Nitrogen Evolution Method

The most common assay method for lead azide used in the United States [12, 13] involves measurement of the nitrogen evolved during reaction with ceiic ammonium nitrate according to the following equation  

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The solution is ca. 2 M. Yields were determined by nitrogen evolution on adding acetic acid, or spectrometrically from the visible absorption band at 500 m fi, which has e 2 as calculated from the nitrogen evolution. Yields estimated by addition of a standard solution of benzoic acid and titration with alkali were consistently much lower. Both methods underestimate the yield, since decomposition with acid gives tetramethyl-ethylene and some acetone azine in addition to the isopropyl ester.3 The nitrogen evolution method (and therefore the spectrometric method) probably underestimates the yield by ca. 10-20%, the titration method by more than 50%. 

Figure 1. Apparatus for lead azide determination using the nitrogen evolution method [3], A, 125-ml flat-bottom reaction flask B, 1.4 X 4.5-cm vial C, 125-ml flat-bottom absorption flask D, water reservoir E, 500-ml gas buret F, water jacket H, 50-ml buret I, 3-way T-stopcock, position B J, 3-way T-stopcock, position A K, thermometers L, leveling bulb.

During a study of azonitrones (70), Forrester and Thomson showed that reaction with toluene-p-sulfinic acid resulted in nitrogen evolution and formation of the hydroxamic acid (66) together with the pyrrolidone (71) and the amidine (72). These workers suggested the following reaction course. Although the yield of hydroxamic acid was high, the method is not likely to be of preparative value. 

Whereas a number of 5-aryl thiatriazoles have been reported, the only previously known true aliphatic and alicyclic representatives were 5-tert-butyl31 and cyclohexyl thiatriazole.32 These are unstable oils that decompose at 0° with nitrogen evolution and formation of sulfur. They are prepared from the corresponding thioacylhydrazides and nitrous acid, but the method is not generally applicable because of difficulties in obtaining the required aliphatic thioacylhydrazides.1 Wijers et o/.17 have found that aliphatic thiatriazoles can be prepared from 1-acetylthio-l-alkynes. Thus a substance believed to be 5-pentylthiatriazole was isolated from the reaction between 1-acetylthio-l-hexyne and ammonium azide. It is an oil that solidifies at about —16° and could not be analyzed because of its explosive character and poor stability at room temperature. Its formation is explained by the following scheme [Eq. 

The kinetic parameters of thermal decomposition of several 2,5-disubstituted tetrazoles 6 in the gas phase and in nitrobenzene solution have been determined using manometric methods. Limiting stages of the stepwise uni-molecular decomposition that determine the experimental rate of nitrogen evolution include reversible formation and subsequent breakdown of the azo-diazo intermediates 186 (Scheme 15) <1996RCB2094>. 

Method B Phenoxypropionyl hydrazide (125.9 g, 0.7 mol) is suspended in 650 ml ice-water and concentrated hydrochloric acid (123 ml, 1.47 mol) was added. The mixture is stirred for 20 min and toluene (350 ml) is added. A solution of sodium nitrite (53.1 g, 0.77 mol) in 200 ml water is added over a period 15 min. The internal temperature is kept below 15°C and if necessary, ice is directly added to the reaction mixture. After the addition is completed the mixture is stirred for a further 1 hour and filtered through Celite. The solid is washed with 30 ml toluene and the filtrate is separated. The aqueous layer is extracted with 200 ml toluene and the combined toluene solutions are dried over MgS04. The dried toluene solution is filtered and added dropwise to a preheated flask at 95°-100°C. Nitrogen evolution occurs as the solution is dropped in. After the addition is complete, the reaction mixture is heated to gentle reflux until nitrogen evolution has ceased. The reaction mixture is cooled to room temperature and can be used directly in subsequent reactions. 1 ml of the reaction mixture is withdrawn and evaporated to dryness, and the weight of the residue is measured. This provides an estimate of the concentration of isocyanate per ml of reaction mixture. 

A new element for simultaneous indirect detection of C and signals in labelled proteins was proposed by Uhrin et The CT- CHs, VT- N-HSQC sequence combines constant-time carbon evolution with variable delay nitrogen evolution. This is achieved by the variation of the position of a 90° pulse creating transverse coherence within the C constant-time period. The maximum indirect acquisition time for both nuclei is determined by constant-time period set to l/ /(C,C) = 28.6 ms. The method is best suited for detection of CH3 signals due to their slower relaxation. The proposed element was incorporated into NOESY-based experiments resulting in 3D NOESY-CH3NH and 3D HSQC-NOESY-CH3NH sequences. The experiments... 

