6-Methylpyridine-2-aldehyde p-nitrophenylhydrazone as an indicator for colorimetric pH measurements

6-Methylpyridine-2-aldehyde p-nitrophenylhydrazone is suggested as an indicator for colorimetric pH measurements in the high-alkaline range. Absorption spectra and indicator constant have been reported. Color change interval, reversibility, and intensity of color have been established. A comparative study with regard to previously proposed pyridine-2-aldehyde and benzaldehyde p-nitrophenylhydrazones is made. A good stability of color is obtained.     

Spectrophotometric determination of palladium by solvent extraction as the Pd(II)-biacetylmonoxime 2-pyridylhydrazone complex

Determination of trace levels of palladium(II) is described. The method relies upon the extraction of palladium(II)-biacetylmonoxime 2-pyridylhydrazone (BMPH) from aqueous acidic solution into chloroform to form a purple-reddish complex. The molar absorptivity of the Pd-BMPH complex is about 7500 liters mol^?1 cm^?1 at 560 nm in the chloroform extract. The highly colored chloroform extract is suitable for spectrophotometric determination. The method devised has been applied to the determination of palladium in $\text{Pd}\text{CaCO}{}_3$ catalyst with good results.     

Oxydehydrogenation of alkylbenzenes on Rh/AlPO4 catalysts

The oxidative dehydrogenation of several alkylbenzens has been carried out at 673–823 K on rhodium supported on AlPO₄. A compensation effect between H and S activation parameters was obtained. This fact allows us to assume an identical mechanism for the dehydrogenation process when carried out on Rh/AlPO₄ or on AlPO₄ supports. Furthermore, the higher catalytic activity of the supports with respect to rhodium catalysts is explained by the higher number of acid sites in these supports.

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, AlPO₄, 673–823 K. H^* S^*. , Rh/AlPO₄ AlPO₄ . , .

     

Effects of diphosphine structure on aurophilicity and luminescence in Au(I) complexes

The effects of diphosphine flexibility and bite angle on the structures and luminescence properties of Au(I) complexes have been investigated. A range of diphosphines based on heteroaromatic backbones [bis(2-diphenylphosphino)phenylether (dpephos), 9,9-dimethyl-4,5-bis(diphenylphosphino)xanthene (xantphos), and 4,6-bis(diphenylphosphino)dibenzofuran (dbfphos)] has been used to prepare mono- and digold derivatives. A clear relationship between the presence of aurophilic contacts and the emission properties of dinuclear complexes has been observed, with one of the complexes studied, [Au(2)Cl(2)(micro-xantphos)], exhibiting luminescence thermochromism.     

Alkylation of phenol with dimethyl carbonate over AlPO4, Al2O3 and AlPO4-Al2O3 catalysts

The vapor-phase catalytic alkylation of phenol with dimethyl carbonate over different AlPO₄ (Al/P=1), Al₂O₃ and AlPO₄-Al₂O₃ (5–25 wt.% Al₂O₃) catalysts produces anisole (O-alkylation) as the major reaction product althougho-cresol (C-alkylation) and methylanisoles were also found. The reaction is first order in phenol while O-and C-alkylation follow parallel processes. As compared with methanol, DMC is far more effective as a methylating agent, and the methylation proceeds at a lower temperature and with higher O-alkylation selectivity.     

From ketenimines to ketenes to quinolones: two consecutive pseudopericyclic events

[reaction: see text] N-[2-(Alkyl- or arylthio)carbonyl]phenyl ketenimines undergo cyclization under mild thermal conditions to afford 2-alkyl(aryl)thio-3H-quinolin-4-ones by means of the 1,5-migration of the alkyl(aryl)thio group from the carbonyl carbon to the central carbon atom of the ketenimine fragment followed by the 6pi-electrocyclization of the resulting vinyliminoketene. These 1,5-migration and electrocyclization processes occur via transition states whose pseudopericyclic characteristics have been established on the basis of their magnetic properties, geometries, and NBO analyses.     

Dinuclear copper(I) and copper(I)/silver(I) complexes with condensed dithiolato ligands

