[Ak]

1. List the types of alkyl halides that can be used to prepare a triphenylphosphonium bromide and explain why only these halides are allowed.

ok so this question is talking about wittig preparation right? and if tht is correct then what i know is tht primary alkyl halides work best and secondary alkyl halides work but give poor yields.  I think aromatic halides also work well.  Is there anything that I'm missing, and did i understand the question.  Thanks

[azmanam]

Aromatic halides are not reactive enough to give a phosphonium salt.  I think you understand the question fine, but you haven't answered why. 

One thing, though.  'wittig preparation' is probably colloquially ok, but not a technical term.  We're preparing phosphonium salts, or perhaps 'Wittig salts', but we aren't forming phosphorus ylides.  It is the ylide that participates in the Wittig reaction.