Titanium compounds reduction

Reduction. Triaryknethane dyes are reduced readily to leuco bases with a variety of reagents, including sodium hydrosulfite, 2inc and acid (hydrochloric, acetic), 2inc dust and ammonia, and titanous chloride in concentrated hydrochloric acid. Reduction with titanium trichloride (Knecht method) is used for rapidly assaying triaryknethane dyes. The TiCl titration is carried out to a colorless end point which is usually very sharp (see Titanium COMPOUNDS, inorganic). 

Scheme 1. Generality of the titanium mediated reductive cyclopropanation of N,N-diakylcarboxamides. More than 60 compounds have been prepared by this route.

An example in this regard is provided by the titanium-promoted reductive dimerization [3-5] pentacyclic monoketones and their monomethylated analogs, as indicated in Scheme 1. We have successfully prepared these compounds in relatively large quantities (i.e., several hundred grams). Samples have been sent to other laboratories for evaluation of their fuel properties, selected thermodynamic properties, and combustion characteristics. 

The amount of amorphous polymer, which is generally produced in small percentage (9-16%) contemporaneously with the non-atactic polymer, is independent of reaction time (see Table II). It is on the contrary closely connected with the nature of the catalytic system employed and changes, for instance, when the triethylaluminum is substituted by other metal alkyls (beryllium alkyls, propylaluminum, isobutylaluminum, etc.) 5,28). It also depends on the purity of the a-titanium trichloride, in particular increasing in the presence of other crystalline modifications of titanium trichloride [i.e. -TiCU (27)] and of titanium compounds obtained by reduction of titanium tetrachloride at low temperature with aluminum alkyls. 

The trivalent iron is hydrolyzed together with the titanium compounds, and adheres to the titanium oxide hydrate. Therefore all the Fe3+ is reduced to Fe2+ by scrap iron during dissolution of the ilmenite product, or immediately afterwards. Reoxidation of the iron during subsequent processing is prevented with Ti3 + which is obtained by reducing a small part of the Ti4+. Alternatively, reduction of Ti4+ to Ti3+ can be carried out in part of the solution under optimized conditions this... 

Table II is a summary of results obtained with soluble bis(cyclopenta-dienyl)titanium compounds as catalysts (52-56). The activity for polymerization increases in each run after a short induction period. After reaching a maximum, a continuous decrease in activity is observed as a consequence of rapid aging processes, such as alkyl exchange, hydrogen transfer, and reduction of the titanium. The average activity is 7-200 kg of PE...

Catalyst Preparation. Catalysts consisting of simple combinations of TiCl4 and A1 (alkyl) 3 have often been used to prepare poly butadiene (20, 35) or poly-isoprene (1, 21, 40, 41, 45). It has been shown by Arlman et al. (8, 9) that on combining these components, TiCL is reduced by part of the alkylaluminum compound to a brown solid compound of lower valence consisting mainly of 13-TiCl3, whereas Cooper and Rose (13) demonstrated that with an excess of alkylaluminum compound, reduction may proceed to compounds of titanium of valence 2 and even lower. 

Titanium-based reductive cyclizations of dicarbonyl compounds provide a good method for preparing heteroar-enes. Treatment of selenoester 128 with titanium tetrachloride in the presence of zinc produced the dihydroseleno-phene 129 (Equation 23) <1998CL645>. The addition of zinc proved to be crucial for this transformation. 

Dams, R., Malinowski, M., Geise, H. J. Reductive couplings with low-valent titanium compounds (McMurry reaction). An ESR investigation into the TiCl3/LiAIH4/ROH system. Transition Metal Chemistry (Dordrecht, Netherlands) 1982, 7, 37-40. 

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