Protecting Triazabutadienes To Afford Acid Resistance

Recent work on triazabutadienes has shown that they have the ability to release aryl diazonium ions under exceptionally mild acidic conditions. There are instances that require that this release be prevented or minimized. Accordingly, a base‐labile protection strategy for the triazabutadiene is presented. It affords enhanced synthetic and practical utility of the triazabutadiene. The effects of steric and electronic factors in the rate of removal are discussed, and the triazabutadiene protection is shown to be compatible with the traditional acid‐labile protection strategy used in solid phase peptide synthesis.     

Light‐Activated Triazabutadienes for the Modification of a Viral Surface

Chemical crosslinking is a versatile tool for the examination of biochemical interactions, in particular host–pathogen interactions. We report the critical first step toward the goal of probing these interactions by the synthesis and use of a new heterobifunctional crosslinker containing a triazabutadiene scaffold. The triazabutadiene is stable to protein conjugation and liberates a reactive aryl diazonium species upon irradiation with 350 nm light. We highlight the use of this technology by modifying the surface of several proteins, including the dengue virus envelope protein.     

Electroless ultrasonic functionalization of diamond nanoparticles using aryl diazonium salts

We report a novel and very handful strategy for the functionalization of diamond nanoparticles (NDs), based on the ultrasound-assisted grafting of aryl groups from the electroless reduction of diazonium salts. For this study, 4-nitrobenzenediazonium salt was used as a model molecule and the reaction was investigated in neutral and acidic aqueous media. Spectroscopic evidence for the successful attachment of aryl groups to nanodiamonds (NDs) was given by IR and XPS which clearly detect characteristic NO₂ peaks. Moreover, the absence of any peaks from the ⁺N≡N group in the IR spectra is a clear indication of the chemical reduction of the parent diazonium salt at the surface of NDs. This spontaneous chemical modification of NDs by aryl diazonium salts was confined to the surface of the ND particles; indeed, XRD measurements have shown that the crystalline structure of the bulk of the particles was unaffected. It opens up new possibilities towards the control of the surface chemical composition of NDs using simple protocols operated in very soft conditions, i.e. in water at room temperature. It shows conclusively that the chemistry toolbox of experts interested in nanodiamonds should contain aryl diazonium salts, given their versatility in forming active platforms.     

Diazotization–azidation of amines in water by using crosslinked poly(4‐vinylpyridine)‐supported azide ion

The use of polymeric reagents simplifies routine azidation of diazonium salts, because it eliminates the traditional purification. An efficient, simple, and effective method for the preparation of aryl azides is described. The synthesis of aromatic azides from the corresponding amines is accomplished under mild conditions with sodium nitrite in the presence of p‐toluenesulfonic acid or concentrated H₂SO₄ at low temperature (0–5°C to room temperature). The obtained relatively stable diazonium salts, followed by treatment with a polymer‐supported azide ion in water at room temperature to produce the corresponding aryl azides. The spent polymeric reagents can be regenerated and reused for several times without losing their activity. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

In situ generation of diazonium cations in organic electrolyte for electrochemical modification of electrode surface

The modification of glassy carbon electrode was achieved by electrochemical reduction of in situ generated diazonium cations in acetonitrile. The in situ generation of 4-nitrophenyl diazonium cations in acetonitrile was investigated by spectroscopic methods. UV-visible spectroscopy revealed slow kinetics for the reaction of 4-nitroaniline with tert-butylnitrite in acetonitrile to form the corresponding diazonium cation. As a result, a coupling reaction, which implies a consumption of the amine and loss of the already formed diazonium cations, was evidenced by ¹H NMR spectroscopy. This spectroscopic study allowed the optimization of the in situ diazonium cations generation prior to the modification step. The electrochemical modification of the carbon electrodes with 4-nitrophenyl, 4-bromophenyl and anthraquinone groups was characterized by cyclic voltammetry and the resulting grafted layer were characterized by electrochemical techniques. The cyclic voltammetric behaviour during the electrochemical grafting was very similar to the one observed for an isolated diazonium salt dissolved in acetonitrile. In the case of the anthraquinone-modified electrode, the use of acetonitrile, into which the corresponding amine is soluble but not in aqueous media, allowed for its grafting by the in situ approach. The barrier properties of these grafted layers are similar to those obtained from isolated diazonium salts. Finally, the chemical composition of the grafted layers was determined by X-ray photoelectron spectroscopy and surface coverage in the range 5-7 × 10⁻¹⁰ mol cm⁻² was estimated for films grown in our experimental conditions.     

