[DoctorDomo]

I want to deprotonate benzyl alcohol to form the alkoxide ion for use as a nucleophile. Is lithium metal strong enough for an aryl-alkyl alcohol? I reckon the phenyl ring should make the -OH group more acidic, even though theres an aliphatic carbon between the ring and the hydroxy group so it should be easy enough to deprotonate, but when I add Li metal to it, I don't see any H2 evolution. I wanna do this without heating if possible. Anyone here have experience with deprotonating this type of compound?

[discodermolide]

Try using lithium hydride.

[zsinger]

Superbases are your best bet .  Any of the Hydrides (which are super bases) will work.
           -Zack

[DoctorDomo]

It worked, but I had to heat it to about 50C to kick start the reaction which is not the conditions I'm after. Maybe if I'd left it stir overnight, it would have done it at room temperature. I was busy with other things so I didn't watch to see what temperature kick started the reaction.

Someone recommended hydrides to me too. I'm an undergrad with limited experience (only used NaH once) so I'd rather avoid hydrides if I can. But if it will deprotonate my substrates at room temperature, then I'm all for it. I've been looking into non nucleophilic bases like LDA and DBU, but I'll ask my supervisor about hydrides and see what he thinks. Thanks for the suggestions.

[zsinger]

DD,
This is constructive criticism, so take this in a positive manner.  You should, no matter what, always always always note the temperature at which the reaction starts.  Provides much useful data.  LDA is a good one here, would stay away from DBU (just doesn't work as well bc too bulky). 

Word to the wise.  When working with hydrides, use a delivery agent such as Na+(OAc)3BH. (Sodium Tri-Acetoxyborohydride, also known as STAB).  Very non toxic, just cannot be used in aqueous solution as I note.  I learned this from an exceptionally smart chemist on this site.  Check the δH Formation of H2 gas, and you will see quite rapidly why I caution you about super bases.  They are absolutely unpredictable, unless very careful considerations are taken.  Just my .02.
             -Zack

[DoctorDomo]

Cheers zsinger, constructive criticism is what I need. I have limited lab experience, so all this info is a massive help. I'm gonna repeat this pilot reaction a few times to learn more, this time I'll monitor the temperature carefully, and I'll setup another reaction to see if it can be done at room temperature over a longer time period (48 hrs). Mild conditions is what I'm after so I want to avoid super bases like hydrides and LDA.

STAB sounds interesting, I'll run that past my supervisor. When you say it cannot be used in aqueous conditions, do you mean that traces of water in the solvent could cause violent reactions, similar to NaH?

[discodermolide]

I would say that in this case lithium hydride is probably milder than lithium metal. Ultimately you get the same thing but lithium hydride is faster and will avoid potential side reactions that may occur over a protracted period.

[zsinger]

Nah, you just can't use STAB in an aqueous system period.  Only anhydrous. .
                -Z

[clarkstill]

Agreed. There's no reason to use STAB here, it's typically used for reductive aminations as a nucleophilic source of hydride, what you need is a basic one (plus think of the atom economy! molecular weight 212 for a single hydrogen atom!).  NaH is probably the most common base I've seen used to deprotonate alcohols such as yours. It comes as a 60% dispersion in mineral oil which makes it easy to handle without requiring stringently anhydrous conditions (although obviously, as with all the strong bases discussed, it should be treated with respect!), so I'd say its a good bet, and much easier to work with than elemental lithium.