Nitrogen compounds, processing

Traces of formaldehyde, present in neat end-capped polymer or produced by processing polymer under abusive conditions, detract from polymer stabihty. Commercial resins typically contain formaldehyde scavengers. Nitrogen compounds, especially amines and amides, epoxies, and polyhydroxy compounds, are particularly efficacious scavengers. 

Nitrogen Compound Autoxidation. CycHc processes based on the oxidation of hydrazobenzene and dihydrophenazine to give hydrogen peroxide and the corresponding azobenzene—phenazine were developed in the United States and Germany during World War II. However, these processes could not compete economically with the anthrahydroquinone autoxidation process. 

Hypochlorous acid reacts very rapidly and quantitatively with a slight excess of free ammonia forming monochloramine, NH2CI, which reacts at a slower rate with additional HOCl forming dichloramine, NHCI2. Trichloramine is formed when three moles of HOCl are added per mole of ammonia between pH 3—4 (100). Hypochlorous acid in the form of chlorine or hypochlorite is used in water treatments to oxidize ammonia by the process of break-point chlorination, which is based on formation of unstable dichloramine. The instabiHty of NHCI2 is caused by presence of HOCl and NCl (101,102). The reaction is most rapid at a pH of about 7.5 (103). Other nitrogen compounds such as urea, creatinine, and amino acids are also oxidized by hypochlorous acid, but at slower rates. Unstable iV-chloro compounds are intermediates in deammination of amino acids (104,105). 

Organic Solids A few organic compounds decompose before melting, mostly nitrogen compounds azides, diazo compounds, and nitramines. The processes are exothermic, classed as explosions, and may follow an autocatalytic law. Temperature ranges of decomposition are mostly 100 to 200°C (212 to 392°F). Only spotty results have been obtained, with no coherent pattern. The decomposition of malonic acid has been measured for both the solid and the supercooled liquid. The first-order specific rates at 126.3°C (259.3°F) were 0.00025/min for solid and 0.00207 for liquid, a ratio of 8 at II0.8°C (23I.4°F), the values were 0.000021 and 0.00047, a ratio of 39. The decomposition of oxalic acid (m.p. I89°C) obeyed a zero-order law at 130 to I70°C (266 to 338°F). 

Nitrogen fixation Conversion of atmospheric nitrogen into organic nitrogen compounds available to green plants a process that can be carried out only by certain strains of soil bacteria. 

A variety of condensation processes can lead to cyclic hydroxamic acids. These involve either the condensation of two molecules or the intramolecular cyclization of a single compound. In some cases, a primary hydroxamic acid function is already present and formation of a cyclic compound can arise by suitable reaction on nitrogen. These processes will be dealt with first. 

Excess fertilizer and combustion processes also can increase nitrous oxide (NnO) and nitrogen oxides (NOx) in the atmosphere. Nitrous oxide is a powerful greenhouse gas, and nitrogen oxides lead to smog and acid rain. The production of fertilizers requires a great deal of energy. The use of fossil fuels to supply the thermal requirements for fertilizer production further increases emission of nitrogen compounds to the atmosphere. 

Certain aromatic, nitrogen compounds (e.g., pyridines and quinolines) are basic and can cause coking on acid catalysts during petroleum processing. 

Prior to World War I the principal sources of nitrogen compounds were some nitrate deposits in Chile. Fritz Haber, a German chemist, successfully developed the process we have just described, thus allowing chemists to use the almost unlimited supply of nitrogen in the atmosphere as a source of nitrogen compounds. 

Each year, about half the 3 X 108 kg of hydrogen used in industry is converted into ammonia by the Haber process (Section 9.12). Through the reactions of ammonia, hydrogen finds its way into numerous other important nitrogen compounds such as hydrazine and sodium amide (see Section 15.2). 

Nitrogen fixation is any process in which N2 in the atmosphere reacts to form any nitrogen compound. Biological nitrogen fixation is the enzyme-catalyzed reduction of N2 to NH3, NH4, or any organic nitrogen compound. 

Ammonia assimilation is the process by which NH3 or NH4 is taken up by an organism to become part of its biomass in the form of organic nitrogen compounds. 

Fig. 12-1 Biological transformations of nitrogen compounds. The numbers refer to processes described in the text.

Loss of nitrogen compounds from soils is also a major pathway into the atmosphere for some compounds (e.g., N2O, NO, and NH3). As in the aquatic systems, parameters that play an important role in this process include the nature of the compound soil temperature, water content, pH, aeration of the soil and a concentration gradient of the gas in question. 

Pyridine and other heterocyclic nitrogen compounds can be aminated with alkali metal amides in a process called the Chichibabin reaction The attack is always in the 2 position unless both such positions are filled, in which case the 4 position is attacked. Substituted alkali metal amides (e.g., RNH and R2N ) have also been used. The mechanism is probably similar to that of 13-15. The existence of intermediate ions such as 15... 

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