Coordination Assisted Distal C−H Alkylation of Fused Heterocycles

Distal C?H bond functionalization of heterocycles remained extremely challenging with covalently attached directing groups (DG). Lack of proper site for DG attachment and inherent catalyst poisoning by heterocycles demand alternate routes for site selective functionalization of their distal C?H bonds. Utilizing non‐productive coordinating property to hold the heterocycle into the cavity of a template system in a host–guest manner, we report distal C?H alkylation (C‐5 of quinoline and thiazole, C‐7 of benzothiazole and benzoxazole) of heterocycles. Upon complexation with heterocyclic substrate, nitrile DG in template directs the metal catalyst towards close vicinity of the specific distal C?H bond of the heterocycles. Our hypothesized pathway has been supported by various X‐ray crystallographically characterized intermediates.     

Ligand‐Enabled PdII‐Catalyzed Iterative γ‐C(sp3)−H Arylation of Free Aliphatic Acid

C?H functionalization of aliphatic carboxylic acids without attaching exogenous auxiliary has been so far limited at the proximal β‐position. In this work, we demonstrate a ligand enabled palladium catalyzed first regioselective distal γ‐C(sp3)?H functionalization of aliphatic carboxylic acids without incorporating an exogenous directing group. Aryl iodides containing versatile functional groups including complex organic molecules are well tolerated with good to excellent yields during the γ‐C(sp3)?H arylation reaction. Interestingly, weak coordination of carboxylate group can be further extended for sequential hetero di‐arylation. Application of the protocol has been showcased by synthesizing substituted α‐tetralone. Mechanistic investigations have been carried out to shed light on the reaction pathway.     

Separation of no-carrier-added <Superscript>107,109</Superscript>Cd from proton induced silver target: classical chemistry still relevant

The classical chemistry like precipitation technique is relevant even in modern days trans-disciplinary research from the view point of green chemistry. A definite demand of no-carrier-added (nca) cadmium tracers, namely, ^107,109Cd, has been realized for diverse applications. Development of efficient separation technique is therefore important to address the purity of the tracers for various applications. No-carrier-added ^107,109Cd radionuclides were produced by bombarding natural silver target matrix with 13 MeV protons, which gave ~15 MBq/μA h yield for nca ¹⁰⁷Cd. The nca cadmium radionuclides were separated from the natural silver target matrix by precipitating Ag as AgCl. The developed method is an example wherein green chemistry is used in trans-disciplinary research. The method is also simple, fast, cost effective and environmentally benign.     

Hydrogen bonding driven self‐assembly of side‐chain amino acid and fatty acid appended poly(methacrylate)s: Gelation and application in oil spill recovery

We report an interesting class of fatty acid appended side‐chain phenylalanine (Phe) containing poly(methacrylate) homopolymers that undergo self‐assembly leading to gelation in selective organic hydrocarbons, due to association among the side‐chain functionalities. Fatty acids of different n‐alkyl chain lengths have been attached to the N‐terminal of the Phe‐based methacrylate and the corresponding homopolymers have been synthesized via reversible addition–fragmentation chain transfer polymerization. These homopolymers undergo gelation in selective organic hydrocarbons. The morphology of these organogels has been characterized by field emission scanning electron microscopy which revealed macroporous structure of the organogels. Viscoelastic properties of organogels and the thermoreversible gel‐to‐sol transition have been investigated by rheological measurements. Powder X‐ray diffraction study has been performed to understand the effect of long n‐alkyl chains on the gelation process. FTIR study reveals inter‐/intra‐chain hydrogen bonding which is the driving force of organogelation of the polymers in suitable solvents. In absence of hydrogen bonding interaction, hydrophobic association fails to direct the self‐assembly process and no gelation is observed. An interesting feature of the homopolymeric gelators is that it can selectively congeal the diesel part from an oil–water biphasic mixture, which might be useful in oil spill treatment. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 511–521     

A reexamination of the degradation of polyvinylchloride by thermal analysis

Degradation of polyvinylchloride has been reexamined in the light of its DT-DSC-TG analytical behavior up to a temperature of 1000°C in an inert atmosphere. Four distinct stages of degradation have been identified. The first stage is almost eventless with no change in weight for untreated PVC samples. The second stage is almost exclusively dehydrochlorination. The third stage appears to be a structural reorganization involving such processes as cis-trans isomerization, aromatization, and crosslinking. The fourth stage appears to be a structural degradation and is associated with the evolution of hydrocarbons. The role of liberated hydrogen chloride has been better appreciated in catalyzing the above secondary reactions on the polyene residue obtained on partial or total dehydrochlorination. The effect of the particle dimension and chemical and physical pretreatments of the samples, such as low temperature dehydrochlorination by an alkali and vacuum heat treatment, respectively, on the degradation pattern has been studied. © 1994 John Wiley & Sons, Inc.     

Reaction-based sensing of fluoride ions using desilylation method for triggering excited-state intramolecular proton transfer

Naphthalene based benzothiazole (NBT) has been investigated as new colorimetric and ratiometric fluorescent chemosensor for fluoride. The selectivity of NBT has been explored based on combination of desilylation reaction and modulation of the excited-state intramolecular proton transfer (ESIPT) from the desilylation product to F^?. The method exhibited a high selectivity and a great sensitivity toward fluoride anions through ‘turn-on’ chromogenic activity and sensitivity. The structure of HNBT has been established by single-crystal XRD. Density functional theory and TDDFT calculations were performed in order to demonstrate the electronic properties of HNBT, NBT and their anion. Upon treatment with fluoride in aqueous CH₃CN solution, the TBS protective group of probe NBT was removed readily and ESIPT of the probe was switched on, which resulted in a decrease of the emission band at 415 nm and an increase in a new fluorescence peak around 586 nm. An easy-to-prepare test paper, obtained by dipping the paper into the solution of NBT, was able to detect fluoride ions in practical samples. The detection limit of the probe in the determination of fluoride ions was 10.18 μM.     

SERS Enhancement on the Basis of Temperature‐Dependent Chemisorption: Microcalorimetric Evidence

The mechanism of surface‐enhanced Raman spectroscopy (SERS) is not very clear in view of the magnitude of the contribution of electromagnetic factor as well as the chemical mechanism. This report presents the extent of adsorption at different temperatures in terms of signal enhancements in SERS employing silver nanoparticles (AgNPs) of various shapes as substrate and dye molecules, crystal violet or Rhodamine 6G, as model Raman probes. Initially, the SERS signal increases with increasing temperature until a maximum intensity is reached, before it gradually decreases with increasing temperature. This trend is independent of the shape of the Raman substrates and probes. However, the temperature at which maximum intensity is obtained may depend upon the nature of the Raman probe. The energetics involved in the chemisorption process between dye molecules and AgNPs were determined through isothermal titration calorimetry and their implications for the observed SERS signals were assessed. The maximum heat change occurred at the temperature at which the maximum signal enhancement in SERS was obtained and the enhanced interaction at optimum temperature was confirmed by absorption spectroscopy.     

A mild and efficient method for oxidative halodecarboxylation of α,β-unsaturated aromatic acids using lithium bromide/chloride and ceric ammonium nitrate

A mild and efficient ecofriendly method for the halodecarboxylation of α,β-unsaturated aromatic acids has been developed by using lithium bromide/chloride and ceric ammonium nitrate in acetonitrile–water at room temperature to afford the vinyl halides in moderate to good yields.