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The nitration reaction is a reaction process that introduces nitro groups (-NO 2 ) into the molecules of organic compounds
The mechanism of the nitration reaction is mainly divided into two kinds.
1.
(1) The amount of reaction exotherm is the first major factor that determines the possibility of the occurrence of a hazard and the severity of the hazard.
(2) Reaction kinetics shows that the speed of reaction exotherm is the second main factor that determines the possibility of danger and the severity of the danger
The intrinsic reaction kinetics is two-stage, and the reaction rate depends on the reaction substrate and nitrating agent:
r=k 1 [aromatic compound][NO 2 + ]
=k 2 [aromatic compound][HNO 3 ]
And it is related to the molecular activity (electron cloud density), medium temperature, concentration, collision frequency, acid activity, impurities and other factors
(3) The product has nitro groups and is inherently unstable.
(4) The distribution of the decomposition enthalpies of 56 nitro compounds has been counted, and most of the decomposition enthalpies are between -240kJ/mol and -360kJ/mol
(5) High-concentration nitric acid or mixed acid (concentrated nitric acid and concentrated sulfuric acid) has strong oxidizing, corrosive and unstable
2.
(1) The main danger of nitration reaction is that the reaction heat of this type of reaction is large, mostly exceeding 600J/g, and the continuously generated reaction heat needs to be removed in time, and the latent heat of reaction cannot be accumulated
(2) The reaction can not be airtight to prevent flushing or explosion, a drying tube can be used
(3) The product cannot be dried by baking, but can be dried under vacuum at room temperature
(4) Examples of reactions involving nitro compounds
The reaction formula of ammonium chloride + iron powder to reduce the nitro group is
Application process: omitted
Remarks: This is an exothermic reaction.
There is an initial process of triggering.
It is easy to cause false appearances and add iron powder or ammonium chloride at one time.
This will cause the accumulation of reaction latent heat.
Once triggered, flushing will occur.
It even caught fire
.
Method 1: Dissolve the substrate in 80% ethanol , add the full amount of iron powder under stirring, increase the temperature to 70°C, and add 20% ammonium chloride aqueous solution dropwise (each portion is 1/20~1/ of the total amount).
10) There should be a temperature rise.
If it does not, increase the temperature by 5-10°C and add the next 20% ammonium chloride aqueous solution.
Be careful not to accumulate the latent heat of reaction to prevent flushing
.
Method 2: Dissolve the substrate in 80% ethanol , add the full amount of 20% ammonium chloride aqueous solution under stirring, heat up to 70℃, add iron powder part by part (each part is 1/20~1/10 of the total ), there should be a temperature rise.
Each time you add, the temperature rises by 2 to 3°C.
After the reaction subsides, continue to add.
If the temperature is not raised, increase the temperature by 5 to 10°C and add the next portion of iron powder.
Be careful not to accumulate the latent heat of reaction
.
Related links: Diazomethane and the reactions it participates in (2)