Solvolysis reactions: Solvolysis is a chemical process whereby a solvent molecule acts as a reactant, leading to the cleavage of a bond inside a solute molecule, often resulting in the substitution or breakdown of the solute. In these reactions, solvent molecules often ionize and engage with solute ions or molecules, therefore enhancing the process.
Hydrolysis (Solvolysis in Water)
| Reaction | Products |
|---|---|
| SiCl₄ + 4H₂O | Si(OH)₄ + 4HCl |
| PCl₅ + 4H₂O | H₃PO₄ + 5HCl |
| FeCl₃ + 3H₂O | Fe(OH)₃ + 3HCl |
| AlCl₃ + 3H₂O | Al(OH)₃ + 3HCl |
| SOCl₂ + 4H₂O | H₂SO₃ + 2HCl + H₂O |
Ammonolysis (Solvolysis in Liquid NH₃)
| Reaction | Products |
|---|---|
| BCl₃ + 6NH₃ | B(NH₂)₃ + 3NH₄Cl |
| AlCl₃ + 6NH₃ | Al(NH₂)₃ + 3NH₄Cl |
| SOCl₂ + 4NH₃ | SO(NH₂)₂ + 2NH₄Cl |
| SiCl₄ + 8NH₃ | Si(NH₂)₄ + 4NH₄Cl |
| TiCl₄ + 8NH₃ | Ti(NH₂)₄ + 4NH₄Cl |
Fluorolysis (Solvolysis in Liquid HF)
| Reaction | Products |
|---|---|
| SOCl₂ + 2HF | SOF₂ + 2HCl |
| PCl₅ + 5HF | PF₅ + 5HCl |
| BCl₃ + 3HF | BF₃ + 3HCl |
| SiCl₄ + 4HF | SiF₄ + 4HCl |
| TiCl₄ + 4HF | TiF₄ + 4HCl |
Solvation and Solvate Formation
1. In many cases, when a solute is dissolved in a solvent and the excess of solvent is removed, a solid product is recovered which contains a number of molecules of the solvent attached to the cation, anion, or neutral molecule of the solute species. These interactions occur through coordinate covalent bonds, hydrogen bonding, or ion-dipole interactions.
2. Solvation reactions in which water is the solvent are called hydration reactions, and if ammonia is the solvent, the reaction is called ammonation. The resulting solvates are known as hydrates and ammoniates, respectively. Other solvents also lead to named solvates such as alcoholates (from alcohol), hydrazinates (from hydrazine), and ethereates (from ether).
3. In many cases, the mechanism of the solvation process and the structure of the resulting solvate are not well known.
Solvate and Adduct Formation Reactions
| Reaction | Type |
|---|---|
| CuSO₄ + 5H₂O → CuSO₄·5H₂O | Hydrate (1:5 Solvate) |
| SO₃ + 2NH₃ → SO₃·2NH₃ | Ammoniate (1:2 Adduct) |
| SiF₄ + 2NH₃ → SiF₄·2NH₃ | Ammoniate (1:2 Adduct) |
| BF₃ + NH₃ → BF₃·NH₃ | Ammoniate (1:1 Adduct) |
Addition Compounds (Solvates) of Liquid SO2
Like water and liquid ammonia, liquid SO2 also forms addition compounds (solvates) with solutes.
Examples include:
\( \mathrm{MI_2 \cdot 4 SO_2 \quad (M = Ca, Ba, Sr), \quad AlCl_3 \cdot 2 SO_2} \)
Complex formation reactions: A complex formation reaction is a chemical process in which a central atom or ion, often a metal, coordinates with surrounding molecules or ions, known as ligands, via coordinate covalent bonds, resulting in the development of a coordination complex.
Complex Formation Reactions in Different Solvents
| Solvent | Reaction |
|---|---|
| H₂O | [Cu(H₂O)₄]²⁺ + 4NH₃ → [Cu(NH₃)₄]²⁺ + 4H₂O [Ag(H₂O)₂]⁺ + 2NH₃ → [Ag(NH₃)₂]⁺ + 2H₂O AlCl₃ + 4NaOH (excess) → 3NaCl + Na[Al(OH)₄] Zn(NO₃)₂ + 4NaOH → Na₂[Zn(OH)₄] (soluble complex) + 2NaNO₃ |
| Liquid SO₂ | SbCl₃ + 3KCl → K₃[SbCl₆] SbCl₅ + KCl → K[SbCl₆] SbCl₅ + CH₃COCl → [CH₃CO][SbCl₆] 2SbCl₃ + 3SOCl₂ → [SO]₃[SbCl₆]₂ SbCl₅ + NOCl → [NO][SbCl₆] |
| Liquid NH₃ | Zn(NO₃)₂ + 4KNH₂ → K₂[Zn(NH₂)₄] (soluble) + 2KNO₃ AlCl₃ + 4KNH₂ → K[Al(NH₂)₄] (soluble amido complex) + 3KCl Al(NH₂)₃ (from reaction of AlCl₃ with NH₃) AgNH₂ + KNH₂ (excess) → K[Ag(NH₂)₂] Zn(NH₂)₂ + 2KNH₂ (excess) → K₂[Zn(NH₂)₄] (soluble amido complex) |
Redox reaction: A redox reaction (short for reduction–oxidation reaction) is a type of chemical reaction in which both oxidation and reduction occur simultaneously.
