal and surface passivation are investigated with atomic force microscopy (AFM) techniques.     

Iminiumsalze in quantitativen Gas/Festköper- und Festkörper/Festkörper-Reaktionen

Iminium Salts in Quantitative Gas/Solid and Solid/Solid Reactions Iminium salts that are highly susceptible to hydrolysis are quantitatively prepared and reacted in the solid state without solvents or liquid phases. Atomic force microscopy AFM helps in elucidating the mechanism of these still unusual gas-solid and solid-solid syntheses by recording surface topographies of reacting crystals of L-histidine (10) and triphenylverdazyl (15) . Various imines add gaseous HCl or HBr to form stable iminium halides (1, 3, 4, 5, 11) even if frozen liquids of very weak heterocyclic bases are treated at low temperatures. Another way for quantitative yields of iminium salt hydrates (6) starts with solid primary ammonium halides and gaseous acetone. o-Phenylenediamines (7) give quantitatively 1,5-benzodiazepines (9) by solid state cyclization of bis-iminium salt intermediates (8) . Crystalline nitroxyls (12) and triphenylverdazyl (15) undergo stoichiometric one-electron transfer with gaseous NO₂ or XeF₂ to give nitrosonium (14) and azonium salts (17) . The solid state chlorination of tetramethylthiuramdisulfide (18) or dimethylthiocarbamoylchloride (20) yields phosgene dimethyliminiumchloride (Viehe salt 21 ) in quantitative yield. Solid Viehe salt is quantitatively treated with gaseous Cl₂ to give the trichloride 19 and solid SbCl₅ or PCl₅ to produce the hexachloroantimoniates (22) , -phosphates (23) . Solid brenzcatechol (24) , mercaptobenzimidazole (27) , p-nitroaniline (30) , N-methylbenzothiazolone-2-hydrazone (34) and acetophenone (41) are treated with 21 to give the corresponding chloroiminium salts (25, 28, 31, 35, 43) . p-Toluenesulfonamide (37) and 22 give the chloroiminium salt 38 . These quantitative solid-solid reactions are most easily run in ball mills with cooling device. The “waste-free” techniques achieve exclusion of moisture in an elegant way. The preparative use of the versatile products with nucleophiles is indicated. The three-step solid-state mechanisms are discussed.     

Some reactions of 1,3-Dichloro-2-azoniaallene Salts with heteronucleophiles

1,3-Dichloro-2-azoniaallene hexachloroantimonates ( 1 ) reacted with H₂S to give 1,2,4-dithiazolium salts 2 . With hydrazines 1,2,4-triazolium salts ( 3, 4 ) were formed. 1,3-Dimethylurea, respectively 1,3-dimethylthiourea or ethyl allophanate, reacted with 1 to afford 2-oxo- or 2-thioxo-1,3,5-triazinium salts ( 5–7 ). With diphenylmethaneimines imino substituted 2-azoniaallene salts 8 were produced. From chloroacetonitrile dichloropyrimidines 9 , and from the tricyanomethyl anion a hexatriene 10 and a triazine 11 could be prepared. The 1,5-dichloro substituted 2-azoniaallene salts 12 reacted as bifunctional electrophiles with nucleophiles such as benzophenone hydrazone or anilines, to furnish 1,3,5-triazinium salts 14 . Against benzohydrazide the allene 12j behaved as trivalent electrophile giving the bicyclic 1,3,5-oxadiazinium salt 13j , the constitution of which has been secured by a crystal structural analysis. The vinyl-2-azoniaallene salt 1i cyclized on heating to the 1,3-thiazinium salts 16, 17 . From 17 the triazinium salts 18 were prepared with alcohols.     

