Thioacetic acid, acetylation

The preparation of the disaccharide III.53 from III.45 was achieved in a similar manner (Scheme 30). Transformation of the azide to the corresponding acetamide was carried out with thioacetic acid. Acetylation and reductive opening of the ben-zylidene unblocked the 4-OH to give III.54. Sulfation, de-esterification, and hydrogenolysis afforded the target 4-O-sulfated disaccharide III.53 in 67% yield over three steps. 

Figure 20 1 shows the structures of various derivatives of acetic acid (acetyl chlo ride acetic anhydride ethyl thioacetate ethyl acetate and acetamide) arranged m order... 

Kumar, S. and Agarwal, S.C. (1983). Biological degradation resistance of wood acetylated with thioacetic acid. International Research Group on Wood Preservation, Doc. No. IRGAVP 3223. 

Kumar, S., Dev, I. and Singh, S.P. (1991). Hygroscopicity and dimensional stabihty of wood acetylated with thioacetic acid and acetyl chloride. Journal of the Timber Development Association of India, 37(1), 25-32. 

Glycosyl halides (7a-e) were stereoselectively transformed into l,2-tra s-thio-glycoses by i) (8a-d, 8j) a two-step procedure via the pseudothiourea derivatives [9,10a] the substitution of halide by thiourea is mostly a S l-type reaction since acetylated 1-thio-a-D-mannose (8b) was obtained from acetobromoman-nose (7b) [9cj ii) (8e-i) using thiolates in protic and aprotic solvents [10], or under phase transfer catalysis conditions [11]. Another approach involved the reaction of thioacetic acid with 1,2-trans-per-O-acetylated glycoses catalyzed with zirconium chloride [12]. The 1,2-trans-peracetylated 1-thioglycoses (8e-h) were obtained in high yield. No anomerized products could be detected in these reactions (Fig. 1). 

The first syntheses of 1,2-cfs-thioglycoses (a-D-gluco- and )3-D-manno- derivatives) have been achieved by the reaction in acetone of alkyl or benzyl xanthate or potassium thioacetate with the corresponding l,2-tra s-glycosyl halides [13]. More recently, tetra-O-acetyl-l-S-acetyl-l-thio-a-D-glucopyranose (10a) (Scheme 3) has been obtained i) by reaction of -acetochloroglucose (9 a) with either potassium thioacetate in HMPA or the tetrabutylammonium salt of thio-acetic acid in toluene [14] ii) by peroxide-induced addition of thioacetic acid to the pseudo-glucal (11) [15]. 

Two species, chir (Pinus roxburghii Sargent.) size 7.5 x 2.75 x 1.25 cm3and mango (Mangifera indica Linn.) size 7.5 x 1.25 x 1.25 cm3 were studied to establish different reaction variables. Four replicates were taken for each treatment and experiments were carried out with oven-dried samples except in case of those where effect of moisture content was studied. Samples were placed in a reaction chamber and reaction was carried out under reflux conditions at 93+1 C, the boiling point of thioacetic acid. Experimental set-up for vapor phase acetylation is shown in Figure 1. 

Figure 1. Vapor phase acetylation assembly. Key 1, reaction chamber 2, wood samples 3, thioacetic acid 4, thermometer 5, water condenser 6, heating mantle 7, magnetic stirrer with heater and 8, acetic anhydride and catalysts.

Effect of Wood Moisture. It has been recommended that for acetylation with acetic anhydride, the moisture content of wood should be about 2% as excess moisture is likely to react with acetic anhydride and produce acetic acid (37). Goldstein et al. (28) observed that raising the moisture to 22% considerably slowed the reaction and each 1 percent of moisture in wood would lead to hydrolysis of about 5.7% acetic anhydride. Low moisture contents are not possible to attain in commercial treatment of wood. With ketene gas it has been possible to acetylate wood with as high as 20% moisture content with WPG about 25% (40). Thioacetic acid is only partially stable in cold water and dissociates at higher temperatures. The presence of moisture in wood could thus be critical in treatments with thioacetic acid also. Results of mango treated at 5 different moisture levels are depicted in Figure 3. As may be seen a moisture content up to 7.5% has no adverse effect on WPG. At 10% moisture content the WPG decreased to 4.6. With further increase in moisture, there was a gradual decrease in WPG attained. 

Figure 3. Effect of different moisture levels on vapor-phase acetylation of wood with thioacetic acid. Reaction time is 3 h.

D d During chemical modification of wood with thioacetic acid, the only by-product formed is H2S gas. This easily escapes from wood favoring a forward reaction. The liberated H2S is recycled to produce thioacetic acid, making the process a closed circuit one. Since there is no crosslinking or polymerization of the reagent, acetylation level can be directly gauged from the WPG. 

Limited tests on strength properties of wood acetylated with thioacetic acid showed that MOR in static bending, impact strength, maximum crushing strength in compression and density improved. It is, therefore, evident that thioacetic acid has either no adverse effect on wood components and their interlinks or the improvements affected by modification far exceed these effects, so as to be of little consequence and ending in net gains. 

Wood acetylated with thioacetic acid showed resistance to decay and termites at low WPG around 12. The available information on pattern of substitution of hydroxyls during acetylation with acetic anhydride suggests substitution of lignin hydroxyls at low acetylation levels. Resistance to micro-organisms, particularly those consuming cellulose, even at low acetylation... 

Pentane-2,4-dione and various a- alkynic ketones are simultaneously sulfurated and acetylated by thioacetic acid in the presence of sodium acetate as shown in Scheme 6 (71 AHC(13)161, p. 183). 

Thioacetic Acid.—On electrolysis this gives acetyl disulphide at the anode (Bunge 6) ... 

Deoxy-6-thio-D-a yfo-hexose forms a 1,6-anhydro compound analogous to 270. S-Acetyl-5-deoxy-l,2-0-isopropylidene-6-thio-a-D-xyZo-hexofuranose is obtained either by nucleophilic displacement on the corresponding 6-p-tolylsulfonyloxy compound with potassium thioacetate or by the photochemical addition of thioacetic acid to... 

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