Classification Classification Tests for Hydrocarbons Authors: Goldie Ann Tejada, Allain Joseph S. Templo, Kristinlyn Trajano, Kevin Viray, Quennie Yu
Group 10, 2F-PH, Faculty of Pharmacy, University of Santo Tomas
ABSTRACT
The test compounds undergo different physical and chemical tests to differentiate their intrinsic physical properties and chemical properties. Physical state, color, and odor were noted through simple observation. Miscibility of the test compounds were noted through color change or a warming effect. Flammability was tested by igniting 3-5 drops of the sample in a small evaporating dish. Baeyer’s test and Bromine test were used for tests for active unsaturation. Aromaticity of the compound was determined through nitration. Oxidation was tested by introducing 8 drops of 2% KMnO 4 solution and 3 drops of 10% NaOH solution to 4 drops of the sample organic compound in a test tube and warming the mixture through water bath. All of the test compounds are liquid and colorless and observed to have a plastic like odor. Miscibility test shows that all of the organic compounds are immiscible and all are flammable flammable.. Tests Tests for active active unsaturat unsaturation ion indicate indicate that hexane, hexane, heptane, heptane, cyclohexa cyclohexane, ne, benzene benzene and toluene toluene are saturate saturated d while while cyclohex cyclohexene ene is actively actively unsaturated. unsaturated. Hexane, heptane, benzene, benzene, and toluene toluene are classifie classified d as aliphatic aliphatic while cyclohexa cyclohexane, ne, and cyclohexene are aromatic. All are not oxidized except for cyclohexene.
Introduction
Hydrocarbons are compounds that contain only car carbon bon and and hydr hydrog ogen en.. Hydroc drocar arbo bons ns can can be aromatic or aliphatic depending on their structure. Hydrocarbons that contain a delocalized ring of pi bonds are called aromatic hydrocarbons and those without a delocalized ring of pi bonds are called ali aliphat phatiic hydr hydroc ocar arbo bons ns.. To be clas classsifi ified as Aromatic, a compound must have an uninterrupted cyclic cloud of pi electrons above and below the plane of the molecule and there should be an odd number of pairs of pi electrons in its pi cloud. To be clas classi sifi fied ed as Alip Alipha hati tic, c, a compo compound und must must have have high higher er hydr hydrog ogen en-t -too-ca carb rbon on rati ratios os.. Alip Alipha hati ticc hydroc hydrocarb arbons ons that that contain contain only only sigma sigma bonds bonds are called saturated hydrocarbons and those containing both both sigma sigma and pi bonds bonds are called called unsatu unsaturat rated ed hydrocarbon hydrocarbon.. Aliphatic Aliphatic hydrocarbons hydrocarbons are divided divided into 3 classes: alkanes are saturated hydrocarbons that that cont contai ain n only only carb carbon on-c -car arbo bon n singl singlee bond bonds. s. Alkenes are unsaturated hydrocarbons that contain at least one carbon-carbon double bond. Alkynes are unsaturated hydrocarbons that contain at least one carbon-carbon triple bond. Most hydrocarbons are colorless and odorless. Solubility of organic compounds in H2SO4 indicates whet whether her the samp sample le is a very very weak base base (can (can be pr proton otonat ated ed)) or a neut neutra rall com compoun pound d (can (can’t ’t be pro proto tona nate ted) d).. The The diss dissol olut utio ion n of comp compou ound ndss in H2SO4 may may also also prod produce uce larg largee amou amount ntss of heat heat and/ and/or or a chang changee in the the colo colorr of the the solu soluti tion on and precipitation; this means that the reaction can be either violent or slow.
