Hydroxyl bands

Infrared spectroscopy can also be used incisively to identify the six main varieties of asbestos fibers. Specific absorption bands in the infrared spectmm can be associated with the asbestos fibers, first in the 3600 3700 cm range (specific hydroxyl bands) and, second, in the ranges 600—800 and 900 1200 cm (specific absorption bands for various siUcate minerals (10)). 

In a 250 ml Erlenmeyer flask covered with aluminum foil, 14.3 g (0.0381 mole) of 17a-acetoxy-3j5-hydroxypregn-5-en-20-one is mixed with 50 ml of tetra-hydrofuran, 7 ml ca. 0.076 mole) of dihydropyran, and 0.15 g of p-toluene-sulfonic acid monohydrate. The mixture is warmed to 40 + 5° where upon the steroid dissolves rapidly. The mixture is kept for 45 min and 1 ml of tetra-methylguanidine is added to neutralize the catalyst. Water (100 ml) is added and the organic solvent is removed using a rotary vacuum evaporator. The solid is taken up in ether, the solution is washed with water and saturated salt solution, dried over sodium sulfate, and then treated with Darco and filtered. Removal of the solvent followed by drying at 0.2 mm for 1 hr affords 18.4 g (theory is 17.5 g) of solid having an odor of dihydropyran. The infrared spectrum contains no hydroxyl bands and the crude material is not further purified. This compound has not been described in the literature. 

Primary and secondary amines can be identified by a characteristic N—H stretching absorption in the 3300 to 3500 cm"1 range of the IR spectrum. Alcohols also absorb in this range (Section 17.11), but amine absorption bands are generally sharper and less intense than hydroxyl bands. Primary amines show a pair of bands at about 3350 and 3450 cm-1, and secondary amines show a single band at 3350 cm-1. Tertiary amines have no absorption in this region because they have no N-H bonds. An IR spectrum of cyclohexylamine is shown in figure 24.7. 

During the reaction, protons are extracted from the brucite lattice. Infrared spectra [24, 25, 31] show that during charge the sharp hydroxyl band at 3644 cm" disappears. This absorption is replaced by a diffuse band at 3450 cm"1. The spectra indicate a hydrogen-bonded structure for ft-NiOOH with no free hydroxyl groups. ft-NiOOH probably has some adsorbed and absorbed water. However, TGA data... 

The adsorbent was treated with hexamethyldisilazane in order to methylate the OH group but the 3750 cm-1 hydroxyl band did not decrease appreciably in intensity. Bands did appear due to Si(CHs)s groups and it was concluded that methylation of the hydroxyls, other than those seen in the Raman spectrum, had occurred. 

Figure 22 shows the spectrum in the OH region for zinc oxide after admission of butene-1 at a pressure of about 8 mm (14). Spectrum (a), taken after 8 min exposures, shows two features (1) the strong surface hydroxyl band at 3615 cm-1 is shifted about 5 cm-1 to lower frequencies (2) a new band appears at 3587 cm-1. This new band, clearly an OH, appears to arise from dissociation of the adsorbed butene. Spectrum (b) shows the same region after exposure to the gas phase for 1 hr. It is clear that the OH band formed from butene grows with time detailed studies, however, reveal that there is little change after the first 20 min. Spectrum (c) was taken after 20 min evacuation. Two features are evident (1) in the absence of the gas phase the hydroxyl band of the zinc oxide has shifted back to its previous position (2) the OH band formed from butene is reduced somewhat in intensity. Spectrum (d) was taken after degassing for 90 min ... 

Calcined and steamed FAU samples also have complex hydroxyl IR spectra. Figure 4.25 shows the difference between an ammonium ion-exchanged FAU before and after steaming and calcination. The very simple, easily interpretable hydroxyl spectrum of the ammonium exchanged FAU sample is transformed into a complex series of overlapping hydroxyl bands due to contributions from framework and non-framework aluminum atoms in the zeolite resulting from the hydrothermal treatment conditions [101]. 

Table 4.6 Hydroxyl band shifts measured by low-temperature CO adsorption for various...

