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Experiment # 8: CHARACTERIZATION TESTS for the OXYGEN-CONTAINING COMPOUNDS SAJOL, Christine Joy. March 2013 Department of Chemical Engineering, Faculty of Engineering University of Santo Tomas España, Manila Abstract Tests such as the dichromate test, DNPH (Dinitrophenylhydrazine) test, Tollen’s test, iodoform test, Fehling’s test and Lucas test would be very useful in determining the type of compound the test solution belongs to. Nine oxygen-bearing organic compounds, the test solutions, were given namely 1° butyl, 2° butyl, 3° butyl, phenol, acetone, formaldehyde, benzoic acid, acetamide and ethylacetate In the experiment, the test solution undergone series of testing to classify the samples from being a primary alcohol, a secondary alcohol, a tertiary alcohol or what functional group that are presented on the mixture. Another goal of this experiment is to know what types of tests are particularly used for a specific oxygen-containing compound. I. Introduction The characterization test of oxygen bearing organic compounds is an experiment in which a variety of tests are available to identify a compound’s property whether it is a primary, secondary or tertiary alcohol or what functional group does it belong to. The tests that are included to come up with such results are interconnected with one another like that of the Dichromate test which is a positive if the mixture turns green-blue, next is DNPH (dinitrophenylhydrazine) test that has a positive of yellow precipitate, followed by the Tollen’s test, a positive if there is a silver mirror coating. Next is iodoform test which has a positive of formation of yellow precipitate. Including the Fehling’s test that has a positive if there’s a red precipitate and finally the Lucas test to test if the mixture became turbid or not. Different test solutions are used in this experiment and have different functional groups. Let us first differentiate and classify the functional groups that are present in this experiment. Alcohols are compounds in which one or more hydrogen atoms in an alkane have been replaced by an –OH group. Note however that there are different types of alcohols that are used in this experiment, the primary, secondary, tertiary and phenol (the –OH group is attached into an aromatic ring). Alcohols (ROH) can be thought of as derivatives of water in which one of the hydrogen atoms has been replaced by an alkyl group. If both of the hydrogen atoms are replaced by alkyl groups, we get ether (ROR). These compounds are named by adding the word ether to the names of the alkyl groups. Aldehydes (RCHO) and ketones (RCOR') are very important functional groups, characterized by the presence of an acyl group (RCO-) bonded either to H (aldehydes) or another C (ketones). Amines (RNH2) are organic derivatives of ammonia, NH3 and have certain similarities with ammonia. Nitrogen containing compounds are biologically very important amines, amino acids, amides, proteins, vitamins etc. Lastly, Carboxylic acids (RCO2H) are the most acidic among of the common organic functional groups. In this experiment, we’ll be able to characterize on what functional group does the test solutions belong to and know what particular characterization test must be used in order to determine a certain functional group of choice. II. Review of Related Literature How does one determine the actual identity and structure of an unknown compound? This is not a trivial task. Modern x-ray and spectroscopic techniques have made the job much easier, but for some very complex molecules, identification and structure determination remain a challenge. In addition to spectroscopic information and information obtained from other instrumental methods, chemical reactions can provide useful structural information, and physical properties can contribute significantly to confirming the identity of a compound. Classification tests, which are simple chemical reactions that produce color changes or form precipitates, can be used to differentiate alcohols, aldehydes, and ketones and also to provide further structural information. (Samal, 2009) The same experiment of characterization test of Tollen’s reagent was conducted by Rehan Qadri. He noted that when adding the aldehyde or ketone to Tollens' reagent, the test tube is put in a warm water bath. If the reactant under test is an