Phosphoric Acid

Definition

Phosphoric acid is a colorless, odorless, and highly corrosive inorganic compound with the chemical formula H3PO4. It is a key player in various chemical reactions, particularly in the context of electrophilic addition reactions of alkenes and the preparation of alkenes through elimination reactions.

5 Must Know Facts For Your Next Test

1. Phosphoric acid is a strong acid that can act as a powerful electrophile in addition reactions with alkenes.
2. The protonation of an alkene by phosphoric acid is the first step in the electrophilic addition of water, forming an alcohol product.
3. Phosphoric acid can also be used as a dehydrating agent in elimination reactions, promoting the removal of water and the formation of alkenes.
4. The conjugate base of phosphoric acid, the dihydrogen phosphate ion (H2PO4-), can participate in acid-base reactions and buffer solutions.
5. Phosphoric acid is widely used in the production of fertilizers, detergents, and various industrial chemicals.

Review Questions

• Explain the role of phosphoric acid in the electrophilic addition reactions of alkenes.
  • In the context of electrophilic addition reactions of alkenes, phosphoric acid acts as a powerful electrophile. The protonation of the alkene by phosphoric acid is the first step, where the electrophilic H+ from the acid adds to the carbon-carbon double bond, forming a carbocation intermediate. This carbocation can then be attacked by a nucleophile, such as water, to form the final alcohol product. The ability of phosphoric acid to participate in this protonation step is crucial for the overall electrophilic addition reaction to occur.
• Describe how phosphoric acid can be used to prepare alkenes through elimination reactions.
  • In the context of preparing alkenes through elimination reactions, phosphoric acid can act as a dehydrating agent. Phosphoric acid can promote the removal of water from an alcohol or other precursor, leading to the formation of a carbon-carbon double bond. This elimination reaction typically occurs through the formation of a carbocation intermediate, which is then deprotonated to yield the alkene product. The strong acidity and dehydrating properties of phosphoric acid make it an effective reagent for driving these elimination reactions and synthesizing alkenes.
• Analyze the significance of the conjugate base of phosphoric acid, the dihydrogen phosphate ion (H2PO4-), in chemical systems.
  • The dihydrogen phosphate ion (H2PO4-), which is the conjugate base of phosphoric acid, plays a crucial role in various chemical systems. As a weak base, H2PO4- can participate in acid-base reactions, acting as a buffer to maintain a relatively stable pH in solutions. This buffering capacity is particularly important in biological systems, where phosphoric acid and its conjugate base help regulate the pH of bodily fluids, such as blood and cellular environments. Additionally, the dihydrogen phosphate ion can form various salts and complexes with other ions, contributing to its widespread use in diverse chemical applications, including the production of fertilizers, detergents, and other industrial chemicals.

Related terms

Electrophile:

An electrophile is a species that is attracted to electron-rich regions and participates in reactions by forming a new bond with an electron-rich atom.

Elimination Reaction:

An elimination reaction is a type of organic reaction where two substituents are removed from a molecule, often resulting in the formation of a carbon-carbon double bond.

Protonation:

Protonation is the process of adding a proton (H+) to a molecule, which can activate the molecule for further reactions.