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NITRATION THEORIES^55

This was based on infra-red absorption spectra which show frequencies of the

oxonium ion bond (O+-H, ca. 2600 cm-1) and of the nitrate ion.

Houben [6] gives the following sequence of transformations for “benzaldehyde

nitrate” :

+ H 2 O -> C 6 H 5 CHO + HNO 3 (a)

left in a hermetic vessel -> C 6 H 5 COOH + HNO 2 (b)

+ (CH 3 CO) 2 O -> C 6 H 5 CH(OOC.CH 3 ) 2 + HNO 3 (c)

C 6 H 5 CHO.HNO 3

+ H 2 SO 4 -> m- C 6 H 4 (NO 2 )CHO + H 2 O (d)

• 
  

  H 2 SO 4 + (CH 3 CO) 2 O -> p- C 6 H 5 (NO 2 )CHO + H 2 O (e)

  
  


• 
  

  C 10 H 8 -> C 6 H 5 CHO + Cl0H 7 .NO 3 (f)

  
  

An interesting point is the influence of the compounds which react with an addi-

tion compound (reactions d and f) on the position of the nitro group introduced.

Following Thiele’s view [7] that any aromatic substitution is preceded by the

formation of an addition product Holleman [8] suggested in 1910 that the reaction

of nitration, like that of chlorination, consisted in addition, followed by splitting

off, according to the following scheme for chlorination:

(5)

A similar scheme for the nitration process was given by Reddelien [5] who

expressed the view that nitration of aromatic hydrocarbons with mixtures of nitric

and sulphuric acids gave addition products, e.g.

(6)

The product (III) undergoes decomposition, the group OH being attached to

H 2 SO 4 as H 2 O (IV). The addition product is hydrolysed by water, and mono- or

polynitro compounds are formed.

Mainly on the basis of Holleman’s hypothesis and studies on the nitration of

olefins, Wieland [9,10] assumed the addition of a nitric acid molecule to the

double bond, resulting in the formation of a cyclohexadiene derivative (V), fol-

lowed by the loss of a water molecule: