6-Chloro-3-hydroxy-2-(5'-methylfuryl)-4H-chromene-4-one as an analytical reagent for micro determination of molybdenum(VI).

6-Chloro-3-hydroxy-2-(5'-methylfuryl)-4H-chromene-4-one (CHMFC) has been used as an analytical reagent for the spectrophotometric determination of molybdenum. Molybdenum(VI) in the presence of several cations, anions and complexing agents forms a yellow 1:2 complex with CHMFC. The complex is quantitatively extractable into 1,2-dichloroethane from 1 mol dm(-3) acetic acid medium and is stable for more than 6 h. The complex shows an absorption maximum at 438 nm with a molar absorptivity of 5.36 x 10(4) dm3 mol(-1) cm(-1) and Sandell's sensitivity equal to 0.0017 microg Mo cm(-2). The method obeys Beer's law up to 1.9 microg Mo ml(-1). The relative standard deviations are 0.2% for solutions and 0.5-1.5% for solid samples. The method is simple, selective, precise and rapid, and has been satisfactorily applied to the micro determination of molybdenum in various synthetic and standard samples.     

Melting temperature of H<Subscript>2</Subscript>, D<Subscript>2</Subscript>, N<Subscript>2</Subscript> and CH<Subscript>4</Subscript> under high pressure

The melting temperatures of H₂, D₂; N₂ and CH₄ are analysed. The computed results are in very good agreement with the experimental data in each solid. Further, the analysis indicates the presence of the melting maximum in these solids.     

Ion–molecule reactions of [ketene]+˙ as a diagnostic probe for distinguishing isomeric alkenes,alkynes and dienes: A study of the C4H8 and C5H8 isomeric hydrocarbons

The gas-phase ion–molecular reactions of [ketene]^+˙ with a number of isomeric alkenes, alkynes and dienes were studied by using tandem mass spectrometry. Ketene was reacted with C₄H₈ (but-1- and ?2-ene and 2-methylpropene) and C₅H₈ unsaturated hydrocarbons (isoprene, penta-1,3- and ?1,4-diene, pent-1- and ?2-yne, cyclopentene and methylenecyclobutane) in a high-pressure chemical ionization source of a tandem mass spectrometer. The collisionally stabilized ion–molecule adducts were analyzed by use of collisionally activated dissociation (CAD) spectra. The three C₄H₈ alkenes were distinguishable on the basis of the distinct CAD spectra of their adducts with ketene. Similarly, the CAD data for the corresponding adducts derived from the C₅H₈ hydrocarbons point to different structures for the C₅H₈ compounds.     

Fast atom bombardment combined with mass spectrometry for characterization of polycyclic aromatic hydrocarbons

A new approach using fast atom bombardment combined with mass spectrometry to characterize polycyclic aromatic hydrocarbons (PAHs) in the range of 128-252 u molecular weight is described. Sulfolane was employed as a liquid matrix for these π-conjugated hydrocarbons. Bombardment of sulfolane solution of certain PAHs with an atom beam produces both radical cation (M^+.) and protonated molecule [(M + H)⁺], with no evidence of fragmentation. Collisional activation of the fast atom bombardment-desorbed M^+. ions, however, results in several structure-specific fragment ions. Structural differences in a few isomeric hydrocarbons can be detected using the [(M + H)⁺]/[M^+.] abundance ratio and in the pyrene-fluoranthene pair by the B/E linked-field-collision-activated dissociation data. The [(M + H)⁺]/[M^+.] was found to be compound-specific and correlated well with certain properties (resonance energy, proton affinity, and ionizing energy) of PAHs.     

Structures of gas phase C5H8 radical cations: A collisional ionization study

Collisional ionization (charge stripping) and charge exchange ionization spectrometry were utilized to determine structures of fourteen cyclic and acyclic C₅H₈ radical cations, including ionized 1,2- 1,3-, 1,4- and 2,3-pentadienes (-PD), isoprene, 1- and 3-methylcyclobutenes (1- and 3-MCB), 3-methyl-1,2-butadiene (3-M-1,2-BD), methenecyclobutane (MECB), cyclopentene, 3-methyl-1-butyne (3-MB), 1- and 2-pentynes and vinylcyclopropane (VCP). The pressure of the charge exchange reagent gas in the ion source was adjusted to generate ions of different energy contents. The structures of the C₅H₈ ions are energy dependent, and their isomerization reactions can be monitored as a function of the amount of internal energy deposited by charge exchange. 1,3-PD, isoprene and cyclopentene radical cations are identified as stable ion structures. 1-MCB, 3-M-1,2-BD and 3-MB radical cations isomerize to isoprene ions, whereas ionized VCP, 3-MCB, 1,2-PD, 2,3-PD, 1,4-PD, 1-pentyne and 2-pentyne ultimately isomerize to the [1,3-PD]⁺˙. Thermodynamic arguments are invoked to corroborate these isomerization reactions. The critical energies of the isomerizations are also estimated.     

Kinetic studies on the n-alkyl acrylate polymerization

Kinetic studies on the polymerization of n-butyl acrylate and n-octadecyl acrylate in toluene at 70°C with benzoyl peroxide as initiator are reported. High monomer orders of 1.55 and 1.75 were obtained for n-butyl and n-octadecyl acrylates, respectively. Though the initiator order in butyl acrylate polymerization was 0.5, the octadecyl acrylate polymerization showed less than square root initiator order. The activation energy for the polymerization of both the acrylates was determined. Autoacceleration was found even at low conversions. The autoacceleration was influenced by both monomer and initiator concentration. Molecular weight data was presented in support of the gel effect. © 1992 John Wiley & Sons, Inc.