Mechanisms ammonium sulfide

Reaction of various aldehydes with hydrogen sulfide leads to substituted thiophenes, dihydrothiophenes, dithiolanes and trithiolane, as well as to six-membered ring thiopyran derivatives and dithiins. Ledl (33) obtained 2,4-dimethylthiophene (1, R Me) as a product of the reaction of propionaldehyde with hydrogen sulfide in the presence of ammonia. Sultan (29) reported the formation of 2,4-diethylthiophene (1, R - Et), 2,4-dibutyl-thiophene (1, R - Bu), and their dehydro derivatives from the reaction of ammonium sulfide with butyraldehyde and caproaldehyde (hexanal), respectively. The mechanism suggested for their formation is depicted in Scheme 1. Space limitations do not allow us to discuss the mechanism here in detail (for additional information, see ref. 29). 

Shu and co-workers (35) identified 2-isobutyl-3,5-diisopropylpyridine, 2-pentyl-3,5-dimethylpyridine, and its dihydro derivative obtained under similar conditions. Sultan (29) confirmed the presence of 3,5-diethyl-2-propylpyridine in a model system consisting of butyraldehyde and ammonium sulfide. Our proposed mechanism of their formation (20) consists of three steps 1) aldol condensation of the starting aldehydes to 2,4-alkadienals, 2) imine formation with ammonia, and 3) subsequent cyclization and oxidation to corresponding pyridines. An alternate mechanism, suggested by Shu and co-workers (33), takes into consideration the isolated dihydro derivatives. Hwang and co-workers described another dihydro derivative (19, R = Bu, R = R" = Pr, R= H) (37). 

To date, Monteiro-Riviere and co-workers [60] have published the only studies using electron microscopy to examine the mechanism of iontophoretic transport. They applied mercuric chloride (7.4%) in vivo in pigs for 1 hr (current density 200 p,A/cm ) and subsequently exposed the biopsies to ammonium sulfide vapor to precipitate and localize the mercury, similar to earlier passive transport studies [28]. The micrographs revealed that mercuric chloride traverses intracellularly through the first few layers and intercellularly through the remainder of the stratum comeum. The authors concluded that the intercellular pathway is the predominant route for passive and iontophoretic drug delivery systems. However, it is difficult to eliminate follicular transport as a possible pathway, since only small areas can be examined at a time ( 1 mm ) and the low density of hair follicles (11/cm ) makes it difficult to study them with the electron microscope. 

Proposed reaction mechanism of l-hydroxy-2-propanone or l-hydroxy-2-butanone with ammonium sulfide is shown in Figure 5. 2-Iminoalcohols, which were derived from the reaction of ammonia and a-hydroxyketones, were condensed with another molecule of a-hydroxyketone to form 2-(l-hydroxymethyl)-2,4-dialkyl-3-oxazolines. The substitution of -OH group with -SH group resulted in the formation of 2-(l-hydroxyemthyl)-2,4-dialkyl-3-thiazolines. No 2-(l-mercaptomethyl)-substituted isomers were found in either reaction. Upon heating, these intermediates were further converted to the corresponding oxazolines, oxazoles, thiazolines and thiazoles. 

Figure 5. Proposed reaction mechanism of l-hydroxy 2-propanone or 1-hydroxy-2-butanone with ammonium sulfide.

Proposed reaction scheme for 2,3-butanedione and ammonium sulfide is summarized in Figure 6. Since there was no acetaldehyde involved in this model reaction, we proposed that the initial step of cleavage of 2,3-butanedione would required to form an acetaldehyde and an acetamide which was similar to the mechanism described by Grimmett and Richards (P) for the interaction of pyruvaldehyde and ammonia in an ammoniacal environment. Thioacetamide was formed as the result of addition of H2S to acetamide. In fact, the presence of 1,2,4-trithiolanes and 1,3,5-trithiane in the reaction mixture also explained the... 

