Nitrite, reaction with iodide

Nitric oxide is the simplest thermally stable odd-electron molecule known and, accordingly, its electronic structure and reaction chemistry have been very extensively studied. The compound is an intermediate in the production of nitric acid and is prepared industrially by the catalytic oxidation of ammonia (p. 466). On the laboratory scale it can be synthesized from aqueous solution by the mild reduction of acidified nitrites with iodide or ferrocyanide or by the disproportionation of nitrous acid in the presence of dilute sulfuric acid ... 

Testing for excess of nitrous acid at the end of the reaction. For this purpose starch-potassium iodide papers are best used, and these indicate nitrite in acid solution by turning blue instantaneously. With some practice, the nitrite reaction can be clearly distinguished from the coloration caused by certain diazo compounds, such as those bearing nitro substituents. The latter react only after 0.5 to 2 seconds. Often the difference becomes more marked after dilution of the diazo solution with concentrated hydrochloric acid. A properly conducted diazotization should exhibit on completion a very weak nitrite reaction, corresponding to an excess of about 10 4 m. 

Cyanide and thiocyanate anions in aqueous solution can be determined as cyanogen bromide after reaction with bromine [686]. The thiocyanate anion can be quantitatively determined in the presence of cyanide by adding an excess of formaldehyde solution to the sample, which converts the cyanide ion to the unreactive cyanohydrin. The detection limits for the cyanide and thiocyanate anions were less than 0.01 ppm with an electron-capture detector. Iodine in acid solution reacts with acetone to form monoiodoacetone, which can be detected at high sensitivity with an electron-capture detector [687]. The reaction is specific for iodine, iodide being determined after oxidation with iodate. The nitrate anion can be determined in aqueous solution after conversion to nitrobenzene by reaction with benzene in the presence of sulfuric acid [688,689]. The detection limit for the nitrate anion was less than 0.1 ppm. The nitrite anion can be determined after oxidation to nitrate with potassium permanganate. Nitrite can be determined directly by alkylation with an alkaline solution of pentafluorobenzyl bromide [690]. The yield of derivative was about 80t.with a detection limit of 0.46 ng in 0.1 ml of aqueous sample. Pentafluorobenzyl p-toluenesulfonate has been used to derivatize carboxylate and phenolate anions and to simultaneously derivatize bromide, iodide, cyanide, thiocyanate, nitrite, nitrate and sulfide in a two-phase system using tetrapentylammonium cWoride as a phase transfer catalyst [691]. Detection limits wer Hi the ppm range. 

The reaction of alkyl halides with metal nitrites is one of the most important methods for the preparation of nitroalkanes. As a metal nitrite, silver nitrite (Victor-Meyer reaction), potassium nitrite, or sodium nitrite (Kornblum reaction) have been frequently used. The products are usually a mixture of nitroalkanes and alkyl nitrites, which are readily separated by distillation (Eq. 2.47). The synthesis of nitro compounds by this process is well documented in the reviews, and some typical cases are listed in Table 2.3.92a Primary and secondary alkyl iodides and bromides as well as sulfonate esters give the corresponding nitro compounds in 50-70% yields on treatment with NaN02 in DMF or DMSO. Some of them are described precisely in vol 4 of Organic Synthesis. For example, 1,4-dinitrobutane is prepared in 41 -46% yield by the reaction of 1,4-diiodobutane with silver nitrite in diethyl ether.92b 1-Nitrooctane is prepared by the reaction with silver nitrite in 75-80% yield. The reaction of silver nitrite with secondary halides gives yields of nitroalkanes of about 15%, whereas with tertiary halides the yields are 0-5%.92c Ethyl a-nitrobutyrate is prepared by the reaction of ethyl a-bromobutyrate in 68-75% yield with sodium nitrite in DMF.92d Sodium nitrite is considerably more soluble in DMSO than in DMF as a consequence, with DMSO, much more concentrated solutions can be employed and this makes shorter reaction times possible.926... 

This method of calibration generates known concentrations of NO based on the reaction of nitrite with iodide in acid according to the following equation ... 

Thiation of [l,2,4]triazino[3,2-h]quinazoline-3,10-dione 782 with phosphorus pentasulfide in pyridine proceeded selectively to give the 3-thioxo analogue 783. The latter was converted to the corresponding 3-methylthio derivative 784 by reaction with methyl iodide. Treatment of 784 with hydrazine gave 785, which was converted to 786 and 787 by cyclization with formic acid or carbon disulfide (90JHC591). Cyclization of 785 with sodium nitrite in hydrochloric acid gave 788 (90JHC591). 

Electrophilic substitution of the ring hydrogen atom in 1,3,4-oxadiazoles is uncommon. In contrast, several reactions of electrophiles with C-linked substituents of 1,3,4-oxadiazole have been reported. 2,5-Diaryl-l,3,4-oxadiazoles are bromi-nated and nitrated on aryl substituents. Oxidation of 2,5-ditolyl-l,3,4-oxadiazole afforded the corresponding dialdehydes or dicarboxylic acids. 2-Methyl-5-phenyl-l,3,4-oxadiazole treated with butyllithium and then with isoamyl nitrite yielded the oxime of 5-phenyl-l,3,4-oxadiazol-2-carbaldehyde. 2-Chloromethyl-5-phenyl-l,3,4-oxadiazole under the action of sulfur and methyl iodide followed by amines affords the respective thioamides. 2-Chloromethyl-5-methyl-l,3,4-oxadia-zole and triethyl phosphite gave a product, which underwent a Wittig reation with aromatic aldehydes to form alkenes. Alkyl l,3,4-oxadiazole-2-carboxylates undergo typical reactions with ammonia, amines, and hydrazines to afford amides or hydrazides. It has been shown that 5-amino-l,3,4-oxadiazole-2-carboxylic acids and their esters decarboxylate. 

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. 

The acid hydrolysis of the 2-aryl-1,3,4-oxadiazoles can be used for their analytical determination. The method used is either to break down the compound by heating with hydrochloric acid under reflux to give the acid hydrazide and then to titrate the hydrazide with iodide in bicarbonate solution,68, 69 or to titrate potentiometrically directly with sodium nitrite in a hydrochloric acid medium.128 In this way the acid hydrazide is formed in the first reaction step and is then converted into the insoluble azide by the sodium nitrite. 

The key step in D. Kim s total synthesis of (-)-brefeldin A was an intramoiecuiar nitriie-oxide cycioaddition. In order to prepare the substrate for this cycioaddition, a doubie Finkeistein reaction was performed first an alkyl tosylate was replaced with iodide then the iodide was exchanged with a nitrite ion to afford the desired alkyl nitro compound. 

For the reaction of the column effluent with the cerium(IV) reagent, instead of a simple injection loop, Fields et al. used a solid-bed reactor with a volume of 2.8 mL. This relatively large volume is necessary to allow the required reaction time of at least two minutes for the oxidation of nitrite ions with cerium(IV). While the reaction of nitrite ions with cerium(IV) is comparatively slow, the maximum fluorescence yield with iodide is obtained in less than ten seconds. On the other hand, the reaction kinetics with thiosulfate appears to be completely different. As seen in the respective diagram in Fig. 6-21, this reaction is characterized by a fast rise of the fluorescence yield within a short time, which increases as the reaction product from Eq. (191), tetrathionate, also reacts slowly with cerium(IV). 

Fig. 6-21. Time dependence of the fluorescence yield for the reaction of nitrite, thiosulfate, and iodide with cerium(lV) (taken from [37]).

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