Ammonium chloride, promoter

Zhu s group also developed an ammonium chloride-promoted three-component synthesis of 5-iminooxazole and subsequent transformation to a macrocyclodepsi-peptide [89]. In this approach, a three-component reaction of an a,a-disubstituted a-isocyanoacetamide 21a, an aldehyde, and an amino alcohol b afforded the 5-iminooxazole c, which was cyclized after saponification under acidic conditions to furnish the macrocyclodepsipetides d (Scheme 21). 

Janvier P, Sun X, Bienayme H et al (2002) Ammonium chloride-promoted four-component synthesis of pyrrolo[3, 4-b]pyridin-5-one. J Am Chem Soc 124 2560-2567... 

The presence of certain salts, e.g., calcium or ammonium chloride, promotes the reaction. Phenylhydroxylamine acts like a base towards acids. If it be warmed with mineral adds, it undergoes a noteworthy transformation into paraamidqphenol ... 

Furthermore, the use of a Lewis acid promoter leads to increased stereoselectivities (Table 19, entry C)252,254. Compared to the aprotic reaction, where allyl silane was used instead of allyl bromide and indium chloride, an almost complete reversal of the diastereos-electivity was found. It was demonstrated recently that the Lewis acid catalysed allylation reaction can be carried out efficiently without any organic solvent in saturated ammonium chloride solution255. Finally, Lewis acid catalysed Mannich reactions can be carried out conveniently in mixtures of organic solvents and water. However, the exact role of the Lewis acid catalyst has not been clarified (Table 19, entry D)253. The same reaction can be carried out in pure water with catalysis by indium trichloride256. 

The synthesis of polyhalide salts, R4NX , used in electrophilic substitution reactions, are described in Chapter 2 and H-bonded complexed salts with the free acid, R4NHX2, which are used for example in acid-catalysed cleavage reactions and in electrophilic addition reactions with alkenes, are often produced in situ [33], although the fluorides are obtained by modification of method I.I.I.B. [19, 34], The in situ formation of such salts can inhibit normal nucleophilic reactions [35, 36]. Quaternary ammonium chlorometallates have been synthesized from quaternary ammonium chlorides and transition metal chlorides, such as IrClj and PtCl4, and are highly efficient catalysts for phase-transfer reactions and for metal complex promoted reactions [37]. 

Anionicallv Activated Alumina. At this time we had also developed an interest in anionically activated alumina. These basic reagents were active in promoting alkylation(42), condensation(43) and hydrolysis(44) reactions. Thus, we impregnated alumina with sodium hydroxide and used this combination both with and without a phase transfer catalyst (benzyltriethyl ammonium chloride). When BTEAC was added, the conversion to ether was decreased and the formation of ester was noted. In the absence of a phase transfer catalyst, the ether became a minor product and methyl phenylacetate became the major product with coproduction of phenylacetic acid. This ester does not result from esterification of the acid as simple stirring of phenylacetic acid with Na0H/A1203 in methanol does not produce methyl phenylacetate. 

Later Parchinsky et al. [131] showed that Groebke reaction promoted by ammonium chloride as mild catalyst, often employing the Ugi-reaction, in the non-nucleophilic aprotic solvent (e.g., toluene) led to the formation of exclusively one product of the reaction - 3-aIkylamino-substimted imidazo[l,2-a]pyrimidines, while the formation of unwanted side-products was excepted in this method. 

Effects of pH on urinary drug elimination may have important applications in medical practice, especially in cases of overdose. For example, one can enhance the elimination of a barbiturate (a weak acid) by administering bicarbonate to the patient. This procedure alka-linizes the urine and thus promotes the excretion of the now more completely ionized drug. The excretion of bases can be increased by making the urine more acidic through the use of an acidifying salt, such as ammonium chloride. 

