Zinc amide basic

I) Metallation of Aliphatics by Zinc. The basic Zn amide, Zn[N(SiMe3)2]2, reacts with cyclopentadiene and with the diazoester, HC(N2)C02Et to give diorganozinc products ... 

Zinc chloride melts at 275°C, bods at 720°C, and is stable in the vapor phase up to 900°C. It is very hygroscopic, extremely water-soluble, and soluble in organic Hquids such as alcohols, esters, ketones, ethers, amides, and nitrides. Hydrates with 1, 1.5, 2.5, 3, and 4 molecules of water have been identified and great care must be exercised to avoid hydration of the anhydrous form. Aqueous solutions of zinc chloride are acidic (pH = 1.0 for 6 M) and, when partially neutralized, can form slightly soluble basic chlorides, eg, ZnCl2 4Zn(OH)2 [11073-22-6] and Zn(OH)Cl [14031-59-5]. Many other basic chlorides have been reported (58). 

A number of basic materials such as hydroxides, hydrides and amides of alkaline and alkaline earth metals and metal oxides such as zinc oxide and antimony oxide are useful catalysts for the reaction. Acid ester-exchange catalysts such as boric acid, p-toluene sulphonic acid and zinc chloride are less... 

The tendency of these compounds to form dimers has a strong influence on their NMR spectra (8). In contrast to the free base seco-pz 158, the 1II NMR spectra of reco-zincporphyrazine (162) and diseco-z i ncp( >rph y niz i nes (163) displayed very broad signals due to the interaction between the zinc center of one macrocycle with the Lewis basic amide oxygen of a second seco-pz resulting in the formation of dimers, and could be disassembled in solution by the presence of the coordinating solvent pyridine. 

The rate is slower in basic aprotic amide solvents, and faster in acidic solvents such as / -cresol. In general, the imidization reaction has been shown to be catalyzed by acid (14,32,33). Thermal imidization of poly(amic acid)s is catalyzed by tertiary amines (34). High temperature solution polymerization in -cresol is often performed in the presence of high boiling tertiary amines such as quinoline as catalyst. Dialkylaminopyridines and other tertiary amines are effective catalysts in neutral solvents such as dichlorobenzene (35). Alkali metal and zinc salts of carboxylic acids (36) and salts of certain organophosphorus compounds (37) are also very efficient catalysts in one-step polycondensation of polyimides. 

It was first prepd in 1892 by Wislicenus (Ref l) by the action of nitrous oxide on Zn amide at 150-250°. Curtius Rissom (Ref 2) obtd the basic zinc azide, ZnOHN, by dissolving the metal in dil HN3 and allowing the soln to evap in air. The product, ill-defined anisotropic crysts, was insol in w. Dennis Isham (Ref 3) prepd Zn(Ns)a-2NH3 and Zn (Nj)a 2Cs Hs N by dissolving Zn in alcoholic HNj, adding dry NH3 or pyridine in excess, and allowing the soln to evap. Both products were wh, crystalline ppts, insol in w, and... 

Aldol condensations of zinc enolates under conditions of thermodynamic control are reasonably discussed in terms of the relative stability of the two chelated aldolates (19), which leads to the syn aldol, and (20), which leads to the anti aldol. If R is larger than R, the anti chelate, with R and R trans in a six-atom ring, is expected to be the more stable form. Heathcock has noted that the most common mechanism for equilibration of aldolate stereochemistry is reverse aldolization (reversal of equation 29). Aldolates obtained by reaction of an enolate with ketone substrates are expected to undergo reverse aldolization at a faster rate than those obtained with aldehyde substrates, in part for steric reasons. Similarly, aldolates derived from ketone enolates are expected to undergo reverse aldolization at a faster rate than those derived from the more basic ester or amide enolates. 

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