Separation of High Boiling Solvents

Contact dryers are typically made out of carbon steel, stainless steel of Ni-alloy materials and are heated using liquid heat transfer fluids via tvelded on double jackets or half pipe coils. 

Typically the maximum operation temperatures of tvelded constructions and heat transfer fluids are in the range of 320-360 °C. 

The evaporation of organic solvents with high boiling temperatures is therefore with standard equipment only possible under vacuum using normal heating temperatures. 

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These alkylation procedures can benefit greatly from the use of microwave activation, which can reduce reaction times by a factor of 60. Moreover, the often tedious separation of high boiling solvents (DMF, DMSO, HMPA) can be omitted, if reactions are conducted under solvent-free conditions in the presence of ferf-BuOK as a base and a phase transfer catalyst such as Aliquat 336. Chemical yields are comparable to those obtained using classical procedures and only traces of dialkylated byproducts have been detected. Moreover, microwave treatment of the diester product with LLF or LiCl (Krapcho procedure) under solvent-free conditions provides the corresponding mono-ester by selective decarbalkoxylation . 

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