Epoxide Modifications

Epoxides can react with alcohols via acidic or basic catalysed reaction mechanisms. However, since both strong acids and bases will degrade the cell wall polymers of wood, the reaction is usually catalysed via the use of amines, which are more strongly nucleophilic than the OH group. For example, whereas the production of epoxy-phenolic resins requires temperatures in the region of 180-205 °C, reaction between epoxides and primary or secondary amines takes place at 15 °C (Turner, 1967). Reaction of epoxides with wood often involves the use of tertiary amines as catalysts (Sherman etal., 1980). The sapwood is more reactive towards epoxides than heartwood (Ahmad and Harun, 1992). 

McKelvey etal. (1959) investigated the reaction of epoxides with cellulose in alkaline conditions, reporting that alkaline cellulose reacted readily once the concentration of sodium hydroxide was sufficiently high. However, no evidence was found of reaction between cotton yarn and cellulose with a range of epoxides under a variety of reaction conditions. It was concluded that the apparent reactivity of cellulose with epoxides was primarily due to alkaline swelling of the cellulose, self-polymerization of the epoxide monomers then occurring within the interior structure of the fibres. It was also noted that the reactivity with phenol OH groups was very low (e.g. only 1 % conversion of ethylene oxide with various phenols). 

In the absence of catalyst, ring opening of the epoxide requires the presence of alkoxide, or phenoxide ions in the cell wall matrix, which are only present in exceedingly 

Sugar maple was reacted with propylene and butylene oxide (Rowell etal., 1982). The modulus of elasticity (MOE) and modulus of rupture (MOR), fibre stress at proportional limit, and maximum crushing strength all exhibited a reduction, compared to unmodified samples. Nilsson and Rowell (1983) reacted ponderosa pine with butylene oxide and exposed the wood in an unsterile soil decay test. At low WPGs, severe surface decay due to soft rot and tunnelling bacteria was observed. Such attack was reduced at 15 % WPG, 

Chen (1994) reacted wood with epicholorohydrin, using triethylamine as a catalyst. Weight loss due to decay by G. trabeum in a 12-week exposure test was less than 3 % for a WPG of 11 %. Some of this weight loss was found to be due to loss of epicholorohydrin. IR and chemical analysis data was presented, which was interpreted as indicating that cross-linking of cell wall polymers had occurred, with reference to other work where this had been found with polysaccharides. However, it is not clear from the evidence presented that such a cross-linking reaction had indeed occurred. 

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Figure 14.14 Additional hydroxyl-particle activation methods include bis-epoxide modification, tosyl activation, and tresyl activation methods. The tosyl chloride and tresyl chloride activation procedures must be done in dry organic solvent, but the coupling of an amine-containing ligand can be done in either organic solvent or aqueous buffer.

Dorn et al. have studied the fate of epifenonane in polluted water (24). When Glatt River water was fortified with epifenonane at 10 ppm and exposed to open air for four weeks, 61% of the applied dose was recovered as intact epifenonane. Volatility losses amounted to 18% of the applied 3H while metabolites contributed a mere 21%. The characterized metabolites are listed in Table VI. The two major degradation routes involved epoxide modification and benzylic oxidation. 

Figure 1. Relationship between antishrink efficiency (ASE) and chemical add-on caused by epoxide modification. Key , butylene oxide and O,...

Additives. Because of their versatility, imparted via chemical modification, the appHcations of ethyleneimine encompass the entire additive sector. The addition of PEI to PVC plastisols increases the adhesion of the coatings by selective adsorption at the substrate surface (410). PEI derivatives are also used as adhesion promoters in paper coating (411). The adducts formed from fatty alcohol epoxides and PEI are used as dispersants and emulsifiers (412). They are able to control the viscosity of dispersions, and thus faciHtate transport in pipe systems (413). Eatty acid derivatives of PEI are even able to control the viscosity of pigment dispersions (414). The high nitrogen content of PEIs has a flame-retardant effect. This property is used, in combination with phosphoms compounds, for providing wood panels (415), ceUulose (416), or polymer blends (417,418) with a flame-retardant finish. 

The third and newest modified natural mbber available is epoxidized natural mbber (ENR). This modification was actually discovered as early as 1922 (50), although the elimination of ring opening and side reactions to give a purely epoxidized material took another 50 years or so to achieve (51). The resulting polymer is a new material, with properties totally different from natural mbber, as iadicated ia Table 5. 

