Pyridine absorption

The effects of post-synthesis alumination on purely siliceous MCM-41 material with A1(NC>3)3 on acidity have been studied by FTIR, NH3-TPD, and IPA decomposition reaction. The FTIR results of pyridine absorption show that both Lewis and Bronsted acid sites are increased by the post-modification. The amount of NH3 adsorbed on the alumina-modified MCM-41 samples increases with the loading of Al onto the surface of MCM-41. Due to the improved acidity, the alumina-modified MCM-41 materials show considerably higher catalytic activity for dehydration of isopropanol than purely siliceous MCM-41. In addition, XRD and N2 adsorption results show that all MCM-41 samples maintained their uniform hexagonal mesoporous structure well after they have been subjected to post-synthesis alumination with the loading of Al species on Si-MCM-41 varied from 0.1 wt. % up to 10 wt. % (calculated based on AI2O3). 

Figure 3. FTIR spectra of pyridine absorption on PSM and AMM materials after degassing at (a) room temperature and (b) 200°C.

Absorption is influenced significantly by the cations in the salts (235). Typical examples for absorption of ethanol are shown in Fig. 46. It is clear that the absorption of H3PW12O40 is greatly suppressed when H+ is replaced by Cs, while the absorptivity varies little when H+ is replaced by Na+. In contrast, there is little difference between the Na and Cs salts when they are characterized by the acid amounts measured by pyridine absorption. 

Fig. 46. Total amount (a) and absorption capacities (b) of Na and Cs salts of H3PW12O40 (O) Na, ( ) Cs. The acid amounts were measured by pyridine absorption (adsorption). (From Ref. 235.)...

Prismatic needles from acetone, ethanol + ether or methanol ethyl acetate, mp 153-154. pKa 7.90, 8.03. Freely sol in water, ethanol, acetone sparingly sol in ether, ethyl acetate, chloroform, pyridine. Absorption spectrum Stacey, Turton, be. dr. 

Crystals from pyridine + acetone, methanol + chloroform, toluene + alcohol (1 ) or chloroform + alcohol + water, [a] +4.5 (c = 2 in pyridine). Absorption spectrum Schwarz er at., Ann. N.Y. Acad. Set 69, 118 (1957). Soluble in hot dioxane, l,l-dichloro-l-nitroethane, butanol and acetonitrile + chloroform. 

Photoexcited fluorescence from spread monolayers may be studied [158,159] if the substance has both a strong absorption band and a high emission yield as in the case for chlorophyll [159]. Gaines and co-workers [160] have reported on the emission from monolayers of Ru(bipyridine)3, one of the pyridine ligands having attached C g aliphatic chains. Ruorescence depolarization provides information about the restriction of rotational diffusion of molecules in a monolayer [161], Combining pressure-area... 

The desired pyridylamine was obtained in 69 % overall yield by monomethylation of 2-(aminomethyl)pyridine following a literature procedure (Scheme 4.14). First amine 4.48 was converted into formamide 4.49, through reaction with the in situ prepared mixed anhydride of acetic acid and formic acid. Reduction of 4.49 with borane dimethyl sulfide complex produced diamine 4.50. This compound could be used successfully in the Mannich reaction with 4.39, affording crude 4.51 in 92 % yield (Scheme 4.15). Analogous to 4.44, 4.51 also coordinates to copper(II) in water, as indicated by a shift of the UV-absorption maximum from 296 nm to 308 nm. 

This bathochromic shift is typical of 77 —> tt transitions. The behavior of the water solution when acidified was attributed by Albert (175) absorption by the thiazolium cation, by analogy with pyridine. However, allowance is made for the very weak basicity of thiazole (pK = 2.52) compared with that of pyridine (pK = 5.2), Ellis and Griffiths (176) consider the differences between the spectrum of thiazole in water and in... 

As in the case of pyridine (185), the quaternization of thiazole induces a bathochromic shift of the ultraviolet absorption spectrum in ethanol the long wavelength maximum at 232.3 nm (3900) for thiazole moves to 240 nm (4200) for 3-methylthiazolium tosylate (186) (Table 1-19). 

A solubihty parameter of 24.5-24.7 MPa / [12.0-12.1 (cal/cm ) ] has been calculated for PVF using room temperature swelling data (69). The polymer lost solvent to evaporation more rapidly than free solvent alone when exposed to air. This was ascribed to reestabUshment of favorable dipole—dipole interactions within the polymer. Infrared spectral shifts for poly(methyl methacrylate) in PVF have been interpreted as evidence of favorable acid—base interactions involving the H from CHF units (70). This is consistent with the greater absorption of pyridine than methyl acetate despite a closer solubihty parameter match with methyl acetate. 

A iridine traces in aqueous solution can be determined by reaction with 4-(p-nitroben25l)pyridine [1083-48-3] and potassium carbonate [584-08-7]. Quantitative determination is carried out by photometric measurement of the absorption of the blue dye formed (367,368). Alkylating reagents interfere in the determination. A iridine traces in the air can be detected discontinuously by absorption in Folin s reagent (l,2-naphthoquinone-4-sulfonate) [2066-93-5] (369,370) with subsequent chloroform extraction and hplc analysis of the red dye formed (371,372). The detection limit is ca 0.1 ppm. Nitrogen-specific thermal ionisation detectors can be used for continuous monitoring of the ambient air. 

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. 

Fig. 2. Effect of solvent on 4-phenyla2o-1-naphthol absorption. A, pyridine B, methanol C, acetic acid.

Z values are obtained from Eq. (8-76) for solvents having Z in the approximate range 63-86. In more polar solvents the CT band is obscured by the pyridinium ion ring absorption, and in nonpolar solvents l-ethyl-4-carbomethoxy-pyridinium iodide is insoluble. By using the more soluble pyridine-1-oxide as a secondary standard and obtaining an empirical equation between Z and the transition energy for pyridine-1-oxide, it is possible to measure the Z values of nonpolar solvents. The value for water must be estimated indirectly from correlations with other quantities. Table 8-15 gives Z values for numerous solvents. 

The 9ai7-quinolizine structure (82) for the labile adduct from 3,5-dimethylpyridine was clearly established by the nuclear magnetic resonance studies of Richards and Higham, and subsequent work showed the labile adduct from 3-methylpyridine was analogous. As the labile adducts from all the pyridines and benzopyridines so far examined have very similar infrared absorption spectra in the 5-7 yn. (carbonyl and aromatic) region and within quite close limits very similar ultraviolet absorption spectra, it can be concluded that all are derivatives of 9aH-quinolizine,... 

The infrared spectra of amino- and methylamino-pyri-dines and -quinolines show absorption bands that are charcteristic of monosubstituted-pyridine " or -quinoline rings and of the amino group. Changes in the infrared and ultraviolet spectra of amino-... 

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