Another limitation is seen when extra strain is included in the compound to be reduced. Dehalogenation of 3,3-dichlorobicyclo[2.2.0]hexan-2-one with zinc/ammonium chloride in methanol gave, at best, a 25% yield of 3-chlorobicyclo[2.2.0]hexan-2-one (14) together with cyclohexenone and 6-chlorohex-5-enoic acid.128 The best results were achieved with the zinc/ acetic acid system, while addition of water, silver-promoted zinc reduction in methanol, tri-butyltin hydride reduction or hydrogenolysis with palladium in methanol did not result in formation of 14, but various other ring-opened products. 

The isolation of an intermediate revealed that the reaction proceeds via a tandem Mannich-Michael addition pathway. The zinc (II) chloride-promoted cascade reaction starts with a Mannich reaction. For a number of reactions, the Mannich-type intermediate can be isolated if the reaction is stopped by addition of diluted ammonium chloride solution [52,53]. 

Protocol 6 involves heating Mannich compound 10 in DMSO, apparently causing elimination of dimethylamine and formation of enone 20 as a reactive intermediate. The corresponding enone has been synthesized in the 9-butyl series,6,22 but comparable yields are obtained in pyridine cyclization reactions involving either the preformed enone or the Mannich HQ salt.7 Prior to addition of 10, ketone 9 is heated with ammonium chloride in DMSO to promote the formation of imine 21. Isomerization of this imine to the enamine tautomer 22, Michael addition of this nucleophile to enone 20, and elimination of water account for the formation of product 11. Like many polycyclic terpyridyl analogues, this product is sparingly soluble in DMSO and is readily isolated by filtration of the reaction mixture. 

INTEX BINDER 18 is also suggested as a nonwoven binder, particularly where a soft hand is desired. Addition of 1.5 to 2.0% of a latent acid catalyst, such as ammonium chloride, is also recommended to promote cross-linking of the polymer. 

This study resulted in a series of reports on a comprehensive evaluation of fire-retardant treatments for wood (2-6). One hundred and thirty single chemicals or combinations of chemicals in the form of various salts were evaluated for flame-spread reduction, smoke, and corrosivity. Diammonium phosphate ranked first in reducing flame spread, followed by monoammonium phosphate, ammonium chloride, ammonium sulfate, borax, and zinc chloride. Zinc chloride, although excellent as a flame retardant, promoted smoke and glowing. Ammonium sulfate was the least expensive, but under certain environmental conditions it was corrosive to metals. None of the 130 compositions tested was considered ideal because of the adverse effects on some of the properties of wood. Several reviews of the subject are available and provide additional background material (J, 7-JO). 

Related to these reactions are the zinc-promoted allylation reactions of oximes. Thus, enantiomerically pure or highly enriched allyglycine and its chain-substituted analogs are easily accessible from the reaction of the sultam derivative of benzyl glyoxylic acid oxime with allylic bromides in aqueous ammonium chloride (Scheme 23) [114]. 

Since the observation that allylation of carbonyl compounds could be mediated by tin in aqueous medium [77], there has been an intensive development of the Barbier-type allylation reaction in water. Three metals were particularly investigated zinc, tin, and indium. In the aqueous zinc-promoted allylation, allylzinc species are considered unlikely. The initiation of the reaction could be attributed to the formation of an allylic radical anion on the metal surface this radical surface could then react with the carbonyl compound to give an alkoxide radical, which could add an electron and form the alcohols [82]. Allyl bromide or even chloride reacts with aldehydes and ketones in the presence of commercial zinc powder in a mixture of tetrahydrofuran and saturated ammonium chloride aqueous solution (Eq. 7) [83]. 

Pinson DM, Schoeb TR, Lin SL, et al. 1988. Promotion of mycoplasma-pulmonis growth in rat tracheal organ cultures by ammonium chloride. Lab Anim Sci 38(2) 143-147. 

Adding ammonium chloride decreases the solubility of aluminum hydroxide and prevents the precipitation of magnesium hydroxide. Scott 13) states that the precipitation of nickel, cobalt, manganese, and zinc sulfides may be incomplete because of the formation of polysulfides in the presence of air or other oxidizing agents. A small amount of ammonium sulfite is therefore added to promote their precipitation. In spite of this precaution, cobalt, nickel, and manganese were never quantitatively recovered and the procedure is not considered entirely satisfactory for these elements. 

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