Synthesis and Chemistry of Alkenes

Experiment 2: SYNTHESIS AND CHEMISTRY OF ALKENES

Objective:

In this experiment, a mixture of different alkenes was synthesized through an acid catalyzed reaction, using simple distillation techniques. The components of the mixture were analyzed using a gas chromatogram, and various alkenes were tested for unsaturation using the bromine and Baeyer test.

Reactions:

Figure 1. Acid catalyzed dehydration of 4-methyl-2-pentanol

Figure 2. The synthesis of major alkene products from the various carbocation shifts of the dehydrated 4-methyl-2-pentanol.

Figure 3. A general bromination as occurs in the bromine test for alkenes.

Figure 4. Oxidation with MnO4- in the Baeyer test for alkenes.

Experimental Data & Observations:

Table 1: Gas chromatography analysis

Compound Retention time Area % composition Conditions used

4-methyl-1-pentene 8 s 128 mm2 5.67% [see attached chromatograms]

4-methyl-2-pentene 32.5 s 1500 mm2 66.4%

2-methyl-1-pentene 24 s 112 mm2 5.0%

2-methyl-2-pentene 40 s 477 mm2 21.1%

3-methyl-2-pentene 15 s 42 mm2 1.86%

Table 2. Test results from the bromine and Baeyer tests for unsaturation. For the bromine test, a positive test was indicated by the rapid dissapearance of the orange bromine colour. For the Baeyer test, a positive test was indicated by the formation of a brown precipitate and the dissapearance of the purple colour.

Compound Bromine Test Baeyer Test

2-methyl-2-pentenol negative negative

Ethanol (blank test) negative negative

Alkene solution positive positive

Cyclohexane negative negative

Limonene positive positive

Isoprene positive positive

Phenyl acetyene negative positive

Toluene negative negative

Table 3. Reagents Used

Compound Molecular Weight Weight Used Moles used Physical and Safety data

4-methyl-2-pentanol 102.17 g/mol 5.00 g 0.0489 moles d. 0.802 g/mL Flammable and toxic, irritant.

85% phosphoric acid 98.0 g/mol 5.00 mL 0.0857 moles 85% in weight by H2O. d. 1.68 g/mL Corrosive, wear protective clothing, eyewear, gloves.

Anhydrous potassium carbonate 138.21 g/mol 0.996 g 0.00721 moles d. 2.43 g/mL Corrosive and harmful if ingested/inhaled.

Chloroform 119.38 g/mol 7.0 mL 0.0875 moles d. 1.492 g/mL Cancer suspect agent, mutagen.

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