Slide 1: Chemistry of p-Block Elements - Group 13 - Trihalides - Lewis acids
- Group 13 elements include boron (B), aluminum (Al), gallium (Ga), indium (In), and thallium (Tl).
- These elements have three valence electrons in their outermost shell.
- The trihalides of these elements, namely boron trihalides (BX₃), aluminum trihalides (AlX₃), gallium trihalides (GaX₃), indium trihalides (InX₃), and thallium trihalides (TlX₃), where X represents a halogen (F, Cl, Br, or I), are important compounds.
- In these trihalides, the central atom is surrounded by three halogen atoms, forming a trigonal planar structure.
- These compounds act as Lewis acids due to the presence of an incomplete octet on the central atom.
Slide 2: Lewis Acids and Bases
- Lewis acids are electron pair acceptors, while Lewis bases are electron pair donors.
- Lewis acid-base reactions involve the formation of coordinate bonds, where the Lewis acid accepts a lone pair of electrons from the Lewis base.
- In the context of group 13 trihalides, the central atom acts as the Lewis acid by accepting a lone pair of electrons from a Lewis base.
- The Lewis acid-base interaction leads to the formation of a coordinate covalent bond.
Slide 3: Boron Trihalides (BX₃)
- Boron trihalides include boron trifluoride (BF₃), boron trichloride (BCl₃), boron tribromide (BBr₃), and boron triiodide (BI₃).
- These compounds are Lewis acids due to the electron deficiency on the boron atom.
- Examples:
- BF₃ + :NH₃ → BF₃:NH₃ (Ammonia donates a lone pair of electrons to boron trifluoride)
- BCl₃ + :NH₃ → BCl₃:NH₃ (Ammonia donates a lone pair of electrons to boron trichloride)
- BBr₃ + :NH₃ → BBr₃:NH₃ (Ammonia donates a lone pair of electrons to boron tribromide)
- BI₃ + :NH₃ → BI₃:NH₃ (Ammonia donates a lone pair of electrons to boron triiodide)
Slide 4: Aluminum Trihalides (AlX₃)
- Aluminum trihalides include aluminum trifluoride (AlF₃), aluminum trichloride (AlCl₃), aluminum tribromide (AlBr₃), and aluminum triiodide (AlI₃).
- These compounds are Lewis acids due to the electron deficiency on the aluminum atom.
- Examples:
- AlF₃ + :NH₃ → AlF₃:NH₃ (Ammonia donates a lone pair of electrons to aluminum trifluoride)
- AlCl₃ + :NH₃ → AlCl₃:NH₃ (Ammonia donates a lone pair of electrons to aluminum trichloride)
- AlBr₃ + :NH₃ → AlBr₃:NH₃ (Ammonia donates a lone pair of electrons to aluminum tribromide)
- AlI₃ + :NH₃ → AlI₃:NH₃ (Ammonia donates a lone pair of electrons to aluminum triiodide)
Slide 5: Gallium Trihalides (GaX₃)
- Gallium trihalides include gallium trifluoride (GaF₃), gallium trichloride (GaCl₃), gallium tribromide (GaBr₃), and gallium triiodide (GaI₃).
- These compounds are Lewis acids due to the electron deficiency on the gallium atom.
- Examples:
- GaF₃ + :NH₃ → GaF₃:NH₃ (Ammonia donates a lone pair of electrons to gallium trifluoride)
- GaCl₃ + :NH₃ → GaCl₃:NH₃ (Ammonia donates a lone pair of electrons to gallium trichloride)
- GaBr₃ + :NH₃ → GaBr₃:NH₃ (Ammonia donates a lone pair of electrons to gallium tribromide)
- GaI₃ + :NH₃ → GaI₃:NH₃ (Ammonia donates a lone pair of electrons to gallium triiodide)
Slide 6: Indium Trihalides (InX₃)
- Indium trihalides include indium trifluoride (InF₃), indium trichloride (InCl₃), indium tribromide (InBr₃), and indium triiodide (InI₃).
