CLASSIFICATION TESTS FOR HYDROXYL AND CARBONYL CONTAINING COMPOUNDS Margarita Ysabel S. Mangahas, Cara Camille M. Matute, Emilyn D. Millares, John Acener C. Padua and Kathryn Cheshire P. Pangilinan Group 5 2A Medical Technology Organic Chemistry Laboratory ABSTRACT Hydroxyl and Carbonyl containing samples were tested in this experiment. The samples were analyzed through tests involving the solubility
of alcohols in water, Lucas test, Chromic Acid test, 2,4-Dinitrophenylhydrazone (2,4-DNP) test,
Fehling’s test, Tollens’ Silver Mirror test, and Iodoform test. Lucas test differentiates primary, secondary and tertiary alcohols. Chromic test was performed to know if the sample is oxidizable. 2,4-Dinitrophenylhydrazone test was performed for aldehydes and ketones. Fehling’s Test and Tollens’ Silver Mirror Test are tests for aldehydes. Iodoform test is a test for methyl carbinol and methylcarbonyl groups. The samples are n-butyl alcohol, sec-butyl alcohol, tertbutyl alcohol, acetaldehyde, n-butylaldehyde, benzandehyde, acetone, and isopropyl alcohol.
INTRODUCTION Hydroxyl group is used to describe the functional group –OH when it is a substituent in an organic compound. [4] Representative organic molecules containing a hydroxyl group are known as alcohols. Hydroxyl groups are especially important in biological chemistry because of their tendency to form hydrogen bonds both as donor and acceptor. This property is also related to their ability to increase hydrophilicity and water solubility [1]. There are three classifications of alcohols by the carbon to which the hydroxyl group is attached. Primary alcohols are those in which the hydroxyl group is attached to the carbon with only one carbon attached. Secondary alcohols are compounds in which the OH- is attached to a carbon which has two other carbons attached to it. Tertiary alcohols are compounds in which a hydroxyl group is attached to a carbon with three attached carbons [3]. Carbonyl group is a family of functional groups composed of a carbon atom double-bonded to an oxygen atom: C=O. The group is a constituent of carboxylic acids, esters, anhydrides, acylhalides, amides, and quinones, and it is the characteristic functional group of aldehydes and ketones [2]. Aldehydes are organic compound containing a terminal carbony lgroup. This functional group, called analdehyde group, consists of a carbon atom bonded to a hydrogen atom with a single covalent bond and an oxygen atom with a double bond. Thus the chemical formula for an aldehyde functional group is -CH=O, and the general formula for analdehyde is R-CH=O.
Ketones features a carbonyl group(C=O) bonded to two other carbon atoms. They differ from aldehydes in a way that the carbonyl is placed between two carbons rather than at the end of a carbon skeleton [3]. They are also distinct from other functional groups, such as carboxylic acids, esters and amides, which have a carbonyl group bonded to a hetero atom. The tests used in this experiment are Lucas test, Chromic Acid test, 2,4Dinitrophenylhydrazone, Fehling’s test, Tollens’ Silver Mirror test and Iodoform test [4]. Lucas test often provides classification information for alcohols, as well as a probe for the existence of the hydroxyl group. Substrates that easily give rise to cationic character at the carbon bearing the hydroxyl group undergo this test readily; primary alcohols do not give a positive result. [4]Chromic acid test detects the presence of a hydroxyl substituent that is on a carbon bearing at least one hydrogen, and therefore oxidizable. 2,4-Dinitrophenylhydrazone test can be used to qualitatively detect the carbonyl functionality of a ketone or aldehyde functional group. Fehling’s Test and Tollens’ Silver Mirror Test are used to detect aldehydes. However, Fehling's solution can only be used to test for aliphatic aldehydes , whereas Tollens' reagent can be used to test for both aliphatic and aromatic aldehydes. Iodoform Test is a test for methylcarbinol (secondary alcohol with adjacentmethyl group) and methyl carbonyl group.
EXPERIMENTAL A. Compounds Used The compounds used are n-butyl alcohol, secbutyl alcohol, tert-butyl alcohol, acetaldehyde, nbutylaldehyde, benzandehyde, acetone, and isopropyl alcohol.
