Deducing a Reaction Mechanism for the Isomerization of Maleic acid to fumaric ac
ID: 900633 • Letter: D
Question
Deducing a Reaction Mechanism for the Isomerization of Maleic acid to fumaric acid. I'm completing my organic chemistry lab report and answering questions and I have very confused and would appreciate any help and explanation please. I appreciate it.
Test Tube
Solids
Solvents
Precipitate
A
1.0 g maleic acid
3.0 mL 6 M HCl
Yes
B
1.0 g maleic acid
3.0 mL 3 M H2SO4
No
C
1.0 g maleic acid
0.5 g ammonium chloride
3.0 mL distilled water
No
D
1.0 g maleic acid
0.5 g ammonium chloride
3.0 mL 6 M HCl
Yes
E
1.0 g malic acid
3.0 mL 6 M HCl
No
F
1.0 g maleic acid
1.5 mL distilled water
2.0 mL conc. HBr
Yes
Possible Mechanisms for the Isomerization.
1. Maleic acid is activiated by visible light, and then rearranges to form fumaric acid. In this mechanism, the pi-bond is momentarily broken, allowing for the free rotation to give the more stable trans isomer. The double bond then reforms.
2. The rearrangement of maleic acid to fumaric acid is accomplished by the thermal excitation of the molecule. In this mechanism, the pi-bond is broken by the application of heat. As described above, this would allow rotation to occur and form the more stable trans isomer.
3. A nudeophilic addition of a chloride ion to maleic acid again permits free rotation, followed by release of the Cl- ion to produce fumaric acid.
4. An electrophilic addition of a proton to maleic acid, followed by rotation and then deprotonation.
5. Water adds to maleic acid (under acid catalysis) to form laic acid. Malic acid then rotates to a new conformation and elimenates water to form fumaric acid.
6. The addition of a proton to maleic acid leads to the formation of a lactone (cyclic ester) which undergoes a ring opening reaction to yield malic acid. Malic acid is then dehydrated to give fumaric acid.
7. A proton adds to the carbonyl oxygen to give an intermediate with a number of resonance structures. One of these resonance structures can freely rotate and deprotonation to give fumaric acid.
8. A proton adds to the carbonyl oxygen, followed by an addtion of a chloride ion. The product of this 1,4 addition then undergoes a free rotation, and hydrochloric acid is eliminated to produce fumaric acid.
So, I understand that I can go through a process and eliminate the first 7 reaction mechanisms to chose the last one #8 is close to the true state of affairs.
Can anyone answer this question:
For mechanism 3 to be correct, which test tubes should contain fumaric acid?
Test Tube
Solids
Solvents
Precipitate
A
1.0 g maleic acid
3.0 mL 6 M HCl
Yes
B
1.0 g maleic acid
3.0 mL 3 M H2SO4
No
C
1.0 g maleic acid
0.5 g ammonium chloride
3.0 mL distilled water
No
D
1.0 g maleic acid
0.5 g ammonium chloride
3.0 mL 6 M HCl
Yes
E
1.0 g malic acid
3.0 mL 6 M HCl
No
F
1.0 g maleic acid
1.5 mL distilled water
2.0 mL conc. HBr
Yes
Explanation / Answer
For mechanism 3 to be correct, test tube E shou;d contain fumaric acid.
It is because maleic acid is transformed into fumaric acid through the process of heating the maleic acid in hydrochloric acid solution. Reversible addition (of H+) leads to free rotation about the central C-C bond and formation of the more stable and less soluble fumaric acid.
As fumaric acid is less soluble, there will be no precipitate form. So, test tube E shou;d contain fumaric acid.
Related Questions
drjack9650@gmail.com
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.