Ammonium acetate azides

A similar microwave-assisted cyclization in the presence of ammonium acetate of an a-ketoamide, obtained by acylation of an a-aminoketone, was recently described for the synthesis of the antifungal agent Nortopsedin D [46]. The problem of the instabiUty of the a-amino ketones was successfully resolved by in situ acylation of the amine derived from Staudinger reaction of the azide 50 with a phosphine (Scheme 16). This ketoamide was... 

Lithium acetate ammonium sulfate azide benzoate borate (meta-) bromate bromide carbonate chlorate chloride... 

Reactions of pyrimido[4,5-3] [l,4]thiazines were discussed in CHEC-II(1996) <1996CHEC-II(7)737> more recently, reported reactions of this system involve nucleophilic substitution in a number of guises. Hemiaminals at C-3 react with ammonium acetate to form aminals (Equation 166) <1999CHE97>. The formation of acyl hydrazides from pyrimido[4,5-3][l,4]thiazine-2-carboxylic acids, along with their subsequent conversion to acyl azides and Curtius... 

Lead Azide do Sensitive to flame and sparks. Ammonium acetate... 

The salts of hydrazoic acid, the azides, have solubilities similar to those of the corresponding chlorides. Sodium azide dissolves in water. Silver azide does not dissolve in water or in nitric acid, but dissolves easily in an aqueous solution of ammonia. Lead azide, like lead chloride, is sparingly soluble in cold water but more soluble in hot water it is also soluble in ammonium acetate. 

Lead azide is insoluble in an aqueous solution of ammonia. Acetic acid causes its decomposition but it is soluble in water and concentrated solutions of sodium nitrate, sodium acetate or ammonium acetate. There are fairly big differences of solubility, depending on temperature. 

Spontaneous explosions of lead azide also take place during crystallization from saturated solution in ammonium acetate. A detailed study of this phenomenon has been made by Taylor and A. T. Thomas [105]. When the concentration of the solutions and the temperature and conditions of cooling were carefully controlled, they were able to predict the time at which spontaneous explosions occur. E.g. ... 

According to Kaufman [91] spontaneous explosion can also take place during the growth of a-lead azide crystals, e.g. when a supersaturated solution of lead azide in ammonium acetate is seeded with crystals of the a-form. Spontaneous explosions have also been observed with mercuric azide and in some cases with cadmium azide. 

Lead azide is dissolved by an aqueous solution of ammonium acetate, but it is not destroyed by it. The solution contains azide ions and lead ions, the latter quantitatively precipitable as lead chromate, PbCr04, by the addition of potassium dichromate solution. Lead azide in aqueous suspension is oxidized by ceric sulfate with the quantitative production of nitrogen gas which may be collected in an azotometer and used for the determination of the azide radical. 

Sample preparation Tissue. Homogenize 20-200 mg brain tissue with 1 mL 1.5 jtg/mL IS in 1% ammonium acetate -I- 1% sodium azide buffer MeCN 99 1, flush apparatus with 1 mL extraction buffer, add 1 mL acetone, shake for 5 min, centrifuge for 10 min. Add sample to an Extrelut-3 SPE cartridge (Kieselguhr), add 1 mL extraction buffer, wait for 10 min, elute with 15 mL extraction solvent. Evaporate the eluate, take up residue in 50 xL MeOH, add 50 p.L water, inject a 10-25 jiL aliquot. Serum. 100 (xL Serum + 1 mL... 

The following procedures have also been reported as advantageous, but are in fact inferior Larger batches were made by mixing equimolar amounts of sodium azide and ammonium acetate as saturated solutions upon cooling to 5°C, N4H4 separated in low yield (approx. 25%). Additional crystallizations from the mother liquor were contaminated with sodium acetate [307]. Or, a distillation method uses dimethylformamide as a vehicle to react and distill sodium azide and ammonium sulfate. The procedure is cumbersome because clogging of the condenser could not be controlled satisfactorily, in spite of elaborate equipment [308]. Not recommended is a dry method in which sodium azide and ammonium nitrate are heat treated, and the product is sublimed off at 200°C. The vapor phase contains free HN3 which tends to explode above room temperature (see p. 25). Reportedly, 5-g batches were made safely, but a 50-g batch exploded at 158°C [303]. 

A second monoclinic modification (7-lead azide) and a triclinic modification (5-lead azide) have been identified (Chapter 3). These modifications form by changing the pH of the growing solution and by doping. It is found that polyvinyl alcohol, added to 5% solutions of ammonium acetate, favor the gamma modification when slow cooled below 40°C [21]. Other additives favor the formation of other polymorphs for example, dextrine favors the a-polymorph and eosin, the j3-polymorph [21]. These latter polymorphs are reported to be more light sensitive than either the alpha or beta polymorphs. 

Crystallization of Lead Azide from a Solvent. In this method a small amount of lead azide is dissolved in, for example, ammonium acetate at 340°K and then allowed to cool to room temperature. Crystals of lead azide form as the solution cools. The method is of particular interest since, by controlling the concentration of lead azide and the cooling conditions, it is possible to reproduce the explosions with a reasonable accuracy (see Table VIII), allowing detailed examination of the crystal growth and the spontaneous explosions. 

Electric Discharge. Taylor and Thomas [121] dissolved 0.7% lead azide in 50 ml of 5% aqueous ammonium acetate solution and allowed it to cool to room temperature. After 11,400 sec (1800 sec before the expected time to explosion), the large crystals were filtered out and the liquid was allowed to stand. At the expected time there was a major explosion in the liquid, but the filtered crystals remained intact. Taylor and Thomas did not examine the liquid for the existence... 

The preferred glycosylating synthon of i-lyxo configuration was the azide 69, obtained by nucleophihc displacement of 4-0-triflate with tetrabutyl-ammonium acetate, as shown in Scheme 11. Chloroacetyl ester 71 and tri-... 

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