[lukas.stib]

Hello chemists,

I mixed malic acid, excess ethanol and H2SO4 as a catalyst. I refluxed for about 1 hour and 15 minutes, then distilled to remove ethanol. I took everything to about 92°C (my thermometer is probably not accurate); I distilled mix of alcohol, diethyl ether, water and about a little diethyl malate. I now have a mixture of thick, brown liquid with (maybe) product and H2SO4. How can I best separate the product? I don't want to use water; I'm afraid everything will dissolve. Should I use salt water?

Thanks very much.

[AWK]

Diethyl malate boils at 92°C at 1 mm Hg.

[lukas.stib]

I don't want to use low pressure or vacuum distillation. I have not adaptation for that.

[AWK]

Synthesis does not start by mixing reagents. Before starting the synthesis, you need to develop a method adapted to your laboratory conditions.
As we can see, your method is mainly wasting reagents. This method seldom manages to synthesize something, but you can learn a lot from your mistakes.
I hope so?

[kriggy]

Synthesis does not start by mixing reagents. Before starting the synthesis, you need to develop a method adapted to your laboratory conditions.
As we can see, your method is mainly wasting reagents. This method seldom manages to synthesize something, but you can learn a lot from your mistakes.

Although this migh sound harsh its great advice.

Anyway, few points
1) I think the diester should be reasonably insoluble in water and you could extract it into suitable solvent
2) I think the acidic condition and elevated temperature can easly dehydrogenate your starting material / product leaving you with fairly common brown/black

[rolnor]

Is it not possible to get ring-closed dimer of this acid?

[wildfyr]

Sounds like it can easily aldol condense.

I do think that the desired product is insoluble in water, and a lot of the side products and starting materials will have some solubility in water.

[Babcock_Hall]

Are you following a literature protocol?

[lukas.stib]

Thank you very much for your answers. I will use water and I will see.

[AWK]

You have tried to obtain esters by the Fischer-Speier method known for 125 years and well described in many textbooks of practical organic chemistry.
Esterification is an equilibrium reaction; therefore a large excess of cheaper reagent is used (5-10 times). Usually the reaction is carried out under reflux. The reaction time depends on the temperature reached - for ethyl esters, the time is about 10 hours. As a catalyst, usually concentrated sulfuric acid, hydrochloric acid or solid p-toluenesulfonic acid is used (hydrochloric acid was used by Fischer for malic acid esterification).
The reaction mixture must be neutralized before further processing - Fischer used sodium or potassium carbonate (NaHCO₃ also can be used).
Further processing of the reaction mixture is carried out differently depending on the properties of the ester (usually they can be predicted or found in manuals) - usually it is extraction (e.g. ethyl acetate), followed by distillation or crystallization.
Although diethyl malate can be distilled under normal pressure, an air cooler and inert gas atmosphere must be used to prevent oxidation or even ignition of ester vapors (boiling point ~ 250°C expected).
With a vacuum obtained by a good water pump, you can use an ordinary cooler without cooling water (expected boiling point of the ester ~ 150°C).

I distilled mix of alcohol, diethyl ether, water and about a little diethyl malate

In this procedure, the temperature is too low for ethyl ether to form.

[lukas.stib]

I used more water, and at the bottom is a brown liquid, which will probably be an ester. But it is very little, according to the stoichiometry I could get 56 g, this is very little. Maybe it dissolved a lot in water, or it was destroyed by H2SO4, or the reaction time was short.

I wanted to neutralize, but I used only clean water.

I did many ester syntheses, but most of them were simple carboxyl esters. Acids, where I used a shorter reaction time in the range of 1-2 hours, and without problems. It is more difficult with tartaric and malic acid.

But, thank you very much for your very interesting informations, you help me very much.

Lukáš S. from the Czech Republic.