Both the above techniques require standardization using a known quantity of sodium azide carried through the same procedure. A semimicro gas-evolution method has been described by Blais [24] which utilizes only a few milligrams of lead azide. Nitrogen is determined by reduction of hydrazoic acid with heated cupric oxide. 

Conventional fuel characterization methods do not always provide sufficient information to evaluate opportunity fuels— particularly with respect to nitrogen evolution and NOx formation. Consequently additional techniques for characterization and analysis have been developed to analyze the fate of fuel nitrogen and its evolution in volatile... 

This reaction also works presumably through the intermediacy of anfinyl radicals, as inferred from the nitrogen evolution that accompanies the process. The use of water, alcohols, or some kind of proton donor is essential. When Cu(0) is used, typical byproducts of oxidation of alcohols are often observed, which also support a radical mechanism. However, the formation of nitrenes cannot be discarded. More selective reaction conditions involve zinc dust in the presence of acetic acid, which have found widespread use in the hterature. An early example of application implied the reduction of geranylazide to geranylamine (Scheme 8.37). This method has been also successfiiUy applied in carbohydrate chemistry. ... 

Method 1. Place 20 g. of crude benzoin (preceding Section) and 100 ml. of concentrated nitric acid in a 250 ml. round-bottomed flask. Heat on a boiling water bath (in the fume cupboard) with occasional shaking until the evolution of oxides of nitrogen has ceased (about 1 -5 hours). Pour the reaction mixture into 300-400 ml. of cold water contained in a beaker, stir well until the oil crystallises completely as a yellow solid. Filter the crude benzil at the pump, and wash it thoroughly with water to remove the nitric acid. RecrystaUise from alcohol or methylated spirit (about 2-5 ml. per gram). The yield of pure benzil, m.p. 94-96°, is 19 g. 

Method 2. Place 0-2 g. of cupric acetate, 10 g. of ammonium nitrate, 21 2 g. of benzoin and 70 ml. of an 80 per cent, by volume acetic acid -water solution in a 250 ml. flask fitted with a reflux condenser. Heat the mixture with occasional shaking (1). When solution occurs, a vigorous evolution of nitrogen is observed. Reflux for 90 minutes, cool the solution, seed the solution with a crystal of benzil (2), and allow to stand for 1 hour. Filter at the pump and keep the mother liquor (3) wash well with water and dry (preferably in an oven at 60°). The resulting benzil has m.p. 94-95° and the m.p. is unaffected by recrystallisation from alcohol or from carbon tetrachloride (2 ml. per gram). Dilution of the mother liquor with the aqueous washings gives a further 1 Og. of benzil (4). 

An alternative method of removing the aniline is to add 30 ml. of concentrated sulphuric acid carefully to the steam distillate, cool the solution to 0-5°, and add a concentrated solution of sodium nitrite until a drop of the reaction mixture colours potassium iodide - starch paper a deep blue instantly. As the diazotisation approaches completion, the reaction becomes slow it will therefore be necessary to teat for excess of nitrous acid after an interval of 5 minutes, stirring all the whUe. About 12 g. of sodium nitrite are usually required. The diazotised solution is then heated on a boiling water bath for an hour (or until active evolution of nitrogen ceases), treated with a solution of 60 g. of sodium hydroxide in 200 ml. of water, the mixture steam-distilled, and the quinoline isolated from the distillate by extrsM-tion with ether as above. 

The anhydrous salt is prepared by several methods, eg, by reacting ZrCl with liquid anhydrous HP. It is necessary to use an excess of HP which also acts as a wetting agent. The reaction is instantaneous and is carried out in a polyethylene jar or carboy. When the evolution of HCl ceases, the material is transferred to a tray and dried under an atmosphere of nitrogen. By proper selection of equipment, purification of raw material, and drying conditions, materials of spectrographic purity can be produced (4). 

Method A To a stirred suspension of 4.28 g (27 mmol) of anhyd chromium(III) chloride in 100 ml. of anhyd THF in a 500-mL three-necked, round-bottom flask, under nitrogen, is added 0.51 g (13.4 mmol) of LiAlH4 at 0 °C in small portions with vigorous stirring. After the evolution of hydrogen has ceased, stirring is continued at 20 C for 30 min. 

Figure 2.20. Transformation of silica supported dinitrosyl complexes of nickel(II) leading to formation of nitrogen dioxide and its final stabilization on the support. The picture shows the molecular structure and the spin density contours calculated with BP/DNP method of the involved species, and evolution of the X-band EPR spectra of the NiN02 Si02 complex due to spillover of the ligand (adopted from [71]).

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