B. Procedure 1. Solubility of Alcohols in Water Low molecular-weight amines and oxygencontaining compounds like alcohols, carboxylic acids, aldehydes, and ketones are the only soluble organic compounds in water. In five different test tubes named as A to E, place ten drops of ethanol, n-butyl alcohol, secbutyl alcohol, tert-butyl alcohol and benzyl alcohol into the appropriate tube. Add 1 mL of water to each of the test tubes and shake thoroughly. If a cloudiness results, continue adding 0.25 mL of water at a time, with vigorous shaking, until a homogenous dispersion results. If no cloudiness resulted after adding 2.0 mL of water, the alcohol is soluble in water.
2. Lucas Test To prepare the reagent for this test, dissolve 16 g of anhydrous zinc chloride in 10 mL of conc. HCL. Allow the mixture to cool. After cooling, add 50 mg of the sample to 1 mL of reagent in a small vial. Cap the vial and shake vigorously for a few seconds. Allow the mixture to stand at room temperature. Perform the test on n-butyl alcohol, sec-butyl alcohol, tert-butyl alcoho, and benzyl alcohol. Observe the rate of formation of the cloudy suspension or the formation of two layers.
3. Chromic Acid Test This test was performed on n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, nbutyraldehyde, benzaldehyde, and acetone. Dissolve 1 drop of liquid or a small amount of solid sample in 1 mL of acetone in a small vial. Add 2 drops of 10% aqueous K2Cr2O7 solution and 5 drops of 6M H2SO4.
4. 2,4-Dinitrophenylhydrazone test This test was performed on acetone, acetaldehyde, n-butyraldehyde, benzaldehyde, and acetophenone.
To prepare the reagent for this test, add a solution of 3 g of 2,4-dinitrophenylhydrazine in 15 mL of conc. H2SO4 slowly, while stirring to a mixture of 20 mL of water and 70 mL of 95% ethanol. Stir and filter it. Place a drop of a liquid sample into a small test tube. Add 5 drops of 95% ethanol and shake it well. Add 3 drops of 2,4-dinitrophenylhydrazine. If no yellow or orange-red precipitate forms, allow the solution to stand for at least 15 minutes.
5. Fehling’s Test This test was performed on acetaldehyde, nbutyraldehyde, acetone, benzaldehyde, and acetophenone. Fehling’s reagent was prepared by mixing equal amounts of Fehling’s A and Fehling’s B. Fehling’s A was prepared by dissolving 7 g of hydrated copper (II) sulfate in 100 mL of water. Fehling’s B was prepared by mixing 35 g of Potassium sodium tartrate and 10 g of Sodium hydroxide in 100-ml water. 1-ml of freshly prepared Fehling’s reagent was placed into each test tube. 3 drops of the sample to be tested was added in to the tube. The tubes were then placed in a beaker of boiling water and changes within 10-15 minutes were observed.
6. Tollens’ Silver Mirror Test This test was performed on acetaldehyde, benzaldehyde, acetone, n-butyraldehyde, and acetophenone. The reagent was prepared by adding 2 drops of 5% Sodium hydroxide solution to 2-ml of 5% Silver nitrate solution and mixing thoroughly. Next, only enough 2% Ammonium hydroxide (concentrated ammonium hydroxide is 28%) was added drop by drop and withstirring to dissolve the precipitate. Adding excess ammonia will cause discrepancies on the result of the test. Four test tubes with 1-ml of freshly prepared Tollens’ reagent were prepared. Two drops each of the samples were then added. The mixture was shaken and allowed to stand for 10 minutes. If no reaction has occurred, the test tube was placed in a beaker of warm water (3550oC) for 5 minutes.
7. Iodoform Test This test was performed on acetaldehyde, acetone, acetophenone, benzaldehyde, and isopropyl alcohol.
2 drops of each sample was placed into its own small vial or test tube. 20 drops of fresh chlorine bleach (5% Sodium hypochlorite) was slowly added while shaking to each test tube and then, mixed. The formation of a yellow participate was noted.
