Glucoisosaccharinic acids

The saccharinic acids formed from hexoses have been especially examined because of the relationships of the a and /8 isomers (C-2 epi-mers). Structures of saccharinic acids derived from D-glucose are glu-cometasaccharinic acid (51), glucoisosaccharinic acid (52), and glucosaccharinic acid (53). The a- and /3- isomers of metasaccharinic acid can reversibly isomerize when exposed to base because of the labile proton at C-2. 

G. Machell and G. N. Richards, Mechanism of saccharinic acid formation. Part II. The a, /3-dicarbonyl intermediate in formation of D-glucoisosaccharinic acid, J. Chem. Soc., (1960) 1932-1944. 

Fig. 2-33. Alkaline peeling reaction of cellulose (R = cellulose chain). 1 — 2, Isomerization 2 — 3, 2,3-enediol formation 3 — 4, j3-alkoxy elimination 4 —> 5, tautomerization 5 — 6, benzilic acid rearrangement leading to glucoisosaccharinic acid.

Fig. 7 -31. Peeling and stopping reactions of polysaccharides (Sjostrom, 1977). R = polysaccharide chain and R = CH2OH (cellulose and glucomannans) or H (xylan). Cellulose and glucomannans (R = CH2OH) (1) 3-Deoxyhexonic acid end groups (metasaccharinic acid), (2) 2-C-methylglyceric acid end groups, (3) 3-deoxy-2-C-hydroxymethylpentonic acid (glucoisosaccharinic acid), (4) 2-hydroxypropanoic acid (lactic acid), and (5) 3,4-dideoxypentonic acid (2,5-dihydroxypentanoic acid). Xylan (R = H) (3) 3-Deoxy-2-C-hydroxymethyltetronic acid (xyloisosaccharinic acid), (4) 2-hydroxypropanoic acid (lactic acid), and (5) 2-hydroxybutanoic acid. 1977. TAPPI. Reprinted from Tappi 60(9), p. 152, with permission.

Large quantities of hydroxy acids as well as acetic and formic acids are formed during kraft pulping (Tables 10-3 and 7-8). Among hydroxy acids from softwood, glucoisosaccharinic acid predominates. Especially when considering that the heat value of these hydroxy acids is only 25-50% of that of kraft lignin, their recovery seems motivated, but adequate markets have not yet been established for these products. Liberation of the aliphatic acids... 

A further study of the use of the Arndt-Eistert reaction in carbohydrate chemistry examined the reactions of the diazoketone (247) (prepared from a-D-glucoisosaccharinic acid), which gave mainly the orthoester (248) and both the ( )- and (Z)-isomers (249) of a 2,3-unsaturated methyl hexonate derivative on treatment with silver oxide in methanol. The 3-C-methylene derivative (248) is a useful precursor of 4-deoxy-3-C-methyl-D-hexoses. 

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