Carboxylic group includes a carbonyl group and a hydroxyl group. Carboxylic acids are weak acids which dissociate partially in the water. Carboxylic acids can be prepared by oxidizing alcohols, aldehydes etc. There are aliphatic and aromatic carboxylic acids in the world.
Active group of carboxylic acid is -COOH.
We can see carboxylic acids are in natural sources.
Formic acid(HCOOH) is the simplest carboxylic acid compound.
IUPAC names of carboxylic acids ends with oic acid. The carbon atom of carboxylic acid group holds number 1. Therefore in the nomenclature, the number of carboxylic group is neglected. Other all IUPAC nomenclature rules are applied for carboxylic nomenclature.
Carboxylic acids dissociates partially in the water. Therefore those solutions are weak acids in aqueous solutions. Ka values of carboxylic acids are usually in 10-4 - 10-8 mol dm-3.
Carboxylic acids can be prepared by oxidizing alcohols and aldehydes.
Alcohols can be oxidized into carboxylic acid using acidic strong oxidizing agents such as KMnO4, K2CrO4, K2Cr2O7.
Ethanoic acid is given as the product. Purple colour of potassium permanganate is changed into colourless or pink colour.
Aldehydes can be oxidized into carboxylic acid using weak oxidizing agent or acidic strong oxidizing agents Ammonical silver nitrate( [Ag(NH3]NO3 ), Fehling's solution( includesCu(I) ions ), H2O2 are weak oxidizing agents which can oxidize aldehydes into carboxylic acids.
Ag+ ions are reduced into Ag. This Ag metal can be identified as a silver mirror.
Cu2+ ions are reduced into red colour Cu2O.
When strong oxidizing agents are in the presence with some alkenes, carboxylic acids can be given as products. This reaction is defined as ozonolysis. H+/ KMnO4 , H+/ K2CrO4 or O3 can be used as reagents.
The double bond of alkene is braked to give products. According to the structure of alkene compounds mixture of carboxylic acids or ketones or CO2 can be given.
2-butene ozonolysis gives ethanoic acid.
2-pentene ozonolysis gives mixture of ethanoic acid and propanoic acid.
A mixture of carboxylic acid and ketone is given.
ethanoic acid given.
propanoic acid is given.
benzoic acid is given.
C atom in the CO2 is polarized as positive. Alkyl group in the grignard reagent has negative charge.
step 1: C atom in the CO2 is attacked by :CH3- in the grignard reagent.
step 2: A H atom in the water molecule is attacked by O-.
From hydrolysis of aryl or alkyl cyanide, carboxylic acids are prepared. Any acid or acidic substance can catalyse this reaction.
Carboxylic compounds show acidic characteristics. Therefore carboxylic acids can react with Na, NaOH, Na2CO3, NaHCO3 as a acid. There are three main types of reactions of carboxylic acids.
Carboxylic acids react with metals such as sodium, potassium and give hydrogen(H2) and salt. Alcohols also react with Na and K. But carboxylic acids react more quickly than alcohols.
Carboxylic acids react with NaOH and give R-COO-Na+. This is a reaction of weak acid and a strong alkali.As an example, ethanoic acid(CH3COOH) reacts with NaOH(aq) and give sodium ethanoate and water as products.
Carboxylic acid reacts with Na2CO3 or NaHCO3 and emits CO2 gas. This reaction can be used to identify phenol and carboxylic acids. Phenol does not react with sodium carbonate or sodium bicarbonate to emit a gas or gases..
Carboxylic acids react with inorganic acid chlorides such as SOCl2, PCl3, PCl5 and give carboxylic acid chlorides.
Carboxylic acid react with alcohol when heating and in the presence concentrated sulfuric acid(catalyst) and give esters. This reaction is a reversible one.
Every carboxylic acids (aliphatic and aromatic carboxylic acids) are subjected to carboxylation. Hydrocarbons are given as products. CaO(s) / Ca(OH)2(s) and NaOH(s) mixture is used as the reagent in carboxylation.
Carboxylic acids react with ammonia gas(NH3) or ammonia hydroxide solution (NH4OH) to produce ammonium salt of carboxylic acid. These ammonium salts are soluble in water and they show ionic characteristics.
3) with NaOH at room temperature. When ammonium salts of carboxylic acid are heated, it is dehydrated and gives amide compounds.
Carboxylic acids are not reduced easily. But a strong oxidizing reagent, lithium aluminum hydride(LiAlH4) can be used to reduce carboxylic acid. Reducing carboxylic acids by LiAlH4 gives alcohols.
Generally we can say acidity of alcohols, phenols and carboxylic acids are
All aromatic carboxylic acids are more acidic than aliphatic carboxylic acids.
Example: benzoic acid is more acidic than acetic acid.
Ethanoic acid partially dissociate in the water and form ethanoate ion (acetate, CH3COO-) and H3O+.
benzoic acid partially dissociate in the water and form benzoate ion. and H3O+.
In the benzoate ion, negative charge overlap with benzene ring. Therefore negative charge decreases. Stability of carbanion is high.
But Alkyl groups repel electrons. Therefore negative charge on oxygen atom increases. Hence Stability of carbanion is less than benzoate ion.
Therefore equilibrium point of benzoic acid trends to the right. Thus acidity of benzoic acid is higher than ethanoic acid.
Halogens are more electro negative than carbon. Carboxylic acids form carboxylate ions in the aqueous solution. If this carboxylate ion is more stable, the acidity increases. In halogens, F is the most electro negative atom.
Comparing Pka values of acids are easy to compare strength of acids. When Pka is decreased, acidic strength is increased.
Formic acid has the lowest molecular mass in carboxylic acids range. Formic acid has special reducing agent. When oxidizing agents are in the presence, formic acid is converted to CO2 and H2O. The H atom which is attached to the acidic C atom is the reason for this reducing characteristics.
Formic acid can be oxidized using following oxidizing agents.
CO2 and H2O are given by the reaction of HCHO and strong oxidizing agents.
HCHO reacts with Hg2Cl2 and give CO2, H2O and Hg2Cl2 white precipitate.
HCHO reacts with tollen's reagent and give CO2, H2O and Ag(silver mirror).
HCHO reacts with fehlingh's reagent and give CO2, H2O and Cu2O(red precipitate).
None of other carboxylic acids are oxidized and give CO2 and H2O like HCHO acid.
Add Na2CO3 to both solutions
Formic acid is the most acidic carboxylic acid because formic acid has reducing characteristics.