Carboxylic Acids

I.OBJECTIVES:
•To investigate the physical and chemical properties of Carboxylic acid and its derivatives
•To understand the reactions of carboxylic compounds and derivatives.

II.EXPERIMENTAL RESULTS
Solubility of Carboxylic acids in 10% NaHCO¬3
Acetic acid – formation of bubbles
Benzoic acid – formation of bubbles
Test for Acetic acid
NaOH + Acetic acid – blue litmus paper turned red
NaOH + Acetic acid + FeCl3 – red colored solution
Test for Benzoic acid
Benzoic acid + NH3 – red litmus paper turned blue
Benzoic acid + NH3+ FeCl3 – orange precipitate/ flesh-colored precipitate formed
Formation of Esters
a.From Carboxylic acids
Acetic acid + ethanol + H2SO4 – produced a sweet smell
b.From Acyl Halides
Ethanol + H2O + H2SO4 – produced a sweet smell
Hydroxamic acid test for the Ester group
Ethyl acetate in ether + NH2OH.HCl + KOH heat effervescence + alcoholic HCl + FeCl3 – red colored solution
Hydrolysis of acid derivatives
H2O + Acetic anhydride 2-immiscible layer formed, blue litmus paper turned red, test tube becomes warm as the reaction took longer time
Pinch of benzamide + NaOH Red litmus paper turned blue III.DISCUSSION

INTRODUCTION
Some tests was conducted with carboxylic acids and its derivatives
1.Solubility of Carboxylic acids in 5% NaHCO3
Carboxylic acids can be easily dissolved in a basic solution, such as of sodium bicarbonate (NaHCO3). This is because there is an acid-base reaction between the carboxylic acid and the bicarbonate anion. RCOOH + HCO3 RCOO- + CO2(g) + H2O

Carboxylate ion

As carboxylic acids lose hydrogen ion, they are transformed to their respective carboxylates, which are negatively charged ions. Because they are ions, they become more soluble to the solution. The reaction also gives off carbon dioxide and these bubbles are visible making this a useful test for carboxylic acids. In the experiment it was observed that both acetic acid and benzoic acid formed bubbles by the addition of 5% Sodium bicarbonate (NaHCO3). This indicates that both compounds have a functional group –COOH and are carboxylic acid. Reactions of both acids are shown below: .

++ H2O

Benzoic acid

CH3 CH3+ H2O
Acetic acid

2.Test for Acetic acid

3.Test for Benzoic acid
Benzoic acid is a solid, white crystalline substance that is chemically classified as an aromatic carboxylic acid. Its molecular formula may be written as C7H6O2. Its chemical properties are based on the fact that each molecule consists of an acidic carboxyl group attached to an aromatic ring structure. The carboxyl group can undergo reactions to form products such as salts, esters, and acid halides.

4. Formation of Ester
Esters have a hydrocarbon either an alkyl or an aryl group replacing the hydrogen in the -COOH group of a carboxylic acid. Esters can be produced when carboxylic acids are heated with alcohols in the presence of an acid catalyst. The catalyst is usually concentrated sulphuric acid H2SO¬4. In the experiment, a sweet smell was observed when acetic acid was added by ethanol and concentrated H2SO¬4. The reaction is both slow and reversible. The equation for the reaction between an acid RCOOH and an alcohol R’OH is: H2SO4

Thus the equation for the reaction of acetic acid to produce ethyl acetate would be: H2SO4

Acetic acid ethanolethyl acetate
Addition of acetic acid to alcohols yielded a homogenous solution. The alpha hydrogen of the hydroxyl group from acetic acid was removed and bonded with the deprotonated hydroxyl group of ethanol to form water. The conjugate base of ethanol then bonds with the nucleophile oxygen of the C=O bond of the acetic acid forming ethyl acetate. Acetic acid and alcohol were warmed together in the presence of a few drops of concentrated sulphuric acid in order to observe the smell of the esters formed. Esters can also be made from the reactions between alcohols and acyl chlorides. Addition of acyl chloride to an alcohol will get a vigorous reaction at room temperature producing an ester and ester can be known by its smell. RCOCl + ROH RCOOR’ + HCL

