Band assignments isocyanates

In order to get information on the surface species responsible for the spectra obtained after adsorption of both cyclic nitro compounds, the adsorption of several potential intermediates has been investigated. It can be concluded from the adsorption of isocyanic acid that the absorption around 2190 cm 1 can be due to surface isocyanate species. To explain the absorption bands in the range 1600-1200 cm1, the first idea was a surface amide structure, such as was observed by Krietenbrink et al.,IS However, considering the low stability of this adsorption complex and the disappearance of the band around 1475 cm1 when going from C6HSN02 to C6D5N02 (a shift down to approximately 1395 cm1), the conclusion is arrived at that such an assignment would be incorrect. 

Preparation and Properties of Polycocyclotrimers of Isocyanates. The formation of isocyanurate rings in the polycyclo-trimerization or polycocyclotrimerization reaction of isocyanates is characterized by the disappearance of the NCO groups (v(N=C=0) 2280 cm ) and by the appearance of a new IR absorption band at 1700 cm-l, assigned for the stretching vibration v(C=0) of the isocyanurate ring (12). 

In GC-DR. experiments CO was adsorbed on a reduced Pt/Ce02-Al203 mostly as linear carbonyls which were observed at 2062 cm (Fig. 7). A band at 2173 cm which was observed in some experiments, was probably due to the Ptn+-CO complex formation [7], Weak bands at 1588,1481, and 1385 cm were assigned to surface carbonate groups. When NO was added into the chamber linear Pt-CO bands disappeared and gaseous NO species at 1877 cm and linear Pt-NO species at 1775 cm were formed. Linear R-NO bands are typically observed at aroimd 1812-1780 cm" [12]. The formation of Pt-NCO species was observed at 2258 cm" but the absorption bands were quite weak. However, when the cham-ber was evacuated strong absorption bands arose at 2258 and 2181 cm indicating the isocyanate and Pt -CO complex [9] formations, respectively. 

The adsorption of 5 mbar NO on CoOx/Si02 is also shown in figure 1. Two characteristic bands for NO boimd to cobalt oxide were visible at 1858 and 1784 cm They were assigned to linear and bent NO, respectively [24,25], Co-adsorption of CO and NO led only to bands of linear and bent NO on cobalt oxide. No indications of the formation of isocyanate groups were found. 

Evidence of the condensation reaction of the isocyanate functions with the OH groups of cellulose was supported by FTIR (bands at 1712 and 1640 cm associated with CO and NH of the urethane, 1630-1500 cm associated with CO and NH of urea, and bands at 2850-2900 cm relative to aliphatic CH moieties of chain aliphatic). This evidence was also often corroborated by C CP-MAS NMR with the emergence of the typical peaks at 12-40 ppm assigned to methylene carbon of the anchored hydrocarbon chain, peaks at 125-136 ppm assigned to aromatic rings of MDI, and peaks at 157.46 ppm related to the carbamate functions. An example of C CP-MAS NMR of the is shown in Figure 17.15. 

Methanol is oxidized to formate ions, acetone and acetaldehyde to acetate species. An enolic form of adsorbed acetone is seen, which accounts for rapid isotopic exchange of -OH. On O2 adsorption two bands at 1155 and 1020 cm are formed,which are however not assigned. Mixtures of CO plus O2 lead to the obvious formation of carbonates and bicarbonates. CO interaction with presorbed NH3 forms carbamate species. Oxidizing properties of the surface are shown by the reaction of trichloroacetone to trichloroacetate species. Nitriles are, however, hydrolysed to acetimidate species R-CNH . Similar reactions with surface -OH are shown by ethyl and phenyl isocyanate, which form urethanes by reaction with isolated -OH groups, and 1,3-diethylurea with -OH pairs. Reaction with surface -OH is also shown by trimethylchlorosilane, which, however, harshly attacks the surface and forms silicone species. ... 

To demonstrate calibration linearity and transferability using a fiber-optic probe and simple peak-area methods, the solution spectra of four solutions of phenylisocyanate in acetone were used. The mid-infrared spectrum of most isocyanates are characterized by a sharp band, sometimes exhibiting shoulders, at 2250-2285 cm which is assigned to the asymmetric stretch of the -N C=0 group. In the spectra of acetone solutions of phenylisocyanate, this band appears at 2261 cm with a substantial shoulder at 2283 cm. Figure 1 shows an expanded view of the band, displayed in a screen shot from the GRAMS peak-fitting software with two Lorentzian peaks fitted at 2261 and 2283 cm. ... 

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