Reactions with Reducing Agents

Pyridines are much more easily reduced than benzenes, for example catalytic reduction proceeds easily at atmospheric temperature and pressure, usually in weakly acidic solution but also in dilute alkali with Ni-Al.  

Of the hydride reagents, sodium borohydride is without effect on pyridines, though it does reduce pyridinium salts (see section 5.13.1), whereas lithium aluminium hydride effects the addition of one hydride equivalent to pyridine and thus the formation of a mixed dihydropyridines aluminate, which has been used as a selective reducing agent.  

The combination lithium/chlorotrimethylsilane produces a 1,4-dihydro doubly silylated product, the enamine character in which can be utilised for the introduction of 3-alkyl groups via reaction with aldehydes.  

Metal/acid combinations, which in other contexts do bring about reduction of iminium gronps, are without effect on pyridines. Samarium(II) iodide in the presence of water smoothly reduces pyridine to piperidine. Sodium in liqnid ammonia, in the presence of ethanol, affords the 1,4-dihydropyridine and 4-pyridones are rednced to 2,3-dihydro derivatives. Birch reduction of pyridines carrying esters. 

Trimethylsilane in the presence of palladium gives 1,4-dihydro-1-trimethylsilylpyr-idine, together with silylated dimer titanium-catalysed hydrosilylation produces a tetrahydro-derivative cleanly.  

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The probable mechanism of action for all of the stable A -halamines involves direct contact of the microorganism with the combined A -halamine, followed by donation of a Cl" or Br" species to a receptor site within the cell, causing oxidation, and subsequent cell inactivation. Once the halogen content is exhausted through reaction with reducing agents, organic impurities. 

As an oxidizing agent, it undergoes oxidation-reduction reactions with reducing agents at ambient and elevated temperatures. 

Reactions with reducing agents at elevated temperatures convert the oxide to metal ... 

Calcium hypochlorite is an oxidizing agent. It undergoes vigorous to violent reactions with reducing agents and organics. In aqueous solution, it dissociates to calcium and hypochlorite ions. The hypochlorite ions form hypochlor-ous acid and molecular chlorine, which coexist in equilibrium. 

Being a strong oxidizing agent, its reactions with reducing agents or oxidizable substances can be violent to explosive. Under controUed conditions, it can be combined with many metals to obtain their chlorite salts. 

Reactions with reducing agents such as H2, H2S, NH3, CO, carbon, and dib-orane, especially under pressure and high temperatures, can be violent. 

Reactions with reducing agents can be explosive. The compound attacks most metals almost as vigorously as fluorine. It spontaneously ignites boron, silicon, phosphorus, arsenic, antimony, and iodine at ordinary temperatures. 

It is an oxidizing agent and undergoes redox reactions with reducing agents. Its oxidizing action, however, is weaker to that of potassium chlorate. Thus the salt is unable to oxidize the iodide ion to iodine in acid medium. 

Reaction with Reducing Agents 3.14.2.8.1 Catalytic reduction... 

OSH A PEL CL 0.1 mg(Cr03)/m3 ACGIH TLV TWA 0.05 mg(Cr)/m3 Confirmed Human Carcinogen NIOSH REL (Chromium(VI)) TWA 25 ng(Cr(VI))/m3 CL 50 ng/mVl5M SAFETY PROFILE A confirmed carcinogen. A poison. See also CHROMIUM COMPOUNDS. Moderately flammable by chemical reaction with reducing agents. A powerful oxidizer. Moderately explosive when heated. When heated to decomposition it emits toxic fumes of NOx and NH3. 

SAFETY PROFILE Confirmed human carcinogen. A powerful oxidizing agent. Flammable by chemical reaction with reducing agents. Moderate explosion hazard when shocked or exposed to heat. Violent or explosive reaction with sulfides (e.g., copper(II) sulfide (explodes) antimony(II) sulfide arsenic(III) sulfide tin(II) sulfide tin(IV) sulfide). When heated to decomposition it emits toxic fumes of Cd and Cr. See also CHLORATES. 

DOT CLASSIFICATION 2.2 Label Nonflammable Gas, Oxidizer SAFETY PROFILE A poison. Mildly toxic by inhalation. Prolonged absorption may cause mottling of teeth, skeletal changes. Severe explosion hazard by chemical reaction with reducing agents, particularly when under pressure. A ver dangerous fire hazard a very powerful oxidizer otherwise inert at normal temperamres and pressures. 

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