Microwave epoxidation

Purpose + Function of the Microwave Reactor

A microwave reactor heats reactions faster, hotter, and more uniformly than a hot plate.

Why it works:

• Microwaves excite molecules directly

• Causes instant internal heating rather than slow conduction

• Reaction mixture heats evenly (no hot spots)

Why we used it for epoxidation:

• Epoxidation is slow under normal heating

• Microwave dramatically increases rate

• Reaction completes in minutes instead of an hour

• Prevents decomposition because heating is controlled

Arrhenius Equation for Microwave Reactions

• Higher temperature → larger k → faster reaction

• Because microwaves heat the sample drastically, k increases a LOT

• Reaction time is much shorter

How to estimate microwave reaction time:

If a reaction takes 30 minutes at 100 °C:

Microwave at 150 °C might cut it to 5–10 minutes.

You compare relative times using the idea that doubling T (in Kelvin) massively boosts the rate constant.

Interpreting a 3-Lane TLC Plate

Lane 1: Starting material (estragole) Lane 2: Standard epoxide (pure product) Lane 3: Reaction mixture

✔ If Lane 3 matches Lane 2

→ Reaction successful
→ All starting material consumed

✔ If Lane 3 has both starting material AND product

→ Reaction incomplete
→ Needs more time or reagent

✔ If Lane 3 only shows starting material

→ Reaction failed
→ No product formed

✔ Rf interpretation:

• Estragole (starting material) = more polar → lower Rf

• Epoxide (product) = less polar → higher Rf

✔ Spots interpretation:

• Number of spots = number of components

• Spot position = polarity

• Spot height = Rf value

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