3-O-Ethyl-l-ascorbic acid

In the crystal structure of the title compound, C8H12O6, molecules are linked to each other by O—H⋯O hydrogen bonding.


3-O-Ethyl-L-ascorbic acid
Shu Jin and Xiaoqin Miao S1. Comment L-Ascorbic acid has been widely employed as an antioxidant for stabilization of nutrients. However, the low lipophilicity of it and its susceptibility to thermal and oxidative degradation restricts its field of application and has raised considerable interest in the study of ascorbic acid derivatives with increased lipophilicity and stability. The title compound is one of the lipophilic ascorbic acid derivatives, which exhibit antioxidative properties (Nihro et al.,1992) and can be used as antioxidant in food (Satoh et al., 1994). As part of our ongoing study on ascorbic acid derivatives, we report here the crystal structure of the title compound ( Fig. 1).
The geometrical parameters of the compound are normal. The C3-C4 bond distance of 1.332 (5) Å and O3-C5 bond distance of 1.215 (4) Å indicate typical C═C and O═C double bonds. Molecules are linked to each other by O-H···O hydrogen bonding (Table 1).

S2. Experimental
0.1 mol 5,6-O,O-Isopropylidene L-ascorbic acid was dissolved in 100 ml DMSO at room temperature, and 0.12 mol NaHCO 3 was added with stirring. After the addition of 0.1 mol ethyl bromide, the mixture was stirred at 313 K for 6 h.
The solvent was distilled of at 333 K under reduced pressure. The residue was dissolved in 50 ml water and extracted five times with ethyl acetate (100 ml/time). The collected organic phase was dried over Na 2 SO 4 and the solvent was evaporated at reduced pressure. 100 ml 0.1 M HCl was added to the residue, refluxed for 15 min and then the solvent was evaporated at reduced pressure. The residue was dissolved in ethyl acetate; single crystals were obtained by slow evaporation of the ethyl acetate solution.

S3. Refinement
Hydroxyl H atoms were located in a difference Fourier map and positional parameters were refined, U iso (H) = 1.5U eq (O).
Other H atoms were positioned geometrically with C-H = 0.96-0.98 Å and refined using a riding model with U iso (H) = 1.2U eq (C) or 1.5U eq (C) (for methyl). As no significant anomalous scattering effect, Friedel pairs were merged.  The molecular structure of (I), with atom labels and 30% probability displacement ellipsoids for non-H atoms. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.