Green Solvents and it's applications, Slides of Chemistry

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Ch.5 Organic

solvents:

Environmentally

benign solutions

Strategies of solvent replacement

 Avoid or minimise solvents in first place

 Use less toxic solvents

 Use renewable solvents (not derived from

petrochemicals)

 Avoid VOC’s – solvents with low vapour pressure /

high boiling points may be preferable as long as this

does not lead to other complications.

‘Solventless ’ chemistry

 Provides one of the simplest solutions to the problem of solvents  Not many reactions amenable to solventless approach, particularly on large scale  Exothermic reactions can be dangerous on large scale – need close collaboration with chemical engineers to overcome such problems  Efficient mixing can be a problem, particularly when have solid reagents or products  Solvents still often required for extraction, separation and purification of products

Water as a reaction medium  One of the most obvious alternatives to VOCs.  Cheap, readily available, and plentiful.  Useful for certain types of reaction but limited because of:  Low solubility of organic substrates  Compatibility with reagents  Clean up of aqueous waste difficult  Useful in biphasic processes in conjunction with other solvents

SOLID GAS LIQUID SUPERCRITICAL FLUID Triple point Critical point

Pressure (bar)

Temperature (ºC)

74

• 56.3ºC 31.1ºC

Phase diagram for pure CO

© Monterey Bay Aquarium Research Institute

• 78 ºC 1

Current industrial applications of CO 2 technology  Union Carbide, Unicarb Technology  Replaces 40-90% of VOCs with CO 2.  Coatings on aerospace parts  Chocolate biscuits Chem. Eng. News , June 14 1999, 77 (24), 13.  CO 2 Refrigeration  Large scale units now in operation.  ASDA distribution centres in Falkirk and Skelmersdale (2003)  Amongst the biggest temperature controlled buildings in the UK (412,000m^3 )

Ionic liquids cont….

 Good solvents for a wide range of organic, inorganic and polymeric compounds  Anion and cation can be fine tuned to give a wide range of solvent properties (e.g. hydrophilic, hydrophobic) which can be exploited  Wide range of reactions already demonstrated in this medium  Can be used in conjunction with other alternative solvents (particularly CO 2 )  Claimed to be recyclable (essential for widespread use) although there may be regulatory problems with this.  Effectively, properties similar to many other high boiling, polar solvents.

Liquid-liquid extraction

A heavy fluorous technique

• Whereas compounds bearing light fluorous tags are miscible in organic solvents, heavy fluorous compounds are soluble in perfluorinated solvents and form a distinct liquid phase.
• This can be exploited if a liquid- liquid separation is preferable, although reactivity is limited to the phase interface.

organic

aqueous

fluorous

Traditional Synthesis of Ibuprofen

• Atom Economy is low
• Waste is too much
• Large number of steps
• involved in synthesis