# What mixing ratio of ethanol and acetone has the lowest freezing point?

I am in the lab trying to make a sample for 1H NMR. It has to remain liquid at the lowest possible temperature.

I was recommended to use a mixture of ethanol and acetone because when they're mixed in the right proportions, the mixture has a very low freezing point.

I can not find this proportion anywhere. Does anyone know where to look for these things?

Here is a picture of what I'm looking for, but with ethanol and acetone instead of water - solvent:

PD:it's very likely that its methanol instead of ethanol, please let me know... I have access to both, I just want the one that will go to the lowest temp.

• Wikipedia has this table en.wikipedia.org/wiki/List_of_cooling_baths – porphyrin Jun 4 '19 at 10:27
• if you need a glass try ethanol, diethyl ether, isopentane in 2:2:5 or 1:4;4 ratio , (EPA glass). – porphyrin Jun 4 '19 at 10:36
• I assume you want to use this as a solvent, right? There's a good chance that whatever it is precipitates at 140K. Otherwise still be prepared to see a spectrum that is not quite as well resolved than at room temperature. – Karl Jun 7 '19 at 21:36

its me again, I want to post the answer I found because I think it might be useful for somebody in the future; it appears a 2:3 molar acetone:methanol proportion gives the lowest freezing temperature ~158 K (see attached picture below).

It appears the difficulty finding these curves was because they are usually called "solid-liquid equilibrium" curves instead of "freezing point curves", as its the same physical situation (Explanation Here)

There is a large database of these in the following link.

EDIT: As commented by "Ivan Neretin", ethanol-acetone mixtures are also good for low freezing temperatures:

• Note that ethanol alone would get you about that low, and ethanol+acetone lower yet, though not by much. – Ivan Neretin Jun 7 '19 at 10:23

In your question, you didn't mention how low freezing temperature solvent system you are looking for instead of telling that the solvent has to remain liquid at the lowest possible temperature. And, Ivan Neretin mentioned that ethanol alone would get you about freezing temperature close enough to get you any ethanol+acetone solvent would get. For example, freezing point of ethanol is about $$\pu{159 K}$$, when compared to ~$$\pu{155 K}$$, the reported freezing point of ethanol:acetone (83:17) system (lowest of the system; see the chart given in your answer). Yet, freezing point of pure diethyl ether is $$\pu{150.6 K}$$, lower than the lowest achieved in acetone/ethanol system. Thus, I decided to list some low temperature systems for your convenience (Ref.1 & 2):

$$\begin{array}{ccc}\hline \text{Solvent} &\text{Solute} & \text{Solvent mole fraction} & \text{Freezing point in}\; \pu{K} \\\hline \text{diethyl ether} & \text{none} & 1.0000 & 150.61 \\ \text{diethyl ether} & \text{acetone} & 0.9737 & 149.53 \\ \text{diethyl ether} & \text{carbon disulfide} & 0.9615 & 149.53 \\ \text{diethyl ether} & \text{methanol} & 0.9586 & 149.34 \\ \text{diethyl ether} & \text{acetone} & 0.9512 & 148.85 \\ \text{carbon disulfide} & \text{toluene} & 0.9393 & 157.30 \\ \text{ethanol} & \text{none} & 1.0000 & 157.93 \\ \text{ethanol} & \text{methanol} & 0.9783 & 156.37 \\ \text{ethanol} & \text{methanol} & 0.9704 & 155.59 \\ \text{ethanol} & \text{water} & 0.88 & 151 \text{ (Ref.2)} \\ \text{methanol} & \text{water} & 0.82 & 155 \text{ (Ref.2)} \\ \hline \end{array}$$

Note that last two entries on the table are from the charts in Ref.2, which are purely approximate values.

References:

1. M. Shinroku, “The Heats of Fusion of some Organic Solvents Whose Melting Points are Relatively Low,” Bulletin of the Chemical Society of Japan 1926, 1(2), 30–34 (https://doi.org/10.1246/bcsj.1.30).
2. K. Takaizumi, T. Wakabayashi, “The Freezing Process in Methanol-, Ethanol-, and Propanol-Water Systems as Revealed by Differential Scanning Calorimetry,” Journal of Solution Chemistry 1997, 26(10), 927–939 (https://doi.org/10.1007/BF02768051).