What are TON and TOF — and why do they matter?

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The Turnover Number (TON) is the total number of moles of product formed per mole of catalyst over the full course of a reaction. It is the definitive measure of how much work a catalyst does before it is deactivated or consumed — a catalyst with a TON of 10,000 converts ten thousand times its own molar quantity into product. The Turnover Frequency (TOF) normalises TON by reaction time, giving the rate of catalytic turnover in units of h⁻¹, and is used to compare the intrinsic activity of different catalyst systems under comparable conditions.

GoalMaximise TON and TOF — a higher TON means less catalyst is needed per mole of product, reducing the environmental and economic cost of catalyst synthesis, separation, and disposal.

WhyCatalyst production often involves precious metals (Pd, Rh, Ru, Ir) or complex ligand synthesis with significant waste. A ten-fold increase in TON directly reduces catalyst-derived waste by 90%, supporting both Principle 9 (Catalysis) and Principle 1 (Prevention).

HowOptimise catalyst loading, temperature, and reaction time. Screen ligands and co-solvents. Consider catalyst recycling and immobilisation on a solid support. Move from batch to continuous flow to extend catalyst lifetime.

The formulae

$$\text{TON} = \frac{n_{\text{product}}}{n_{\text{catalyst}}}$$

$$\text{TOF} = \frac{\text{TON}}{t_{\text{reaction}}} = \frac{n_{\text{product}}}{n_{\text{catalyst}} \times t_{\text{reaction}}}$$

Symbol	Term	Units
$\text{TON}$	Turnover Number — total moles of product per mole of catalyst	dimensionless (mol mol⁻¹); higher is better; ideal value → ∞
$\text{TOF}$	Turnover Frequency — TON per unit time	h⁻¹; higher is better
$n_{\text{product}}$	Moles of desired product actually isolated	mol
$n_{\text{catalyst}}$	Moles of catalyst introduced into the reaction	mol
$t_{\text{reaction}}$	Reaction time from catalyst addition to quench or isolation	h

TON uses the actual moles of product isolated, not the theoretical maximum. If catalyst loading is reported as a mol% of substrate, convert: $n_{\text{catalyst}} = \text{mol\%} \times n_{\text{limiting reagent}} / 100$. TOF is meaningful only when measured at a defined conversion, ideally under initial-rate conditions; the value reported here is an average TOF over the full reaction time.

Typical TON by catalyst system

Catalyst system	Typical TON	Key factor
Enzymes (biological catalysts)	10⁶ – 10⁹	Precisely evolved active site; product release not rate-limiting
Industrial heterogeneous (e.g. Fe/Haber–Bosch)	10⁵ – 10⁸	Continuous flow; catalyst regenerated in situ; very long lifetime
Homogeneous precious metal (Pd, Rh, Ru, Ir)	10³ – 10⁶	Highly active but sensitive to poisoning; difficult to recycle
Non-precious metal homogeneous (Fe, Ni, Co, Cu)	10² – 10⁴	Lower intrinsic activity; more sustainable metal source
Organocatalyst (e.g. proline, NHC)	10 – 10³	Metal-free; activity limited by loading and substrate scope
Stoichiometric reagent (not a true catalyst)	≤ 1	TON ≤ 1 means the "catalyst" is consumed; not catalytic

Strengths and limitations

Strengths

Directly measures how efficiently the catalyst is used — the core metric of catalytic greenness
Simple to calculate: only moles of product and moles of catalyst are needed
Dimensionless and scale-independent — directly comparable across laboratories
Immediately reveals whether a system is truly catalytic (TON > 1) or stoichiometric
High TON drives adoption of catalysis over stoichiometric reagents — a central GC goal

Limitations

Does not capture selectivity: a catalyst producing by-products inflates TON without being "green"
Sensitive to how catalyst loading is defined (e.g. Pd complex vs. Pd atoms in nanoparticles)
Average TOF over a full reaction masks induction periods and catalyst deactivation profiles
Does not account for catalyst synthesis waste, solvent use, or energy consumption
Must be paired with E-factor, yield, and atom economy for a complete greenness picture

TON in context: complementary green metrics

Metric	What it measures	Stage
TON / TOF	Moles of product per mole of catalyst (and per unit time)	Experimental
% Yield	Fraction of theoretical product actually isolated from limiting reagent	Experimental
Atom Economy (AE)	Theoretical fraction of reactant mass incorporated into desired product	Design
E-factor	Mass of all waste per mass of product (solvents, excess, by-products)	Experimental
Space-Time Yield (STY)	Product mass per reactor volume per unit time — reactor productivity	Experimental
PMI (Process Mass Intensity)	Total mass of all inputs per mass of product; E-factor + 1	Experimental

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Experiment details

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Experiment / reaction name

Researcher(s)

Date

Lab / institution

Reaction type

Solvent

Temperature

Catalyst / loading

Reference / DOI

Notes

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Reactants

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Enter the mass and molecular weight of each reactant used. The tool identifies the limiting reagent (lowest moles/coefficient ratio) and calculates theoretical yield for context. Reactant masses appear in the breakdown charts. This section is optional — TON and TOF are calculated from the product and catalyst data in the next section.

