Nitrobenzene

Key takeaways

Nitrobenzene belongs to physics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Nitrobenzene to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Nitrobenzene from memory before moving on to harder problems.

Reference excerpt

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.

Production Nitrobenzene is prepared by nitration of benzene with a mixture of concentrated sulfuric acid, water, and nitric acid. This mixture is sometimes called "mixed acid."

The production of nitrobenzene is one of the most dangerous processes conducted in the chemical industry because of the exothermicity of the reaction (ΔH = −117 kJ/mol). The nitration process involves formation of the nitronium ion (NO2+), followed by an electrophilic aromatic substitution reaction of it with benzene. The nitronium ion is generated by the reaction of nitric acid and an acidic dehydration agent, typically sulfuric acid:

HNO3 + H+ ⇌ NO2+ + H2O World capacity for nitrobenzene in 1985 was about 1,700,000 tonnes.

Uses Approximately 95% of nitrobenzene industrially produced is hydrogenated to aniline:

C6H5NO2 + 3 H2 → C6H5NH2 + 2 H2O Aniline is a precursor to urethane polymers, rubber chemicals, pesticides, dyes (particularly azo dyes), explosives, and pharmaceuticals.

Specialized applications Nitrobenzene is used to mask unpleasant odors in shoe and floor polishes, leather dressings, paint solvents, and other materials. Redistilled, as oil of mirbane, nitrobenzene had been used as an inexpensive perfume for soaps. It has been replaced by less toxic chemicals for this purpose. A significant merchant market for nitrobenzene is its use in the production of the analgesic paracetamol (also known as acetaminophen). Nitrobenzene is also used in Kerr cells, as it has an unusually large Kerr constant. Evidence suggests its use in agriculture as a plant growth/flowering stimulant. Historically, Nitrobenzene was used by the Provisional Irish Republican Army to make improvised explosive devices during The Troubles, specially after the British Army raids cut off their supplies of explosives in the early 1970s.

Chemical properties

Electrophilic substitution Nitrobenzene can be further nitrated using a mixture of concentrated HNO3 and H2SO4 to produce 1,3-dinitrobenzene (1,3-DNB) as a major product. Typical byproducts of the reaction are 1,2-dinitrobenzene (1,2-DNB), 1,4-dinitrobenzene (1,4-DNB) and 4-nitrophenol (4-NP).

Sulfonation of nitrobenzene with 65% fuming sulfuric acid gives 3-nitrobenzenesulfonic acid (3-NBSA). Usually 3-NBSA is not isolated in a form of a free acid, the reaction mass is quenched and converted to the sodium salt of 3-NBSA.

Nitrobenzene chlorination in the presence of FeCl3 yields a mixture that predominantly contains 3-nitrochlorobenzene (3-NCB) and small amount of the other isomers: 2-nitrochlorobenzene (2-NCB) and 4-nitrochlorobenzene (4-NCB).

Other organic reactions Aside from its conversion to aniline, nitrobenzene can be selectively reduced to azoxybenzene, azobenzene, nitrosobenzene,Org. Synth. 1945, 25, 80 DOI: 10.15227/orgsyn.025.0080 hydrazobenzene, and phenylhydroxylamine. It has been used as a mild oxidant in reactions like the Skraup quinoline synthesis.

Safety Nitrobenzene is toxic (Threshold Limit Value 5 mg/m3) and readily absorbed through the skin. Prolonged exposure may cause serious damage to the central nervous system, impair vision, cause liver or kidney damage, anemia and lung irritation. Nitrobenzene is considered a likely human carcinogen by the United States Environmental Protection Agency, and is classified by the IARC as a Group 2B carcinogen which is "possibly carcinogenic to humans". It has been shown to cause liver, kidney, and thyroid adenomas and carcinomas in rats. It is classified as an extremely hazardous substance in the United States as defined in Section 302 of the U.S. Emergency Planning and Community Right-to-Know Act (42 U.S.C. 11002), and is subject to strict reporting requirements by facilities which produce, store, or use it in significant quantities.

References

External links International Chemical Safety Card 0065 NIOSH Pocket Guide to Chemical Hazards IARC Monograph: "Nitrobenzene" US EPA factsheet https://patents.google.com/patent/US9113628

Illustrations

Worked examples

Example 1 — a first encounter with Nitrobenzene

Start with the simplest possible case. Write down what Nitrobenzene claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Nitrobenzene before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Nitrobenzene ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Nitrobenzene

In research: Nitrobenzene appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Nitrobenzene in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Nitrobenzene is common in secondary-school and first-year university syllabi. It links to neighbouring topics Aromatic solvents, IARC Group 2B carcinogens, Nitro solvents, so understanding it makes those chapters shorter.
In everyday life: Look for Nitrobenzene outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Nitrobenzene in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Nitrobenzene means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Nitrobenzene out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Nitrobenzene in simple terms?

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.

Why does Nitrobenzene matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Nitrobenzene?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Nitrobenzene.