ARTICLE 1: ORGANIC CHEMISTRY EXPERIMENT

DETERMINATION THE NAME AND STRUCTURE OF UNKNOWN SAMPLE ORGANIC SUBSTANCE BY QUALITATIVE ANALYSIS

By

Ni Ketut Sepmiarni

Chemistry Education Department, FMIPA, UNDIKSHA

Udayana Street Singaraja, Bali

Emai: arnisepmiarni@yahoo.com

Abstract

The aim of the experiment was to determine the name and structure of organic substance that contain in unknown sample through determine physical properties namely melting point, identify component of organic compound through identification of carbon and hydrogen, identification of oxygen, identification of sulfur, nitrogen, and halogens, detect functional group such as unsaturated, aliphatic or aromatic, hydroxyl group of alcohol, fenolat group, aldehyde group, carboxyl group, ester, eter, and nitro group, and derivative compound of organic substance that contain in unknown sample. The object of this research is unknown sample (white powder) of organic substance that already prepared and only known by laboratory assistant. The method used in this experiment was qualitative analysis. The result of this research indicated that the unknown sample is benzoic acid by IUPAC name with chemical formula (C₇H₆O₂). This result was supported by the melting point 121.5^oC – 122^oC , positive content element carbon, positive contain unsaturated bond means has double bond, has carboxyl group, positive hydroxyl group of alcohol,  aromatic compound, positive of ester that indicated derivate of carboxylic acid, and produce fruit aroma.

Key word: organic compound, qualitative analysis, benzoic acid

INTRODUCTION

Organic chemistry is the study of compounds that contain carbon. The element carbon that justifies living organisms are making it the basis of a whole branch of chemistry, whereas substances that may contain any of the others elements. The bonding of organic substances is almost entirely covalent. The substances may be gases, liquids, or solids with low melting points (less than 360^oC). They are mostly insoluble in water, but soluble in organic solvents such as gasoline, benzene, and carbon tetrachloride (Frederick, 1995).  The reactions are usually slow and almost all burn. Then, to determine and identify the type of organic substance, the qualitative analysis can be used as well as involves chemical and physical properties of unknown organic substance.

   Qualitative analysis is important to be done for knowing the unknown sample of organic substances. It involves the physical and chemical properties of the unknown substances. The physical properties are such as melting point and solubility. Chemical properties are improving the reaction that take place. The crystal of pure organic compound has certain and sharp melting point. The difference of melting point between start melting and perfect melting is not more than 0.5⁰C (Pengantar Praktikum Kimia Organik, 24).

Carbon and hydrogen for identification the presence of carbon and hydrogen elements in organic compounds can be done by adding substances Copper (II) oxide or CuO. In addition to the CuO content of carbon and oxygen tests can proceed with testing of CO₂ and H₂O. The emergence of H₂O can be observed in the presence of water vapor and CO₂ tests can be done by inserting incense into a test tube which contained substances that were tested after heating. If positive for CO₂, the flame will be extinguished in the incense. The reaction is as follows.

C_xH_y CuO + Cu _(s)  à H₂O _(g) + CO_{2 (g)}

The sulfur compounds are quite easily found in nature is SO­ or sulfur dioxide. SO₂ sulfur compounds have a characteristic odor and sharp. In sulfur compound is in the form of the anion, the anion sulfite and sulfate anions.

SO₂ + OH^-  à   H⁺ + SO₃^2-

SO₃ + OH^-  à   H⁺ + SO₄^2-

Sulfite anion can be changed the form become sulfate ion by react it with porexide (H₂O₂). Identification of sulfite anion can be conducted by using BaCl₂.

          Nitrogen The element nitrogen can be in the form of nitrite and nitrate to identify it can be done by reacting the sample with a solution resorcinol 20% in acetic acid was then added Mohr salt (FeSO₄ (NH₄) ₂SO₄). If positive for the presence of nitrogen it will form an emerald green color in one minute. In addition, it can also be done with a brown ring test. The sample is treated with concentrated H₂SO₄ and FeSO₄. A brown ring is formed at the place where the two fluids meet. Brown ring is caused by the formation of complex [Fe(NO)]²⁺.

