Solvents Flashcards
What are the benefits of organic solvents?
Good heat and mass transfer, low viscosities lead to good kinetics, wide availability gives wide choice of solvent properties
What are the problems with organic solvents?
Often toxic and volatile, can form street-level ozone and smog if released
It may not always be more green to swap out organic solvents - why?
Replacing them may increase energy input due to boiling points and other manufacturing - focus is left on eliminating toxic organic solvents first
What is required for a solvent to be a good solvent?
Separation from aqueous phases is good for recovery, low hazards (e.g. CPME and peroxide formation), high stability under basic/acidic conditions, wide liquid range (high BP, low MP), low latent heat of vapourisation, low solubility of salts in solvent, good polarity
What is a biphasic system and what types of biphasic systems can we employ?
Biphasic system is with two phases that do not intermix - phase-transfer catalyst required. Examples of biphasic systems are organic-organic (polar-apolar), aqueous-organic, and fluorous-organic
What are the benefits of biphasic systems?
Aids separation of products and reagents, allows for easy separation of homogeneous catalysts, may be able to tweak phase separation using temperature
What are some of the limitations of biphasic systems?
Organic-organic of limited applicability, sometimes specialised reagents needed which can be expensive, need to make reagents/products preferentially soluble in one phase
What is a super critical fluid (sc-fluid)?
A substance above its critical temperature and pressure (above critical point) - essentially in phase that is both liquid and gas
What are the benefits of sc-fluids?
Sc-fluids often have densities of liquids and viscosities of gases, and can be tuned by varying temperature and pressure. They can be easily separated from the product (form gas).
What types of sc-fluids make good solvents?
Ones with achievable/accessible critical points, medium polarity, non-toxic and flammable, readily obtained and recycled, unreactive
What are the drawbacks of sc-fluids?
High pressures and temperatures needed, materials required to contain reactions, may have solubility problems (e.g. sc-CO2 poorly polar)
What is an ionic liquid?
Fused salts which are liquids - salts in which the ions are poorly coordinated resulting in a low-melting salt (e.g. achieved by limited coordination with organic shrubbery)
What are the benefits of ionic liquids?
Highly polar, good solvents for inorganics and organics, can be immiscible with organic solvents, non-volatile, tunable, strongly acidic and basic
What are the drawbacks of ionic liquids?
Non-bio-degradable, concerns over toxicity, synthesis uses haloalkanes, product isolation still needs extraction and distillation, polarity may make separation harder
What are the benefits of using water as a solvent?
Non-toxic, cheap, biorenewable, non-flammable, high specific heat capacity (acts as safety control), may have more solute-solvent interactions
What are the problems with using water as a solvent?
Removal via distillation (energy intensive), difficult to treat waste streams, many reagents water-sensitive, and organics struggle to dissolve, solute-solvent interactions may be higher
What is HTW?
High temperature water - water at >200 under its own pressure, starts acting like an organic solvent
What are the benefits of using HTW?
Water starts acting like an organic solvent and allows organic solubility, more ionic so increased acidity and basicity, tuneability of properties using temperature and pressure
What are the challenges with using HTW?
Engineering controls difficult as under high pressure and HTW able to cut through stainless steel
What are the benefits in going solvent-free?
Removal of some work up steps, reduction in input materials
What are the challenges in going solvent-free?
Some solvents will still be required during work up and extraction, poor heat transfer to reagents in the solid state
What is mechanochemistry?
Reactions of solids induced by input of mechanical energy
What are the benefits of mechanochemistry?
Clean reactions to avoid work ups, avoidance of solvent effects,
What are the challenges of mechanochemistry?
Mechanism poorly understood
