[Dan]

Hi,

I am trying to find a reference book for pKa/pKb tables of organic compounds.

At the moment I've only been able to find fairly extensive pKa tables, which is fine but I really would like tabulated pKb's for very weak bases such as carbonyls, alcohols, ethers, phosphines, thiols, thioethers etc. Ideally in protic and non-protic solvents.

Obviously pKa tables which extend to things like oxonium/ammonium/sulfonium/phosphonium ions/salts etc. will be fine but I haven't yet found anything this far-reaching.

It would be very useful as a teaching aid to have a resource of this kind.

Does such a collection exist? Am I living in a dream world?

Dan

[Borek]

I did some searching on several occasions. My access to literature is very limited, so I can't say I know everything - but I am not aware of such a collection.

[renge ishyo]

I have not seen a book that gives extensive pKa and pKb tables together. In fact, I was told from a professor that the reason that book sources only list pKa values in tables is that you can always calculate pKb using the appropriate pKw value given for water together with the relationship pKw = pKa + pKb. This fact allows books to save a ton of space by omitting "redundant" pKb values from tables. There are a lot of things like this in scientific data books (i.e. a lot of the data books I have provide only "baseline" thermodynamic quantities because they expect that you know how to calculate the derived quantities from them).

You won't be able to easily find pKa or pKb values for non-aqueous solvents because the concentration of water (approx. 55M) was actually multiplied into the equilibrium constant to obtain the Ka or Kb at some point when these quantities were derived.

[Borek]

I am more than sure Dan will be satisfied with book containing only pKa values

[Dan]

the reason that book sources only list pKa values in tables is that you can always calculate pKb

Yes, but the problem is I can't find the pKa values i want either. Say for example I want a quantitative value for the basicity of ethanol - in this case I need the pKa value for the ethyloxonium ion to calculate the pKb of ethanol. The pKa for free ethanol is no use to me in this situation - it allows me to calculate the pKb of ethoxide but that's not what I need. I want a table that gives the pKbs of weak bases or a pKa table that extends to the conjugate acids of these weak bases.

[renge ishyo]

That sort of table specifically may be hard to come by as a lot of times strong "+" charged species such as an ethyloxonium ion have negative pKa's that are "off the scale" and are obtained theoretically in many cases because they are too transiently formed to obtain reliable experimental measurements. Even H₃0⁺ has a pKa of -1.7 and only because of it's importance does it end up on pKa tables like the following:

http://research.chem.psu.edu/brpgroup/pKa_compilation.pdf

I see what you mean though, no pKa tables are "complete" because in a sense they limit themselves to pKa values that correspond to the standard pH ranges of 1-14, listing negative values of pKa's only rarely and merely classifying such species as "strong" if they fall off the chart (or very weak if they are far above 14). It would be an interesting project for someone to try and tabulate pKa values for strong acids (or very weak bases) like you desire, but it would be quite expensive I should think as it would require sensitive instruments.  The payoff would also be small, because the 100% approximation for such species is sufficiently accurate to handle them anyways.

[Dan]

It would be an interesting project for someone to try and tabulate pKa values for strong acids (or very weak bases) like you desire, but it would be quite expensive I should think as it would require sensitive instruments.

Yeah, this is what I thought and I was wondering if it had been done. I suppose the answer is not on the scale I was looking for... Thanks for your input.

[daloy]

Another source of pKa's is the U W chem website: http://www.chem.wisc.edu/areas/reich/pkatable/index.htm