Nitration

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In organic chemistry, nitration is a general class of chemical processes for the introduction of a nitro group (−NO2) into an organic compound. The term also is applied incorrectly to the different process of forming nitrate esters (−ONO2) between alcohols and nitric acid (as occurs in the synthesis of nitroglycerin). The difference between the resulting molecular structures of nitro compounds and nitrates (NO−3) is that the nitrogen atom in nitro compounds is directly bonded to a non-oxygen atom (typically carbon or another nitrogen atom), whereas in nitrate esters (also called organic nitrates), the nitrogen is bonded to an oxygen atom that in turn usually is bonded to a carbon atom (nitrito group).

Contents

There are many major industrial applications of nitration in the strict sense; the most important by volume are for the production of nitroaromatic compounds such as nitrobenzene. The technology is long-standing and mature. [1] [2] [3]

Nitration reaction equation example.svg

Nitration reactions are notably used for the production of explosives, for example the conversion of guanidine to nitroguanidine and the conversion of toluene to trinitrotoluene (TNT). Nitrations are, however, of wide importance virtually all aromatic amines (anilines) are produced from nitro precursors. Millions of tons of nitroaromatics are produced annually. [2]

Aromatic nitration

Typical nitrations of aromatic compounds rely on a reagent called "mixed acid", a mixture of concentrated nitric acid and sulfuric acids. [4] [2] This mixture produces the nitronium ion (NO2+), which is the active species in aromatic nitration. This active ingredient, which can be isolated in the case of nitronium tetrafluoroborate, [5] also effects nitration without the need for the mixed acid. In mixed-acid syntheses sulfuric acid is not consumed and hence acts as a catalyst as well as an absorbent for water. In the case of nitration of benzene, the reaction is conducted at a warm temperature, not exceeding 50 °C. [6] The process is one example of electrophilic aromatic substitution, which involves the attack by the electron-rich benzene ring:

AromaticNitrationMechanism.svg

Alternative mechanisms have also been proposed, including one involving single electron transfer (SET). [7] [8]

Scope

Selectivity can be a challenge. Often alternative products act as contaminants or are simply wasted. Considerable attention thus is paid to optimization of the reaction conditions. For example, the mixed acid can be derived from phosphoric or perchloric acids in place of sulfuric acid. [2]

Regioselectivity is strongly affected by substituents on aromatic rings (see electrophilic aromatic substitution). For example, nitration of nitrobenzene gives all three isomers of dinitrobenzenes in a ratio of 93:6:1 (respectively meta, ortho, para). [9] Electron-withdrawing groups such as other nitro are deactivating. Nitration is accelerated by the presence of activating groups such as amino, hydroxy and methyl groups also amides and ethers resulting in para and ortho isomers. In addition to regioselectivity, the degree of nitration is of interest. Fluorenone, for example, can be selectively trinitrated [10] or tetranitrated. [11]

The direct nitration of aniline with nitric acid and sulfuric acid, according to one source, [12] results in a 50/50 mixture of para- and meta-nitroaniline isomers. In this reaction the fast-reacting and activating aniline (ArNH2) exists in equilibrium with the more abundant but less reactive (deactivated) anilinium ion (ArNH3+), which may explain this reaction product distribution. According to another source, [13] a more controlled nitration of aniline starts with the formation of acetanilide by reaction with acetic anhydride followed by the actual nitration. Because the amide is a regular activating group the products formed are the para and ortho isomers. Heating the reaction mixture is sufficient to hydrolyze the amide back to the nitrated aniline.

Alternatives to nitric acid

Mixture of nitric and acetic acids or nitric acid and acetic anhydride is commercially important in the production of RDX, as amines are destructed by sulfuric acid. Acetyl nitrate had also been used as a nitration agent. [14] [15]

In the Wolffenstein–Böters reaction, benzene reacts with nitric acid and mercury(II) nitrate to give picric acid.

