CLASSIFICATION TESTS FOR HYDROCARBONS USING SOLUBILITY, IGNITION, NITRATION, BAEYER’S TEST, BROMINE TEST AND BASIC OXIDATION TEST

Jasher Christian Boado, Alyanna Cacas, Phoebe Calimag, Caryl Angelica Chin, Haidee Cosilet, John Francis Creencia

Group 2, 2BMT, Faculty of Pharmacy, University of Santo Tomas

ABSTRACT

Hydrocarbons are classified as saturated, actively unsaturated, aromatic or an arene based on various classification tests involving test for solubility in concentrated H2SO4, ignition, active unsaturation using Baeyer’s test and Bromine test, aromaticity using nitration test, and basic oxidation test. This experiment aims to differentiate the intrinsic physical and the chemical properties of hydrocarbons, and to determine if it is saturated, actively unsaturated, aromatic or an arene. The sample compounds hexane, heptane, cyclohexane, cyclohexene, benzene and toluene were analyzed for their physical state in room temperature, color, and odor.

Using solubility test, a drop of a sample was added cautiously into 1ml of concentrated H2SO4. Using the

Baeyer’s Test and/or Bromine test in which 2 drops of 2% KmnO4 solution and 10 drops of 0.5% Br2 in CCl4 reagent, respectively, was added into 5 drops of a sample in a dry test tube, was shaken vigourously until the reagent is decolorized compared with water. Using Nitration test, 8 drops of nitrating mixture was added into 5 drops of a sample in a dry test tube, was observed for the formation of a yellow oily layer or droplet and was diluted with 20 drops of water. Using Basic Oxidation test, 8 drops of 2% KmnO4 solution and 3 drops of 10% NaOH solution was added into 4 drops of a sample in a dry test tube and was heated in a water bath for 2 minutes. A sample was described as immiscible or immisicible using solubility test, as actively unsaturated using Baeyer’s and Bromine tests, as aromatic using nitration test and as an arene using basic oxidation test.

INTRODUCTION

Hydrocarbons are the simplest organic bonds attached to it. Thus, a hydrocarbon that is compounds containing only the elements carbon saturated has all sigma bonds however it is actively and hydrogen. They can be classified in many unsaturated when it has both sigma bond and pi ways. One, a hydrocarbon skeleton can be acyclic bonds. Moving on, aromatic hydrocarbons can be (open chained) or cyclic (closed chain). Two, a classified as an arene when it contains an alkyl side hydrocarbon can be classified as aliphatic or chain (Brown & Poon, 2014). aromatic based on its sources and properties. Aliphatic (from the Greek: aleiphar meaning fat or The sample compounds used in this oil) describes a hydrocarbon that resembles long experiment are hexane, heptane, cyclohexane, carbon-chain molecules derived from animal fats, cyclohexene, benzene and toluene. Hexane, C6H14, but more conviniently, when the chemical structure is a chemical made from crude oil. Heptane, C7H16, contains no ring. Aromatic describes a hydrocarbon is a chemical derived from the fractional distillation that resembles pleasant smelling plant extracts, but of petroleum. Cyclohexane, C6H12, is a colorless more conviniently, when the chemical structure liquid cycloalkane that is made by passing benzene contains a ring (Carey, 2014). Aliphatic and hydrogen under pressure over a heated Raney o hydrocarbons can be divided into an alkane, alkene nickel catalyst at 150 C or by the reduction of or alkyne based on the types of bonds they contain. cyclohexanone. Cyclohexene, C6H10, is a colorless Alkanes are saturated hydrocarbons that contain liquid cycloalkene that is prepared by dehydration of only carbon-carbon single bonds. Alkenes and cyclohexanol by thermal reaction of ethylene- Alkynes are unsaturated hydrocarbons that contain propylene-butadiene. Benzene, C6H6, is a liquid a carbon-carbon double bond or triple bond, aromatic hydrocarbon found in gasoline and other respectively. As mentioned, “saturated” is a way to fuels (National Center for Biotechnology describe a bond, meaning each carbon (a Information, n.d.). Toluene, C7H8, is a liquid tetravalent atom) contains the maximum number of aromatic hydrocarbon that occurs naturally in crude 5 drops of the sample was placed in a oil and in the tolu tree (ATSDR, 2011). dry test tube. Then, 2 drops of 2%

