QUALITATIVE ANALYSIS OF UNKNOWN ORGANIC COMPOUND THROUGH PHYSICAL PROPERTIES ANALYSIS, ELEMENT ANALYSIS AND FUNCTIONAL GROUP ANALYSIS

By

I Kadek Irvan Adistha Putra

Chemistry Education Departement, Faculty of Mathematics and Natural Science,

Ganesha University of Education

Jalan Udayana Singaraja-Bali

Email: irvan.adistha@gmail.com

Abstract

The objectives of this experimental research are (1) to determine the physical properties of the unknown organic sample, (2) to analyze the elements contained in unknown organic sample, (3) to analyze the functional group contained in unknown organic sampled and (4) to determine the derivative compound contained in unknown organic sample. The subject of this experiment is unknown sample which was prepared by laboratory staff. The object of this experiment is the unknown sample of organic compound, especially the structure of organic compounds. From the analysis of physical properties, it is obtained the boiling point of the unknown sample of organic compound, 111^oC. Data from the element analysis show that only carbon and hydrogen contained in this unknown organic sample. It has unsaturated bonding and positive as aromatic compound. It does not have any derivative compound. All of the data obtained direct the unknown sample into Toluene, which has similar properties with the unknown sample. Therefore, the unknown sample is toluene.

Keyword: Qualitative analysis, unknown organic compound, toluene

INTRODUCTION

The qualitative analysis of organic compound is series of procedural analysis in order to determine the identity of organic compound, especially name, constituent and structure of organic compound. According to Suja and Nurlita (2004), there are four important steps that must be done to identify the unknown organic compounds, namely (1) physical properties determination, (2) qualitative analysis of elements, (3) determination of functional groups, and (4) making of derivative of the compound.

First analysis that must be conducted is the physical properties analysis. The physical properties analysis cover the iden-tification of melting points, identification of boiling points and identification of refractive index. Both of them are important in determination of organic compounds. They are present the physical properties of organic compounds.

The second analysis is the analysis of the constituent element of the organic compounds. There are analysis of carbon, analysis of hydrogen, analysis of nitrogen, analysis sulfur and analysis of Halogen. If the constituent elements is known it can be considered the possible formula of the unknown organic compounds.

The third analysis is analysis of contained functional group. There are analysis of unsaturated bond, analysis of aromatic compounds, analysis of phenolate group, analysis of ketones and aldehyde groups, analysis of hydroxyl group and analysis of ether group. If the contained functional group known, the structure of unknown organic compounds can be more specified. Then it can be proven by making the derivatives as the last step.

Generally, organic compounds is already compound is already contained element of carbon and hydrogen. Therefore, test for carbon and hydrogen is not necessary. But, in order to make more valid data, test of carbon and hydrogen is conducted. To identify the existence of carbon and hydrogen in organic compound, addition of Cupper (II) oxide (CuO) can be done. Then, it is continued by CO₂ and H₂O test. The existence of H₂O can turn the silica gels into blue. CO₂ gas is flowed into lime water. The CO₂ gas will make the solution become turbid. The reactions occur is as follows

C_xH_y + CuO  à  Cu_(s) + H₂O_(g) + CO_2(g)

Oxygen can be identified by Ferox reagent. Ferox reagent is mixture of KCNS and FeCl₃ in methanol. The change of red color in ferox paper into brighter red indicates the existence of oxygen.

Additional elements are usually detected by Lassaigne's test. In this test, organic compounds fused with sodium metal to convert the elements into water-soluble sodium salt. And then the extract was used to test additional elements in organic compounds, namely nitrogen, sulfur and halogen.

As written before, the functional group analysis is important. Baeyer test is used to detect saturated compounds. It uses an alkaline solution of KMnO₄, if the sample contains a double bond then the reaction will occur as follows:

 

When an organic compound containing unsaturated bonds or double bonds (-C = C-), then the solution of KMnO₄ color fading.

