Spectrophotometr1c determination of palladium : Bismuthiol i as an analytical reagent

The reagent, bismuthiol l, has been successfully utilized for the spectrophotometric determination of palladium. The colour reaction is instantaneous and the system is stable for at least 24 hours in the pH range 6 to 10 but shows no sharp peak of maximum absorption. The system obeys Beer's law at a palladium concentration of 0.8 μg to 8.0 μg per ml at any wavelength between 400 mμ and and 410 mμ giving a sensitivity of 0.08 μg of palladium per cm² (practical); 0.01 μg of palladium per cm² (sandell). Ethyl alcohol stabilizes the system against any deviation due to appearance of turbidity. A large excess of the reagent and almost all thc cations and anions, except platinum, gold, copper, chromium, iron, mercury, silver, thallium, uranium, vanadate and cyanide, do not interfere. By applying job's method of continuous variation it was found that the complex contains thc reactants in 1 : 1 ratio and that the average value of the dissociation constant of the complex is 3.2$\text{.}\text{?}$ 10^-5 at 25°.     

Kinetic and mechanistic studies of the interaction of 2-mercapto pyridine with dichloro[1-alkyl-2-(arylazo)imidazole]palladium(II) complexes

Nucleophilic substitution of Pd(RaaiR′)Cl₂ [(RaaiR′ = 1-alkyl-2-(arylazo)imidazole, p-R-C₆H₄-N=N-C₃H₂NN-1-R′; where R = H(a)/ Me(b)/ Cl(c) and R′ = Et(1)/Bz(2)] with 2-Mercaptopyridine (2-SH-Py) in acetonitrile (MeCN) at 298 K, to form [Pd₂(2-S-Py)₄], has been studied spectrophotometrically under pseudo-first-order conditions and the analyses support the nucleophilic association path. The reaction follows the rate law, Rate = {k ₀ + k [2-SH-Py] ₀ ² }[Pd(RaaiR′)Cl₂]: first order in Pd(RaaiR′)Cl₂ and second order in 2-SH-Py. The rate of the reaction follows the order: Pd(RaaiEt)Cl₂ (1) < Pd(RaaiBz)Cl₂ (2) and Pd(MeaaiR′)Cl₂ (b) < Pd(HaaiR′)Cl₂ (a) < Pd(ClaaiR′)Cl₂ (c). External addition of Cl⁻ (LiCl) and HCl suppresses the rate (Rate ∝ 1/[Cl⁻]₀ & ∝1/[HCl]₀). The reactions have been studied at different temperatures (293–308 K) and activation parameters (Δ^‡ H° and Δ ^‡ S°) of the reactions were calculated from the Eyring plot and support the proposed mechanism.     

2-Mercapto-benzothiazole as an analytical reagent

Summary The reagent 2-mercapto-benzothiazole quantitatively precipitates palladium at a PH 5.6 to 10.2. The red coloured compound, Pd(C₇H₄NS₂)₂, is diamagnetic and is stable up to a temperature of 388 C. Palladium is separated from alkalis, alkaline earths, Mg, Fe³⁺, Cr, Th, Zr, Ti, UO₂ ²⁺, Be, rare earths, Ce³⁺, Ce⁴⁺, Zn, Mn, Co, Ni, Pb, Bi, Sb³⁺, As³⁺, Sn⁴⁺, Tl+, Cu²⁺, Cd, Ir⁴⁺, Rh³⁺, Ru³⁺, Os⁴⁺, CrO₄ ^2–, MoO₄ ^2–, WO₄ ^2–, VO₃ ^–, PO₄ ^3– and AsO₄ ^3– at apH 6–8 in presence of EDTA and tartaric or citric acid. Besides Pb, Ag and Hg²⁺ are kept in solution with potassium iodide and Au in a limited quantity forms a soluble complex with thiosulphate. The palladium complex is either weighed after drying and determined gravimetrically or dissolved in an excess of cyanide and determined volumetrically by back titrating the latter with silver nitrate.     