The Cu(III) complex Pr 4N[Cu{S 2C=( t-Bu-fy)} 2] ( 1) ( t-Bu-fy = 2,7-di- tert-butylfluoren-9-ylidene) reacts with [Cu(PR 3) 4]ClO 4 in 1:1 molar ratio in MeCN to give the dinuclear complexes [Cu 2{[SC=( t-Bu-fy)] 2S}(PR 3) n ] [ n = 2, R = Ph ( 2a); n = 3, R = To ( 3b); To = p-tolyl]. The analogue of 2a with R = To ( 2b) can be obtained from the reaction of 3b with 1/8 equiv of S 8. Compound 2b establishes a thioketene-exchange equilibrium in solution leading to the formation of [Cu 4{S 2C=( t-Bu-fy)} 2(PTo 3) 4] ( 4b) and [Cu 2{[SC=( t-Bu-fy)] 3S}(PTo 3) 2] ( 5b). Solid mixtures of 4b and 5b in varying proportions can be obtained when the precipitation of 2b is attempted using MeCN. The reactions of 1 with AgClO 4 and PPh 3, PTo 3 or PCy 3 in 1:1:4 molar ratio in MeCN afford the heterodinuclear complexes [AgCu{[SC=( t-Bu-fy)] 2S}(PR 3) 3] [R = Ph ( 6a), To ( 6b), Cy ( 6c)]. Complex 6c dissociates PCy 3 in solution to give the bis(phosphine) derivative [AgCu{[SC=( t-Bu-fy)] 2S}(PCy 3) 2] ( 7c), which undergoes the exchange of [M(PCy 3)] (+) units in CD 2Cl 2 solution to give small amounts of [Cu 2{[SC=( t-Bu-fy)] 2S}(PCy 3) 2] ( 2c) and [Ag 2{[SC=( t-Bu-fy)] 2S}(PCy 3) 2] ( 8c). Complexes 6a and b participate in a series of successive equilibria in solution, involving the dissociation of phosphine ligands and the exchange of [M(PCy 3)] (+) units to give 2a or 3b and the corresponding disilver derivatives [Ag 2{[SC=( t-Bu-fy)] 2S}(PR 3) 2] [R = Ph ( 8a), To ( 8b)], followed by thioketene-exchange reactions to give [AgCu{[SC=( t-Bu-fy)] 3S}(PR 3) 2] [R = Ph ( 9a), To ( 9b)]. Complexes 9a and b can be directly prepared from the reactions of 1 with AgClO 4 and PPh 3 or PTo 3 in 1:1:3 molar ratio in THF. The crystal structures of 3b, 6b, 6c, 7c, and 9a have been solved by single-crystal X-ray diffraction studies and, in the cases of 7c and 9a, reveal the formation of short Ag...Cu metallophilic contacts of 2.8157(4) and 2.9606(6) A, respectively.     

Acetonimine and 4-imino-2-methylpentan-2-amino platinum(II) complexes: synthesis and in vitro antitumor activity

The reaction of [Pt(dmba)(PPh3)Cl] [where dmba = N,C-chelating 2-(dimethylaminomethyl)phenyl] with aqueous ammonia in acetone in the presence of AgClO4 gives the acetonimine complex [Pt(dmba)(PPh3)(NH=CMe2)]ClO4 (1). The reaction of [Pt(dmba)(DMSO)Cl] with aqueous ammonia in acetone in the presence of AgClO4 gives a mixture of [Pt(dmba)(NH=CMe2)2]ClO4 (2) and [Pt(dmba)(imam)]ClO4 (3a) (where imam = 4-imino-2-methylpentan-2-amino). [Pt(dmba)(DMSO)Cl] reacts with [Ag(NH=CMe2)2]ClO4 in a 1:1 molar ratio to give [Pt(dmba)(DMSO)(NH=CMe2)]ClO4 (4). The reaction of [Pt(dmba)(DMSO)Cl] with 20% aqueous ammonia in acetone at 70 degrees C in the presence of KOH gives [Pt(dmba)(CH2COMe)(NH=CMe2)] (5), whereas the reaction of [Pt(dmba)(DMSO)Cl] with 20% aqueous ammonia in acetone in the absence of KOH gives [Pt(dmba)(imam)]Cl (3b). The reaction of [NBu4]2[Pt2(C6F5)4(mu-Cl)2] with [Ag(NH=CMe2)2]ClO4 in a 1:2 molar ratio produces cis-[Pt(C6F5)2(NH=CMe2)2] (6). The crystal structures of 1 x 2 Me2CO, 2, 3a, 5, and 6 have been determined. Values of IC50 were calculated for the new platinum complexes against a panel of human tumor cell lines representative of ovarian (A2780 and A2780 cisR) and breast cancers (T47D). At 48 h incubation time complexes 1, 4, and 5 show very low resistance factors against an A2780 cell line which has acquired resistance to cisplatin. 1, 4, and 5 were more active than cisplatin in T47D (up to 30-fold in some cases). The DNA adduct formation of 1, 4, and 5 was followed by circular dichroism and electrophoretic mobility.     

Polar hetero-Diels-Alder reactions of 4-alkenylthiazoles with 1,2,4-triazoline-3,5-diones: an experimental and computational study

The hetero-Diels-Alder reactions of 4-alkenylthiazoles with 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD) lead to new heteropolycyclic systems in excellent yields and high levels of stereocontrol through an exclusively suprafacial approach. 4-Alkenylthiazoles with a stereogenic center placed at the alkenylic substituent react with PTAD giving the corresponding chiral cycloadducts in moderate diastereomeric excesses. The stereochemical course is dominated by the steric interactions at the two diastereomeric transition states. A computational study of these processes with structurally simpler reagents has been carried out. A concerted pathway via a highly asynchronous transition state is preferred for 2-unsubstituted 4-vinyl and 4-styrylthiazoles. However, two alternative and equally likely pathways, concerted and stepwise, have been found to be followed by 2-methyl- or 2-phenyl-substituted 4-styrylthiazoles. The concerted pathway features a highly asynchronous transition state. For the stepwise pathway, the rate-determining step is the first one, as the energy barrier for the second step is virtually nonexistent.