Denitration

Sir Joseph Swan, as a result of his quest for carbon fiber for lamp filaments (2), learned how to denitrate nitrocellulose using ammonium sulfide. In 1885 he exhibited the first textiles made from this new artificial sHk, but with carbon fiber being his main theme he failed to foUow up on the textile possibihties. Meanwhile Count Hilaire de Chardoimet (3) was researching the nitrocellulose route and had perfected his first fibers and textiles in time for the Paris Exhibition in 1889. There he got the necessary financial backing for the first Chardoimet silk factory in Besancon in 1890. His process involved treating mulberry leaves with nitric and sulfuric acids to form cellulose nitrate which could be dissolved in ether and alcohol. This collodion solution could be extmded through holes in a spinneret into warm air where solvent evaporation led to the formation of soHd cellulose nitrate filaments. 

Although this first route was simple in concept, it proved slow in operation, difficult to scale up safely, and relatively uneconomical compared with the other routes. Denitration of the fibers, necessary to allow safe use wherever the fabrics may risk ignition, spoiled their strength and appearance. Nevertheless, Chardoimet earned and truly deserved his reputation as the Eather of Rayon. His process was operated commercially until 1949 when the last factory, bought from the Tubize Co. in the United States in 1934 by a Bra2iUan company, burned down. 

In TBP extraction, the yeUowcake is dissolved ia nitric acid and extracted with tributyl phosphate ia a kerosene or hexane diluent. The uranyl ion forms the mixed complex U02(N02)2(TBP)2 which is extracted iato the diluent. The purified uranium is then back-extracted iato nitric acid or water, and concentrated. The uranyl nitrate solution is evaporated to uranyl nitrate hexahydrate [13520-83-7], U02(N02)2 6H20. The uranyl nitrate hexahydrate is dehydrated and denitrated duting a pyrolysis step to form uranium trioxide [1344-58-7], UO, as shown ia equation 10. The pyrolysis is most often carried out ia either a batch reactor (Fig. 2) or a fluidized-bed denitrator (Fig. 3). The UO is reduced with hydrogen to uranium dioxide [1344-57-6], UO2 (eq. 11), and converted to uranium tetrafluoride [10049-14-6], UF, with HF at elevated temperatures (eq. 12). The UF can be either reduced to uranium metal or fluotinated to uranium hexafluoride [7783-81-5], UF, for isotope enrichment. The chemistry and operating conditions of the TBP refining process, and conversion to UO, UO2, and ultimately UF have been discussed ia detail (40). 

Fig. 2. Gas-fired denitration pots for denitration of U02(N02)2 6H20. (a) The large pot (1.68 M ID, 0.81 m height) is heated by three concentric rings of small radiant gas burners, (b) The small pot (76 cm ID, 46 cm height) is heated by four gas burners iaside a ceramic furnace (40).

Fig. 3. Pilot-plant fluidized-bed denitiatoi for denitration of U02(N0 )2 bHjO where UNH = utanyl nitrate liexahydrate (40),...

Methylation of free OH groups, followed by denitration, hydrolysis, reduction, and glc analysis has been suggested as a method for determining the location of nitrate (82). This method has been suggested for CP and CS (82) as the phosphate and sulfate groups are stable to methylation and can then be removed. Periodate oxidation has been used to determine the DS of CS (81). 

Imidazole, 2-methyl-1,4-dinitro-rearrangement, 5, 378 Imidazole, 5-methyl-1,4-dinitro-denitration, 5, 378 Imidazole, l-methyl-4,5-diphenyl-synthesis, 5, 478... 

Only 22-45% yields of m-fluoronitrobenzene are obtained from the fluoro-denitration of m dinitrobenzene by potassium fluoride in Af-methyl-2-pyrrolidone or hexamethylphosphoramide, along with significant amounts of 3,3 dinitro-diphenyl ether [107, 108, 109] (equation 32)... 

