Synthesis of a hydrogel by grafting of acrylamide-co-sodium methacrylate onto chitosan for effective adsorption of Fuchsin basic dye.

This work was designed to produce effective adsorbent from acrylamide (AAm), sodium methacrylate (SMA), and chitosan (CTS) through free radical grafting polymerization for removing the Fuchsin dye from its solution. The gel fraction and the grafting parameters were studied, and the results showed maximum grafting percentage (1014.3%) and gel fraction (83.5%) when the molar ratio of SMA to AAm was 1: 1 (the best ratio). In addition, incorporation of SMA into the gel structure enhanced the swelling of the gel by 6.63-10.25-fold as compared with the AAm-graft-CTS gel. FT-IR, TGA, DTG, DTA, and SEM were utilized to investigate the gels. Capacity for the adsorption of Fuchsin basic dye via batch process was tested and the impact of SMA, contact time, agitation rate, gel dose, dye concentration, temperature, and pH were studied. The maximum removal % (97.2%) was achieved at the best ratio. Best fitting was found by pseudo-second-order kinetic and Freundlich isotherm. Evaluation of the thermodynamic parameters was done, and it was found that the adsorption process was exothermic in nature and spontaneous and unfavorable at high temperature. The negative value of ∆S (-0.148 KJ K-1 mol-1) indicated the decrease in randomness at the solid-liquid interface.

Potassium isopropoxide: for sulfination it is the only base you need!

PEPPSI max: KOiPr has been identified as the key ingredient for Pd-catalyzed sulfination. Potassium is essential to keep the thiol concentration low, and isopropoxide is necessary for precatalyst activation and to break up Pd-sufide-based resting states. Together with the reactive Pd-PEPPSI-IPent(Cl) o-picoline catalyst, this system couples profoundly deactivated partners at RT that other catalysts cannot accomplish in refluxing toluene.

Sulfination by using Pd-PEPPSI complexes: studies into precatalyst activation, cationic and solvent effects and the role of butoxide base.

The activation of PEPPSI precatalysts has been systematically studied in Pd-catalysed sulfination. Under the reactions conditions of the sulfide and KOtBu in toluene, the first thing that happens is exchange of the two chlorides on the PEPPSI precatalyst with the corresponding sulfides, creating the first resting state; it is via this complex that all Pd enters the catalytic cycle. However, it is also from this same complex that a tri-Pd complex forms, which is a more persistent resting state. Under standard reaction conditions, this complex is catalytically inactive. However, if additional pyridine or a smaller base (i.e., KOEt) is added, this complex is broken down, presumably initially back to the first resting state and it is again capable of entering the catalytic cycle and completing the sulfination. Of note, once the tri-Pd complex forms, one equivalent of Pd is lost to the transformation. Related to this, the nature of the cation of the sulfide salt and solvent dielectric is very important to the success of this transformation. That is, the less soluble the salt the better the performance, which can be attributed to lowering sulfide concentration to avoid the movement of the Pd-NHC complex into the above described off-cycle sulfinated resting states.

The development of bulky palladium NHC complexes for the most-challenging cross-coupling reactions.

Palladium-catalyzed cross-coupling reactions enable organic chemists to form C-C bonds in targeted positions and under mild conditions. Although phosphine ligands have been intensively researched, in the search for even better cross-coupling catalysts attention has recently turned to the use of N-heterocyclic carbene (NHC) ligands, which form a strong bond to the palladium center. PEPPSI (pyridine-enhanced precatalyst preparation, stabilization, and initiation) palladium precatalysts with bulky NHC ligands have established themselves as successful alternatives to palladium phosphine complexes. This Review shows the success of these species in Suzuki-Miyaura, Negishi, and Stille-Migita cross-couplings as well as in amination and sulfination reactions.

Pd-PEPPSI-IPent: an active, sterically demanding cross-coupling catalyst and its application in the synthesis of tetra-ortho-substituted biaryls.

Incredible Bulk: A series of N-heterocyclic carbene catalysts (see picture) were prepared and evaluated in the Suzuki-Miyaura reaction. A variety of sterically encumbered tetra-ortho-substituted biaryl products were formed from unreactive aryl chlorides using the isopentyl-substituted catalyst at temperatures ranging from 65 degrees C to room temperature. The cyclopentyl-substituted catalyst was virtually inactive, demonstrating that "flexible bulk" is essential to promote these transformations.

Pd-catalyzed aryl amination mediated by well defined, N-heterocyclic carbene (NHC)-Pd precatalysts, PEPPSI.

Pd-N-heterocyclic carbene (NHC)-catalyzed Buchwald-Hartwig amination protocols mediated by Pd-PEPPSI precatalysts is described. These protocols provide access to a range of hindered and functionalized drug-like aryl amines in high yield with both electron-deficient and electron-rich aryl- and heteroaryl chlorides and bromides. Variations in solvent polarity, base and temperature are tolerated, enhancing the scope and utility of this protocol. A mechanistic rationalization for base strength (pKb) requirements is also provided.

Synthesis and catalytic application of chiral 1,1'-Bi-2-naphthol- and biphenanthrol-based pincer complexes: selective allylation of sulfonimines with allyl stannane and allyl trifluoroborate.

New easily accessible 1,1'-bi-2-naphthol- (BINOL-) and biphenanthrol-based chiral pincer complex catalysts were prepared for selective (up to 85% enantiomeric excess) allylation of sulfonimines. The chiral pincer complexes were prepared by a flexible modular approach allowing an efficient tuning of the selectivity of the catalysts. By employment of the different enantiomeric forms of the catalysts, both enantiomers of the homoallylic amines could be selectively obtained. Both allyl stannanes and allyl trifluoroborates can be employed as allyl sources in the reactions. The biphenanthrol-based complexes gave higher selectivity than the substituted BINOL-based analogues, probably because of the well-shaped chiral pocket generated by employment of the biphenanthrol complexes. The enantioselective allylation of sulfonimines presented in this study has important implications for the mechanism given for the pincer complex-catalyzed allylation reactions, confirming that this process takes place without involvement of palladium(0) species.

Organocatalytic enantioselective conjugate addition of aldehydes to maleimides.

The highly enantioselective direct organocatalytic conjugate addition of aldehydes to maleimides is presented.