II. CHEMISTRY 185 



groups which are acetyhitecl with difhculty chsplay unusual acidic prop- 

 erties, and evidently they are enolic in character inasmuch as they undergo 

 methjiation with diazomethane.'- The methoxyl groups thus introduced 

 are etheric in nature, since they are stable to alkali.''- The two hydroxyl 

 groups which do ikot react with diazomethane are of the normal type, since 

 the dimethyl ascorbic acid, prepared with this methylating agent, can be 

 condensed with acetone to give a monoisopropylidene derivative*^- *^ and 

 a di-p-nitrohenzoate.''^ It may also be deduced that one of these normal 

 alcoholic groups that react with acetone and p-nitrobenzoyl chloride is of 

 the primary type because the dimethyl ascorbic acid can be converted into 

 a trityl compound.** The presence of a primary alcohol group in the 

 dimethyl ascorbic acid also follows from the fact that it gives formaldehyde 

 when treated with lead tetraacetate.'^' 



Ascorbic acid also shows strong selective absorption of light in the ultra- 

 violet region of the spectrum having a band at X = 2450 A. moving to 

 X = 2050 A. upon addition of alkali, thus indicating the presence of a con- 

 jugated system carrjang one or more enoliza))le hydroxyl groups.*'-^ That 

 a double liond was present in this conjugated system followed from the fact 

 that catalytic reduction of ascorbic acid adds two atoms of hydrogen, giving 

 L-idonic acid.-*' When ascorbic acid is oxidized with two atomic proportions 

 of iodine, two equivalent proportions of hydrogen are removed to give 

 dehydroascorbic acid. The latter no longer contains a conjugated sj^stem, 

 since it shows no selective alisorption band in the ultraviolet; but the main 

 structure of the molecule remains intact, for from the dehydro acid the orig- 

 inal ascorbic acid may be regenerated by reduction w'ith hydrogen 

 sulfide'-' '^ Further oxidation of the dehydro acid (II or III) with iodine 

 in alkaline solution gives oxalic acid, the latter being readily isolated as 

 its phenylhydrazine salt. Oxidation of ascorbic acid with acid permanganate 

 gives L-threonic acid (l\), recognized by its oxidation with nitric acid to 

 L-tartaric acid (V). The L-threonic acid was also identified by methylation 

 to 2,3,4-trimethyl-L-threonic acid (VI) which formed a crystalline amide.'- 



Of important structural significance was the observation that oxidation 

 of ascorbic acid w ith chlorine or iodine to give dehydroascorbic acid trans- 

 formed a strongly acidic substance into an almost neutral substance, the 

 properties of which showed that it was probably a 7-lactone.*^ This accumu- 

 lated evidence established the fact that ascorbic acid contained a double 

 bond which was located l)etween C2 and C3, a deduction previously made 



« p. Karrer, H. Saloman, K. Schopp, and R. Morf, Helv. Chiin. Acta 16, 181 (1933); 



P. Karrer, H. Saloman, R. Morf, and K. Schopp, Biochem. Z. 258, 4 (1933); P. 



Karrer, G. Schwarzenbach, and K. Schopp, Helv. Chim. Acta 16, 302 (1933). 

 « F. Micheel and K. Kraft, Hoppe-Seyler's Z. phjjsiol. Chem. 215, 215 (1933). 

 " W. N. Haworth, E. L. Hirst, F. Smith, and W. J. Wilson, /. Chem. Soc. 1937, 829. 

 « E. L. Hirst, Chemistry & Industry 52, 221 (1933). 



