Acetylation partial

An apparatus for the continuous fibrous acetylation of cellulose in benzene has been described (68,69). The process involves continuous activation, acetylation, partial saponification of the resulting triacetate, and drying of the product. 

Glycosyl-linkages were determined by GC-EIMS of the partially methylated alditol acetates. RG-II samples (2 mg) were methylated using sodium methyl sulfmyl carbanion and methyl iodide in dimethyl sulfoxide [24] followed by reduction of the uronosyl groups with lithium triethylborodeuteride (Superdeuteride , Aldrich) [23,25]. Methylated and carboxyl-reduced samples were then submitted to acid hydrolysis, NaBIlt reduction and acetylation, partially methylated alditol acetates being analysed by EIMS on two fused-silica capillary columns (DB-1 and DB-225) [20]. 

The four related compounds oxalomycin (157), neooxalomycin (158), cur-romycin A (159), and curromycin B (160) were reported in 1985 157 and 158 were isolated from a yet to be identified Streptomyces species (79, 80) and 159 and 160 from an ethidium bromide-treated strain of S. hygroscopicus (81, 82). The absolute configuration of oxalomycin (157) and neooxalomycin (158) has been determined by application of a combination of X-ray crystallography and chemical correlation to degradation products, the important derivatives being the p-bromobenzoate 161, obtained from 157 by ozonolysis-reduction, acetylation, partial hydrolysis, and reacylation with p-bromobenzoyl chloride, and the erythro acetate 162 which was obtained along with the threo compound 163 after acetylation of the ozonolysis products of 157 (79, 80). No stereochemical infor-... 

The final common intermediate for the syntheses of vitamin A and P,p-carotene (3) is the Ci4-aldehyde 23, which is obtained from p-ionone f/7) by glycidic ester synthesis. Grignard coupling of the C6-unit (Z)-19 yields the C2o-diol 24, which has the carbon skeleton of vitamin A (22). The four conjugated double bonds in the side chain are formed by selective acetylation, partial hydrogenation to give 25 [19], and acid-catalysed elimination of water results in vitamin A acetate (26) (Scheme 4) [8]. 

The relative stereochemistry of alditols can be deduced by formation of borate complexes, acetylation, partial hydrolysis to the polyol acetates, and then n.m.r. analysis. Borate complexes form preferentially in the sequence l,2-syn> 1,3-syn > 1,2-anti, 1,3-anti, and terminal diols (in staggered conformation). ... 

The partially hydrolysed product may be purified by recrystallisation from one-tliird its weight of pure benzene containing 10-20 per cent, of acetyl chloride, and washing the crystals with light petroleum (b.p. 60-80°) to which a little acetyl chloride has been added. 

Robba and Le Guen (91) have shown that 4,5-dicyanothiazole and various Grignard reagents react partially to give 4-acetyl-5-cyano-thiazoles. As previously mentioned, the cyano group in the 5-position is the least reactive. 

Partial rate factors may be used to estimate product distributions in disubstituted benzene derivatives The reactivity of a particular position in o bromotoluene for example is given by the product of the partial rate factors for the corresponding position in toluene and bromobenzene On the basis of the partial rate factor data given here for Fnedel-Crafts acylation predict the major product of the reaction of o bromotoluene with acetyl chlonde and aluminum chloride... 

By-product acetic acid is obtained chiefly from partial hydrolysis of cellulose acetate [9004-35-7]. Lesser amounts are obtained through the reaction of acetic anhydride and cellulose. Acetylation of saHcyHc acid [69-72-7] produces one mole of acetic acid per mole of product and the oxidation of allyl alcohol using peracetic acid to yield glycerol furnishes by-product acid, but the net yield is low. 

The predominant cellulose ester fiber is cellulose acetate, a partially acetylated cellulose, also called acetate or secondary acetate. It is widely used in textiles because of its attractive economics, bright color, styling versatiUty, and other favorable aesthetic properties. However, its largest commercial appHcation is as the fibrous material in cigarette filters, where its smoke removal properties and contribution to taste make it the standard for the cigarette industry. Cellulose triacetate fiber, also known as primary cellulose acetate, is an almost completely acetylated cellulose. Although it has fiber properties that are different, and in many ways better than cellulose acetate, it is of lower commercial significance primarily because of environmental considerations in fiber preparation. 

A Acetylation, O-Phosphorylation, and O-Adenylylation. A/-Acetylation, O-phosphorjiation, and O-adenyljiation provide mechanisms by which therapeutically valuable aminocyclitol antibiotics, eg, kanamycia [8063-07-8] gentamicin [1403-66-3] sisomicin [32385-11-8], streptomycia [57-92-1], neomycin, or spectinomycin are rendered either partially or completely iaactive. Thus, eg, kanamycia B [4696-78-8] (50) can be iaactivated by modification at several sites, as shown. The elucidation of these mechanisms has allowed chemical modification of the sites at which the iaactivation occurs. Several such bioactive analogues, eg, dibekacia and amikacin have been prepared and are not subject to the iaactivation hence, they inhibit those organisms against which the parent antibiotics are iaeffective (96) (see Antibacterial agents, synthetic). 

Fig. 9. Partial structural formulas and shorthand notations for principal hemiceUuloses found in wood, where the sugar units ate noted as P-D-xylopyranose (Xylp), 4-Omethyl-a-D-glucopyranosyluronic acid (GlupU), a-L-arabinofuranose (Araf), P-D-glucopyranose (Glup), P-D-mannopyranose (Manp), and P-D-galactopyranose (Galp) for (a) arabino-4-O-methylglucuronoxylan from softwood, (b) 0-acetyl-galactoglucomannan from softwood, and...

Acetates. Because of the significant interest in selective acetylation reactions of sucrose, the need for a convenient and unambiguous method of identification has been recognized (34,35). The position of an acetyl group in a partially acetylated sucrose derivative can be ascertained by comparison of its H-nmr acetyl methyl proton resonances after per-deuterioacetylation with those of the assigned octaacetate spectmm. The synthesis of partially acetylated sucroses has generally been achieved either by way of selectively protected derivatives such as trityl ethers and cychc acetals or by direct selective acetylation and deacetylation reactions. 

Cholestanone has been prepared by the oxidation of dihydro-eholesterol with chromic anhydride in acetic acid solution.1 The yield is sometimes diminished as a result of the partial acetylation of the sterol. 

The cellulose molecule is rigid and forms strong hydrogen bonds with adjacent molecules. It is thus insoluble and decomposes before softening on heating. Partial replacement of hydroxyl groups by acetyl groups has a number of effects ... 

Fig 33 Differentiation of primary (citronellol), secondary (menthol) and tertiary alcohols (linalool) by in situ prechromatographic acetylation citronellol reacts completely, menthol partially and linalool not at all. 

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