Nanoparticles of organosilane-based nitrite ionic liquid immobilized on silica for the diazotization of aniline derivatives and subsequent synthesis of azo dyes

Imidazolium based nitrite ionic liquid containing trimethoxysilyl group was prepared from the reaction of N-methylimidazole and (3-chloropropyl) trimethoxysilane. This ionic liquid was immobilized on silica covalently to give nanoparticles with the imidazolium nitrite moiety remaining intact. The diazotization reaction was performed as a model reaction to examine the activity of these nanoparticles as a nitrosonium source. Excellent performance was exhibited in the diazotization reaction of various aniline derivatives in the presence of HCl under mild heterogeneous conditions (room temperature and short reaction time). In-situ coupling of diazonium salts to a range of tertiary anilines, phenols and naphthols afforded the requisite azo dyes in good yield, using standard experimental procedures.     

Multicomponent Synthesis of 1,2,3‐Triazoles in Water Catalyzed by Copper Nanoparticles on Activated Carbon

Copper nanoparticles on activated carbon have been found to effectively catalyze the multicomponent synthesis of 1,2,3‐triazoles from different azide precursors, such as organic halides, diazonium salts, anilines and epoxides in water. The first one‐pot transformation of an olefin into a triazole is also described. The catalyst is easy to prepare, very versatile and reusable at a low copper loading.     

The Interaction of Isopenicillin N Synthase with Homologated Substrate Analogues δ‐(L‐α‐Aminoadipoyl)‐L‐homocysteinyl‐D‐Xaa Characterised by Protein Crystallography

Isopenicillin N synthase (IPNS) converts the linear tripeptide δ‐(L ‐α‐aminoadipoyl)‐L ‐cysteinyl‐D ‐valine (ACV) into bicyclic isopenicillin N (IPN) in the central step in the biosynthesis of penicillin and cephalosporin antibiotics. Solution‐phase incubation experiments have shown that IPNS turns over analogues with a diverse range of side chains in the third (valinyl) position of the substrate, but copes less well with changes in the second (cysteinyl) residue. IPNS thus converts the homologated tripeptides δ‐(L ‐α‐aminoadipoyl)‐L ‐homocysteinyl‐D ‐valine (AhCV) and δ‐(L ‐α‐aminoadipoyl)‐L ‐homocysteinyl‐D ‐allylglycine (AhCaG) into monocyclic hydroxy‐lactam products; this suggests that the additional methylene unit in these substrates induces conformational changes that preclude second ring closure after initial lactam formation. To investigate this and solution‐phase results with other tripeptides δ‐(L ‐α‐aminoadipoyl)‐L ‐homocysteinyl‐D ‐Xaa, we have crystallised AhCV and δ‐(L ‐α‐aminoadipoyl)‐L ‐homocysteinyl‐D ‐S‐methylcysteine (AhCmC) with IPNS and solved crystal structures for the resulting complexes. The IPNS:Fe^II:AhCV complex shows diffuse electron density for several regions of the substrate, revealing considerable conformational freedom within the active site. The substrate is more clearly resolved in the IPNS:Fe^II:AhCmC complex, by virtue of thioether coordination to iron. AhCmC occupies two distinct conformations, both distorted relative to the natural substrate ACV, in order to accommodate the extra methylene group in the second residue. Attempts to turn these substrates over within crystalline IPNS using hyperbaric oxygenation give rise to product mixtures.     

Synthesis and characterization of N‐methyl‐2‐nitrodiphenylamine‐4‐diazonium salt and its diazoresin

A new substituted diphenylamine diazonium salt, N‐methyl‐2‐nitrodiphenylamine‐4‐diazonium salt (MNDDS) and its diazoresin (MNDDS‐resin) were synthesized and their thermostability as well as photosensitivity were investigated. The results show that MNDDS and resin exhibit much higher thermostability than that of the parent compound, diphenylamine‐4‐diazonium salt (DDS) and resin (DDS resin) in solid state or in coating but the photosensitivities of them are confirmed to be in same level. The excellent thermostability of MNDDS and its diazoresin is very important because the storage life of a negative presensitized plate is mainly dependent on it. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 189–193, 1999     

α-Arylamino-cyanomethylen-pyrazolinone aus Azomethinfarbstoffen und Malonsäuredinitril

α-Arylamino-cyanomethylene-pyrazolinones from Azomethine Dyes and Malonodinitrile The reaction of azomethine dyes ( 1a–g ) with malonodinitrile ( 2 ) gives dicyanomethylene-pyrazolin-5-one ( 4 ) which immediately reacts with the eliminated anilines by HCN-amine exchange giving the deeply coloured arylamino-cyanomethylene-pyrazolinones ( 5a–g ). Structural investigations and a study of the absorption characteristic are described.     

