196 



ASCORBIC ACID 



propylidene-2-keto-L-gulonic acid (LIII). Upon autohydrolysis or treat- 

 ment with acid, LIII gives rise to 2-keto-L-gulonic acid (XXXIII). In 

 forming the acetone derivative (LII), there appears to be some advantage 

 in doing the reaction at lower temperatures than those normally used.^^ 



L-Sorbose 



XLIX 



I 

 .0— C— CHjOH 



^0-C— H 



I 

 H— C- 



■0 



CHjOH 



CO 



I 

 HO— C— H 



I 

 H— C— OH 



I 

 H— C— OH 



I 



CHsOH 



LIV 



\ 



-OC— H I„ 

 I /" 



CH,— 



LII 



COOH 

 I 

 CO 



I 



HO— C— H 



I 

 H— C— OH 



I 

 H— C— OH 



I 



CHjOH 



LV 



I 

 ,0— C— COOH 



^0-C- 



I 



H— C- 



-H 



■OC 



CHj— O 

 LIII 



COOMe 

 I 

 CO 



I 



HO— C— H 



I 

 H— C— OH 



I 

 H— C— OH 



I 



CHjOH 



LVI 



2-Kcto-L- 

 gulonic acid 



XXXIII 



CO 



I 



HO— C 



II 



HO— C 



I 



H— CO- 



I 



H— C— OH 

 I 

 CH2OH 



LVII 



A similar series of reactions has been applied in the conversion of d- 

 fructose (LIV) to 2-keto-D-gluconic acid (LV) which is readily transformed 

 into its methyl ester (LVI) and then into D-araboascorbic acid 

 (LVII).«^- ««• 8« 



Numerous references are to be found in the patent literature relating to 

 methods of making L-ascorbic acid which are fundamentally related to 

 those mentioned above. Mention may be made here, perhaps, of the pro- 

 cedure whereby the 2,3-4,6-diisopropylidene-2-ketogulonic acid is con- 

 verted directly into L-ascorbic acid by treatment with an acid catalyst, for 

 example hydrogen chloride, in a solvent or mixture of solvents in which 

 the diisopropylidene compound is soluble but in which L-ascorbic acid is 

 insoluble. Such conditions result in the crystallization of L-ascorbic acid 

 from the reaction mixture.^'"^' In another method, molten diiospropylidene- 



" I. T. Strukov and N. A. Kapylova, Farmatsiya 10, No. 3, 8 (1947) [C.A. 44, 8327 

 (1950)]. 



88 D. Heslop, E. Salt, and F. Smith, J. Chem. Soc. 1944, 225. 



89 T. Reichstein, British Pat. 446,548 (1937). 



9» R. Pasternak and G. O. Cragwell, U. S. Pat. 2,184,383 (1940). 



91 V. M. Berezovskil and L. I. Strel'chunas, Zhur. Priklad. Khim. 22, 1113 (1949) 

 [C.A. 45, 5627 (1951)]. 



92 H. W. Bassford, Jr., W. S. Harmon, and J. F. Mahoney, U. S. Pat. 2,462,251 (1949). 



