Process chemistry alternative synthesis

Basic process chemistry using less hazardous materials and chemical reactions offers the greatest potential for improving inherent safety in the chemical industry. Alternate chemistry may use less hazardous raw material or intermediates, reduced inventories of hazardous materials, or less severe processing conditions. Identification of catalysts to enhance reaction selectivity or to allow desired reactions to be carried out at a lower temperature or pressure is often a key to development of inherently safer chemical synthesis routes. Some specific examples of innovations in process chemistry which result in inherently safer processes include ... 

Photochemistry is used commercially in the synthesis of Vitamin A and Vitamin D3, Figure 3.14. Vitamin A is formed via a photochemical isomerisation process and the synthesis of Vitamin D3 involves a photochemical electrocyclic ring-opening step. The industrial relevance of this process is due to the lack of a viable thermal alternative and therefore, if unusual and useful chemistry is only possible via photochemistry, an industrial process may result, due to the high intrinsic value of the chemical product. 

Ionic liquids have attracted great attention as an alternative reaction media in organic synthesis. These highly polar solvents often lead to enhanced reaction kinetics and product selectivity [13], Despite promising and spectacular results, practical drawbacks, such as product isolation and recovery of the catalyst, are still important barriers to their wide spread use in medicinal and process chemistry. 

From the viewpoint of azide chemistry, the synthesis of Oseltamivir is very interesting in many aspects because azides are used at more than one point and the azide synthesis processes used have prevailed over azide-free alternatives. ... 

Hudlicky, Thomas, Green Chemistry Alternatives for the Processing of Aromatic Compounds. Tandem Strategies in Biocatalysis and Synthesis, Chapter 10 in Green Chemistry Frontiers in Benign Chemical Synthesis and Processes, Oxford University Press, New York, 1998, pp. 166-177. 

In the BASF synthesis, a Wittig reaction between two moles of phosphonium salt (vitamin A intermediate (24)) and C q dialdehyde (48) is the important synthetic step (9,28,29). Thermal isomerization affords all /ra/ j -P-carotene (Fig. 11). In an alternative preparation by Roche, vitamin A process streams can be used and in this scheme, retinol is carefully oxidized to retinal, and a second portion is converted to the C2Q phosphonium salt (49). These two halves are united using standard Wittig chemistry (8) (Fig. 12). 

In the field of polymer chemistry the regio- and stereoselectivity of the Diels-Alder reaction is used for the concerted synthesis of structurally homogeneous double-stranded ladder polymers [39], which are useful materials with nonlinear optical properties and high electrical conductivity. It has turned out that the repeated Diels-Alder method is superior to an alternative two-step process, in which first an open chain precursor is formed followed by polymer ring closure as structural defects can occur [40]. 

---