aldehyde, Tollens' test results in a silver mirror. If the reactant is a ketone, it will not react because a ketone cannot be oxidized easily. A ketone has no available hydrogen atom on the carbonyl carbon that can be oxidized - unlike an aldehyde, which has this hydrogen atom. Dona Trainor, Adrian Huang and Jim Moyer have stated these things on their website:24 DNP test is for the classifications of aldehydes and ketones and that the positive test for this classification test is the formation of precipitate. Tollen’s test is also for aldehyde and the positive test for this is the formation of silver mirror. While the positive test of iodoform test for methyl ketones is the formation of solid iodoform (yellow). Still on their study, Lucas test for alcohols have the positive test of appearance of cloudy second layer or emulsion. The time factor of formation of emulsion for tertiary alcohols is immediate to 2-3 minutes, 510 minutes for secondary and no reaction for primary alcohols. Lastly, the dichromate test, also known as Jones oxidation, has a positive test for aldehydes and primary or secondary alcohols consist in the production of an opaque suspension with a green to blue color. Aldehydes are reducing reagents; they may be oxidized to carboxylic acids (in acidic solutions) or their salts (in alkaline solution). Positive tests for aldehydes depend on these facts. For acidified potassium dichromate, if the color changes from orange to green, the dichromate (VI) has been reduced to chromium (III) and an aldehyde is confirmed. In tollen’s reagent, if a silver mirror is confirmed in the test tube, this confirms the presence of an aldehyde. Lastly, for Fehling’s (or Benedict’s) solution, both Fehling’s and Benedict’s solutions contain complexed copper (II) ions in an alkaline solution. If a red precipitate of copper oxide is formed, this confirms the presence of an aldehyde. Same experiment of characterization test was also conducted by Achas M.L., Alvarez M.A., Bangot K.A., and Bayani K. The experiment dealt with differentiating the various types of oxygen-bearing organic compounds through several tests, namely Dichromate Test, Tollen’s Test, DNPH Test, Iodoform Test, and Lucas Test. It was through the use of different reagents and techniques that the characteristics of each standard compounds were observed and distinguished. After the reactions have been noted, it was compared to the reactions with that of the unknown. III. Methodology a. Materials and Equipments Test Tubes Beaker Hot plate Droppers 6M H2SO4 10% K2Cr2O7 2, 4 DNPH Tollen’s Reagent 10% KI 5% NaClO Fehling’s A Fehling’s B Concentrated HCL Anhydrous ZnCl2 95% Ethanol 1° Butyl 2° Butyl 3° Butyl Phenol Acetone Formaldehyde Benzoic Acid Acetamide Ethylacetate b. Procedure For the dichromate test, 3 drops of the test solution was putted on a test tube. Then 2 drops of 10% K2Cr2O7 and 5 drops of 6M H2SO4 were added. The color change and other observable change were then recorded. In using the DNPH (dinitrophenylhydrazine) test, 2 drops of the test solution was dropped on a test tube, 1mL of 95% ethanol was then added and it was followed by the addition of 20 drops of DNPH. The solutions that don’t have precipitate after 15 minutes was heated for 15 minutes more. 5 drops of the test solution was added to 2mL of Tollen’s reagent and the observation after 5 minutes was recorded. The solutions that have no visible change were warmed in a hot bath for 5 minutes. This procedure is for the Tollen’s reagent test. In Iodoform test, 5 drops of the test solution was putted on a test tube and added with 20 drops of 10% potassium iodide. 20 drops of 5% NaClO was carefully added to the test tube and was warmed in a water bath. The changes in appearance and odor was observed and recorded. For the Fehling’s test, the 5 drops of the test solution was added with 10 drops of Fehling’s A and another 5 drops of Fehling’s B. The mixture was warmed until changes are observed. The changes were then recorded. In Lucas test, 5 drops of the test solution, 15 drops of concentrated HCL and a pinch of anhydrous ZnCl2 was combined in a single test tube. The mixture was shaken until an insoluble layer was formed. The mixtures that no change has occurred were warmed until the formation of turbidity. IV. Results and Discussions The initial appearance of the compounds was recorded and can be seen in Table 1. Table 1: