Nonaqueous diazotization of 5-amino-1-aryl-1H-pyrazole-4-carboxylate esters

5-Amino-1-aryl-1H-pyrazole-4-carboxylate esters are converted to the corresponding desamino, chloro, bromo, iodo, and methylthio esters by processes involving nonaqueous diazotization. Diazotizing agents are alkyl nitrites except in the case of chlorine where nitrosyl chloride is used. Evidence is presented that the latter reagent leads to the formation of cationic rather than radical intermediates.     

N-Aminoarylpyridinium perchlorates and their behavior in diazotization

N-Aminoarylpyridinium salts react with nitrosyl perchlorate to give diazonium dications, which undergo diazo coupling, exchange a diazo group, and are cyclized by the Pschorr method.     

Determination of nitrite by simple diazotization method

A simple and rapid spectrophotometric method for the determination of nitrite is described. This is based upon simple diazotization reactions involving p-nitroaniline (PNA) and sulfanilamide (SA) with ethyl acetoacetate (EAA) as the coupling agent. The absorbance was measured at 507 and 356 nm, respectively. The method is optimized for acidity, amount of reagents required, amount of sodium hydroxide and the tolerance amount of other ions. The range of linearity for PNA-EAA couple was 0.05-6.0 μg ml⁻¹ of nitrite with molar absorptivity of 1.59×10⁴ l mol⁻¹ cm⁻¹; while that for SA-EAA couple was found to be 0.2-3.0 μg ml⁻¹ and 1.22×10⁴ l mol⁻¹ cm⁻¹, respectively. The method has been applied to various water and soil samples.     

Aromatic allylation via diazotization: metal-free C-C bond formation

A new method for the synthesis of allyl aromatic compounds not involving any metal-containing reagent or catalyst has been developed. Arylamines substituted with a large number of different substituents were converted via diazotizative deamination with tert-butyl nitrite in allyl bromide and acetonitrile to the corresponding allyl aromatic compounds. The allylation reaction was found to be suitable for larger scale synthesis due to short reaction times, a nonextractive workup, and robustness toward moisture, air, and type of solvent.     

Nonaqueous diazotization of 4-amino-3-arylisothiazole-5-carboxylate esters

4-Amino-3-arylisothiazole-5-carboxylate esters are converted to the corresponding desamino, chloro, bromo, and iodo esters by processes involving nonaqueous diazotization. These related procedures open up the possibility for the conversion of readily available heterocyclic ortho-amino esters and nitriles to related heterocyclic derivatives, which are not easily obtained by alternate routes.     

Ultrasound assisted diazotization and diazo coupling reactions using trichlorotriazine

A high rate and efficient procedure for the synthesis of azo dyes has been developed. This concluded the sequential diazotization-diazo condensation of aromatic amines such as 4,4′-sulfonyldianiline with NaNO₂, or trichlorotriazine with coupling agents under ultrasound irradiation at room temperature. This method applied to several types of coupling agents led to corresponding azo dyes in high yield within short reaction time. The mild reaction conditions and inexpensive procedure are clear advantages of this method.     

‘Interrupted’ diazotization of 3-aminoindoles and 3-aminopyrroles

‘Interrupted’ diazotization of 3-aminoindoles and 3-aminopyrroles, achieved by quenching with cold water immediately after the addition of nitrite, led, in good yields, to stable compounds whose structures were identified to be the diazonium species with nitrate as the counter ion, which show no saline character.     

The automatic amperometric and potentiometric microtitration of pharmaceutically important sulfanilamide derivatives by diazotization with nitrite

The automatic amperometric and potentiometric microtitration of pharmaceutically important sulfanilamide derivatives by diazotization with nitrite is described. Optimal conditions for diazotization and amperometric indication are discussed. A new cathodic amperometric indication of nitrite in M hydrochloric acid-25% ($\text{w}\text{v}$) of potassium bromide medium is proposed; the electrode processes involved are interpreted on the basis of current-potential curves. The effects of the hydrochloric acid and bromide concentrations, and of temperature on the limiting current are described. Sulfamethazine, sulfadimethoxine, sulfamethoxypyridazine and sulfamethoxypyrazine were titrated amperometrically in the range 10^?3–10^?6 M. Potentiometric titrations of these sulfanilamides were possible in the range 10^?3–10^?4 M.     

A new one-pot solvent-free synthesis of pyridinyl tosylates via diazotization of aminopyridines

A new, convenient, one-pot method for the synthesis of pyridinyl tosylates is developed. The procedure involves sequential diazotization/tosylation of aminopyridines with sodium nitrite and p-toluenesulfonic acid under solvent-free conditions in a water paste at room temperature.     

