Classification Tests for Hydrocarbons Formal Report

CLASSIFICATION TESTS FOR HYDROCARBONS Margarita Ysabel S. Mangahas, Cara Camille M. Matute, Emilyn D. Millares, John Acener C. Padua and Kathryn Cheshire P. Pangilinan Group 5 2A Medical Technology Organic Chemistry Laboratory ABSTRACT In the experiment, hydrocarbons were classified by observing their solubility, flammability, active unsaturation, aromaticity, and oxidation to their appropriate and suitable tests. Hexane, heptanes, cyclohexane, cyclohexene, benzene, and toluene were the hydrocarbon compounds studied. First, physical properties of the compounds were observed to identify their physical state or phase, color and odor. All of the compounds were in clear liquid form and are colorless, while they vary in odor. To test for solubility, concentrated H2SO4 or sulfuric acid was used as reagent. Each of the compounds were tested according to their flammability by an ignition test. All of them were flammable and the alkanes produced a yellow flame. In addition to that, only the cyclic compounds produced soot. Their active unsaturation was also tested by using Baeyer’s test and Bromine test. In Baeyer’s test, the compounds reacted with 2% KMnO4 solution. Decolorization from violet to brown was seen only in cyclohexene. As for the Bromine test, the compounds were studied through their reaction with 0.5% Br 2 in CCl4 reagent. It can be drawn from the results that there was no change in benzene and toluene, while immediate decolorization occurred in cyclohexene. Moreover, there was a slow reaction in hexane, heptane, and cyclohexane, but produced rapid reactions of turning to a colorless solution under sunlight. Next, aromaticity of the hydrocarbons were tested. This was done by combining a nitrating mixture composed of concentrated HNO3 and concentrated H2SO4 to the hydrocarbons. Heat was also applied to have an apparent reaction. Aromatic compounds were found out to be benzene and toluene, by which both produced a unique yellow oily layer. Lastly, test for basic oxidation was performed. In this test, the compounds reacted with 2% KMnO4 and 10% NaOH. The only distinctive change was seen in cyclohexene which changed from violet to brown, indicating that it is oxidized. The other compounds did not decolorize. [1]

INTRODUCTION Hydrocarbons are the simplest organic compounds. They are Carbon compounds that can be designated as aliphatic hydrocarbons or as aromatic hydrocarbons. Aliphatic hydrocarbons which are saturated are alkanes, and if found in a closed-chain are named as a cycloalkane. If they are unsaturated, they can be an alkene or cycloalkene, alkyne or cycloalkyne. [5] Hydrocarbons may be saturated which means that each carbon is bonded to four other atoms through single covalent bonds, thus it creates the maximum number of hydrogen in a compound due to the absence of any substituent. Hydrogen atoms usually occupy all available bonding positions after the carbons have bonded to each other. While, unsaturated hydrocarbons contain either double or triple bonds. Alkenes as unsaturated compounds are also called olefins and they form oily liquids on reaction with halides like bromine gas. [2] Hydrocarbons may also be aromatic compounds. They follow Huckel’s Rule, their structure is stabilized by resonance, and are all cyclic. They undergo electrophilic substitution reactions and nucleophilic aromatic substitutions. [3]

The objectives of this experiment were to identify and classify the different hydrocarbons. The hydrocarbons were to be tested according to their solubility, flammability, active unsaturation, aromaticity, and basic oxidation. To elaborate, they were categorized and from the results were inferred whether miscible or immiscible, saturated or unsaturated, actively unsaturated or not actively unsaturated, aromatic or not aromatic, and oxidized or not. This experiment also aim to identify the different physical and chemical properties of hydrocarbon compounds.

EXPERIMENTAL A. Sample Used The samples used or compounds tested in the experiment were hexane, heptane, cyclohexane, cyclohexene, benzene, and toluene.

B. Procedure 1. Physical State, Color, Odor The compounds were first observed to know their physical properties. The state and color of the compounds were observed, and the odor was also sensed by wafting or fanning the hands above the test tube.

2. Solubility in Concentrated H2SO4

One milliliter of of conc. H2SO4 was applied to a drop of each of the compounds in separate test tubes by using calibrated droppers, afterwhich, change in color and warming effect were observed.

3. Ignition Test Flammability of the compounds was tested by an ignition test. One by one, 3 drops of each of the compounds were placed in an evaporating dish and lighted with a match.

