Alkoxide metathesis

Question

I am attempting a synthesis for acetylacetone. The preparation I wish to carry out is described on orgsynth by condensation of acetone and ethyl acetate with a base catalyst.

The problem for me is that I only have $\ce{t-BuOK}$, no THF and $\ce{t-BuOH}$ in sight, only $\ce{EtOH}$. First I searched for solubility of $\ce{t-BuOK}$ in ethanol, only to find nothing. It gave me some ideas why there is no data for the solubility so I assumed already that they react (Why didn't I think of this in the first place). I instantly looked up for this procedure but I could not find anything satisfactory for this specific reaction, only patents about metathesis reactions of alkoxides with higher carbon chain alcohols. On the Wikipedia site there is a line of information that was somewhat useful, which states that "many alkoxides are prepared by salt metathesis from sodium ethoxide", but still not satisfactory since its the reverse what I am looking for.

The $\mathrm{p}K_\mathrm{a}$ of $\ce{EtOH}$ is 15.9 while $\mathrm{p}K_\mathrm{a}$ of $\ce{t-BuOH}$ is 16.5 in water. Looking at the values in DMSO the value of $\ce{EtOH}$ is still lower, so perhaps it can be generally stated the ethanol molecule has more tendency to deprotonate. Assuming and without cited literature by using excess $\ce{EtOH}$ (and as a solvent of course) I am expecting them to produce $\ce{EtOK}$ and $\ce{t-BuOH}$ by equilibration the mixture. I think that which base I use does not really matter in the reaction, but I'm short of solvents for solving $\ce{t-BuOK}$ efficiently and a little tertiary alcohol wont mess up my experiment. I am very confident about this simple metathesis reaction, but I would like to hear your ideas too before doing anything.

So my question, in short is the following: Will $\ce{t-BuOK}$ react with $\ce{EtOH}$ to produce $\ce{EtOK}$ and $\ce{t-BuOH}$?

I am of course aware of the dangers of these compounds, and have a basic experience in doing simple preparations like these.

Answer 1

The answer is yes, it will be in following equilibrium:

$$\ce{EtOH + t-BuO- <=>[$K$] EtO- + t-BuOH}$$

$$K = \frac{[\ce{EtO-}][\ce{t-BuOH}]}{[\ce{EtOH}][\ce{t-BuO-}]} = \frac{[\ce{EtO-}][\ce{H3O+}]}{[\ce{EtOH}]} \times \frac{[\ce{t-BuOH}]}{[\ce{t-BuO-}][\ce{H3O+}]} = \frac{K_\mathrm{a}(\ce{EtOH})}{K_\mathrm{a}(\ce{t-BuOH})} \\ = \frac{1.26 \times 10^{-16}}{3.16 \times 10^{-17}} \approx 4$$

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Edit:

Although the individual $\mathrm{p}K_\mathrm{a}$ values used to determine the $K$ in this equilibrium are calculated for solutions in water (some of those are only available in DMSO other than water), I assumed the ratio might be closer to the real value. However, an empirical conversion method that transforms $\mathrm{p}K_\mathrm{a}$ values of arbitrary organic compounds from one solvent to the other is introduced in this reference (Ref.1). Unfortunately, the full paper is behind paywall, but its abstract states that:

An empirical conversion method (ECM) that transforms $\mathrm{p}K_\mathrm{a}$ values of arbitrary organic compounds from one solvent to the other is introduced. We demonstrate the method’s usefulness and performance on $\mathrm{p}K_\mathrm{a}$ conversions involving water and organic solvents acetonitrile ($\ce{MeCN}$), dimethyl sulfoxide ($\ce{Me2SO}$), and methanol ($\ce{MeOH}$). We focus on the $\mathrm{p}K_\mathrm{a}$ conversion from the known reference value in water to the other three organic solvents, although such a conversion can also be performed between any pair of the considered solvents. The ECM works with an additive parameter that is specific to a solvent and a molecular family (essentially characterized by a functional group that is titrated). We formally show that the method can be formulated with a single additive parameter, and that the extra multiplicative parameter used in other works is not required. The values of the additive parameter are determined from known $\mathrm{p}K_\mathrm{a}$ data, and their interpretation is provided on the basis of physicochemical concepts. The data set of known $\mathrm{p}K_\mathrm{a}$ values is augmented with $\mathrm{p}K_\mathrm{a}$ values computed with the recently introduced electrostatic transform method, whose validity is demonstrated. For a validation of our method, we consider $\mathrm{p}K_\mathrm{a}$ conversions for two data sets of titratable compounds. The first data set involves 81 relatively small molecules belonging to 19 different molecular families, with the $\mathrm{p}K_\mathrm{a}$ data available in all four considered solvents. The second data set involves 76 titratable molecules from 5 additional molecular families. These molecules are typically larger, and their experimental $\mathrm{p}K_\mathrm{a}$ values are available only in $\ce{Me2SO}$ and water. The validation tests show that the agreement between the experimental $\mathrm{p}K_\mathrm{a}$ data and the ECM predictions is generally good, with absolute errors often on the order of 0.5 $\mathrm{pH}$ units. The presence of a few outliers is rationalized, and observed trends with respect to molecular families are discussed.

For example, $\mathrm{p}K_\mathrm{a}$ values of phenol in water, DMSO, methanol, and acetnitrile are illustrated in following diagram:

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Reference:

1. Emanuele Rossini, Art D. Bochevarov, Ernst Walter Knapp, "Empirical Conversion of $\mathrm{p}K_\mathrm{a}$ Values between Different Solvents and Interpretation of the Parameters: Application to Water, Acetonitrile, Dimethyl Sulfoxide, and Methanol," ACS Omega 2018, 3(2), 1653–1662 (https://doi.org/10.1021/acsomega.7b01895).