CII.—Optically active dimethoxysuccinic acid and its derivatives
Journal of the Chemical Society Transactions
PREVIOUS papers on the use of silver oxide and alkyl iodide in alkylating the esters of hydroxy-acids have shown that optically active mono-and di-alkyloxysuccinic and alkyloxypropionic acids can be readily obtained from active malic, tartaric, and lactic acids by this method. The alkyloxysuccinic acids mentioned are substances of considerable interest from a stereochemical point of view. Their close relationship to the common hydroxy-acids, which have formed the subject of so much research in
... his particular field, imparts of itself a special interest to them. Their etheric character protects them from the disturbing effects which the hydroxyl group is known to exercise on optical activity, and unlike most of the acyl derivatives of the hydroxyacids, they can be examined as free acids or salts i n solution without risk of decomposition. They are endowed with much higher optical activity than the parent acids, and are therefore well adapted for the investigation of problems relating to this property. W e have already described various representatives of this class of optically active compounds, but i t is evident that if general conclusions are to be reached on the points raised by their study, more extensive series of them must be examined. The present paper deals with dimethoxysuccinic acid, its methyl, ethyl, and prop91 esters, and some of its metallic salts. Jfetlql d-l)inLetl~o~~succiIaate. The observed rotation of the methyl tartrate used in the prepara. tion of this compound was + 2.82' in the superfused state ( I 3 1, t = 20'), the corresponding value recorded by A. Pictet being 2.84O. On adding the silver oxide (3 mols.) to the solution of the tartrate (1 mol.) in methyl iodide (6 mols.), a vigorous action ensued, which had to be moderated by cooling. After heating the mixture for some time on a water-bath, filtering, and distilling off the ether which was used in washing the silver iodide, a liquid was obtained which boiled nearly constantly at 132' under 12 mm. pressure and gave a distillate which crystallised quickly in radiating prisms. The substance, after being recrystallised from ether, melted a t 51°, and gave on analysis : I. C = 4 6 * 7 0 ; H=7.12. 11. C = 4 6 * 5 5 ; H=6*98. C,H"O, requires C = 46.60 ; H = 6.80 per cent, was produced. From 41 grams of ethyl tartrate we obtained 45.5 grams of a thick, yellowish oil, which boiled at a cearly constant temperature, and gave the rotation a2O0== 95*96O (Z= 1). The methods used in the case of the methyl ester, for assuring ourselves t h a t the action was complete, not being available, the product was subjected to further treatment with silver oxide and methyl iodide. h second treatment with a third of the quantities of the reagents originally used raised the rotation to 98.66'; after a third similar treatment, the rotation found was 98-47', and after another distillation (b. p. 155' under 25 mm. pressure) 98.61'. The substance was accordingly regarded as pure. Analysis gave : C = 51.33 ; H = 7.82. C"H"O, requires C = 5P28 ; H = 7.69 per cent.