Nitrite acidification

Sodium nitrite is stable in alkaline solutions. Acidification liberates nitrous acid which is unstable. The decomposition of nitrous acid yields nitric acid [7697-37-2] HNO, according to the following reaction ... 

The need for low levels of 3-isomer in 2-thiophenecarboxyhc acid [527-72-0] which is produced by oxidation of 2-acetylthiophene [88-15-3] and used in dmg appHcations, has been the driving force to find improved acylation catalysts. The most widely used oxidant is sodium hypochlorite, which produces a quantity of chloroform as by-product, a consequence that detracts from its simplicity. Separation of the phases and acidification of the aqueous phase precipitate the product which is filtered off. Alternative oxidants have included sodium nitrite in acid solution, which has some advantages, but, like the hypochlorite method, also involves very dilute solutions and low throughput volumes. 

Nitrous acid, HNO2, has not been isolated as a pure compound but it is a well known and important reagent in aqueous solutions and has also been studied as a component in gas-phase equilibria. Solutions of the free acid can readily be obtained by acidification of cooled aqueous nitrite solutions but even at room temperature disproportionation is noticeable ... 

The preservation of nutrient solutions at the concentrations occurring in natural seawater is a major challenge to the routine production of a nutrient reference material. Preservation techniques must be developed that maintain concentrations stable for periods of at least one to two years. Gamma radiation will produce nitrite that is unstable. Therefore this method appears to be problematic. The feasibility of other techniques, such as autoclaving, ultra-violet or microwave radiation, freezing, and acidification, should be evaluated. 

Oxygen depletion + Acidifying compounds Acidification + Toxic compounds (e.g. nitrite, metals)... 

The reaction of aminoguanidine with sodium nitrite under neutral conditions yields tetra-zolylguanyltetrazene hydrate (85), a primary explosive commonly known as tetrazene. Tetrazene (85) is only formed in the absence of free mineral acid and so a common method for its preparation treats the bicarbonate salt of aminoguanidine (84) with one equivalent of acetic acid followed by addition of aqueous sodium nitrite. " Tetrazene (85) is decomposed by aqueous alkali to form triazonitrosoaminoguanidine (86) which is isolated as the cuprate salt (87) on addition of copper acetate to the reaction mixture. Acidification of the copper salt (87) with mineral acid leads to the formation of 5-azidotetrazole (88) (CHN7 = 88 % N).55 56... 

Aminotetrazole (91) reacts with potassium permanganate in excess aqueous sodium hydroxide to yield the disodium salt of 5-azotetrazole (92). 5-Azotetrazole is unstable and attempts to isolate it by acidification yields 5-hydrazinotetrazole (93). Diazotization of 5-aminotetrazole (91) in the presence of excess sodium nitrite yields 5-nitrotetrazole (94), a powerful explosive whose mercury and silver salts are primary explosives. ... 

The chemistry of nitrite at acidic pH is closely related to that of nitrosonium ion described earlier. The pfC, of nitrous acid is around 3.4-3.6, though precise measurement is difficult because of its rapid secondary reactions. Acidification of nitrite produces nitrous acid, which is in reversible equilibrium with nitrosonium ion and hydroxide ion (Turney and Wright, 1959), although in aqueous solu-... 

In an aqueous solution, water-soluble amides have been nitrosated in the presence of sodium nitrite on acidification with mineral acids. This procedure appears to be restricted to amides which are water-soluble. Evidently, only amides derived from primary carbinamines may be prepared by this method. The reaction is somewhat slow, requires a large excess of sodium nitrite, evolves... 

Nitrogen trioxide may be obtained by the acidification of an aqueous solution of sodium nitrite or by the reduction of nitric acid. 

Ammonium nitrite is explosive and very sensitive to heating. Explosive decomposition can occur even when an aqueous solution is heated to 60-70°C. Acidification of an aqueous solution with a drop of concentrated hydrochloric, sulphuric or nitric acid produces a spontaneous decomposition even at room temperature. 

The microwave unit of the sample-preparation system provides heating during sample acidification and oxidation procedures. Heating promotes the dissolution of Al(OH)3 precipitates formed during the acidification step, as well as the removal of nitrites, as gaseous NOx species, which could interfere with subsequent oxidation. 

