Tetraalkyl titanate

Dialkylaminoethyl acryhc esters are readily prepared by transesterification of the corresponding dialkylaminoethanol (102,103). Catalysts include strong acids and tetraalkyl titanates for higher alkyl esters and titanates, sodium phenoxides, magnesium alkoxides, and dialkyitin oxides, as well as titanium and zirconium chelates, for the preparation of functional esters. Because of loss of catalyst activity during the reaction, incremental or continuous additions may be required to maintain an adequate reaction rate. 

The standard manufacturing method for tetraalkyl titanates, such as TYZOR TPT, or tetra- -butyi titanate, TYZOR TBT [5593-70 ] involves the addition of TiCl to an alcohol. In a series of reversible displacement reactions, the alkoxy substitution products and hydrochloric acid form as follows ... 

The reaction can be driven to the tetraalkoxide stage by addition of an amine or ammonia to scavenge the Hberated hydrochloric acid. The amine or ammonium hydrochloride that forms can be filtered from the reaction mass and the tetraalkyl titanate purified by distillation. If the reaction is mn in the starting alcohol as solvent, the chloride salts formed are in a finely divided state and difficult to filter. When the reaction is mn in the presence of an inert hydrocarbon solvent such as heptane or toluene, a much more readily filterable salt is obtained. The solution of cmde tetraalkyl titanate can be distilled to remove solvent and give a pure product (1,2). 

High purity tetraalkyl titanates can be obtained by a process whereby the Hquid organic titanate esters are subjected to partial hydrolysis to form a sohd that can be separated from the reaction mass. The remaining Hquid is distilled to give a high purity product (4). For example, tetraisopropyl titanate purified in this manner contains ... 

Mixed esters can be prepared from Cl Ti(OR)4 and a second alcohol in the presence of a base or by mixing a tetraalkoxide and the second alcohol in the desired proportions and flash-evaporating the mixed alcohols. Mixing of two pure tetraalkoxides of titanium also leads, via a rapid ester interchange reaction, to a mixture of ah. possible combinations of tetraalkyl titanates. 

The less branched, more associated tetraalkyl titanates are more slowly hydroly2ed because titanium is more fully coordinated. The hydrolysis of tetraethyl titanate has also been considered ia terms of its trimeric form ... 

Several excellent reviews discussiag the hydrolysis of tetraalkyl titanates are available (19,21—23). 

Titanoxanes can also be prepared by reaction of a tetraalkyl titanate and carboxyUc acids (25). If the ratio of carboxyUc acid to tetraalkyl titanate is 1 1, a simple polymeric titanate ester is formed. If two or more moles of acid are used per mole of tetraalkyl titanate, the resulting polymeric titanate ester contains ester carboxylate groups. 

Similar ester carboxylate group containing polymeric titanate esters are obtained by the reaction of titanoxanes with carboxyUc acids (26), by reaction of a tetraalkyl titanate with a carboxyUc acid and 1—2 moles of water (27), or by reacting a polymeric metal acylate with a higher boiling carboxyUc acid and removing the lower boiling carboxyUc acid by distillation (28). 

Titanoxanes can also be prepared by pyrolysis of tetraalkyl titanates at 200—250°C. Higher temperatures, however, can lead to thermal decomp o sition. 

Alternatively, titanoxanes can be prepared by reaction of tetraalkyl titanates with carboxyUc acid anhydrides (30) ... 

If more than one acid anhydride group per mole of tetraalkyl titanate is used, a polytitanyl acylate is formed ... 

Organic-solvent-soluble, higher molecular weight polytitanoxanes, having a proposed mdder-shaped stmcture, can be prepared by careful addition of an alcohol solution of 1.0—1.7 moles of water per mole of tetraalkyl titanate, followed by distillation of the low boiling alcohol components. Polytitanoxanes having molecular weights up to 20,000 have been prepared by this method (31). 

Reaction with Lactones. Hydroxycarboxyhc acid ester complexes of titanium are formed by reaction of a tetraalkyl titanate with a lactone, such as P-propiolactone, y-butyrolactone, or valerolactone (35). For example. 

Reactions with Acids. Oigaiiic acids form acylates when heated with tetraalkyl titanates. Best results ate obtained using only one or two moles of acid, as attempts to force the reaction with three or four moles of acid can yield polymers. 

