Hydration, catalysts for

Traces of perchloric acid used as hydration catalyst for ring opening of nitrogenous epoxides caused precipitation of an organic perchlorate salt which was highly explosive. The concentration of acid was less than 1% by vol. 

The usage of metal sulfates as catalysts is not new. In 1901, aluminum sulfate was used as the dehydration catalyst for the formation of 2-methylpropene from 2-methyl-2-propanol (29) and, in 1923, as the hydration catalyst for the formation of ethanol from ethylene 30). 

Tsunoda, T. and Nomura, K. (2002) Process for producing 1,3-propanediol through acrolein hydration and hydrox-ypropanal hydrogenation and active hydration catalysts for use in the process. WO Patent 2002070447, PCX International Applications. 

Iron(III) bromide [10031-26-2], FeBr, is obtained by reaction of iron or inon(II) bromide with bromine at 170—200°C. The material is purified by sublimation ia a bromine atmosphere. The stmcture of inoa(III) bromide is analogous to that of inon(III) chloride. FeBr is less stable thermally than FeCl, as would be expected from the observation that Br is a stronger reductant than CF. Dissociation to inon(II) bromide and bromine is complete at ca 200°C. The hygroscopic, dark red, rhombic crystals of inon(III) bromide are readily soluble ia water, alcohol, ether, and acetic acid and are slightly soluble ia Hquid ammonia. Several hydrated species and a large number of adducts are known. Solutions of inon(III) bromide decompose to inon(II) bromide and bromine on boiling. Iron(III) bromide is used as a catalyst for the bromination of aromatic compounds. 

Barium acetate [543-80-6] Ba(C2H202)2, crystallines from an aqueous solution of acetic acid and barium carbonate or barium hydroxide. The level of hydration depends on crystallization temperature. At <24.7°C the trihydrate, density 2.02 g/mL is formed from 24.7 to 41 °C barium acetate monohydrate [5908-64-5] density 2.19 g/mL precipitates and above 41 °C the anhydrous salt, density 2.47 g/mL results. The monohydrate becomes anhydrous at 110°C. At 20°C, 76 g of the monohydrate dissolves in 100 g of water. Barium acetate is used in printing fabrics, lubricating grease, and as a catalyst for organic reactions. 

Many catalysts for the hydration of olefins in general, and of ethylene in particular, are described in the patent Hterature. Practically all of them are acidic. There has been a patent Hterature review through 1937 of the types of catalysts used (47,48) and a general review of olefin hydration (88). 

Many other acids and acidic oxides have been mentioned as catalysts for ethylene hydration (99—103) as have ion-exchange resias (104,105). 

Chitosan (Fig. 27) was deposited on sihca by precipitation. The palladium complex was shown to promote the enantioselective hydrogenation of ketones [80] with the results being highly dependent on the structure of the substrate. In the case of aromatic ketones, both yield and enantioselectiv-ity depend on the N/Pd molar ratio. Low palladium contents favored enan-tioselectivity but reduced the yield. Very high conversions were obtained with aliphatic ketones, although with modest enantioselectivities. More recently, the immobilized chitosan-Co complex was described as a catalyst for the enantioselective hydration of 1-octene [81]. Under optimal conditions, namely Co content 0.5 mmolg and 1-octene/Co molar ratio of 50, a 98% yield and 98% ee were obtained and the catalyst was reused five times without loss of activity or enantioselectivity. 

Silylation-amination of 4(lH)-quinohnone 255 with a twofold excess of dopamine hydrochloride 256 as amine and an acidic catalyst affords, on heating with excess HMDS 2 for 21 h at 145 °C and subsequent transsilylation in excess boihng methanol, 75% of the crystalline hydrate of 257 (Scheme 4.28). The silylation-amination of 2-thio-6-azauracil 258 with homoveratrylamine 259, HMDS 2, and SnCLj as catalyst for 48 h at 145 °C furnishes 63% of the diamine 260, and MesSiOSiMes 7 and Me3SiSH or Me3SiSSiMe3 601 as leaving groups. 

