Initiator aluminium compounds

In Experiments C7 and C9, the initiator solutions remained clear and colourless throughout the addition of isobutylene. At the end of the experiments the solutions were hydrolysed, and immediately the cloudy precipitate of Al(OH)3 was observed. This showed that under the conditions of the Experiment the initiator solution had not been hydrolysed and that the aluminium was still there, i.e., it had not been distilled out of the conductivity cell as a volatile organo-aluminium compound. 

Another general type of mechanism has been proposed for the reaction of a-haloalkyl aluminium compounds with olefins (Hoberg, 1962). This involves initial addition of the organometallic compound across the double bond followed by a y-elimination (equation 18). The evidence... 

Lithium aluminates. The compounds Li0H-2Al(0H)3-mH20 and LiCl-2Al(0H)3-mH20 (here m = 0.5 1.0 2.0) are easily synthesized under very low mechanical loading (blade mixer) in stoichiometric Al(0H)3+Li0H H20 and Al(0H)3+LiCl H20 mixtures [1,2]. It was stated that the dispersion of the initial aluminium hydroxide strongly influenced on the kinetics of mechanochemical interaction. The interaction rate increases linearly with the specific surface of the initial hydroxide. Fig. 6.1 shows the data on reactivity of initial hydroxide with different specific surface area (6 and 2 mVg, respectively). 

As in the case of the zinc catalysts, active catalysts are formed by reaction of alkyl aluminium compounds with water. It is generally felt that since aluminium compounds are usually fairly strong Lewis acids, the catalysts also are somewhat more acidic in nature. Thus a coordinate cationic mechanism is generally favoured for these polymerizations. In contrast, a more anionic coordinate mechanism is usually suggested for the zinc catalysts. In fact, as will be seen in the discussion of the higher cyclic ethers, some of these catalysts are distinctly able to initiate true cationic polymerizations. However, the catalysts under discussion here as applied to epoxides are clearly considered to be coordinate. 

Products of propylene dimerization contain 74 wt.17o methylpentene, 24% n-hexene and 2% 2,3-dimethylbutene. The composition of products depends neither on the type of nickel and aluminium compounds nor the solvent used. This implies that active sites of nickel GCS have similar properties which do not depend on the structure and composition of initial components of catalytic systems. 

This is followed in fast subsequent steps by elimination of nitrogen and polymerization. Aluminium compounds usually behave similarly. At low temperatures, however, dialkylaluminium halides and diazomethane give, initially, dialkylhalomethylaluminium derivatives, which are stabilized as adducts with ether. 

Alternatively, polymerization of 3,3-bis(chloromethyl)oxacyclobutane may be effected by aluminium compounds such as alkoxides, amalgam and hydride at elevated temperatures (150—200°C). The mode of operation of these initiators is unknown they are usually associated with anionic reactions whereas the polymerization of cyclic ethers (other than epoxides) generally involves homogeneous cationic mechanisms. It may be that at high temperatures either the monomer is activated and anionic polymerization can occur or there is reaction between the initiator and monomer to form cationic species. 

Both boron and aluminium chlorides can be prepared by the direct combination of the elements. Boron trichloride can also be prepared by passing chlorine gas over a strongly heated mixture of boron trioxide and carbon. Like boron trifluoride, this is a covalent compound and a gas at ordinary temperature and pressure (boiling point 285 K). It reacts vigorously with water, the mechanism probably involving initial co-ordination of a water molecule (p, 152). and hydrochloric acid is obtained ... 

The Stephen s method allows the reduction of nitriles by stannous chloride in acid medium. If the amine chlorhydrate initially formed is hydrolyzed, the corresponding aldehyde is obtained (37, 91). Harington and Moggridge (37) have reduced 4-methyl-5-cyanothiazole by this method (Scheme 23). However, Robba and Le Guen (91) did not obtain the expected products with 4.5-dicyanothiazole and 2-methyl-4,5-dicyanothiazole. These compounds have been reduced with diisobutyl-aluminium hydride with very low yields (3 to 6%) (Scheme 24). In other conditions the reaction gives a thiazole nitrile aldehyde with the same yield as that of the dialdehyde. 

Since sulphones 204 are easily available compounds one would expect that they could be used as starting materials for the preparation of sulphoxides via the selective removal of one oxygen atom from the sulphonyl group (equation 112). Up to now, there is only one example reported of a direct reduction of a sulphone to a sulphoxide. The bicyclic dideuterio sulphone 205 after 24 h treatment with three-fold excess of diisobutyl aluminium hydride in boiling dichloromethane gave the corresponding sulphoxide 206 in 36% yield (equation 113). A two-step procedure for the selective reduction of sulphones to sulphoxides, which involves an initial reaction of sulphone 204 with aryldiazonium tetrafluoroborate 207 to form aryloxysulphoxonium salt 208 and its subsequent reduction (equation 114), was alluded to by Shimagaki and coworkers and... 

Many metal oxo-compounds (nitrates, oxides and particularly sulfates) and sulfides are reduced violently or explosively (i.e. undergo thermite reaction) on heating an intimate mixture with aluminium powder to a suitably high temperature to initiate the reaction. Contact of massive aluminium with molten salts may give explosions [1], Application of sodium carbonate to molten (red hot) aluminium caused an explosion [2]. 

For our idea that initiation is due to the cations present in the initiator solution, there is some very relevant evidence, and once again it has been available for many years although its import was not appreciated. This evidence is the ZAV effect [4], i.e., the antibatic correlation between the conductivity of an initiator solution (containing aluminium chloride and an oxygen compound, e.g., ethanol) and the molecular weight of the polymer resulting from its addition to an isobutene solution [19]. The now evident conclusion... 

Subsequently, Marek and Chmelir used a closely related set of ideas to explain their findings concerning two-component initiator systems, the most typical of which consists of aluminium bromide and titanium tetrachloride. In the presence of both these compounds the polymerisation of isobutene in heptane is much faster than when either of them is... 

Solid lithium aluminium hydride can be solublized in non-polar organic solvents with benzyltriethylammonium chloride. Initially, the catalytic effect of the lithium cation in the reduction of carbonyl compounds was emphasized [l-3], but this has since been refuted. A more recent evaluation of the use of quaternary ammonium aluminium hydrides shows that the purity of the lithium aluminium hydride and the dryness of the solvent are critical, but it has also been noted that trace amounts of water in the solid liquid system are beneficial to the reaction [4]. The quaternary ammonium aluminium hydrides have greater hydrolytic stability than the lithium salt the tetramethylammonium aluminium hydride is hydrolysed slowly in dilute aqueous acid and more lipophilic ammonium salts are more stable [4, 5]. 

Electrolytic reduction of H SO /HjSeO mixtures using aluminium electrodes results in the formation of a sulfur-selenium coating at the elwtrode Irradiation of a solution of SCg in carbon disulfide by sunhght for 1-2 hours at 20 °C results in the formation of various cyclic selenium sulfides The formation of Se Sg compounds is also initiated by refluxing the above solution . ... 

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