3538
COMMUNICATIONS TO THE EDITOR
acid-catalyzed conditions which have proved effective with 17~z-hydroxy-20-ketosteroids,31but only unreacted starting material was recovered. (31) Cf.Huang-Minlon, E. Wilson, PI'. L. Wendler and M. Tishler, THIS J O U R N A L , 74, 5394 (1952); R. B. Turner, ibid., 76, 3489 (1953).
Vol. 7 8
Acknowledgment.--We should like to acknowledge the benefit of a stimulating discussion wit. Prof. Gilbert Stork of Columbia University. DETROIT,MICHIGAN
COMMUNICATIONS T O T H E EDITOR T H E RESOLUTION O F 0-ETHYL ETHYLPHOSPHONOTHIOLIC ACID
Sir: We wish to record the successful resolution of 0-ethyl ethylphosphonothiolic acid (C?Hs(C*HsO)P(O)SH).l The compound was resolved by fractional recrystallization of its quinine salt (I) from acetone-ether. The more insoluble diastereoisomeric salt (Ia) crystallized as a monohydrate : prisms, m.p. 151-153O (with loss of its water of hydration), [ a I g 6 D -96.6 + 0.S' (sobs -1.990 + 0.015O, acetone, 2-dcm., c = 1.130), equiv. wt., 492 (calcd. 497 for the monohydrate). IVhen vacuum dried over phosphorus pentoxide for three hours a t looo,I a gave rise to anhydrous product. m.p. 15S-1GOo, [ c u ] ~ ~-9'7.6 D =k 0.6' (aohs -1.0'70 0.007', acetone, 1-dcm., c = 1.096), equiv. wt., 469 (calcd. 479). The acid was separated from I a as its sodium salt in an essentially aqueous solution b y treating I a in methanol with an equivalent amount of aqueous base. T h a t the phosphorus atom maintains its tetrahedral configuration in the anion is demonstrated by the optical activity of the product recovered from the sodium salt. The acid was recovered b y the addition of an equivalent amount of dilute hydrochloric acid to the sodium salt solution and extraction of the product from the resulting solution with ether. The acid was characterized as its dicyclohexylamine salt: m.p. 139- 160.5' [a]?'D -7.11 zk 0.23' ( a n b e -0.153 =I= 0.003', methanol, 1-dcm., c = 2.150), found: C, 37.38; H , 10.00 (calcd. for C16Hd403NP: C, 5'7.2s; H , 10.22). After the removal of a mixed middle crop of I, the more soluble diastereoisomeric salt (Ib) crystallized as soft anhydrous needles: m.p. 166- 16S0, [CU]?~D -S1.'7 + 0.6' ( m o b s -1.613 f 0.012, acetone, 2-dcm., c = 0.9868); equiv. wt., 475 (calcd. 479). The dicyclohexylamine salt of this enantiomorph of the acid gave m.p. 158-160', (c~)'~D +6.85 0.23' (sobs 0.221 + 0.008", methanol, 1-dcm., c = 3.230), found: C, 57.30, H 10.02, mixed melting point with the enantiomorphic dicyclohexylamine salt, above. 163- 165'. Racemic 0ethyl ethylphosphonothiolic acid forms a dicyclohexylamine salt, m.p. 166- 16s'. This communication represents the first reported resolution of a phosphorus acid, the optical acti\ity of which is due solely to the presence of an asymmetric phosphorus atom. AIoreover, the
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( 1 ) T h e preparation o f alkylph~,sphonath,~,lic a c ~ d . \\,I1 be d e w r l b p d in a forthcoming paper h > I* XT' Hufim,inn a n d r i ! iT
