Production using small amounts strong catalysts

Furfural Production Using Small Amounts of Strong Catalysts... 

Figure 5. Flow diagram of furfural production using small amounts of strong catalysts.

Gravitis et al. (2001) also reported a novel technology consisting of a two-step selective catalysis of wood and other pentosan-containing raw materials for the production of various chemicals (i.e. furfural, levoglucosan, ethanol) by using small amounts of strong catalysts. Furfural could be used for the production of dyes, plastics and fumaric acid. 

In a seminal paper in Nature in 2005, Hughes et al. [165] reported catalytic activity of supported Au nanoparticles in the epoxidation of aUcenes using small amounts of peroxide initiators. Strong solvent effects were estabhshed, yet, wide particle size distributions (5-50 nm) did not allow pinpointing any size effects. Medium-to-high selectivity toward epoxide formation was achieved by careful tuning. For example, in the case of styrene as substrate with a 1% Au/C catalyst, a selectivity toward partial oxidation products (cf. the complete oxidation product, COj) of 97% was achieved with an epoxide selectivity of about 23%. 

The distilled product can be used as a catalyst, although it usually has a relatively strong phenylphosphine odor. It is quite deliquescent, and it has not been satisfactorily recrystallized. If rigorous purification and deodorization are desired, the product is dissolved in water, a small amount of hydrogen peroxide is added to oxidize the phosphines, the solution is reneutralized, saturated with salt, and extracted with chloroform, and the product is refractionated. One cycle is normally enough. Pure product is essentially odorless, very hygroscopic, and soluble in polar solvents. 

An interesting example for the preparation of functional disiloxanes by use of organometallic techniques is the synthesis of l,3-bis(4-hydroxybutyl)t.etramethyl-disiloxane as shown in React ion Scheme VI. The first, part of the reaction is conducted at the reflux temperature of tetrahydrofuran (THF) and methyl iodide is used as catalyst. The ratio of dichlorodimethylsilane to magnesium and to THF affects the yield of the cyclic product very strongly. The disiloxane is obtained in about 70% yield by aqueous hydrolysis of the purified cyclic intermediate under mild conditions and in the presence of a small amount of hydrochloric acid. 

Gutfelt et al. (1997) have evaluated various ME formulations as reaction media for synthesis of decyl sulphonate from decylbromide and sodium sulphite. The reaction rate was fast both in water-in-oil and in bicontinuous ME based on non-ionic surfactants. A comparison was made with this reaction being conducted in a two-phase. system with quats as phase-transfer catalyst but was found to be much less efficient. However, when two other nucleophiles, NaCN and NaNOj, were used the PTC method was almost as efficient as the ME media. It seems that in the case of decyl sulphonate there is a strong ion pair formation between the product and the PTC. The rate in the ME media could be further increased by addition of a small amount of a cationic surfactant. 

Synthesis and characterization of polyols. The procedure described above yields PHBA-modifled oligomers, apparently with minimal side reactions. The odor of phenol was barely detectable in the products, indicating that little phenol had been formed. p-TSA catalyst plays a crucial role. When p-TSA was not used in the 30/70 PHBA/diol reaction only 75% of theoretical distillate was collected, and the product smelled strongly of phenol. Solvent plays an important role by helping control temperature and by facilitating removal of water. If desired, the products can be purified as described to remove small amounts of unreacted PHBA and phenol. 

Liquid-phase fluorination of methyl-substituted benzene derivatives depends strongly on the structure and concentration of the substrate, its molar ratio to xenon difluoride and the catalyst used (Scheme 32). HF-catalyzed fluorination of 1,2,4,5-tetramethylbenzene with an equimolar amount of xenon difluoride gave a small amount of 1,4-difluoro product, while reaction with two equivalents of xenon difluoride also gave the demethylated product l-fluoro-2,4,5-trimethylbenzene, which was also formed by HF-catalyzed fluorination of 1,3,4-trimethylbenzene34. In contrast, trifluoroacetic acid catalyzed fluorination is much more complex, and forms the four products l-(trifluoromethyl)-2,3,5,6-tetrametylbenzene, 2,4,5-trimethylbenzyl trifluoroacetate, l-fluoro-2,3,5,6-tetramethyl-benzene and l-(trifluoromethyl)-2,3,4,5-tetramethylbenzene, the distribution depending on the amount of trifluoroacetic acid used. Similar results were also observed in the fluorination of 1,2,3-trimethylbenzene and 1,3,5-trimethylbenzene34. 

Barium hydroxide [33, 34] is a strong base which has been employed not only in organic synthesis but also for other purposes. The commercially available octahydrate, l a(OI 1)2 8 11,/) is often used after transformation to the anhydrous form at 200-500 °C. Dehydrated Ba(OH)2 activated at 200°C is denoted C-200. It is known to be a heterogeneous basic catalyst in the Horner-Wadsworth-Emmons (HWE) reaction of triethyl phosphonoacetate (69) with aldehydes 70 to give the 3-substituted ethyl acrylates 71 (Scheme 5.13) [35]. The HWE reaction proceeds at 70 °C in 1,4-dioxane with a small amount of water. The yields of products 71 are usually better than those provided by typical basic catalysts such as NaOH or... 

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