Bromine test is also used to detect unsaturated bonds. If the sample to be tested contains a double bond (-C = C-), then the brown color of bromine disappears. The reaction is as follows:

 

Aliphatic or aromatic compounds is tested by using smoke test. If smoke is formed, the unknown organic compounds is belong to aromatic compounds.

Hydroxyl group test performed with the 2 test fiber-ammonium-nitrate and acetyl chloride test. Test fiber-ammonium-nitrate reagent solution using fiber-ammonium-nitrate to test for the presence of hydroxyl groups on organic compounds. Test will be positive when there is a red color to the mixture. Acetyl chloride test is a test that uses acetyl chloride reagent to produce a gas that will be tested further with NH₄OH solution. Test will be positive if the smoke is formed when gas approximated with NH₄OH solution.

Phenolic group test is the test to determine whether there is the presence of phenol groups in organic compounds. Tests were conducted using the test ferrichloride FeCl₃ reagent. Test will be positive if the mixture of FeCl₃ with organic substances dissolved in alcohol change color to purple, blue, green, or red wine.

Aldehyde test can be done with a test Fehling and Tollens test. Fehling tests using a mixture of Fehling's solution A and Fehling B as a reagent to test the existence of un-aldehyde. This test will be positive if after mixed Fehling and organic matter is heated in a water bath to form a brick red precipitate that Cu₂O. Tollens test is also a test to test for aldehydes using the Tollens reagent mixture of AgNO₃, NaOH, and NH₄OH. This test will be positive if the Tollens reagent mixtures and organic substances to form a silver mirror on the wall of the reaction tube.

Ketone group test performed with 2 test which tests DNP (2,4-dinitrofenil hid-resin) and iodoform test. Tests using the reagent 2,4-DNP hydrazine dinitrophenyl to test the un-organic substances. Test will be positive if a precipitate is formed after download DNP reagent mix and organic substances in dilute HCl. Iodoform test uses a solution of iodine in the KI as a reagent. The test will be positive if the color fades and iodine iodoform yellow precipitate formed.

Carboxyl group test can be done with the 2 test of Na-bicarbonate and the formation of esters. Na-bicarbonate test is a test used to test for the presence of carboxyl groups with sodium bicarbonate reagent. This test will be positive if the bubbles are formed when the addition of a solution of sodium bicarbonate. This can be supported by the following equation.

CH₃COOH + NaHCO₃ → CH₃COONa (aq) + H₂CO₃ (aq) H₂CO₃ → H₂O (g) + CO₂ (g)

Ester group test is done by using a saturated solution of reagent hydroxylamine hydrochloride, KOH, a solution of FeCl₃ and HCl solution. This test will be positive if the color changes to red wine.

Ether group test performed using a mixture of reagent cupriacetate and benzydine hydrochloride. This test will be positive if the filter paper changes color changed to blue.

Nitro group test performed using nitrite solvent and reagent NaOH. This test aims to determine whether classified nitro-alkane primary or secondary nitroalkane. Will be classified as primary nitroalkane when after the addition of NaOH reagent turns red and the primary would fall if there is no change in color after the addition of reagents

MATERIALS, EQUIPMENT AND METHODS

     This experiment was conducted three times at Organic Chemistry Laboratory of Chemistry Education Department, Faculty of Mathematics and Natural Sciences, Ganesha Education University on 2^nd of September 2013, 9^th of September 2013 and 16^th of September 2013.

Materials:

The sample used was liquid samples. This experiment was conducted in some steps, namely (1) determining the boiling point (2) element analysis (3) determining the functional group (4) determining the derivatives compound. On the first and second step, the materials used namely oil, unknown liquid sample which is colorless, dry copper oxide powder, silica gel, solid potassium thiocyanate (KSCN), solid iron (III) chloride (FeCl₃), toluene, sodium, ethanol, aquades, acetic acid solution, Pb-acetate solution, sodium nitrorupsid solution, Mohr salt solution (FeSO₄), sodium hydroxide (NaOH) solution, concentrated sulfuric acid (H₂SO₄), concentrated nitric acid (HNO₃), silver nitrate (AgNO₃)solution, ammonium hydroxide (NH₄OH) solution, and limestone. Then, for the third and fourth step, it needed some materials namely, unknown liquid sample, aquades, Baeyer solution (KMnO₄ solution), carbon tetrachloride (CCl₄) solution, and bromine (Br₂) solution.

