science

Lithium borohydride

Lithium borohydride 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 Lithium borohydride rather than just read about it. In short: Lithium borohydride (LiBH4) is a borohydride and known in organic synthesis as a reducing agent for esters. Although less common than the related sodium borohydride, the lithium salt offers some advantages, being a stronger reducing agent and highly soluble in ethers, whilst remaining safer to handle than lithium aluminium hydride.

Key takeaways

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

Reference excerpt

Lithium borohydride (LiBH4) is a borohydride and known in organic synthesis as a reducing agent for esters. Although less common than the related sodium borohydride, the lithium salt offers some advantages, being a stronger reducing agent and highly soluble in ethers, whilst remaining safer to handle than lithium aluminium hydride.

Preparation Lithium borohydride may be prepared by the metathesis reaction, which occurs upon ball-milling the more commonly available sodium borohydride and lithium bromide:

NaBH4 + LiBr → NaBr + LiBH4 Alternatively, it may be synthesized by treating boron trifluoride with lithium hydride in diethyl ether:

BF3 + 4 LiH → LiBH4 + 3 LiF

Reactions Lithium borohydride is useful as a source of hydride (H−). It can react with a range of carbonyl substrates and other polarized carbon structures to form a hydrogen–carbon bond. It can also react with Brønsted–Lowry-acidic substances (sources of H+) to form hydrogen gas.

Reduction reactions As a hydride reducing agent, lithium borohydride is stronger than sodium borohydride but weaker than lithium aluminium hydride. Unlike the sodium analog, it can reduce esters to alcohols, nitriles and primary amides to amines, and can open epoxides. The enhanced reactivity in many of these cases is attributed to the polarization of the carbonyl substrate by complexation to the lithium cation. Unlike the aluminium analog, it does not react with nitro groups, carbamic acids, alkyl halides, or secondary and tertiary amides.

Hydrogen generation Lithium borohydride reacts with water to produce hydrogen. This reaction can be used for hydrogen generation. Although this reaction is usually spontaneous and violent, somewhat-stable aqueous solutions of lithium borohydride can be prepared at low temperature if degassed, distilled water is used and exposure to oxygen is avoided.

Lithium borohydride is renowned as one of the highest-energy-density chemical energy carriers. Although of no practicality, the solid liberates 65 MJ/kg heat upon treatment with atmospheric oxygen. Since it has a density of 0.67 g/cm3, oxidation of liquid lithium borohydride gives 43 MJ/L. In comparison, gasoline gives 44 MJ/kg (or 35 MJ/L), while liquid hydrogen gives 120 MJ/kg (or 8.0 MJ/L). The high specific energy density of lithium borohydride has made it an attractive candidate to propose for automobile and rocket fuel, but despite the research and advocacy, it has not been used widely. As with all chemical-hydride-based energy carriers, lithium borohydride is very complex to recycle (i.e. recharge) and therefore suffers from a low energy conversion efficiency. While batteries such as lithium-ion carry an energy density of up to 0.72 MJ/kg and 2.0 MJ/L, their DC-to-DC conversion efficiency can be as high as 90%. In view of the complexity of recycling mechanisms for metal hydrides, such high energy-conversion efficiencies are not practical with present technology.

Structure Four polymorphs have been described. The stable forms feature tetrahedral BH4- anions.

Illustrations

Worked examples

Example 1 — a first encounter with Lithium borohydride

Start with the simplest possible case. Write down what Lithium borohydride 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 Lithium borohydride 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 Lithium borohydride 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 Lithium borohydride

In research: Lithium borohydride 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 Lithium borohydride 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: Lithium borohydride is common in secondary-school and first-year university syllabi. It links to neighbouring topics Borohydrides, Lithium salts, Reducing agents, so understanding it makes those chapters shorter.
In everyday life: Look for Lithium borohydride 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 Lithium borohydride in 20 minutes

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

Frequently asked questions

What is Lithium borohydride in simple terms?

Why does Lithium borohydride 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 Lithium borohydride?

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 Lithium borohydride.