Other modifications of the polyamines include limited addition of alkylene oxide to yield the corresponding hydroxyalkyl derivatives (225) and cyanoethylation of DETA or TETA, usuaHy by reaction with acrylonitrile [107-13-1/, to give derivatives providing longer pot Hfe and better wetting of glass (226). Also included are ketimines, made by the reaction of EDA with acetone for example. These derivatives can also be hydrogenated, as in the case of the equimolar adducts of DETA and methyl isobutyl ketone [108-10-1] or methyl isoamyl ketone [110-12-3] (221 or used as is to provide moisture cure performance. Mannich bases prepared from a phenol, formaldehyde and a polyamine are also used, such as the hardener prepared from cresol, DETA, and formaldehyde (228). Other modifications of polyamines for use as epoxy hardeners include reaction with aldehydes (229), epoxidized fatty nitriles (230), aromatic monoisocyanates (231), or propylene sulfide [1072-43-1] (232). 

More recent work in the corticosteroid senes has involved modification of the dihydrox-yacetone side chain at the 17 position Activity is retained, for example, when the hydroxyl group at the 17 position is omitted Thus, addition of the elements of hypobromous acid to tnene 36 [8], gives the bromohydnn 37, treatment with base leads to internal elimination to form the p-epoxide 38, opening of the oxir.ine with hydrogen fluoride gives desoximetasone, 39, [9]... 

C. Karavasilis, S. Bebelis, and C.G. Vayenas, Non-Faradaic Electrochemical Modification of Catalytic Activity 10. Ethylene epoxidation on Ag deposited on stabilized Zr02 in presence of chlorine moderators, J. Catal. 160, 190-204 (1996). 

Electrochemical promotion, or non-Faradaic Electrochemical Modification of Catalytic Activity (NEMCA) came as a rather unexpected discovery in 1980 when with my student Mike Stoukides at MIT we were trying to influence in situ the rate and selectivity of ethylene epoxidation by fixing the oxygen activity on a Ag catalyst film deposited on a ceramic O2 conductor via electrical potential application between the catalyst and a counter electrode. 

Modification of the cyclohexenyl moiety has been carried out by use of the cyclohexadiene epoxides 243 and 244, which were coupled with methyl 4-amino-4-deoxy- and -4,6-dideoxy-0 -D-glucopyranoside (385a and 385b) to give the isomers (395 and 396). 

Vitamin K is the cofactor for the carboxylation of glutamate residues in the post-synthetic modification of proteins to form the unusual amino acid y-carboxygluta-mate (Gla), which chelates the calcium ion. Initially, vitamin K hydroquinone is oxidized to the epoxide (Figure 45-8), which activates a glutamate residue in the protein substrate to a carbanion, that reacts non-enzymically with carbon dioxide to form y-carboxyglut-amate. Vitamin K epoxide is reduced to the quinone by a warfarin-sensitive reductase, and the quinone is reduced to the active hydroquinone by either the same warfarin-sensitive reductase or a warfarin-insensitive... 

In this work, highly active epoxidation catalysts, which have hydrophobic surface of TS-1, were synthesized by the dry gel conversion (DGC) method. Ti-MCM-41 was synthesized first by a modifed method and the TS-l/MCM-41 catalysts were subsequently synthesized by the DGC method. The catalysts were characterized by the XRD, BET, FT-IR, and UV-VIS spectroscopy. TS-l/MCM-41 catalysts were applied to the epoxidation of 1-hexene and cyclohexene with aqueous H202to evaluate their activities for the epoxidation reaction. ... 

This is not discussed in detail since mechanisms of resistance have been carefully reviewed (Ghannoum and Rice 1999). It was pointed out that resistance has not been associated with modification of the structure. For the 1,2,4-triazoles that have been widely used, their effect is due to inhibition of the synthesis of ergosterol that is the dominant component of fungal cell membranes. Resistance is generally associated with modification of the target enzymes, for example, the epoxidation of squalene (Terbinafine) or 14a-demethylase (Fluconazole). Resistance of Candida albicans to the azole antifungal agent fluconazole demonstrated, however, the simultaneous occurrence of several types of mechanism for resistance (Perea et al. 2001) ... 

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