Symmetric 2,5-bisazopyrroles 2(a-d) were synthesized by a one-step reaction of substituted phenyl diazonium salts [R'(Ph)N2(+)Cl-] [a, R' = 4-N(CH3)2; b, R' = 2-OH; c, R' = 2-CO2H; d, R' = 4-NO2] with pyrrole under basic conditions. Asymmetric 2,5-bisazopyrroles 3(a-d) were synthesized by reacting substituted phenyl diazonium salts [R''(Ph)N2(+)Cl-] (a, R'' = 4-OCH(3); b, R'' = H; c, R'' = 4-Br; d, R'' = 4-NO2) with 2-(4-dimethylaminophenylazo)-1H-pyrrole (1a) under the same conditions. The reactions of 2a with boron trifluoride and iodomethane provided a BF2-azopyrrole complex of 1H-pyrrolo[2,1-c]-1,2,4,5-boratriazole (4) and 2,5-bisazo-1-methylpyrrole 5. X-ray crystallographic and spectral analysis of 1a, 2a, 2b, and 4 showed that 1a has three crystal forms: 1a(I), 1a(II), and 1a(III), the latter two bearing a bicyclic ring system formed via intermolecular hydrogen bonding. Complex 4 was found to be the most planar due to a rigid trans-azo configuration and has the longest N horizontal lineN bond distances (1.322 and 1.300 Angstrom) and wavelength of maximum absorption (754 nm). The N horizontal lineN bond distances increase in the sequence of monoazopyrrole [1a(I): 1.253 Angstrom], bisazopyrrole (2a: 1.283 Angstrom), bisazopyrrole with intramolecular hydrogen bonding (2b: 1.293 and 1.293 Angstrom), and the BF2-azopyrrole complex. Their maximum absorptions shift bathochromically in the sequence of monoazopyrrole (1a: 443 nm), bisazopyrroles [2(a-d), 3(a-d), 5: 486-615 nm], and the BF2-azopyrrole complex. These results are important for the design of near-infrared absorbing azo dyes and suggest an efficient path for the preparation of near-infrared absorbing azo dyes by effectively enhancing pi-electron delocalization.

Near-Infrared Absorbing Azo Dyes: Synthesis and X-ray Crystallographic and Spectral Characterization of Monoazopyrroles, Bisazopyrroles, and a Boron−Azopyrrole Complex

DDQ-mediated formation of carboncarbon bonds: Oxidation of imines

A highly sensitive spectrophotometric determination of chromium using leuco Xylene cyanol FF

Cooperative intramolecular hydrogen bonding induced azo-hydrazone tautomerism of azopyrrole: Crystallographic and spectroscopic studies

Spectrophotometric determination of microgram amounts of adrenaline with chloranil

Spectrophotometric determination of microgram amounts of aromatic aldoximes with chloranil

Indirect spectrophotometric determination of chromium(VI)

A sensitive spectrophotometric method for the determination of trace amounts of pyrrole in aqueous solution is described. The method is based on the reaction of pyrrole with diazotised 4-nitroaniline to produce, in the presence of sodium acetate, an intense yellow, water-soluble, stable monoazo dye, which shows maximum absorption at 420 nm. A graph of absorbance versus concentration indicates that Beer's law is obeyed over the concentration range 5–100 µg of pyrrole in a final volume of 25 ml, i.e., 0.2–4 p.p.m., with a molar absorptivity of 2.32 × 104 l mol–1 cm–1, a Sandell sensitivity of 0.0029 µg cm–2, a relative error of +0.9 to –1.7% and a relative standard deviation of 0.6–2.0%, depending on the concentration. A study has been made to determine the optimum conditions of the colour reaction. Interferences from foreign organic compounds have been examined and the structure of the monoazo dye is suggested.

Diazotised 4-nitroaniline as a chromogenic reagent for the determination of trace amounts of pyrrole in aqueous solution

Reagent for the spectrophotometric determination of iron (II) in alkaline solution

A spectrophotometric method for the determination of trace amounts of indole in aqueous solution is described. The method is based on the coupling reaction of the determinand with diazotised sulphanilic acid to form, in an acidic medium, an intense yellow, water-soluble, stable azo dye, which shows maximum absorption at 445 nm. The graph of absorbance versus concentration in linear, indicating that Beer's law is obeyed over the range 30–90 µg of indole in a final volume of 25 ml, i.e., 1.2–3.6 p.p.m., with a molar absorptivity of 33.4 × 103 l mol–1 cm–1, a sensitivity index of 0.0035 µg cm–2, a relative error of 0 to –1.6% and a relative standard deviation of 0.2–1.9%, depending on the determinand concentration. The optimum reaction conditions and interferences from foreign organic compounds have been investigated.

Younis I. Hassan

Papers

Spectrophotometric determination of microgram amounts of aromatic aldoximes with chloranil

Indirect spectrophotometric determination of chromium(VI)

Diazotised 4-nitroaniline as a chromogenic reagent for the determination of trace amounts of pyrrole in aqueous solution

Reagent for the spectrophotometric determination of iron (II) in alkaline solution

Diazotised sulphanilic acid as a spectrophotometric reagent for the determination of trace amounts of indole in aqueous solution