Functionalized polymers can serve as scaffolds for process intermediates, as reagents, as co-reactants, as catalysts, or as a solvent phase; however, using polymers in process chemistry violates “atom economy” in a massive way. Using polymers in any capacity adds to the mass used without incorporating that mass into the product; therefore, using functionalized polymers must provide a large compensating benefit.
The compensating benefit could be:
In safety and regulatory affairs by avoiding
- smelly reagents like sulfides and thiols
- explosive reagents such as aromatic peracids, sulfonyl azides
- toxic waste by immobilizing Cr, Sn, Se, Ni
- trace heavy metals that are avoided Ag
- reagents that are toxic: crown ethers, HMPA cosolvent, cryptates
- reagents that cause sensitization: carbodiimides
Avoiding normal small-molecule reagents that cause difficulties in work-up
- triphenylphosphine oxide
- ureas from carbodiimides
- emulsifiers
- phase transfer catalysts
- mineral or organic acids by replacement with cation-exchange resin
- mineral bases that introduce water-soluble alkali and alkali earth salts with anion-exchange resins
Avoiding reagent degradation (where the regular reagent is too unstable)
- Lewis acid impregnated microporous resin AlCl3 impregnated into carbon
- chromic acid impregnated charcoal
- potassium impregnated graphite
- polymeric trityllithium
Polymeric Protection as a Phase Tag
- scavenger resins to remove residual excess reagent
- starting reagent so that an excess can be used
- capture and release purifications
- cosolvent extraction phase (macroreticular polystyrene)
Removal of Trace Components by selective reactivity
- removal of oxygen (example)
- removal of heavy metals (like using EDTA)
- removing singlet oxygen
- removal of water: carboxymethylcellulose sodium, butyrolactone
- removal of organic solvents: molecular sieves
- removal of carbonyls: semicarbazide on silica; site isolation
- mono protection of symmetrical substrates
- telescoping process steps using two antagonistic reagents immobilized on separate resins such as periodic acid/ borohydride for first cleaving then reducing 1,2-diols
Recovery of Expensive Catalysts
Solvents
- polyethylene glycol as a solvent for sodium hydroxide or potassium hydroxide
- polyethylene glycol as a dispersing agent during solvent switches based on evaporation to dryness
- polyethylene glycol as distillation chaser
Because of the lack of atom economy to be cost-effective reactions using polymers as processing chemicals or reagents should be used in the latter portion of reaction sequences when small improvements in yield can produce overwhelming cost benefits.
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