Hydroxyl groups nitrates/nitrites

The hydroxyl groups on glycols undergo the usual alcohol chemistry giving a wide variety of possible derivatives. Hydroxyls can be converted to aldehydes, alkyl hahdes, amides, amines, a2ides, carboxyUc acids, ethers, mercaptans, nitrate esters, nitriles, nitrite esters, organic esters, peroxides, phosphate esters, and sulfate esters (6,7). 

For the oxidation of primary hydroxyl groups, three times the amount of nitrite is required when compared with nitrate, and three times as much of the toxic NO would be formed. This oxidation procedure has been applied to the glucans cellulose, amylose, and pullulan. A study of this system with cyclomaltoheptaose (/J-cyclodextrin) showed that the reaction is autocatalytic. 

Nitration of phenols by peroxidases can occur through two different mechanisms. The reaction requires phenol, nitrite, and hydrogen peroxide. In the principal mechanisms, compound I and compound II are formed. Upon one-electron oxidation of the substrates, phenoxy radical and nitrogen dioxide are produced. Coupling of these species gives the nitrophenol derivatives, where the nitro group is in the ortho or para position with respect to the phenol hydroxyl group. This reaction will be described in more detail in Sect. 6.1.5. 

Hydrogen atom abstraction does not take place at room temperature. The nitro, nitrite, nitrate, carbonyl and hydroxyl groups are formed at T > 373 K. The following mechanism was postulated ... 

The use of NO and sulphur tetrafluoride (SF4) gas treatments allows more precise identification and quantification of hydroxyl (OH) and hydroperoxy (OOH) groups (as nitrites and nitrates, respectively, after NO reaction) and carboxylic acids (after SF4 treatment to produce acid fluorides) (cf. section 10.17.1.5) and ketones (after removal of the overlapping acid absorptions and hydrogen-bonding effects with —OH groups by SF4 reactions) [362]. The NO reaction products are particularly informative because of their intense absorptions (up to 4-7 times stronger than those of the original OH species) and because primary, secondary and tertiary products have different IR absorptions [362]. 

In general, there are three regions of the infrared (IR) spectra that merit special attention. Bands in the range 2400-2100 cm can be assigned to the N-N stretching frequency of adsorbed N2 or N20, bands below 1700 cm" can be attributed to oxidized nitrogen species (nitrite, nitrate, and nitro compounds), and those around 3800-3600 cm" to hydroxyl groups.Table 4.1 summarizes the main IR bands identified for a Rh/ceria catalyst in contact with a NgO/He flow. 

The direct use of nitric oxide (NO) reactions to identify and quantify hydroxyl (OH) and/or hydroperoxy (OOH) groups is complicated by the formation of equimolar mixtures of nitrates (with absorption bands at 1630, 1302, 1290, 1278 and 860 cm ) and nitrites (with a strong absorption band at 1645, and weak bands at 780-760 cm " ) ... 

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