Compound name	Formula	MW (g/mol)	Mass used (g)	Coeff.	Moles

Σ Reactant mass — g · Limiting reagent: —

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Product & catalyst

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Enter the desired product (with its molecular weight so the tool can convert mass to moles), then the actual mass isolated. Then enter your catalyst details. TON = n_product ÷ n_catalyst; TOF = TON ÷ reaction time.

Desired product

Product name	Formula	MW (g/mol)	Coeff.	MW × n

Actual mass of product isolated

g

Enter the mass of pure, dry product actually isolated from your experiment.

Catalyst

Enter the catalyst used, its molecular weight, and the mass charged to the reaction. If using a catalyst loading given as mol%, convert using: n_catalyst = mol% × n_{limiting reagent} / 100.

Catalyst name	Formula	MW (g/mol)	Mass used (g)	Moles	mol%

Reaction time

h

Hours from catalyst addition to quench or start of product isolation. Convert minutes ÷ 60.

n_catalyst — mol · Theoretical yield: — g (from limiting reagent)

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Results

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Turnover Number

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mol product / mol catalyst

Turnover Frequency

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h⁻¹

n_product

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mmol

n_catalyst

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mmol

TON scale — 0 to ≥ 10,000 (higher is better)

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01,0005,000≥ 10,000

Reactant mass contributions

Actual vs. theoretical product mass

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Detailed breakdown & interpretation

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Compound	Role	Formula	MW (g/mol)	Mass (g)	Moles	Coeff.	% of total mass	Visual
Enter reactants, product, and catalyst above to see breakdown.

Interpretation

Enter product mass, catalyst details, and reaction time above to generate an interpretation.

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Save & load sessions

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Sessions are stored in your browser only. No data leaves your device.

No saved sessions yet.

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Export

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Export your TON/TOF calculation as a PDF report or CSV data file. PDF opens in a new tab and uses your browser's print function. CSV downloads directly.

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Where can I read more?

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References are sorted alphabetically by first author.

P. T. Anastas and J. C. Warner, Green Chemistry: Theory and Practice, Oxford University Press, 1998. ISBN 978-0-19-850698-0. — Original statement of the 12 Principles; Principle 9 on catalysis frames TON as a key measure of catalyst efficiency.
A. Behr and L. Johnen, ChemSusChem, 2008, 1, 483–484. DOI. — Myrcene as a natural base chemical in sustainable chemistry; discusses TON in the context of renewable feedstocks.
D. J. C. Constable et al., Green Chem., 2002, 4, 521–527. DOI. — Green chemistry metrics for the pharmaceutical industry; discusses catalyst turnover as a key green metric.
R. A. Sheldon, Green Chem., 2007, 9, 1273–1283. DOI. — The E-factor fifteen years on; discusses TON/TOF in context of catalysis and waste prevention.
R. A. Sheldon, Green Chem., 2017, 19, 18–43. DOI. — The E-factor 25 years on; comprehensive metrics landscape including TON and catalyst efficiency.
D. Sinou, Top. Curr. Chem., 1997. — Discusses turnover numbers as a benchmark for homogeneous catalyst performance; foundational context for interpreting TON in organic synthesis.
B. M. Trost, Science, 1991, 254, 1471–1477. DOI. — Atom economy — a search for synthetic efficiency; introduces atom economy and discusses catalyst role in step economy.

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Contributors

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Roles follow the CRediT taxonomy (Contributor Roles Taxonomy), adapted for educational software. Hover a contributor's name for a summary, or a column header for the definition of that role.

Contributor

This portal was built with the assistance of a large language model (Claude, Anthropic), which was used to generate and refine code, articulate and structure contributed ideas within the defined page format, and support iterative design decisions. All scientific content, conceptual frameworks, pedagogical choices, and final outputs were directed, reviewed, and verified by the contributors listed above.

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How do I cite this page?

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If you use this tool in teaching or published work, please cite the DodecaGreen portal as the source.

Reference

BibTeX

Turnover number & frequency calculator.