Uronic acid anhydride

Fehling solution. It contained anhydro-D-xylose units and 11% of it was uronic acid anhydride. D-Glucuronic acid was identified in hydrolyzates, but a test for D-galactose was negative. Hemicellulose-B (Hd —120° in 0.5% sodium hydroxide) yielded 4.8% of galactose (galactaric acid test), an undetermined amount of L-arabinose, and 64 % of uronic acid identified as galacturonic acid. ... 

Source [ ] "d in 2% NaOH Asht % Uronic acid anhydride, % Xylan, % Melhoxyl, % Total organic material accounted for, %... 

The carbohydrate analyses reported by Sundman, Saarnio and Gustafs-son for sulfate pulps are listed in Table XVII. These results were obtained by quantitative, paper chromatography on completely hydrolyzed samples. In another study,"" the uronic acid anhydride content of some wood pulps was determined. It was noted " that sulfate pulps prepared from hardwoods retain a considerable proportion of uronic acid, whereas sulfate pulps from softv oods may be entirely free from polyuronides. 

When certain softwoods are pulped by the sulfite process, the resulting pulp usually contains a considerable proportion of uronic acid anhydride which cannot be removed entirely in subsequent alkaline refining. When the sulfate process is used on softwoods, a pulp which is free from uronic acid anhydride may be obtained. This important difference between the sulfite and sulfate pulps from softwoods does not apply to hardwoods, which, when pulped by either process, still retain a considerable proportion of uronic acid anhydride in the final product. 

Computed from uronic acid assuming molecular weight of 176 for uronic acid anhydride. 

Pentoses have frequently been determined in soils by the furfural-phloro-glucinol method.But phloroglucinol also gives precipitates with a variety of other aldehydes, such as 5-methyl-2-furaldehyde, 5-(hydroxymethyl)-2-furaldehyde, and formaldehyde. Orcinol and aniline acetate are much more specific reagents, and no aldehyde present in the hydrochloric acid distillate from soils has been found to interfere in the furfural determination by the orcinol method. The orcinol and aniline acetate methods give, for various Swiss and Norwegian soils, a pentose anhydride content of 0.5 to 8.5 % of the soil organic matter (see Table III) no corrections were made for the furfural derived from uronic acids. 

Another chromium(VI) oxidant for the preparation of uronic acids is PDC [28]. The oxidation is carried out in an aprotic solvent like dimethylformamide (DMF) or dichloromethane. Acetals and sulfides are stable under these conditions [59]. Although PDC is also used for oxidation of primary alcohols to aldehydes, use of a larger excess and/or a longer reaction time will give the carboxylic acid [60]. PDC can be further activated by addition of acetic anhydride which will shorten the reaction time [61]. If tert-butanol is added to the reaction, the terf-butyl ester can be obtained directly as shown by the conversion of 15 into 16 (O Scheme 5) [62]. Presumably, the intermediate aldehyde forms a hemiacetal with terf-butanol which is then further oxidized to the ester. 

Sharpless oxidation method (RuCls, NaI04 in CHsCN-CC -water) has been shown to oxidise 2, 3 -0-isopropylidene derivatives of ribonucleosides to the uronic acid nucleosides in very high yield under mild, neutral conditions, and potassium persulfate is also effective for recycling the ruthenium reagent in such oxidations the latter procedure was used to make, inter alia, the uronic acid analogue of ACT. Oxidation of isopropylidene uridine with CrOa, PCC or PDC in the presence of acetic anhydride leads to the formation of lactone nucleoside 154 in 50% yield, and several similar cases were reported,... 

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