CLASSIFICATION TESTS FOR HYDROCARBONS

AUTHORS: Dizon, S., *Donato, A.K., Dy, A., Enriquez, K.B., Fauni, M.B.

ABSTRACT:

The organic compounds hexane, heptane, cyclohexane, cyclohexene, benzene, and toluene were subjected to different physical and chemical tests to differentiate their intrinsic physical properties and chemical properties in terms of structure and behavior. The physical state, color, and odor were noted by simple physical observation. Miscibility was tested by introducing a drop of the sample to 1 ml concentrated H2SO4. Flammability was tested by placing 3-5 drops of the sample to an evaporating dish and lighting it with a match. Active unsaturation was tested using the Baeyer’s and Bromine test and aromaticity was determined by subjecting the organic compounds to Nitration. Oxidation was tested by introducing 8 drops of 2% KMnO4

solution and 3 drops of 10% NaOH solution to 4 drops of the sample organic compound in a test tube. All organic compounds showed immiscibility in concentrated H2SO4 and flammability in the ignition test. All but cyclohexane were not actively unsaturated. All turned out to be aromatic compounds except cyclohexane and cyclohexene. All are not oxidized except cyclohexene.

I.) INTRODUCTION

Hydrocarbons are compounds that contain only carbon and hydrogen atoms. Hydrocarbons may be divided into two large classes namely: Saturated hydrocarbons and Unsaturated hydrocarbons. Saturated hydrocarbons are the simplest type of organic compounds. They are hydrocarbons in which all carbon-carbon bonds are single bonds. An example of a saturated hydrocarbon is an alkane. Unsaturated hydrocarbons are hydrocarbons that contain one or more carbon-carbon multiple bonds like double bonds, triple bonds, or both. Saturated and

Unsaturated hydrocarbons have similar physical properties, but their chemical properties are different. Unsaturated hydrocarbons are chemically more reactive than saturated ones. This is because of the presence of carbon-carbon multiple bonds in such compounds and these multiple bonds serve as locations were chemical reactions can occur.

Fig. 1 (Unsaturated hydrocarbon)Cyclohexane is a cycloalkane

Fig. 2 (Saturated hydrocarbon)

Fig. 3 (Summary of classification of organic compounds)

Hexane is an alkane hydrocarbon with a chemical formula of C6H14, molar mass of 86.18 g/mol, and a boiling point of 69°C. Isomers of hexane are mostly non-reactive, and are frequently used as solvents in organic reactions because they are very non-polar. They are common constituents of gasoline and leather products.

Fig. 4 (Structure of hexane)industrial solvent and a precursor in the production of drugs, plastics, synthetic rubber, and dyes.

with the molecular formula C6H12, molar mass of 84.160 g/mol, and boiling point of 80.74°C. It is used as a non-polar solvent and a raw material for the production of adipic acid and caprolactam. Cyclohexane is produced on an industrial scale by reacting benzene with hydrogen.

Fig. 5 (Structure of Cyclohexane)

Cyclohexene is a cycloalkene with a chemical formula of C6H10, molar mass of 82.143 g/mol, and a boiling point of 82.98°C. It is not very stable upon long term storage and exposure to light and air should be distilled before use to eliminate peroxides. It has a very sharp smell resembling an oil refinery.

Fig. 6 (Structure of cyclohexene)

Benzene is an organic chemical compound with a molecular formula of C6H6, molar mass of 78.11 g/mol, and a boiling point of 80.1°C. It is a colorless, highly flammable liquid with a sweet smell. It is a known carcinogen, therefore its role as an additive in gasoline is now limited, though it is an important The miscibility is determined by the weight percentage of the hydrocarbon chain. The

Fig. 7 (Structure of Benzene)

Toluene is an aromatic hydrocarbon with a molecular formula of C7H8, molar mass of 92.14 g/mol, and a boiling point of 110.6°C. Toluene reacts as a normal aromatic hydrocarbon towards electrophilic aromatic substitution. It is a water-insoluble liquid with a smell of paint thinners, and it is widely used as an industrial feedstock and solvent.

Fig. 8 (Structure of Toluene)

Miscibility is the property of liquids to to mix in all proportions, therefore forming a homogenous solution. By contrast, substances are considered immiscible if in any proportion, they do not form a solution. In organic compounds,

Baeyer’s test is a test for the presence of unsaturation (double bonds). A similar test can be done using bromine. Baeyer’s test uses a solution called the

solvent used in the experiment is concentrated H2SO4. If a compound is unsaturated, it is said to be easily sulfonated, or possesses a functional group containing oxygen, it will dissolve in sulfuric acid. Alkanes, cycloalkanes, and their halogen derivatives are insoluble in sulfuric acid. Simple aromatic hydrocarbons and their halogen derivatives do not undergo sulfonation and are also insoluble in sulfuric acid. Nevertheless, the presence of two or more alkyl groups on the aromatic ring permits the compound to be sulfonated easily. Many secondary and tertiary alcohols are dehydrated readily by concentrated sulfuric acid, which results to the formation of olefins which then undergo polymerization. The polymers formed are insoluble in concentrated sulfuric acid and forms a distinct layer on top of the acid.