KmnO4 solution was added into it and The objectives of this experiment are to was shaken vigorously. The extent of differentiate the intrinsic physical and the chemical decolorization of the reagent was properties of hydrocarbons using these compunds, observed. and to determine if they are saturated, actively unsaturated, aromatic or an arene. b. Bromine test MATERIALS AND METHODS 5 drops of the sample was placed in a The sample compounds used in this dry test tube. Next, 10 drops of 0.5% experiment are hexane, heptane, cyclohexane, Br2 in CCl4 reagent was added into it cyclohexene, benzene and toluene. The reagents and was shaken vigorously. The extent used in the different classification tests are of decolorization of the reagent was concentrated H2SO4, concentrated HNO3, 2% observed or when the red-brown

KmnO4 solution, 0.5% Br2 in CCl4 reagent, and 10% bromine was discharged. Optionally, a NaOH solution. blue litmus paper on a glass rod was put on the mouth of the test tube and Members of the group were assigned tasks any color changed was noted. Then the and collected the materials used in the experiment. sample was compared with water as a negative control. A. Physical State, color, and odor E. Nitration test The sample compounds hexane, heptane, cyclohexane, cyclohexene, benzene and toluene A nitrating mixture was prepared by adding were observed and noted for their physical state as 2ml of concentrated HNO3 and 2ml of concentrated solid, liquid or gas at room temperature, for their H2SO4 in an erlenmeyer flask immersed in an color and for their appearance as either clear or evaporating dish containing water. The sample was turbid. Next, the odor was described by wafting the cooled at room temperature. hand over the mouth of the test tube containing a sample. 5 drops of the sample was placed in a dry test tube. Then, 8 drops of the nitrating mixture was B. Solubility in Concentrated H2SO4 added on the sample and was shaken. Any formation of a yellow oily layer or droplet was A drop of the sample compound was added observed and was diluted with 20 drops of water. A in a test tube containing 1 ml of concentrated sample that resulted in no apparent reaction was H SO A sample was described as immiscible or o 2 4. heated in a water bath at approximately 50 C for 10 misicible when they form a layer or not. minutes and was observed. C. Ignition Test F. Basic Oxidation test 3 drops of the liquid sample was placed in a 4 drops of the sample was placed in a dry small evaporating dish and was observed as test tube. Then, 8 drops of 2% KmnO4 solution and flammable or not by putting a lighted match on it. 3 drops of 10% NaOH solution was added into it The flame was observed as either luminous or non- and heated in a water bath for 2 minutes. Any color luminous, and if it produced soot or not. change and formation of a brown precipitate was observed. D. Tests for active unsaturation a. Baeyer’s test

RESULTS AND DISCUSSION

Table 1: Results

HEXANE HEPTANE CYCLOHEXANE CYCLOHEXENE BENZENE TOLUENE

Condensed structural formula

Physical Liquid Liquid Liquid Liquid Liquid Liquid state at RT

Appearance Clear Clear Clear Clear Clear Clear

Color Colorless Colorless Colorless Colorless Colorless Colorless

Odor Plastic balloon- Chlorine odor Detergent-like Acetone-like Flowery odor Rugby-like like

Solubility in Formation of a Formation of a Formation of a Formation of an Formation of Formation concentrated black layer clear oily layer clear oily layer orange layer a yellow of a clear

H2SO4 green layer oily layer

Inference Immiscible Immiscible Immiscible Immiscible Immiscible Immiscible

Ignition test Luminous Luminous flame Luminous flame Luminous flame Luminous Luminous flame flame with flame with soot soot

Inference Flammable Flammable Flammable Flammable Flammable Flammable

Baeyer’s test No formation No formation of No formation of Formation of No formation No of brown brown suspension brown brown of brown formation of suspension suspension suspension suspension brown suspension

Bromine test No change No change No change Reddish Brown No change No change to colorless

Inference Not actively Not actively Not actively (+) actively Not actively Not actively unsaturated unsaturated unsaturated unsaturated unsaturated unsaturated

Nitration Formation of a Formation of a Formation of a Black Formation of Formation clear oily layer clear oily layer clear oily layer a yellow oily of a yellow layer oily layer with brown ppt

Inference Aliphatic Aliphatic Aliphatic Not aromatic Aromatic Aromatic

Basic No precipitate No precipitate No precipitate Bluish green to No Bluish black oxidation brown precipitate precipitate