In the second half of the 20th century, new reagents were developed for laboratory usage, mainly N-nitro heterocyclic compounds. [16]

Ipso nitration

With aryl chlorides, triflates and nonaflates, ipso nitration may also take place. [17] The phrase ipso nitration was first used by Perrin and Skinner in 1971, in an investigation into chloroanisole nitration. [18] In one protocol, 4-chloro-n-butylbenzene is reacted with sodium nitrite in t-butanol in the presence of 0.5 mol% Pd2(dba)3, a biarylphosphine ligand and a phase-transfer catalyst to provide 4-nitro-n-butylbenzene. [19]

See also

Related Research Articles

<span class="mw-page-title-main">Aromatic compound</span> Compound containing rings with delocalized pi electrons

Aromatic compounds or arenes usually refers to organic compounds "with a chemistry typified by benzene" and "cyclically conjugated." The word "aromatic" originates from the past grouping of molecules based on odor, before their general chemical properties were understood. The current definition of aromatic compounds does not have any relation to their odor. Aromatic compounds are now defined as cyclic compounds satisfying Hückel's Rule. Aromatic compounds have the following general properties:

<span class="mw-page-title-main">Nitric acid</span> Highly corrosive mineral acid

Nitric acid is an inorganic compound with the formula HNO3. It is a highly corrosive mineral acid. The compound is colorless, but samples tend to acquire a yellow cast over time due to decomposition into oxides of nitrogen. Most commercially available nitric acid has a concentration of 68% in water. When the solution contains more than 86% HNO3, it is referred to as fuming nitric acid. Depending on the amount of nitrogen dioxide present, fuming nitric acid is further characterized as red fuming nitric acid at concentrations above 86%, or white fuming nitric acid at concentrations above 95%.

<span class="mw-page-title-main">Pyridine</span> Heterocyclic aromatic organic compound

Pyridine is a basic heterocyclic organic compound with the chemical formula C5H5N. It is structurally related to benzene, with one methine group (=CH−) replaced by a nitrogen atom (=N−). It is a highly flammable, weakly alkaline, water-miscible liquid with a distinctive, unpleasant fish-like smell. Pyridine is colorless, but older or impure samples can appear yellow, due to the formation of extended, unsaturated polymeric chains, which show significant electrical conductivity. The pyridine ring occurs in many important compounds, including agrochemicals, pharmaceuticals, and vitamins. Historically, pyridine was produced from coal tar. As of 2016, it is synthesized on the scale of about 20,000 tons per year worldwide.

<span class="mw-page-title-main">Phenyl group</span> Cyclic chemical group (–C₆H₅)

In organic chemistry, the phenyl group, or phenyl ring, is a cyclic group of atoms with the formula C6H5, and is often represented by the symbol Ph or Ø. The phenyl group is closely related to benzene and can be viewed as a benzene ring, minus a hydrogen, which may be replaced by some other element or compound to serve as a functional group. A phenyl group has six carbon atoms bonded together in a hexagonal planar ring, five of which are bonded to individual hydrogen atoms, with the remaining carbon bonded to a substituent. Phenyl groups are commonplace in organic chemistry. Although often depicted with alternating double and single bonds, the phenyl group is chemically aromatic and has equal bond lengths between carbon atoms in the ring.

The Friedel–Crafts reactions are a set of reactions developed by Charles Friedel and James Crafts in 1877 to attach substituents to an aromatic ring. Friedel–Crafts reactions are of two main types: alkylation reactions and acylation reactions. Both proceed by electrophilic aromatic substitution.

Thiophene is a heterocyclic compound with the formula C4H4S. Consisting of a planar five-membered ring, it is aromatic as indicated by its extensive substitution reactions. It is a colorless liquid with a benzene-like odor. In most of its reactions, it resembles benzene. Compounds analogous to thiophene include furan (C4H4O), selenophene (C4H4Se) and pyrrole (C4H4NH), which each vary by the heteroatom in the ring.

<span class="mw-page-title-main">Nitrobenzene</span> Chemical compound

Nitrobenzene is an aromatic nitro compound and the simplest of the nitrobenzenes, with the chemical formula C6H5NO2. It is a water-insoluble pale yellow oil with an almond-like odor. It freezes to give greenish-yellow crystals. It is produced on a large scale from benzene as a precursor to aniline. In the laboratory, it is occasionally used as a solvent, especially for electrophilic reagents. As confirmed by X-ray crystallography, nitrobenzene is a planar molecule.

In organic chemistry, an aryl halide is an aromatic compound in which one or more hydrogen atoms, directly bonded to an aromatic ring are replaced by a halide. Haloarenes are different from haloalkanes because they exhibit many differences in methods of preparation and properties. The most important members are the aryl chlorides, but the class of compounds is so broad that there are many derivatives and applications.

In electrophilic aromatic substitution reactions, existing substituent groups on the aromatic ring influence the overall reaction rate or have a directing effect on positional isomer of the products that are formed.

