Free chemical reaction timer for timing lab procedures. Reflux, stirring, crystallisation, and workup stages. Configurable for any reaction duration. Start instantly.
Reaction time determines yield, selectivity, and product quality. Under-reaction: starting materials remain. Over-reaction: over-oxidation, racemisation, side reactions, or decomposition of product. For kinetically controlled reactions, stopping at the optimal time window is the difference between 80% and 20% yield.
Press Start when the solvent begins to reflux (visible condensation returning to the flask). Reflux time is measured from first reflux, not from when heating is applied. After the timer, turn off heat and allow to cool before workup — hot workup of reactive mixtures is a significant safety hazard.
For reactions running 30–120 minutes: monitor by TLC every 15–20 minutes. For reactions running several hours: every 30–60 minutes. TLC every 5 minutes is rarely necessary. Use the timer to remind you to check reaction progress rather than checking continuously.
Dissolve in minimum hot solvent, cool to room temperature (30–60 minutes), then cool in ice bath (30–60 minutes), collect crystals. Total: 1–3 hours. For better crystal quality, slow cooling (refrigerator, several hours) vs. fast ice-bath cooling. Time the stages individually.
A quench is the controlled addition of a substance to stop a reaction (e.g. water quench of a lithiation, saturated NH₄Cl quench of a Grignard). Quenches are often exothermic — careful timed dropwise addition is essential to prevent thermal runaway, boiling, or fire.