Main Uses of Carboxylic Acid Explained

A carboxylic acid is an organic compound that holds a carboxyl group (C(=O) OH). The general formula of a carboxylic acid is R–COOH, with R mentioning the rest of the (possibly quite large) atom. Carboxylic acids occur broadly and cover the amino acids (which make up proteins) and acetic acid (which is part of vinegar and takes place in metabolism).

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Ester and salt of carboxylic acids are known as carboxylates. When a carboxyl group loses a proton, its conjugate base processes a carboxylate anion. Carboxylate ions are resonance-steady, and this improvement in stability makes carboxylic acids more acidic than alcohols, sideways with the electron-withdrawing effect of the carbonyl bond, which creates the terminal oxygen-hydrogen bond fragile and thus makes acid split-up more favourable (lowers pKa). Carboxylic acids can be seen as a reduced or alkylated type of Lewis acid carbon dioxide; under some situations, they can be decarboxylated to create carbon dioxide CO2.

Nomenclature

Carboxylic acids are normally identified using their trivial names, and typically have the suffix -ic acid. IUPAC-recommended names also exist; in this method, carboxylic acids have an -oic acid suffix. For classification of a complex atom having a carboxylic acid, the carboxyl can be considered position one of the parental chains even if there are other substituents, for instance, 3-chloropropanoic acid. The carboxylate anion (R–COO−) of a carboxylic acid is typically named with the suffix -ate, in keeping with the regular pattern of -ic acid and -ate for a conjugate acid and its conjugate base, in that order. For instance, the conjugate base of acetic acid is acetate.

Structure:

The CO2H component is planar and reliable with sp2 hybridization and a resonance contact of the lone pairs of the hydroxyl oxygen with the Pi (π) system of the carbonyl.

Physical Properties

• Solubility

• Boiling points

• Acidity

• Odour

Solubility

Carboxylic acids are polar in nature. Because they are both hydrogen-bond acceptors (the carbonyl –C=O) and hydrogen-bond contributors or donors (the hydroxyl –OH), they also contribute to hydrogen bonding. Together with the hydroxyl and carbonyl group procedures the functional group carboxyl. Carboxylic acids usually exist as dimeric pairs in a nonpolar region due to their ability to "self-associate". Minor carboxylic acids (1 to 5 carbons) are water-soluble, whereas higher carboxylic acids are less soluble in water due to the growing hydrophobic nature of the alkyl chain. These longer chain acids have a habit to be rather soluble in less polar solvents such as Alcohols and Ethers.

Boiling Points

Carboxylic acids have a tendency to have higher boiling points than water H2O, not only due to their bigger surface area but also due to their ability to form stabilized dimers. The dimer bonds must be broken or the entire dimer configuration must be evaporated for boiling to take place, both of which rise the enthalpy of vaporization requirements considerably.

Acidity

• Carboxylic acids are Brønsted–Lowry acids due to their proton (H+) donor’s nature. Carboxylic acids are the mainly acidic simple organic compounds (pKa ~ 5).

• But they are only weak acids as compared with acids like HCl or H2SO4.

• Carboxylate ion’s Resonance stabilization will allow the negative charge to be delocalized among the two electronegative oxygen atoms (compare with alcohols, pKa ~ 16).

• Neighbouring electron drawing substituents will increase the acidity by extra stabilizing the carboxylate.

Odour

Carboxylic acids regularly have a strong smell, especially volatile products. Most typical are acetic acid (vinegar) and butyric acid (human vomit). Equally esters of carboxylic acids tend to have a pleasing smell and many are used in perfume.

Classes of Carboxylic Acid

The various types of carboxylic acids, which are briefly described below. 

Saturated Aliphatic Acids

Formic acid, HCOOH, is not only found in ants but also in the droplets on the minute hairs of the stinging nettle plant and the acidity of this compound will create the stinging sensation felt when these hairs are touched.

Unsaturated Aliphatic Acids

A large number of acids vital in organic chemistry have carbon-carbon (C-C) double bonds. Their presence α, β-unsaturated acids, in which the double bond is among the second and third carbons of the chain, and also unsaturated acids, in which the double bond formed in other positions. Although many of these latter acids are present in nature, as they are less easy to produce than α, β-unsaturated acids. Acrylic acid esters of (ethyl and butyl acrylate) and methacrylic acid (methyl methacrylate) are the main monomers for the synthesis of polymers.

