 Wysłany: Czw 13:35, 31 Mar 2011 Temat postu: Phase transfer catalysis _66 |
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| Phase transfer catalysis
+: CC (dichloro carbene) in water and NaOH effect of a quaternary QX generate quaternary ammonium ions on the QOH a base, which is extracted into the organic phase and reacts Dichlorocarbene chloroform. Dichlorocarbene hydrolysis in the organic phase is very slow, because the organic phase and trichloromethyl dichlorocarbene quaternary ammonium in a balanced system, does not occur if dichlorocarbene further reaction, it remains in the organic phase activity was retained up to several days long. 2.2 Synthesis of nitrobenzene ether ether nitrochlorobenzene by ethanol and sodium hydroxide role in the system, the reaction is as follows: Water C2HsOH + NaOHC2H50 a NaH20 organic phase o2N-a - CI + C2H5o-Na a o2N a > + NaCI according to traditional methods without phase transfer catalyst, the reaction heated to tens of hours in high pressure situations occur, only 75% conversion rate. Addition of phase transfer catalyst,belstaff outlet, only a few hours under normal temperature and pressure, the conversion rate of nitrochlorobenzene more than 99%. This is because the quaternary ammonium salt phase transfer catalyst is insoluble in the original QX a nitrochlorobenzene into ethanol soluble in sodium nitro chlorobenzene and nitrobenzene ether QH50 the sake of one ion pair. 2.3 Synthesis of esters. * By the diethoxy thiophosphoryl nitrophenol sodium chloride and a sodium hydroxide in water prepared in toluene ethyl parathion reaction is as follows: SSlllI (C2H5o) 2P-cI + Na + o one by one > - N02-~ (C2H5o) 2P a - NO ~ + NaCI ethyl parathion the reaction without addition of phase transfer catalyst the reaction rate is very slow, and there hydrolysis side reaction. However, if a small amount of salt, in the 2540 ~ C l-hour reaction, ethyl parathion production rate can reach 95% of 99.5%. Here the role of a quaternary QX is not soluble in toluene nitrophenol sodium ions into toluene soluble Q · a OC6I-h + on the reason. 2.4 fluoride ion nucleophilic substitution reaction in the presence of phase transfer catalyst may be a 3,4-dichloro-step reaction of nitrobenzene with potassium fluoride prepared directly from 3-Chloro-4 a Fluoronitrobenzene, production rate more than 92%. CIIO ~ N - o-CI + KF sulfolane a quaternary ammonium CIIO ~ N --- F + NaCI nucleophilic aromatic substitution reaction on the difficult, if not using the phase transfer catalyst to take the 3,4 or two nitrate benzene ammonia solution and the first by diazotization and then converted to fluorine-based diazo base. Phase transfer catalysis in the water phase, solid catalyst, the organic phase between this phase. Advantage of this approach are: direct implementation of water phase and organic phase of the reaction, simple operation, easy separation after the reaction, the catalyst can be recovered completely, lower the energy required to produce high, good for laboratory synthesis and industrial production. [ ,],[ |
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