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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 H 2SO4, 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% KmnO 4 solution and 10 drops of 0.5% Br 2 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 compounds containing only the elements carbon and hydrogen. They can be classified in many ways. One, a hydrocarbon skeleton can be acyclic (open chained) or cyclic (closed chain). Two, a hydrocarbon can be classified as aliphatic or aromatic based on its sources and properties. Aliphatic (from the Greek: aleiphar meaning fat or oil) describes a hydrocarbon that resembles long carbon-chain molecules derived from animal fats, but more conviniently, when the chemical structure contains no ring. Aromatic describes a hydrocarbon that resembles pleasant smelling plant extracts, but more conviniently, when the chemical structure contains a ring (Carey, 2014). Aliphatic hydrocarbons can be divided into an alkane, alkene or alkyne based on the types of bonds they contain. Alkanes are saturated hydrocarbons that contain only carbon-carbon single bonds. Alkenes and Alkynes are unsaturated hydrocarbons that contain a carbon-carbon double bond or triple bond, respectively. As mentioned, “saturated” is a way to describe a bond, meaning each carbon (a tetravalent atom) contains the maximum number of

bonds attached to it. Thus, a hydrocarbon that is saturated has all sigma bonds however it is actively unsaturated when it has both sigma bond and pi bonds. Moving on, aromatic hydrocarbons can be classified as an arene when it contains an alkyl side chain (Brown & Poon, 2014). The sample compounds used in this experiment are hexane, heptane, cyclohexane, cyclohexene, benzene and toluene. Hexane, C6H14, is a chemical made from crude oil. Heptane, C7H16, is a chemical derived from the fractional distillation of petroleum. Cyclohexane, C 6H12, is a colorless liquid cycloalkane that is made by passing benzene and hydrogen under pressure over a heated Raney o nickel catalyst at 150 C or by the reduction of cyclohexanone. Cyclohexene, C 6H10, is a colorless liquid cycloalkene that is prepared by dehydration of cyclohexanol by thermal reaction of ethylenepropylene-butadiene. Benzene, C6H6, is a liquid aromatic hydrocarbon found in gasoline and other fuels (National Center for Biotechnology Information, n.d.). Toluene, C7H8, is a liquid

aromatic hydrocarbon that occurs naturally in crude oil and in the tolu tree (ATSDR, 2011). The objectives of this experiment are to differentiate the intrinsic physical and the chemical properties of hydrocarbons using these compunds, and to determine if they are saturated, actively unsaturated, aromatic or an arene.

5 drops of the sample was placed in a dry test tube. Then, 2 drops of 2% KmnO4 solution was added into it and was shaken vigorously. The extent of decolorization of the reagent was observed.

b. Bromine test

MATERIALS AND METHODS The sample compounds used in this experiment are hexane, heptane, cyclohexane, cyclohexene, benzene and toluene. The reagents used in the different classification tests are concentrated H 2SO4, concentrated HNO 3, 2% KmnO4 solution, 0.5% Br2 in CCl4 reagent, and 10% NaOH solution. Members of the group were assigned tasks and collected the materials used in the experiment. A. Physical State, color, and o dor The sample compounds hexane, heptane, cyclohexane, cyclohexene, benzene and toluene were observed and noted for their physical state as solid, liquid or gas at room temperature, for their color and for their appearance as either clear or turbid. Next, the odor was described by wafting the hand over the mouth of the test tube containing a sample. B. Solubility in Concentrated H 2SO4 A drop of the sample compound was added in a test tube containing 1 ml of concentrated H2SO4. A sample was described as immiscible or misicible when they form a layer or not. C. Ignition Test 3 drops of the liquid sample was placed in a small evaporating dish and was observed as flammable or not by putting a lighted match on it. The flame was observed as either luminous or nonluminous, and if it produced soot or not. D. Tests for active unsaturation a. Baeyer’s test