In this method, sodium azide solution is added before acidification into the sample mixture containing Mn4+ flocculent. Azide prevents any possible reaction of nitrite with iodide. Interference from Fe3+ is overcome by adding a small amount of KF solution (1 mL of 40% soln.) before acidification. 

A new heterocyclic ring system, 5//-pyrazolo[3,4- /]-l, 2,3-thiadiazoles (41), results from a one-pot, two-step reaction of the pyrazolodithiazolium chlorides (29). Sequential treatment of the derivatives (29) with base, sodium dithionite, and sodium nitrite followed by acidification afforded (41) (Scheme 3). For substrates (29a,b) potassium hydroxide was chosen, whilst for (29c,d) sodium bicarbonate was found to be superior. In the latter cases, potassium hydroxide caused appreciable hydrolysis of the ester substituent. A further point of interest is the significant quantity of disulfide (43) which can form on reaction of 6-carboethoxy-5-methylpyrazolodithiazolium chloride (29c). This, however, need not represent a problem since compound (43) can be converted in situ or isolated and converted to the desired product (41c) in good yield (Scheme 4) <84JOCl224>. 

Again V. Meyer was the first to describe the reaction. As in the formation of nitrolic acids, here also it is the aci-form of the secondary nitro compound that takes part in the reaction. It reacts with sodium nitrite to give a compound which, after acidification, forms pseudonitrole. 

Workers in the dinitrophenol plant should be protected in the usual way (i.e. gloves, respirators, chMige of clothes, bath, etc.). Selection of workers hMidling dinitrophenol is also recommended since it has been shown that a great mMiy people are resistant to its toxic effects, Selection is based on 15 days medical observation of each new worker in the dinitrophenol plant, in particular in the analysis of the mine every other day. A test for the presence of Mninonitrophenols is particularly importance. Usually Denien s reaction [33] is used. According to Lazarev [31], the reaction comprises acidification of the mine with 10% sulphuric acid and diazotization with sodium nitrite, followed by shaking up the prepMed solution with an ammoniacal solution of p- naphthol. If a red colour appeMS it indicates the presence of 4-amino-2-nitrophenol in the mine, while a violet shade is evidence for the presence of 2-Mnino-4-nitrophenol. 

Several preparations of dicarbonyl dinitrosyl iron have been reported including treatment of [Fe3(CO)i2] or [Fe2(CO)9] with nitric oxide,86,87 acidification of a mixture of [HFe(CO)4]- and nitrite ion,88 reaction of iron pentacarbonyl with nitrosyl chloride89 and acidification of a mixture of [Fe(CO)3NO]- and nitrite ion90 as in equations (2) and (3). 

Potassium iodide solution The addition of a nitrite solution to a solution of potassium iodide, followed by acidification with acetic acid or with dilute sulphuric acid, results in the liberation of iodine, which may be identified by the blue colour produced with starch paste. A similar result is obtained by dipping potassium iodide-starch paper moistened with a little dilute acid into the solution. An alternative method is to extract the liberated iodine with chloroform or carbon tetrachloride (see Section IV.16, reaction 4). 

Sodium nitrite solution On warming this reagent with a solution of the chlorate, the latter is reduced to a chloride, which may be identified by adding silver nitrate solution after acidification with dilute nitric acid. The nitrite must,... 

A mixture of 100 g. (0.75 mole) of o-nitroaniline and 500 ml. of a 1 1 mixture of water and concentrated hydrochloric acid is diazotized by the careful addition of an aqueous solution of 55 g. (0.80 mole) of sodium nitrite at 10°. The mixture is stirred for 15 minutes after the completion of the addition, the solution is filtered, and the filtrate is added slowly with agitation and cooling below 0° to 550 ml. of 25 sodium hydroxide solution. The resulting solution is added to a solution of 135 g. of sodium arsenite in 1250 ml. of water, and the mixture is heated to 60-70° for 2 hours, care being taken not to overheat it. This is followed by acidification with acetic acid, treatment with activated carbon, and the addition of hydrochloric acid until the mixture is strongly acid to Congo red. Cooling the mixture in ice precipitates 110 g. (61 ) of yellow powder, which after one recrystallization from water melts at 235-240° (dec.). 

This generation of NO was also described on the skin surface. Weller et al. [75] were able to increase the NO generated from skin by the topical addition of nitrite or by acidification of the skin. This was not inhibitable bv classical NOS inhibitors and was... 

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