[nox]

A friend asked me if all organic bases were nitrogen based, I said no and he challenged me to name a few non-nitrogenous organic bases.

The most obvious examples are of course carbon-based ones like BuLi. After further research it seems that certain alkyl phosphines (eg PMe₃ has a pKa of 8.65¹) could be considered as bases. However, I always figured there should be more variety than just C, N, P. And let's not forget that carbon bases are invariably anionic in nature.

So I ask this, can you think of any neutral organic base that is NOT based on nitrogen or phosphorus?


¹JACS, 1960, 82(22), 5791

[Honclbrif]

Carbene

[azmanam]

Neutral alcohols are basic if the price is right (pK_a of protonated alcohols is ~-3ish).  Anything with a pK_a less than ~-3 will be deprotonated by an alcohol (things like mineral acids, etc).

Neutral carbonyl groups (ketones, aldehydes, etc) are basic, again if the price is right.  pK_a of protonated carbonyl groups is also ~-3ish.  Sulfuric acid is readily deprotonated by ketones and aldehdyes to form protonated carbonyl groups.

[Honclbrif]

Let's not forget what Olah taught us: a strong enough acid will protonate methane or xenon.

[nox]

Geez guys now we're just grasping at straws here, I mean if Bob Barker even nitric acid can act as a base!

[Honclbrif]

All acid/base behavior is by definition relative. You need to set your boundary conditions better next time.

[nox]

Fine, let's restrict ourselves to only those bases whose conjugate acid has a pKa of at least 7.

[Åke]

I was hoping to say phosphazenes¹ but then I noticed that phosphorus was not allowed. 

1: http://en.wikipedia.org/wiki/Phosphazene

[nox]

^Those are semi-well known, at least for Schwesinger's P4 base. Regardless, the site of basicity is still at nitrogen, so I would still classify those as nitrogenous bases.

[Åke]

Thanks - I'll look that up. Going down the group 15, I suppose arsines should be at least weakly basic but I'm guessing again: http://en.wikipedia.org/wiki/Triphenylarsine

Edit: Actually, tricyclohexylphosphine or PCy₃ is a stronger base (pK_a = 9.70) than trimethylphosphine (pK_a = 8.75).¹ Thus, tricyclohexylarsine should be a good candidate.

1. Hu, B.; Gay, I. D. ³¹P NMR Investigation of Surface Acidity Using Adsorbed Tricyclohexylphosphine as a Probe. Langmuir 1995, 11, 3845 http://pubs.acs.org/doi/pdf/10.1021/la00010a039