Several cationic palladium(II) aqua complexes, [Pd(H20)4], cis-[PdL(H20)2] (L = en, methionine methyl ester, l,5-dithiacycloocta-3-ol), and [Pd(dien)(H20)], serve as the active catalyst for the selective hydration of various nitriles to the corresponding carboxamides, e.g., CHCI2CN was hydrated to CHCl2C(0)NH2 in the presence of... 

Hydration of unactivated alkynes is an important method for functionalizing this plentiful hydrocarbon source. Therefore, a variety of metal ions have been proposed as catalysts for this reaction, and almost all of the reported additions of water to terminal alkynes follow the Markonikov rule. The hydration of l-aUcynes with Hg(II) salts in sulfuric acid [85], RuCh/aq.HCl [86, 87], K[Ru (edta-H)Cl] 2H20 [88], RhCl,.3H20/aq. HCl [89], RhCl3/NR4 [90], Zeise-type Pt(II) complexes [91-93], and NaAuCl4 [94] produced exclusively methyl ketones (Eq. 6.46). 

The hydration of propylene with sulfuric acid catalyst in high-temperature water was investigated using a flow reaction system.31 The major product is isopropanol. A biopolymer-metal complex, wool-supported palladium-iron complex (wool-Pd-Fe), has been found to be a highly active catalyst for the hydration of some alkenes to the corresponding alcohols. The yield is greatly affected by the Pd/Fe molar ratio in the wool-Pd-Fe complex catalyst and the catalyst can be reused several times without remarkable change in the catalytic activity.32... 

Si. rra(pentafluorophenyl)boron was found to be an efficient, air-stable, and water-tolerant Lewis-acid catalyst for the allylation reaction of allylsilanes with aldehydes.167 Sc(OTf)3-catalyzed allylations of hydrates of a-keto aldehydes, glyoxylates and activated aromatic aldehydes with allyltrimethylsilane in H2O-CH3CN were examined. a-Keto and a-ester homoallylic alcohols and aromatic homoallylic alcohols were obtained in good to excellent yields.168 Allylation reactions of carbonyl compounds such as aldehydes and reactive ketones using allyltrimethoxysilane in aqueous media proceeded smoothly in the presence of 5 mol% of a CdF2-terpyridine complex (Eq. 8.71).169... 

Kostic et al. reported the use of various palladium(II) aqua complexes as catalysts for the hydration and alcoholysis of nitriles,435,456 decomposition of urea to carbon dioxide and ammonia, and alcoholysis of urea to ammonia and various carbamate esters.457 Labile aqua or other solvent ligands can be displaced by a substrate. In many cases, the coordinated substrate thus becomes activated toward nucleophilic addition of water or alcohols. 

Kostic et al. recently reported the use of various palladium(II) aqua complexes as catalysts for the hydration of nitriles.456 crossrefil. 34 Reactivity of coordination These complexes, some of which are shown in Figure 36, also catalyze hydrolytic cleavage of peptides, decomposition of urea to carbon dioxide and ammonia, and alcoholysis of urea to ammonia and various carbamate esters.420-424, 427,429,456,457 Qggj-jy palladium(II) aqua complexes are versatile catalysts for hydrolytic reactions. Their catalytic properties arise from the presence of labile water or other solvent ligands which can be displaced by a substrate. In many cases the coordinated substrate becomes activated toward nucleophilic additions of water/hydroxide or alcohols. New palladium(II) complexes cis-[Pd(dtod)Cl2] and c - Pd(dtod)(sol)2]2+ contain the bidentate ligand 3,6-dithiaoctane-l,8-diol (dtod) and unidentate ligands, chloride anions, or the solvent (sol) molecules. The latter complex is an efficient catalyst for the hydration and methanolysis of nitriles, reactions shown in Equation (3) 435... 