- These compounds are Lewis acids due to the electron deficiency on the indium atom.
- Examples:
- InF₃ + :NH₃ → InF₃:NH₃ (Ammonia donates a lone pair of electrons to indium trifluoride)
- InCl₃ + :NH₃ → InCl₃:NH₃ (Ammonia donates a lone pair of electrons to indium trichloride)
- InBr₃ + :NH₃ → InBr₃:NH₃ (Ammonia donates a lone pair of electrons to indium tribromide)
- InI₃ + :NH₃ → InI₃:NH₃ (Ammonia donates a lone pair of electrons to indium triiodide)
- Aluminum Trihalides (AlX₃)
- Aluminum trihalides include aluminum trifluoride (AlF₃), aluminum trichloride (AlCl₃), aluminum tribromide (AlBr₃), and aluminum triiodide (AlI₃).
- These compounds are Lewis acids due to the electron deficiency on the aluminum atom.
- They are commonly used as catalysts in various chemical reactions.
- AlCl₃ is widely used in Friedel-Crafts reactions to introduce alkyl or acyl groups onto aromatic compounds.
- Example reaction: AlCl₃ + CH₃Cl → CH₃AlCl₂ + HCl
- The Lewis acid-base interaction between aluminum trichloride and chloromethane leads to the formation of a compound with a new carbon-aluminum bond.
- Gallium Trihalides (GaX₃)
- Gallium trihalides include gallium trifluoride (GaF₃), gallium trichloride (GaCl₃), gallium tribromide (GaBr₃), and gallium triiodide (GaI₃).
- These compounds are Lewis acids due to the electron deficiency on the gallium atom.
- GaCl₃ is used as a catalyst in the production of polyethylene terephthalate (PET) plastics.
- Example reaction: GaCl₃ + H₂O + CH₃OH → Ga(OCH₃)₃ + 3HCl
- The Lewis acid-base interaction between gallium trichloride, water, and methanol leads to the formation of gallium methylate and hydrochloric acid.
- Indium Trihalides (InX₃)
- Indium trihalides include indium trifluoride (InF₃), indium trichloride (InCl₃), indium tribromide (InBr₃), and indium triiodide (InI₃).
- These compounds are Lewis acids due to the electron deficiency on the indium atom.
- InI₃ is used as a sensitizer in the production of photographic film.
- Example reaction: InI₃ + Ag → In + AgI₃
- The Lewis acid-base interaction between indium triiodide and silver leads to the reduction of silver iodide and the formation of indium metal.
- Thallium Trihalides (TlX₃)
- Thallium trihalides include thallium trifluoride (TlF₃), thallium trichloride (TlCl₃), thallium tribromide (TlBr₃), and thallium triiodide (TlI₃).
- These compounds are Lewis acids due to the electron deficiency on the thallium atom.
- TlCl₃ and TlBr₃ are used as precursors in the synthesis of organometallic compounds.
- Example reaction: 3TlCl₃ + 2Na(C₅H₅) → 3Tl(C₅H₅) + 6NaCl
- The Lewis acid-base interaction between thallium trichloride, sodium cyclopentadienide, and sodium chloride leads to the formation of thallium cyclopentadienide and sodium chloride.
- Application of Lewis Acids in Organic Synthesis
- Lewis acids find extensive application in organic synthesis as catalysts.
- They can facilitate the activation of certain functional groups and promote desired reactions.
- The Friedel-Crafts reaction is one such example where aluminum or boron trihalides act as catalysts to introduce alkyl or acyl groups onto aromatic compounds.
- Lewis acids are also used in the Diels-Alder reaction, where they can coordinate with dienophiles and dienes to facilitate the formation of cyclic products.
- Examples: AlCl₃, BCl₃, FeCl₃, and ZnCl₂ are commonly used Lewis acids in organic synthesis.
- Limitations of Lewis Acids
- Lewis acids are not suitable for all types of reactions and can sometimes exhibit limitations.
- They may be too reactive and cause undesired side reactions.
