Nitration the introduction of nitro groups, —NO2, into molecules of organic compounds by the action of various nitrating agents. The products of aromatic nitrations are very important intermediates in industrial chemistry.
Nitration of unsaturated aliphatic compounds—for example, by a mixture of acetic anhydride and Aromatic nitration acid—starts with an attack by a nitronium cation on a double bond; the cation thus formed III is stabilized by the splitting-off of a proton, with the formation of the nitroolefin IVor by addition of the anion X—, which is present in the reaction mixture: A proton then splits off, with the formation of the nitro compound II.
In the presence of mercury Aromatic nitration, nitration of aromatic compounds is accelerated and may be accompanied by oxidation both nitro compounds and nitrophenols are formed. The nature of the substituents significantly affects the orientation of the entering nitro group.
Heating the reaction mixture is sufficient to hydrolyze the amide back to the nitrated aniline. Mechanism Resonance forms of the intermediate can be seen in the generalized electrophilic aromatic substitution Sulfonation of Benzene Sulfonation is a reversible reaction that produces benzenesulfonic acid by adding sulfur trioxide and fuming sulfuric acid.
Nitration can be accelerated by activating groups such as aminohydroxy and methyl groups also amides and ethers resulting in para and ortho isomers.
As such, the nitration of aromatics was one of the early miniaturized reactions to be reported, with Burns and Ramshaw investigating the use of a stainless-steel Aromatic nitration flow reactor for the nitration of benzene 92 and toluene 93 using two-phase slugs of organic and aqueous reactants.
Fuming sulfuric acid, also refered to as oleum, is a concentrated solution of dissolved sulfur trioxide in sulfuric acid.
Further Applications of Nitration and Sulfonation Nitration is used to add nitrogen to a benzene ring, which can be used further in substitution reactions. Having demonstrated the viability of the microreactor, no scale-up steps were required in order to increase the throughput to meet previously discussed targets; the authors simply employed a production unit consisting of eight microreactors two banks of four microreactors and the unit operated under the previous conditions.
The investigation illustrated the ability to safely operate hazardous reactions, attain the desired chemical selectivity, design a predictable and reliable production unit, and prepare high-quality chemicals in a short time frame, all of which was achieved through the use of microreaction technology.
The reaction is reversed by adding hot aqueous acid to benzenesulfonic acid to produce benzene. DSM recently published details of a collaboration with Corning Incorporated, which resulted in the development of a glass microreactor capable of performing a selective organic nitration, using neat HNO3, under cGMP conditions Scheme 26 Braune et al.
Nitration of alkanes by nitrogen oxides or concentrated nitric acid takes place primarily by a radical mechanism: Having nitrogen present in a ring is very useful because it can be used as a directing group as well as a masked amino group.
Deactivating meta-directing substituents include sulfonylcyano groups, ketoestersand carboxylates. The authors comment that although the reaction enthalpy is moderate, it is the potential exothermic decomposition of the product that is problematic.
First, a complex I is formed between the nitronium cation and benzene: Such groups deactivate slow the reaction and directs the electrophilic nitronium ion to attack the aromatic meta position.
Because sulfonation is a reversible reaction, it can also be used in further substitution reactions in the form of a directing blocking group because it can be easily removed.
The reaction products are usually mixtures of nitro compounds. Benzenesulfonic acids are also used in the synthesis of detergents, dyes, and sulfa drugs.
Sulfuric Acid Activation of Nitric Acid The first step in the nitration of benzene is to activate HNO3with sulfuric acid to produce a stronger electrophile, the nitronium ion.
In mixed-acid syntheses sulfuric acid is not consumed and hence acts as a catalyst as well as an absorbent for water. To perform the organic nitration, the substrate and solvent were brought together in a microstructure that afforded a fine emulsion; this was followed by the addition of neat nitric acid at which point the reaction started immediately.
The presence of functional groups, which supply the ring with additional electron density for example, amino, sulfo, and hydroxyl groupsfacilitates nitration, and in some cases such groups may be replaced by nitro groups. Mechanism To produce benzenesulfonic acid from benzene, fuming sulfuric acid and sulfur trioxide are added.
Nitration of Benzene The source of the nitronium ion is through the protonation of nitric acid by sulfuric acid, which causes the loss of a water molecule and formation of a nitronium ion.
Thus, in the nitration of phenolsulfonic acids, the sulfo group is replaced by a nitro group. Link to this page:Nitration of benzene firstly involves the formation of a very powerful electrophile, the nitronium ion, which is linear. This occurs following the interaction of two strong acids, sulfuric and nitric acid.
In direct nitration, a maximum of three nitro groups may be introduced into an aromatic system. The presence of functional groups, which supply the ring with additional electron density (for example, amino, sulfo, and hydroxyl groups), facilitates nitration, and in some cases such groups may be.
As nitration reactions are notoriously difficult to perform on a commercial scale, the main challenge was the target production volumes which were in the range of tons day −1. The authors comment that although the reaction enthalpy is moderate, it is the potential exothermic decomposition of the product that is problematic.
Nitration and sulfonation of benzene are two examples of electrophilic aromatic substitution. The nitronium ion (NO 2 +) and sulfur trioxide (SO 3) are the electrophiles and individually react with benzene to give nitrobenzene and benzenesulfonic acid respectively.
Nitration is a general class of chemical process for the introduction of a nitro group into an organic chemical compound. More loosely the term also is applied incorrectly to the different process of forming nitrate esters between alcohols and nitric acid, as occurs in the synthesis of nitroglycerin.
Nitration of Benzene. Reaction type: Electrophilic Aromatic Substitution.
Summary. Overall transformation: Ar-H to Ar-NO 2 Reagent: for benzene, HNO 3 in H 2 SO 4 / heat; Electrophilic species: the nitronium ion (i.e.
NO 2 +) formed by the loss of water from the nitric acid.Download