Analysis of Hydrocarbons

Analysis of Hydrocarbons Leonise Gelito, Godwin Evan Halfon*, Antonio Hernandez, and Jose Carmelo Javier Department of Chemistry, University of Santo Tomas, Manila, Philippines

Abstract The objectives of this experiment entitled, “Analysis of Hydrocarbons", are to differentiate various types of hydrocarbons; to device a scheme to distinguish hydrocarbons from each type; and to characterize an unknown hydrocarbon through parallel chemical tests. Hydrocarbons are divided into Aliphatic (saturated or unsaturated) and Aromatic (with or without sidechain). Chemical Analysis is a foolproof way of correctly evaluating the reaction of an unknown sample to a given chemical test with the use of reference standard. The reference standards used for this experiment were Hexane, Cyclohexane, Naphthalene and Toluene. There are also three tests utilized to characterize the unknown sample, which are the Nitrate, Bromine and Permanganate tests.

Introduction Hydrocarbons are the simplest organic compounds. Containing only carbon and hydrogen, they can be straight-chained, branched chain, or cyclic molecules. Carbon tends to form four bonds in a tetrahedral geometry. Hydrocarbon derivatives are formed when there is a substitution of a functional group at one or more of these positions. Hydrocarbons are usually of general use by utilizing chemical reactions that are either classified as addition or bond-rupture reactions.

Four different hydrocarbons are usually the most common subject to test for the analysis of hydrocarbons. These are the Hexane, Cyclohexane, Naphthalene and Toluene. These four are also classified to different types of hydrocarbons, which are the Saturated Aliphatic Hydrocarbons, Unsaturated Aliphatic Hydrocarbons, Alkylated Aromatic Hydrocarbons and Non-alkylated Aromatic Hydrocarbons. Refer to Figure 1.

Saturated Aliphatic Hydrocarbon

Unsaturated Aliphatic Hydrocarbon

Hexane

Cyclohexane

Aromatic without Side Chain

Aromatic with Side Chain

Naphthalene

Toluene

Figure 1: Hydrocarbons

Results and Discussions Four different hydrocarbons were subjected to different in order to differentiate and analyze what type of hydrocarbon are the samples. The observed results of the tests are shown in Table 1.

Class of Hydrocarbon Saturated Aliphatic Unsaturated Aliphatic

Sample

Hexane

Cyclohexane

Aromatic without side

Naphthalene

Bromine Test

Clear pink color

Orange color

Purple color

(-)

(-)

(-)

Rusty dark red color

Clear colorless

Brown precipitate

(-)

(+)

(+)

Yellow precipitate

Clear red color

Purple color

(+)

(-)

(-)

Yellow precipitate

Yellow color

Purple color

(+)

(-)

(-)

chain Aromatic with side chain

Toluene

Permanganate

Nitration Test

Table 1: Observed results in the experiment

Test

In

the

Nitration

Test,

concentrated

H2SO4 and concentrated HNO3 with 1:1 ratio was used as the nitrating reagent. This test will give

a

positive

result

for

the

Aromatic

Figure 2: Nitration of Naphthalene

Hydrocarbons. The positive result will be determined if the reaction shows a yellow oil or yellow precipitate.

In the Bromine Test, 5% Br2 in CH2Cl2

Figure 4: Nitration of Toluene

was used as the reagent. This test will give a positive result for Unsaturated Hydrocarbons. The positive result will be determined if the solution in the reaction decolorizes or changes to a colorless liquid.

In

the

Figure 3: Bromination of Cyclohexane

Permanganate

Test,

0.1%

aqueous KMnO4 and 10% NaOH were used as the reagents. This test will give a positive result for Alkylated Hydrocarbons or Aromatic

Figure 5: Toluene in KMnO4

Hydrocarbons with side chain. The positive result will be determined if the reaction shows a brown precipitate.

Tests Nitration

Bromine

Permanganate

Reagents 1:1 conc. H2SO4 and conc. HNO3 5% Br2 in CH2Cl2

Positive for

Visible Result

Aromatic Hydrocarbons

Yellow oil or precipitate

Unsaturated

Decoloration of solution

Hydrocarbons

(colorless)

0.1% aq. KMnO4

Alkylated Aromatic

10% aq. NaoH

Hydrocarbons

Table 2: Summary of the results

Brown precipitate

Hydrocarbons

Aliphatic

Saturated

Unsaturated

Aromatic

Alkylated

Non-alkylated

Figure 6: Schematic Analysis of Hydrocarbons

Experimental Nitration Test: Ten drops each of the sample were placed in four separate test tubes. Then ten drops of the nitrating reagent were added to each of the sample. The mixtures were shaken and placed in a hot water bath for 5 minutes. 20 drops of distilled water were added to each of the test tubes. And lastly, the observations were recorded. Bromine Test: Ten drops each of the sample were placed in four separate test tubes. Then ten drops of the bromine reagent were added to each of the sample. The mixtures were shaken and the observations were recorded. Permanganate Test: Ten drops each of the sample were placed in four separate test tubes. Then five drops of 0.1% of KMnO4 and five drops of 10% NaOH were added to each of the sample. The mixtures were shaken and placed in a hot water bath for 2 minutes. And lastly, the observations were recorded.

References Klein, D., (2012). Organic Chemistry. USA: John Wiley & Sons Inc. R.J. Fesseden and J.S. Fesseden, Organic Chemistry, 4th Edition, California, U.S.A, Pacific Grove, 1990, Pages 103, 431, 477. Michelle, J. Sienko, Robert A. Plane, Chemistry, 5th Edition, London, McGraw-Hill Book Company, 1981, Pages 455-465.