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Wittig olefination: methyltriphenylphosphonium bromide + benzaldehyde → styrene

[Ph3P=CH2] + Ar–CHO → Ar–CH=CH2 + Ph3P=O

Canonical Wittig olefination — the textbook 'make an alkene from an aldehyde' demo. The ylide (methylenetriphenylphosphorane) is generated in situ from methyltriphenylphosphonium bromide + base (typically n-BuLi at −78 °C, or NaH in DMSO), then reacts with benzaldehyde to give styrene. The triphenylphosphine oxide byproduct precipitates from cold ether and is the diagnostic end-of-reaction signal.

Conditions: Step 1 — Suspend Ph3P+CH3 Br− (1.05 equiv) in dry THF under N2; cool to −78 °C; add n-BuLi (1.05 equiv, 2.5 M in hexanes) dropwise. Stir 30 min — solution turns yellow-orange (ylide formation). Step 2 — Add benzaldehyde (1.0 equiv) dropwise; warm to RT over 1–2 h; stir 4–12 h. Workup — Quench with sat. NH4Cl; extract with Et2O; wash brine; dry MgSO4. Concentrate carefully (styrene is volatile, bp 145 °C). Triphenylphosphine oxide precipitates from cold pentane/ether — filter off. Distil residue under reduced pressure for clean styrene.

Expected yield: 70–88 %
Expected duration: 4–12 h at RT after −78 °C ylide formation

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Anchor reagent — fix this amount, scale everything else Substrate concentration · M

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Reactants

Reactants for Wittig olefination: methyltriphenylphosphonium bromide + benzaldehyde → styrene: stoichiometric quantities derived from the anchor amount.
Reagent	Equiv	Moles · mmol	Mass · g	Volume · mL
1779-49-3 1779-49-3 · C19H18BrP density unavailable — volume not calculable.	1.05	105.00	37.509	—
Benzaldehyde 100-52-7 · C7H6O	1.0	100.00	10.612	10.11

Solvent

Solvent for Wittig olefination: methyltriphenylphosphonium bromide + benzaldehyde → styrene: stoichiometric quantities derived from the anchor amount.
Reagent	Equiv	Moles · mmol	Mass · g	Volume · mL
109-99-9 109-99-9 · C4H8O	—	5060.32	364.900	410.00

Product

Product for Wittig olefination: methyltriphenylphosphonium bromide + benzaldehyde → styrene: stoichiometric quantities derived from the anchor amount.
Reagent	Equiv	Moles · mmol	Mass · g	Volume · mL
Styrene 100-42-5 · C8H8	1.0	100.00	10.415	11.45

Expected isolated yield

What you should actually weigh out of the recrystallisation flask, scaled from the limiting reactant via the canonical-procedure yield window.

Product: Styrene 100-42-5 · C8H8
Theoretical max: 10.42 g (100.00 mmol)
Expected isolated · 70–88 % yield: 7.29 – 9.17 g

Stoichiometry: moles_X = (moles_anchor / equiv_anchor) × equiv_X. Mass = moles × MW; volume = mass / ρ. Solvent volume = total reactant moles ÷ substrate concentration.

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Stoichiometry Calculator Limiting reagent, theoretical yield, and reaction quantities with full unit propagation. Molar Mass Calculator Molecular weight and percent composition to weigh out each reagent. Chemical Equation Balancer Balance the reaction before you scale it. Fractional Distillation Predictor Plan the work-up — predict which fractions distil and where azeotropes bite.