Metal carboxylates consumption

Owing to metal chlorides titration by the coulometric method, and carboxylic acid titration by the potentiometric method, it is possible to follow the metal soaps consumption during thermomechanical heat treatments. This new technique provides a better understanding of the stabilization mechanisms of PVC with the calciumr-zinc system, and offers a better explanation of synergistic effects between metal soaps and secondary stabilizers such as epoxidized soya-bean oil, a-phenylindole, and butanediol-p-aminocroto-nate. The influence of these last stabilizers on zinc chloride formation enables us to classify them into short- and longterm stabilizers. 

A recent stndy (13,27) describes the use of Co-Si-TUD-1 for the liquid-phase oxidation of cyclohexane. Several other metals were tested as well. TBHP (tert-butyl hydroperoxide) was used as an oxidant and the reactions were carried out at 70°C. Oxidation of cyclohexane was carried out using 20 ml of a mixture of cyclohexane, 35mol% TBHP and 1 g of chlorobenzene as internal standard, in combination with the catalyst (0.1 mmol of active metal pretreated overnight at 180°C). Identification of the products was carried out using GC-MS. The concentration of carboxylic side products was determined by GC analysis from separate samples after conversion into the respective methyl esters. Evolution and consumption of molecular oxygen was monitored volumetrically with an attached gas burette. All mass balances were 92% or better. 

For each stabilizing system we have drawn the total amount of transformed carboxylates versus heating time from metal chloride titration (Curve 1) or stearic acid titration (Curve 2), according to the stoichiometry of Reaction 1 (Figures 1, 2, and 3). Curves 1 and 2 would be superposed on each figure if the stabilizer consumption was caused only by Reaction 1 however, experimentally they are not. 

Copper The catalytic activity of copper(II) triflate for cyclizations of alkenols or intermolecular additions of alcohols and carboxylic acids to norbomene has been reported [62, 63]. In dioxane at 80°C, high conversions were achieved at prolonged reaction times, and those were superior to those obtained with Lewis acids such as Yb(OTf)3, though the latter also displayed catalytic activity [62]. In a control experiment with triflic acid (10 mol%) only little product (29%) resulted with low stereoselectivity. However, it is now clear that this control experiment was flawed, as too much triflic acid and overly long reaction times had been applied. The previously mentioned study by Carpentier and coworkers on copper triflate catalyzed hydroaUcoxylations has established that Cu(OTf)2 decomposes to CuOTf and triflic acid when heated in organic solvents [50]. Triflic acid is catalytically active in hydroaUcoxylation at levels down to 0.1 mol%, if a polymerization inhibitor is present to prevent consumption of the olefinic substrate. Indeed, Cu (OTf)2 is an excellent reagent for releasing small amounts of triflic acid in this case, because the coreleased CuOTf acts as polymerization inhibitor for the acrylic substrate (Scheme 12) [50]. Other metal triflates like Sc(OTf)3 or Yb(OTf)3 displayed catalytic activity at the 1 mol% level in the reaction of Scheme 12. Additional experiments were presented to support the conclusion that triflic acid is the actual catalyst in this and other Lewis acid catalyzed hydroalkoxylations [50]. 

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