Acids Titanium chloride

It is possible to titrate two substances by the same titrant provided that the standard potentials of the substances being titrated, and their oxidation or reduction products, differ by about 0.2 V. Stepwise titration curves are obtained in the titration of mixtures or of substances having several oxidation states. Thus the titration of a solution containing Cr(VI), Fe(III) and V(V) by an acid titanium(III) chloride solution is an example of such a mixture in the first step Cr(VI) is reduced to Cr(III) and V(V) to V(IV) in the second step Fe(III) is reduced to Fe(II) in the third step V(IV) is reduced to V(III) chromium is evaluated by difference of the volumes of titrant used in the first and third steps. Another example is the titration of a mixture of Fe(II) and V(IV) sulphates with Ce(IV) sulphate in dilute sulphuric acid in the first step Fe(II) is oxidised to Fe(III) and in the second jump V(IV) is oxidised to V(V) the latter change is accelerated by heating the solution after oxidation of the Fe(II) ion is complete. The titration of a substance having several oxidation states is exemplified by the stepwise reduction by acid chromium(II) chloride of Cu(II) ion to the Cu(I) state and then to the metal. 

A similar dependence of the stereoselectivity on the solvent and reaction temperature was found with the x-oxo amides 9 derived from phenylglyoxylic acid (R = C6H5) and 2-oxopropanoic acid (R = CH3) with amine F (Table 23)15. Thus, the highest selectivity was observed under chelation-controlled conditions in the presence of the Lewis acid titanium(IV) chloride. 

As Lewis acids, titanium(IV) chloride39-377-378 or titanium(IV) isopropoxide in combination with titanium(IV) chloride can be used in stoichiometric amounts40 4l. but triphenylmelhyl perchlorate or chlorotriphenylmethane with tin(II) chloride offers a mild, catalytic alternative42 46. 

As shown in Table IV, the highest catalytic activity of metal halides used as Lewis acid for the alkylation reaction of ferrocene with 2 was observed in methylene chloride solvent. Among Lewis acids such as aluminum chloride, aluminum bromide, and Group 4 transition metal chlorides (TiCl4, ZrCU, HfCU), catalytic efficiency for the alkylation decrea.ses in the following order hafnium chloride > zirconium chloride > aluminum chloride > aluminum bromide. Titanium chloride... 

Nitric Acid/Sulfuric Acid-Titanium(III) Chloride-Sodium Nitrite-N-(l-Naphthyl)-ethylenediamine... 

The preparation of imines, enamines, nitroalkenes and N-sulfonylimines proceeds via the azeotropic removal of water from the intermediate in reactions that are normally catalyzed by p-toluenesulfonic acid, titanium(IV) chloride, or montmorillonite K 10 clay. A Dean-Stark apparatus is traditionally used which requires a large excess of aromatic hydrocarbons such as benzene or toluene for azeotropic water elimination. 

Fig. 2. Sequential extraction of Arsenic (MG-magnesium chloride, PHOS-sodium hypo phosphate, HCL-hydrocihoric acid, OX-oxalic acid, ToCEB- titanium chloride with EDTA, NIT- nitric acid).

Sodium hydride Sodium hydrosulfite Sulfur chlorides Sulfuric acid Sulfuryl chloride Tetraethyl lead Tetramethyl lead Thionyl chloride Titanium tetrachloride Toluene diisocyanate Trichlorosilane Triethylaluminum Triethylborane Triisobutylaluminum Trimethylaluminum Trimethylchlorosilane Tripropyl aluminum Vanadium tetrachloride Vinyl trichlorosilane Zirconium tetrachloride... 

Abstract The term Lewis acid catalysts generally refers to metal salts like aluminium chloride, titanium chloride and zinc chloride. Their application in asymmetric catalysis can be achieved by the addition of enantiopure ligands to these salts. However, not only metal centers can function as Lewis acids. Compounds containing carbenium, silyl or phosphonium cations display Lewis acid catalytic activity. In addition, hypervalent compounds based on phosphorus and silicon, inherit Lewis acidity. Furthermore, ionic liquids, organic salts with a melting point below 100 °C, have revealed the ability to catalyze a range of reactions either in substoichiometric amount or, if used as the reaction medium, in stoichiometric or even larger quantities. The ionic liquids can often be efficiently recovered. The catalytic activity of the ionic liquid is explained by the Lewis acidic nature of then-cations. This review covers the survey of known classes of metal-free Lewis acids and their application in catalysis. 

