The use of the microwave (MW) technique in organic syntheses spred gradually in research laboratories, and after more than two decades it knocks at the door of industry. At the beginning, only domestic MW ovens were available, but later, different variations of professional MW equipment were developed and utilized in a variety of syntheses, such as substitutions, additions, eliminations, condensations, acylations, esterifications, alkylations, C–C coupling reactions, cycloadditions, rearrangements and the formation of heterocycles .
The main problem with industrial application is scale-up [2,3]. On the one hand, there is a problem with the structural material, as the batch reactors may be made of only teflon or glass. On the other hand, the limited penetration depth of MWs into the reaction mixtures prevents the construction of bigger size batch reactors. Presently, the only possibility for a certain degree of scale-up is the use of continuous-flow reactors [2,4]. A batch MW reactor (CEM) may be supplied with a flow cell where the mixture is moved by HPLC pumps. In another variation, a continuous tube reactor with a diameter of up to 6–9 mm was elaborated (Milestone) that makes possible the processment of ca 300 l/day . A capillary microreactor consisting of four parallel capillary tubes was also described. The above equipment may be used well in industrial laboratories. The only criterion of the application is that the reaction mixtures must not be too viscous and heterogeneous. The author of this paper believes that “bundle of tubes” reactors incorporating a number of glass tubes with a diameter of several mm-s may bring a breakthrough in the industry. Another good accomplishment is to apply an assembly line-type equipment that transports the solid reaction components placed in suitable vessels into a tunnel, where the irradiation takes place .
The most common benefits from MW irradiation is the considerable shortening of reaction times and the increase in the selectivities. However, the most valuable benefit is when a reaction can be accomplished that is otherwise impossible under traditional thermal conditions. This may be the consequence of a so-called special MW effect . There are, of course, other advantages as well that will be shown below within the discipline of organophosphorus chemistry. Organophosphorus chemistry is a dynamically developing field within organic chemistry. Organophosphorus compounds including P-hetereocycles find applications in the synthetic organic chemistry as reactants, solvents (ionic liquids), catalysts and P-ligands and, due to their biological activity, also as components of drugs and plant protecting agents [8–10]. The utilization of MW irradiation in organophosphorus chemistry is a relatively new field [11,12]. In this article, the attractive features of the application of the MW technique in organophosphorus syntheses are summarized. The chain of thoughts are grouped around three points.