          Halogen (chlorine, bromine, and iodine) Chlorine, Bromine, and Iodine classified as a class of organic halogens. Where, organic halogen can be joined by hydrogen from cellulose wrapping paper and form hydrogen halides. Identification of an anion of halogen groups can be done with a test of silver nitrate (AgNO₃). Testing positive for the presence of chlorine can be observed from the formation of a white precipitate of AgCl is soluble in dilute ammonia but insoluble in dilute HNO₃. If the AgCl precipitate was filtered, washed with distilled water and then shaken with sodium arsenite, deposits will be converted into a yellow silver arsenite. This reaction can be used as a test of ascertainment of chloride (Pengantar Praktikum Kimia Organik, 30).

          Testing positive for bromine can be seen from the formation of AgBr pale yellow precipitate that is insoluble in dilute ammonia, but soluble in concentrated ammonia. The precipitate is also soluble in a solution of potassium cyanide and sodium thiosulfate, but not soluble in dilute HNO₃ .

Br^- + Ag⁺ à    AgBr  _{(yellow pale ppt)}

AgBr+2NH_{3concentrated}à [Ag(NH₃)₂]⁺ + Br^-

AgBr  + 2CN^-     à    [Ag(CN)2]- + Br^-

AgBr  + 2S₂O₃^2- à    [Ag(S₂O₃)₂]^3- + Br^-

          Positive test of iodine can be seen from the formation of a yellow precipitate AgI is easily soluble in a solution of potassium cyanide and sodium thiosulphate in solution, very slightly soluble in concentrated ammonia solution and insoluble in dilute nitric acid.

          Functional group identification is the second steps for identifying the unknown organic substances. Ethers has formula type R-O-R. As a rule, ethers are known by trivial names rather than Geneva names; the Geneva (systematic) names use –oxy- prefixed by the appropriate group name (Principle of Organic Chemistry, 224). Ketone and aldehide are the functional groups isomers. The nomenclature of aldehyde has suffix –nal and for ketone has suffix –non. Carboxylic acid derivatives are prepared from hydrolysis, esterification, subsitution, etc.

DNP test is a test identification of ketones using a solution of 2,4-DNP (dinitrophenylhydrazine). If such compounds containing a ketone group, then when the added compound DNP 2.4 will produce a crystal orange, red or yellow that is a descendant compound 2,4-DNP. Dinitrophenylhydrazine not react with other carbonyl such as, carboxylic acids, amides and esters. For carboxylic acids, amides and esters are related to the stability of resonances as a lone-pair p electrons interacting with the carbonyl carbon resulting in increased delocalization within the molecule. Therefore, this compound is more resistant to addition reactions.

            Iodoform test conducted to test the presence of ketone group in a solution. This test gives positive results for carbonyl compounds which have hydrogen atoms α position. In these reactions occur α position hydrogen substitution react with halogen atoms alkaline conditions. This substitution reaction continues and the subsequent termination of the C = O followed by the C-Halogen. If the halogen is iodine used to produce a yellow precipitate of iodoform (mp 119^oC).

            Tollens reagent test with ease based on the aldehyde group oxidized to carboxylic acid. Tollens reagent is prepared by dissolving AgNO₃ in water (solution A) and NaOH in water (solution B). If the reagent will be used, mix solution A and B with the same volume into a test tube and add dilute ammonia solution drop wise until all Ag₂O dissolved. Reaction of aldehydes with reagent tollens is the following.

 Figure 1.Reaction of aldehyde with reagent tollens

Fehling solution consists of two parts. Fehling A solution prepared by dissolving crystals of Cu (II) sulfate in water containing a few drops sulfuric acid and added water up to a certain volume. B Fehling solution is made by dissolving NaOH and sodium potassium (Rochelle salt) into the water until a certain volume. Aldehyde solution reduces Fehling produce Cu₂O precipitate a yellow or red.

