Ethyl_acetate

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Ethyl acetate

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Ethyl acetate (systematically, ethyl ethanoate, commonly abbreviated EtOAc or EA) is the organic compound with the formula CH₃COOCH₂CH₃. This colorless liquid has a characteristic, pungent smell (similar to pear drops) like certain glues or nail polish removers, in which it is used. Ethyl acetate is the ester from ethanol and acetic acid; it is manufactured on a large scale for use as a solvent.

Properties

Ethyl acetate is a moderately polar solvent that has the advantages of being volatile, relatively non-toxic, and non-hygroscopic. It is a weak hydrogen bond acceptor, and is not a donor due to the lack of an acidic proton (one directly bonded to an electronegative atom such as fluorine, oxygen, or nitrogen). Ethyl acetate can dissolve up to 3% water and has a solubility of 8% in water at room temperature. At elevated temperature its solubility in water is higher. It is unstable in the presence of strong aqueous bases and acids.

Preparation

Ethyl acetate is synthesized via the Fischer esterification reaction from ethanol and acetic acid, typically in the presence of an acid catalyst such as concentrated sulfuric acid.

CH₃CH₂OH + CH₃COOH → CH₃COOCH₂CH₃ + H₂O

It can also be prepared through Tishchenko reaction, by combining two equivalents of acetaldehyde in the presence of an alkoxide base as catalyst. This way is a commercial method of producing ethyl acetate.

CH₃CHO + CH₃CHO → CH₃COOC₂H₅

Industrial production

Industrially, ethyl acetate can be produced by the catalytic dehydrogenation of ethanol. For cost reasons, this method is primarily applied to conversion of surplus ethanol feedstock as opposed to predetermined generation on an industrial scale. In addition, it is commonly accepted as far less practical and less cost effective.

Catalysts for dehydrogenation include copper, operating at an elevated temperature but below 250 °C. The copper may have its surface area increased by depositing it on zinc, promoting the growth of snowflake, fractal like, structures. This surface area can be again increased by deposition onto a zeolite, typically ZSM-5. Traces of rare earth metals or alkalies, such as that of sodium and potassium, have also been found to be beneficial to the process. Byproducts of hydrogenation include diethyl ether (thought to primarily arise due to aluminum sites in the catalyst), acetaldehyde, acetaldehyde aldol products, higher esters and ketones. Acetaldehyde and MEK complicate conversion and purification as ethanol forms an azeotrope with water, as does ethyl acetate with ethanol and water and MEK with both ethanol and the acetate. To obtain a high purity product, these azeotropes must be "broken", and this can be achieved by making use of pressure swing distillation.

The composition of the distillate removed from the conversion products is biased towards acetate at atmospheric pressure and ethanol at increased pressure. First, the raw product is fed into a high pressure column where the bulk of the contaminating ethanol is removed. By then feeding the ethanol depleted distillate into a low pressure column, the acetate can be removed from the remaining ethanol azeotrope.

MEK forms during the conversion process from 2-butanol. The latter fails to form an azeotrope with the acetate and so MEK can be removed by hydrogenation of the contaminated product over nickel and further distillation to strip away 2-butanol. This provides the simultaneous benefit of removing the acetylaldehyde contaminant by returning it to an ethanol form and is easily accomplished as hydrogen is a byproduct of the initial dehydrogenation process.

It may also be possible to break the azeotropes with the use of membrane distillation, molecular sieves, an entrainer or absorption medium.

The distilled ethanol and rehydrogenated contaminants can then be recycled into the raw feedstock.

Uses

Solvent

Ethyl acetate is primarily used as a solvent. For example, it is commonly used to clean circuit boards to wash away any remaining flux residue, to dissolve the pigments for nail varnishes, and is responsible for the solvent-effect of some nail varnish remover (acetone and acetonitrile are also used). Industrially it is used to decaffeinate coffee beans and tea leaves. It is also used in paints as an activator or hardener.

In the laboratory, mixtures of ethyl acetate and other solvents are commonly used in chromatography. It is also used as a solvent for extractions. Ethylacetate is rarely selected as a reaction solvent because it is prone to hydrolysis.

Like most simple esters, ethyl acetate has a fruity smell. Ethyl acetate is present in confectionery, perfumes, and fruits. In perfumes, it evaporates quickly, leaving but the scent of the perfume on the skin.

Occurrence in wines

Ethyl acetate is the most common ester found in wine, being the production of the most common volatile organic acid-acetic acid and the ethanol alcohol created during the fermentation of wine. The aroma of ethyl acetate is most vivid in younger wines and contribute towards the general perception of "fruitiness" in the wine. Sensitivity varies with most people having a perception threshold around 120 mg/l. Excessive amounts of ethyl acetate is considered a wine fault. Exposure to oxygen can exacerbate the fault due to the oxidation of ethanol creating acetaldehyde. This can leave the wine with a sharp vinegar like taste.

Other uses

In the field of entomology, ethyl acetate is an effective poison for use in insect collecting and study. In a killing jar charged with ethyl acetate, the vapors will kill the collected (usually adult) insect quickly without destroying it. Because it is not hygroscopic, ethyl acetate also keeps the insect soft enough to allow proper mounting suitable for a collection.

Reactions

Ethyl acetate can be hydrolyzed in acid or basic conditions to regain acetic acid and ethanol. The use of an acid catalyst such as sulfuric acid gives poor yields due to it being an equilibrium — the reverse reaction of the Fischer esterification.

To obtain high yields, it is preferable to use a stoichiometric amount of strong base, such as sodium hydroxide. This reaction gives ethanol and sodium acetate, which is not able to react with ethanol any longer:

CH₃CO₂C₂H₅ + NaOH → C₂H₅OH + CH₃CO₂Na

References

Chembytes e-zine - Team effort: Steve Colley describes work to develop a new route to make ethyl acetate starting from low grade renewable feedstocks (2001)

Ingenia Online - Renewable Processing: The Green Alternative; Using Bio-Ethanol To Manufacture An Industrial Solvent by Mike Ashley (Issue 29, 2006)

Some industrial plants use Ethylene----> Acetic Acid in the presence of an tungstasilic acid on a silica support. This is the catalyst and the Exothermic reaction is cooled by water/ethanol/acetic acid.