- Oxidation: Loss of electrons or increase in oxidation number.
- Reduction: Gain of electrons or decrease in oxidation number.
- The substance that is reduced acts as the oxidizing agent.
- The substance that is oxidized acts as the reducing agent.
Redox Reactions in Water
A redox reaction in water involves the transfer of electrons between chemical species in an aqueous medium.
Example 1: Displacement Reaction
- Oxidation: Zn → Zn2+ + 2e⁻
- Reduction: Cu2+ + 2e⁻ → Cu
Example 2: Acidic KMnO4 Oxidation
- Oxidation: Fe2+ → Fe3+ + e⁻
- Reduction: MnO4– + 8H+ + 5e⁻ → Mn2+ + 4H2O
- Zn + CuSO4 → ZnSO4 + Cu
- Fe + CuSO4 → FeSO4 + Cu
- Mg + 2HCl → MgCl2 + H2
- Zn + 2HCl → ZnCl2 + H2
- 2KMnO4 + 10FeSO4 + 8H2SO4 → K2SO4 + 2MnSO4 + 5Fe2(SO4)3 + 8H2O
- H2O2 + 2KI + 2H2SO4 → I2 + K2SO4 + 2H2O
Redox Reactions in Liquid Ammonia (NH3)
a. Reactions where liquid NH3 serves as a medium only
-
KMnO4 as a weak oxidising agent:
6KMnO4 (Mn=+7) + 6KNH2 (N=-3) → 6K2MnO4 (Mn=+6) + 6NH3 + N2 (N=0) -
Iodine as a weak oxidising agent:
I2 (I=0) + K4[Sn(NH2)6] (Sn=+2) → K2[Sn(NH2)6] (Sn=+4) + 2KI (I=-1)
b. Reactions where liquid NH3 acts as a reducing agent
- 4NH3 (N=-3) + 5O2 (O=0) → 4NO (N=+2) + 6H2O (O=-2)
- 2NH3 (N=-3) + 3CuO (Cu=+2) → N2 (N=0) + 3Cu (Cu=0) + 3H2O
c. Reactions where alkali metals in liquid NH3 act as reducing agents
- 2Na (Na=0) + 2NH4Br (H=+1) → 2NaBr (Na=+1) + H2 (H=0)
- 2K (K=0) + NH3 + N2O → KNH2 (K=+1) + KOH + N2 (N=0)
- S (S=0) + 2Na (Na=0) → Na2S (Na=+1, S=-2)
-
2K (K=0) + O2 (O=0) → K2O2 (peroxide, white)
K (K=0) + O2 (O=0) → KO2 (superoxide, yellow) - CuI (Cu=+1) + Na (Na=0) → Cu (Cu=0) + NaI (Na=+1)
- 30K (K=0) + 20NH3 + 6KMnO4 (Mn=+7) → 6MnO (Mn=+2) + 18KNH2 (K=+1) + 18KOH + 3H2 + N2
- 4ZnI2 (Zn=+2) + 9Na (Na=0) → NaZn4 (Zn=-1/4) + 8NaI (Na=+1)
- K2[Ni(CN)4] (Ni=+2) + excess K (liq. NH3, -33°C) → K4[Ni(CN)4] (Ni=0)
- [Pt(NH3)4]Br2 (Pt=+2) + excess K (liq. NH3, -33°C) → [Pt(NH3)4]0 (Pt=0)
Redox Behavior in Liquid SO2
Liquid sulfur dioxide (liq. SO2) itself does not act as a strong oxidizing or reducing agent, but it can serve as an excellent medium for redox reactions.
Reduction of iodine but not bromine:
Oxidation of iodide ions by antimony pentachloride (SbCl5):
This demonstrates that while liquid SO2 is chemically inert regarding redox, it provides a stable medium for complex redox equilibria.