Pyrazolo[1,5-a]pyrimidines are fused N-heterocyclic systems of a pyrazole.
They are considered as a key structural motif in many vital applications, such as medicinal,
pharmaceuticals, pesticides, dyes and pigments. Their synthetic routes have escalated
dramatically in the last decades. The current review is a recent synthetic survey of pyrazolo[
1,5-a]pyrimidines and their applications until recently.
A tricyanofuran hydrazone (TCFH) spectroscopic probe was produced to visually recognize Fe(III) ions in aqueous environments. The synthesis was started by reacting tricyanofuran with 4‐aminophenol diazonium chloride. All the synthesized compounds were characterized by spectroscopic analyses. TCFH showed distinctive solvatochromic behaviour in various organic polar solvents due to intramolecular charge transfer. Its behaviour towards sensing Fe(III) was studied using ultraviolet–visible spectrophotometry. The sensing behaviours of the proposed probe for other metal ions, namely Co(II), Cr(III), Mg(II), Pb(II), Cd(II), Ba(II), Hg(II), Mn(II), Ni(II), Cu(II), Zn(II), Ca(II), Al(III), Na(I) and K(I), were also investigated, but no spectral changes were observed, indicating the probe's potential use as a highly selective and Fe(III)‐sensitive colorimetric and fluorescent chemical sensor. The TCFH probe using EtOH/H2O (5:1; v/v) served as a colorimetric and fluorescent chemosensor for identification of Fe(III) by the naked eye owing to both its high sensitivity and selectivity towards Fe(III) compared with the other examined metal ions. The proposed TCFH probe can therefore be utilized as an effective spectroscopic sensor for Fe(III). Both colorimetric and fluorescence recognition of the analyte depended on the concentration of Fe(III) ions and was accomplished at a pH of 7. A rapid colour change from yellow to red occurred when an aqueous solution of Fe(III) ions was added. The intensity of the colour increased at higher Fe(III) concentrations. Cyclic voltammetry measurements in the dimethylformamide solvent indicated a nonreversible redox potential. This study also explained the possible mechanisms for both solvatochromism and the detection of Fe(III) through TCFH–Fe(III) complex formation. The binding constant of the generated TCFH–Fe(III) complex was explored. Computational modelling was conducted to explain the deprotonation‐triggered changes that occur in the photophysical properties of TCFH dyes.
Palladium(II) phthalocyanine (PdPc) tetrasulfonate was chemically bonded to an amine moiety of chitosan aerogel. The reaction was promoted by the transformation of sulfonic acid groups of PdPc to sulfonyl chloride, which is highly active for amination. The porous composite showed good catalytic activity in the oxidation reaction of some alkylarenes, aliphatic and benzylic alcohols, and cyclohexanol. High conversions and excellent selectivities were obtained for the solvent-free reactions under aerobic conditions at 80 °C during 24 h. While many oxidation reactions have been reported catalysed with palladium phthalocyanine, this is the first reported oxidation of alkylarenes via this catalyst. The organometallic compound is applicable as a heterogeneous catalyst having high chemical stability with recyclability up to six times.
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