<span class="mw-page-title-main">Nitro compound</span> Organic compound containing an −NO₂ group

In organic chemistry, nitro compounds are organic compounds that contain one or more nitro functional groups. The nitro group is one of the most common explosophores used globally. The nitro group is also strongly electron-withdrawing. Because of this property, C−H bonds alpha (adjacent) to the nitro group can be acidic. For similar reasons, the presence of nitro groups in aromatic compounds retards electrophilic aromatic substitution but facilitates nucleophilic aromatic substitution. Nitro groups are rarely found in nature. They are almost invariably produced by nitration reactions starting with nitric acid.

<span class="mw-page-title-main">Azo compound</span> Organic compounds with a diazenyl group (–N=N–)

Azo compounds are organic compounds bearing the functional group diazenyl.

In organic chemistry, an electrophilic aromatic halogenation is a type of electrophilic aromatic substitution. This organic reaction is typical of aromatic compounds and a very useful method for adding substituents to an aromatic system.

<span class="mw-page-title-main">Nitrosation and nitrosylation</span> Process of converting organic compounds into nitroso derivatives

Nitrosation and nitrosylation are two names for the process of converting organic compounds or metal complexes into nitroso derivatives, i.e., compounds containing the R−NO functionality. The synonymy arises because the R-NO functionality can be interpreted two different ways, depending on the physico-chemical environment:

Arene substitution patterns are part of organic chemistry IUPAC nomenclature and pinpoint the position of substituents other than hydrogen in relation to each other on an aromatic hydrocarbon.

<span class="mw-page-title-main">Aromatic sulfonation</span> Chemical reaction which replaces a hydrogen on an arene with sulfonic acid, –NH–SO3H

In organic chemistry, aromatic sulfonation is an organic reaction in which a hydrogen atom on an arene is replaced by a sulfonic acid functional group in an electrophilic aromatic substitution. Aryl sulfonic acids are used as detergents, dye, and drugs.

<span class="mw-page-title-main">Nucleophilic aromatic substitution</span> Chemical reaction mechanism

A nucleophilic aromatic substitution (SNAr) is a substitution reaction in organic chemistry in which the nucleophile displaces a good leaving group, such as a halide, on an aromatic ring. Aromatic rings are usually nucleophilic, but some aromatic compounds do undergo nucleophilic substitution. Just as normally nucleophilic alkenes can be made to undergo conjugate substitution if they carry electron-withdrawing substituents, so normally nucleophilic aromatic rings also become electrophilic if they have the right substituents.

Electrophilic aromatic substitution (SEAr) is an organic reaction in which an atom that is attached to an aromatic system is replaced by an electrophile. Some of the most important electrophilic aromatic substitutions are aromatic nitration, aromatic halogenation, aromatic sulfonation, alkylation Friedel–Crafts reaction and acylation Friedel–Crafts reaction.

<span class="mw-page-title-main">2-Nitrochlorobenzene</span> Chemical compound

2-Nitrochlorobenzene is an organic compound with the formula ClC6H4NO2. It is one of three isomeric nitrochlorobenzenes. It is a yellow crystalline solid that is important as a precursor to other compounds due to its two functional groups.

<span class="mw-page-title-main">Trifluoroperacetic acid</span> Chemical compound

Trifluoroperacetic acid is an organofluorine compound, the peroxy acid analog of trifluoroacetic acid, with the condensed structural formula CF
3COOOH. It is a strong oxidizing agent for organic oxidation reactions, such as in Baeyer–Villiger oxidations of ketones. It is the most reactive of the organic peroxy acids, allowing it to successfully oxidise relatively unreactive alkenes to epoxides where other peroxy acids are ineffective. It can also oxidise the chalcogens in some functional groups, such as by transforming selenoethers to selones. It is a potentially explosive material and is not commercially available, but it can be quickly prepared as needed. Its use as a laboratory reagent was pioneered and developed by William D. Emmons.

Ortho effect is an organic chemistry phenomenon where the presence of a chemical group at the at ortho position or the 1 and 2 position of a phenyl ring, relative to the carboxylic compound changes the chemical properties of the compound. This is caused by steric effects and bonding interactions along with polar effects caused by the various substituents which are in a given molecule, resulting in changes in its chemical and physical properties. The ortho effect is associated with substituted benzene compounds.

