Acids Titanium isopropoxide

PA-11/poly (lactic acid)/titanium isopropoxide catalyst (0-0.1 wt%) Melt blended/failure of catalyst to promote copolymer formation over simple degradation irrespective of catalyst level and mixing time/DSC/SEM/mechanical properties/ NMR Patel et al. 2013... 

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. 

A major advantage that nonenzymic chiral catalysts might have over enzymes, then, is their potential ability to accept substrates of different structures by contrast, an enzyme will select only its substrate from a mixture. Striking examples are the chiral phosphine-rhodium catalysts, which catalyze die hydrogenation of double bonds to produce chiral amino acids (10-12), and the titanium isopropoxide-tartrate complex of Sharpless (11,13,14), which catalyzes the epoxidation of numerous allylic alcohols. Since the enantiomeric purities of the products from these reactions are exceedingly high (>90%), we might conclude... 

A similar study was made on various titanium compounds. It was found that titanium dichloride diacetate and titanium dichloride di-isopropoxide produced high amounts of crystalline polyvinylisobutylether. On the other hand, the more acidic titanium tetrachloride produced more amorphous polymers. The insoluble titanium trichloride and titanium dichloride were ineffective as polymerization catalysts. The less acidic tetraisopropyltitanate and diethyltitanium dichloride were completely ineffective as catalysts. 

Balan and Adolfsson [28] reported a direct catalytic enantioselective three-component aza Baylis-Hillman reaction between arylaldehydes, tosylamides, and Michael acceptors using the quinidine-based Hatekayama catalyst 96 [29] together with titanium isopropoxide as a Lewis acid cocatalyst (Scheme 9.18). High chemical yields and stereoselectivity ranging between 49 and 74% ee were obtained using various substituted arylaldehydes. 

In term of diversity-oriented strategies, multicomponent reactions (MCR) represent an attractive and rapid access to libraries of macrocycles inspired by biologically active natural products. Combined with Passerini and Ugi reactions, M-RCM has already shown promising synthetic potential, as illustrated by the pioneering work of Domling and coworkers [46]. Condensation of isocyanide 69 with carboxylic acid 70 in the presence of paraformaldehyde leads to bis-olefin 71, which is subsequently submitted to RCM in the presence of G1 and titanium isopropoxide to give the 22-membered macrocycle 72 (Scheme 2.27). 

With chiral ligands, the transition-metal catalyst-hydroperoxide complex yields optically active oxiranes. " One of the most significant advances in the formation of chiral epoxides from allyl alcohols has recently been reported by the Sharpless group. Using (-l-)-tartaric acid, ferf-butylhydroperoxide, and titanium isopropoxide, they were able to obtain chiral epoxides in very high enantiomeric excess. The enantiomeric epoxide can be obtained by employing (—)-tartaric acid (Eq. 33a). 

Lu et al. prepared dense ceramic fibers of PbixLa,Ti03 (PLT, x = 0-0.2) by a sol-gel method from lead acetate trihydrate, lanthanum acetate, and titanium isopropoxide in triethanolamine and acetic acid, followed by solvothermal treatment in a mixture of xylene and triethylamine at 200°C for 12 h. They reported... 

Titanium isopropoxide (a Lewis acid) induces ring opening of 2,3-epoxy alcohols and 2,3-epoxy carboxylic acids with a variety of nucleophiles under mild experimental conditions with fair to excellent C(3) regio- and stereoselectivity.The 2,3-epoxy carboxylic acids are readily available by RUO4 oxidation of the corresponding epoxy alcohols. ... 

From Isopropoxide in the Presence of Organic Acids Acetic, propanoic, or butanoic acid was added at 30 cmVmin to titanium isopropoxide with stirring at 1 1 mole ratio, and the mixture was allowed to cool to room temperature. A sample without organic acid was also studied. The mixture was slowly added to water at a Ti water molar ratio of 1 50 at 25 or 75°C. The particles were washed with water. 

Ways to increase membrane durability have been examined by various researchers across the country. Maurtiz et al. examined the use of metal-oxide metal particles to increase the properties of the membrane. A titanium isopropoxide (Figure 11.4) addition to Nation membranes generates quasi-network particles this improves membrane modulus and dimensional stability [17], In addition, the titanium matrix reduces fuel crossover and minimizes chemical degradation. Table 11.2 shows the increase in modulus along with stress and strain and stress changes after the addition of the titanium matrix [17], With a 20% load of the titanium matrix, performance criteria remain comparable. Acid functionality remains intact however, water uptake is reduced as volume inside clusters is occupied. Conductivity is reduced due to chain mobility [17],... 

Pb(Zr,Ti)03 Lead (II) acetate, titanium isopropoxide, zirconium n-propoxide Glacial acetic acid, ethylene glycol 4... 

Epoxidation of oleic and linoleic acid was readily achieved by treatment with the acetonitrile complex of hypofluorous acid (55). Phase-transfer-catalyzed biphasic epoxidation of unsaturated triglycerides was accomplished with ethylmethyldioxirane in 2-butanone (56). The enantioselective formation of an a,P-epoxy alcohol by reaction of methyl 13()S)-hydroperoxy-18 2(9Z,llfi) with titanium isopropoxide has been reported (57). An immobilized form of Candida antartica on acrylic resin (Novozyme 435) was used to catalyze the perhydrolysis and the interesterification of esters. Unsaturated alcohols were converted with an ester in the presence of hydrogen peroxide to esters of epoxidized alcohols (e.g., epoxystearylbutyrate) directly (58). Homoallyl ethers were obtained from olefinic fatty esters by the ethylaluminium-in-duced reactions with dimethyl acetals of formaldehyde, acetaldehyde, isobutyralde-hyde, and pivaldehyde (59). Reaction of 18 2(9Z, 12Z) with 50% BF3-methanol gave monomethoxy and dimethoxy derivatives (60). A bulky phosphite-modified rhodium catalyst was developed for the hydroformylation of methyl 18 1 (9Z)and 18 1(9 ), which furnished mixtures of formylstearate and diformylstearate (61). 

Guizard et al. [84,85] studied the acid-catalyzed hydrolysis and condensation of titanium alkoxides [i.e., titanium isopropoxide (TIPO) and titanium tetrabutoxide (TTBO)] in polyoxyethylene- )-octylphenyl ether/decane/water microemulsions. The nonionic surfactants used were Triton X-15 (TX-15), TX-35, and TX-45. Dynamic light scattering [85] showed that the hydrodynamic radii of droplets in the TX-35/decane/water system increased from about 2,2 nm in the absence of water to about 4 nm at water/surfactant molar ratio R = 2. The radius remained approximately constant up to about R = 4, above which phase separation occurred. The constant droplet size observed above R = 2 suggests that 2 mol HiO per mole of surfactant is needed for the hydration of the polar groups. 

Another titanium isopropoxide complex 38, supported by a monoanionic bidentate N-heterocyclic carbene (NHC)-containing alcoholate ligand, was tested in ROP of rac-LA (Scheme 6.5). Complex 38 exhibited exceptionally fast ROP catalysis at room temperature (1 min, LA Ti = 100, conv. = 60%, PDI = 1.19), but with poor chain control. All analysis suggests that catalyst 38 behaves bifunctionally with the titanium centre acting as a Lewis acid for the... 

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