chemistry

Hydrogenolysis

Hydrogenolysis 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 Hydrogenolysis rather than just read about it. In short: Hydrogenolysis is a chemical reaction whereby a carbon–carbon or carbon–heteroatom single bond is cleaved or undergoes lysis (breakdown) by hydrogen. The heteroatom may vary, but it usually is oxygen, nitrogen, or sulfur.

Key takeaways

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

Reference excerpt

Hydrogenolysis is a chemical reaction whereby a carbon–carbon or carbon–heteroatom single bond is cleaved or undergoes lysis (breakdown) by hydrogen. The heteroatom may vary, but it usually is oxygen, nitrogen, or sulfur. A related reaction is hydrogenation, where hydrogen is added to the molecule, without cleaving bonds. Usually hydrogenolysis is conducted catalytically using hydrogen gas.

History The term "hydrogenolysis" was coined by Carleton Ellis in reference to hydrogenolysis of carbon–carbon bonds. Earlier, Paul Sabatier had already observed the hydrogenolysis of benzyl alcohol to toluene, and as early as 1906, Padoa and Ponti had observed the hydrogenolysis of furfuryl alcohol. Homer Burton Adkins and Ralph Connor were the first to call the carbon–oxygen bond cleavage "hydrogenolysis".

In the petrochemical industry

In petroleum refineries, catalytic hydrogenolysis of feedstocks is conducted on a large scale to remove sulfur from feedstocks, releasing gaseous hydrogen sulfide (H2S). The hydrogen sulfide is subsequently recovered in an amine treater and finally converted to elemental sulfur in a Claus process unit. In those industries, desulfurization process units are often referred to as hydrodesulfurizers (HDS) or hydrotreaters (HDT). Catalysts are based on molybdenum sulfide containing smaller amounts of cobalt or nickel. Hydrogenolysis is accompanied by hydrogenation. Another hydrogenolysis reaction of commercial importance is the hydrogenolysis of esters into alcohols by catalysts such as copper chromite. The hydrodeoxygenation reaction used in the Neste Renewable Diesel process, the vegetable oil refining process of largest production capacity, is a hydrogenolysis of triglycerides into alkanes.

In the laboratory In the laboratory, hydrogenolysis is used in organic synthesis. Debenzylation is most common and involves the cleavage of benzyl ethers:

R−OCH2C6H5 + H2 → R−OH + CH3C6H5 Thioketals undergo hydrogenolysis using Raney nickel in the Mozingo reduction. Laboratory hydrogenolysis is operationally similar to hydrogenation, and may be accomplished at atmospheric pressure by stirring the reaction mixture under a slight positive pressure of hydrogen gas, having flushed the apparatus with more of this gas. The hydrogen may be provided by attaching a balloon to a needle, filling it from a bottle, and inserting the needle into the reaction flask via a rubber septum. At high pressure, a hydrogenation autoclave (i.e., a Buchi or Parr hydrogenator) or similar piece of equipment is required.

References

Worked examples

Example 1 — a first encounter with Hydrogenolysis

Start with the simplest possible case. Write down what Hydrogenolysis 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 Hydrogenolysis 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 Hydrogenolysis 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 Hydrogenolysis

In research: Hydrogenolysis 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 Hydrogenolysis 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: Hydrogenolysis is common in secondary-school and first-year university syllabi. It links to neighbouring topics Hydrogen, Organic redox reactions, so understanding it makes those chapters shorter.
In everyday life: Look for Hydrogenolysis 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 Hydrogenolysis in 20 minutes

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

Frequently asked questions

What is Hydrogenolysis in simple terms?

Why does Hydrogenolysis 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 Hydrogenolysis?

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 Hydrogenolysis.