Transition metal stearates

Transition metal stearates have been shown not to have catalytic activity (206). The considerable literature on these systems, developed by Tulupov, has been reviewed, and the unique mechanism presented has been questioned (/, p. 384). 

Metal phthalocyanine complexes are also frequently used as autoxidation catalysts (see Section II.B.2). They have generally been found to be more active than the corresponding stearates or acetylacetonates. Thus, Uri145 compared the catalytic activity of a series of transition metal stearates with the corresponding metal phthalocyanines in the autoxidation of methyl linoleate. The phthalocyanine complexes afforded faster rates of oxidation. In addition, the phthalocyanine ligand is stable and is not easily destroyed under autoxidizing conditions. Interest in metal phthalocyanine catalysts has also been stimulated by their resemblance to the metal-porphyrin structures contained in many oxidative enzymes (see Sections II.B.2 and V). 

Effects of a series of transition metal stearates, the concentration of the copper stearate, the solvent, various additives, and other factors on the thermal oxidation of polypropylene were studied in trichlorobenzene solution. The mechanism of copper catalysis is discussed. The order of decreasing catalytic activity of the metal stearates was Cu > Mn > Fe > Cr > Al Ni Co control Ti >> Zn >> V. The addition of propionic acid to the solvent accelerated the oxidation of the polymer. The presence of the copper leveled off oxygen uptake of the polymer after a certain time. The amount of oxygen absorbed decreased with increasing concentration of the copper, and at higher concentration (7.9 X 10 3M) the polymer oxidation was inhibited. 

In this chapter, the effect of a series of transition metal stearates on the thermal oxidation of polypropylene in homogeneous solution is examined, and the results obtained are compared with that in bulk reported previously (16). In addition, the effects of the anion of copper compounds, the concentration of copper, the solvent, and the additives on the copper compound-catalyzed thermal oxidation of polypropylene are studied, and the mechanism of the copper catalysis in solution is discussed. 

Effect of Metal Stearates. The oxygen uptake curves of isotactic and atactic polypropylene in the presence of transition metal stearates in trichlorobenzene are shown in Figures 1 and 2, respectively. The order of decreasing catalytic effect of the metal stearates at the early stage of the oxidation of the polymers is for isotactic PP, Cu > Mn > Fe > Cr > Co > Ni > Ti > control > A1 > > Zn > > V and for atactic PP, Cu > Mn> Fe > Cr > Ah Ni Co control Ti >> Zn >> V. The order of the catalytic effect of the metals is quite different from that in bulk reported previously (16). In particular, V-stearate inhibits the thermal oxidation, and Co-stearate is not as effective as in bulk. In the presence of effective metal stearates such as Cu and Fe, the oxygen uptake levels off after a certain time. However, the amount of oxygen absorbed in the isotactic polypropylene is higher than that in the atactic polypropylene. 

Effect of Anions in Copper Compounds. Since the copper stearate was the most effective catalyst among the transition metal stearates for the early stage of the thermal oxidation of polypropylene, the effect of anions in copper compounds on the thermal oxidation of atactic polypropylene was examined. The oxygen uptake curves of the polymer in the presence of various copper compounds (acetate, propionate, butylate, stearate, laurate, polyacrylate, and cupric oxide) are shown in Figure 4. In the absence of the copper compounds, oxygen uptake of the polymer increases linearly with time. In the presence of copper compounds of fatty acids (acetate, propionate, butyrate, laurate, and stearate), the oxygen uptake of the polymer levels off at ca. 25-30 O2 mL/g polymer after... 

Similar results were obtained when transition metal stearates were added to cyclohexanol (Table 5). The dioxymine complexes of Co, Cu and Fe retard oxidation of 2-propanol [274] by termination of chains. The rate of termination obeys the equation... 

Several applications of polymers placed in contact with metals require detailed study on the effect of this kind of materials upon the durability of plastics. Ozawa and Tsurumi studied by chemiluminescence the consequence of various transition metal stearates (concentration 0.5 phr) on the thermo-oxidative degradation of polypropylene even at low temperature (105 C). They stated the relative decreasing catalytic order of these compounds as follows [8901] ... 

Metals. Transition-metal ions, such as iron, copper, manganese, and cobalt, when present even in small amounts, cataly2e mbber oxidative reactions by affecting the breakdown of peroxides in such a way as to accelerate further attack by oxygen (36). Natural mbber vulcani2ates are especially affected. Therefore, these metals and their salts, such as oleates and stearates, soluble in mbber should be avoided. 

