Display omitted
The susceptibility of Zn-based materials to corrosion in an aggressive environment limits their broad applications. Innovative conversion treatment is the most interesting approach ...for enhanced corrosion performance of zinc. This review covers recent research that has led to advances in conversion coating technology for zinc; including the application of contemporary methods for chemical conversion coating, the establishment of a corrosion protection framework for zinc, the illumination of processing control effects, and the attempts at the inhibition mechanisms of zinc by coatings. This review drawing from many sources provides an impartial focus on new achievements. The environmentally acceptable conversion coating is reviewed in detail. This review also covers engineering application aspects, including cost-effectiveness technology and process productivity. Finally, future prospects and present challenges in the field of conversion treatment are reviewed, identifying the demerit of each technique, meanwhile attempting to also identify future developments and directions.
A two-step surface treatment was applied on the surfaces of polyacrylonitrile(PAN)-based carbon fibers (CFs) including the electrochemical oxidation process followed by grafting of silane coupling ...agent KH550. The evolution of the physiochemical structure of the fiber surface during the surface treatment was investigated using Infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and surface tension/dynamic contact angle measurements. The results showed that the CF surface exhibited a significant increase in the relative content of oxygen-containing functional groups after surface treatment while its crystal structure had little change after the grafting of KH550 agents. Effects of surface treatment on the mechanical properties of CFs and the interfacial properties, including the interfacial shear strength (IFSS) and interlaminar shear strength (ILSS) of carbon fiber reinforced epoxy (CF/EP) composites were evaluated in detail. Both the electrochemical oxidation and the introduction of KH550 agents onto CF surfaces improved the IFSS and ILSS values of CF/EP composites by comparison with untreated fibers. In particular, the maximum interfacial properties of CF/EP composites were obtained by the electrochemical oxidation together with the grafting of KH550 agents onto CF surfaces.
•The grafting of KH550 onto fiber surfaces had little influence on surface crystal structure.•The introduction of KH550 resulted in decreased contact angle and increased surface energy.•The tensile strength of KH550 modified fibers also increased.•The IFSS and ILSS values of CF/EP composites increased by 73.1% and 61.2%, respectively, after surface treatment.
A method for the synthesis of benzylsilanes starting from the corresponding ammonium triflates is reported. Silyl boronic esters are employed as silicon pronucleophiles, and the reaction is catalyzed ...by copper(I) salts. Enantioenriched benzylic ammonium salts react stereospecifically through an SN2‐type displacement of the ammonium group to afford α‐chiral silanes with inversion of the configuration. A cyclopropyl‐substituted substrate does not undergo ring opening, thus suggesting an ionic reaction mechanism with no benzyl radical intermediate.
SiR, the NMe has surrendered: Benzylic ammonium salts can be transformed into the corresponding silanes by a copper‐catalyzed SN2‐type displacement. The enantioenrichment of the precursors is completely retained in the α‐chiral silanes. A cyclopropyl group at the benzylic carbon atom remains intact, thereby supporting an ionic reaction mechanism.
The chemoselective reduction of amides in the presence of other more reactive reducible functional groups is a highly challenging transformation, and successful examples thereof are most valuable in ...synthetic organic chemistry. Only a limited number of systems have demonstrated the chemoselective reduction of amides over ketones. Until now, the aldehyde functionality has not been shown to be compatible in any catalytic reduction protocol. Described herein is a Mo(CO)6‐catalyzed protocol with an unprecedented chemoselectivity and allows for the reduction of amides in the presence of aldehydes and imines. Furthermore, the system proved to be tunable by variation of the temperature, which enabled for either C−O or C−N bond cleavage that ultimately led to the isolation of both amines and aldehydes, respectively, in high chemical yields.
The choice is yours: Mo(CO)6 is demonstrated to be an efficient catalyst for the chemoselective reduction of tertiary amides in the presence of a large number of reducible groups, including imines and aldehydes. The reaction is tunable by variation of the temperature, and either an amine or an aldehyde can be obtained as the major product from the corresponding amide. TMDS=1,1,3,3‐tetramethyldisiloxane.