4. Tests for Active Unsaturation Two different tests were done to analyze active unsaturation of the compounds. The first test was the Baeyer’s test. This was done by the combination of 5 drops of each of the compounds and 2 drops of 2% KMnO4 solution. Bromine test was performed by adding 10 drops of 0.5% Br2 in CCl4 reagent to 5 drops of each compound. Shaking of the mixture was done. If the mixture did not decolorize, it must be exposed to sunlight.

Condensed Structural Formula

CH3CH2CH2 CH2CH2CH3

CH3CH2C H2CH2CH 2CH2CH3

A. Physical state at RT

Clear liquid

Clear liquid

Clear liquid

Color

Colorless

Colorless

Colorless

Odor

Plastic balloon

Chlorinelike

Alcohollike

Oily layer

Oily layer

Oily layer

Immiscible

Immiscib le

Immiscibl e

Flammable

Flammab le

Flammabl e Yellow flame No decoloriza tion

Not actively unsaturate d

Yellow flame No decoloriz ation Fast change from orange to colorless under sunlight Not actively unsatura ted

Clear oily layer

Clear oily layer

Clear oily layer

Not aromatic

Not aromatic

Not aromatic

B. Solubility in concentr ated H2SO4 Inference C. Ignition Test Inference

5. Test for Aromaticity: Nitration Preparation of the nitrating mixture must first be accomplished by placing 2 ml of conc. HNO3 in an Erlenmeyer flask and immersing it into water from an evaporated dish, and conc. H2SO4 was added gradually. Eight drops of the nitrating mixture was added to 5 drops of each compound. The mixture was diluted with water after shaking. If no apparent reaction was seen, heat must be applied by conducting a water bath that is not more than 50°C in 10 mins. Lastly, the mistures was diluted again with water.

D. Baeyer’s Test

Bromine Test

6. Basic Oxidation 2% KMnO4 solution and 10% NaOH solution with 8 and 3 drops respectively, were combined to 4 drops of each hydrocarbon compound. The mixture was warmed by a water bath for 2 mins.

RESULTS AND DISCUSSION Different tests like solubility in conc. H2SO4, Ignition Test, Baeyer’s Test, Bromine Test, Test for Aromaticity, and Basic Oxidation were conducted to be able to differentiate and classify the different hydrocarbon compounds.

Table 1. Results and Inferences classification tests for hydrocarbons

of

Compounds Studied Hexane

Heptane

Cyclohex ane

Inference E. Test for Aromatici ty Nitration Inference F. Basic Oxidation Inference

Yellow flame No decolorizat ion Fast change from orange to colorless under sunlight

No No decolorizat decoloriz ion ation Not Not oxidized oxidized Compounds Studied Cyclohex Benzene e

Fast change from orange to colorless under sunlight Not actively unsaturat ed

No decoloriza tion Not oxidized Toluene

were in clear liquid state. They are all colorless but they differ in odor. Hexane smelled like a plastic ballon, heptanes as chlorine-like and cyclohexane as alcohol-like. Cyclohexene and benzene have both a gas-like odor, while toluene was rugby-like.

Condensed Structural Formula

A. Physical state at RT Color Odor B. Solubility in concentr ated H2SO4 Inference C. Ignition Test Inference

D. Baeyer’s Test

Bromine Test

Inference

E. Test for Aromatici ty Nitration Inference F. Basic Oxidation Inference

Clear liquid

Clear liquid

Clear liquid

Colorless

Colorless

Colorless

Gas-like

Gas-like

Rugbylike

Orange oily layer

Clear oily layer

Clear oily layer

Miscible

Miscible

Miscible

Flammabl e

Flammabl e

Flammabl e

With soot

With soot

With soot

No decoloriza tion

No decoloriza tion

No decoloriza tion

No decoloriza tion

Not Actively Unsaturat ed

Not Actively Unsaturat ed

Immediat e decoloriza tion from violet to brown Immediat e decoloriza tion from reddish brown to colorless Actively Unsaturat ed Yellow solution

Yellow oily layer

Yellow oily layer

2. Solubility in Concentrated H2SO4 Clear oily layer was the result in almost all of the compounds except cyclohexene. A clear orange oily layer was produced by cyclohexene with conc. H2SO4. These results indicate that cyclohexene are miscible and the others are immiscible in conc. H2SO4.

3. Ignition Test All of the compounds tested were flammable. Thus, it can be inferred that all hydrocarbons are combustible. The only difference seen was the production of soot during the process. Only the cyclohexene, benzene, and toluene had a soot wiye.