1,2,3-Triazabutadiene. V. Untersuchungen zum Mechanismus der thermischen cis-trans-Isomerisierung von substituierten 1-Aryl-3-[methylbenzthiazolinyliden-(2)]-triazenen

1,2,3-Triazabutadienes. V. Investigations of the Mechanism of the Thermal cis-trans Isomerisation of Substituted 1-aryl-3-[methylbenzthiazolinyliden-(2)]-triazenes The velocity of the thermal cis-trans-isomerisation of substituted 1-aryl-3-[methyl-benzthiazolinyliden-(2)]-triazenes was determined, varying the substituents in the aryl resp. benzo residue, the temperature and the solvent. Electron- withdrawing substituents in ortho- resp. para-position of the aryl residue and electron-releasing substituents in position 6 of the benzo residue increase the velocity of isomerisation as it do polar solvents and acid catalyst. In the aryl residue electron-releasing substituted and in meta-position electron-withdrawing substituted derivatives do not thermically isomerise in solution under the given conditions. From these results a polar rotation mechanism of the isomerisation around the NN-double bound of the triazabutadiene chain is concluded.     

Grafting and properties of a porous poly(methyl methacrylate) film on a silicon surface by a one‐step dipping method

In this study, we prepared a porous poly(methyl methacrylate) (PMMA) film on an Si surface with a novel dipping method. We conducted the process by directly dipping the Si substrate into acidic aqueous media in a simple flask at 10 °C. First, 4‐nitrobenzene diazonium tetrafluoroborate (NBD) was spontaneously reduced at the Si surface. Then, the aryl radicals during the reduction of NBD were directly grafted onto the Si surface. Meanwhile, the aryl radicals initiated the polymerization of methyl methacrylate (MMA) monomers, and the radical‐terminated PMMA chains formed in the solution were grafted onto the Si surface. Because water was a poor solvent for MMA, the grafted PMMA chains easily aggregated together, and this resulted in a porous polymer film. The porosity of the film depended on the grafting time and the MMA concentration. Furthermore, the permittivity of the porous PMMA film was relatively low, and its dielectric dissipation factor was extremely small. Therefore, its excellent dielectric properties should allow the porous film to have many applications in industry. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44930.     

Electroreduction of oxygen on glassy carbon electrodes modified with in situ generated anthraquinone diazonium cations

The electrochemical reduction of oxygen on glassy carbon (GC) electrodes modified with in situ generated diazonium cations of anthraquinone (AQ) has been studied using the rotating disk electrode (RDE) technique. The electrografting of the GC electrodes was carried out in two different media: in acetonitrile and in an aqueous acidic solution (0.5 M HCl). 1- and 2-Aminoanthraquinone were used as starting compounds for the formation of the corresponding diazonium derivatives. The anthraquinone diazonium cations were generated by reaction of the aminoanthraquinones with tert-butyl nitrite and sodium nitrite in acetonitrile and in 0.5 M HCl, respectively. For comparison purposes, the previously synthesised and crystallised diazonium tetrafluoroborates of anthraquinone were used for the GC surface modification. Cyclic voltammetry was employed to determine the surface concentration of AQ in O₂ free 0.1 M KOH. The electrocatalytic behaviour towards O₂ reduction was similar for all the AQ-modified electrodes studied. The kinetic parameters of oxygen reduction were determined using a surface redox catalytic cycle model. The rate constant of the reaction between the semiquinone radical anion of AQ and molecular oxygen was virtually independent of the point of attachment of the quinone to the electrode surface.     

Polarographic reduction of aryl hydrazono alloxans

The polarographic reduction of a number of coupled products of aryl diazonium salts with 1,3-dimethyl barbituric acid have been studied over a wide pH range. The effects of substituent groups, solvent composition, ionic strength, different cations and surface active compounds on the electrode reaction is discussed.     

An insight into the functionalisation of carbon nanotubes by diazonium chemistry: Towards a controlled decoration

The derivatisation of materials including iron, gold, and carbon by addition of diazonium salts is a reliable process to tune their interfacial interaction with the surrounding media. In this regard, the functionalisation of carbon nanostructures by diazonium chemistry is a versatile strategy to obtain soluble nanomaterials with degrees of functionalisation among the highest ever reported. Starting from these premises we have studied the functionalisation of multi-walled carbon nanotubes by addition of the aryl diazonium salts generated in situ by treatment of 4-methoxyaniline with isopentylnitrite. Following a thorough purification and characterisation protocol (UV–vis, TGA, ATR-IR, cyclic voltammetry, AFM and other surface analytical techniques), we have investigated the key parameters to obtain both functionalised multi-walled carbon nanotubes, where the amount of functional groups anchored to the carbon surface is less than a monolayer, and superfunctionalised carbon nanotubes, with a carbon nanotube core and a multilayered aryl coating. The results outlined provide the basis for the design and controlled processing of novel decorated carbon nanostructures that would be useful for a number of technological applications.     

