Aldehydes infrared spectroscopy

Polyester composition can be determined by hydrolytic depolymerization followed by gas chromatography (28) to analyze for monomers, comonomers, oligomers, and other components including side-reaction products (ie, DEG, vinyl groups, aldehydes), plasticizers, and finishes. Mass spectroscopy and infrared spectroscopy can provide valuable composition information, including end group analysis (47,101,102). X-ray fluorescence is commonly used to determine metals content of polymers, from sources including catalysts, delusterants, or tracer materials added for fiber identification purposes (28,102,103). 

An unusual method for the preparation of syndiotactic polybutadiene was reported by The Goodyear Tire Rubber Co. (43) a preformed cobalt-type catalyst prepared under anhydrous conditions was found to polymerize 1,3-butadiene in an emulsion-type recipe to give syndiotactic polybutadienes of various melting points (120—190°C). These polymers were characterized by infrared spectroscopy and nuclear magnetic resonance (44—46). Both the Ube Industries catalyst mentioned previously and the Goodyear catalyst were further modified to control the molecular weight and melting point of syndio-polybutadiene by the addition of various modifiers such as alcohols, nitriles, aldehydes, ketones, ethers, and cyano compounds. 

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... 

The widespread use of infrared spectroscopy at that time was probably due to the observation that many chemical groups absorb in a very narrow range of frequency. Furthermore, within this frequency range, the observed frequency may be correlated to specific chemical structures. For example, aldehydes can be differentiated from ketones by the characteristic stretching frequency of the carbonyl group near 1700 cm-1, and the spectral pattern may be likened to a molecular fingerprint. ... 

Regarding ozonation processes, the treatment with ozone leads to halogen-free oxygenated compounds (except when bromide is present), mostly aldehydes, carboxylic acids, ketoacids, ketones, etc. [189]. The evolution of analytical techniques and their combined use have allowed some researchers to identify new ozone by-products. This is the case of the work of Richardson et al. [189,190] who combined mass spectrometry and infrared spectroscopy together with derivatization methods. These authors found numerous aldehydes, ketones, dicarbonyl compounds, carboxylic acids, aldo and keto acids, and nitriles from the ozonation of Mississippi River water with 2.7-3 mg L 1 of TOC and pH about 7.5. They also identified by-products from ozonated-chlorinated (with chlorine and chloramine) water. In these cases, they found haloalkanes, haloalkenes, halo aldehydes, haloketones, haloacids, brominated compounds due to the presence of bromide ion, etc. They observed a lower formation of halocompounds formed after ozone-chlorine or chloramine oxidations than after single chlorination or chlorami-nation, showing the beneficial effect of preozonation. 

Infrared spectroscopy is extremely useful for identifying aldehydes and ketones. Carbonyl groups absarh In the JR range 1660-1770 cm . with the exact position highly diagnostic of the kind of carbonyl up... 

PCC on alumina (7.5g, 6.1 mmol) is added to a flask containing a solution of citronellol (0.60 g, 3.8 mmol) in 10 mL of n-hexane. After stirring or shaking for up to 3 h (follow the course of the reaction by TLC), remove the solid by filtration, wash it with three 10-mL portions of ether, and remove the solvents from the filtrate by distillation or evaporation. The last trace of solvent can be removed under vacuum. (See Fig. 9 in Chapter 3.) The residue should be pure citronellal, bp 90°C at 14 mm. Check its purity by TLC and infrared spectroscopy. A large number of other primary and secondary alcohols can be oxidized to aldehydes and ketones using this same procedure. 

Infrared spectroscopy is extremely useful in analyzing all carbonyl-containing compounds, including aldehydes and ketones. See the extensive discussion in Chapter 19. 

In 1976, Pecsok, Painter, Shelton, and Koenig (14) developed a mechanism for the thermal oxidation of cls-l,4-polybutadlene which Incorporated both the Bolland and Bevllacqua structures. Using Fourier transform infrared spectroscopy, the lultial oxidative changes In the polymer were obtained for the temperature range of 25-60°C. An oxidative cls/trans conversion was observed as well as formation of dl-alkyl peroxide, unsaturated aldehyde, and saturated aldehyde. 

Puddington first reported that small proportions of acids and aldehydes are present in the gases liberated when potato starch is pyrolyzed at about 200°. The identification of these compounds by conventional techniques, including infrared spectroscopy, is difficult this is particularly true of the latter method, as the water present in the mixture absorbs very strongly and masks other bands. These difficulties are readily overcome by the use of gas chromatography. 

Infrared spectroscopy has been used to show that the acyclic form of this sugar is not present to any appreciable extent because it equilibrates to give different cyclic forms. The acyclic form of the glucose has an aldehyde group present and thus should obviously produce a significant carbonyl absorption in its IR spectrum. As the spectrum does not show this absorption, it is clear that the acyclic form cannot be present... 

Using a similar technique, Nlkl and co-workers (151) have obtained rate constant data for the reaction of OH radicals with a series of aldehydes from their rates of disappearance, as measured by long path Fourier transform infrared spectroscopy. 

A reaction similar to that of formaldehyde is not observed with aldehyde molecules having two or more carbon atoms, such as acetaldehyde and propionaldehyde. The two types of addition product, -C-O-C- and -C-C- compounds, can be distinguished by infrared spectroscopy (see Fig. 1). 

---