As noted earlier, most classical antidepressant agents consist of propylamine derivatives of tricyclic aromatic compounds. The antidepressant molecule tametraline is thus notable in that it is built on a bicyclic nucleus that directly carries the amine substituent. Reaction of 4-phenyl-l-tetralone (18) (obtainable by Friedel-Crafts cyclization of 4,4-diphenyl butyric acid) with methyl amine in the presence of titanium chloride gives the corresponding Schiff base. Reduction by means of sodium borohydride affords the secondary amine as a mixture of cis (21) and trans (20) isomers. The latter is separated to afford the more active antidepressant of the pair, tametraline (20). 

Modification of the metal itself, by alloying for corrosion resistance, or substitution of a more corrosion-resistant metal, is often worth the increased capital cost. Titanium has excellent corrosion resistance, even when not alloyed, because of its tough natural oxide film, but it is presently rather expensive for routine use (e.g., in chemical process equipment), unless the increased capital cost is a secondary consideration. Iron is almost twice as dense as titanium, which may influence the choice of metal on structural grounds, but it can be alloyed with 11% or more chromium for corrosion resistance (stainless steels, Section 16.8) or, for resistance to acid attack, with an element such as silicon or molybdenum that will give a film of an acidic oxide (SiC>2 and M0O3, the anhydrides of silicic and molybdic acids) on the metal surface. Silicon, however, tends to make steel brittle. Nevertheless, the proprietary alloys Duriron (14.5% Si, 0.95% C) and Durichlor (14.5% Si, 3% Mo) are very serviceable for chemical engineering operations involving acids. Molybdenum also confers special acid and chloride resistant properties on type 316 stainless steel. Metals that rely on oxide films for corrosion resistance should, of course, be used only in Eh conditions under which passivity can be maintained. 

The use of a Lewis acid (e.g., friethylfluoroborate, zinc chloride, stannous chloride, titanium chloride, iron(m)chloride) and other reagents (e.g., iodine, trimethylsilane, trifluoiomethane-sulfonylsilane) have also been recommended. Exhaustive lists of catalysts and conditions can be found in reviews devoted to carbohydrates [5-7], or to general organic chemistry [27,28], However, one can add the new catalyst, which has been introduced for the smooth formation of p-methoxybenzylidene acetals and p-methaxy-phenylmethyl methyl ether [29], namely 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), and has been applied very recently [30] to the synthesis of isopropylidene mixed acetals. 

Abbasi [234] has described a spectrophotometric method employing N-p-methoxyphenyl-2,-furohydroxic acid for the determination of titanium in soils. In this method, the soil sample was subjected to alkali fusion. The ash was treated with nitric acid to adjust it to pH 2.0 and filtered prior to adjustment to 10 pM with respect to hydrochloric acid. Stannous chloride (5M) was added to the filtrate, and the chromogenic reagent was dissolved in chloroform. The chloroform extract was evaluated spectrophotometrically at 385 nm against the reagent solution as blank. Approximately 61 ppm of titanium was found in a soil sample by this method. 

In this section, we probe the reactivity of titanium chloride vs. ion-radicals and molecules that represent Lewis acids or bases. 

Allyl silanes react with a wide variety of electrophiles, rather like the ones that react with silyl enol ethers, provided they are activated, usually by a Lewis acid. Titanium tetrachloride is widely used but other successful Lewis acids include boron trifluoride, aluminium chloride, and trim ethyls ilyl tri-flate. Electrophiles include the humble proton generated from acetic add. The regiocontrol is complete. No reaction is observed at the other end of the allylic system. All our examples are on the allyl silane we prepared earlier in the chapter. 

Standardization of the Titanium Chloride Solution Drain any standing titanium chloride (TiCl3) from the feed lines and buret, and refill with fresh solution. Add 3.0 g of Ferrous Ammonium Sulfate to a wide-mouth Erlenmeyer flask followed by 200 mL of water, 25 mL of 50% sulfuric acid, 25 mL of 0.1 N Potassium Dichromate Solution (by pipet), and 2 or 3 boiling chips. Boil the solution vigorously on a hot plate for 30 s to remove dissolved air, then quickly transfer the flask to the titration apparatus, securely connect the stopper assembly, and start the carbon dioxide flow and stirrer. Pass carbon dioxide over the solution for 1 min before beginning the titration. 

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