Studies in [3, 3] Sigmatropic Rearrangement: Regioselective Cyclization of 5-(Cyclohex-2-Enyl)-6-Hydroxy-1-Methylquinolin-2(1H)-One

Thermal [3,3] sigmatropic rearrangement of 6-cyclohex-2-enyloxy-1-methylquinolin-2(1H)-one (3) afforded 5-cyclohex-2-enyl-6-hydroxy-l-methyl-quinolin-2(1H)-one (4) in 86% yield. Compound 4 on treatment with pyridine hydrotribromide in CH₂Cl₂ gave exclusively non-bridged product 6 (85%) whereas compound 4 by a different route viz., acetylation followed by bromine addition and cyclization gave the bicyclic product 7 (80%). Compound 4 also furnished a bicyclic product 11 (80%) on treatment with cone. H₂SO₄.     

Regioselective Synthesis of Flindersine Analogues

6-Alkylpyrano [3,2-c] quinolin-5(2H)-ones(11a-e) were obtained in excellent yields by simply refluxing propynyl and butymyl ethers (6) of 4-hydroxy-1-alkylquinolin-2H-ones (2) in chlorobenzene for 10h, 5-Prop-2-ynyloxy-2H-pyrano [3,2-c] quinoline (12) was also obtained from the thermal rearrangement of 2,4-bis prop-2-ynyloxyquinoline (4).     

Studies in Competitive [3,3] Sigmatropic Rearrangement: Synthesis of Oxygen Heterocycles

[3,3] Sigmatropic rearrangement of unsymmetrically substituted 1,4-but-2-ynes exhibit preference for rearrangement on the aryloxy prop-2-ynyl moiety to N-methyl-N-pyrimidinyl amino prop-2-ynyl moiety in case of 5-substituted uracils (la-f).     

Practical Synthesis of N‐Alkyl‐N‐alkyloxycarbonylaminomethyl Prodrug Derivatives of Acetaminophen,Theophylline, and 6‐Mercaptopurine

We report a novel synthesis of N‐alkyl‐N‐alkyloxycarbonylaminomethyl (NANAOCAM) prodrugs of acetaminophen, theophylline, and 6‐mercaptopurine by alkylation of the corresponding drug molecule with N‐alkyl‐N‐alkyloxycarbonylaminomethyl chlorides in good yield. Most of the alkylating agents were efficiently synthesized by chloromethylation of N‐alkyl carbamic acid alkyl esters, which in turn were made from alkyl amines and alkyl chloroformates. In cases where the alkyl chloroformates were not available, synthesis of N‐alkyl carbamic acid alkyl esters was accomplished by converting an alcohol to a chloroformate or to an activated acylating agent such as acyl imidazoles or p‐nitrophenylcarbonate esters, followed by their reaction with alkyl amines.     

Regioselective Synthesis of 1,8-Naphthyridinone-Annulated Oxygen and Sulfur Heterocycles by Tri-n-butyl Tinhydride–Mediated Aryl Radical Cyclization

The tin hydride–mediated cyclizations of a number of ethers, sulfides, and sulfones under mild, neutral conditions have been investigated. While the 2-bromobenzyloxy ethers were prepared in 62–65% yields by the alkylation of 4-hydroxy-1-phenyl-1,8-naphthyridin-2(1H)-one with 2-bromobenzyl bromides in refluxing acetone in the presence of anhydrous potassium carbonate, the sulfides were derived from 4-mercapto-1-phenyl-1,8-naphthyridin-2(1H)-one and 2-bromobenzyl bromides in 82–84% yields by a phase-transfer catalysis (PTC) reaction. The corresponding sulfones were prepared by treatment of the sulfides with m-CPBA in refluxing dichloromethane. The ethers, sulfides, and the sulfones were treated with ⁿ Bu₃SnH-AIBN to give regioselectively 1,8-naphthyridinone-annulated oxygen and sulfur heterocycles in 70–78% yields.     

Para Substituted Benzaldehydes as Expedient Reagents for the Oxidative Aromatization of Hydroquinoline

A Cannizzaro‐type reaction of tetrahydro‐5(1H)‐quinolinones with para substituted benzaldehydes in the presence of a base formed the corresponding quinoline and aryl methanol rather than arylidene derivatives because of the oxidation of tetrahydroquinoline and reduction of benzaldehydes as a result of unprecedented hydride transfer from tetrahydroquinoline to arylaldehydes. The reaction proceeds best with the participation of substituents with +M effect in substrate molecule.