digglover wrote:Quote:In the classroom, maleic acid is transformed into Fumaric acid through the process of heating the maleic acid to a high temperature in a 12mol HCl solution. The heated molecule loses a water molecule and becomes an acid anhydride while in the heated solution. Once the heat is removed, the acid anhydride takes back the water molecule, but reforms as fumaric acid, the more stable isomer of butenedioic acid. This isomer is more stable because the carboxyl groups are no longer on the same side of the molecule, but are now on opposite sides, causing the molecule to become non-polar. That is why it comes out of the polar HCl solution, as a polar solvent will not dissolve a non-polar solute.
Source: wikipedia
this is the only post here mentioning this, for good reasons yes i know since maleic is not so common either, but let me tell you my experience with this anyways, since i have lots of maleic acid and wanted some fumaric. many .edu sites will have this conversion because it is very simple and is a useful teaching experiment. concentrations and everything is not very important IME. this is summarized from Durst's Experimental Organic Chemistry:
dump 10 g. maleic acid in a 125 ml. Erlenmeyer, add 30 ml. 24% HCl, and heat gently with swirling.
after dissolving, heat strongly for 30 minutes and cool to room temp.
filter the fumaric acid precipitate and wash it on the filter with cold water.
recrystallization from 1N HCl gives pure product.
but really this is so easy measuring anything is not required, the maleic acid can be dissolved in water and heated with excess HCl, precipitation of fumaric acid being copious and fast. do not heat so much that you rust out everything you own with HCl fumes. recrystallize from boiling water to give fumaric acid which contains some water, oven drying at 250F removes most if not all water.
i noted that dissolving some of this acid in acetone and evaporating in air, some discolored acid was produced, leaving me wondering if fumaric acid gives a little aldol condensation of acetone.