 Figure 2.  Reaction of aldehyde solution reduce Fehling produce Cu₂O

Carboxylic acids are compounds that contain carboxyl group (carboxyl derived from carbonyl and hydroxyl). Carboxylic acid has the general formula R-COOH or C_nH_2nO₂, R can be hydrogen atom, an alkyl, aryl even another form of carboxyl groups. A molecule containing a carboxylic acid group (-OH) and by itself can form hydrogen bonds with water. Therefore the existence of hydrogen bonding, carboxylic acids containing one to four carbon atoms can be mixed with water. In addition, carboxylic acids also form hydrogen bonds with other carboxylic acid molecules. Here there are two hydrogen bonds between two carboxyl group. In a solution which has no hydrogen bonding, carboxylic acid as a pair of molecules that join the so-called dimmer (Buku Ajar Praktikum Kimia Organik, 10).

Carboxylic acid is recognizable by their solubility in aqueous sodium bicarbonate solution, to form carboxylic acid salts are soluble in water and carbonic acid which decomposes into CO₂ and H₂O.

CH₃COOH + NaHCO₃ → CH₃COONa + H₂CO₃

                                   CH₃COONa + CO₂ + H₂O

Carboxyl group test can be performed by reacting organic compound to be identified with sodium bicarbonate (NaHCO₃). The results of the reaction, if positive for the carboxyl group will produce an acid that will bicarbonate decomposes into CO₂ and H₂O.

R – COOH + NaHCO₃   → R- COO – Na +  H₂CO₃

H₂CO₃ → CO₂ + H₂O

Potassium permanganate oxidizes alkenes to vicinal diol at room temperature. This reaction is characterized by loss of KMnO₄ purple color changed to brown and the resulting brown precipitate MnO₂. Although this reaction is easily observed but is less selective because KMnO₄ also oxidize other functional groups such as alkynes, alcohols, aldehydes, and phenols which all give the same change to the reagent between KMnO₄ with alkenes.

In addition, for the reaction with KMnO₄ oxidation can be done in the media or KMnO₄ concentrated aqueous KMnO₄. In an atmosphere of dilute KMnO₄ oxidation will occur only π bond of the alkenes to form the diol compounds adduct 2 hydroxyl groups to alkenes. Both, the OH groups are located on the same side (cis addition).

            Alkenes react with bromine compound vicinal dibromide as a result of addition reactions, with the following reaction.   

Etena  +   Br₂    à      Br-CH­₂-CH₂-Br

Addition of bromine has long been a qualitative way to identify the carbon-carbon unsaturated. Bromine in carbon tetrachloride, brown-red solution, dropped into the compound under study. If there are double bond or a triple, that formed colorless dibromide. The loss of color in a solution of bromine indicates that there has been addition. Other functional groups can also react with bromine, so that further information is needed to prove the existence of alkenes and alkynes. As already known both, bromine and chlorine are two kinds of halogen used for these halogenations. Fluorine is very reactive so that not only tied to the double bond but can replace all the existing hydrogen and the reaction is also very hard. While the iodine may be added at low temperature, but the resulting iodide normally unstable and will decompose back into alkenes at room temperature.

Test whether the properties of organic compounds aliphatic or aromatic, can be done by doing a smoke test. When the organic compound is positive for benzene ring (aromatic) then there will be fumes when heated. This is because the stability of the benzene ring which makes it difficult to oxidized. So that when the combustion process (warming) caused by smoke arising incomplete combustion (hard oxidized). But if the organic compound aliphatic then, when heating (combustion) does not arise smoke, because the combustion process that goes perfectly.

METHOD

The experiment was conducted at Organic Chemistry Laboratory practice of Chemistry Education Department, Ganesha University of Education Singaraja on September 2^th,9^thand 16^th  2013 from 13.30 – 18.30 WITA.

Equipment and Materials

The experiment needs some equipment and materials for conducting the research. The equipment used are capillary pipette, spiritus, spatula, watch glass, metal block, thermometer, beaker glass, test tube and rack, graduated cylinder, erlenmeyer, funnel, drop pipette, stirrer road, holder, bunsen burner, filter paper, heater, electrical balance, and matches.

