Titanium halogenations with

Titanium reacts with all halogens at high temperatures. It reacts with fluorine at 150°C forming titanium tetrafluoride, TiF4. Reaction with chlorine occurs at 300°C giving tetrachloride TiCR. Bromine and iodine combine with the metal at 360°C forming their tetrahahdes. 

It is interesting to compare the reaetion schemes for the titanium derivatives with these proposed for eyclopentadienyliron dicarbonyls. In both cases C5H5 transfer occurs. In the former case the electron-deficient compound is the substrate, in the latter case the substrate is the electron donor. Thus ligand transfer from the titanium is a nucleophilic substitution, whereas the similar reaction for the iron derivatives can be described in terms of electrophilic substitution. The latter conclusion is in agreement with the results of Cramer (S5), w ho has suggested that CO substitution by halogens in the above-mentioned iron eomplexes follows an electrophilic mechanism 218, 219). 

Reductive 1,2-eIimination of chlorine and bromine from adducts of l-bromo-2-chlorocyclo-propene (see Section 5.2.2.1.2.5.) with oxygen and sulfur hetarenes has served in the synthesis of a number of cycloproparenes. This transformation is effected by low-valent titanium together with lithium aluminum hydride or an organolithium compound. Thus, reaction of the adduct 3 of l-bromo-2-chlorocyclopropene and 1,3-diphenylisobenzofuran with tita-nium(III) chloride and lithium aluminum hydride overnight in tetrahydrofuran led to elimination of both halogens together with extrusion of the oxygen and formation of 2,7-diphenyl-l/f-cyclopropa[ ]naphthalene (4) in 72% yield. 

Ordinary cleaners and solvents such as isopropyl alcohol and acetone are used on titanium. Halogen compoimds, such as trichlorethylene, should not be used, unless the titanium is pickled in acid after deaning. Titanium that has been straightened or formed with tools made of lead or low-melting alloy should be cleaned in nitric add. (These tool materials are not recommended for forming titanium). 

The role of antimony oxide is not entirely understood. On its own it is a rather weak fire retardant although it appears to function by all of the mechanisms listed above. It is, however, synergistic with phosphorus and halogen compounds and consequently widely used. Other oxides are sometimes used as alternatives or partial replacements for antimony oxide. These include titanium dioxide, zinc oxide and molybdenic oxide. Zinc borate has also been used. 

Applications Basic methods for the determination of halogens in polymers are fusion with sodium carbonate (followed by determination of the sodium halide), oxygen flask combustion and XRF. Crompton [21] has reported fusion with sodium bicarbonate for the determination of traces of chlorine in PE (down to 5 ppm), fusion with sodium bisulfate for the analysis of titanium, iron and aluminium in low-pressure polyolefins (at 1 ppm level), and fusion with sodium peroxide for the complexometric determination using EDTA of traces of bromine in PS (down to 100ppm). Determination of halogens in plastics by ICP-MS can be achieved using a carbonate fusion procedure, but this will result in poor recoveries for a number of elements [88]. A sodium peroxide fusion-titration procedure is capable of determining total sulfur in polymers in amounts down to 500 ppm with an accuracy of 5% [89]. 

Attempts to synthesize transition metal alkyl compounds have been continuous since 1952 when Herman and Nelson (1) reported the preparation of the compound C H6>Ti(OPri)3 in which the phenyl group was sigma bonded to the metal. This led to the synthesis by Piper and Wilkinson (2) of (jr-Cpd)2 Ti (CH3)2 in 1956 and a large number of compounds of titanium with a wide variety of ligands such as ir-Cpd, CO, pyridine, halogen, etc., all of which were inactive for polymerization. An important development was the synthesis of methyl titanium halides by Beerman and Bestian (3) and Ti(CH3)4 by Berthold and Groh (4). These compounds show weak activity for ethylene polymerization but are unstable at temperatures above — 70°C. At these temperatures polymerizations are difficult and irreproduceable and consequently the polymerization behavior of these compounds has been studied very little. In 1963 Wilke (5) described a new class of transition metal alkyl compounds—x-allyl complexes,... 

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