Equipment:

Some equipment used to support this experiment namely beaker glasses 100 mL, beaker glass 500 mL, graduated cylinder10 mL, graduated cylinder 25 mL, Erlenmeyer flask 100 mL, Thiele tube, thermometer, capillary pipe, test tubes, small test tube, a non-Pyrex test tube, a test tube rack, spatula, drop pipette, watch glass, funnel, glass flowing, test tube holder, and spirits burner.  

Methods:

            The methods used in this experiment exactly follows the practicum manual proposed by Nurlita and Suja (2004). Firstly,  in the determination of boiling point, one tip of capillary pipe was melted until covered. While, 0.25-0.5 mL ofliquid unknown sample was poured into small test tube. Then , the capillary pipe which has been melted (covered tip of capillary pipe was on the top) was entered into the small test tube which already contains liquid unknown sample. After that , the small test tube was bounded to the tip of thermometer. This set of equipment was entered into steam bath of oil (Thiele tube which contains oil). Last , the boiling point of this liquid unknown sample was record.

Next ,it was done analysis of the elemnt. Fisrt, detection of carbon and hydrogen. The sample was mixed with dry powder of copper oxide (CuO).  This mixture then was poured into test tube and dried. The test tubes was heated until all the substance changed into CO₂ and H₂O.  Gas of CO₂ was tested by flowing the gas produced,  then flowing the lime water with the gas diverter (when contains CO₂, it raised the turbidity). Water (H₂O) was tested by flowing the gas through silica gel CuSO₄ anhydrate (when the silica gel changed become blue, there was H₂O).

Second, it was caaried out the detection of oxygen. The sample was dissolved in toluene as solvent. On the other hand, the filter paper (which already given ferox reagent) was prepared and dried. Then, the sample was dropped on the ferox paper (when the ferox paper turn into red color, it means that the sample contains oxygen).

Third, detection of nitrogen, sulfur and halogen that it should be started by making extraction of sodium. The sample was placed in the test tube. Then, a piece of sodium metal (which already dried by filter paper) was added into the test tube. This incandescent sample was heated to get perfect reaction. In this process, ethanol was added to remove the excess of sodium. The mixture was heated until produced red color. After that, the mixture was dissolved in distilled water (breaking the test tube). Last, the solution was filtered to get the filtrate (lassaigne filtrate).

In the detection of sulfur, sodium extraction (± 2 mL) was pickled by acetic acid and heated (it was tested by litmus paper to know its acidity). While , filter paper was added to the solution of Pb-acetate 10% and then filter paper was approximated to the test tube (gasses testing). Then, the change on the filter paper was observed (black color indicated the existence of sulfur). Last, sodiumnitropusid solution was dropped on the rest of filtrate on the test tube (black color indicated the existence of sulfur).

In the detection of nitrogen, sodium extraction (± 2 mL) was added into FeSO₄ solution (Mohr salt). Then, it was heated until boiled. Then, it was cooled and acidified by H₂SO₄ solution until the precipitate was soluble. Last, the change was observed and recorded (when it appeared blue-green or blue passion color, it indicated the existence of nitrogen).

In the detection of halogen, extraction of sodium (± 2 mL) was acidified by using concentrated HNO₃ and then it was boiled. Then, it was cooled and added by 1 mL l of AgNO₃ solution.  The white or yellowed precipitate indicated the existence of halogen.

Then, it was done detection of unsaturated compound. This experiment was conducted by using Baeyer test and Bromine test. In Baeyer test, Baeyer solution (solution of alkaline KMnO₄) was added drop by drop into the sample in water while shaken. When the color of KMnO₄ was faded, it indicated positive of unsaturated bond. In the test of bromine, sample was dissolved in CCl₄ and added solution of 5% Br₂ in CCl₄ drop by drop while shaken. When the brown color turned into colorless, it indicated positive of unsaturated bond.