An interesting end product, tetramethylpyrazine was also presented in the reaction mixture (27.3% of peak area of the total volatiles). Previous study of the model reaction of 2,3-butanedione and ammonium acetate did not yield any tetramethylpyrazine. It is probably due to the reducing environment provided by H2S which reduced 2,3-butanedione to 3-hydroxy-2-butanone. This explained that both 3-hydroxy-2-butanone and 3-mercapto-2-butanone were found in the reaction mixture. This study also supported the mechanism proposed by Elmore and Mottram 10) who observed that, during the reactions of hydroxyketones with aldehydes and ammonium sulfide, the formation of thiazoles was discouraged due to reducing environment provided by H2S derived from ammonium sulfide. It is also interesting to note that con aring to previous a-hydroxyketone series tetramethylpyrazine was present at trace levels whereas in the a-dicarbonyl series it was the major product under comparable tenq)erature conditions. The reason for this observed phenomenon is not obvious. It is possible that in the reaction system of acetoin and ammonium sulfide, the... 

MRH Aluminium 10.71/33, iron 4.35/50, magnesium 10.88/40, manganese 5.06/50, sodium 5.56/55, phosphorus 7.32/25, sulfur 4.27/20 Mixtures of the chlorate with ammonium salts, powdered metals, phosphorus, silicon, sulfur or sulfides are readily ignited and potentially explosive [1], Residues of ammonium thiosulfate in a bulk road tanker contaminated the consignment of dry sodium chlorate subsequently loaded, and exothermic reaction occurred with gas evolution during several hours. Laboratory tests showed that such a mixture could be made to decompose explosively. A reaction mechanism is suggested. 

The tin (II) sulfide so obtained is ground with 7.5g of sulfur and 6g of ammonium chloride and heated in a sand bath under the hood at 400°C for about 2 hours. When the ammonium chloride and the excess of sulfur have completely volatilized the mass is cooled, removed mechanically and the impurities floated away by decantation with water. The sulfide (D — 4.2g/cc) remains behind. It is dried at 100°C and sublimed. 

Recently we presented (23) the results of an experimental study on the kinetics and mechanisms of the reaction of lepidocrocite (y-FeOOH) with H2S. With respect to the interaction between iron and sulfur, lepidocrocite merits special attention. It forms by reoxidation of ferrous iron under cir-cumneutral pH conditions (24), and it can therefore be classified as a reactive iron oxide (19). The concept of reactive iron was established by Canfield (19), who differentiated between a residual iron fraction and a reactive iron fraction (operationally defined as soluble in ammonium oxalate). The reactive iron fraction is rapidly reduced by sulfide or by microorganisms. 

The oxidation of methyl phenyl sulfide with hydrogen peroxide, in the presence of ammonium hydrogencarbonate, takes place by a mechanism involving HCO4-... 

Vent fluids are acidic, but not as acid as may first appear from pH values measured at 25 °C and 1 atm (i.e., in shipboard laboratories). The cation H in vent fluids is also present as a chloro-complex with the extent of complexation increasing as P and T increase. At the higher in situ conditions of P and T experienced at the seafloor, therefore, much of the H" " is incorporated into the HCl-aqueous complex hence, the activity of H is reduced and the in situ pH is substantially higher than what is measured at laboratory temperatures. The for water also changes as a function of P and T such that neutral pH is not necessarily 7 at other P-T conditions. For most vent fluids, the in situ pH is 1-2 pH units more acid than neutral, not the 4 units of acidity that the measured (25 °C, 1 atm) data appear to imply. Most high-temperature vent fluids have (25 °C measured) pH values of 3.3 0.5 but a few are more acidic whilst several are less acid. If fluids are more acid than pH 3.3 0.5, it is often an indicator that metal sulfides have precipitated below the seafloor because such reactions produce protons. Two mechanisms are known that can cause fluids to be less acidic than the norm (i) cases where the rock substrate appears to be more highly altered—the rock cannot buffer the solutions to as low a pH (ii) when organic matter is present, ammonium is often present and... 

Treatment of cyclopropyl sulfides bearing a hydroxy group in the side chain with ceric ammonium nitrate (CAN) in methanol gives five- and six-membered cyclic ethers.In this reaction, the formation of cyclic ethers is understood by assuming a single electron transfer mechanism, which involves ring opening of the cation intermediate followed by intramolecular nucleophilic addition. 

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