Zinc salt, additive mechanism

The kinetics of the zinc diisopropyl dithiophosphate-in-hibited oxidation of cumene at 60°C. and Tetralin at 70°C. have been investigated. The results cannot be accounted for solely in terms of chain-breaking inhibition by a simple electrow-transfer mechanism. No complete explanation of the Tetralin kinetics has been found, but the cumene kinetics can be explained in terms of additional reactions involving radical-initiated oxidation of the zinc salt and a chain-transfer step. Proposed mechanisms by which zinc dialkyl dithiophosphates act as peroxide-decomposing antioxidants are discussed. 

In order to enable melt processing of ion containing polymers, such as S-EPDM, it is necessary to introduce a mechanism that weakens the ionic interactions. This can be achieved by the addition of a polar ingredient that would plasticize" ionic domains at elevated temperatures only. A variety of such ionic-plasticizers were described by Makowski and Lundberg (10). A particularly attractive combination was found to be zinc stearate with a zinc salt of S-EPDM. It was shown that for such a combination melt... 

C2-alkynylation of (benzo)furans 7 and 12 was achieved selectively under gold catalysis with hypervalent ethynylbenziodoxolone reagents (TIPS-EBX (10)) (Scheme 3) (2013AGE6743, 2013BJOC1763). Under mild conditions, a broad set of substituted furans 7 and benzofiirans 12 were successfully alkynylated (11 and 13) albeit for the latter a higher reaction temperature and an additional (super)stoichiometric zinc salt was needed. Waser has shown the instantaneous formation of bis(triisopropyl-silyl)diyne via reaction of TIPS-EBX 10 with AuCl (2012CEJ5655). Therefore the mechanism likely involves oxidative addition of Au with TIPS-EBX 10 followed by electrophUic C—H auration, with elimination of 14 and reductive elimination (Scheme 4). 

Lithiation at C2 can also be the starting point for 2-arylatioii or vinylation. The lithiated indoles can be converted to stannanes or zinc reagents which can undergo Pd-catalysed coupling with aryl, vinyl, benzyl and allyl halides or sulfonates. The mechanism of the coupling reaction involves formation of a disubstituted palladium intermediate by a combination of ligand exchange and oxidative addition. Phosphine catalysts and salts are often important reaction components. 

The mechanism of inhibition by the salts of the long chain fatty acids has been examined . It was concluded that, in the case of the lead salts, metallic lead was first deposited at certain points and that at these points oxygen reduction proceeded more easily, consequently the current density was kept sufficiently high to maintain ferric film formation in addition, any hydrogen peroxide present may assist in keeping the iron ions in the oxide film in the ferric condition, consequently the air-formed film is thickened until it becomes impervious to iron ions. The zinc, calcium and sodium salts are not as efficient inhibitors as the lead salts and recent work has indicated that inhibition is due to the formation of ferric azelate, which repairs weak spots in the air-formed film. This conclusion has been confirmed by the use of C labelled azelaic acid, which was found to be distributed over the surface of the mild steel in a very heterogeneous manner. ... 

While the mechanism of the ammonium salt catalyzed alkylation is unclear, in polar solvents the enantioselectivity of the addition of dialkylzincs to aldehydes generally drops considerably, probably due to uncatalyzed product formation or complexation of the zinc reagent with the polar solvent rather than with the chiral auxiliary. 

The silver is dissolved from the ore by an aqueous solution of a salt, and then precipitated as metal or sulphide. The cyanide process2 is the most important of the lixiviation methods, its application having been considerably extended in recent years, especially in Mexico. The ore is very finely crushed with cyanide solution in a stamp-mill, and the sludge produced submitted to agitation and aeration in contact with cyanide solution. The liquid is separated from the ore by the aid of mechanical filters, and the silver precipitated from the clear solution by addition of zinc in the form of dust or shavings. The product is smelted with nitre, and is sometimes refined by blowing air through the molten mass. 

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