UNIVERSITY OF SANTO TOMAS FACULTY OF PHARMACY ORGANIC CHEMISTRY LABORATORY Organic Chemistry Laboratory – CH 200L (2012 – 2013) 2B-Ph Group 3 Experiment 7
CLASSIFICATION TESTS FOR HYDROCARBONS Colleen C. Caragay, Rizzalaine P. Caringal*, Bett Shannen M. Carpio, Ancell Julienn C. Cruz, John Matthew C. Cruz Department of Pharmacy, Faculty of Pharmacy University of Santo Tomas, Espana Street, Manila 1008 Date Submitted: Sept. 4, 2012
________________________________________________________________________________________ Abstract In the experiment, the organic compounds hexane, heptane, cyclohexane, cyclohexene, benzene and toluene were subjected to physical tests to differentiate their intrinsic physical properties and chemical tests to determine their chemical properties in terms of structure and behavior. The physical state was noted through the different color and odor characteristics of each compound used. Miscibility was also tested by mixing a drop of each sample to 1 ml of concentrated H2SO4. Flammability test was accomplished by placing 3-5 drops of each sample to a small evaporating dish and lighting it with a match. Test for active unsaturation was completed by performing Baeyer’s and Bromine test. The test for aromaticity of each compound was determined through Nitration. Lastly, the test for basic oxidation was performed through the addition of 8 drops of 2% KMNO4 and 3 drops of 10% NaOH solution to 4 drops of each of the sample. All the organic compounds are clear solutions with their own characteristic odor. Each compound was immiscible in concentrated H2SO4 and flammable in the ignition test. All were not actively unsaturated except cyclohexene. Benzene and toluene were found to be aromatic. All are not oxidized except cyclohexene. _________________________________________________________________________________________________
Introduction The number of known organic compounds totals into the millions. Of these compounds are the simplest types called hydrocarbons. Hydrocarbons are organic compounds containing carbon and hydrogen atoms that are covalently bonded to each other. Because of the number and variety of hydrocarbons that can exist, some means of classification is necessary. One means of classification depends on the way in which carbon atoms are connected. Aliphatic hydrocarbons are non-aromatic which can be classified as acyclic and cyclic. Openchained or acyclic hydrocarbons are compounds consisting of carbons linked either in a single or a branched chain. On the other hand, closed –chained or cyclic hydrocarbons are compounds that have carbon atoms linked in a closed polygon or ring.
Another means of classification is dependent on the type of bonding that exists between carbons. Hydrocarbons that contain only carbon-to-carbon single bonds are called alkanes which are also referred to as saturated molecules. Hydrocarbons containing at least one carbon-to-carbon double bond are called alkenes, and compounds with at least one carbon-to-carbon triple bond are called alkynes. Both compounds are also referred to as unsaturated molecules.
(Figure 1. Saturated Hydrocarbon of Alkane)
(Figure 2. Unsaturated Hydrocarbon - Alkene)
Aromatic hydrocarbons are cyclic and planar. It can be stabilized by resonance and it obeys the Huckel’s rule (4n+2 = πe). Aromatic hydrocarbons that contain alkyl side chains are called arenes. Six organic compounds was used in the experiment, namely hexane, heptane, cyclohexane, cyclohexene, benzene and toluene. The first compound used was hexane. Hexane is a hydrocarbon with the chemical formula C6H14; that is, an alkane with six carbon atoms.
(Figure 3. Hexane) On the other hand, n-Heptane is a straightchain alkane with the chemical formula H3C(CH2)5CH3 or C7H16. The first two compounds are both aliphatic and unsaturated hydrocarbons.
(Figure 6. Cyclohexene) Benzene is an aromatic hydrocarbon composed of 6 carbon atoms in a ring, with 1 hydrogen atom attached to each carbon atom, and with the molecular formula C6H6.
(Figure 7. Benzene) Lastly, Toluene is also an aromatic hydrocarbon which is a monosubstituted benzene derivative, i.e., one in which a single hydrogen atom from the benzene molecule has been replaced by a univalent group, in this case CH3.
(Figure 4. Heptane) Cyclohexane is a cyclic hydrocarbon with the molecular formula C6H12.
(Figure 5. Cyclohexane) Cyclohexene is also a cyclic hydrocarbon with the formula C6H10. It is unsaturated because of its double bond. Meanwhile, Cyclohexane is a saturated compound.