- The electron-deficient nature of Lewis acids can result in strong Lewis acid-base interactions, leading to the formation of stable complexes that might not readily dissociate.
- Some Lewis acids may be toxic or hazardous, requiring careful handling.
- It is essential to consider the specific reaction conditions and the compatibility of Lewis acids with the other reactants to achieve the desired outcome.
- Introduction to Lewis Bases
- Lewis bases are electron pair donors in Lewis acid-base reactions.
- They have a lone pair of electrons available for donation.
- Common examples of Lewis bases include ammonia (NH₃), water (H₂O), alcohols (ROH), and amines (RNH₂).
- The Lewis base donates its lone pair of electrons to the Lewis acid, resulting in the formation of a coordinate covalent bond.
- Lewis Acid-Base Reactions
- Lewis acid-base reactions involve the transfer of a lone pair of electrons from the Lewis base to the Lewis acid.
- This transfer leads to the formation of a coordinate covalent bond between the two species.
- The Lewis acid-base interaction is often reversible, allowing the products to dissociate back into their respective reactants.
- The strength of the Lewis acid-base interaction depends on factors such as electron density, size, and charge of the species involved.
- Lewis Acid-Base Addition Mechanism
- In Lewis acid-base addition reactions, the Lewis acid and the Lewis base directly react with each other.
- The Lewis acid accepts the lone pair of electrons from the Lewis base, resulting in bond formation.
- The addition mechanism is often observed in reactions involving boron, aluminum, and other p-block elements.
- Example reaction: BCl₃ + :NH₃ → BCl₃:NH₃
- The Lewis base (:NH₃) donates a lone pair of electrons to boron trichloride (BCl₃), forming a coordinate covalent bond.
- Summary of Lewis Acids and Bases
- Lewis acids are electron pair acceptors, while Lewis bases are electron pair donors.
- Group 13 trihalides, such as boron, aluminum, gallium, indium, and thallium trihalides, are Lewis acids due to their electron deficiency.
- Lewis acids find extensive application as catalysts in various chemical reactions.
- Lewis acid-base reactions involve the formation of coordinate covalent bonds.
- The strength of the Lewis acid-base interaction depends on various factors like electron density, size, and charge.
Slide 21: Lewis Acid-Base Mechanism
- Lewis acid-base reactions involve the formation of coordinate covalent bonds between the Lewis acid and the Lewis base.
- The Lewis acid acts as an electron pair acceptor, while the Lewis base acts as an electron pair donor.
- The reaction can be represented as: Lewis Acid + Lewis Base → Lewis Acid-Base Adduct
- The adduct is a stable compound where the Lewis acid and the Lewis base are bonded through the shared electron pair.
Slide 22: Lewis Acid-Base Complexes
- Lewis acid-base complexes are formed when the Lewis base donates a lone pair of electrons to the Lewis acid.
- These complexes have enhanced stability due to the formation of coordinate covalent bonds.
- The Lewis acid and the Lewis base in the complex are held together by electrostatic forces.
- The stability of the complexes can be influenced by factors such as the strength of the Lewis acid-base interaction and the polarity of the molecules involved.
Slide 23: Lewis Acidity Trends in Group 13 Trihalides
- As we move down the group 13 in the periodic table, the Lewis acidity of the trihalides decreases.
- Boron trihalides are the strongest Lewis acids in the group, while thallium trihalides are the weakest.
- This trend is attributed to the increase in atomic size and the decrease in electronegativity as we move down the group.
- The larger size and lower electronegativity of the lower group elements result in decreased electron deficiency and decreased ability to accept electron pairs.
Slide 24: Lewis Acidity Trends in Period 3 Group 13 Elements
- The Lewis acidity of group 13 elements in period 3 (aluminum, gallium, and indium) increases as we move from left to right across the period.
- This trend is associated with the decreasing atomic size and increasing charge-to-size ratio of the elements.
- The smaller size and higher charge-to-size ratio make the central atom more electron-deficient, enhancing its ability to accept electron pairs and act as a Lewis acid.