Compounds and their initial apperance Compound n-butyl Sec-butyl Tert-butyl Phenol Acetone Formaldehyde Benzoic Acid Acetamide Ethyl Acetate HCl Appearance Colorless Colorless Colorless Red Colorless Clear precipitate Colorless Colorless Colorless Colorless fume Compound K2Cr2O7 H2SO4 Ethanol DNPH Tollen’s reagent Potassium Iodide NaClO Fehling’s A Fehling’s B Anhydrous ZnCl2 Appearance Orange Colorless Colorless Dark Orange Colorless Colorless Colorless Sky blue Colorless Colorless goo Each test solution undergone the different test namely, dichromate test, DNPH test, Tollen’s reagent, iodoform test, Fehling’s test and lastly Lucas test. The changes that have been observed on the experiment performed can be reflected on Table 2. Tollen’s Reagent Iodoform Test Fehling’s Test Lucas Test Dark Orange solution, black precipitate No visible change Yellow solution, red upper layer to clear Indigo solution, light blue precipitate No visible change From pumpkin orange to dark blue green Dark Orange solution, black precipitate No visible change Light yellow green to clear Indigo solution, light blue precipitate Formed turbidity after heating 3° Butyl Precipitate and pumpkin orange layer form Dark Orange solution, black precipitate No visible change Orange to clear light yellow Indigo solution, light blue precipitate Unclear white glass color. Fast emulsion, bubbles at top layer Phenol From layer of red & orange to hot smelly dark red brown From light red to dark orange. Black precipitate Ash gray color to blackening of test tube wall. Black precipitate From dirty white solution to clear. Bloody red precipitate From indigo to dark blue Clear solution, red upper layer Acetone From pumpkin orange to brownish solution Yellow orange colloidal precipitate From colorless to very light pink color solution. Light yellow green to clear. Yellow green moss like precipitate Indigo solution, light blue precipitate Became slight light yellow after heating Table 2 Dichromate Test DNPH Test 1° Butyl From pumpkin orange to dark blue green 2° Butyl Formaldehyde From pumpkin orange to dark cyan blue Yellow ash like precipitate A silver mirror deposit covering the bottom Pumpkin orange color to clear Indigo solution goes up then subsided to clear color. Dark brick red precipitate formed No visible change Benzoic Acid Dense light yellow condensed precipitate. pumpkin orange solution Orange solution. Black precipitate No visible change Yellow orange to yellow color Light blue upper layer. Indigo solution. No visible change Acetamide No color change Orange solution. Black precipitate No visible change Light yellow green solution. White gelatinous web like precipitate Light blue upper layer. Indigo solution. No precipitate No visible change Ethylacetate From pumpkin orange to green blue Orange solution. Black precipitate No visible change Dark red orange color and Black precipitate to dis apperance of the precipitate Light blue upper layer. Indigo solution. No precipitate No visible change The items that are in bold letters in the table are all have positive results in the test. The positive reactions that occur in the dichromate test are 1° butyl alcohol, 2° butyl alcohol and the formaldehyde. First, the dichromate was added to the solutions and made the mixture have the color of pumpkin orange, then after the addition of sulphuric acid the mixture change its color to a dark blue green signalling that it is a positive test. In the DNPH test, almost all of the solutions have a black precipitate besides from acetone and formaldehyde which both have a yellow precipitate. In testing the acetone, addition of ethanol didn’t make the mixture to have a precipitate but after adding the DNPH mixture forms a yellow-orange colloidal precipitate. While in testing the formaldehyde, the the the the addition of ethanol also didn’t make the mixture to have a precipitate and after adding the DNPH, it also didn’t form any precipitate but when the mixture was heated, it formed a yellow ash like precipitate. In performing the Tollen’s reagent test, majority of the solutions made no visible reactions besides from the phenol, acetone and formaldehyde. The phenol made a black precipitate while the acetone made a very light pink color solution but what gotten our attention most is the formaldehyde. After the addition of tollen’s reagent and warming the mixture, it made a silver mirror effect at