(Figure 8. Toluene) Different tests were performed to be able to differentiate hydrocarbons in terms of intrinsic physical properties and chemical properties in terms of structure and behavior. Various tests were also accomplished to be able to analyze a hydrocarbon and determine if it is saturated, actively unsaturated, aromatic or an arene. The first test was done to determine the drugs miscibility in Concentrated H2SO4. 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, The miscibility is determined by the weight percentage of the hydrocarbon chain. The second test performed was ignition test to determine the flammability and the presence of unsaturation or high carbon to hydrogen ratio of each organic compound. Flammability is the measure of the extent to which a material or a substance will support combustion. The degree of luminosity can be assessed by the presence of yellow flame and soot. Aromatic compounds burn with sooty flame due to the incomplete combustion which causes the formation of an unburned carbon. In terms of degree of luminosity, aromatic compound > unsaturated hydrocarbon > saturated hydrocarbon. Baeyer’s test and Bromine test was performed to determine which compound is actively unsaturated. Baeyer’s test is a test for unsaturation or double bonds. Baeyer’s test uses a solution called the Baeyer’s reagent, which is a solution of alkaline potassium permanganate. A positive result or a compound which is actively unsaturated leads to a result of decolorization of a purple solution and formation of a brown precipitate. Along with Baeyer’s test is the Bromine test which is also a test for double bonds. The reagent used is 0.5% Br2 in CCl4. A positive result in the test will lead to decolorization of an orange solution. The compound which immediately decolorized would be the most actively unsaturated compound. To determine for the Aromaticity of a compound, Nitration test was accomplished. The samples were reacted with HNO3 and H2SO4. A positive result would produce a yellow globule/ yellow oily layer. The last test performed was Basic Oxidation, a test for alkylated aromatics or arenes. The reagents used were 2% KMnO4 and 10% NaOH. A positive result in the test leads to a violet solution (MnO4) or brown precipitate (MnO2).
METHODOLOGY There were six different compounds used in the experiment, namely hexane, heptane, cyclohexane, cyclohexene, benzene and toluene. Different tests were performed to determine the type of hydrocarbon used in each sample. A.) Physical State, Color and Odor The first step in the experiment was to determine the physical characteristics of the samples. The physical state and color were noted and the odor was recorded by wafting each sample to determine its smell. The first test accomplished was the test for solubility or miscibility of the compound in concentrated H2SO4.
B.) Solubility in Concentrated H2SO4 CAUTION! CONCENTRATED H2SO4 IS CORROSIVE AND DEHYDRATING. (It is exothermic with water and may react with water violently.)
A dry and calibrated dropper was used to add a drop of the sample cautiously added to about 1 ml of conc. H2SO4. The color change or any warming effect was noted immediately. C.) Ignition Test For the ignition test, 3-5 drops of the sample was placed in a small evaporating dish and lighted with a match. The flammability, color of flame produced and formation of soot was observed during the test. D.)Test for Active Unsaturation Two different tests were accomplished to check for the Active Unsaturation of a compound. a.)Baeyer’s Test
In the Baeyer’s test, 2 drops of 2% KMnO4 was added to 5 drops of the sample in a dry test tube. The tube was shaken vigorously and the rate and extent at which the reagent is decolorized was observed. The formation of a brown suspension was also noted. Water as the negative control was compared. b.) Bromine Test Besides the Baeyer’s test, Bromine test was also performed. 10 drops of 0.5% Br2 in CCl4 was placed with 5 drops of the sample in a dry test tube. Similar to the Baeyer’s test, the test tube was shaken vigorously and the rate and extent by which the reagent is decolorized was observed. Water, as a negative control was also compared. If the reaction failed to decolorize within 1 minute, the mixture was exposed to the sunlight. E.) Test for Aromaticity: Nitration The next test performed was the test for Aromaticity through Nitration. CAUTION! CONCENTRATED H2SO4 IS CORROSIVE AND DEHYDRATING. 2 ml CONCENTRATED of conc. HNO3 HNO was3 IS placed in an Erlenmeyer flask. AND The flask was immersed in CORROSIVE OXIDIZING an evaporating dish containing water and was gradually added with 2 ml of conc. H2SO4. The resulting mixture was cooled to room temperature. The solution served as the nitrating mixture. Then, 8 drops of the nitrating mixture was added to 5 drops of the sample in a dry test tube and was shaken to ensure complete mixing. The formation of a yellow oily layer or droplet was noted. The mixture was then diluted with 20 drops of water. The test tube was placed in a water bath for 10 minutes if there is no apparent reaction observed within a minute. F.) Basic Oxidation
The last test was for alkylated aromatics or arenes which was the Basic Oxidation test. 8 drops of 2% KMnO4 solution and 3 drops of 10% NaOH solution was added to 4 drops of the sample in a test tube. Each test tube was warmed in a water bath for 2 minutes and the color change and formation of a brown precipitate was observed. RESULTS / DISCUSSION
Compound Studies Hexane
Heptane
Cyclohexane
Cyclohexene
Benzene
Toluene
Liquid
Liquid
Liquid
Liquid
Liquid
Liquid
Colorless
Colorless
Colorless
Colorless
Colorless
Colorles s
Strong odor
Strong odor
Strong odor
Strong odor
Strong odor
Strong odor
Immiscible Immiscible