Acyl chloride Alcohol Esters
In the experiment benzoyl chloride was added to ethanol and the solution was further added by Sodium hydroxide (NaOH). Benzoyl chloride has the formula C6H5COCl. The -COCl group is attached directly to a benzene ring and it is much less reactive than simple acyl chlorides like ethanoyl chloride. Ethanol was first converted into the ionic compound sodium ethoxide by the addition of sodium hydroxide solution. The reaction can be written as:

CH3CH2OH + NaOH CH3CH2O-Na+ + NaCl
EthanolSodium ethoxide
The ethoxide ion reacts more rapidly with benzoyl chloride than the original ethanol does, and the result goes further by the reaction of sodium ethoxide and benzoyl chloride.

+ CH3CH2O-Na+ + NaCl
-CH2CH3
benzoyl chlorideethyl benzanoate
The observed sweet odor in the experiment was caused by the formation of ethyl benzanoate, an ester. Sodium hydroxide (NaOH) was also used as an “acid trap” to reveal the odor of the ester. 5. Hydroxamic acid test for the ester group

A hydroxamic acid is a class of organic compounds bearing the functional group RC(O)N(OH)R’, with R and R’ as hydrocarbons and CO as a carbonyl group. Hydroxamic acids are prepared usually from esters. Esters do not easily present themselves as good candidates for analysis as they do not give any special tests except perhaps for the hydroxamic acid test. In this test, hydroxylamine is treated with esters which substitute a hydroxylamino (NH-OH) group for the ester alkoxyl radical. The resulting product is known as a hydroxamic acid. On acidification and addition of ferric chloride, the magenta-coloured iron (III) complex of the hydroxamic acid is formed.

Magenta Colored Complex
In the experiment, the color of the solution was red even with many trials done; it is assumed that the solution lacked the right amount of heat needed for the solution to yield a magenta colored solution. The reaction of the test done using ethyl acetate in ether is shown below: 6. Hydrolysis of acid derivatives

All acid derivatives can be hydrolysed to yield carboxylic acids; the conditions required range from mild to severe, depending on the compound involved. In a hydrolysis reaction, a chemical bond is broken by the addition of water. Hydrolysis is typically carried out in the presence of a salt of a weak acid or weak base. Water auto ionizes into hydroxyl ions (OH-) and hydronium ions (H3O+) and acts as a source of a nucleophile and catalyzing acid. In the experiment, first was the hydrolysis of esters but this reaction was not conducted in. Theoretically, the reaction with pure water is so slow that it is never used. The usual way of hydrolysing ester is when ester is heated under reflux with a dilute alkali like sodium hydroxide solution. There are two big advantages of doing this rather than using a dilute acid. The reactions are one-way rather than reversible, and the products are easier to separate. After the reaction, a sour smell is expected to be observed and this is because the formation of carboxylic acid. A sample reaction of ethyl acetate added by sodium hydroxide is shown below: O O

C H3O+ C
H3C OCH2CH3 + H2O H3C OH + CH3CH2OH Ethyl acetateacetic acid

Next was the hydrolysis of acetic anhydride.
And lastly was the hydrolysis of amides. In the experiment benzamide was added by Sodium hydroxide and urine like smell was observed. This is because during the reaction, ammonia gas was given off with a solution left containing sodium ethanoate. The solution was also test using the litmus paper. Red litmus paper turned blue because ammonia that given off is basic. IV.CONCLUSION

V.ANSWERS TO QUESTION
1.Write the chemical reactions involved in tests 1-6
2.Why would acyl halides give higher yields of amides compared to carboxylic acids?
3.Why should excess alkali be avoided in FeCl3 test for CH3COOH and benzoic acid?