Zinc alkyls oxide

Neither reaction excludes the other, nor are these the only routes possible. The oxidation of alkylanions on a metallic anode is likely. Other processes are more clearly indicated when, instead of Cd, Zn is used as a cathode. In the latter case, zinc alkyls R2Zn and RZnI are formed by cathodic reaction of RI. This allows an efficient preparation of R4M where M = Pb, Sn and R = propyl, butyl or pentyl39, in contrast to the cathodic reduction of alkyl halides which is practically limited to the methyl and ethyl groups. 

Zinc and cadmium alkyls have not been successful as stereospecific catalysts in the absence of co-catalysts, presumably because they do not complex strongly enough with the monomer and the metal-carbon bonds are too covalent. Cadmium alkyls were first reported by Furukawa and coworkers (260) to induce vinyl polymerization, but it was shown later (267, 262) that oxygen was a co-catalyst and the reactions were free radical in nature. Similar free radical results were obtained with zinc alkyls (261—263) and vinyl monomers. However, with more basic and more easily polarized monomers, such as olefin oxides and aldehydes, the zinc catalysts operate by a coordinated anionic mechanism (250). 

Frankland here aigucs tiiat if cacodyl and zinc alkyls are radicals, they should form the same number of oxides as there are states of oxidation for the free metal. However, the highest oxide predicted by this view can never be prepared. Frankland therefore proposes that these so-called radicals are, in fact, stable compounds, and correspond without further combination to the lowest oxidation state of the metals.—O.T.B.]... 

In 1958, poly(ethylene oxide)s of very high molecular weight became available. These products range in molecular weight from about 100 000 to 5 x 10 and above. Details of the techniques used to manufacture these polymers have not been disclosed, but the essential feature is the use of (generally) heterogeneous initiator systems. Effective initiators are mainly of two types, namely alkaline earth compounds (e.g., carbonates and oxides of calcium, barium and strontium) and organometallic compounds (e.g., aluminium and zinc alkyls and alkoxides, commonly with added co-catalysts). 

The polymerization kinetics were studied in detail. It appeared that the rate of reaction decreased as the concentration of complex increased. This anomalous behavior was explained in terms of the ability of all the zinc atoms in the complex to form coordination complexes with propylene oxide monomer, but only the inner methoxyls were effective in opening the oxirane ring of monomer coordinated with the central zinc atom. In support of this explanation, it is noted that neither diethylzinc alone nor ethylzinc methoxide initiate propylene oxide polymerization under the conditions described here however, both will form complexes with propylene oxide, about two methyl oxiranes per zinc. Addition of either zinc alkyl to Tsuruta Catalyst/... 

If, however, a complex initiator based on aluminum or zinc alkyls is used, a product with identical chemical constitution but entirely different physical characteristics results. The reason for this is that the individual polymer chains are produced from either one or the other of the two stereoisomers. The polymer formed from the racemic mixture of d- and /-propylene oxides is a solid thermoplastic with a crystalline melting point of about +75°C. An even more dramatic result was obtained by Vandenberg with the polymerization of 2,3-epoxybutane ... 

The lower molecular weight polyethylene oxides are viscous, water-soluble liquids or waxy solids used as surfactants, lubricants, humectants, and cosmetic and pharmaceutical formula bases. Metal oxides and organometallic initiators, such as aluminum and zinc alkyls, produce higher molecular weight polyethylene oxides. The resins are low-melting, easy-to-process solids that are soluble in a broad range of solvents. They find use as thickeners, water-soluble packaging, and latex stabilizers. 

The pathway of H/D exchange for C-n-C alkanes with involvement of Zn-alkyl species is outlined in Scheme 4 (pathway 1). Dissociative adsorption of the deuterated alkane on zinc oxide sites, which precedes the reaction of H/D exchange, leads to Zn-alkyl species and Zn-OD groups. Protonafion of the zinc-alkyl species by the vicinal acidic OH group of the zeolite with synchronous reverse transfer of the deuterium from the Zn-OD to the... 

A AlI lation. A number of methods are available for preparation of A/-alkyl and A[,A/-dialkyl derivatives of aromatic amines. Passing a mixture of aniline and methanol over a copper—zinc oxide catalyst at 250°C and 101 kPa (1 atm) reportedly gives /V-methylaniline [100-61-8] in 96% yield (1). Heating aniline with methanol under pressure or with excess methanol produces /V, /V-dimethylaniline [121 -69-7] (2,3). 

Alkyl Isoquinolines. Coal tar contains small amounts of l-methylisoquinoline [1721-93-3] 3-methylisoquinoline [1125-80-0] and 1,3-dimetliylisoquinoline [1721-94-4J. The 1- and 3-methyl groups are more reactive than others in the isoquinoline nucleus and readily oxidize with selenium dioxide to form the corresponding isoquinoline aldehydes (174). These compounds can also be obtained by the hydrolysis of the dihalomethyl group. The 1- and 3-methyhsoquinolines condense with benzaldehyde in the presence of zinc chloride or acetic anhydride to produce 1- and 3-styryhsoquinolines. Radicals formed by decarboxylation of carboxyUc acids react to produce 1-aIkyhsoquinolines. 

Halobutyl Cures. Halogenated butyls cure faster in sulfur-accelerator systems than butyl bromobutyl is generally faster than chlorobutyl. Zinc oxide-based cure systems result in C—C bonds formed by alkylation through dehydrohalogenation of the halobutyl to form a zinc chloride catalyst (94,95). Cure rate is increased by stearic acid, but there is a competitive reaction of substitution at the halogen site. Because of this, stearic acid can reduce the overall state of cure (number of cross-links). Water is a strong retarder because it forms complexes with the reactive intermediates. Amine cure may be represented as follows ... 

This was also accomplished with BaRu(0)2(OH)3. The same type of conversion, with lower yields (20-30%), has been achieved with the Gif system There are several variations. One consists of pyridine-acetic acid, with H2O2 as oxidizing agent and tris(picolinato)iron(III) as catalyst. Other Gif systems use O2 as oxidizing agent and zinc as a reductant. The selectivity of the Gif systems toward alkyl carbons is CH2 > CH > CH3, which is unusual, and shows that a simple free-radical mechanism (see p. 899) is not involved. ° Another reagent that can oxidize the CH2 of an alkane is methyl(trifluoromethyl)dioxirane, but this produces CH—OH more often than C=0 (see 14-4). ... 

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