5 drops of the sample was placed in a dry test tube. Next, 10 drops of 0.5% Br2 in CCl4 reagent was added into it and was shaken vigorously. The extent of decolorization of the reagent was observed or when the red-brown bromine was discharged. Optionally, a blue litmus paper on a glass rod was put on the mouth of the test tube and any color changed was noted. Then the sample was compared with water as a negative control. E. Nitration test A nitrating mixture was prepared by adding 2ml of concentrated HNO 3 and 2ml of concentrated H2SO4 in an erlenmeyer flask immersed in an evaporating dish containing water. The sample was cooled at room temperature. 5 drops of the sample was placed in a dry test tube. Then, 8 drops of the nitrating mixture was added on the sample and was shaken. Any formation of a yellow oily layer or droplet was observed and was diluted with 20 drops of water. A sample that resulted in no apparent reaction was o heated in a water bath at approximately 50 C for 10 minutes and was observed. F. Basic Oxidation test 4 drops of the sample was placed in a dry test tube. Then, 8 drops of 2% KmnO4 solution and 3 drops of 10% NaOH solution was added into it and heated in a water bath for 2 minutes. Any color change and formation of a brown precipitate was observed.

RESULTS AND DISCUSSION Table 1: Results HEXANE

HEPTANE

CYCLOHEXANE

CYCLOHEXENE

BENZENE

TOLUENE

Physical state at RT

Liquid

Liquid

Liquid

Liquid

Liquid

Liquid

Appearance

Clear

Clear

Clear

Clear

Clear

Clear

Color

Colorless

Colorless

Colorless

Colorless

Colorless

Colorless

Odor

Plastic balloonlike

Chlorine odor

Detergent-like

Acetone-like

Flowery odor

Rugby-like

Solubility in concentrated H2SO4

Formation of a black layer

Formation of clear oily layer

Formation of a clear oily layer

Formation of an orange layer

Formation of a yellow green layer

Formation of a clear oily layer

Inference

Immiscible

Immiscible

Immiscible

Immiscible

Immiscible

Immiscible

Ignition test

Luminous flame

Luminous flame

Luminous flame

Luminous flame

Luminous flame with soot

Luminous flame with soot

Inference

Flammable

Flammable

Flammable

Flammable

Flammable

Flammable

Baeyer’s test

No formation of brown suspension

No formation of brown suspension

No formation of brown suspension

Formation brown suspension

No formation of brown suspension

No formation of brown suspension

Bromine test

No change

No change

No change

Reddish Brown to colorless

No change

No change

Inference

Not actively unsaturated

Not actively unsaturated

Not actively unsaturated

(+) actively unsaturated

Not actively unsaturated

Not actively unsaturated

Nitration

Formation of a clear oily layer

Formation of clear oily layer

Formation of a clear oily layer

Black

Formation of a yellow oily layer

Formation of a yellow oily layer with brown ppt

Inference

Aliphatic

Aliphatic

Aliphatic

Not aromatic

Aromatic

Aromatic

Basic oxidation

No precipitate

No precipitate

No precipitate

Bluish green to brown precipitate

No precipitate

Bluish black

Inference

Not an arene

Not an arene

Not an arene

Not an arene

Not an arene

Arene

Condensed structural formula

a

a

of

A. Physical State, Color, and Odor The Physical properties of hydrocarbons determine thier reactivity. Aliphatic hydrocarbons: alkane (C nH2n+2), cycloalkane (CnH2n), alkene (CnH2n-2) and alkyne (CnH2n-4) consist only of weak dispersion forces. This forces account for their low boiling points thus they exist in such physical state at room temperature. They are less dense than water, thus they are non-polar and soluble in each other (Brown & Poon, 2014). Aromatic hydrocarbons have physical properties that vary depending on the nature of their substituent. Alkylbenzenes, such as the sample toluene, are like aliphatic hydrocarbons. They are nonpolar and have lower boiling point than benzenes with a polar substituent. These account for their physical state at room temperature. Being an aromatic hydrocarbon, toluene has a distinct smell (Greenshields & Rossini, 1958).

