In this study we demonstrate a successful sulfur-MOF composite synthesis and their application in the Willgerodt-Kindler reaction. We showed the MIL-53(Al), CAU-10-H and MIL-101(Cr) encapsulate the sulfur without MOF decomposition by melt-diffusion technique whereas MIL-88A and MIL-101(Fe) were unable to form S@MOF composites. Various techniques, including, XRD, SEM, EDS, and porometry were used to characterize the synthesized S@MOF composites. The influence of MOF nature, temperature, reaction time and reagent ratio on the Willgerodt-Kindler reaction product formation was evaluated. The S@CAU-10-H composite led to the thiomorpholides from various arylaldehydes, acetophenones and propiophenones in 56–91 % isolated yields. The reaction proceeds at near equimolar reactant concentrations. Product isolation is straightforward and does not require tedious chromatographic purification. The MOF was easily separated and reused in five runs, achieving a good performance without significant framework degradation. We postulate that a MOF has a multiple role, acting as a reaction medium, sulfur carrier, amine absorber and dehydration agent.

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