In real systems (hydrocarbon-02-catalyst), various oxidation products, such as alcohols, aldehydes, ketones, bifunctional compounds, are formed in the course of oxidation. Many of them readily react with ion-oxidants in oxidative reactions. Therefore, radicals are generated via several routes in the developed oxidative process, and the ratio of rates of these processes changes with the development of the process [5], The products of hydrocarbon oxidation interact with the catalyst and change the ligand sphere around the transition metal ion. This phenomenon was studied for the decomposition of sec-decyl hydroperoxide to free radicals catalyzed by cupric stearate in the presence of alcohol, ketone, and carbon acid [70-74], The addition of all these compounds was found to lower the effective rate constant of catalytic hydroperoxide decomposition. The experimental data are in agreement with the following scheme of the parallel equilibrium reactions with the formation of Cu-hydroperoxide complexes with a lower activity. 

Zinc soaps, which are complexes of long chain fatty acids, find similar applications in the curing and hardening of coatings to other transition metal soaps. A summary is available.123 The more important anions are 2-ethylhexanoate, naphthenate and stearate. Mixtures of zinc and calcium soaps are also effective stabilizers for poly(vinyl chloride).124 The complexes [Zn 0P(0)-(OBun)2 2] and [Zn SP(S)(OBun)2 2] both promote antiwear properties of lubricating oils.125... 

The oxidation of benzaldehyde is catalyzed by certain metallic tons, including those of the transition metals (Co, Fe, Ni, Cr, Cu, V, etc.) usually introduced in the form of naphthenates, benzoates, stearates etc, at the rate of 500 to 1000 ppm in relation to toluene. Certain initiators, such as bromine compounds, increase the reaction rate obtained with metallic salts by a factor of 10 to 30. 

Transition metal cations can be made organically soluble by complexation with a crown ether, a polyethylene glycol) or its dimethyl ether (an open crown) or tris(3,6-dioxaheptyl)amine (TDA-1, an open cryptand, 1). TDA-1 is very hydrophilic and is most useful for the solubilization of solid salts. On the other hand, it also forms complexes with some metal carbonyls. Alternatively, a very lipophilic anion (for instance stearate) can make a salt organic. Finally, some other special ligand (e.g., a bipyridine-N,N -dioxide derivative) can be used. In all these cases positively charged species are brought into the organic phase for reaction. 

Differential scanning calorimetry was used by Murrill and co-workers (43-45) to elucidate solid - solid phase transitions in a large number of organic compounds. First-order transitions were reported for tetrahedral compounds of the type CR1R2R2R4, where R is methyl, methylol, amino, nitro, and carboxy, as well as for octahedral-type compounds. This technique was also used to detect phase transitions in alkali metal stearates (46), some dibenzazepines, carbazoles, and phenothiazines (16), and the half esters of O-phthalic acid (31). The solid-state decomposition kinetics and activation parameters of N-aryl-N -tosyl-oxydt-imide N-oxides were determined using DSC by Dorko et al. (49). 

The interactions of various polar agents with the ionic groups and the ensuing property changes are unique to ionomer systems. This plasticization process is also important in membrane applications. A different application of ionic cluster plasticization involves the interaction of metal stearates to induce softening transitions. The plasticization process is required to achieve the processability of TPEs based on this technology. 

The most popular cationic catalysts are soluble Co " and Cr " salts and mixtures thereof Examples of such salts that are added to catalyze the oxidation are cobalt stearate and cobalt naphthenates. Applied concentrations of these transition metals range from more than 10 ppm down to sub-ppm levels. These catalysts also catalyze the decomposition of CHHP, reducing the residual concentrations of CHHP. Nevertheless, both for economic and safety reasons, the residual CHHP is decomposed to mainly cyclohexanone and cyclohexanol. This reaction is carried out in an after-reactor either in a monophasic system in cyclohexane or in a biphasic system with an aqueous caustic solution as second phase. 

These reactions can be accelerated by adding pro-oxidant additives to polymers, usually transition metals, such as carbamic compounds of iron or nickel, or stearic compounds such as stearates of cobalt or manganese, etc. 

Heavy transition metal ions such as iron, manganese, and copper catalyze oxidation of elastomers. Compounds of manganese or copper such as oleates and stearates are readily soluble in rubber, enabling rapid oxidation of the polymer. /7flra-Phenylenediamine antidegradants are used to hinder the activity of such metal ions. 

Cadmium is a transition metal in group IIB of the periodic table of elements. The metal is bluish-white to silver-white. At room temperature, it has a hexagonal close-packed crystal structure. Eight stable isotopes are known to be present in natui . The atomic weight of cadmium is 112.4 and the atomic number 48. The density at 25°C is 8.6 g/cm the melting point 321°C and the boiling point 765°C. The most common oxidation state is +2. " The most important compounds are cadmium acetate, cadmium sulfide, cadmium sulfoselenide, cadmium stearate, cadmium oxide, cadmium carbonate, cadmium sulfate, and cadmium chloride. The acetate, chloride, and sulfate are soluble in water, whereas the oxide and sulfide are almost insoluble. ... 

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