Homogenous Two-Component Reactions

Efficient interaction of two or more components occurs if they are combined in a single liquid phase. The Diels-Alder reaction between (2 , 4 )-2,4-hexadien-l-ol and maleic anhydride occurs without solvent as the two components melt together over approximately 3 min [6], This reaction can be performed safely at a 5 mmole scale in a beaker, but doubling the reaction scale or performing the reaction in a smaller vessel causes an extremely exothermic reaction due to the lack of solvent as a heat sink. 

It is common to control fast reactions by adding one of the reactants over a period of time to a solution of the other(s). Under these conditions, the added component does not become diluted by all the solvent in the reaction flask, and locally high concentrations exist. This is usually of no consequence, but with especially reactive reagents, competing reactions 

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