Reactions with OC-Amino Acids. On heating two moles of an a-amino acid, such as alanine, in the presence of a tetraalkyl titanate and an alcohol, reaction that gives a 2,5-pipetazineclione and an oxytitanate occurs (36). 

Reactions with Sahcylaldehydes. Tetraalkyl titanates react in benzene with sahcylaldehyde in a 1 1 or 1 2 molar ratio to give sahcylaldehydotrialkoxy and dialkoxy products, which when heated at reflux seem to undergo a Meewein-Pomidorf reaction to give an aldehyde derived from the alcohol group on the titanate and a reduced titanate complex (37) ... 

Thermolysis. Lower tetraalkyl titanates are reasonably stable and can be distilled quickly at atmospheric pressure. Protracted heating forms condensation polymers plus, usually, alcohol and alkene. Longer or more branched chains are less stable. Thus, tetra- -pentyl titanate [10585-24-7] can be distilled at 314°C and 101.3 kPa (1 atm), whereas tetra- -hexyl titanate [7360-52-3] must be distilled at below 18.7 kPa (140 mm Hg) and tetra- -hexadecyl... 

Titanium chelates are formed from tetraalkyl titanates or haUdes and bi- or polydentate ligands. One of the functional groups is usually alcohoHc or enoHc hydroxyl, which interchanges with an alkoxy group, RO, on titanium to Hberate ROH. If the second function is hydroxyl or carboxyl, it may react similarly. Diols and polyols, a-hydroxycarboxyflc acids and oxaUc acid are all examples of this type. P-Keto esters, P-diketones, and alkanolamines are also excellent chelating ligands for titanium. 

The 1 1 molar addition products of a primary diol and a tetraaLkyl titanate, Ti(OGO)(OR)2 may react with water to give either Ti(OGO)(OH)2 or condensed products (Ti(OGO)O), which can be used as esterification catalysts (64). 

Solvent-soluble polymeric products of stmctures (1 3) can be obtained upon reaction of tetraaLkyl titanate, 2-methyl- -pentane-2,4-diol, and water in a 2 4 1 molar ratio (71). The tetraptimary glycol titanate complexes have been used as catalysts for the production of polyisocyanurates and polyoxa2ohdones (72). 

Products similar to (4) are obtained if one starts with TiCl instead of a tetraaLkyl titanate (75). These products are useful as adhesives (qv), as textile-treating agents to impart water repeUency, and as coatings and sizes for treating paper. 

Highly cross-linked polyol polytitanates can be prepared by reaction of a tetraaLkyl titanate with a polyol, such as pentaerythritol, followed by removal of the by-product alcohol (77). The isolated soHds are high activity catalysts suitable for use in the preparation of plasticizers by esterification and/or transesterification reactions. The insoluble nature of these complexes faciUtates their... 

Sohd, water-soluble a-hydroxycarboxyhc acid and oxaUc acid titanium complexes can be formed by reaction of the acid and a tetraaLkyl titanate in an inert solvent, such as acetone or heptane. The precipitated complex is filtered, rinsed with solvent, and dried to give an amorphous white soHd, which is water- and alcohol—water-soluble (81,82). 

Water-soluble, alkaline-stable ammonium or metal titanium malates and citrates can be formed by adding a tetraalkyl titanate to an aqueous solution of the ammonium or metal titanium malate or citrate (84). A typical formula is M TiO(citrate), where M is NH, Na, K, Ca, or Ba. 

Oxahc acid behaves as an a-hydroxy acid, yielding crystalline ammonium or potassium salts from either aqueous titanium(IV) solutions or tetraalkyl titanates (86). These are written as ... 

Beginning with a mixture of tetraalkyl titanates, the resultant bis-ethyl acetoacetate contains a mixture of all possible combinations of alkoxy groups, resulting in a reduction in viscosity and improved cold-storage stabiHty of the product (97). 

These mixed phosphate ester titanium complexes or their amine salts are useful as fuel additives to help maintain cleanliness of carburetors and inhibit surface corrosion. Chloride-free mixed alcohol phosphate esters can be obtained if a tetraalkyl titanate is used (101). 

