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Demonstration of Microscale Projection Experiments - Chemistry en miniature

Debromination of 2,3-Dibromosuccinic acid

Objective: Elimination

Peter Keusch




German version




Chemicals:
5 mmol meso-2,3-dibromosuccinic acid / N,N-dimethylformamide  (1.380 g / 50 mL)
5 mmol DL-2,3-dibromosuccinic acid / N,N-dimethylformamide  (1.380 g / 50 mL)
10 mmol NaI / N,N-dimethylformamide  (1.490 g / 50 mL)
0.5 % aqueous solution of starch


Hazards and safety precautions:

DMF is harmful by inhalation, ingestion or skin contact. May act as a carcinogen. Ingestion or absorption through skin may be fatal. Exposure may result in foetal death. Long-term exposure may result in kidney or liver damage. Irritant.

Safety glasses, protective gloves, good ventilation. The solutions of meso-2,3-dibromosuccinic acid, DL-2,3-dibromosuccinic acid and NaI in DMF are prepared in a fume hood!


Experimental procedure:

The temperature of the water in the cuvette is approx. 50 °C (water bath).

Three test tubes are set up as as described in the table below.

Test tube 1   0.5 mL of meso-2,3-dibromosuccinic acid / DMF    0.5 mL of NaI / DMF  
Test tube 2 1 mL of solution of starch
Test tube 3 0.5 mL of DL-2,3-dibromosuccinic acid / DMF    0.5 mL of NaI / DMF
Test tube 4 1 mL of solution of starch


Results:

The solutions in T1 and T3 turn immediately yellow. The yellow color in T1 becomes more intense.


immediately after 1 minute
Test tube 1 yellow orange
Test tube 3 pale-yellow yellow


When a drop of the orange solution in T1 is pipetted into the starch solution in T2, blue 'schlieren' appear immediately  (Photo 1).  The yellowish solution in T3 responds negatively to the test  (Photo 2).


Photo 1
Photo 1
Photo 2
Photo 2

























Discussion:

·   The meso-dibromosuccinic acid reacts much faster than the DL-form.

·   The Newman projection formulas  (1)  and  (2)  demonstrate, that the transition state leading from the meso form to the formation of fumaric acid is more favorable than the transition state leading from the DL form to the formation of maleic acid (steric hindrance of the two carboxyl groups).




General experimental instructions and index of experiments






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