Detection of aromatic compound was started by placing the sample on the spatula, and then it was heated on the spirtus. The existence of smokes indicated the aromatic compound. The detection of functional group that contain oxygen is not conducted because the sample is already known that is not contain oxygen. The making of derivative compounds is also not conducted.

RESULT AND DISCUSSION

            In this experiment, the sample used was liquid samples. So, it was started by determining the boiling point of the sample. It used Thiele equipment. From the observation, it can be determined that the boiling point of the sample is 111⁰ C.

The results for the element analysis and functional group can be seen as the following tables:

Table 1. Observation Result of Element Analysis of Unknown Organic Sample

Element	Observation	Identification
Carbon	Carbon dioxide gas was produced	Positive toward carbon
Hydrogen	Water vapor was produced	Positive toward hydrogen
Oxygen	No red color was produced on the ferox paper after the sample was added.	Negative toward oxygen
Nitrogen	No green suspension was produced	Negative toward nitrogen
Sulfur	No black color was formed on filter paper containing Pb(CH3COOH)210%	Negative toward sulfur
Halogen	No white precipitate was formed	Negative toward halogen

Table 2. Result of Functional Group

Functional Group	Observation	Identification
Unsaturated bond	a)   In Baeyer test, addition of sample solution turned the violet color KMnO4 to become faded. b)  Addition of sample solution turned solution to colorless (Bromine test)	Positive
Aromatic  compound	in the smoke test, black smoke was formed by using smoke test	Positive

Since the result from the element analysis yield that the unknown organic substance only contain carbon and hydrogen, therefore it was only detected the unsaturated compound and the aromatic compound.

The test for functional group that contain oxygen is not conducted because the sample is already known not contain oxygen. Therefore, it is not possible for the sample to contain functional group that contain oxygen.Based on the experiment it is obtained data, namely the boiling point of the unknown sample of organic compounds is 111^oC, the constituent element are only carbon and hydrogen. The unknown sample of organic compounds also detected to has unsaturated bonds and aromatic rings. By using the data it can be identified the possible structure of the compound.

The unknown organic compound must has aromatic ring, because the aromatic ring test resulted in positive. Then, by considering the only constituent element are carbon and hydrogen, and the boiling point is 111^oC, the most possible structure for this unknown organic compound is Toluene.

Morrison and Boyd (1989) report that Toluene has the same characteristics as the writers reported. The toluene only has carbon and hydrogen, and the boiling point is ±111^oC. Jespersen, Brady and Hyslop (2012) strengthen the Morrison explanation by providing some additional information. Wade (2010) also stated that toluene has the same characteristics as the writers reported.   Therefore, by considering the three textbooks, it can be stated the unknown organic compound is toluene.  

The general structure of toluene is as follows.

CONCLUSION

Based on the explanation above, it can be concluded that the unknown organic compound is toluene which has boiling point ±111^oC.

ACKNOWLEDGEMENT

            Writer want to say thanks to Mr.I Nyoman Tika, as the lecturer, who always give the writer guidance, Mrs. Dewi Wirmandiyanthi, as the assistant lecturer, who assist writer in doing the practicum and Mr. Ketut Lasia as the laboratory staff who provide writer equipment and materials for practicum. Thanks also for writers group and all of writer’s beloved friends.

REFERENCES.

Jespersen, N. D., Brady, J. E., & Hyslop, A. (2012). Chemistry: The Molecular Nature of Matter. Hoboken: John Wiley & Sons, Inc

Morrison and Boyd. 1983. Organic Chemistry Fourth Edition. Singapore: Allyn and Bacon Inc.

Nurlita, F., & Suja, I. W. (2004). Buku Ajar: Praktikum Kimia Organic. Singaraja: IKIP Negeri Singaraja.

Wade Jr, L.G. (2010). Organic Chemistry. Upper Saddle River: Pearson Eduation, Inc.