Fast, efficient and convenient method for the preparation of arylazo sulfides using aryl diazonium silica sulfates under mild and solvent-free conditions

An efficient, fast, and straightforward procedure for the synthesis of arylazo sulfides and arylazo thiosulfonates is described in the present paper by using aryl diazonium silica sulfates and sodium thiolates. Using the present method, different kinds of aryl diazonium silica sulfates, containing electron-withdrawing groups as well as electron-donating groups, were rapidly converted to the corresponding arylazo sulfides in good yield and short reaction time. These reactions were carried out at room temperature under mild and solvent-free conditions. The use of non-toxic and inexpensive materials, simple and clean work-up, short reaction times and good yields are the advantages of this method.     

Polarographic studies on the coupled product of β-diketones with aryl diazonium chloride

Polarographic reduction of some coupled product of acetyl acetone with aryl diazonium chloride takes place in a single 4-electron transfer, giving a diffusion controlled irreversible waves in B.R. buffers of pH range 2–11.8. The reduction in these compounds takes place at the ---NH---N=C bond. Effect of various cations, anions, surfactant and solvent percentage on the reduction has been discussed.     

From α-arylation of olefins to acylation with aldehydes: a journey in regiocontrol of the Heck reaction

The Pd-catalyzed Mizoroki-Heck reaction of olefins with aryl halides, more often simply called the Heck reaction, was recently recognized with the 2010 Nobel Prize in chemistry. Although highly selective with electron-deficient olefins, which generally yield the linear β-arylated product exclusively, the Heck reaction is less satisfactory with electron-rich olefins. This substrate typically generates a mixture of both α- and β-arylated regioisomeric products, hampering wider application of the reaction in chemical synthesis. Pioneering studies by a number of researchers revealed that high α-regioselectivity could be obtained under Pd-diphosphine catalysis either through (i) the substitution of aryl triflates for halides or (ii) the addition of stoichiometric silver or thallium salts when aryl halides are used. Under these conditions, the arylation is believed to proceed via an ionic pathway. However, silver introduces added cost, thallium salts are toxic, and triflates are generally commercially unavailable, base sensitive, and thermally labile. Believing that the ionic pathway would be promoted in an ionic medium, in the early 2000s, we attempted the Pd-catalyzed arylation of the benchmark electron-rich olefin butyl vinyl ether with aryl bromides in an imidazolium ionic liquid. We were delighted to observe that highly regioselective α-arylation could readily be accomplished, with no need for silver additives, thallium additives, or aryl triflates. A range of other electron-rich olefins has since been shown to be viable as well. The high α-selectivity probably results from the high ionic strength of the medium, which facilitates the dissociation of halide anions from the [L(2)Pd(Ar)X] intermediate, channeling the arylation into the ionic pathway. Hydrogen bonding interactions may also play a role, however. We subsequently discovered that the α-arylation can indeed be significantly accelerated by a hydrogen bond donor salt, in both ionic liquids and common solvents. Evidence shows that the concentration of the cationic Pd(II)-olefin species along the ionic pathway is increased as a result of hydrogen bonding between the hydrogen bond donor and the halide anion. More recently, we reported that cheaper and greener alcohols allow the Heck arylation of electron-rich olefins to proceed in a much faster, productive, and totally α-regioselective manner, circumventing the need for an ionic medium or hydrogen bond donor salt. In particular, aryl chlorides with diverse properties have been demonstrated to be viable substrates for the first time. Significantly, it appears that ethylene glycol facilitates both the oxidative addition of ArCl to Pd(0) and the subsequent dissociation of chloride from Pd(II). A closely related reaction, acylation of aryl halides with aldehydes, was also developed. Proceeding via the intermediacy of an electron-rich enamine, this Pd-pyrrolidine cooperative catalysis affords alkyl aryl ketones in a straightforward manner, extending the Heck reaction from olefins to aldehydes.     

Temperature-Assisted Removal of Triphenylmethane Dyes from Water with Novel Hydrophobic Benzothiazolium Ionic Liquids

In this work, a simple and effective extraction method for triphenylmethane dyes from their aqueous solution was developed. Three novel task-specific ionic liquids based on N-alkylbenzothiazolium cations were prepared and their extraction performance in this new method was evaluated in self-prepared and real water samples. Through the control of temperature, the ionic liquids could be dispersed into the aqueous solution, first, to fully contact with the dyes and then easily recovered as tiny particles enriching these target compounds. Parameters of the extraction conditions including the amount of the ionic liquid, volume of the dispersing solvent, dissolving temperature, extraction time, pH value, and ionic strength have been investigated. The results showed that the major driven forces for the extraction were hydrogen bonding and hydrophobic interactions between the ionic liquids and the dyes. The proposed method combined the advantages of both homogeneous mixing and heterogeneous solid-liquid separation in extraction process, which was expected to lay the foundation for actual application in future.     

