An ester is a chemical that is formed when an organic acid reacts with an alcohol. Esters frequently have distinctive odors, and are found in the flavorings of many fruits and plants. The general form of a reaction between an organic acid and an alcohol is shown below:
Organic Acid + Alcohol Ester + Water
In the formulas above, R and R’ represent general groups of hydrocarbons. The circled groups on the acid and alcohol combine to form water, and the pieces left behind form the ester. A little bit of concentrated sulfuric acid is added as a catalyst, and also to remove the water molecules as they are formed. Click here for a list of alcohols used in this lab, and their formulas. Click here for a list of acids used in the lab, and their formulas.
If methyl alcohol is combined with acetic acid, the result is called methyl acetate. This is a systematic way of naming any ester from the compounds from which it was made.
In today’s activity you will be preparing small samples of several different esters. For each combination you will record the appearance, odor, and name.
|acids as listed in the data table||alcohols as listed in the data table|
|small test tubes||250 mL beaker|
|400 mL beaker||hot plate or Bunsen burner|
|ring stand & wire gauze||concentrated sulfuric acid|
|baking soda (for acid spills)|
|N||The concentrated acetic acid is “corrosive to flesh” and the concentrated sulfuric acid can cause severe skin burns. Use caution when handling them.|
|N||Besides being poisons, the alcohols are flammable. Do not heat directly over a flame – always use a water bath.|
|N||Methyl alcohol is absorbed through the skin. It attacks the optic nerve and can cause blindness, and the liver metabolizes it into formaldehyde.|
|N||Remember to smell your products by wafting them, not smelling them directly.|
|methyl alcohol||+ acetic acid, benzoic acid, salicylic acid, 2-aminobenzoic acid|
|ethyl alcohol||+ acetic acid, benzoic acid, salicylic acid|
|iso-amyl alcohol||+ acetic acid, benzoic acid, salicylic acid|
|Alcohols:||n-propanol, isopropyl alcohol, n-decyl alcohol, methyl alcohol, ethyl alcohol, iso-amyl alcohol, n-butyl alcohol, t-butyl alcohol, and sec-butyl alcohol|
|Acids:||salicylic acid, acetic acid, sulfanilic acid, stearic acid, fumaric acid, citric acid, benzoic acid, p-aminobenzoic acid, nicotinic acid, lauric acid|
|acetic acid +||n-propanol, isopropyl alcohol, n-butyl alcohol, t-butyl alcohol, and sec-butyl alcohol|
|Alcohol||Acid||Ester||Description of Odor|
Follow Up Question
Can you think of any products in your house that might contain esters? List a few of them, and check their ingredients. Are any esters listed? [You must list at least four products that you think contain esters, but you get bonus points for any ingredient lists that you bring in listing esters.]
[MHS Chem page]