Infrared spectroscopy acids

Still another type of adsorption system is that in which either a proton transfer occurs between the adsorbent site and the adsorbate or a Lewis acid-base type of reaction occurs. An important group of solids having acid sites is that of the various silica-aluminas, widely used as cracking catalysts. The sites center on surface aluminum ions but could be either proton donor (Brpnsted acid) or Lewis acid in type. The type of site can be distinguished by infrared spectroscopy, since an adsorbed base, such as ammonia or pyridine, should be either in the ammonium or pyridinium ion form or in coordinated form. The type of data obtainable is illustrated in Fig. XVIII-20, which shows a portion of the infrared spectrum of pyridine adsorbed on a Mo(IV)-Al203 catalyst. In the presence of some surface water both Lewis and Brpnsted types of adsorbed pyridine are seen, as marked in the figure. Thus the features at 1450 and 1620 cm are attributed to pyridine bound to Lewis acid sites, while those at 1540... 

Eden G J, Gao X and Weaver M J 1994 The adsorption of suiphate on goid(111) in acidic acqueous media Adiayer structurai interferences from infrared spectroscopy and scanning tunneiing microscopy J. Electroanal. Chem. 375 357-66... 

Infrared spectra of fats and oils are similar regardless of their composition. The principal absorption seen is the carbonyl stretching peak which is virtually identical for all triglyceride oils. The most common appHcation of infrared spectroscopy is the determination of trans fatty acids occurring in a partially hydrogenated fat (58,59). Absorption at 965 - 975 cm is unique to the trans functionaHty. Near infrared spectroscopy has been utilized for simultaneous quantitation of fat, protein, and moisture in grain samples (60). The technique has also been reported to be useful for instmmental determination of iodine value (61). 

Finally, the techniques of nmr, infrared spectroscopy, and thin-layer chromatography also can be used to assay maleic anhydride (172). The individual anhydrides may be analyzed by gas chromatography (173,174). The isomeric acids can be determined by polarography (175), thermal analysis (176), paper and thin-layer chromatographies (177), and nonaqueous titrations with an alkaU (178). Maleic and fumaric acids may be separated by both gel filtration (179) and ion-exchange techniques (180). 

Analytical and Test Methods. o-Nitrotoluene can be analyzed for purity and isomer content by infrared spectroscopy with an accuracy of about 1%. -Nitrotoluene content can be estimated by the decomposition of the isomeric toluene diazonium chlorides because the ortho and meta isomers decompose more readily than the para isomer. A colorimetric method for determining the content of the various isomers is based on the color which forms when the mononitrotoluenes are dissolved in sulfuric acid (45). From the absorption of the sulfuric acid solution at 436 and 305 nm, the ortho and para isomer content can be deterrnined, and the meta isomer can be obtained by difference. However, this and other colorimetric methods are subject to possible interferences from other aromatic nitro compounds. A titrimetric method, based on the reduction of the nitro group with titanium(III) sulfate or chloride, can be used to determine mononitrotoluenes (32). Chromatographic methods, eg, gas chromatography or high pressure Hquid chromatography, are well suited for the deterrnination of mononitrotoluenes as well as its individual isomers. Freezing points are used commonly as indicators of purity of the various isomers. 

Amides can be titrated direcdy by perchloric acid ia a nonaqueous solvent (60,61) and by potentiometric titration (62), which gives the sum of amide and amine salts. Infrared spectroscopy has been used to characterize fatty acid amides (63). Mass spectroscopy has been able to iadicate the position of the unsaturation ia unsaturated fatty amides (64). Typical specifications of some primary fatty acid amides and properties of bisamides are shown ia Tables 5 and 6. 

Several properties of the filler are important to the compounder (279). Properties that are frequentiy reported by fumed sihca manufacturers include the acidity of the filler, nitrogen adsorption, oil absorption, and particle size distribution (280,281). The adsorption techniques provide a measure of the surface area of the filler, whereas oil absorption is an indication of the stmcture of the filler (282). Measurement of the sdanol concentration is critical, and some techniques that are commonly used in the industry to estimate this parameter are the methyl red absorption and methanol wettabihty (273,274,277) tests. Other techniques include various spectroscopies, such as diffuse reflectance infrared spectroscopy (drift), inverse gas chromatography (igc), photoacoustic ir, nmr, Raman, and surface forces apparatus (277,283—290). 

