Nitration of benzaldehyde

The behavior of aromatic aldehydes is typical Nitration of benzaldehyde takes place sev eral thousand times more slowly than that of benzene and yields m mtrobenzaldehyde as the major product... 

Use of medium-scale heat flow calorimeter for separate measurement of reaction heat removed via reaction vessel walls and via reflux condenser system, under fully realistic processing conditions, with data processing of the results is reported [2], More details are given elsewhere [3], A new computer controlled reaction calorimeter is described which has been developed for the laboratory study of all process aspects on 0.5-2 1 scale. It provides precise data on reaction kinetics, thermochemistry, and heat transfer. Its features are exemplified by a study of the (exothermic) nitration of benzaldehyde [4], A more recent review of reaction safety calorimetry gives some comment on possibly deceptive results. [5],... 

The only satisfactory method for the preparation of -nitro-benzaldehyde is the direct nitration of benzaldehyde with a mixture of nitric and sulfuric acids. The procedure described is essentially that of Baker and Moffitt. ... 

Avoid sequences which may lead to unwanted reactions at other sites in the molecule. Thus nitration of benzaldehyde gives only 50% m-nitrobenz-aldehyde since the nitric acid oxidises CHO to CO2H. One way round this particular problem is to nitrate benzoic acid and reduce CO2H to CHO. 

The influence of meta-directing substituents can be explained using the same kinds of arguments used for ortho and para directors. Look at the nitration of benzaldehyde, for instance (Figure 16.16). Of the three possible carbocation intermediates, the meta intermediate has three favorable resonance forms, but the ortho and para intermediates have only two. In both ortho and para intermediates, the third resonance form is unfavorable because it places the positive charge directly on the carbon that bears the aldehyde group, where it is disfavored by a repulsive interaction with the positively polarized carbon atom of the C=0 group. Hence, the meta intermediate is more favored and is formed faster than the ortho and para intermediates. 

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