RESULTS AND DISCUSSION Table 1. Solubility of Alcohol in Water Alcohol
Ethanol n-butyl alcohol secbutyl alcohol tertbutyl alcohol Benzyl alcohol
Condensed Structural Formula
CH3CH2OH CH3CH2CH2OH
Amount of water (in mL) needed to produce homogenous dispersion 1 mL 2 mL
Solubility in water
1.25 mL
miscible
miscible miscible
1 mL
miscible
6.5 mL
immiscible
Table 3. Chromic acid test results Substance n-butyl alcohol
tert-butyl alcohol nbutyraldehyde benzaldehyde
Table 3 shows the reaction of n- butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, nbutyraldehyde, benzaldehyde, and acetone to Chromic Acid test. N-butyl alcohol, sec-butyl alcohol, benzaldehyde, and n-butyraldehyde green solution whereas tert-butyl alcohol, and acetone resulted to a yellow solution.
Table 2. Lucas test results Condensed Results
acetaldehyde nbutyraldehyde Benzaldehyde acetone
n-butyl alcohol secbutyl alcohol tertbutyl alcohol Benzyl alcohol
Inference
no reaction no reaction
miscible
Cloudy formation
immiscible
no reaction
miscible
miscible
Table 2 shows the reaction of butanol derivatives to Lucas Test. N-butyl alcohol, secbutyl alcohol, and benzyl alcohol yielded a clear solution when subjected to Lucas Test whereas tert-butyl alcohol resulted to a cloudy immiscible suspension which eventually formed two layers.
Orange to red layer Light yellow layer to light green layer
acetone
Substance
Structural Formula CH3CH2CH2OH
Results Light yellow layer to light green layer Yellow layer to light green layer Yellow green layer Orange layer
sec-butyl alcohol
Table 1 shows that ethanol, n-butyl alcohol, sec-butyl alcohol, and tert-butyl alcohol are all miscible with water with the exception of benzyl alcohol which exhibited insolubility.
Substan ce
Condensed Structural Formula
Table 4. 2,4-DNP results Condensed Structural Formula
Results Orange ppt. Orange ppt. Orange ppt. Orange ppt.
Table 4 shows the reaction of acetaldehyde, nbutyraldehyde, benzaldehyde, and acetone to 2,4-DNP test. All the samples exhibited positive result because they all formed an orange precipitate. Hence, 2,4-DNP test proved that the samples are carbonyl-containing compounds and are either aldehydes or ketones. Table 5. Fehling’s test results Substance acetaldehyde
nbutyraldehyde
Condensed Structural Formula
Results Brick red ppt. 2 layer: green, brown Brick red ppt. 3 layers: Colorless, light
blue, royal blue Blue solution with orange ppt. No change
Benzaldehyde acetone
It is shown in Table 5 that acetaldehyde, nbutyraldehyde, and benzaldehyde exhibited positive result. Acetaldehyde, in particular turned from blue to muddy green then formed a crude red precipitate upon heating. These three sample compounds which exhibited positive result to Fehling’s test are all aldehydes. Table 6. Tollens’ Silver Mirror test results Substance
Condensed Structural Formula
acetaldehyde
Results Silver mirror; black ppt. gray solution
nbutyraldehyde Benzaldehyde acetone
Clear solution Gray solution
In table 6, acetaldehyde prdouced a silver mirror with a black ppt when subjected to Tollens’ test while the other compounds did not formed any silver mirror. The formation of the silver mirror may be affected by the preparation of the Tollens’ reagent. Table 7. Iodoform test results Substance acetaldehyde nbutyraldehyde Benzaldehyde Isopropyl alcohol
Condensed Structural Formula
Results Brown ppt. Redish briwn ppt. Yellow ppt. Red solution
Table 7 shows that among the sample compounds tested, acetaldehyde, acetone, acetophenone, and isopropyl alcohol exhibited positive
REFERENCES [1] Bayguen, A.V., Cruz, C.T., de Guia, R.M, Lampa, F.F., Peña, G.T., Sarile, A.S. and Torres, P.C. (2009),Laboratory Manual in Organic Chemistry,C&E Publishing, Inc. [2] Carbonyl http://en.wikipedia.org/wiki/Carbonyl
[3] Hydroxyl Group. (2010). In Encyclopædia Britannica. Retrieved September 19, 2010, from Encyclopædia Britannica Online: http://www.daviddarling.info/encyclopedia /P/phenol.html. [4] Shriner, Fuson, Curtin. (1964). Systematic Identification of Organic Compound: A Laboratory Manual Fifth Edition. John Wiley & Sons, Inc. New York: Van Hoffmann Press
