A simple one-pot procedure for the direct conversion of alcohols into azides using TsIm

A facile and efficient method for one-pot conversion of alcohols into azides using N-(p-toluenesulfonyl)imidazole (TsIm) is described. In this method, alcohols are refluxed with a mixture of NaN₃, TsIm and triethylamine in the presence of catalytic amounts of tetra-n-butylammonium iodide (TBAI) in DMF affording the corresponding alkyl azides in good yields. This methodology is highly efficient for various structurally diverse alcohols with selectivity for ROH: 1° > 2° > 3°.     

Tetrabutylammonium cyanide catalyzed diasteroselective cyanosilylation of chiral α-hydroxyketones

Tetrabutylammonium cyanide has been used as non-metallic catalyst for the diastereoselective cyanosilylation of α-hydroxyketones derived from the chiral pool. This affords α-substituted-α,β-dihydroxynitriles with high levels of asymmetric induction.     

Palladium-catalyzed homocoupling of aryl halides in the presence of fluoride

This report describes the fluoride-mediated homocoupling of aryl iodides and bromides catalyzed by palladium(0). This coupling protocol is tolerant of electron-donating and electron-withdrawing substitutents on the aryl halide, as well as ortho substitution. Optimum reaction conditions entail 10 mol% Pd(dba)₂, 3 equiv of tetrabutyl ammonium fluoride (TBAF) in DMF at 90 °C.     

Flow‐Injection Amperometric Detection with Solvent Polymeric Membrane Ion Sensors

An amperometric detector for hydrophobic ions based on a plasticized poly(vinyl) chloride (PVC) membrane incorporated in a flow‐injection system was developed. A four‐electrode potentiostat with ohmic drop compensation was used, while a flow‐through cell incorporated the four electrodes and the membrane, which contained tetrabutylammonium tetraphenylborate. When the influence of the applied potential and of the flow‐injection variables on the determination of tetrabutylammonium was studied, a linear relationship was observed between current peak height and ion concentration over a range of 5×10^?6–6×10^?5 M tetrabutylammonium. Good repeatability and between‐day reproducibility and high sample frequency were obtained. The effect of other ions was studied. Two different amperometric methods, indirect and direct, were also developed for the determination of dodecylsulfate in the concentration range 3×10^?5–9×10^?4 M.     

Competitive demethylation and substitution in N,N,N-trimethylanilinium fluorides

Fluorination of aromatic compounds by nucleophilic displacement of trimethylanilinium salts by fluoride is a commonly used reaction for radiotracer synthesis. Though the liberated trimethylamine is thought to be an excellent leaving group for this type of S_NAr reaction, scattered reports show that amine demethylation (reverse Menschutkin reaction) sometimes dominates over substitution, particularly when relatively electron rich fluoroarenes are the desired targets. Here we provide systematic experimental and theoretical studies of trimethylanilinium demethylation and substitution. Results from these studies highlight the limits of this leaving group in fluoroarene synthesis and have important ramifications for the design of nucleophilic fluorinating agents featuring ammonium cations.     

Evaluation of single-ion conductances in nonaqueous solvents at 25°C by the use of tetrabutylammonium tetrabutylboride as a reference electrolyte

Precise conductances for tetrabutylammonium tetrabutylboride (Bu₄NBBu₄) at 25°C have been measured in a number of nonaqueous solvents, and the data have been analyzed by the 1957 Fuoss-Onsager conductance equation. Limiting ion conductances for the Bu₄N⁺ ion at infinite dilution ₀(Bu ₄ N ⁺) in various solvents have been evaluated by dividing ₀ values of the salt into two equal parts. The ₀(Bu ₄ N ⁺) values so obtained are in fairly good agreement (within±0.1–3.5%) with the corresponding values determined from direct transference number measurements in these solvents.     

Retention of ionizable compounds on high-performance liquid chromatography. VII. Characterization of the retention of ionic solutes in a C18 column by mass spectrometry with electrospray ionization

The elution of ions from a C₁₈ column with mobile phases containing methanol (60%, v/v) and aqueous buffers is studied by mass spectrometry. It is demonstrated that the anions are excluded from the stationary phase by the ionized silanols. However, the ionized silanols interact strongly with cations, which are retained in the column. These cations are later eluted from the column by ion exchange with the cations present in the pH buffered mobile phase. The size of the ions, the mobile phase cation concentration and the mobile phase pH are the main parameters that affect elution of the retained cations. It is also demonstrated that there are at least two different types of ionizable silanols, with different acidities, that contribute to the retention of cations. An estimate of the pK_a values of these two groups of silanols in 60% methanol is given.     

Leitfähigkeitsmessungen an Tetraethylammoniumhexacyanoferrat(III) und Tetrabutylammoniumhexacyanoferrat(III) in verschiedenen Lösungsmitteln

Based on conductivity measurements, the dissociation of tetraalkylam-moniumhexacyanoferrates(III) in water, ethanol, formamide,N-methylformamide,N,N-dimethylformamide, propylenecarbonate and acetonitrile is discussed. Interactions of the solvent as donor and as acceptor, the latter interaction being dominant, with (et ₄N)₃Fe(CN)₆ and (bu ₄N)₃Fe(CN) were found to be important factors in the formation of solvated ions.

     

Hydroxy- and aminomethylation reactions in the formation of oligomers from l-tyrosine and formaldehyde in basic medium

The study of the reaction of l-tyrosine or its tetrabutylammonium salt with formaldehyde was performed. The results established that this reaction does not lead to macrocyclic amino acid-type compounds, and in all cases, mixtures of linear oligomers of two or more l-tyrosine units bound by methylene groups were obtained. The formation of ion pair-type linear aggregates in the tetrabutylammonium salt hinders the oligomerization reaction, allowing the isolation of an l-tyrosine dimer, unlike the l-tyrosine reaction, in which a trimer could be isolated.     

Electrogenerated acetonitrile anions/tetrabutylammonium cations: an effective catalytic system for the synthesis of novel chromeno[3′,4′:5,6]pyrano[2,3-d]pyrimidines

An efficient and convenient synthesis of novel chromeno[3′,4′:5,6]pyrano[2,3-d]pyrimidines is described, using the electrogenerated anion of acetonitrile as the base in the presence of tetrabutylammonium fluoride as an effective supporting electrolyte in a one-pot, three-component condensation of barbituric acid, an aromatic aldehyde or isatin, and 4-hydroxycoumarin. The reaction is carried out in an undivided cell containing an iron electrode as the cathode and a Pt electrode as the anode, at a constant current at room temperature.