For nitration of benzene

The value of the second-order rate constant for nitration of benzene-sulphonic acid in anhydrous sulphuric acid varies with the concentration of the aromatic substrate and with that of additives such as nitromethane and sulphuryl chloride. The effect seems to depend on the total concentration of non-electrolyte, moderate values of which (up to about 0-5 mol 1 ) depress the rate constant. More substantial concentrations of non-electrolytes can cause marked rate enhancements in this medium. Added hydrogen sulphate salts or bases such as pyridine... 

Figure 12 11 compares the energy profile for nitration of benzene with those for attack at the ortho meta and para positions of (trifluoromethyl)benzene The presence of the electron withdrawing trifluoromethyl group raises the activation energy for attack at all the ring positions but the increase is least for attack at the meta position... 

OS 31] [R 16a] [P 23] On increasing the temperature, the reaction rate for nitration of benzene increases (Figure 4.53), as usually to be expected for most organic reactions [31]. For a capillary-flow micro reactor, more than doubling of the reaction rate was determined on increasing the temperature from 60 to 90 °C. 

This method was investigated at PicArsn, Dover, NJ and found to have only a very limited application (Ref 1). The azeotropic method seems to be suitable for nitration of benzene (Ref 2)... 

Because the sigma complexes for ortho and para attack have resonance forms with tertiary carbocations, they are more stable than the sigma complex for nitration of benzene. Therefore, the ortho and para positions of toluene react faster than benzene. 

Many of the metal oxide materials used for making ceramic membranes, particularly the porous type, have also been used or studied as catalysts or catalyst supports. Thus, they are naturally suitable to be the membrane as well as the catalyst. For example, alumina surface is known to contain acidic sites which can catalyze some reactions. Alumina is inherently catalytic to the Claus reaction and the dehydration reaction for amine production. Silica is used for nitration of benzene and production of carbon bisulfide from methanol and sulfur. These and other examples are highlighted in Table 9.6. 

The most common reagent for nitration of benzene, simple alkylbenzenes and other less reactive compounds is a mixture of concentrated nitric and sulfuric acids. However, nitration of activated substrates, such as aniline, phenol or pyrrole, occurs with nitric acid alone or in water, acetic acid or acetic anhydride. Concentrated sulfuric acid can oxidize these substrates. A description of the use of other nitrating reagents is outside of the scope of this review, but can be found in Smith and March s Advanced Organic Chemistry29 or Larock s Comprehensive Organic Transformations30. 

Superacid W0x/Zr02 catalysts for isomerization of n-hexane and for nitration of benzene... 

Mechanism B has the distinctive feature that it is zero-order in the substrate benzene, since the rate-determining step occurs prior to the involvement of benzene. Mechanism B has in fact been established for nitration of benzene in several organic solvents, and the absence of a benzene concentration term in the rate law is an important part of the evidence for this mechanism. ... 

FIGURE 4.4 Structures of stationary points for nitration of benzene in aqueous solution optimized at the PCM-M06-2X/6-311G(d,p) level. Bond lengths in angstroms and bond angles in degrees. 

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