ORGANIC SALTS: PROPERTIES, USES AND EXAMPLES - CHEMISTRY - 2025

The organic salts are dense number of ionic compounds with many features. They are previously derived from an organic compound, which has undergone a transformation that allows it to carry a charge, and also, its chemical identity depends on the associated ion.

Two very general chemical formulas for organic salts are shown in the image below. The first of these, R-AX, is interpreted as a compound in whose carbon structure an atom, or group A, carries a positive + or negative (-) charge.

Source: Gabriel Bolívar

As can be seen, there is a covalent bond between R and A, RA, but in turn, A has a formal charge that attracts (or repels) the ion X. The sign of the charge will depend on the nature of A and the chemical environment.

If A were positive, how many X's could it interact with? With only one, given the principle of electroneutrality (+ 1-1 = 0). However, what is the identity of X? The anion X could be CO ₃ ^2–, requiring two RA ⁺ cations; a halide: F ^-, Cl ^-, Br ^-, etc.; or even another RA ^- compound. The options are incalculable.

Also, an organic salt can have an aromatic character, illustrated by the brown benzene ring. The benzoate salt of copper (II), (C ₆ H ₅ COO) ₂ Cu, for example, consists of two aromatic rings with negatively charged carboxyl groups, which interact with the Cu ²⁺ cation.

Physical and chemical properties

From the image it can be stated that organic salts consist of three components: the organic, R or Ar (the aromatic ring), an atom or group that carries the ionic charge A, and a counterion X.

Just as the identity and chemical structure are defined by such components, in the same way their properties depend on them.

From this fact, certain general properties that the vast majority of these salts fulfill can be summarized.

High molecular masses

Assuming mono or polyvalent inorganic anions X, organic salts tend to have much larger molecular masses than inorganic salts. This is mainly due to the carbon skeleton, whose single CC bonds, and their hydrogen atoms, contribute a lot of mass to the compound.

Therefore, R or Ar are responsible for their high molecular masses.

Amphiphilics and surfactants

Organic salts are amphiphilic compounds, that is, their structures have both hydrophilic and hydrophobic ends.

What are such extremes? R or Ar represent the extreme hydrophobic, because their C and H atoms do not have great affinity for water molecules.

A ^{+ (-)}, the charge-bearing atom or group, is the hydrophilic end, since it contributes to the dipole moment and interacts with water, forming dipoles (RA ⁺ OH ₂).

When the hydrophilic and hydrophobic regions are polarized, the amphiphilic salt becomes a surfactant, a substance widely used for the production of detergents and demulsifiers.

High boiling or melting points

Like inorganic salts, organic salts also have high melting and boiling points, due to the electrostatic forces that govern the liquid or solid phase.

However, since there is an organic component R or Ar, other types of Van der Waals forces participate (London forces, dipole-dipole, hydrogen bonds) that compete in a certain way with the electrostatic ones.

For this reason, the solid or liquid structures of organic salts are, in the first instance, more complex and varied. Some of them can even behave like liquid crystals.

Acidity and basicity

Organic salts are generally stronger acids or bases than inorganic salts. This is because A, for example in amine salts, has a positive charge due to its bond with an additional hydrogen: A ⁺ -H. So, in contact with a base, donate the proton to become a neutral compound again:

RA ⁺ H + B => RA + HB

H belongs to A, but is written because it is involved in the neutralization reaction.

On the other hand, RA ⁺ can be a large molecule, unable to form solids with a sufficiently stable crystal lattice with the hydroxyl or hydroxyl anion OH ^-.

When this is so, the RA ⁺ OH ^- salt behaves like a strong base; even as basic as NaOH or KOH:

RA ⁺ OH ^- + HCl => RACl + H ₂ O

Note in the chemical equation that the Cl ^- anion replaces the OH ^-, forming the RA ⁺ Cl ^- salt.

Applications

The use of organic salts will vary according to the identity of R, Ar, A and X. Furthermore, their application also depends on the type of solid or liquid they form. Some generalities in this regard are:

-Serve as reagents for the synthesis of other organic compounds. RAX can act as a “donor” for the R chain to add to another compound replacing a good leaving group.

-They are surfactants, so they can also be used as lubricants. Metal salts of carboxylates are used for this purpose.

-Allows the synthesis of a wide range of colorants.

Examples of organic salts

Carboxylates

Carboxylic acids react with a hydroxide in a neutralization reaction, giving rise to the carboxylate salts: RCOO ^- M ⁺; where M ⁺ can be any metal cation (Na ⁺, Pb ²⁺, K ⁺, etc.) or the ammonium cation NH ₄ ^+.

Fatty acids are long aliphatic chain carboxylic acids, they can be saturated and unsaturated. Among the saturated ones are palmitic acid (CH ₃ (CH ₂) ₁₄ COOH). This originates the palmitate salt, while stearic acid (CH ₃ (CH ₂) ₁₆ COOH forms the stearate salt. Soaps are made up of these salts.

In the case of benzoic acid, C ₆ H ₅ COOH (where C ₆ H ₅ - is a benzene ring), when it reacts with a base, it forms benzoate salts. In all carboxylates the group -COO ^- represents A (RAX).

Lithium diakylcuprates

Lithium diakylcuprate is useful in organic synthesis. Its formula is ^- Li ⁺, in which the copper atom carries a negative charge. Here, the copper represents atom A in the image.

Sulfonium salts

They are formed from the reaction of an organic sulfide with an alkyl halide:

R ₂ S + R'X => R ₂ R’S ⁺ X

For these salts, the sulfur atom carries a positive formal charge (S ⁺) as it has three covalent bonds.

Oxonium salts

Likewise, ethers (the oxygenated analogs of sulfides) react with hydracids to form oxonium salts:

ROR '+ HBr <=> RO ⁺ HR' + Br ^-

The acidic proton of HBr binds covalently to the oxygen atom of the ether (R ₂ O ⁺ -H), charging it positively.

Amine salts

Amines can be primary, secondary, tertiary or quaternary, as can their salts. All of them are characterized by having an H atom linked to the nitrogen atom.

Thus, RNH ₃ ⁺ X ^- is a primary amine salt; R ₂ NH ₂ ⁺ X ^-, of secondary amine; R ₃ NH ⁺ X ^-, from tertiary amine; and R ₄ N ⁺ X ^-, from quaternary amine (quaternary ammonium salt).

Diazonium salts

Finally, the diazonium salts (RN ₂ ⁺ X ^-) or aryldiazonium (ArN ₂ ⁺ X ^-) represent the starting point of many organic compounds, especially azo dyes.

References

1. Francis A. Carey. Organic Chemistry. (Sixth ed., Pages 604-605, 697-698, 924). Mc Graw Hill.
2. Graham Solomons TW, Craig B. Fryhle. Organic Chemistry. Amines. (10th edition.). Wiley Plus.
3. Wikipedia. (2018). Salt (Chemistry). Taken from: en.wikipedia.org
4. Steven A. Hardinger. (2017). Illustrated Glossary of Organic Chemistry: salts. Recovered from: chem.ucla.edu
5. Chevron Oronite. (2011). Carboxylates.. Recovered from: oronite.com