Aromatic Acids

Aromatic acids contain compounds that have a COOH group bonded to an aromatic ring. An example of aromatic acids is the simplest aromatic acid is benzoic acid.

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Aromatic carboxylic acids display not only the acidity and several other reactions likely of carboxylic acids (as an acid, benzoic acid is slightly stronger than acetic acid) but, parallel to other aromatic compounds, also experience electrophilic substitution reactions.

Polycarboxylic Acid

Unbranched-chain dicarboxylic acids have two COOH sets or groups. As a result, they can produce two types of salts. For instance, if oxalic acid, HOOCCOOH, is 50% neutralized with sodium hydroxide NaOH and, HOOCCOONa, known as sodium acid oxalate or monosodium oxalate, is produced. Because one COOH group or set still exists in the compound, it has the characteristic of both a salt and an acid. Complete neutralization (treatment of oxalic acid with NaOH in a 1:2 acid-to-base molar ratio) produces NaOOCCOONa, sodium oxalate

Hydroxyl and Keto Acid

The 2-, 3-, 4-, and 5-hydroxycarboxylic acids all upon heating lose water, although the yields are not the same. The 2-hydroxy acids form cyclic dimeric esters (made by the esterification of two atoms of the acid) known as lactides, while the 3- and 4-hydroxy acids undergo intermolecular esterification to produce cyclic esters known as lactones.

Amino Acids

Compounds having both a carboxyl group and an amino group are known as amino acids. 20 of these are present in proteins, all of which are α-amino acids with the formula:

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Synthesis 

The different methods of synthesis are described below.

Industrial Method

In general, industrial routes to carboxylic acids differ from those used on a lesser scale as they require specialized equipment.

• Oxidations of aldehydes with air help cobalt and manganese catalysts. The needed aldehydes are readily found from alkenes by hydroformylation.

• Oxidation of hydrocarbons using air. For simple alkanes, this technique is low-cost but not selective enough to be useful. Allylic and benzylic compounds experience more selective oxidations. Alkyl groups on a benzene ring will oxidize to the carboxylic acid, irrespective of its chain length. Benzoic acid from toluene, terephthalic acid will form para-xylene, and phthalic acid will from ortho-xylene are explanatory large-scale conversions. Acrylic acid is produced from propane.

• Base-catalyzed dehydrogenation of alcohols occurs.

• Carbonylation is the adaptable method when joined to the addition of water. This technique is more effective for alkenes that create secondary and tertiary carbocation, e.g. isobutylene to pivalic acid. In the Koch reaction, the addition of water and carbon monoxide to alkenes is catalyzed by solid acids. Acetic acid and formic acid are made by the carbonylation of methanol, lead with iodide and alkoxide promoters, correspondingly, and often with great pressures of carbon monoxide, typically involving extra hydrolytic steps. Hydrocarboxylation includes the simultaneous addition of water and CO. Such reactions are sometimes known as "Reppe chemistry":

HCCH + CO + H2O → CH2 = CHCO2H

• Some long-chain carboxylic acids are produced by the hydrolysis of triglycerides derived from plant or animal oils; these approaches are related to soap making.

• fermentation of ethanol is used in the manufacture of vinegar.

Laboratory Method

Oxidation of (10) primary alcohols or aldehydes with heavy-duty oxidants such as potassium permanganate, potassium dichromate, Jones reagent, or sodium chlorite.

The technique is responsive to laboratory conditions compared to the industrial use of air, which is "greener" since it produces less inorganic side yields such as chromium or manganese oxides.

• Oxidative cleavage of olefins by potassium permanganate, ozonolysis, or potassium dichromate.

• Carboxylic acids can also be derived by the hydrolysis of nitriles, esters, or amides, in common with acid- or base catalysis.

• a mixture of a Grignard and organ lithium reagents:

RLi + CO2 → RCO2Li

RCO2Li + HCl → RCO2H + LiCl

• Hydrolysis of methyl ketones in the haloform reaction followed by Halogenation

• The Kolbe–Schmitt reaction delivers a route to salicylic acid, a precursor to aspirin.

