Approaches for scale-up of microwave-promoted reactions
In this report, we look at a range of classes of reaction involving microwave heating and show how different processing techniques can be used to address scale-up needs. We look at both batch and continuous-flow processing. We have shown that when using batch methodologies working using an open reaction vessel offers operational advantages while still giving good yields of desired products. In cases where open-vessel conditions are not amenable or where particularly volatile or toxic reagents are used, parallel sealed vessels can offer an alternative approach. For continuous-flow processing, homogeneity of the reaction mixture is key. When the mixture is homogeneous, it is possible to move from small-scale sealed-vessel conditions to the continuous-How apparatus without any modification of reaction conditions or loss in product yield. When either the starting materials or the product mixture contains particulate matter, continuous processing can prove a challenge, but reoptimization of reaction conditions as well as reduction of the concentration may allow these difficulties to be overcome.