Kinetics and mechanism of oxidation of indigo carmine by hypohalites

Kinetics of oxidation of indigo carmine (IC) by sodium hypohalites, NaOX (X ? Cl or Br), in alkaline buffer of pH 9–11 has been studied spectrophotometrically at λ = 610 nm. The experimental rate law obtained is ?d[IC]/dt = k[OX^?][IC][OH^?]^x where x <1. Variation of ionic strength or dielectric constant of the medium had no effect on the reaction rate while the addition of halide ions slightly retarded the rate. A most plausible mechanism proposed on the basis of experimental results involves the formation of isatin sulphonate which undergoes further oxidation to anthranilate. Activation parameters have been evaluated.     

Estimation of allyl alcohol by chloramine-T

A simple but rapid and accurate method for the estimation of allyl in aqueous solution has been developed, based on its oxidation with chloramine-T at room temperature, in 0.5-1.0M hydrochloric acid medium. The reaction involves a two-electron change. The effect of such variables such as pH of the medium, presence of foreign ions and perchloric or sulphuric acid on the rate of oxidation is discussed.     

A rapid method for the estimation of glutamic acid with chloramine-T

Chloramine-T (added in excess) oxidizes glutamic acid in various solvent media and the reaction is rapid and stoichiometric with a 4-electron change in buffers of pH 1-6, in 0.01 M sulphuric and perchloric acids and in 0.1M hydrochloric acid. A back-titration procedure using a pH-4 buffer or 0.1M hydrochloric acid as reaction medium has been developed. rho-Toluenesulphonamide and a nitrile have been identified in the reaction products. The effect of other species on the oxidation has been investigated.     

Some analytical applications of aromatic sulfonyl haloamines: Estimation of indigocarmine by chloramine-B,bromamine-T,and dibromamine-T

Sodium N-chlorobenzenesulfonamide (chloramine-B, CAB), sodium N-bromo-p-toluenesulfonamide (bromamine-T, BAT) and N,N′-dibromo-p-toluenesulfonamide (dibromamine-T, DBT) are employed as analytical reagents for estimating indigocarmine (IC) in solution. A four-electron stoichiometry is observed within 30 min in the following media: CAB, 0.1–1.0 N HCl or H₂SO₄ and pH 1 buffer; BAT, 0.01–0.10 N NaOH; DBT, glacial acetic acid. The back titration methods are fairly rapid, simple, and accurate. The product of oxidation, isatinsulfonate, was estimated by spectrophotometric measurements at 410 nm. The sulfonamides formed by reduction of the haloamines are detected by TLC and paper chromatography.     

Excluded Volume in Macromolecules

Abstract

The excluded volume in macromolecules has been discussed in an elementary way, and has been compared with that of the real gases. The excluded volume has been classified into two categories, namely, inter-and intramolecular excluded volumes, and have been discussed in greater length in terms of their origin and their influence on configurational and hydrodynamic properties. It is concluded that the calculation of inter-molecular excluded volume is not difficult, while the intramolecular excluded volume requires detailed knowledge about the nature and the various interactions between the polymer segments.     

Kinetic and mechanistic studies of oxidation of arginine,histidine, and threonine in alkaline medium by N-chloro-N-sodio-p-toluenesulfonamide

The kinetics of oxidation of arginine, histidine, and threonine by chloramine-T (CAT) have been investigated in alkaline medium at 35°C. The rates are first order in both [CAT] and [amino acid] and inverse fractional order in [OH^?] for arginine and histidine. The rate is independent of [OH^?] for threonine. Variation of ionic strength and addition of the reaction product, p-toluenesulfonamide, or Cl^? ions had no effect on the rate. A decrease of the dielectric constant of the medium by adding methanol decreased the rate with arginine, while the rates increased with histidine and threonine. The solvent isotope effect was studied using D₂O. (k_obs)/(k_obs) was found to be 0.55 and 0.79 for arginine and histidine, respectively. The reactions were studied at different temperatures, and activation parameters have been computed. The oxidation process in alkaline medium, under conditions employed in the present investigations, has been shown to proceed via two paths, one involving the interaction of RNHCl (formed rapidly from RNCl^?), with the amino acid in a slow step to form monochloroamino acid, which subsequently interacts with another molecule of RNHCl in a fast step to give the products, p-toluenesulfonamide (RNH₂), and the corresponding nitrile of the amino acid (R'CN). The other path involves the interaction of RNCl^? with the amino acid in a similar way to give RNH₂ and R'CN. Mechanisms proposed and the derived rate laws are consistent with the observed kinetics. The rate constants predicted using the derived rate laws, as [OH^?] varies, are in excellent agreement with the observed rate constants, thus justifying these rate laws and hence the proposed mechanistic schemes.     

Spectroscopic characterization of aminoacetonitrile,its ions and protonated aminoacetonitrile using quantum chemical methods

We present theoretical vibrational and absorption spectra of aminoacetonitrile, its cation, anion, cyanoprotonated, and aminoprotonated aminoacetonitrile. We used second‐order Moller–Plesset perturbation method (MP2) with TZVP basis set to obtain ground state geometries and vibrational spectra. Time dependent density functional theory method was used to obtain absorption spectra. Shifts in vibrational modes for aminoacetonitrile upon ionization and protonation are determined. The C≡N stretching mode which is the most important mode in detection of nitriles in space is more intense in aminoacetonitrile ions and its two protonated form and is less IR active for neutral aminoacetonitrile. The nature of electronic transition for these molecules is identified. All the electronic transitions for neutral aminoacetonitrile and its cation are the σ → σ* electronic transitions, whereas its anion and protonated aminoacetonitrile display the σ → σ* as well as π → π* transitions. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Kinetics and mechanism of oxidation of some aliphatic esters by sodium N-bromo-p-toluenesulfonamide

The kinetics of oxidation of methyl, ethyl, n-propyl, isopropyl, and n-butyl acetates to acetic acid and the corresponding aldehyde by the title oxidant in aqueous HCl medium at 40°C has been studied. The reaction shows first-order with respect to [oxidant] and fractional orders in [H⁺] and [ester]. An isokinetic relationship was observed with β = 374 K indicating enthalpy as the rate controlling factor. Attempts have been made to arrive at a linear free energy relationship through the Taft treatment. Electron releasing groups in the ester moiety increase the rate with ρ* = ?9.88. A two-pathway mechanism, consistent with the observed kinetic data, has been proposed. © 1993 John Wiley & Sons, Inc.