•  Base-catalyzed cleavage of non-enolizable ketones, particularly aryl ketones.

RC(O)Ar + H2O → RCO2H + ArH

Ozonolysis of Alkenes

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Reaction type: Electrophilic Addition

Summary:

• Overall alteration: C=C to 2 x C=O

• Ozonolysis suggests that ozone will cause the alkene to break (-lysis)

• Reagents used: ozone followed by:

• a reducing work-up, either Zn in dimethyl sulfide (CH2)2S or acetic acid 

• an oxidizing work-up, typically H2O2 

• It is suitable to understand the process as cleaving the alkene into two carbonyls

• The substituents on the C=O rely on the substituents on the original C=C.

• The work-up regulates the oxidation state of the produces

Carbonation of Grignards

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The reaction usually in Et2O or THF followed by H3O+ work-up

Type of reaction:  Nucleophilic Addition

Summary:

Grignard reagents react with dry ice (solid CO2) followed by aqueous acid work-up to produce carboxylic acids. Carbon dioxide CO2 can be thought of as being a di-carbonyl compound: O=C=O. Remember that the carboxylic acid has one extra C molecules compared to the original halide from which the Grignard reagent was made.

Oxidation of 1o Alcohols

Type of reaction: Oxidation-reduction

Summary:

Primary alcohols (1° alcohol), that is, RCH2OH, can be oxidized to carboxylic acids, that is, RCO2H, under aqueous conditions.

Usual reagents are based on aqueous Cr (VI):

Chromate salts, e.g. Na2CrO4, chromic acid, H2CrO4, dichromate salts, e.g. K2Cr2O2

The oxidation goes first to the aldehyde followed by the carboxylic acid.

R can be alkyl or aryl.

Oxidation of Aldehydes

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Type of reaction: Oxidation-reduction

Summary:

Aldehydes, RCHO, oxidized to carboxylic acids, RCO2H, under aqueous conditions.

Usual reagents are based on aqueous Cr Chromic acid, H2CrO2, chromate salts, e.g. Na2CrO2

The oxidation essentially proceeds on the hydrate, RCH(OH)2, is formed by the reaction of water with the aldehyde. R can be aryl or alkyl

Oxidation of Alkyl Benzene

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Type of reaction: Oxidation

Summary:

When reacted under strongly oxidizing conditions, benzylic-H are oxidized all the way to the carboxylic acid.

Basic reagents: Hot, acidic KMnO4

The alkyl substituent can be methyl-, primary 1o or secondary 2o alkyl.3o alkyl is not oxidized because they lack a benzylic-H.

Simple alkane C-H cannot be oxidized in this manner.

This gives a potential route to aromatic carboxylic acids

Spectroscopic Analysis:

• IR - The -O-H and C=O should be understandable

13C NMR

COOH carbon 160 - 185 ppm (de- shielded due to O, but not as much as ketones and aldehyde 190-215 ppm) 

UV-VIS

Carboxylic acids absorb UV-Vis light at a wavelength of 210 nm, but this is too low to be mainly useful.   

Mass Spectrometry

The highest for the molecular ion, M+ is usually prominent. Remains due to loss of OH (M - 17) + and the loss of CO (M - 45) +

Uses of Carboxylic Acid

If we eat a meal with unsaturated fat, the glucose and other nutrients will straightly rush into the bloodstream without being absorbed. Whereas if there is a consumption of saturated fat, digestion will slow down, and the body will get more time to absorb the energy and nutrients from the nutrition. The next points will state other significant uses of carboxylic acids:

1. Production of soaps need higher fatty acids. Soaps are usually sodium or potassium salts of higher fatty acids such as stearic acid.

2. The food industry uses numerous organic acids for the manufacture of soft drinks, food products etc. For instance, acetic acid is used in making vinegar. Sodium salts of organic acids find use in preservatives.

3. In the pharmaceutical industry organic acids are used in numerous drugs

4. Acetic acids are often used as a coagulant in the production of rubber.

5. Organic acids find vast application in making dyestuff, perfumes, and rayon.