4. Tests for Active Unsaturation Baeyer’s Test Potassium permanganate did not react with the alkane compounds tested because they are saturated. When the reagent was added to alkanes, the purple color does not change. [4] Only cyclohexene gave out a reaction that changed its color from violet to brown. Then it may be concluded that cyclohexene was the only actively unsasturated compound due to its positive result against the reagents in Baeyer’s Test.

Figure 1. Chemical reaction of alkene in Baeyer’s Test R

R C

R

HO

+ 2KMnO4 + 2CH3OH

C

R

R

OH C

R

C

R R

(purple) + 2MnO2 + 2KOCH3

Not aromatic

Not aromatic

Not aromatic

Decoloriza tion from violet to brown

No decoloriza tion

No decoloriza tion

Oxidized

Not oxidized

Not oxidized

1. Physical State, Color, Odor All of the hydrocarbon compounds tested

(brown)

When KMnO4 solution was added to an alkene, the purple color slowly disappeared and a brown MnO2 precipitate formed. The appearance of the brown precipitate indicate a positive test for unsaturation.

Figure 2. Decolorization of alkene in Baeyer’s Test

A purple result was first produced by the Baeyer’s Test for Unsaturation, this diluted into light purple until it produced a brown precipitate which indicated that the compound was already unsaturated. The bromine test was used to determine if the colorless organic compounds contain any double Carbon to Carbon bonds. Bromine did not react with any alkane because the alkane has only single C-C bonds which cannot add the bromine. Alkanes merely dilute the red-brown bromine color to an orange or yellow color in the absence of a strong catalyst which was visible in the result in hexane, heptane and cyclohexane. Due to their C=C double bonds in cyclohexene, which can be broken, alkenes react readily with bromine to produce saturated dibromoalkanes. When an alkene is reacted with bromine, the red-brown color of the bromine is immediately lost due to the reaction of the bromine. [4]

The red aqueous layer as bromine, was used to test the organic chemicals for a reactive carbon double bond to decolourize the liquid. The organic layer formed by cyclohexene, decolourized the liquid slowly into orange because cyclohexene contains a reactive double bond. The reddish brown color of Bromine that slowly diluted to orange indicated that there was no reaction between the reagents, thus, the compound is saturated. But, when the mixture was exposed to sunlight, immediate decolorization took place, wherein the orange solution became colorless, which presented that the mixture was already unsaturated. Benzene and toluene are also alkenes but, they are both aromatic that make them very stable but also less reactive than cyclohexene because their atoms are less available to be given off. [6]

5. Test for Aromaticity: Nitration Aromatic compounds are extremely stable and will not react without a catalyst so they act like alkanes but are still unsaturated compounds.

Figure 4. Chemical reaction aromatic compounds in nitration

of

Figure 3. Chemical reaction of alkene in Bromine Test R

R C

R

UV light +

C

Br2

R

Br R

C R

(reddish brown)

R C

R Br

(colorless)

Due to their C=C double bonds in cyclohexene, which can be broken, alkenes react readily with bromine to produce saturated dibromoalkanes.

A nitrite compound attached to benzene was produced as seen in the chemical reaction of benzene from a nitrating mixture composed of conc. HNO3 and conc. H2SO4, and with aid of heat.

Figure 4. Decolorization of alkene in Bromine Test

Nitrobenzene as well as p-nitrotoluene both gave a yellow oily layer above a colorless solution. This indicated that both compounds possess aromaticity.

6. Basic Oxidation This test was done by using an inorganic chemical compound, KMnO4 which is a strong oxidizing reagent. An oxidation reaction occurred in this test. Furthermore, NaOH had been used to test if precipitate was to be formed. From the results, only cyclohexene produced a change

wherein it decolorized from violet to brown. That occurrence perceived that it is the only oxidized compound.

REFERENCES [1] Bayguen, A.V., et al. (2009). Laboratory Manual in Organic Chemistry. Pearson Education, Inc. pp 81-93 [2] http://www.elmhurst.edu/~chm/vchem book/500hy drocarbons.html [3] http://www.encyclopedia.com/topic/aromatic _com pound.aspx#0-1E1:aromatic-full [4] http://homepages.ius.edu/dspurloc/c122/hy d.htm [5] http://hyperphysics.phyastr.gsu.edu/hbase/ organic/hydrocarbon.html [6] http://sciencephoto.com/media/4388/enla rge