CO3 species was formed and the X-ray structure solved. It is thought that the carbonate species forms on reaction with water, which was problematic in the selected strategy, as water was produced in the formation of the dialkyl carbonates. Other problems included compound solubility and the stability of the monoalkyl carbonate complex. Van Eldik and co-workers also carried out a detailed kinetic study of the hydration of carbon dioxide and the dehydration of bicarbonate both in the presence and absence of the zinc complex of 1,5,9-triazacyclododecane (12[ane]N3). The zinc hydroxo form is shown to catalyze the hydration reaction and only the aquo complex catalyzes the dehydration of bicarbonate. Kinetic data including second order rate constants were discussed in reference to other model systems and the enzyme carbonic anhy-drase.459 The zinc complex of the tetraamine 1,4,7,10-tetraazacyclododecane (cyclen) was also studied as a catalyst for these reactions in aqueous solution and comparison of activity suggests formation of a bidentate bicarbonate intermediate inhibits the catalytic activity. Van Eldik concludes that a unidentate bicarbonate intermediate is most likely to the active species in the enzyme carbonic anhydrase.460... 

We are applying the principles of enzyme mechanism to organometallic catalysis of the reactions of nonpolar and polar molecules for our early work using heterocyclic phosphines, please see ref. 1.(1) Here we report that whereas uncatalyzed alkyne hydration by water has a half-life measured in thousands of years, we have created improved catalysts which reduce the half-life to minutes, even at neutral pH. These data correspond to enzyme-like rate accelerations of >3.4 x 109, which is 12.8 times faster than our previously reported catalyst and 1170 times faster than the best catalyst known in the literature without a heterocyclic phosphine. In some cases, practical hydration can now be conducted at room temperature. Moreover, our improved catalysts favor anti-Markovnikov hydration over traditional Markovnikov hydration in ratios of over 1000 to 1, with aldehyde yields above 99% in many cases. In addition, we find that very active hydration catalysts can be created in situ by adding heterocyclic phosphines to otherwise inactive catalysts. The scope, limitations, and development of these reactions will be described in detail. 

When either 7 or 8 were applied as catalysts for the hydration of 1-hexyne, neither hexanal nor 2-hexanone were detected. Intriguingly, however, because we monitored the reactions carefully by H and 31P NMR spectroscopy, we realized that both 7 and 8 were converted cleanly to another species. Repeating the reactions of 7 or 8 with 1-hexyne on larger scale in the absence of added water led to isolation of metallacycles 9 and 10, which were fully identified by NMR spectroscopy, and ultimately, by X-ray diffraction. 

The hydrated complexes 266c and 265c offer the distinct advantage of stability and ease of use. Their effectiveness as catalyst precursors in the Diels-Alder reaction has been addressed (200). A comparison of the behavior of these catalysts in the presence and absence of sieves in the reaction of acryloylimide and piperylene has revealed that the hydrated catalysts are effective precursors for this reaction. The triflate-derived catalyst 266c is ineffective unless the reaction is conducted in the presence of molecular sieves, Table IV. On the other hand, hydration does not adversely impact the performance of the hexafluoroantimonate catalyst 265c. The presence of sieves has a deleterious effect on this catalyst, leading to greatly reduced reactivity for reasons that are unclear. 

The hetero-Diels-Alder reaction between a,p-unsaturatcd ketoesters and nucleophilic alkenes has been described in two concurrent and independent reports (220, 222). As with acylphosphonates, these proved to be excellent substrates for catalyst 269c. The reaction proceeds efficiently in THF at low temperatures providing the cycloadduct in >99% ee at -78°C. Indeed, the impressive selectivity exhibited under these conditions allows the reaction to be conducted at a convenient temperature of 0°C, using the hydrated catalyst 266c in the presence of molecular sieves, Eq. 181. Observed diastereoselectivities... 

Heteropoly acids such as H3PW12O40 (PW) are good catalysts for the hydration of limonene and other monoterpenes. PWs can be used as homogeneous catalysts in solution or supported on, for example, silica or MCM-41 materials. In aqueous acetic acid limonene gives, in the presence of PW, mainly a-terpineol (7) and a-terpinyl acetate (8) [17]. 

Its hydration opened the route26 to a large scale production of solvents such as n-butanol and 2-ethylhexanol (>2 million tons in 1990). Most of these processes have involved the use of metal catalysts for activation of the jr-system. The first catalysts used were mainly expensive noble or environmentally non-friendly metals, such as Rh, Pd or Ni. In this context, a number of works from academic laboratories reported in this review have been devoted to the catalytic activity of various other metals27. Their results on the selectivities of these catalyzed reactions were sometimes surprising and have not yet received consistent mechanistic interpretations. 

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