Difference Between Protonation and Deprotonation

Main Difference – Protonation vs Deprotonation

Protonation and deprotonation are important chemical reactions in the synthesis of different chemical compounds. Protonation is the addition of a proton to a chemical species. Deprotonation is the removal of a proton from a chemical compound.  The main difference between protonation and deprotonation is that protonation adds a +1 charge to a compound whereas deprotonation removes a +1 charge from a chemical compound.

Key Areas Covered

1. What is Protonation
     – Definition, Examples
2. What is Deprotonation
     – Definition, Explanation
3. What is the Difference Between Protonation and Deprotonation
     – Comparison of Key Differences

Key Terms: Acid, Brønsted–Lowry Acid, Deprotonation, Hydrogen, Isotope, Proton, Protonation

What is Protonation

Protonation is the addition of a proton to an atom, molecule, or ion. The addition of a proton causes the formation of a conjugated acid of a chemical species. Protonation causes the change in electrical charge of a chemical species. This is because a proton is always +1 charged. The symbol for proton is given as H⁺ (the +1 charged hydrogen atom is a proton).

A hydrogen atom can be found as three major isotopes: protium, deuterium and tritium. All these isotopes have one proton in their nucleus along with varying numbers of neutrons. All these isotopes have one electron in the surrounding electron shell (orbital). When this electron is removed from the hydrogen atom, the only remaining charged subatomic particle is a proton. Hence the H⁺ ion resembles a proton.

Some examples for protonation are given below:

1. Protonation of ammonia gives ammonium ion

NH₃   +   H⁺      →     NH₄⁺

2. Protonation of water gives hydronium ion

H₂O   +   H⁺      ↔   H₃O⁺

Figure 1: Protonation of Water Molecule

3. Protonation of Alcohols

C₂H₅OH   +   H⁺    →     C₂H₅OH₂⁺

What is Deprotonation

Deprotonation is the removal of a proton from a Brønsted–Lowry acid during an acid-base reaction. (Brønsted–Lowry acids are compounds that can release protons to form its conjugate base). This directly affects the overall charge of a chemical species because the proton is +1 charged and the removal of a proton equals the removal of +1 charge. Deprotonation gives the conjugate base of a chemical species.

Water molecule is an amphoteric compound that can either donate or accept protons. Hence, it undergoes both protonation and deprotonation reactions. The deprotonation of a water molecule gives hydroxide anion (OH^–).

H₂O     ↔   H⁺   +   OH^–

In organic chemistry, deprotonation is very important in different synthesis routes. For example, the deprotonation of alkynes by bases such as NaNH₂ gives the sodium salt of alkyne via deprotonation. This happens because the terminal hydrogen of alkynes are very acidic and are easily removed. Then a different organic compound can be attached to this salt.

Figure 2: Reaction between Acetylene and NaNH₂

(C₂H₂   +     NaNH₂       →     HC₂^–Na⁺   +   NH₃)

Difference Between Protonation and Deprotonation

Definition

Protonation: Protonation is the addition of a proton to an atom, molecule, or ion.

Deprotonation: Deprotonation is the removal of a proton from a Brønsted–Lowry acid during an acid-base reaction.

Proton Transfer

Protonation: Protonation adds a proton to a compound.

Deprotonation: Deprotonation removes a proton from a compound.

Change in Electrical Charge

Protonation: Protonation adds a +1 charge to a compound.

Deprotonation: Deprotonation removes a +1 charge from a compound.

Conclusion

Protonation and deprotonation are two basic chemical reactions. The main difference between protonation and deprotonation is that protonation adds a +1 charge to a compound whereas Deprotonation removes a +1 charge from a chemical compound.

Reference:

1. Helmenstine, Anne Marie. “Protonation Definition and Example.” ThoughtCo, Feb. 11, 2017, Available here.
2. “Alcohol Protonation: Synthesis Intermediate for a Plethora of Reactions.” Quirky Science, 23 Jan. 2018, Available here.
3. “Alkynes: Deprotonation and SN2.” Master Organic Chemistry RSS, Available here.

Image Courtesy:

1. “Alcohol protonation” By Esmu Igors – Own work (CC BY-SA 3.0) via Commons Wikimedia