Ignition test indicates the presence of unsaturation or high high carb carbon on to hydr hydroge ogen n rati ratio. o. The The Degr Degree ee of lumi luminos nosit ity y can can be asse assess ssed ed by the the pres presen ence ce of yellow flame and soot. Aromatic compounds burn with sooty flame due to the incomplete incomplete combustion combustion which causes the formation of an unburned carbon. Bayer’s test is a test for double bonds or alkenes. The The reag reagen entt used used for for the the tes test is 2% KMnO KMnO4. Aromatic compounds show no reation in the test, bec becaus ausee of thei theirr stabi stabili lity ty.. A posi positi tive ve resu result lt for for Baye Bayer’ r’ss test test show showss decol decolor oriz izat atio ion n of a purp purple le solu soluti tion on and form format atio ion n of a brow brown n prec precip ipit itat atee (MnO2). Bayer’s test involves a redox reaction were in Mn7+ is reduced to Mn4+ and alkene is oxidized to a diol. Alkenes react with potassium permanganate (KMnO4) to give a diol and MnO2. Bromine test, like Bayer’s test, is a test for double bon bonds ds and and arom aromat atic ic comp compou ound ndss also also show show no react reactio ion n in the the test test as they they are are known known for for thei their r stability. The reagents used are 0.5% Br2 in CCl4. A Positive result shows decolorization of an orange solu soluti tion on.. Brom Bromin inee test test invo involv lves es elec electr trop ophil hilic ic addition reaction were in Alkenes react with Br 2 to form a trans-dibromoalkane. Test Test for Aromat Aromatici icity ty is determ determine ined d throug through h Nitration. The reagents used are HNO3, H2SO4. A Posi Positi tive ve resu result lt shows shows a yell yellow ow oily oily laye layer. r. The The reaction involves electrophilic substitution reaction were in H2SO4 acts as a catalyst and facilitates the formation of nitronium ion (electrophile) and one hydrogen atom in the benzene ring is substituted by the nitronium ion. Oxidation was tested using 2% KMnO4 and 10% NaOH. A Positive result shows a green solution and a brown brown precip precipita itate. te. The reacti reaction on involv involves es redox redox
reaction and NaOH is used to provide a basic environment. The alkyl group of the aromatic compound is oxidized to a carboxylic acid while Mn7+ is reduced to Mn6+ or Mn4+ depending on the extent of the reaction. Experimental
Physical state, color, and odor The physical states of the sample were observed at room temperature. Then the color and odor was noted.
cool at room temperature. The resulting mixture will serve as nitrating mixture. 8 drops of the nitrating mixture was added to 5 drops of the sample in a dry test tube and was vigorously shaken to ensure complete mixing. The formation of a yellow layer or droplet was noted and 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. Basic Oxidation
Solubility in Concentrated H 2SO4 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. Ignition Test 3-5 drops of the sample were placed in a small evaporating dish and was lighted by using a match. Presence and color of the flame were noted. Tests for Active Unsaturation Baeyer’s Test 2 drops of 2% KMnO4 was added to 5 drops of the sample in a dry test tube. The solution was vigorously shaken and the rate and extent at which the reagent is decolorized was observed. The formation of a brown suspension was noted and compared to water as a negative control. The result must be noted, once the reagent decolorized within a minute. Bromine Test 10 drops of 0.5% Br 2 in CCl4 reagent were added 5 drops of the sample. The mixture was vigorously shaken and the rate and extent by which the reagent is decolorized was observed. It was compared to water as a negative control. If the reagent failed to decolorize within a minute, expose the reaction mixture to sunlight and note down the results. Test for Aromaticity 2 mL of conc. HNO3 was placed in an Erlenmeyer flask and was immersed in an evaporating dish containing water. 2mL of conc. H2SO4 was gradually added to the flask and was allowed to
8 drops of 2% KMnO4 and 3 drops of 10% NaOH solution were added to 4 drops of the sample in a test tube. Each test tube was warmed in a water bath for 2 minutes and formation of a brown precipitate was noted. Results and Discussions
It was observed that all 6 test compounds are immiscible in concentrated H2SO4; since alkanes, alkyl halides, aryl halides, and most hydrocarbons are insoluble in concentrated H2SO4. All 6 test compounds are flammable. All except hexane and heptane produced soot due to incomplete combustion which causes the formation of an unburned carbon. Only cyclohexene behaved as an actively unsaturated hydrocarbon. Hexane, Heptane, Benzene, and Toluene were considered as aromatic while the cyclohexane and cyclohexene are aliphatic. Only cyclohexene was oxidized.
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