While the materials used are solid of unknown sample, powder of dry, copper oxide, KSCN solid, FeCl₃ solid, methanol, benzene, toluene, sodium, hydrocarbon, ethanol, aquades, CH₃COOH solution, Pb-acetate solution, sodium nitropusid solution, FeSO₄ solution, NaOH solution, H₂SO₄ solution, concentrated, HNO₃ solution, AgNO₃ solution, NH₄OH solution, limestone, CCl­₄ solution, fiber-ammonium-nitrate solution, Br₂ solution 5% , acetyl chloride solution, strong ammonia solution, FeCl₃ solution, fehling A solution (acetate of CuSO₄), fehling B solution (NaOH of Rochelle salt), AgNO₃ solution, ammonia solution, diluted HCl solution, 2,4 dinitrofenilhidrazin solution, I₂ solid, KI solid, NaOH 10% solution, NaHCO₃ solution, ethyl alcohol solution, strong H₂SO₄ solution, saturated hydroxylamine hydrochloride solution, methanol solution, KOH solution, benzidin-hydrochloride, nitric acid solution, dimethyl formamide solution, CaCl₂ solution, dry aceton, benzyl amine solution, NaHCO₃ solution 5%, KBr solid, phenol solution, perchlorate acid solution 60%, ethanol solution 10-20%, 2,4-DNP solid, semicarbaside solid, sodium acetate solid, pyridine solution, tyonilchloride solution, carbonyl compound, carboxylate acid solution, trong ammonium hydroxide solution, triethylamine solid, fenasilbromide solution, ethyl or ester ethyl, NH₄Cl solid, bromine solution, NaHSO₃ liquid solution.

Procedure

The method of this experiment was qualitative analysis. The unknown sample analyzed contain of organic substance is solid sample (white powder) that already prepared and only known by laboratory assistant. There were some procedures already done.

Determination of physical properties

First determination of physical properties in unknown sample namely melting point. In determination the melting point, some procedure was done. First, solid unknown sample was refined by using spatula then capillary pipe was filled by the refine sample. The filled capillary pipette was entered to the appropriate hole in metal block and also thermometer to measure the melting point was entered. They ware heated. The temperature when the sample begins to melt until perfect melt was noted.

After determine the melting point, the next procedure is element analysis. This is purposed to identify component of organic compound contain in unknown sample through identification of carbon, oxygen, nitrogen, sulfur, and halogen.

Identification of carbon

          The unknown sample was mixed with powder copper oxide (CuO). The mixture was pour into a clean test tube and heated until all substance changes become CO_2. For testing the existence of CO₂, the gas was flow to lime water by gas diverter.

Identification of oxygen

          The unknown sample was dissolved in one of organic solvent (toluene). Filter paper which is given ferox reagent was prepared. The unknown sample solution (unknown sample already dissolved) was dropped on the ferox paper.

Identification of sulfur, nitrogen, and halogen

Before the identification, extraction of sodium or Lassaigne Filtrate must be prepared. Sample of organic substance was placed in test tube. Small amount of sodium which is dried by filter paper was added to the test tube. Incandescent sample was heated for getting the perfect reaction. The mixture was added by ethanol to remove excess of sodium. The mixture was heated until produce red colour. Then, it was dissolve in distilled water (test tube was broken). The solution resulted was filtered to get the filtrate (Lassaigne filtrate).

After the extraction of sodium or Lassaigne filtrate was prepared, continued by identification of sulfur. Two milliliters of sodium extract was added by acetic acid and heated. Litmus paper was used to test the acidity. Then, filter paper was added by Pb-acetate 10%. It was closed to the top of test tube and the color change was observed. Sodium nitroprusid solution was drop to the rest of filtrate in the test tube.

Then, the experiment was continued by identification of nitrogen. Two milliliters of sodium extract was added into FeSO₄ solution Mohr salt. Then, they was cooled and acidified with H₂SO₄ solution until precipitate dissolved. The change of color was observed.