By measuring the shifts of the various hydroxyl bands of the zeolite, a direct measure of the relative acid site strengths can be made without the need for thermal desorption. Table 4.6 lists the measured hydroxyl band shifts for a variety of hydroxyl groups on different zeolites using low temperature CO adsorption. This data indicates that there is indeed a difference in the intrinsic acid strength of the bridging hydroxyl groups in different zeolites as well as in the same zeolite structure with different framework aluminum content. 

Jacobs, P.A. and Uytterhoevin, J.B. (1973) Assignment of the hydroxyl bands in the infrared spectra of zeolites X and Y part 2. After different treatments. /. Chem. Soc. Faraday Trans. 

A series of Beta zeolites have been synthesized in the presence of tetraethylammonium hydroxide (TEA). Samples with Si/Al ratio in the 7-100 range have been characterized by X-ray powder diffraction, I.R. spectroscopy, and pyridine adsorption. The fraction of TEA which is compensating the charge of the framework aluminum is removed at temperatures higher than those required to remove "occluded" TEA. Three hydroxyl bands are observed at 3740 cm l (silanol groups), 3680 cm" (extraframework Al) and 3615 cm 1 (acid hydroxyl groups interacting with pyridine). 

However, the plot of the intensity of the hydroxyl bands as a function of the Al fraction (Figure 5) shows a maximum for samples with Si/Al ratio %10, indicating that extensive dealumination has taken place during activation of aluminum-rich crystals. 

Hydroxyl bands at 3615 and 3680 cm have been observed by I.R. spectroscopy. The 3680 cm OH band has been assigned to extraframework Al, while the 3615 cm band corresponds to framework Al and is acid enough to interact strongly with pyridine. 

Irradiation of hexafluorobiacetyl in the vapor phase produces a 2 1 mole ratio of carbon monoxide and hexafluoroethane, products consistent with an initial carbon-carbon bond cleavage.62 However, vapor phase irradiation of hexafluorobiacetyl in the presence of a large excess of 2,3-dimethylbutane vapor or in 2,3-dimethylbutane solution gave less than 1% carbon monoxide and trifluoromethane. No trifluoroacetaldehyde or hexafluoroacetone was produced in the latter reaction. Instead a complex mixture of products, which was not separated and identified but whose infrared showed the presence of a hydroxyl band and a diminished carbonyl band, was obtained. This observation is consistent with product formation via hydrogen abstraction. 

In structures such as 2,6-di-r-butylphenol, in which steric hindrance prevents hydrogen bonding, no bonded hydroxyl band is observed, not even in spectra of neat samples. 

Figure 7.10. Time course for reaction 11. All spectra were normalized by making the intensity of the polystyrene band at 1945 cm 1 equal. The area integration for the hydroxyl band from 3181 to 3637 cm-1 (circles), aldehyde C-H band from 2664 to 2766 cm-1 (squares), and aldehyde carbonyl band from 1641 to 1765 cm-1 (triangles) for spectra at various times are plotted against time. Lines were calculated from the best fit to a first-order reaction equation with the rate constant shown. The amount of catalyst TPAP was 0.2 eq in A, 0.1 eq in B and 0.05 eq in C.

Fig. 110. Hydroxyl bands in infra-red spectrum of cellulose (Nikitin...

Infrared Spectroscopy. The spectrum of the solid C showed only weak and unresolved hydroxyl bands (Figure 5). The introduction of CO under an equilibrium pressure of 50 torr did not modify the i>oh bands. After evacuation of the carbon monoxide at room temperature, the IR spectrum showed two bands at 2135 and 2110 cm-1 caused by strongly chemisorbed... 

The exchange data for each hydroxyl band were evaluated following a first-order equation ... 

The depletion of epoxide groups can therefore be followed by observing the intensities of the epoxide peak at 912 cm-1 and the hydroxyl band at 3500 cm-1. 

On comparing the spectrum of the epoxy resin in Fig. 4a with that obtained after reaction with APS dried at 25°C (Fig. 4b), one can see the disappearance of the epoxide peak at 912 cm and the appearance of a strong band at 3500 cm-1 due to —OH groups, as expected from the above reaction. However, after reaction for the same duration with APS dried at 170°C, the disappearance of the epoxide peak at 912 cm"1 and the appearance of the hydroxyl band at 3500 cm 1 are both less significant. The ratio of peak intensities, 912/3500 cm, remains high, indicating inhibition of the amine-epoxide reaction when APS is dried at 170°C. 

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