Generally, saturated hydrocarbons specifically alkanes are not as reactive as other hydrocarbons. The reasons are alkanes do not have double or triple bonds that can react with acid to form carbocations and they have no leaving groups making them incapable of E1, E2, SN1 or SN2 reactions. However, unsaturated hydrocarbons specifically alkenes are more reactive than alkanes because they can undergo addition reactions (Carey, 2014). Thus, sulfuric acid reacts differently with both alkenes and aromatic hydrocarbons (refer to Figure 1). In alkenes, sulfuric acid adds to cyclohexene via an acid catalyzed addition however it won’t react with cyclohexane. In aromatic hydrocarbons, sulfuric acid reacts with toluene via sulfonation. This is conferred by the formation of an orange layer (refer to Figure 2). Aromatic hydrocarbons such as toluene are also reactive because they undergo nucleophilic aromatic substitution reactions (Giovine, 2011). C. Ignition Test

B. Solubility in Concentrated H 2SO4

Most hydrocarbons burn over a flame since 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 H2SO 4 can indicate their acidity and basicity. They can indicate a weak base (can be protonated) or a neutral compound (cannot be protonated) (Smith, 2006) .

Figure 4: Ignition of toluene produced soot

The ignition test was performed in essence 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). D. Tests for active unsaturation a. Baeyer’s test

Figure 5: Nitration test result

Baeyer’s test result indicates that cyclohexene is positive for active unsaturation confirming that it contains a double bond in its chemical structure. Cyclohexene decolorized the purple solution then formed a brown precipitate. 7+ The addition of KmnO4 solution caused Mn to be 4+ reduced to Mn in the process of redox reaction. (Smith, 2006). Alkenes react with potassium permanganate (KMnO4) to give a diol and MnO 2 while Aromatic compounds do not react because of their stability (Greenshields & Rossini, 1958). b. Bromine test Bromine solution in carbontetrachloride is used to identify alkanes, alkenes and alkynes. Bromine test only reacted with cyclohexene thus it is actively (+) unsaturated. Saturated hydrocarbons will only react with bromine only if there is UV light thus no reaction occurred. Aromatic hydrocarbons will only react with bromine if there is a strong Lewis acid catalyst such as FeBr3 (Giovine, 2011). E. Nitration test Nitration test is used to determine aromaticity. Benzene and toluene gave a positive result by forming a yellow oily layer; hence, the two compounds are aromatic. The H 2SO4 acts as a catalyst facilitating the formation of the electrophile nitronium ion (NO2+). The reaction involves electrophilic substitution because hydrogen is replaced by nitronium ion (Hoggett, et.al., 1971).

F. Basic Oxidation test

Figure 6: Basic Oxidation Reaction Mechanism

Basic oxidation used potassium 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 (oxidized). When it dissolves in water, it produces intense purple solution. NaOH was used to determine whether the samples will form a precipitate (Giovine, 2011). REFERENCES Bathan, G. I., Bayquen, A, V., Cruz, C, T., et.al. (2014). Laboratory Manual in Organic Chemistry Revised Edition. Manila: C&E Publishing Inc. Carey, F. (2014). Hydrocarbon. In Encyclopædia Britannica. http://www.britannica.com/EBchecked/topic/278321/hydrocarbon Brown, W., & Poon, T. (2014). Introduction to Organic Chemistry: International Edition (5th ed.). New Jersey: John Wiley & Sons Inc. National Center for Biotechnology Information. (n.d.). Benzene. National Library of Medicine. Retrieved from http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=807 8 ATSDR: Agency for toxic substances and disease registry. (2011). Toluene. Atlanta: (np). Greenshields, J., & Rossini, F. (1958). Molecular Structure and Properties of Hydrocarbons and Related Compounds. Journal of Physical Chemistry, 271–280. Smith, J. (2006). Organic Chemistry (3rd ed.). New York: McGraw-Hil Giovine, M. (2011). Properties of hydrocarbons. Texas: (np). Retrieved from http://www.mendelset.com/articles/689/properties_hydrocarbons Hoggett, J. G., Moodiej, R. B., Penton, J. R. and Schofield, K. (1971). Nitration and aromatic reactivity. London: Cambridge University Press...