Slide 25: Application of Group 13 Trihalides as Catalysts
- Group 13 trihalides, particularly aluminum and boron trihalides, find extensive application as Lewis acid catalysts in organic synthesis.
- They can activate certain functional groups, promote desired reactions, and enhance reaction rates.
- Examples of their applications include Friedel-Crafts reactions, Diels-Alder reactions, and polymerization reactions.
- Aluminum trichloride (AlCl₃) is commonly used in the synthesis of dyes and perfumes, while boron trifluoride (BF₃) is used in organic synthesis and as a catalyst for polymerization reactions.
Slide 26: Limitations of Group 13 Trihalides as Catalysts
- While group 13 trihalides are valuable catalysts, they also have certain limitations.
- They can exhibit high reactivity and may cause undesired side reactions.
- Some trihalides, such as boron trifluoride (BF₃), are highly volatile and require careful handling.
- Overuse of Lewis acid catalysts can lead to overfunctionalization or crosslinking in reaction products.
- It is crucial to optimize reaction conditions and catalyst concentrations to achieve the desired outcome.
Slide 27: Environmental Impact of Group 13 Trihalides
- Group 13 trihalides, especially those containing fluorine and chlorine, can have environmental impacts.
- Fluorinated trihalides, such as boron trifluoride (BF₃) and aluminum trifluoride (AlF₃), are potent greenhouse gases with high global warming potentials.
- Chlorinated trihalides, such as aluminum trichloride (AlCl₃), can contribute to water pollution if not properly managed.
- It is important to handle and dispose of these compounds responsibly to minimize their impact on the environment.
Slide 28: Boron Trifluoride - Successful Applications
- Boron trifluoride (BF₃), one of the group 13 trihalides, has found successful applications in various fields.
- It is widely used as a Lewis acid catalyst in organic synthesis, particularly in reactions involving alcohols and carboxylic acids.
- BF₃ is an essential component in the production of high-quality aluminum and magnesium metal.
- It is also used in the petroleum industry for the refining and purification of hydrocarbon fuels.
- Additionally, BF₃ has applications in the production of plastics, detergents, and pharmaceutical intermediates.
Slide 29: Aluminum Trichloride - Successful Applications
- Aluminum trichloride (AlCl₃), an important member of group 13 trihalides, has numerous successful applications.
- It is widely used as a catalyst in the production of polyethylene terephthalate (PET) plastics.
- AlCl₃ is an essential ingredient in the Friedel-Crafts reaction, enabling the synthesis of various aromatic compounds.
- It also finds applications in the synthesis of dyes, fragrances, and pharmaceuticals.
- Furthermore, aluminum trichloride is used as an electrolyte in the production of aluminum metal.
Slide 30: Summary
- Group 13 trihalides, including boron, aluminum, gallium, indium, and thallium trihalides, act as Lewis acids due to their electron deficiency.
- Lewis acid-base reactions involve the formation of coordinate covalent bonds between the Lewis acid and the Lewis base.
- The strength of the Lewis acid-base interaction depends on factors such as electron density, size, and charge.
- Group 13 trihalides find extensive application as catalysts in various organic synthesis reactions.
- It is essential to consider the limitations and environmental impact of these compounds in their applications.
- Each member of the group has specific successful applications, such as boron trifluoride in organic synthesis and aluminum trichloride in PET plastic production.
Slide 1: Chemistry of p-Block Elements - Group 13 - Trihalides - Lewis acids Group 13 elements include boron (B), aluminum (Al), gallium (Ga), indium (In), and thallium (Tl). These elements have three valence electrons in their outermost shell. The trihalides of these elements, namely boron trihalides (BX₃), aluminum trihalides (AlX₃), gallium trihalides (GaX₃), indium trihalides (InX₃), and thallium trihalides (TlX₃), where X represents a halogen (F, Cl, Br, or I), are important compounds. In these trihalides, the central atom is surrounded by three halogen atoms, forming a trigonal planar structure. These compounds act as Lewis acids due to the presence of an incomplete octet on the central atom.