Etherification surface

A/-substituted, long-chain alkyl monomethylol cycHc ureas have also been used to waterproof cotton through etherification. Other water repellent finishes for cotton are produced by cross-linked siHcone films (56). In addition to the polymeri2ation of the phosphoms-containing polymers on cotton to impart flame retardancy and of siHcone to impart water repeUency, polyduorinated polymers have been successfuUy appHed to cotton to impart oil repeUency. Chemical attachment to the cotton is not necessary for durabUity oU repeUency occurs because of the low surface energy of the duorinated surface (57). 

Arguably the most challenging aspect for the preparation of 1 was construction of the unsymmetrically substituted sec-sec chiral bis(trifluoromethyl)benzylic ether functionality with careful control of the relative and absolute stereochemistry [21], The original chemistry route to ether intermediate 18 involved an unselective etherification of chiral alcohol 10 with racemic imidate 17 and separation of a nearly 1 1 mixture of diastereomers, as shown in Scheme 7.3. Carbon-oxygen single bond forming reactions leading directly to chiral acyclic sec-sec ethers are particularly rare since known reactions are typically nonstereospecific. While notable exceptions have surfaced [22], each method provides ethers with particular substitution patterns which are not broadly applicable. 

Etherification to produce cyanoethyolated, benzylated or allylated wood surfaces does not result in an improvement in UV resistance, but the latter two treatments have been found to improve the performance of clear coatings on the modified substrate (Kiguchi, 1990b). Kalnins (1984) methylated wood by pre-treating with concentrated aqueous... 

Kiguchi, M. (1990a). Chemical modification of wood surfaces by etherification. I. Manufacture of surface hot-melted wood by etherification. Mokuzai Gakkaishi, 36(8), 651-658. 

To increase the yield of triethoxysilane, it is necessary to eliminate the hydrogen chloride formed from the reaction zone as soon as possible. It is hardly conceivable in periodical bubble reactors with a small phase contact surface. Because it is difficult to bring large amounts of heat for HCI desorption to the reactive mixture, packed towers do not allow for a continuous process either. The most convenient apparatus for the etherification of trichlorosilane is film-type, which allows for a continuous process. 

The pioneer work in this field was carried out on polystyrene-supported acid catalysts [161]. Thereafter, several works on the use of sulfonic, strong acidic cation exchangers as acid catalysts were reported for alkylation, hydration, etherification, esterification, cleavage of ether bonds, dehydration, and aldol condensation [162,168-171], Besides, industrial applications of these materials were evaluated with reactions related to the chemistry of alkenes, that is, alkylation, isomerization, oligomerization, and acylation. [163,169], Also, Nation, an acid resin which has an acid strength equivalent to concentrated sulfuric acid, can be applied as an acid catalyst. It is used for the alkylation of aromatics with olefins in the liquid or gas phases and other reactions however, due to its low surface area, the Nation resin has relatively low catalytic activity in gas-phase reactions or liquid-phase processes where a nonpolar reactant or solvent is employed [166],... 

Kiguchi [ 10] reported that hot-melted wood surfaces treated by benzylation and allylation lost surface glossiness by weathering because of the benzyl or allyl groups induced by the etherification of the surfaces. These groups can absorb ultraviolet rays and degrade the surfaces. As a result of ESC A, the... 

Rgure 10 Etherification treatments for surface thermoplasticization of wood. 

Kiguchi [55] used ESCA to monitor surface changes in chemically modified sugi during and after exposure to UV light from 20-W UV fluorescent lamps. Chemical modification treatments included (1) methylation and reduction and (2) etherification with butylene oxide. In addition, wood samples that had been benzylated and then thermoplasticized by hot pressing were coated with... 

Amorphous Sn-, Si-, and Al-containing mixed oxides with homogeneous elemental distribution, elemental domains, and well-characterized pore architecture, including micropores and mesopores, can be prepared under controlled conditions by use of two different sol-gel processes. Sn-Si mixed oxides with low Sn content are very active and selective mild acid catalysts which are useful for esterification and etherification reactions [121]. These materials have large surface areas, and their catalytic activity and selectivity are excellent. In the esterification reaction of pentaerythritol and stearic acid catalytic activity can be correlated with surface area and decreasing tin content. The trend of decreasing tin content points to the potential importance of isolated Sn centers as active sites. 

On the basis of derivatograhpic examinations and analysis of infrared spectrums it was found that the surface ethers are generated and their formation is similar to the process of etherification ... 

Reductive Etherifications and Acetal Reductions. Additional applications of triethylsilane in the reduction of C-0 bonds also continue to surface. The Kusanov-Pames dehydrative reduction of hemiacetals and acetals with trifluorosulfonic acid/EtsSiH has proven especially valuable. Under such conditions, 4,6-O-benzyli-dene acetal glucose derivatives can be asymmetrically deprotected to 6-0-benzyl-4-hydroxy derivatives (eq 28) and thioketone derivatives can be converted to syn-2,3-bisaryl (or heteroaryl) di-hydrobenzoxanthins with excellent stereo- and chemoselectivity (eq 29). Triethylsilane is also useful in a number of related acetal reductions, including those used for the formation of C-glycosides. For example, EtsSiH reductively opens 1,3-dioxolan-4-ones to 2-alkoxy carboxylic acids when catalyzed by HCU. Furthermore, functionalized tetrahydrofurans are generated in good yield from 1,2-0-isopropylidenefuranose derivatives with boron trifluoride etherate and EtsSiH (eq 30). These same conditions lead to 1,4- or 1,5-anhydroalditols when applied to methyl furanosides or pyranosides. ... 

Polyethers (e.g. polyethylene glycol = PEG) possess the ability of nonionic substances to attach water molecules by secondary valencies. This is based on the ether groups — C — O — C — that regularly recur in their structures. The secondary valancies are produced by etherification of the monomers and can be saturated by the attachment of water. In the example given an association occurs between the O atom of the ether group of the PEG with the ion of the Me — OH surface group of the raw material particle (Fig. 1/3). The consequence is particles of like charge, which repel each other and which can thus slip readily by each other. 

The idea of generating a corrqrosite matmal based exclusively on cellulose fibres precursors arose in recent years through the concept of the partial chemical modification of the fibres, not limited this time to their surface OH groups, but, instead, to an in-depth process, itself limited to a modest thickness. In this way, a matmal could be generated in which the inner core maintains the original mechanical propaties of the urrmodified parts of the cellulose fibres, while its outer sleeve could now possess thamoplastic features given a suitable choice of chemical modification. Examples of this approach include esterification with carboxylic acids [17] and etherification with berrzyl chloride [18]. 

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