The nitro group of ct-nitro ketones is readily removed either by treatment v/ith BiuSnH or reduction v/ith LiAlHl of the cotrespondmg tosylhydrazones fEq 3 58 Details of denitration are discussed in Section 7 2, and some applications of this process are shovm in Schemes 35-37... 

Construction of the carbon frameworks by using the activating property of the nitro group followed by denitration provides a useful tool for the preparation of various naniral products as shovm in Schemes 3 5-3 7 For example, fZ -jasmone and dihydrojasmone, constinients of the essential oilof jasmone flowers, have been prepared as shown in Scheme 3 5 Schemes 3 6 and 3 7 present a synthesis of pheromones via denitration of ct-nitro ketones " ... 

The Michael addition of ct-nitro ketones to a,fi-unsaiurated ketones followed by radical denitration provides a useful strategy for the preparation of 1,4-diketones TPhenylheptane-1,5-dione, isolated from the decayed heart wood of aspens, is prepared by this strategy fEq... 

Photoredncdon of aromadc and aliphadc nitro compounds gives hydtoxylamines or amines, which is well reviewed The radicid reacdon of primary nitro compounds v/ith dn hydnde does not give the denitrated product fsee Chapter 7, but give the corresponding oximes fEq... 

The Knoevnagel reaction of 6-methoxytetralc nediamine followed by the nitro-aldol reach allylic nitro compounds Subsequent group Base catalyzed cyclizadon gives the I by radical denitration fsee Section 7 2 ... 

Table 7.1. Denitration of nitro eomponnds with MeSNa or 8038111 ...

The Michael dclclidon of nitro ilkdnes followed by denitration is also a useful method fot the pteparadon of C-disaccharide. The Michael addidon of glncosyl nitromethane to the levogln-cosenone ptoceeds steteoselecdvely, and subsequent denitradon gives the C-disaccharide in 68% yield fScheme 1.%) ... 

Enarnioselective nitro-dlclol reacdon Csee Secdon 3.3 or Michael reaction Csee Secdon 4.4 followed by radical denitration is useful as an altemadve indirect method of enandose-lecdve 1,3- or 1,4-addidon of alkyl anions fsee Eq. 7.70 and Eq. 7.71 . ... 

Denitration of nitro compounds with Bu- SnD provides an elegant method fci the synthesis of deiuerated compounds Recently, the synthesis of deuterium labeled plant sterols has been reported fsee Eq 11%)... 

Other applications of radical denitration in organic synthesis are summarized in Table 7.3. 

Although this method is aot a geaeral procedure, bemg specific for ct-nitroketoues, k has several merits to avoid the use of toxic reageuts such as organodn compounds Functionalized ketones have been prepared by this denitration reaction, in which functionalized nitroalkanes are used as alkyl anion synthons For example, 3-nitropropanal ethylene acetal can be used as synthon of the 3-oxo-propyl anion and 1,4-dicarbonyl compounds are prepared, as shovm In Eq 7 88... 

Denitriermittel, n. denitrating agent, Denitrierung, /. denitration, denitrifizieren, v.t. denitrify,... 

Process (3) may be slow, hence under industrial conditions it may be broken off before equilibrium is established. This means that chemical reaction (3) is not completed. As a final product, a not very homogeneous nitrocotton is obtained. The higher the nitrating temperature, the more rapid the denitration process, the sooner the reaction balance is established, and hence the more uniform the product ... 

The reaction products were shown to contain the expected product of rearrangement (XXXVI) together with the denitration product (XXXVII) and nitrophenol (XXXVIII). 

The complete chemistry of plutonium 1 iquid-to-solid conversion processes, especially peroxide and oxalate precipitation, should be further studied. Research and development of direct thermal denitration methods should also be pursued. 

Precipitation Processes. Plutonium peroxide precipitation is used at Rocky Flats to convert the purified plutonium nitrate solution to a solid (14) the plutonium peroxide is then calcined to Pu02 and sent to the reduction step. The chemistry of the plutonium peroxide precipitation process is being studied, as well as alternative precipitation processes such as oxalate, carbonate, fluoride, and thermal denitration. The latter method shows the most promise for cost and waste reduction. 

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