CLASSIFICATION TESTS FOR CARBOXYLIC ACID AND DERIVATIVES Jason Montesa, Rizziel Nemes, Peter Nocon, Yancee Oliva, Joel Piansay, Piansay, Magnolia Quinto Group 6, 2E Pharmacy, Faculty of Pharmacy, University of Santo Tomas
ABSTRACT Carboxylic acids are a class of organic compounds containing a carbonyl and hydroxyl group. The derivatives of this group are acid halides, anhydrides, esters, amides, and nitriles. This experiment aims to classify, differentiate, and identify carboxylic acids and its derivatives. Four kinds of tests were conducted: hydrolysis, alcoholysis, aminolysis, and the hydroxamic acid test. The hydrolysis of the sample compounds was done by adding water, AgNO 3, and NaHCO 3. Alcoholysis was carried out by adding ethanol, concentrated H 2SO4, and NaOH. Aniline, on the other hand, was added in the aminolysis test. And lastly, ethanol, HCl, alcoholic NH 2OH•HCl, KOH, and FeCl3 were the ones added in the hydroxamic acid test. Acid halides, acetyl chloride, were the fastest to react to the hydrolysis test. Acetic acid and acid chloride produced fruity odor in the alcoholysis test. Acetyl chloride and acetic anhydride both produced an amide in the aminolysis test. And ethyl acetate gave a positive visible result of deep burgundy-colored solution in the hyrdroxamic test. This experiment proved that carboxylic acid derivatives differ in reactivity, although almost same in structure, but possess different functional group, classified and differentiated through the various tests.
INTRODUCTION Carboxylic acids are another class of organic compounds containing the carbonyl group. Their occurrence in nature is widespread, and they are important components of foodstuffs such as vinegar, butter, and vegetable oils. The most important chemical property of carboxylic acids is their acidity. Furthermore, carboxylic acids form numerous important derivatives, including esters, amides, anhydrides, and acid halides.
The functional group of carboxylic acid is a carboxyl group, so named because it is made up of a carbonyl group and a hydroxyl group. (Brown, 2013). Carboxylic acids are classified according to the substituent bonded to the carboxyl group. An aliphatic acid has an alkyl group bonded to the carboxyl group, and an aromatic acid has an aryl group. The simplest acid is formic acid, with a hydrogen atom bonded to the carboxyl group. (Wade, 2013)
Acid halides, anhydrides, esters, and amides are all acyl compounds of the general structure. These compounds are also known as acid derivatives, because historically they were first derived from carboxylic acids. (Jones, 2010). Esters are of utmost importance to the fragrance and flavoring industry. The sweet odors of fruits and perfumes are usually results of volatile esters. Amides are found throughout throughout biochemistry. It is the amide group that defines enzyme structure, which in turn defines us. Acyl compounds are quite polar and have boiling points substantially higher than those of the alkanes. Amides, like carboxylic carboxylic acids, form hydrogen-bonded dimmers and oligomers, and are exceptionally high boiling. Resonance stabilization in these derivatives of carboxylic acids (acyl compounds) requires maximum overlap between the carbonyl π orbital and the 2 p orbital containing a pair of nonbonding electrons on the adjacent atom. This overlap has important consequences for both structure and reactivity. So, for example, although amines are pyramidal, amides are flat. Acyl compounds compounds lack the hydroxyl group of carboxylic acids and so are not strong Brønsted acids. However, they are good Lewis acids, they act as electrophiles. The carbonyl group is the source of this Lewis acidity. (Jones, 2010) Hydrolysis is a chemical process whereby a bond in a molecule is broken
by its reaction with water. The water molecule is also typically split into H + and OH-. (Brown, 2013) The objectives of this experiment were: to differentiate the reactivities of carboxylic acid and derivatives, to distinguish carboxylic acid derivatives using classification tests, and to explain through chemical equations and mechanisms the reactions involved in each test.
MATERIALS AND METHODS Materials The following materials were used in this experiment: hot plate, litmus paper, acetyl chloride, acetic anhydride, ethyl acetate, acetamide, benzamide, 2% silver nitrate, saturated sodium bicarbonate, 10% and 20% sodium hydroxide, 10% hydrochloric acid, acetic acid, 95 % ethanol, concentrated sulfuric acid, aniline, 5% ferric chloride, alcoholic hydroxylamine hydrochloride, and 1M potassium hydroxide.
Methods A. Hydrolysis of of Acid Derivatives Derivatives For acyl halides and acid anhydrides, the following procedure was used: One milliliter of water was placed in a test tube and 10 drops of the sample were cautiously added dropwise. The resuting mixture was divided into two portions. The first portion was added with 1ml of 2% silver nitrate while 1 ml of saturated sodium bicarbonate was added to the second portion.
For esters, the following was conducted: Two milliliters of 25% sodium hydroxide were added to 1ml of ethy acetate. The test tube mouth was covered with parafilm and was subjected to a water bath for 5 minutes. The mixture was neutralized using 10% hydrochloric acid solution. The hydrolysis of amides was observed through the following: One milliliter of benzamide was added with 5 ml of 10% sodium hydroxide solution and was heated to boiling. A moist red litmus paper was held at the mouth of the test tube during the heating process. B. Alcoholysis: Schotten-Baumann Reaction Ten drops of acetic acid, 1 ml of ethanol and 5 drops of concentrated sulfuric acid were mixed and warmed in a water bath for 2 minutes. In another test tube, 0.5 ml of ethanol, 1 ml of water, and 0.2 ml of acyl halide or acid anhydride sample were placed and was added with 2ml of 20% sodium hydroxide solution. The test tube was covered with a parafilm and the mixture was agitated for several minutes.
ethanol and 1M hydrochloric acid and a drop of 5% ferric chloride was added. Two drops of the samples (ethyl acetate and acetamide) were added to 2ml alcoholic hydroxylamine hydrochloride and 1ml 1M potassium hydroxide. The mixture was heated in a water bath for 2 minutes and was allowed to cool down. Then, 1 ml of ferric chloride was added.