Fotochemische Primärprozesse von Xanthenfarbstoffen. X. Zum Einfluß ionischer Mizellen auf die Löschung der Fluoreszenz von Xanthenfarbstoffen durch Diazoniumionen

Photochemical Primary Processes of Xanthene Dyes. X. The Influence of Ionic Micelles on the Fluorescence Quenching of Xanthene Dyes with Diazonium Ions The steady-state and the time-resolved fluorescence quenching of xanthene dyes by diazonium salts is investigated. The fluorescence of anionic dyes is more efficiently quenched than that of cationic dyes, due to the opposite charge. In the presence of anionic micelles the fluorescence quenching of cationic dyes by diazonium ions is more effective than in water, because the dye and diazonium ions are solubilized in the Stern region of the micelles. In the presence of cationic micelles the fluorescence of anionic dyes is effectively quenched by p-dodecyloxybenzene-diazonium salt solubilized in the micelles like a tensid ion. The equilibrium constants for the distribution of the diazonium ions between the micelles and the water phase are determined. The importance of the singlet state for the sensitized photolysis of diazonium salts is discussed.     

Hafnium Triflate as an Efficient Catalyst for Direct Friedel–Crafts Reactions of Chromene Hemiacetals

The direct Friedel–Crafts reaction of chromene hemiacetals with indoles, furans and sterically hindered anilines has been accomplished with high selectivity and excellent yields in the presence of a catalytic amount of hafnium triflate [Hf(OTf)₄, 0.1 mol%, 0–40 °C]. The mild conditions tolerate various sensitive functional and protecting groups, and the products were confirmed unambiguously from their spectra and by single‐crystal X‐ray analysis. This direct Friedel–Crafts reaction of chromene hemiacetals should inspire and encourage the consideration of hafnium triflate in the development of mild reaction conditions for the efficient derivatization of hemiacetal‐containing compounds.     

A new nitrite ionic liquid (IL-ONO) as a nitrosonium source for the efficient diazotization of aniline derivatives and in-situ synthesis of azo dyes

A new task-specific nitrite containing ionic liquid derived from the O-nitrosation of N-methyl-N-hydroxybutylimidazolinium chloride was synthesized and used as a source of nitrosonium ion to affect the efficient diazotization of arylamines. The diazonium salts thus obtained were coupled, using standard experimental procedures, to a range of tertiary anilines, phenols and naphthols to afford the requisite azo dyes in good yield. The diazotization and subsequent azo-coupling generated the related azo dyes at 0-5 °C in short reaction times with a simple experimental procedure.     

Rapid expansion of cellulose triacetate from ethyl acetate solutions

Rapid‐expansion‐of‐supercritical‐solution (RESS) experiments were performed for solutions of cellulose triacetate [CTA; weight‐average molecular weight = 145,700, polydisperity = 2.07] in ethyl acetate [EA] over a range of concentrations and conditions of polymer–solvent phase behavior. Solid‐solubility experiments were carried out beforehand and identified hot and compressed liquid EA at approximately 175°C as a good solvent for CTA. Cloud‐point measurements were then used to locate the region of liquid–liquid equilibrium (LLE) for this system. The RESS results indicate that the phase state of the pre‐expansion mixture determines the product size, and the overall concentration of the pre‐expansion mixture determines the product morphology. However, we have also discovered a new constraint: for the production of well‐formed fibers and particles, the rapid‐expansion path must include penetration into a region of LLE, which must exist over a sufficient pressure range so that a separate, polymer‐rich liquid phase has time to develop before the onset of vapor–liquid equilibrium (VLE). If rapid expansions are carried out at temperatures near or below the lower critical end point, the expansion path leads directly into a region of VLE, and a disruptive vapor expansion occurs within the continuous liquid phase. In this case, hollow particles, hollow structures, and even foams are produced. By the proper choice of operating conditions, we were able to produce continuous CTA fiber from a 5 wt % solution in EA at 250°C and 69 bar. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 290–299, 2005     