Flammability the measure of the extent to which a material or a substance will support combustion. The degree of difficulty required to cause the combustion of a substance is subject to quantification through fire testing or ignition test. Vapor pressure is an important parameter in determining the ease of ignition of a substance or material. The higher the vapor pressure, the more flammable vapor is evolved from a free liquid surface at a given temperature. Many compounds are determined by the characteristics of their flame when they burn. Aromatic hydrocarbons burn with a yellow, sooty flame due to their high carbon content. Aliphatic hydrocarbons burn with flames that are yellow, but less sooty.

In this experiment, the group should be able to attain the following objectives: (1) differentiate hydrocarbons in terms of intrinsic physical properties, and (2) differentiate hydrocarbons in terms

Baeyer’s reagent, which is a solution of alkaline potassium permanganate. Reaction with double or triple bonds in an organic material causes the color to fade from purplish-pink to brown. Easily oxidized compounds like aldehydes, formic acid and its esters, alcohols with trace of impurities, phenols, and thioethers give positive results. Quantitatively, the iodine value is used to determine the presence of unsaturation.

Fig. 9 (Baeyer’s test in an alkene)

Aromaticity is the special stability of planar, cyclic, fully conjugated molecules with 4n + 2∏ electrons. Such molecules have orbital systems with all bonding molecular orbitals completely filled with all antibonding and nonbonding orbitals empty. The criterion for a compound to be aromatic is expressed by the Huckel’s rule.

The oxidation was tested using potassium permanganate. Potassium permanganate is an inorganic compound and a very strong oxidizing agent. It is used in the determination of the total oxidizable organic material in an aquaeous sample. The value determined is known as the permanganate value.

of chemical properties by noting their structure and behavior towards different tests.

II.) EXPERIMENTAL

A.) Physical state, color, and odor

The physical states of the sample compounds HEXANE, HEPTANE, CYCLOHEXANE, CYCLOHEXENE, and BENZENE were observed at room temperature. The color and odor was noted.

Fig. 10 (Schematic diagram 1)

B.) Solubility in concentrated H2SO4

1 ml of concentrated H2SO4

was added to each 6 test tubes. By using dry and calibrated droppers, a drop of each sample was added to the test tubes. Any color change or warming effects were noted.

Reagent was considered immediate if it occurred within a minute. The results were noted down.

Fig. 11 (Schematic diagram 2)

C.) Ignition test

3-5 drops of the liquid sample (pinch amount of solid) were placed in an evaporating dish and was lighted using a match. Any flame produced was noted.

Fig. 12 (Schematic diagram 3)

D.) Active unsaturation

(1) Baeyer’s test

2 drops of 2% KMnO4 were added to 5 drops of the sample in a dry test tube. The test tube was shaken vigorously and the rate and extent at which the reagent is decolorized was observed. The formation of a brown suspension was noted. It was compared with water as a negative control. The decolorization of the

E.) Aromaticity: Nitration

Fig. 13 (Schematic diagram 4)

(2) Bromine test

10 drops of 0.5% Br2 in CCl4

reagent were added to 5 drops of the sample in a dry test tube. The test tube was shaken vigorously and the rate and extent of decolorization was observed. It was compared with water as a negative control. If the reagent failed to decolorize within a minute, the reaction mixture was exposed to sunlight.

Fig. 14 (Schematic diagram 5)

F.) Basic oxidation

8 drops of 2% KMnO4 solution and 3 drops of 10% NaOH solution were added to 4 drops of the sample in a test

2 ml concentrated HNO3 was placed in an Erlenmeyer flask. The flask was immersed in an evaporating dish containing water and 2 ml of concentrated H2SO4 was added gradually. The resulting mixture (nitrating mixture) was cooled in room temperature.

8 drops of the nitrating mixture was added to 5 drops of the sample in a dry test tube. The test tube was shaken to ensure complete mixing. The formation of a yellow oily layer or droplet was noted, and then it was diluted with 20 drops of water. If there was no apparent reaction observed within a minute, the test tube was placed in a water bath (50°C) for 10 minutes. It was diluted with 20 drops of water and the results were noted down.

Fig. 15 (Schematic diagram 6)

After subjecting all 6 organic samples to different physical and chemical

tube. Each test tube was subjected to a water bath for 2 minutes. Any color change and formation of brown precipitate was observed and noted down.

Fig. 16 (Schematic diagram 7)

Stoker, S. Organic and Biological Chemistry. 1998. Houghton Mifflin Company. p. 5

Stoker, S. Organic and Biological Chemistry. 1998. Houghton Mifflin

tests, it was observed that all 6 organic samples were flammable and immiscible in concentrated H2SO4. All except hexane and heptane produced soot when ignited. Only cyclohexene behaved as an actively unsaturated hydrocarbon. All were aromatic compounds except cyclohexane and cyclohexene. The only compound oxidized was cyclohexene.

IV.) SOURCES

Books:

Hornback, J.M. 1998. Organic Chemistry. Brooks/ Cole Publishing Company, Pacific grove. p.p 816-817

Maitland, J.J. 1997. Organic Chemistry. w.w Norton and Company, USA. pp. 616

Shriner, Hermann, Morill, et. Al. 2004. The Systematic Identification of Organic Compounds. John Wiley and Sons Inc. USA. p. 24

Shriner, Hermann, Morill, et. Al. 2004. The Systematic Identification of Organic Compounds. John Wiley and Sons Inc. USA. p. 128

Shriner, Hermann, Morill, et. Al. 2004. The Systematic Identification of Organic Compounds. John Wiley and Sons Inc. USA. p. 130

Company. p. 35-36