Synthesis of Trisubstituted Ureas by a Multistep Sequence Utilizing Recyclable Magnetic Reagents and Scavengers

Abstract

Unprecedented magnetic borohydride exchange (mBER), magnetic Wang aldehyde (mWang) and magnetic amine resins were prepared from highly magnetic polymer-coated cobalt or iron nanoparticles. Microwave irradiation was used to obtain excellent degrees of functionalization (>95 %) and loadings (up to 3.0 mmol g(-1)) in short reaction times of 15 min or less. A small library of ureas and thioureas was synthesized by the exclusive application of these magnetic resins. As a first step, a reductive amination of aromatic and aliphatic aldehydes was carried out with mBER. The excess of primary amine needed to complete the reaction was subsequently scavenged selectively by mWang. Simple magnetic decantation from the resins resulted in secondary amines in good to excellent yields and purities. The used magnetic resins were efficiently regenerated and reused for the next run. In a second step, the secondary amines were converted to trisubstituted (thio)ureas in excellent yields and purities by stirring with an excess of iso(thio)cyanate, which was scavenged by addition of the magnetic amine resin after completion of the reaction. The whole reaction sequence is carried out without any purification apart from magnetic decantation; moreover, conventional magnetic stirring can be used as opposed to the vortexing required for polystyrene resins.

Reversible magnetic mercury extraction from water

“…Improved extraction capacity (73%) was found for Co/C-PS-PAMAM G2 5, which can be ascribed to increased loadings of terminal amino groups made possible through the additional polystyrene layer on the surface of the NPs. 24,25,29,34,38 For both materials no signicant cobalt leaching was detected.…”

“…Carbon-coated nanobeads have proved their effectiveness in a variety of applications such as supports for scavengers, reagents or catalysts. [22][23][24][25][26][27][28] Relevant for this study, this type of nanoparticles was previously used for complexation/extraction of cadmium, copper, lead, 11 arsenic 29 ions as well as noble metal ions based on gold 19,30 and platinum. 30 However, no studies for the removal of mercury(II) from contaminated water were reported.…”

Recent Advances in the Application of Magnetic Nanoparticles as a Support for Homogeneous Catalysts

“…Very interesting magnetic catalytic exchange resins were prepared by Reiser et al [ 69 ] using polymer coated cobalt and iron nanoparticles and microwave irradiation. The magnetic resins were employed to produce a library of ureas and thioureas using various reactions.…”

Magnetic Nanocolloids

“…Depending on the target of interest, different particle coating and functionalization strategies need to be developed to attach the target to the magnetic NP. 117,124 If we focus now on the use of magnetic NPs as magnetic separators in biological systems, the mechanism by which the separation agent works is the same as in wastewater applications; however, the target is different. 114,115 Water-stable magnetite/maghemite NP dispersions have been intensively researched for the treatment of wastewater based on their ability to act as magnetic separators.…”