RESULTS AND DISCUSSION Results Table 1. Results of the Hydrolysis of Acid Derivatives Derivatives A. Hydrolysis of Acid Derivatives
Acetyl chloride A.1.
Acetic anhydride
C. Aminolysis A few drops of acetyl chloride or acetic anhydride sample was added to 0.5ml aniline and was transferred to a new test tube containing 5ml of water. D. Hydroxamic Hydroxamic Test For the preliminary test, 2 drops of the sample was mixed with 1ml of 95%
A.2. ethyl ethyl acetate
A.3. benzamide benzamide
Observations Turbid, warming effect (water), white ppt (AgNO3), no ppt but with effervescence (NaHCO3) Clear colorless soln, 2 layers (water), no ppt (AgNO3), no ppt/effervescence (NaHCO3) Clear colorless solution with plastic balloonlike odor Red to blue litmus paper (Basic)
Table 2. Results of Alcoholysis: Schotten-Baumann Reaction B. Alcoholysis: SchottenBaumann Reaction Acetic acid
Acetyl chloride chloride
Observations
Strong plastic plastic balloon-like/fruity odor Faint plasticballoonlike/fruity odor
Table 3. Results of Aminolysis: Anilide Formation C. Aminolysis: Anilide Formation Acetyl chloride chloride Acetic anhydride anhydride
Observations White ppt with with oily layer White ppt with with oily layer
Table 4. Results of Hydroxamic Acid Test D. Hydroxamic Acid Test Preliminary Preliminar y Test Ethyl acetate Acetamide
Observations Yellow solution Deep burgundy color Chocolatey brown color
Discussion Table 1 shows the results of the hydrolysis of the different carboxylic acid derivatives. In hydrolysis, the water molecules are split into H + and OH-. The easiest acid derivatives to hydrolyze are acyl chlorides, which require only
the addition of water. Carboxylic acid salts are converted to the corresponding acids instantaneously at room temperature simply on treatment with water and a strong acid such as hydrochloric acid. According to Brown (2013), acid chlorides (also called acyl chlorides), acetyl chloride sample, react very rapidly with water to form carboxylic acids and HCl. The positive visible result is the turbidity of the substance and its warming effect due to the presence of HCl. Silver nitrate also reacted to the acetyl chloride producing silver chloride (AgCl) which was the white precipitate. Introducing NaHCO3 to the sample did not produce any precipitate but effervescence was observed due to the production of carbon dioxide in the form of gas. Although acid anhydrides anhydrides are generally less reactive than acid chlorides (Brown, 2013), the hydrolysis of acetic anhydride (an example of acid anhydride) yields two carboxylic acids, which did not produce any visible and observable change to the sample and also displayed a clear colorless solution with no warming effect. The hydrolysis of esters, ethyl acetate was used, occurs very slowly and only becomes rapid with the introduction of an aqueous acid or base. Hydrolysis of esters in aqueous base is often called saponification (Brown, 2013). In the experiment, ethyl acetate when reacted with sodium hydroxide produced the sodium salt of the carboxylic acid and an alcohol thus a plastic balloon-like odor was observed. The hydrolysis of amides results to the formation of salt and ammonia. In
the experiment, benzamide when reacted with 10% NaOH, produced a sodium salt and ammonia, turning the red litmus paper into blue, an indication of presence of a basic substance. In the second table, it shows the results of alcoholysis using the Schotten-Baumann reaction. Acetic acid when reacted with ethanol produced ethyl acetate, an ester, which was accounted for the strong plastic balloonlike odor, and water. Acetyl chloride also produced ethyl acetate, an ester with a plastic balloon-like odor, and HCl. The third table shows the results obtained from the aminolysis of the samples. Acetyl chloride showed a white precipitate with an oily layer. Brown (2013) stated that acid chlorides react readily with ammonia and with 1º and 2º amines to form amides. Acetyl chloride readily formed an amide in the form of N-phenylacetanamide or commonly knwn as acetanilide, as the white precipitate, and HCl, which accounts for the oily layer. Acetic anhydride anhydride reacted with aniline also produced acetanilide, the white precipitate and acetic acid, the oily layer. Table 4 shows the results to the Hydroxamic Acid Test. A preliminary test was conducted before proceeding to the main test. It was done to prevent the formation of phenols and enols that might give colors to the solution, thus giving the test an erroneous result. In test proper, hydroxylamine is treated with esters, in this experiment ethyl acetate was used, which substitute a hydroxylamino (NH-OH) group for the
ester alkoxyl radical. The resulting product is known as hydroxamic acid, observed as the deep burgundy color of the solution when added with FeCl 3. Acetamide, did not produce produce a perfect deep burgundy color, therefore, hydroxamic acid was not produced.
REFERENCES Brown, W., Poon, T. (2013) Introduction to Organic Chemistry (5th edition). Asia: John Wiley & Sons, Inc. Jones, M., Fleming S. (2010) Organic Chemistry (4 Chemistry (4th edition). New York: W.W. Norton & Company Wade, L. G. (2013) Organic Chemistry (8th edition). USA: Pearson Education Inc. Encyclopedia Britannica Online (Retrieved September 22, 2013) http://global.britannica.com/EBchecked/t opic/95261/carboxylicacid/277744/Hydr olysis-of-acid-derivatives
