chemistry

Trimethylborane

Trimethylborane is a chemistry 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 Trimethylborane rather than just read about it. In short: Trimethylborane (TMB) is a toxic, pyrophoric gas with the formula B(CH3)3 (which can also be written as Me3B, with Me representing methyl). Properties As a liquid it is colourless.

Key takeaways

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

Reference excerpt

Trimethylborane (TMB) is a toxic, pyrophoric gas with the formula B(CH3)3 (which can also be written as Me3B, with Me representing methyl).

Properties As a liquid it is colourless. The strongest line in the infrared spectrum is at 1330 cm−1 followed by lines at 3010 cm−1 and 1185 cm−1. Its melting point is −161.5 °C, and its boiling point is −20.2 °C. Vapour pressure is given by log P = 6.1385 + 1.75 log T − 1393.3/T − 0.007735 T, where T is temperature in kelvins. Molecular weight is 55.914. The heat of vapourisation is 25.6 kJ/mol.

Preparation Trimethylborane was first described in 1862 by Edward Frankland, who also mentioned its adduct with ammonia. Due to its dangerous nature the compound was no longer studied until 1921, when Alfred Stock and Friedrich Zeidler took advantage of the reaction between boron trichloride gas and dimethylzinc. Although the substance can be prepared using Grignard reagents the output is contaminated by unwanted products from the solvent. Trimethylborane can be made on a small scale with a 98% yield by reacting trimethylaluminium in hexane with boron tribromide in dibutyl ether as a solvent. Yet other methods are reacting tributyl borate with trimethylaluminium chloride, or potassium tetrafluoroborate with trimethylaluminium, or adding boron trifluoride in ether to methyl magnesium iodide.

Reactions Trimethylborane spontaneously ignites in air if the concentration is high enough. It burns with a green flame producing soot. Slower oxidation with oxygen in a solvent or in the gas phase can produce dimethyltrioxadiboralane, which contains a ring of two boron and three oxygen atoms. However the major product is dimethylborylmethylperoxide, which rapidly decomposes to dimethoxymethylborane. Trimethylborane is a strong Lewis acid. B(CH3)3 can form an adduct with ammonia: (NH3):B(CH3)3. as well as other Lewis bases. The Lewis acid properties of B(CH3)3 have been analyzed by the ECW model yielding EA= 2.90 and CA= 3.60. When trimethylborane forms an adduct with trimethylamine, steric repulsion between the methyl groups on the B and N results. The ECW model can provide a measure of this steric effect. Trimethylborane reacts with water and chlorine at room temperature. It also reacts with grease but not with teflon or glass. Trimethylborane reacts with diborane to disproportionate to form methyldiborane and dimethyldiborane: (CH3)BH2.BH3 and (CH3)2BH.BH3. It reacts as a gas with trimethylphosphine to form a solid Lewis salt with a heat of formation of −41 kcal per mol. This adduct has a heat of sublimation of −24.6 kcal/mol. No reaction occurs with trimethylarsine or trimethylstibine. Methyl lithium reacting with the Trimethylborane produces a tetramethylborate salt: LiB(CH3)4. The tetramethylborate ion has a negative charge and is isoelectronic with neopentane, tetramethylsilane, and the tetramethylammonium cation.

Use Trimethylborane has been used as a neutron counter. For this use it has to be very pure. It is also used in chemical vapour deposition where boron and carbon need to be deposited together.

References

Illustrations

Worked examples

Example 1 — a first encounter with Trimethylborane

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

In research: Trimethylborane appears in chemistry 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 Trimethylborane 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: Trimethylborane is common in secondary-school and first-year university syllabi. It links to neighbouring topics Alkylboranes, Gases, Methyl compounds, so understanding it makes those chapters shorter.
In everyday life: Look for Trimethylborane 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 Trimethylborane in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Trimethylborane 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 Trimethylborane out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Trimethylborane in simple terms?

Trimethylborane (TMB) is a toxic, pyrophoric gas with the formula B(CH3)3 (which can also be written as Me3B, with Me representing methyl). Properties As a liquid it is colourless.

Why does Trimethylborane matter?

Because it connects several chemistry 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 Trimethylborane?

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 Trimethylborane.