Effect of particle tethering and Scale‐Up on solid–liquid mass transfer in Three‐Phase fluidized beds of light particles

Solid–liquid mass transfer in three‐phase fluidized beds with low‐density particles was studied using a tethered benzoic acid particle dissolution technique. Two columns with air, water and polypropylene cylinders were used for experiments. The solid–liquid mass transfer coefficient was found to increase with column diameter but decrease with tether length. The effect of tethering on solid particle movements was also evaluated using radioactive particle tracking (RPT) technique. RPT showed that tethered particles exhibited slower movements. Statistical analysis suggests that tether lengths 3 times the column radius are sufficient to reduce the effects of tethering.     

Heck–Matsuda Arylation of Olefins Through a Bicatalytic Approach: Improved Procedures and Rationalization

The scope of the palladium‐catalyzed Heck–Matsuda reaction, proceeding through the catalytic activation of anilines into the corresponding diazonium salts, has been considerably extended and is now working with deactivated electrophiles. Two different procedures, using catalytic amounts of both palladium and acid, have been optimized allowing the concept of bicatalysis to cover the complete electronic range of anilines. These environmentally friendly procedures proceed under very mild conditions, at room temperature in methanol, and only generate tert‐butyl alcohol, water and nitrogen as by‐products. Rationalization of reaction outcomes encountered in this work has been discussed with the support of computational studies.

     

二苯胺型重氮盐在乙醇中的光,热分解

芳基重氮盐在乙醇中的光热分解已有很多研究［１～７］,但分解产物及提出的分解机理不完全统一．就一般的观点,芳基重氮盐在光热的作用下可以采取异裂或均裂的分解方式,以苯基重氮盐为例,可表示如下：式中Ｘ－为Ｃｌ,ＨＳＯ４,ＢＦ４等负离子异裂产生芳基正离子中间...     

Synthesis and characterization of tetrakis‐ derivatives of bisphenol‐A with 4‐phenylazoaniline and 5‐(4‐aminophenylazo)‐25,26,27‐tribenzoyloxy‐ 28‐hydroxycalix[4]arene

The synthesis of tetrakis‐ derivatives of bisphenol‐A containing azo groups at their 2,2′,6,6′‐positions is reported. Novel examples of bisphenol‐A, coupled with diazonium salts and derived from 4‐phenylazoaniline and 5‐(4‐aminophenylazo)‐25,26,27‐tribenzoyloxy‐28‐hydroxycalix [4]arene, have been synthesized. It has been observed that the coupling reaction of diazonium salt obtained from 4‐phenylazoaniline with bisphenol‐A gives tetrakis‐ while those derived from 5‐(4‐aminophenylazo)‐25,26,27‐tribenzoyloxy‐28‐hydroxycalix [4]arene give partially substituted bisphenol‐A analogues. The newly prepared tetrakis‐azo substituted bisphenol‐A compounds ( 1 and 2 ) are characterized by using UV‐vis, FT‐IR, ¹H‐NMR spectroscopic methods as well as elemental analysis techniques. These azo compounds give rise to bathochromic shifts in the absorption spectra, which can even be detected by “naked eye.” © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Modelling and simulation of trickle‐bed reactors using computational fluid dynamics: A state‐of‐the‐art review

