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O-Phenylenediamine

O-Phenylenediamine is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand O-Phenylenediamine rather than just read about it. In short: o-Phenylenediamine (OPD) is an organic compound with the formula C6H4(NH2)2. This aromatic diamine is an important precursor to many heterocyclic compounds.

O-Phenylenediamine — main illustration
O-Phenylenediamine — illustration

Key takeaways

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

Reference excerpt

o-Phenylenediamine (OPD) is an organic compound with the formula C6H4(NH2)2. This aromatic diamine is an important precursor to many heterocyclic compounds. OPD is a white compound although samples appear darker owing to oxidation by air. It is isomeric with m-phenylenediamine and p-phenylenediamine.

Preparation Commonly, 2-nitrochlorobenzene is treated with ammonia to generate 2-nitroaniline, whose nitro group is then reduced:

ClC6H4NO2 + 2 NH3 → H2NC6H4NO2 + NH4Cl H2NC6H4NO2 + 3 H2 → H2NC6H4NH2 + 2 H2O In the laboratory, the reduction of the nitroaniline is effected with zinc powder in ethanol, followed by purification of the diamine as the hydrochloride salt. Darkened impure samples can be purified by treatment of its aqueous solution with sodium dithionite and activated carbon.

Reactions and uses o-Phenylenediamine condenses with ketones and aldehydes to give rise to various valuable products. Its reactions with formic acids to produce benzimidazole. Other carboxylic acids give 2-substituted benzimidazoles. The herbicides benomyl and fuberidazole are made in this manner. Thiophanate-methyl is another herbicide produced from o-phenylenediamine. Condensation with potassium ethylxanthate gives 2-mercaptobenzimidazole. With nitrous acid, o-phenylenediamine condenses to give benzotriazole, a corrosion inhibitor. Quinoxalinedione may be prepared by condensation of o-phenylenediamine with dimethyl oxalate. Mercaptoimidazole are commonly used as antioxidants in rubber production, obtained by condensing xanthate esters. Condensation of substituted o-phenylenediamine with diketones yields various pharmaceuticals. OPD is a ligand in coordination chemistry. Oxidation of metal-phenylenediamine complexes affords the diimine derivatives. OPD condenses with salicylaldehyde to give chelating Schiff base ligands. It reacts with thionyl chloride to give 2,1,3-benzothiadiazole: C6H4(NH2)2 + 2 SOCl2 → C6H4(N)2S + SO2 + 4HCl

Safety With an LD50 of 44 mg/L (in water), o-phenylenediamine is about 1000 times less toxic than the para-isomer. Anilines are typically handled as if they are carcinogenic. For many applications, OPD has been replaced by safer alternatives such as 3,3',5,5'-tetramethylbenzidine.

References

Illustrations

O-Phenylenediamine illustration
O-Phenylenediamine illustration
O-Phenylenediamine illustration
O-Phenylenediamine illustration
O-Phenylenediamine illustration

Worked examples

Example 1 — a first encounter with O-Phenylenediamine

Start with the simplest possible case. Write down what O-Phenylenediamine claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, 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 O-Phenylenediamine 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 O-Phenylenediamine 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 O-Phenylenediamine

In research
O-Phenylenediamine appears in science 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 O-Phenylenediamine 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
O-Phenylenediamine is common in secondary-school and first-year university syllabi. It links to neighbouring topics Anilines, Chelating agents, Diamines, so understanding it makes those chapters shorter.
In everyday life
Look for O-Phenylenediamine 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.
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How to study O-Phenylenediamine in 20 minutes

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

Frequently asked questions

What is O-Phenylenediamine in simple terms?

o-Phenylenediamine (OPD) is an organic compound with the formula C6H4(NH2)2. This aromatic diamine is an important precursor to many heterocyclic compounds.

Why does O-Phenylenediamine matter?

Because it connects several science 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 O-Phenylenediamine?

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 O-Phenylenediamine.

Tags

  • Anilines
  • Chelating agents
  • Diamines

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