Radical Reactions in Aqueous Media

Abstract

The recent focus in the field of biomaterials has been on the design of intelligent materials. Toward this goal, materials have been developed, which can provide specific bioactive signals to control the biological environment around them during the process of materials integration and wound healing. In addition, materials have been developed that can respond to changes in their environment, such as a change in pH or cell‐associated enzymatic activity. In designing such novel biomaterials, researchers have sought not merely to create bioinert materials, but rather materials that can respond to the cellular environment around them to improve device integration and tissue regeneration. Since their discovery, β‐cyclodextrins (CDs) and, more recently, chitosan have served as prototypes for novel host compounds and catalysts. The use of CDs and chitosan as microvessels to perform chemical reactions has attracted the interest of chemists since the 1960s. This review mainly concentrates on the recent developments of organic reactions mediated by native or simply modified CDs and chitosan and in the use of the CDs as well as chitosan as the extra reaction field rather than the enzyme model in aqueous and alternative media as well as the recent use of the materials as bioactive restorative materials in dentistry, highlighting the enormous potential of such materials in biomedical applications and health sciences in general.

Opportunities for the Replacement/Minimization of Selective Hazardous Solvents: Applications, Concerns and Approaches To Identify Alternatives

“…The types of organic reactions are broad including reaction of carbocation and carbanion equivalents (70), transition-metal catalysts (71), pericyclic reactions (72), reactions of carbenes (73) and radicals (74), and oxidations-reductions (75,76). Several organic solvent-based cleaners are replaced with water-based cleaners for cleaning operations (77).…”

Highly Selective Radical Monoreduction of Dihalides Confined to a Dynamic Supramolecular Host

“…Also, no differences were observed in the 1 H NMR spectra of bound 7 in 1 after 8 h at 45 °C in the absence of reducing agent (see SI6 and SI7). Typically, silanes such as (TMS) 3 SiH are efficient reducing agents in water, [30] and excellent yields can be obtained when stoichiometric or excess silanes are used on alkyl halides [31] . When a solution of 2 @ 1 was treated with 1 equivalent of (TMS) 3 SiH, characteristic peaks for remaining 2 are observed (see Figure 3; blue squares).…”

“…Activation and termination reactions ( k 1 and k 3 in Scheme 1, respectively) are faster when (TMS) 3 SiH is involved, due to its lower Si−H bond dissociation enthalpy (BDE) with respect to Ph 3 SiH that allows a faster hydrogen abstraction in presence of radical initiators. For example, k 3 is reported to be approximately 10 4 –10 5 m −1 s −1 in benzene for (TMS) 3 SiH while a value of approximately 10 3 m −1 s −1 is reported for Ph 3 SiH [31] . Radical reduction of bound 2 – 5 in 1 was performed in the presence of 1 equivalent of Ph 3 SiH, in order to explore the effect of a slower termination processes on conversion and selectivity.…”

“…Typically,s ilanes such as (TMS) 3 SiH are efficient reducing agents in water, [30] ande xcellent yields can be obtained when stoichiometrico re xcess silanes are used on alkyl halides. [31] When as olution of 2@1 was treated with 1equivalent of (TMS) 3 SiH, characteristicp eaks for remaining 2 are observed (see Figure 3; blue squares). The mono-reduced product is seen at 1.29 and À4.56 ppm (see Figure 3B,C), as two different complexes 8a and 8b,w hich interconvert slowly on the NMR timescale.…”

β‐Cyclodextrin: A Green and Efficient Supramolecular Catalyst for Organic Transformations

“…However, some of these protocols are generally associated with one or more disadvantages, such as long reaction times, high reaction temperatures, low yields, complex handling procedures, problematic side reactions, environmental concerns associated with the use of metal and acidic catalysts, use of organic solvents, etc. Water is a safe, economical and environmentally benign solvent ,,. But; the fundamental problem with performing reactions in water is that many organic substrates are hydrophobic and insoluble in water.…”