Hydroxyl groups infrared spectroscopy

The acetyl content of cellulose acetate may be calculated by difference from the hydroxyl content, which is usually determined by carbanilation of the ester hydroxy groups in pyridine solvent with phenyl isocyanate [103-71-9J, followed by measurement of uv absorption of the combined carbanilate. Methods for determining cellulose ester hydroxyl content by near-infrared spectroscopy (111) and acid content by nmr spectroscopy (112) and pyrolysis gas chromatography (113) have been reported. 

These structural problems are also insoluble by physical methods alone. The infrared spectrum often gives an unambiguous decision about the structure in the solid state the characteristic bands of the carbonyl or the hydroxyl group decided whether the compound in question is a carbinolamine or an amino-aldehyde. However, tautomeric equilibria occur only in solution or in the liquid or gaseous states. Neither infrared nor ultraviolet spectroscopy are sufficiently sensitive to investigate equilibria in which the concentration of one of the isomers is very small but is still not negligible with respect to the chemical reaction. 

Several assumptions were made in order to analyze kinetic data in terms of this expression (2). First it was assumed that k 2 m kj, k2 k 3, and kj/k j k /k ( - If). Second it was assumed that the rate constants were independent of the extent of reaction i.e., that all six functional groups were equally reactive and that the reaction was not diffusion controlled. The concentration of polymer hydroxyl functionality was determined experimentally using infrared spectroscopy as described elsewhere (7). A major unknown is the instantaneous concentration of methanol. Fits to the kinetic data were made with a variety of assumptions concerning the methanol concentration. The best fit was achieved by assuming that the concentration of methanol was initally constant but decreased at a rate proportional to the concentration of residual polymer hydroxy groups towards the end of the reaction. As... 

In addition to the simple chemical methods for following these processes, infrared spectroscopy may also be used. In Fig. 9 is shown the spectrum of silica dried at 200°C before and after reaction with Zr(allyl)4- The characteristic absorption bands of the transition metal-allyl group are clearly displayed, also a significant reduction in the number of hydroxyl groups (3740 cm-1) is also clearly evident. 

Note that in all the examples discussed so far, infrared spectroscopy gives its information on the catalyst in an indirect way, via hydroxyl groups on the support, or via the adsorption of probe molecules such as CO and NO. The reason why it is often difficult to measure the metal-oxide or metal-sulfide vibrations of the catalytically active phase in transmission infrared spectroscopy is that the frequencies are well below 1000 cm-1, where measurements are difficult because of absorption by the support. Infrared emission and Raman spectroscopy, discussed later on in this chapter, offer better opportunities in this respect. 

Using infrared spectroscopy, Yates (299) proved the existence of hydroxyl groups on anatase as well as on rutile. Both forms still contained some adsorbed molecular water after evacuation at 150°, as evidenced by the bending vibration at 1605 cm b After outgassing at 350°, no free water was detected. There remained two OH stretching absorptions in the case of anatase (at 3715 and 3675 cm ) and one weak band at 3680 cm with rutile. This is indication of the existence of two different types of OH groups on anatase. These results were confirmed by Smith (300). 

Glemser and Rieck (317) demonstrated by infrared spectroscopy that most of the aluminum oxides intermediate between the hydroxides and ot-AlaOg contain hydroxyl groups which may be removed reversibly by heating. This result was confirmed by proton magnetic resonance measurements (318). 

Russell, J.D. (1979) Infrared spectroscopy of fer-rihydrite evidence for the presence of structural hydroxyl groups. Clay Min. 14 109—114 Russell, J.D. Parfitt, R.L., Eraser, A.R. Farmer,... 

Few authors considered the reactivity of hydroxyl groups at catalyti-cally interesting temperatures. In situ infrared spectroscopy showed that in the cumene cracking reaction the 3550 cm-1 hydroxyls in a HY sample are only affected above 325° C. The 3650 cm-1 hydroxyl decreased in intensity at 250° C (6). During the cracking of hexane on a similar sample the gradual deactivation of the catalyst is accompanied by the progressive... 

Infrared Spectroscopy. The following bands are seen in the ir spectrum of PPG 2970, 2940, 2880 cm-1 (C—H stretch, m) 1460,1375 cm-1 (C—H bend, m) 1100,1015 cm-1 (C—O stretch, m) of which the 2940 and 1015 band are specific. The latter are also present in copolymers of EO and PO. Absorptions due to unsaturated end groups are found at 1650 cm-1 (allyl ether) and 1672 cm-1 (1-propenyl ether). The O—H stretching band at 3470 cm-1 shows the greatest variation for different hydroxyl number polyols and has been used to estimate the hydroxyl number (169). 

Analysis of oligomers for phenolic hydroxyl end groups was conducted by quantitative infrared spectroscopy. Hydroxyl absorbance at 3580 cm-1 was measured for a number of synthetic mixtures of bisphenol-A and bisphenol-A homopolycarbonate. A calibration curve for hydroxyl absorbance vs. weight percent hydroxyl end groups was constructed. Hydroxyl content of bisphenol-A oligomers was calculated from the calibration data. 

Moffat and Neeleman (139) investigated the adsorption of ammonia on boron phosphate by means of infrared spectroscopy. Ammonia appear to dissociate on this solid. Although absorption bands arising from NH4+ and coordinated ammonia were obtained, the authors feel that the presence of NH + does not necessarily indicate that Br0nsted sites were initially present on the BP04 surface. Hydroxyl groups that might be formed when ammonia dissociates could react with dry ammonia to form NHi+. 

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