Continuous multiple liquid-liquid separation: diazotization of amino acids in flow

A second-generation laboratory-scale, modular liquid-liquid separation device based on computer-controlled high-pressure pumps and a high-resolution digital camera has been invented. The diazotization of amino acids to produce valuable chiral hydroxyacids is demonstrated in flow for the first time. The use of a triple-separator system in conjuction with the developed diazotization process allows the safe and efficient production and automated isolation of multigram quantities of valuable chiral hydroxyacids.     

Flow injection spectrophotometric determination of bromoxynil herbicide by diazotization method.

A flow injection spectrophotometric method is proposed for the determination of bromoxynil herbicide. Bromoxynil was hydrolyzed with HCl and the resulting product, 3,5-dibromo-4-hydroxyaniline, was diazotized with nitrite and coupled with aniline. The absorbance of the azo dye was measured at 500 nm. The conditions were optimized for diazotization using FIA. The range of linearity was found to be 0.01 to 5 ppm with a molar absorptivity of 1.27 x 10(5) L mol(-1) cm(-1). The % recovery for the determination of bromoxynil was found to be 91%. The sampling frequency was 80 samples per hour for FIA. The method is simple, fast, and has been successfully applied to the determination of bromoxynil in commercial formulations and food samples.     

A base-free, one-pot diazotization/cross-coupling of anilines with arylboronic acids

Pd-catalyzed one-pot diazotization/cross-coupling is realized for the synthesis of biaryls directly from anilines and arylboronic acids.     

Flow-injection spectrophotometry of nitrites based on the diazotization reactions of azine dyes

The diazotization reactions of azine dyes (safranin, Neutral Red, ethacridine, and trypaflavine) were studied under flow conditions. These reactions are accompanied by the formation of intensely colored diazo compounds with a high contrast (more than 100 nm). The formation, stability, and optical properties of these compounds in solutions were supported by quantum-chemical calculations. The kinetic stability of diazo compounds was found to be sufficient for the flow-injection detection of an output peak. Trypaflavine was found to be the best and most sensitive reagent; in this case, the diazotization reaction in 0.2 MHCl occurred especially rapidly and almost completely with a degree of conversion of 0.98. A procedure for the determination of nitrite ions based on the reaction with trypaflavine was developed. The combination of on-line preconcentration on an EDE-10P anion-exchange resin and the reaction at the instant of elution in a flow system allowed us to determine selectively low nitrite concentrations in water with the limit of detection equal to 2 ng/mL, as calculated according to Kaiser (3s) or IUPAC. The procedure developed was used for the monitoring of nitrite concentrations in various water samples; the throughput was 100 samples per hour.     

Spectrophotometric determination of trace amounts of aniline by diazotization coupling with N-(1-naphthyl)ethylenediamine and extraction

A spectrophotometric procedure is proposed for the determination of trace amounts of aniline by diazotization, coupling with N-(1-naphthyl)ethylenediamine in sodium acetate medium, extraction of the yellow dye with chloroform, and conversion into a reddish purple dye. Two methods are available for the conversion. In the first, the chloroform extract is shaken with hydrochloric acid and the dye is converted and transferred into the aqueous phase. In the other, the chloroform extract is evaporated to dryness and the residue is dissolved in glacial acetic acid. The hydrochloric acid extraction method is the more rapid. The minimum detection limits for the two methods are 0.8 and 0.6 mug/ml respectively. Both methods show satisfactory accuracy and precision.     

The non-intermediacy of benzo[1,2-d:2,3-d']bistriazole during the diazotization of a 4-aminobenzotriazole

Labeling studies with ¹⁵N demonstrate that a diazonium ion prepared from a 4-aminobenzotriazole does not cyclize to a tricyclic intermediate.     

Spectrophotometric determination of flavonoids using their diazotization with (4-nitrophenyl)diazonium tetrafluoroborate

(4-Nitrophenyl)diazonium tetrafluoroborate (4-NPD) has been proposed as the reagent for the spectrophotometric determination of flavonoids. 4-NPD has been demonstrated to undergo diazotization reaction with quercitin, naringenin, chrysin, morin, rutin, and naringin in an alkaline medium leading to the formation of yellow-orange products. The conditions of the spectrophotometric reaction have been optimized. A procedure for the spectrophotometric determination of flavonoids with the detection limits (1.5–3.9) × 10⁻⁷ M (0.05–0.16 μg/ml) has been developed. Quercitin has been determined in pharmaceutical preparations.