Described herein is that the catalytic construction of N‐substituted five‐ and six‐membered lactams from keto acids with primary amines by reductive amination, using an indium/silane combination. ...This relatively benign and safe catalyst/reductant system tolerates the use of a variety of functional groups, especially ones that are reduction‐sensitive. A direct switch from synthesizing lactams to synthesizing cyclic amines is achieved by changing the catalyst from In(OAc)3 to InI3. This conversion occurs by further reduction of the lactam using the indium/silane pair.
Making the switch: Catalytic construction of N‐substituted lactams from keto acids and primary amines using an In(OAc)3/PhSiH3 reducing system was achieved. A variety of functional groups can be tolerated during the transformation. By simply changing the catalyst from In(OAc)3 to InI3, the cyclic amines, rather than lactams, are formed from the same starting materials.
The strong boron Lewis acid tris(pentafluorophenyl)borane B(C6F5)3 is known to catalyze the dehydrogenative coupling of certain amines and hydrosilanes at elevated temperatures. At higher ...temperature, the dehydrogenation pathway competes with cleavage of the C−N bond and defunctionalization is obtained. This can be turned into a useful methodology for the transition‐metal‐free reductive deamination of a broad range of amines as well as heterocumulenes such as an isocyanate and an isothiocyanate.
I mean defunct. Combinations of the boron Lewis acid B(C6F5)3 and hydrosilanes enable the reductive cleavage ofC−N bonds in various, mainly benzylic amines and heterocumulenes. By this, these functionalized substrates can be converted into the corresponding hydrocarbons in moderate to good yields.
An iron‐catalyzed hydrofluorination of unactivated alkenes has been developed. The use of a multidentate ligand and the fluorination reagent N‐fluorobenzenesulfonimide (NFSI) proved to be critical ...for this reaction, which afforded various fluorinated compounds in up to 94 % yield.
H(igh)–F(ive): The combination of a multidentate ligand, (EtO)3SiH, and N‐fluorobenzenesulfonimide (NFSI) proved critical in facilitating an iron‐catalyzed hydrofluorination of unactivated alkenes to provide a variety of substituted fluorinated compounds. The reaction was shown to proceed by a radical mechanism and to be suitable for the fluorination of various biologically active substrates.
Functionalization reactions of the refrigerants HFO‐1234yf (2,3,3,3‐tetrafluoropropene) and HFO‐1234ze (1,3,3,3‐tetrafluoropropene) were developed. The selectivity and reactivity towards CF3 groups ...of C−F activation reactions can be controlled by employing either a germane or a silane as the hydrogen source. Unique transformations were designed to accomplish consecutive hydrogermylation and C−F activation steps. This allowed for an unprecedented transformation of an olefinic C−F bond into a C−H bond by heterogeneous catalysis. These reactions are catalyzed by nanoscopic aluminum chlorofluoride (ACF) under very mild conditions.
Functionalizations of tetrafluoropropenes such as HFO‐1234yf were developed. The transformation of the CF3 group into an olefinic CF2 group was achieved at nanoscopic aluminum chlorofluoride (ACF) with silane. Consecutive hydrogermylation and C−F activation steps enabled the transformation of an olefinic C−F into a C−H bond.
CF3 on C sp 3: Trifluoromethylation of allylsilane derivatives was accomplished through the use of CuI and Togni's reagent (1) under mild conditions. The reaction of allylsilanes without a ...substituent in the 2‐position gave vinylsilane derivatives, while 2‐substituted allylsilanes afforded desilylated products. The utility of the products was demonstrated through their further transformation.
Natural fiber reinforced polymer composites (NFPCs) provide the customers with more alternatives in the material market due to their unique advantages. Poor fiber–matrix interfacial adhesion may, ...however, negatively affect the physical and mechanical properties of the resulting composites due to the surface incompatibility between hydrophilic natural fibers and non-polar polymers (thermoplastics and thermosets). A variety of silanes (mostly trialkoxysilanes) have been applied as coupling agents in the NFPCs to promote interfacial adhesion and improve the properties of composites. This paper reviews the recent progress in using silane coupling agents for NFPCs, summarizes the effective silane structures from the silane family, clarifies the interaction mechanisms between natural fibers and polymer matrices, and presents the effects of silane treatments on the mechanical and outdoor performance of the resulting composites.
PDF
