Synthesis environmentally friendly routes

Innovative chemical synthesis procedures have been proposed as offering potential for economical and environmentally friendly routes to a variety of chemicals. These novel chemical reactions also offer potential for increasing the inherent safety of processes by eliminating hazardous materials, eliminating chemical intermediates, or allowing... 

Microwave-assisted synthesis provides an environmentally friendly route for synthesis as it reduces the reaction time from days and hours to minutes and increases product yield [19] consequently, this method is also applied to the synthesis of amphiphilic... 

The unique selling proposition of the tandem-assembly process is its contribution to the field of green chemistry in obtaining closed-shell colloidal structures through an environmentally friendly route, as the entire synthesis is carried out in water, at near neutral pH, and at room temperature. Further, the size of the colloidal template can be controlled by the charge ratios of reactants, which results in structures with sizes ranging from 100nm to 2p,m [32-35,80,81]. 

Thermal reactivity of a-carbonyl- and a-thiocarbonyl-stabilized methylenet-riphenylphosphoranes has been investigated. The kinetic data provided valuable support and insight into the mechanism of pyrolysis and a quantitative basis for structure/molecular reactivity correlations. The pyrolysis reactions of triphenylphos-phonium ylides stabilized by sulfone and C=X (X=0, S) groups represent alternative and environmentally friendly routes to the synthesis of novel alkene and alkyne compounds. 

A highly optimized and concise large-scale synthesis of a purine bronehodilator was developed by the Astra Production Chemical company from Sweden [6], Supplies for the initial biological studies were generated by the medieinal ehemistry route shown in Scheme 5. The overall yield was about 14%, which was improved in the environmentally friendly manufacturing process to about 51% (Seheme 6 and Scheme 7). 

A phosgene-free route to aromatic isocyanates, such as M DI and TDI, was reported by Fernandez et al. [42] (Scheme 5.7) According to the patent, the one-pot synthesis involves the use of an immobilized Schiff base type of ligand catalyst that facilitates the oxidative carbonylation of aromatic amines to the corresponding isocyanates. However, 2,2,2-trifluoroethanol (TFE), 1,2-dichlorobenzene, and carbon monoxide were used in this process, so this would not be a totally environmentally friendly process even if these reagents could be recycled and reused. 

Several other photocatalytic environmentally friendly processes may also be considered. Photocatalytic synthesis of chemicals may serve as a clean alternative route to traditional synthetic methods (see section 6.5). Palmisano et al. reviewed various types of organic reactions that could be achieved by heterogeneous photocatalysis... 

In contrast to the chemical alkaline hydrolysis of 3-cyanopyridine with 4% byproduct of nicotinic acid (96% yield) the biotransformation works with absolute selectivity and no acid or base is required. The biotransformation (a continuous process) is operated at low temperature and atmospheric pressure. In contrast to the old synthesis route of nicotinamide at Lonza, the new one is environmentally friendly and safe. There is only one organic solvent used throughout the whole process in four highly selective continuous and catalytic reactions. The process water, NH3 and H2 are recycled. 

Chalcones are important intermediates in the synthesis of flavanoids and are used industrially in bactericides, antibiotic drugs and UV-stabilisers in plastics. Other base catalysts such as magnesium /-butoxide and barium hydroxides have been used to perform the synthesis.31 However, the Cs+-exchanged zeolites offer a more environmentally friendly alternative route. 

Interesting results have been obtained in the synthesis of biologically active compounds such as insect pheromones. Conventional synthetic routes to these pheromones are often multistep sequences, which make many pheromones too expensive for widespread use [23]. Metathesis offers a shorter, alternative route to pheromone synthesis, generating these compounds in a few steps only. The use of insect sex pheromones is an environmentally friendly, effective, and selective method of pest control. Kiipper and Streck [24] synthesized insect sex pheromones by cross-metathesis reactions between linear olefins. In the presence of the catalyst Re207/Al203, 9-tricosene was synthesized by cross-metathesis of the readily available aUcenes 2-hexadecene and 9-octadecene (Eq. 8). 

The medicinal chemistry synthesis produced 1300 L of waste per kilo of product, the majority of which was methylene chloride. After 4 year of chemical development, this had been reduced to 100 L/kg including a snbstantial reduction in methylene chloride use. However, a major step forward in implementing an environmentally friendly process was the introduction of a commercial route, which not only dramatically improved the yield but also set up the process for solvent recovery. In the mannfactnre of pharmaceuticals, diligent solvent recovery is very often required to fully optimize the environmental performance of a synthesis. The recovery of ethyl acetate and toluene was introdnced in 1998, the year Viagra was launched, and this was followed by the recovery of... 

A new citrate route for the synthesis of catalysts easy to scale-up and environmentally friendly. 

BASF in Germany on the other hand have developed a route which they claim to be an environmentally friendly process which does not use hydrocyanic acid and does not generate waste acid in the form of ammonium sulphate [16]. Their multistage synthesis is based on two base chemicals ethylene and synthesis gas. The only byproduct is water. 

However, to compare alternative routes solely on the basis of waste generation is an oversimplification. An environmentally friendly or favorable process, such as HF-based synthesis of ibuprofen, is not always a safer process. 

An environmentally friendly safe method developed for the preparation of 3-carbamoyl cephalosporin derivative such as cefuroxime uses o-transcarbomylase, an enzyme of microbial origin for the conversion of 3-hydroxy function to the desired 3-carbomyl group. This new synthesis replaces the conventional chemical route, which employs hazardous isocyanates such as dichlorophosphenyl isocynate or chlorosulfinyl isocyanate to achieve the same conversion (Scheme 57). ... 

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