The next identification is identification of halogen. Two milliliters of sodium extract was added by drops HNO₃ solution qualitatively and heated. After that, it was cooled then added by 1 mL of AgNO₃ solution. Precipitate formed was observed.

Beside determine melting point and identification of element, for making sure about the name and structure of unknown sample content organic substance, the detection of functional group as well as derivate compound of substance also done.

Detection of unsaturated bond

The name of this detection is Baeyer test. Solid unknown sample was added by alcohol and then Baeyer solution (KMnO₄). The color change was observed. For making sure, the solid unknown sample was added by CCl₄ and Br₂ 5% in CCl₄. The color change was observed.

Detection of aliphatic or aromatic (fume test)

          Solid unknown sample was placed on spatula. It was heated on the fume room. The black smoke indicates aromatic compound.

Detection hydroxyl group of alcohol

          There are two test for this detection. First is Fiber test. Sample was added by fiber solution (ammonium nitrate). The color formed was observed. Second is acetil chloride test. Sample was added by 3 drops of acetil chloride. The gas produced was closed to the concentrated ammonia solution. White smoke indicated hydroxyl group of alcohol.

Detection Fenolat group (ferrichloride test)

          Sample was added by alcohol and FeCl₃ drop by drop qualitatively. The change of color was observed.

Detection Aldehide group (Tollen Test)

       The tollen solution was prepared by AgCl₃ added by NaOH, it green produce precipitate. Then, it added by excess of ammonia until the precipitate was dissolved. Then, it heated. If it produces silver mirror so indicates aldehyde group.

Detection of Carboxyl group   

       Saturated solution of NaHCO₃ was added by unknown solid sample. If bubbles formed so indicates carboxyl group.

Detection of ester

       Sample was added by saturated solution of hydroxilaminhydrochloride in methanol and KOH in methanol qualitatively. Then it was heated. After that, it was cooled and added by two drops of FeCl₃ and continued by adding HCl. The formed of reddish turbid solution indicated positive of ester.

RESULT AND DISCUSSION

          Physical properties of unknown substance were  insoluble in water but soluble in toluene. It has melting point 121.5^oC – 122^oC and has white crytals powder.

Figure 3.Melting process by using metal block

The physical properties could be observed by senses.  Physical properties were not enough to determine the unknown substance.

       Element identification was the second steps of this experiment. The elements that must be tested were carbon, oxygen, hydrogen, nitrogen, sulphur, and halogen. The other tests that were conducted of functional group detection The result can be shown on table below.

Table 1. Result of Element Analysis of Solid Unknown Sample

Element	Identification
Carbon	Positive
Oxygen	Negative
Sulfur	Negative
Nitrogen	Negative
Halogen	Negative

         

Table 2. Result of Functional Group Analysis of Solid Unknown Sample

Functional Group	Identification
Unsaturated bond	Positive
Aliphatic or Aromatic	Positive Aromatic
Hydroxyl Group	Positive
Phenol  Group	Negative
Aldehyde Group	Negative
Carboxyl Group	Positive
Ester Group	Positive

Discussion     

          The carbon detection was positive. It could be detected because when the sample was mixed with copper oxide (CuO) and heated until the gas produced. The function of CuO is to react with organic substance, so that can change the carbon becomes CO₂  and hydrogen becomes H₂O. The gas produced was flow into lime water, the solution was turbid. The reaction is as follows.

Figure 4. Limestone solution was turbid

          So, it means carbon contain in unknown sample. But, the identification of hydrogen could not conduct because there was not silica gel CuSO₄ to support the identification. That means hydrogen not conducted.

          The oxygen detection was given negative result. It could be detected because there was not red color formed when the filter paper that given of ferox reagent dropped by the mixture of sample and toluene. So, it was indicated negative oxygen.