Alkoxy titanium acylate derivatives coordinated with a phosphite diester (phosphonate diester) can be prepared by reaction of a tetraalkyl titanate and an equal molar amount of a carboxyUc acid, such as methacrylic acid or isostearic acid, and a phosphite or phosphonate diester, such as dibutyl hydrogen phosphite (103). These materials reduce the viscosity of a composite system, improve... 

Alkanolamine Chelates. Alkanolamine chelates, which are prepared by reaction of tetraalkyl titanates with one or more alkanolamines, are used primarily in cross-linking water-soluble polymers (qv) (see Alkanolamines) (104). The products are used in thixotropic paint emulsion paints, in hydrauhc fracturing and drilling of oil and gas wells, and in many other fields. The stmcture of... 

The 1-alkoxytitatranes can be synthesized by the reaction of equimolar amounts of tetraalkyl titanates and triethanolamine (105). X-ray crystallographic analysis of the soHd isolated from the reaction of one mole of triethanolamine and one mole of TYZOR TPT confirms the stmcture as a centrosymmetric dimer having a Ti isopropoxy nitrilotriethoxy ratio of 1 1 1. The titanium atoms have achieved a coordination number of six via a rather unsymmetrical titanium—oxygen bridge (106). 

The alkoxy titanate compounds formed by reaction of one mole of tetraalkyl titanate with one mole of a dialkanolamine are excellent esterification catalysts for the manufacture of phthalate-based plasticizers (112). If a 1 1 molar mixture of alkanolamine and water is used ia place of the alkanolamine, oligomeric titanate complexes are formed, which have high catalyst activity and can be used as thixotropic additives to paints and other aqueous coating formulations (113). 

Acylates. Titanium acylates are prepared either from TiCl or tetraalkyl titanates. Because it is difficult to obtain titanium tetraacylates, most compounds reported are either chloro- or alkoxyacylates. Under most conditions, TiCl and acetic acid give dichlorotitanium diacetate [4644-35-3]. The best method iavolves passiag preheated (136—170°C) TiCl and acetic acid simultaneously iato a heated chamber. The product separates as an HCl-free white powder (125) ... 

A2iaes form an interesting class of nitrogen donor ligands, which can react ia a 1 1 or 2 1 ratio with a tetraalkyl titanate to form complexes of stereochemical iaterest (18) (149). 

Composite Oxyalkoxides. Composite oxyalkoxides can be prepared by reaction of tetraalkyl titanates and alkaline-earth metal hydroxides. These oxyalkoxides and their derivatives can be hydroly2ed and thermally decomposed to give alkaline-earth metal titanates such as barium titanate (150). 

Barium titanate thin films can be deposited on various substances by treating with an aqueous solution containing barium salts and an alkanolamine-modifted titanate such as TYZOR TE (151). In a similar fashion, reaction of a tetraalkyl titanate with an alkah metal hydroxide, such as potassium hydroxide, gives oxyalkoxide derivatives (KTi O(OR) ), which can be further processed to give alkali metal titanate powders, films, and fibers (152—155). The fibers can be used as adsorbents for radioactive metals such as cesium, strontium, and uranium (156). 

Polymetallocarbosilanes. PolymetaHocarbosilanes having a number-average molecular weight of 700—100,000 can be prepared by reaction of polycarbosilane, /2 2 fx where R is H, or lower alkyl, with a tetraalkyl titanate, to give a mono-, di-, tri-, or tetrafunctional polymer... 

Titanium(III) alkoxides can be produced by photoreduction of the tetraalkyl titanates in the presence of a base, such as pyridine (180), and by reduction of tetraalkyl titanates by organosiUcon compounds containing Si—H groups (181). 

Esterification. Esterification of an acid and an alcohol can be catalyzed by small quantities of tetraalkyl titanates (see Esterification). Although the water that forms can hydrolyze and kiactivate the titanate, titanoxane oligomers are cleaved by carboxyHc acids to bicoordinated monomeric acylates. A simplified mechanism is illustrated ... 

For ink vehicles based on hydroxyl group containing binders such as nitrocellulose and cellulose acetate, the tetraalkyl titanates cross-link the binder prematurely, limiting the storage stabiUty of the printing ink. Chelated organic titanates such as TYZOR AA and TYZOR TE are preferred for use in these cases because they only initiate cross-linking when the ink is heated to temperatures above 80°C (503). 

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