Experiment 15. Reactions of carboxylic acids

Experiment 15Reactions of Carboxylic Acids

Pre-laboratory Questions:

DRAW THE STRUCTURAL FORMULA OF THE FOLLOWING COMPOUNDS:

Acetic acid, monochloroacetic acid, trichloroacetic acid, benzoic acid, oxalic acid, succinic acid, lactic acid, tartaric acid, citric acid and propionic acid.

Acetic acid

Monochloroacetic acid

Trichloroacetic acid

Benzoic acid

Oxalic acid

Succinic acid

Lactic acid

Tartaric acid

Citric acid

Propionic acid

WRITE THE EQUATION THAT SHOWS THE IONIZATION OF VALERIC ACID IN WATER.

+ H2O H3O +

+

WRITE EQUATIONS SHOWING THE REACTIONS OF VALERIC ACID WITH NAOH AND NAHCO3.

+ NaOH

+ NaHCO3 + CO2 + H2O

RESULTS & DISCUSSIONS

A. ACIDITY AND STRUCTURE

Acetic acid Monochloroacetic acid

Trichloroacetic acid

pH 3.0 2.0 1.0

Trichloroacetic acid is more acidic because of the presence of the 3 chlorine atoms which tend to pull the electrons closer leaving the

Hydrogen more prone to leave

DISCUSSION:

B. SOLUBILITY

Water NaHCO3

Acetic Acid - 0.5 mL

Benzoic Acid Did not dissolve 0.5 mL

Oxalic Acid 0.5 mL 0.5 mL

Lactic Acid 0.5 mL 1 mL

EFFECT OF OXIDIZING AGENTSKMnO4 Tollens’ Reagent

Formic acid Purple to green (w/o heating)Green to brown (after heating)

Silver mirror formed

Acetic acid No change in color No silver mirror formed

Lactic acid Purple to green (w/o heating)Green to brown (after heating)

No silver mirror formed

Tartaric acid Purple to bloody red (w/o heating)Bloody red to clear sol’n (after

heating)

No silver mirror formed

Citric acid Purple to clear sol’n No silver mirror formed

Oxalic acid No change in color No silver mirror formed

Benzoic acid No change in color No silver mirror formed

Propionic acid Purple to reddish brown (after heating)

White precipitate

Water No change in color No silver mirror formed

FORMIC PROPIONIC TARTARIC CITRIC ACETIC

OXALIC LACTIC BENZOIC

DISCUSSION for KMnO4

•Carboxylic acids are relatively resistant to oxidation. However, some acids, like alpha-hydroxy acids may be oxidized.

Acetic acid Lactic acid

DISCUSSION for Tollen’s Reagent

• Mild oxidizing agents like Tollen’s reagent are easily reduced by aldehydes to silver mirror.

O

CH OH

Formic acid

ESTERIFICATION

• Smells like Guava ; • Did not dissolve in water

DISCUSSION:

There are two evidences of esterification reactions:

1. The change in solubility – the product ester is not water soluble, so two layers were formed

2. A distinctive change in odor – they are usually sharp and extremely pleasant

CARBOXYLIC ACID AND ITS SALTS

Cold water: salicylic acid did not dissolve

Hot water: salicylic acid dissolved

When cooled to room temperature: crystals were formed

Addition of 3M NaOH in erlenmeyer flask: crystals were dissolved

Addition of 3M HCl in erlenmeyer flask: crystals were reformed

QUESTIONS

1. What is the effect of Cl on the acidity of carboxylic acids?

Cl is electronegative which tends to pulls electrons closer to them leaving the hydrogen more readily to leave making it highly acidic

2. Explain the effect of the structure of the

samples used on solubility behavior.

Acetic acid

Monochloroacetic acid

Trichloroacetic acid

Benzoic acid

Oxalic acid

Succinic acid

Lactic acid

Tartaric acid

Citric acid

Propionic acid

3. Write the equation showing the ester

formation.

Conclusion

• In conclusion, the structure of the compounds plays an important role in its solubility.

• Electronegativity plays a big role on the carboxylic acid’s acidity.

• Carboxylic acids are usually resistant to oxidization but there are some cases that they can be oxidized.