Fischer esterification
Entry posted by crazyboy25
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Esters often have a fruity smell and are used in flavoring and perfume. Fischer esterification a type of esterification and the process of forming an ester by refluxing a carboxylic acid and an alcohol in the presence of an acid catalyst. Carboxylic acids are organic acids characterized by the presence of a carboxyl group. Carboxylic acids include formic acid, aceitc acid, benzoic acid, butyric acid, salicylic acid and anthranilic acid. An alcohol is any organic compound in which a hydroxyl group (-OH) is bound to a carbon atom of an alkyl or substituted alkyl group. Alcohols include isopropyl alcohol, ethanol, octyl alcohol and methyl alcohol.
A common ester commonly synthesized is methyl salicylate; an ester with an intense minty smell. It is relatively easy to determine what a simple ester is made of. The first part is the alcohol group, the second the carboxylic acid. The prefix "methyl-" indicates this ester is made from methyl alcohol (methanol) and the suffix "-salicylate" tells us the carboxyl acid (salicylic acid).
Most alcohols can be refluxed with carboxylic acids in the presence of sulfuric acid to produce an ester. Keep in mind however similar alcohols with the same carboxylic acid will often smell similar (methyl and ethyl alcohol are only 1 carbon apart so methyl and ethyl salicylate both smell minty although they may be slightly different).
Synthesis of methyl salicylate.
Step 1: extraction of acetylsalicylic acid (ASA) from aspirin
Step 2: synthesis of salicylic acid (SA) via hydrolysis of ASA
Step 3: synthesis of methyl salicylate
Step 4: purification of methyl salicylate (optional)
Step 1: extraction of acetylsalicylic acid (ASA) from aspirin
ASA is found in aspirin tablets along with a small amount of talc, starch and binders. To separate the ASA from the impurities the tablets are crushed. The crushed tablets are added to warm isopropyl alcohol. Most of the solids will dissolve and a small amount will not (the undissolved solids are the binders) the solution is filtered and the solids discarded. The isopropyl alcohol can be boiled to reduce its volume then cooled to crystallize the pure ASA.
Step 2: synthesis of salicylic acid (SA) via hydrolysis of ASA
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10g ASA are added to a 1L erlenmeyer flask. 700ml hot water are added and the ASA dissolves with stirring and gentle heating. A small amount of concentrated hydrochloric acid is slowly added until a ph of 2 is reached. Several boiling stones are added to promote even boiling and the mixture is heated to a light boil for one hour. The solution is poured into a 600l beaker and SA precipitates as the solution cools.
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The fluffy mass is filtered and washed with 200ml ice cold water. Yield: 5.15g
Step 3: synthesis of methyl salicylate
5g SA are added to a 500ml round bottom flask. To this is added 50ml methanol. 6ml sulfuric acid is slowly added drop wise. Several boiling stones are added to promote even boiling. The boiling flask is fitted with a condenser and the solution is refluxed with a heating mantle for four hours.
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The resulting solution is methyl salicylate with a small amount of sulfuric acid.
Step 4: purification of methyl salicylate (optional)
The methyl salicylate can be purified by washing with water and sodium bicarbonate solution followed by distillation.
Other esters include:
Banana (isoamyl acetate)- isoamyl alcohol and acetic acid
Apricot (isoamyl butyrate)- isoamyl alcohol and butyric acid
Apple (methyl butyrate)- methyl alcohol and butyric acid
Grape (methyl anthranilate)- methyl alcohol and anthranilic acid
Honey (ethyl phenylacetate)- ethyl alcohol and phenylacetic acid
'Juicy Fruit' (isopentyl acetate)- isopentyl alcohol and acetic acid
Orange (octyl acetate)- n-octyl alcohol and acetic acid
Peach (benzyl acetate)- benzyl alcohol and acetic acid
Pear (n-propyl acetate)- n-propyl alcohol and acetic acid
Pineapple (butyl butyrate)- butanol and butyric acid
Pineapple (isoamyl salicylate)- isoamyl alcohol and salicylic acid
Raspberry (isobutyl formate)- isobutyl alcohol and formic acid
Rum (isobutyl propionate)- isobutyl alcohol and propionic acid
Walnut (ethyl valerate)- ethyl alcohol and valeric acid
Wintergreen (methyl salicylate)- methyl alcohol and salicylic acid
Fruity (ethyl benzoate)- ethyl alcohol and benzoic acid
They can be produced by following about the same procedure.
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