Trickle‐bed reactors (TBRs), which accommodate the flow of gas and liquid phases through packed beds of catalysts, host a variety of gas–liquid–solid catalytic reactions, particularly in the petroleum/petrochemical industry. The multiphase flow hydrodynamics in TBRs are complex and directly affect the overall reactor performance in terms of reactant conversion and product yield and selectivity. Non‐ideal flow behaviours, such as flow maldistribution, channelling or partial catalyst wetting may significantly reduce the effectiveness of the reactor. However, conventional TBR modelling approaches cannot properly account for these non‐ideal behaviours owing to the complex coupling between fluid dynamics and chemical kinetics. Recent advances in the application of computational fluid dynamics (CFD) to three‐phase TBR systems have shown promise of achieving a deeper understanding of the interactions between multiphase fluid dynamics and chemical reactions. This study is intended to give a state‐of‐the‐art overview of the progress achieved in the field of CFD simulation of TBRs over the past two decades. The fundamental modelling framework of multiphase flow in TBRs, advances in important constitutive models, and the application of CFD models are discussed in detail. Directions for future research are suggested.     

Effects of calcium on setting mechanism of metakaolin‐based geopolymer

Geopolymer setting is seen to be substantially accelerated by addition of calcium and the objective of this study was to determine the mechanism for this effect by examining metakaolin geopolymers with and without calcium. Solid‐state ²⁷Al NMR tests were used to examine the dissolution extent both qualitatively and quantitatively. Solid‐state ²⁹Si NMR tests were conducted to determine the amount and structure of each phase. Prior to the quantitative tests, chemical extractions were used to facilitate assignment of peaks in each spectrum. On addition of calcium, it was found that both the rate and the extent of metakaolin dissolution were enhanced. Accelerating dissolution increases the Al concentration in solution, thus reducing Si/Al available for geopolymer gel formation and further accelerating the gel formation to cause faster setting. Although C‐A‐S‐H was observed in the calcium mix, no evidence indicated that it is directly involved in setting.     

Synthesis and thermal properties of bismaleimides with mesogen aromatic amide–ester and flexible polymethylenic group

Four bismaleimides with mesogen “amide–ester” aromatic and flexible polymethylenic group variable length (8 ≤ n ≤ 11) were synthesized in two stages, producing yields exceeding 80%. These bismaleimides (BMIs) were obtained after several purifications by dissolution—precipitation in dimethylformamide–methanol (1/4) with over 94% purity (high‐performance liquid chromatography). These pure BMIs were characterized by nuclear magnetic resonance, Fourier transform infrared spectroscopy, and elemental analysis and studied by differential scanning calorimetry, thermogravimetric analysis, polarized light microscopy, and X‐ray diffraction. Solubilities and thermal properties show effects of parity. The even BMIs are more difficult to solubilize than the odd BMI. The melting points of the even BMI (approximately, 220°C) are far higher than those of odd BMI (approximately, 160°C). Crosslinking temperatures of even BMI are close to 230°C, whereas odd BMI crosslinking temperatures are higher (approximately, 250°C). Even BMIs give rise to a liquid crystal state upon melting. Under the same conditions, odd BMIs give rise to an amorphous state; however, after crosslinking, the four bismaleimides give rise to an ordered liquid crystal state of smectic type. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

3‐D numerical simulations on flow and mixing behaviors in gas–liquid–solid microchannels

Three‐dimensional (3‐D) gas‐liquid–solid flow and mixing behaviors in microchannels were simulated by coupled volume of fluid and discrete phase method and simulations were validated against observations. The detachment time and length of gas slug are shortened in liquid–solid flow, compared with those in liquid flow due to higher superficial viscosity of liquid–solid mixture, which will move the bubble formation toward the dripping regime. Solid particles mainly distribute in liquid slug and particle flow shows obvious periodicity. With the increase of contact angle of the inner wall, gas slug (0–50°), stratified (77–120°), and liquid drop (160°) flows are observed. The residence time distributions of solid and liquid phases are similar because particles behave as tracers. The backmixing of solid and liquid phases in liquid drop flow is the weakest among the three flow patterns, and the backmixing of gas phase in slug flow is weaker than that in both stratified and liquid drop flows. The results can provide a theoretical basis for the design of microreactors. © 2013 American Institute of Chemical Engineers AIChE J, 59: 1934–1951, 2013