Question

Metal alkyl compounds (i.e. those with an alkyl group directly bound to a metal atom) are sometimes pyrophoric. Of the following metal alkyl compounds, which are especially likely to be pyrophoric? The compounds are as follows: tBuLi, tBuMgBr, Et₂Zn, Me₂Hg, MeMn(CO)₅, (Ph₃P)₂PdMe₂.

Answer 1

Answer: Pyrophoric substances are those which can ignite in atmosphere (air or moisture ) spontaneously .

Among the given compound, the Pyrophoric materials are:

1) t-BuLi - it is Pyrophoric (all alkyl lithium are Pyrophoric they react immediately if there is any sort of moisture present) and ignite.

2) t-BuMgBr - it is non Pyrophoric ( many of the grignard reagents are Pyrophoric if in t-BuMgBr , if Br is replaced by Cl it becomes Pyrophoric , pyrophoricity of grignard reagent depend on their reactivity to abstract proton from moisture )

Since alkyl lithium are strong base than grignard reagent , so all alkyl lithium are Pyrophoric but not all grignard reagent.

Note: t-BuMgBr also ignite in atmosphere on long exposure

3) Et_{​​​​​2}​​​​Zn - it is Pyrophoric and immediately catches fire on exposure to atmosphere

4) Me_{​​​​​2}​​​​Hg it is also Pyrophoric compound

5) MeMn(CO)₅ is not Pyrophoric in nature however carbonyl of Co and Fe are Pyrophoric

6)( Ph_{​​​​​3}​​​​P)₂PdMe₂ it is also not Pyrophoric however activated palladium is Pyrophoric.