Infrared absorption of gaseous ClCS detected with time-resolved Fourier-transform spectroscopy.
A transient infrared absorption spectrum of gaseous ClCS was detected with a step-scan Fourier-transform spectrometer coupled with a multipass absorption cell. ClCS was produced upon irradiating a flowing mixture of Cl2CS and N2 or CO2 with a KrF excimer laser at 248 nm. A transient band in the region of 1160-1220 cm-1, which diminished on prolonged reaction, is assigned to the C-S stretching (nu1) mode of ClCS. Calculations with density-functional theory (B3P86 and B3LYP/aug-cc-pVTZ) predict the geometry, vibrational wave numbers, and rotational parameters of ClCS. The rotational contour of the spectrum of ClCS simulated based on predicted rotational parameters agrees satisfactorily with experimental observation; from spectral simulation, the band origin is determined to be at 1194.4 cm-1. Reaction kinetics involving ClCS, CS, and CS2 are discussed.
Diminished cage effect in solid p-H2: infrared spectra of ClSCS, ClCS, and ClSC in an irradiated p-H2 matrix containing Cl2 and CS2.
Irradiation of a p-H(2) matrix containing Cl(2) and CS(2) at 3.3 K with laser emission at 340 nm followed by annealing of the matrix produced main features at 1479.5 and 1480.8 cm(-1). These lines are attributed to nu(1) (SCS antisymmetric stretching) mode of ClSCS. Irradiation of the matrix at 355 nm decomposes ClSCS. Products CS (1272.2 and 1271.1 cm(-1)), ClCS (1193.9/1191.9 and 637.5 cm(-1)), and ClSC (1137.0 cm(-1)) were observed upon annealing. The assignments were based on comparison of observed vibrational wavenumbers and (13)C- and (34)S-isotopic ratios with those predicted with density-functional theories (B3LYP and BPW91/aug-cc-pVTZ). These results demonstrate that the cage effect of solid p-H(2) is diminished so that isolated Cl was produced via photodissociation of Cl(2) in situ and subsequently reacted with CS(2) to form ClSCS, but not ClC(=S)SCl, upon annealing; typically ClC(=S)SCl was produced as the major product on irradiation of noble-gas matrices containing Cl(2) and CS(2). Observation of ClSCS but not ClCS(2) is consistent with the theoretical prediction that only formation of the former proceeds via a barrierless path. Similarly, upon irradiation of ClSCS at 355 nm, Cl, CS, and CS(2) were produced; subsequent annealing of the irradiated matrix produced ClSC and ClCS via barrierless paths.
Novel method for the determination of the methoxyl content in lignin by headspace gas chromatography.
The paper reports on a headspace gas chromatographic (HS-GC) method for the determination of methoxyl in lignin. The method involves the quantitive cleavage of methoxyl with hydroiodic acid (HI) to form methyl iodide in a closed headspace sample vial at 130 °C for 30 min. After HI has been added, the sample is neutralized by injecting a sodium hydroxide solution; the methyl iodide in the vial was determined by HS-GC using a flame ionization detector. The results showed that the method has an excellent measurement precision (RSD < 0.69%) and accuracy (RSD < 3.5%) for the quantification of methoxyl content in lignin. The present method is simple and accurate and can be used for the efficient determination of methoxy1 content in lignin and related materials.