Inference Not an arene Not an arene Not an arene Not an arene Not an arene Arene

A. Physical State, Color, and Odor Generally, saturated hydrocarbons specifically alkanes are not as reactive as other The Physical properties of hydrocarbons hydrocarbons. The reasons are alkanes do not determine thier reactivity. Aliphatic hydrocarbons: have double or triple bonds that can react with acid alkane (CnH2n+2), cycloalkane (CnH2n), alkene to form carbocations and they have no leaving (CnH2n-2) and alkyne (CnH2n-4) consist only of weak groups making them incapable of E1, E2, SN1 or dispersion forces. This forces account for their low SN2 reactions. However, unsaturated hydrocarbons boiling points thus they exist in such physical state specifically alkenes are more reactive than alkanes at room temperature. They are less dense than because they can undergo addition reactions water, thus they are non-polar and soluble in each (Carey, 2014). Thus, sulfuric acid reacts differently other (Brown & Poon, 2014). with both alkenes and aromatic hydrocarbons (refer to Figure 1). In alkenes, sulfuric acid adds to Aromatic hydrocarbons have physical cyclohexene via an acid catalyzed addition however properties that vary depending on the nature of their it won’t react with cyclohexane. In aromatic substituent. Alkylbenzenes, such as the sample hydrocarbons, sulfuric acid reacts with toluene via toluene, are like aliphatic hydrocarbons. They are sulfonation. This is conferred by the formation of an nonpolar and have lower boiling point than orange layer (refer to Figure 2). Aromatic benzenes with a polar substituent. These account hydrocarbons such as toluene are also reactive for their physical state at room temperature. Being because they undergo nucleophilic aromatic an aromatic hydrocarbon, toluene has a distinct substitution reactions (Giovine, 2011). smell (Greenshields & Rossini, 1958). C. Ignition Test

Most hydrocarbons burn over a flame since B. Solubility in Concentrated H2SO4 carbon and hydrogen react with oxygen to produce carbon dioxide and water (refer to figure 3) (Giovine, 2011).

Figure 1: Solubility Reaction Mechanism

Figure 3: Ignition Reaction Mechanism

Figure 2: Solubility in concentrated H2SO4

The solubility of hydrocarbons is based on the principile “Like dissolves Like”. The solubility or miscibility of the compoundsin H SO can indicate 2 4 their acidity and basicity. They can indicate a weak Figure 4: Ignition of toluene produced soot base (can be protonated) or a neutral compound (cannot be protonated) (Smith, 2006).

The ignition test was performed in essence F. Basic Oxidation test that high carbon to hydrogen ratio equates to high luminosity. A high degree of luminosity accounts for the luminous flame, an orange flame which may produce soot. Aromatic compounds, such as benzene and toluene (refer to figure 4), burn with sooty flame due to incomplete combustion causing the formation of an unburned carbon. Complete combustion is indicated by a non-luminous flame which is a blue flame. It produces more heat than light; hence the carbon is completely oxidized (Smith, 2006). Figure 6: Basic Oxidation Reaction Mechanism D. Tests for active unsaturation Basic oxidation used potassium a. Baeyer’s test permanganate which is a strong oxidizing agent. Figure 6 shows the reaction as potassium permanganate oxidizes the carbon-carbon double or triple bond by replacing them with a hydroxy group (-OH group). Thus the carbon’s charge changes from being +1 to +2 by losing an electron Figure 5: Nitration test result (oxidized). When it dissolves in water, it produces Baeyer’s test result indicates that intense purple solution. NaOH was used to cyclohexene is positive for active unsaturation determine whether the samples will form a confirming that it contains a double bond in its precipitate (Giovine, 2011). chemical structure. Cyclohexene decolorized the REFERENCES purple solution then formed a brown precipitate. 7+ The addition of KmnO4 solution caused Mn to be Bathan, G. I., Bayquen, A, V., Cruz, C, T., et.al. (2014). reduced to Mn4+ in the process of redox reaction. Laboratory Manual in Organic Chemistry Revised Edition. (Smith, 2006). Alkenes react with potassium Manila: C&E Publishing Inc. permanganate (KMnO4) to give a diol and MnO2 Carey, F. (2014). Hydrocarbon. In Encyclopædia Britannica. while Aromatic compounds do not react because of http://www.britannica.com/EBchecked/topic/278321/hydrocarbon their stability (Greenshields & Rossini, 1958). Brown, W., & Poon, T. (2014). Introduction to Organic Chemistry: b. Bromine test International Edition (5th ed.). New Jersey: John Wiley & Sons Inc.

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