Figure 5. Ferox paper show white color

          The sulfur, nitrogen, and halogen detection also give negative result. When the filter paper was added Pb-acetate and then closed to test tube that filled by Lassaigne filtrate where contain of sample, there were not change of color formed. It should be black color form indicated sulfur. Then, in detection of nitrogen, the last result of solution after adding H₂SO₄ should be blue green or blue suspension but the color formed was brown yellowiest color. After that, the result of Lassaigne filtrate that contain of sample when added by AgNO₃ in last procedure it should precipitate formed. But, there was not precipitate formed. So, it means unknown sample negative contain of sulfur, nitrogen, and halogen.

          The other tests that were conducted of functional group detection such as baeyer test (+) means unknown sample has unsaturated bond where contains double bond, aromatic detection (+), hydroxyl group of alcohol (+), Fenolat and aldehyde group detection (-), carboxyl group (+), and detection esters (+).

          The reaction of baeyer test is R₁(R₂)-X=X-(R₃)R₄ + KMnO₄ → X(OH)₂ + MnO₂ + MnO₄^2-. When added by the Baeyer solution the sample becomes young purple. It is caused KMnO₄ reacts with substance that tested, so that KMnO₄ is reduced to become MnO₂^- and the color of KMnO₄ will be pale. Based on the theory, it indicates that the sample is positively contained of unsaturated bond.

Figure 6.The color of solution changes into pale purple

          Then, Bromine test, bromine solution has orange color and CCl_{4 ­}is colorless. The sample poured into CCl₄ and added by Br_2. the color changes into light brown. Its mean the sample has unsaturated bond.

Figure 7.  The light brown is unsaturated   bond

          The aliphatic and aromatic detection, the unknown sample was tested by fuming test. The unknown sample is white powder, when heated the sample produce black smoke and the sample was melt. It is caused the sample contain of stable benzene ring and difficult to oxidize. So the sample is aromatic compound.

Figure 8. The black smoke indicates aromatic compound

         

          The carboxyl group could be indicated by fruit aroma. The carboxyl group that was found was esters that supported by esters detection with chemical formula RCOOR. But, there was positive hydroxyl group of alcohol. The result has deviation. The Fischer esterification converts carboxylic acids and alcohol directly to esters by an acid-catalyzed nucleophilic acyl substitution.

          The net reaction is replacement the acid – OH group by the – OR group of the alcohol (L.G Wade JR, 2010). This explanation supported the hypothesis that the unknown sample is benzoic acid. 

CONCLUSION

Based on the experiment result, discussion, and accordance with theory could be concluded the unknown sample was benzoic acid (C₇H₆O₂). The structure is as follows.

Figure 9. Structure of Benzoic Acid (design from chemsketch)

It was supported by the melting point ranges of 121.5^oC – 122^oC, positive content element carbon, positive contain unsaturated bond means has double bond, has carboxyl group, positive hydroxyl group of alcohol,  aromatic compound, positive of ester that indicated derivate of carboxylic acid, and produce fruit aroma.

ACKNOWLEDGEMENT

In writing this article, the author has of a lot of support, guidance and encouragement from many quarters. For this reason, the author respectfully thank for Dr. I Nyoman Tika, M.Si as lecturer on the practicum, Ms. Dewi as lecturer assistant, Mr. Lasia as the laboratory assistant and also all member of RKBI’11 of chemistry class for the always good partners.

REFERENCES

Allen M, Scholfstall, and friends. 2004. Organic Chemistry Laboratory Experiment. New York: McGraw-Hill.

Betelheim, Frederick. 1995. Introduction to General, Organic, & Biochemistry. USA: Saunders College Publishing.

Chairil Anwar, dkk. 1994. Pengantar Praktikum Organik. Yogyakarta: Depdikbud.

English Jr, James and friends. 1971. Principle of Organic Chemistry. Tokyo: McGraw-Hill

L.G.Wade, JR. 2010. Organic Chemistry Seventh Edition. USA: Pearson Educatin, Inc.

Suja, I Wayan, Frieda Nurlita. 2004. Buku Ajar Praktikum Kimia Organik. Singaraja: Jurusan Pendidikan Kimia IKIP Singaraja.