Table of Contents
Objetives
Perform an isomerization reaction of C=C double bonds in acidic medium.
Background
Double bonds are rigid structures where interconversion between Z- and E-isomers (cis and trans) does not occur. However, in acidic media protonation of the double bond can occur, with a consequent change in hybridization.
Then, (unlike the π double bond) the σ bond allows rotation of the substituents around the bond, which through an additional loss of protons regenerates the double bond again. Under equilibrium conditions, the thermodynamically most stable double bond is formed. Maleic acid is isomerized to fumaric acid by heating with acid catalysis.
Experimental procedure
In a conical vial fitted with a rotating paddle, place 2 g of maleic acid, 3 mL of deionized water and 2.5 mL of concentrated HCl. Attach the vial to a condenser and reflux with stirring for 20 min. A precipitate will appear and become more visible when the reaction liquid cools after the reflux time is completed.
After reaching room temperature, separate the precipitate completely by vacuum filtration. Recrystallize the solid in water; dry, weigh and determine the yield (melting point = 130 °C) and calculate the reaction yield (estimated 85 %). Verify the purity of the product by CCF using ethyl acetate / EtOH (absolute) (1: 1) as eluent.
International Chemical Identifier
The IUPAC InChI key identifiers for the main compounds used in this experiment are provided to facilitate the nomenclature and formulation of chemical compounds and the search for information on the Internet for these compounds.
| ethyl acetate | XEKOWRVHYACXOJ-UHFFFAOYSA-N |
| fumaric acid | VZCYOOQTPOCHFL-OWOJBTEDSA-N |
| maleic acid | VZCYOOQTPOCHFL-UPHRSURJSA-N |
| EtOH | LFQSCWFLJHTTHZ-UHFFFAOYSA-N |
| HCl | VEXZGXHMUGYJMC-UHFFFAOYSA-N |