Infrared Spectroscopy (ir). Infrared curves are used to identify the chemical functionality of waxes. Petroleum waxes with only hydrocarbon functionality show slight differences based on crystallinity, while vegetable and insect waxes contain hydrocarbons, carboxyflc acids, alcohols, and esters. The ir curves are typically used in combination with other analytical methods such as dsc or gc/gpc to characterize waxes. 

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. 

The importance of ring size holds also for tautomerism of -pyrrol-5-ones and. d -dihydro-6-pyridones. While the former compounds behave as cyclic 1-methyl-2-alkyl-2-hydroxy-5-pyrrolidones 179) (76) [or, on distillation, as the dehydrated l-methyl-2-alkyl-J -pyrrolones (77)], the latter compounds exist as acyclic N-methylamides of 8-oxo-acids (78) [as shown by infrared spectroscopy (/80)j. The dehydration of 78 during distillation to form l-methyl-2-alkyl-. -dihydro-6-pyridones (79) is achieved only with difficulty. 

Into a mixture of 1.6 g of 2-amino-4-methylpyrlmidine with 10 ml of glacial acetic acid is slowly added 2.13 g of concentrated sulfuric acid. A mixture of 2.4 g of 2-formyl-1-methyl-5-nitroimidazole in 20 ml of glacial acetic acid is slowly added to the mixture of the pyrimidine under stirring. The reaction mixture is maintained at a temperature of about 55°C for 4 hours. The resultant mixture is then diluted with 200 ml of distilled water and neutralized with a saturated aqueous solution of sodium bicarbonate. A brownish-yellow precipitate (MP 232° to 235°C) is formed and recovered. The product is analyzed by infrared spectroscopy and is found to conform to 2-amino-4-[2-(1-methyl-5-nitro-2-imidazolyI)vinyl] pyrimidine. 

Recent developments in the mechanisms of corrosion inhibition have been discussed in reviews dealing with acid solutions " and neutral solu-tions - . Novel and improved experimental techniques, e.g. surface enhanced Raman spectroscopy , infrared spectroscopy. Auger electron spectroscopyX-ray photoelectron spectroscopyand a.c. impedance analysis have been used to study the adsorption, interaction and reaction of inhibitors at metal surfaces. 

Infrared radiation, electromagnetic spectrum and, 419, 422 energy of. 422 frequencies of, 422 wavelengths of, 422 Infrared spectroscopy, 422-431 acid anhydrides, 822-823 acid chlorides, 822-823 alcohols. 428, 632-633 aldehydes, 428. 730-731 alkanes, 426-427 alkenes, 427 alkynes, 427 amides. 822-823 amines, 428, 952 ammonium salts, 952-953 aromatic compound, 427-428, 534 bond stretching in, 422... 

Tests, The acid absorbs strongly in the infrared at i 739cm"1 and can be detd by infrared spectroscopy (Ref 7)... 

The treatment of LB films of copper behenate (10-50 layers) with H2S gas resulted in formation of the semiconductor CU2S [177]. In this case, the LB films of behenic acid alone were formed and then exposed to solutions of copper chloride. Conversion of the carboxyl groups to carboxylate groups upon copper complexation was confirmed by infrared spectroscopy. Resistivity measurements versus temperature confirmed the formation of semiconducting CU2S in one case, and showed a linear increase in log(R) versus IT K). All of the samples became insulators on exposure to air maintaining the conductivity required storage under vacuum. The formation of CuiS sheets in some of the sample was concluded from optical microscopy and resistivity data. 

Moreira, J.L. and Santos, L., Analysis of organic acids in wines by Fourier-transform infrared spectroscopy, Anal. Bioanal. Chem., 382, 421, 2005. 

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