References

  1. ↑
    • Schofield, K. (1971). Nitration and Aromatic Reactivity. Cambridge: Cambridge University Press.
  2. 1 2 3 4 Gerald Booth (2007). "Nitro Compounds, Aromatic". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a17_411. ISBN   978-3527306732.
  3. ↑ Olahfirst1=G.A.; Malhotra, R.; Narang, S.C. (1989). Nitration: Methods and Mechanisms. NY: VCH. ISBN   978-0-471-18695-3.{{cite book}}: CS1 maint: numeric names: authors list (link)
  4. ↑ John McMurry Organic Chemistry 2nd Ed.
  5. ↑ George A. Olah and Stephen J. Kuhn. "Benzonitrile, 2-methyl-3,5-dinitro-". Organic Syntheses ; Collected Volumes, vol. 5, p. 480.
  6. ↑ "Nitration of benzene and methylbenzene".
  7. ↑ Esteves, P. M.; Carneiro, J. W. M.; Cardoso, S. P.; Barbosa, A. G. H.; Laali, K. K.; Rasul, G.; Prakash, G. K. S.; e Olah, G. A. (2003). "Unified Mechanism Concept of Electrophilic Aromatic Nitration Revisited: Convergence of Computational Results and Experimental Data". J. Am. Chem. Soc. 125 (16): 4836–49. doi:10.1021/ja021307w. PMID   12696903.
  8. ↑ Queiroz, J. F.; Carneiro, J. W. M.; Sabino A. A.; Sparapan, R.; Eberlin, M. N.; Esteves, P. M. (2006). "Electrophilic Aromatic Nitration: Understanding Its Mechanism and Substituent Effects". J. Org. Chem. 71 (16): 6192–203. doi:10.1021/jo0609475. PMID   16872205.
  9. ↑ Smith, Michael B.; March, Jerry (2007), Advanced Organic Chemistry: Reactions, Mechanisms, and Structure (6th ed.), New York: Wiley-Interscience, p. 665, ISBN   978-0-471-72091-1
  10. ↑ E. O. Woolfolk and Milton Orchin. "2,4,7-Trinitrofluorenone". Organic Syntheses ; Collected Volumes, vol. 3, p. 837.
  11. ↑ Melvin S. Newman and H. Boden. "2,4,5,7-Tetranitrofluorenone". Organic Syntheses ; Collected Volumes, vol. 5, p. 1029.
  12. ↑ Web resource: warren-wilson.edu Archived 2012-03-20 at the Wayback Machine
  13. ↑ Mechanism and synthesis Peter Taylor, Royal Society of Chemistry (Great Britain), Open University
  14. ↑ Louw, Robert "Acetyl nitrate" e-EROS Encyclopedia of Reagents for Organic Synthesis 2001, 1-2. doi : 10.1002/047084289X.ra032
  15. ↑ Smith, Keith; Musson, Adam; Deboos, Gareth A. (1998). "A Novel Method for the Nitration of Simple Aromatic Compounds". The Journal of Organic Chemistry. 63 (23): 8448–8454. doi:10.1021/jo981557o.
  16. ↑ Yang, Tao; Li, Xiaoqian; Deng, Shuang; Qi, Xiaotian; Cong, Hengjiang; Cheng, Hong-Gang; Shi, Liangwei; Zhou, Qianghui; Zhuang, Lin (2022-09-26). "From N–H Nitration to Controllable Aromatic Mononitration and Dinitration─The Discovery of a Versatile and Powerful N -Nitropyrazole Nitrating Reagent". JACS Au. 2 (9): 2152–2161. doi:10.1021/jacsau.2c00413. ISSN   2691-3704. PMC   9516713 . PMID   36186553.
  17. ↑ Prakash, G.; Mathew, T. (2010). "Ipso-Nitration of Arenes". Angewandte Chemie International Edition in English. 49 (10): 1726–1728. doi:10.1002/anie.200906940. PMID   20146295.
  18. ↑ Perrin, C. L.; Skinner, G. A. (1971). "Directive effects in electrophilic aromatic substitution ("ipso factors"). Nitration of haloanisoles". Journal of the American Chemical Society. 93 (14): 3389. doi:10.1021/ja00743a015.
  19. ↑ Fors, B.; Buchwald, S. (2009). "Pd-Catalyzed Conversion of Aryl Chlorides, Triflates, and Nonaflates to Nitroaromatics". Journal of the American Chemical Society. 131 (36): 12898–12899. doi:10.1021/ja905768k. PMC   2773681 . PMID   19737014.
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