method 1:
Take a briquette of menthol (usually about 80-100 mg), dissolve that in dry THF (~2 mL) and then add 1-2 mg (you don't need to really weight it) of triphenylmethane. You can roughly calculate how much of your lithium reagent you will need, and then add it dropwise to the solution of menthol/Ph3CH/THF. When all the menthol is deprotonated the triphenylmethane will be deprotonated abnd the solution will turn pink (eventually dark red if you add to much), then you can back calculate the concentration based on the volume of alkyl lithium you added. I usally carry this procedure out in triplicate ad average the results. It really only takes about 30 mins start to finish and it doesn't take much material either.
note:
1,1'-dipyridyl can also be used instead of triphenylmethane.
a link:
http://www.chemistry.mcmaster.ca/emslie/Titrating%20Alkyllithium%20Reagents%202.pdf
Friday, January 16, 2009
Subscribe to:
Post Comments (Atom)
3 comments:
Wow! This is an amazing resource. Thanks for the link.
What the hell is 1,1'-dipyridyl ?? This compound cannot exist without counter ions (1,1' would have a N-N bond at the pyridine nitrogens which would both therefore be positively charged). Do you mean 2,2'-bipyridine?
yes, it is 2,2'-bipyridine.
1,1'-dipyridyl is the old name, which can only be found on some very old bottle.
Post a Comment