Immiscible
Miscible
Immiscible
Immisci ble
Not weak base
Not weak base
Not weak base
Weak base
Weak base
Not weak base
Flammabl e
Flammabl e
Flammable
Non flammable
Flammable
Flamma ble
Inference
Luminous flame
Luminous flame
Luminous flame
Non luminous flame
Luminous flame
Luminou s flame
D. Baeyer’s Test
No decoloriza tion
No decoloriza tion
No decolorizatio n
Immediate decolorizati on
No decolorizatio n
No decolori zation
Bromine Test
Slow decoloriza tion
Slow decoloriza tion
No decolorizatio n
Slow decolorizati on
Slow decolorizatio n
Immedia te decolori zation
Inference
Saturated
Saturated
Not actively saturated
Not actively saturated
Not actively saturated
Not actively saturate d
Immiscible, oily layer
Immiscible, oily layer
Immiscible, oily layer, slightly yellow
Immisci ble, oily layer, slight yellow
Condensed Structural Formula
A. Physical state at RT Color
Odor
B. Solubility in concentrated H2SO4 Inference
C. Ignition Test
E. Test for aromacity nitration
Inference
F. Basic Oxidation
Immiscible Immiscible , oily layer , oily layer
Not aromatic
Not aromatic
Not aromatic
Not aromatic
Not aromatic
Aromati c
No decoloriza tion
No decoloriza tion
No decolorizatio n
No decolorizati on
No decolorizatio n
Fast decolori zation
The physical characteristics of each sample were noted. All the organic compounds used are clear, colorless liquid. Each compound has their own characteristic odor that makes them distinguishable from the others. The solubility or miscibility of the compounds in H2SO4 indicates whether the sample is a very weak base (can be protonated) or a neutral compound (cannot be protonated). The dissolution of compounds in H2SO4 may also produce large amounts of heat and/or a change in the color of the solution, precipitation or any combination of these. *H2SO4 -soluble (very weak base) Esters, Ketones, Alkenes, Aldehydes Alcohols *H2SO4 -insoluble (neutral compound) Alkanes, Aryl halides, most aromatic hydrocarbons
Alkyl halides,
The ignition test was performed to indicate the presence of unsaturation or high carbon to hydrogen ratio. Generally, high carbon to hydrogen ratio equals high luminosity and the more the flame produces black smoke or soot. The degree of luminosity can be assessed by the presence of yellow flame and soot. Aromatic compounds burn with sooty flame due to the incomplete combustion which causes the formation of an unburned carbon. Aromatic compound is greater than unsaturated hydrocarbon, and unsaturated hydrocarbon is greater than saturated hydrocarbon in terms of degree of luminosity. Complete combustion is indicated by a blue flame (non-luminous) and there is more heat than light; hence the carbon is completely oxidized. On the other hand, incomplete combustion is indicated by a yellow flame (luminous) and there is much light than heat; hence the carbon is not completely oxidized. Complete combustion CxHy + O2 CO2 + H2O Incomplete combustion CxHy + O2 CO2 + CO + C(soot) + H2O The test for Active Unsaturation was accomplished in two ways: Baeyer’s test and Bromine test. Both
determine the presence of double bond in each organic compound. In the Baeyer’s test, the reagent used was 2% KMnO4 solution. The positive result that must be obtained in the test is the decolorization of a purple solution followed by formation of a brown precipitate. All but cyclohexene gave a negative result to the test. It indicates that cyclohexene is positive for the active unsaturation test and that it contains double bond in its chemical structure. In the reaction, Mn7+ is reduced to Mn4+ which means that alkene is oxidized to a diol in the process of redox reaction. Alkenes react with potassium permanganate (KMnO4) to give a diol and MnO2. Aromatic compounds do not react in this test because of their stability. Cyclohexene + KMnO4 1,2-cyclohexanediol + MnO2 (purple) (colourless) (brown)
The reagent used in Bromine test was 0.5% Br2 in CCl4. A positive result is obtained by decolorization of an orange solution. In this case, cyclohexene decolorized immediately and became a clear solution while the other compounds still needed exposure to UV light in order to decolorize. From there, the test readily gave a positive result to cyclohexane which makes it actively unsaturated in the two different tests performed. The alkenes react with Br2 to form a transdibromoalkane. The reaction involves electrophilic addition. Aromatic compounds do not react because of their stability; however, they will react slowly upon using FeBr3 or through the action of UV light. The test for Aromaticity was performed through Nitration. The reagents used were HNO3 and H2SO4. A positive result in the test is obtained when a yellow oily layer is formed. Benzene and toluene gave a positive result and therefore the two compounds are considered aromatic. Other than that, the two compounds are also cyclic and planar in their chemical structure and they obey Huckel’s rule that is why they are considered aromatic compounds. The H2SO4 acts as a catalyst and facilitates the formation of nitronium ion (NO2+), an electrophile. Onehydrogen in the benzene ring is substituted by the nitronium ion that is why
the reaction substitution.
involves
electrophilic
HNO3 + H2SO4 NO2+ + 2H2SO4- + H3O+ Benzene + NO2+ nitrobenzene The last test performed was Basic Oxidation, a test for alkylated aromatics or arenes. The reagents used were 2% KMnO4 and 10% NaOH. A positive result in the test will produce a violet solution (MnO4) or brown precipitate (MnO2). NaOH provides a basic environment. The alkyl group of the aromatic compound is oxidized to a carboxylic acid, therefore involves a redox reaction. Mn7+ is reduced to Mn6+/4+ depending on the extent of the reaction.
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