Products and intermediates formed during the biacetyl-sensitised photo-oxidation of some azo dyes

The flash irradiation for a few microseconds of aqueous aerobic solutions of biacetyl(2,3-butanedione) and a number of different o-arylazonaphthols resulted in the formation of the corresponding diazonium ions and α-naphthoquinones. This was verified from the intermediate spectra obtained after the flash. Verification for the formation of diazonium ions was also obtained from flow experiments, in which the diazonium ion was identified by coupling it to H-acid, forming a new azo compound. Less than equimolar formation of the diazonium ion from one of the azo dyes investigated indicated the occurrence of side reactions in which diazenyl radicals could play a role.     

Probing Site-Selective Conjugation Chemistries for the Construction of Homogeneous Synthetic Glycodendriproteins

Methods that site-selectively attach multivalent carbohydrate moieties to proteins can be used to generate homogeneous glycodendriproteins as synthetic functional mimics of glycoproteins. Here, we study aspects of the scope and limitations of some common bioconjugation techniques that can give access to well-defined glycodendriproteins. A diverse reactive platform was designed via use of thiol-Michael-type additions, thiol-ene reactions, and Cu(I)-mediated azide-alkyne cycloadditions from recombinant proteins containing the non-canonical amino acids dehydroalanine, homoallylglycine, homopropargylglycine, and azidohomoalanine.     

Rhodium‐Catalyzed Oxidative ortho‐Acylation of Aryl Ketone O‐Methyl Oximes with Aryl and Alkyl Aldehydes

The rhodium‐catalyzed oxidative ortho‐acylation of aryl ketone O‐methyl oximes with aryl and alkyl aldehydes via C H bond activation is described. The cross‐coupling reaction exhibits high functional group tolerance and regioselectivity under relatively mild conditions and constitutes a versatile route to a diverse library of diaryl ketones, which are difficult to obtain by the classical Friedel–Crafts acylation. Moreover, this reaction proceeds via an unprecedented Rh‐catalyzed oxidative ortho‐acylation of aryl ketone O‐methyl oximes with highly electron‐deficient aryl aldehydes followed by a direct addition of the second ortho C H bond to aldehydes in a one‐pot reaction, to generate two C C bonds simultaneously.     

Recent advantages in the metal (bulk and nano)-catalyzed S-arylation reactions of thiols with aryl halides in water: a perfect synergy for eco-compatible preparation of aromatic thioethers

Transition-metal-catalyzed C–S cross-coupling reactions comprise one of the most efficient methods for the synthesis of biologically and synthetically important aryl sulfide derivatives. Among the various solvents used in this cross-coupling reaction (ionic liquids, water, organic, and aqueous biphasic solvents), neat water have attracted notable interest in recent years due to its properties such as non-toxicity, non-flammability, renewability, and widely availability compared with other solvents. Since several catalytic systems for this green synthesis of aryl sulfides have been reported from 2007 to present, a comprehensive review on this interesting field seems to be timely. In this study, we discuss the most representative and interesting reports on the synthesis of aryl sulfides via metal-catalyzed cross-coupling of thiols with aryl halides in water. Mechanistic aspects of the reactions are considered and discussed in detail.     

Cation adsorption at a distearoylphosphatidic acid layer adsorbed at a liquid/liquid interface

The interfacial behaviour of tetraethylammonium cations (TEA⁺) at a liquid-liquid interface modified with an anionic phospholipid layer, distearoyl phosphatidic acid (DSPA), is analysed, with the purpose of characterising the permeation properties of the film. The TEA⁺ concentration in aqueous solution and the amount of DSPA solution employed to generate the lipidic layer, were varied. The results indicate that the layer is tightly compact and the transfer of TEA⁺ cations by permeation does not take place. Instead of this, TEA⁺ ions adsorb at the polar head groups of DSPA, and these adsorbed cations could be acting as nucleation centres of DSPA molecules when the DSPA amount is low.     

Removal of Divalent Metal Cations and Their Mixtures from Aqueous Streams Using Micellar-Enhanced Ultrafiltration

ABSTRACT

Micellar-enhanced ultrafiltration (MEUF) is a novel membrane-based separation technique that can be used to remove multivalent metal cations from aqueous streams. In this technique an anionic surfactant is added to the aqueous stream containing the metal cations to be removed. The surfactant forms highly charged aggregates called micelles onto which the metal cations adsorb or bind. The aqueous stream is then passed through an ultrafiltration membrane with pores small enough to block the passage of the micelles and adsorbed metal cations. In this study, MEUF has been shown to remove divalent cadmium, zinc, copper, and calcium ions and their mixtures with rejections of at least 96%. A previously developed equilibrium binding model describes the results successfully. Under reasonable conditions the flux rates are not substantially below that of pure water, indicating the feasibility of MEUF for industrial application.