Hydrogen sulfide, addition

This fact gives enough reason to suppose that the reaction of hydrogen sulfide addition to nitrile groups starts with the attack of the nucleophilic mercapto anion... 

Due to the fact that the nitrile groups interact with the positively charged carbon atoms of the carboxyl or ester groups more easily than the less mobile nitrile groups in the PAN macromolecules interact with each other, the electrophilicity of the nitrile groups in the macromolecules of the copolymers increases to a greater extent, which, naturally, manifests itself in the increase of the rate of hydrogen sulfide addition. 

When heated, the hydrosuUide dissociates into ammonia and hydrogen sulfide addition of sulfur produces ammonium sulfide ... 

The hydrogen sulfide addition is temporarily suspended, and 100 ml. of pyridine is added rapidly in one portion through the condenser as the solution is stirred vigorously (Note 1). The solution becomes clear, and then 2,5-diamino-3,4-dicyanothio-phene begins to precipitate immediately. The hydrogen sulfide addition is resumed and is continued for abcMt 30 minutes while the temperature of the reaction mixture is maintained at 0-5°. Finally, the reaction mixture is stirred for an additional 30 minutes at 0 5°, then the yellow precipitate of the thiophene is... 

In actual practice in a continuous reaction system, the hydrogen sulfide addition rate must be controlled to obtain the final reactor conditions of pH and thiosulfate concentration. In this regard, Figure 4 illustrates an important feature of the citrate process. It can be seen that, if slightly more or less than the stoichiometric amount of hydrogen sulfide is used, the effect will be merely to cause small variations in the pH and thiosulfate content of the liquor returned to the absorption step. 

Reduction of nitroaromatics with hydrogen sulfide Additive reduction with elimination... 

To study the effect of increasing sulfur content in the reformate, sulfur dioxide was added in small amounts of between 100 and 400 ppm to the feed mixture of the autothermal diesel reformer. Sulfur dioxide was chosen because under the conditions of autothermal reforming most sulfur components are converted into sulfur dioxide (see Section 3.5). Activity measured as hydrogen yield showed a drastic decrease from 75 to 40%, when 200 ppm sulfur dioxide were added to the feed. However, no further detrimental effects were recorded when more sulfur dioxide was added. A similar behaviour was observed when hydrogen sulfide was added. This is because the plateau had already been reached at 75 ppm hydrogen sulfide addition. 

Some reaction systems, which have been described in the patent literature for the production of meat aromas, regard thiamine as precursor. 3-Methyl-2-butene-l-thiol is one of the roast odorants of coffee (cf. 21.1.3.3.7) and can cause on off-flavor in beer (cf. Table 5.5). In general, only very small amounts are formed which are still aroma active on account of the very low odor threshold (Table 5.21). The formation of the thiol is explained by the fact that the 3-methyl-2-butene radical is formed from terpenes by photolysis (beer) or under the drastic conditions of the roasting process (coffee). This radical then meets a SH -radical formed from cysteine under these conditions. In the case of beer, humulons (cf. 20.1.2.3.2) are under discussion as the source of the alkyl radical. In coffee 3-methyl-2-butene-l-ol (prenyl alcohol) is also a possible precursor, which yields the thiol after water elimination and hydrogen sulfide addition. 

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