Zinc chloride, catalytic effect

Different types of other coal liquefaction processes have been also developed to convert coals to liqnid hydrocarbon fnels. These include high-temperature solvent extraction processes in which no catalyst is added. The solvent is usually a hydroaromatic hydrogen donor, whereas molecnlar hydrogen is added as a secondary source of hydrogen. Similar but catalytic liquefaction processes use zinc chloride and other catalysts, usually under forceful conditions (375-425°C, 100-200 atm). In our own research, superacidic HF-BFo-induced hydroliquefaction of coals, which involves depolymerization-ionic hydrogenation, was found to be highly effective at relatively modest temperatnres (150-170°C). 

H2SnClg 6H20, CISO H + CH OH, CH COOH, as well as ben2ene-, naphthalene-, and -toluenesulfonic acids (44). Zinc chloride is probably the most frequentiy used catalyst. Its activity is sometimes increased by fusion with a small amount of aluminum chloride. In other instances, however, sufficient catalytic effect is obtained with a mineral acid alone. 

The major problem of these diazotizations is oxidation of the initial aminophenols by nitrous acid to the corresponding quinones. Easily oxidized amines, in particular aminonaphthols, are therefore commonly diazotized in a weakly acidic medium (pH 3, so-called neutral diazotization) or in the presence of zinc or copper salts. This process, which is due to Sandmeyer, is important in the manufacture of diazo components for metal complex dyes, in particular those derived from l-amino-2-naphthol-4-sulfonic acid. Kozlov and Volodarskii (1969) measured the rates of diazotization of l-amino-2-naphthol-4-sulfonic acid in the presence of one equivalent of 13 different sulfates, chlorides, and nitrates of di- and trivalent metal ions (Cu2+, Sn2+, Zn2+, Mg2+, Fe2 +, Fe3+, Al3+, etc.). The rates are first-order with respect to the added salts. The highest rate is that in the presence of Cu2+. The anions also have a catalytic effect (CuCl2 > Cu(N03)2 > CuS04). The mechanistic basis of this metal ion catalysis is not yet clear. 

Lewis acids such as zinc chloride, boron trifluoride, tin tetrachloride, aluminum chloride, methylaluminum dichloride, and diethylaluminum chloride catalyze Diels-Alder reactions.22 The catalytic effect is the result of coordination of the Lewis acid with the dienophile. The complexed dienophile is more electrophilic and more reactive toward electron-rich dienes. The mechanism of the addition is believed to be concerted and enhanced regio- and stereoselectivity is often observed.23... 

Zinc was effectively activated from zinc chloride using lithium and a catalytic amount (10%) of naphthalene in order to prepare secondary or tertiary alkylzinc bromides 517 (starting from the corresponding aUcyl bromides 516). These reagents react with acyl chlorides or a,/3-unsaturated ketones to give the expected ketones 15 and 518 (Scheme 143). 

In the absence of additives the yield of the alcohol 212 is only 17%, and 53% in the presence of CeCls. Catalytic amounts of zinc chloride in the presence of LiCl were found to have a similar positive effect on the outcome of the 1,2-addition reaction of alkylmagnesium halides to enolizable ketones (equations 138 and 139). Due to the low price of ZnCli, this method seems promising for large-scale applications. 

The catalytic effect of several alcohols in the preparation of dichlorotetrakis(pyridine)rhodium(III) cation has long been known.1 In recent years, a variety of reducing agents, present in catalytic quantities, have been used in the preparation, of several rhodium(III) complexes.2 In the absence of catalysts, these reactions are often laborious, and/or incomplete, by comparison with the catalyzed reaction, for example, the preparation of pentaamminechlororhodium(III) chloride (Claus salt) by the method of Lebedinsky.3 Conversion of [Rh(NII3)[,CI]Cl2 to the pentaamminehydridorhodium(III) salt [Rh(NII3) I 1JW()4 by treatment with zinc and ammonia is rapid, and the reaction is relatively clean.4 The formation of hydrido species by tetrahydroborate treatment6 is not a satisfactory preparative procedure. 

CATALYST LCN is a magnesium salt catalyst for textile finishing resins which has been modified to provide stronger catalytic action than that provided by magnesium chloride catalysts. It provides catalytic action equivalent to that of zinc nitrate or zinc chloride without the deleterious effects on whiteness and shade which zinc catalysts sometimes produce. 

The catalytic activity of hydrogen chloride was found by Tarbell and Kincaid 34g). Continuing this work, Tarbell et al. 36) showed that certain acids and bases affect the yields of urethanes obtained from a-naphthyl isocyanate and phenols. Thus, catalytic effects were observed with sodium carbonate and acetate, pyridine, triethylamine, acetic acid, trichloroacetic acid, zinc chloride, hydrogen chloride, and boron fluoride etherate. The latter catalyst and triethylamine were found to be the most effective acidic and basic catalysts, respectively. 

Zinc chloride also showed a catalytic effect (Figure 13) but was not as effective as the potassium catalyst. Kinetic analysis of the rate data gave average values for b of 0.37 and 0.35 at 500 and 1000 psi, respectively, and average values for K of 0.0015 and 0.0039 (Table IV). Figure 13 also shows a direct comparison of relative effectiveness of the zinc and potassium salt catalysts. 

Self-condensation of the formamidine (368) in xylene with a catalytic quantity of 4-toluenesulphonic acid gave amitraz (369) Scheme 5.84.) [492]. Dimethyl carbamoyl chloride and ethyl trifluoroacetate are also catalysts for this reaction. A one-pot condensation of 2,4-dimethylaniline, triethyl orthoformate and methylformamide with or without zinc chloride was reported to give amitraz in high yield [493, 494]. The drug is used as an insecticide and acaricide particularly against several species of cattle ticks in South Africa [495, 496] and is very effective in the treatment of refractory Demodecosis canis (mange) in the dog [497]. 

The effect of metal oxides and chelates has already been mentioned. The metals involved can react with HCl and their products of reaction are catalytic to PVC thermal degradation and thus HCl is produced more rapidly, which contributes to increase flammability. Zinc borate is a quite popular metal salt used in this application. In addition to zinc chloride, boron chloride reduces flammability. Some studies show that when boron chloride is produced, the B2O3 glass layer is destroyed and boron is volatilized, which reduces its flame stability action. 

The influence of additives on thermal degradation may be exemplified by the FTIR-EGA study of the effect of zinc oxide on the pyrolysis of polychloroprene (15). This effect (fig 5) has been recognised for some time (16-18) and has generally been attributed to the catalytic action of zinc chloride formed during cross-linking of the polychloroprene (19). We have examined the effect of ZnO, ZnS, ZnCl2 and ZnS04 on the pyrolysis of polychloroprene and found that only zinc oxide results in the effects seen in fig 5. 

For preparative reactions, the catalytic effect of Lewis acids is often utilized. Zinc chloride or ferric chloride are used in chlorinations, and metallic iron, which... 

Lewis acids such as zinc chloride, aluminum chloride, and diethylaluminum chloride catalyze Diels-Alder reactions. The catalytic effect is the result of coordination of the Lewis acid with the dienophile. 

Earlier, the reduction of y-nitro esters with zinc and ammonium chloride had been shownto provide a suitable route to A-hydroxy 2-pyiTolidones, e.g., 42. Various catalytic hydrogenation procedures can also effect the same reductive cyclization. ... 

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