the bottom of the test tube. In the iodoform test, the acetone has no visible change after the addition of potassium iodide but when the NaClO was added, the solution became light yellow-green in color and has a moss like precipitate. After heating the mixture, it became clear and had the yellow-green moss like precipitate at the bottom. The test solutions almost have the same result after undergone the Fehling’s test but the formaldehyde is an exception. The clear color of formaldehyde became light blue after adding fehling’s A and turned into an indigo mixture after the fehling’s B was added. The mixture was then warmed and unexpectedly, the mixture’s volume was raised and after a second, the mixture settled down having a clear solution and a dark brick-red precipitate. Lastly, the Lucas test has only notable change in sec-butyl and tert-butyl. In sec-butyl the formation of turbidity is slow and needed the mixture to be heated first before it forms the emulsions while the tert-butyl has a significant fast emulsions. After the addition of anhydrous zinc chloride, we waited for a while and it created turbidity. V. Conclusion and Recommendation From this experiment and enough research we conclude that: In dichromate test, the positive result is the green to blue color of the precipitate. This test is for testing if the solution is a 1° alcohol, 2° alcohol or an aldehyde. For DNPH, the positive test is the formation of yellow, orange or reddish-orange precipitate. DNPH is used to test the presence of ketone or aldehyde. On the other hand, the presence of aldehydes can also be determined by using the Tollen’s reagent test resulting into a silver mirror deposit. While the Iodoform test is used to detect the presence of of methyl ketones and has a positive test of formation of yellow precipitate. The formation of red precipitate is formed signalling the presence of aldehyde using the Fehling’s test. Lucas test has the most difficult signalling of a positive test because it has confirmatory test of appearance of emulsions or turbid solutions. It is positive for 2° and 3° alcohols. The tests that have been used it this experiment has a negative characterization test for phenol, acetamide, ethylacetate and benzoic acid. To summarize things up we can refer to Table 3. Table 3: Summary Tests Reagents Positive for Visible Results Dichromate K2Cr2O7 H2SO4 1° and 2° alcohols Aldehydes Green to blue solutions DNPH 2-4 DNPH 95% ethanol Ketone Aldehydes Yellow precipitates Tollen’s Tollen’s reagent Aldehydes Silver mirror Iodoform 10% KI 5% NaClO Methyl Ketones Yellow Precipitates Fehling’s Fehling’s A Fehling’s B Aldehydes Red Precipitates Lucas HCl ZnCl2 2° and 3° alcohols Cloudy or turbid solutions It is highly recommended to be not ignorant on the effects or changes that each test solutions has undergone and be sure to be able to record each change that have occurred. Keep your eyes critical on judging if the a reaction has already occurred especially on the formation of turbidity in Lucas test.Proper and organized recording of data will be a great help for the group to minimize data errors and wrong assumption when analysing the data. Be sure to be careful on handling these chemicals because some of them are highly corrosive. Safety equipment are recommended to minimize accidents. VI. References: Achas M.L., Alvarez M.A., Bangot K.A., and Bayani K. 2012. Analysis of OxygenBearing Compounds. http://www.studymode.com/essays/Analysis-Of-Oxygen-BearingOrganic-Compounds-1118013.html http://www.lgschemistry.org.uk/PDF/Organic_functional_group_tests.pdf Trainor D., Huang A., Moyer. 2012. Tests for Alcohols. http://academics.wellesley.edu/Chemistry/chem211lab/Orgo_Lab_Manual/Appendix/Cla ssificationTests/alcohol.html Trainor D., Huang A., Moyer. 2012. Tests for Aldehydes and Ketones. http://academics.wellesley.edu/Chemistry/chem211lab/Orgo_Lab_Manual/Appendix/Cla ssificationTests/aldehyde_ketone.html http://science.uvu.edu/ochem/index.php/alphabetical/s-t/tollens-test/ 2011. Identification of Organic Compounds. http://www.123helpme.com/view.asp?id=149691 Prof. Robert J. Lancashire. 2005. http://wwwchem.uwimona.edu.jm/lab_manuals/c10expt25.html McGraw-Hill Companies. 2000. Organic Chemistry 4e Carey. http://www.mhhe.com/physsci/chemistry/carey/student/olc/ch04summary.html http://chemed.chem.purdue.edu/genchem/topicreview/bp/2organic/alcohols.html#alcohol s