II. CIIKMISTRY 



195 



COOH 



CHOH 

 I 

 R 



XLV 



CO— CI 



I 

 CHOH 



I 

 R 



XLVI 



ON 



I 

 CO 



I 



CHOH 

 I 

 R 



XLVII 



COOH 

 I 

 CO 



I 



CHOH 



I 

 R 



XLVIII 



4. Oxidation of ketoses or certain of their carbonyl compounds. Ketoses 

 such as L-sorbose (XLIX) can be oxidized directly with nitric acid to the 

 corresponding 2-keto acid. The early experiments were carried out by warm- 

 ing L-sorbose with dilute nitric acid,®^'^° but more recently it has been 

 recommended that the use of higher concentrations of nitric acid and a 

 lower temperature^' gives an increased yield of 2-keto-L-gulonic acid. 



CHjOH 



CO 

 I 

 HO— C— H Hxo, 



COOH 

 I 

 CO 



,-i- 



H— C— OH Pt + Oa 



HO— C— H 

 I 

 CHsOH 



XLIX 



HO— C— H 



: I 



H— C-OH 

 I 

 HO— C-H 



I 

 CHjOH 



XXXIII 



COOH 

 I 

 CO 



I 



Pt -f 0; HO— C— H 



H— C— OH 

 I 

 HO— C— H 

 i 

 COOH 



L 



CO— I 



I 

 HO— C 



II 

 HO— C 



I 

 H— CO— ' 



I 

 HO— C— H 



I 



COOH 



LI 



The direct oxidation of L-sorbose to 2-keto-L-gulonic acid has also been 

 carried out in neutraP- or slightly alkaline solution^^ by catalytic oxidation 

 using a platinum catalyst. Conditions have also been so established that 

 catalytic oxidation will proceed to 2-keto-L-gulosaccharic acid (L), and 

 this in turn has been converted into L-gulosaccharoascorbic acid (6-carboxy- 

 L-ascorbic acid, LI).*' It is also reported that 2-keto-L-gulonic acid can be 

 obtained from L-sorbose by electrolytic oxidation*'* and by oxidation with 

 halooxygen compounds such as chlorites and chlorates.*^ 



^^^lat appears to be the best and certainly the most convenient method 

 of making 2-keto-L-gulonic acid (XXXIII) involves the conversion of 

 L-sorbose (XLIX) to its 2,3-4,6-diisopropylidene derivative (LII). The 

 latter, ha\^ng a free primary alcoholic group, can be oxidized with per- 

 manganate in either acid*^ or alkaline solution^' to yield 2,3-4,6-diiso- 



8" J. Overhoff and W. Huyser, U. S. Pat. 2,467,442 (1949). 



8' Dutch Pat. 59,301 (1947). 



8'- N. R. Trenner, U. S. Pat. 2,483,251 (1949). 



" K. Heyns, Ann. 558, 177 (1947). 



" Danish Pat. 68,836 (1949). 



" S. Goldschmidt, Dutch Pat. 57,143 (1946). 



8« E. Boasson, S. Goldschmidt, and A. Middlebeck, Dutch Pat. 57,142 (1946). 



