Experiment 2 sko - sssssssssssssssss PDF

Preview

Summary

EXPERIMENT 2: PREPARATION OF CIS AND TRANS ISOMER1 INTRODUCTIONMalic acid and fumaric acid have the same molecular formula: C4H4O4. Each compound contains two carboxyl groups, -COOH, and a double bond. The compounds are isomers because their structures differ in the geometry, or arrangement in space...

Description

EXPERIMENT 2: PREPARATION OF CIS AND TRANS ISOMER

1.1 INTRODUCTION Malic acid and fumaric acid have the same molecular formula: C4H4O4. Each compound contains two carboxyl groups, -COOH, and a double bond. The compounds are isomers because their structures differ in the geometry, or arrangement in space of the atoms in the molecule. Cis-trans isomers are a kind of stereoisomers called geometrical isomers. Due to the inability of rotation about the C=C bond, some compounds possess cis and trans isomers. Cis and trans isomers have different physical properties such as boiling point, solubility, density and stability. 1.2 METHODS 1) Chemicals a) Malic acis b) Concentrated hydrochloric acid 12M c) Magnesium ribbon (3 cm strips) d) Sodium carbonate e) pH paper 2) Apparatus a) Erlenmeyer flask 125 mL b) Watch glass c) Beaker 100mL d) Test tubes e) Filter paper f) Melting point apparatus 3) Procedure https://youtu.be/6iwMN0dWr_0

1.3 RESULT Part A: Conversion of maleic acid to fumaric acid Mass of filter Mass of filter paper and fumaric acid Mass of fumaric acid Percentage yield

1.2109g 1.7589g 0.548g %actual yield=

actual yield ×100 theoretical yield

%actual yield=

Melting point of fumaric acid Melting point of malic acid

0.548 g × 100 2.0 g

%actual yield=27.4 % 310˚C - 325˚C 140˚C - 155˚C

Part B: Comparison of two isomers Solubility test Observations Chemical properties pH using Ph paper Magnesium ribbon

Malic acid Dissolve completely Malic acid 2 Fast reaction producing

Fumaric acid Dissolve slightly Fumaric acid 3 Slower reaction and less bubble

Sodium carbonate

bubble Fast reaction with bubble

created Slower reaction and less bubble

1.4 DISCUSSION In this experiment, maleic acid was converted to fumaric acid by heating it in concentrated HCl solution, a catalyst. The melting point of the product, which is the fumaric acid, exhibits a melting point higher than the maleic acid. Generally, the trans isomer has the higher melting point than the cis isomer. It is because trans isomers pack better than cis isomers. The "U" shape of the cis isomer doesn't pack as well as the straighter shape of the trans isomer. The poorer packing in the cis isomers means that the intermolecular forces aren't as effective as they should be and so less energy is needed to melt the molecule which results a lower melting point. Also, trans isomers have higher melting point because they are more stable than cis isomers. This stability arises due to their shape, trans are straight which allows H intermolecular forces to increase and make the trans stable. Also depending on the R groups, if they are next to each other, It will increase the repulsion force between the substance, thus decreasing the melting point of cis. Also, as we can see, a concentrated HCl was used in the experiment rather than any inorganic catalysts such as iodine, bromine, hydrobromic acid, sulfuric acid, potassium thiocyanate and sodium bromide. Hydrochloric acid is a very efficient inversion catalyst and is soluble in the crude aqueous solution of maleic acid. Such a process for the preparation of fumaric acid involves heating an aqueous solution of maleic acid containing hydrochloric acid or other inversion catalysts such as an inorganic catalyst given above. As the inversion process progresses and fumaric acid is formed, the fumaric acid crystallizes out

of the reaction mixture because of its low solubility in the reaction mixture and the fumaric acid crystals are subsequently recovered by filtration or by centrifuging. 1.5 CONCLUSION From the experiment, we were able to synthesize fumaric acid from maleic acid using a heatcatalysed reaction and examine the differences in their physical and chemical properties using a few common laboratory tests. The yield of the fumaric acid synthesized from maleic acid was0.548g with a percentage yield of 27.40%. Also, cis and trans isomers have different physical and chemical properties. Maleic acid is a cis-butenedioic acid and fumaric acid is trans-butenedioic acid. It was known that trans isomers have more symmetry, a higher melting point and lower solubility. Cis isomers are not as stable and have higher heats of formation which makes it possible to be converted into trans isomer by heating. 1.6 REFERENCES 1) Brown, D. (2002). The Chemical Bond In Organic Chemistry. New York: Oxford UniversityPress. 2) Shakhashiri, Z. B. (1983). Chemical Demonstrations: A Handbook for Teachers of Chemistry,Volume 3. Wisconsin: University of Wisconsin Press. 3) Silberberg, M. S. (2013). Chemistry : The Molecular Nature of Matter and Change (GlobalEdition). New York: McGraw-Hill 1.7 QUESTIONS 1) Assume that equilibrium concentrations were achieved in Part A. Which acid is the most stable? Fumaric acid 2) Some diacids can lose a molecule of water when the two carboxyl groups react to form acyclic anhydride. Phthalic acid is a diacid that reacts as follows.

Maleic acid also can lose a molecule of water of water and form malic anhydride. Which structural isomer, cis or trans, do you predict it is? Fumaric acid cannot do this. Explain. Maleic acid has cis configuration:

Therefore, maleic acid can lose one molecule of water and the carboxyl group can be bridged by a single atom to form cyclic anhydride

In fumaric acid, the COOH’s are too far apart to be bridged by a single oxygen atom, because of its trans configuration

3) What does each of the following experiments contribute to your knowledge of the structure of each isomer? a) The melting point determination. Maleic acid has higher solubility than fumaric acid. The molecules of maleic acid have a stronger net dipole moment than fumaric acid. The molecules of maleic acid are polar and are easily hydrated by the polar water molecules. Moreover, the molecules of fumaric acid are more tightly packed compared with those of maleic acid. b) The reactions of each with magnesium. Maleic acid reacts with magnesium faster than fumaric acid. Since both acids are weak acids, their acidity depends on the first ionization of the carboxyl group. Maleic acid is much stronger than fumaric acid in the first ionization. Since the reaction with magnesium depends on the acid strength, maleic acid reacts faster. c) The reaction of each with sodium carbonate. Maleic acid reacts with sodium carbonate faster than fumaric acid. Since both acids are weak acids, their acidity depends on the first ionization of the carboxyl group. Maleic acid is much stronger than fumaric acid in the first ionization. Since the reaction with sodium carbonate depends on the acid strength, maleic acid reacts faster....