Non-Halogenic Solvents

Wang, F. J., and Wang, C. H. Sustained release of etanidazole from spray dried microspheres prepared by non-halogenated solvents. J. Contr. Rel. 81(3) 263—280, 2002. 

The advantages of this industry scale synthesis are the use of non-halogenated solvents, formation of inert inorganic salts as waste products, recycling of valuable side products, ambient temperatures, relinquishment of protecting groups and purification by crystallization or filtration. 

To study the effects of water and other solvents on titanocene(III)-mediated processes we used the transannular cychzation of epoxygerma-crolides as a model reaction [47]. Thus, we found that in anhydrous, non-halogenated solvents such as THF the reaction led selectively to decalins with an exocyclic double bond (Scheme 5). In an aqueous medium (THF/H2O), however, the characteristic lime green color of Cp2TiCl turned deep blue and the main product was a reduced decalin (Scheme 5). Under these conditions, water (either H2O or D2O) proved to be more effective than the toxic and expensive hydrogen-atom donor 1,4-cyclohexadiene for the reduction of tertiary radicals [47]. This is an unusual phenomenon in free-radical chemistry [48-50], subsequently exploited by us for the selective reduction of aromatic ketones as we shall see later [51,52]. 

Pulse radiolysis in chlorinated solvents leads to the formation of radical cations of almost all organic compounds including aryls. In most non-halogenated solvents, pulse radiolysis results in the formation of solvated electrons and radical anions of the solute. Therefore, depending on the selected solvent, the same donor-acceptor system could be used for the electron and hole transfer studies. 

The following spent non-halogenated solvents xylene, acetone, ethyl ace- (I) tate, ethyl benzene, ethyl ether, methyl isobutyl ketone, n-butyl alccAol, cyclohexanone, and methanol and the still bottoms from the recovery of these solvents. 

Li, C., Shih, T.-L., Jeong, J.U. era/. (1994) The use of tetramethylguanidinium azide in non-halogenated solvents avoids potential explosion hazards. Tetrahedron Letters, 35, 2645-2646. 

Non-halogenated solvent extraction (antisolvent method) Haloferax mediterranei Acetone Purity 98.4% recovery 91.4% [3]... 

Non-halogenated solvent extraction Comamonas sp. EB172 recombinant Cupriavidus necator NaOH and water Purity 96.6% recovery 96.9% [32]... 

Non-halogenated solvent extraction Recombinant Cupriavidus necator Water and ethanol Purity 81% recovery 95% [33]... 

Non-halogenated solvent extraction Ralstonia eutropha Methyl isobutyl ketone, methyl ethyl ketone, butyl acetate and ethyl acetate Purity 99% recovery 84% for methyl isobutyl ketone [34]... 

Non-halogenated solvent extraction Mixed microbial cultures DMC or combination with NaClO Recovery 82% 137]... 

Two layers of the Earth s atmosphere are known to be adversely impacted by solvents - flic troposphere and the stratosphere. These two layers are closest to Earth, and have distinct chemical and physical properties. The troposphere (our breathable atmosphere) is flic closest layer, extending from the Earth to a height of between 10 to 15 km. The rate of chemical reaction generally determines the spatial scale over which emissions have an impact in the troposphere. Most non-halogenated solvents have lifetimes of a week or less, and elevated concentrations will only be found near the sources. Compounds that do not react rapidly in the troposphere (e.g., CFCs) are relatively uniformly distributed, and may eventually reach the stratosphere. The stratosphere is the next vertical layer of the atmosphere, extending from the tropopause (the top of the troposphere) to about 50 km in altitude. Little vertical mixing occurs in the stratosphere, and mixing between the troposphere and the stratosphere is slow. 

Non-halogenated solvents tend to have a very short atmospheric lifetime of only a few hours to a few weeks, depending on the climatic conditions. Even the presence of one hydrogen atom enormously shortens the lifetime of halogenated material as in, for example, methylene chloride. Therefore, both these kinds of material, in themselves, never build up in the atmosphere to levels that cause environmental or health problems. In contrast, some halogenated compounds which are not degraded in the troposphere, such as the... 

Park et al. used Hansen solubility parameters and showed that non-halogenated solvent blends with the same Hansen parameters as o-DCB can be used to reach comparable device performance [53]. They mixed mesitylene (MS) with acetophenone (AP) in different ratios to match o-DCB Hansen parameters. Different mixtures of AP and MS were used with different ratios resulting in PCEs ranging from 1.5% (pure MS) to 3.38% (20 vol.% acetophenone) for PlHTPCsjBM cells with best external quantum efficiency (EQE) match with o-DCB. This has so far been... 

For non-halogenated solvents, the obvious answer to the above question is that it depends — on the cosolvents, and how they are being used. But there is one key difference between management of residual water level in non-halogenated solvents and that in halogenated solvents. 

It is that it is possible to lower the retained water level in non-halogenated solvents to nearly nil, by use of the desiccator bed noted above , and in Figure 3.31... 

Cupriavidus necator 58.8 Non-halogenated solvent extraction using isoamyl propionate, propyl butyrate, isoamyl valerate or isoamyl isoamylate (isovalerate) (3-methyl-l-butanoate of 3-methyl-l-butanol) 90.0 1 000 000 550 000-735 000 57... 

Cupriavidns necator 60-75 Non-halogenated solvent extraction using isoamyl alcohol 98.0 1 000 000 650 000-780 000 58... 

Currently, most PHA extraction processes are based on halogenated solvent extraction which is costly and may cause environmental problems and toxicity to humans. Thus, it seems that a practical commercial extraction system with a clean, simple and efficient process for PHA recovery at a reasonable cost focusing on a non-halogenated solvent extraction-based recovery needs to be developed. However, halogen-free methods require further adjustment, depending on both significant process parameters and external factors influencing their performance, to make the process suitable for polymer recovery on an industrial scale. 

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