i~-i/~reo-3-Uichli,ro:icet3llii~o-~~-iiitr~~phenyl) -1,3uroparicdiol iniclo-~4-inetliyliiiercapto~1 ,:j-
'71 258 224
niido-(4-itict1iylsulfonyl)-1 ,:Ipropancdiol
2fjG
,J7.4
~)rotiucesa further hypsochromic shift 117ith the :tppearance of a "memory" of the benzene envelope. -1s would be expected, the spectra of these latter two (:O:T~:NLII~~S aii1:rc)xiniate quite closely tliose o1it:tiriecl ior thioaiiisole3 and methyl phenyl SUIfolie, respectively. However in the latter cxsc the n-i/zreo-"-dichloroacetalnido- 1 ,:l-l)i-o~)anediol portioji of the molecule quenches the Leiizene reso:i.iiic'e to a slight degree ancl only a shoulder a t N O I I I ~and a. doublet a t 266 arid 27.1 inp are now in :ippearance. The successive hypsochromic shifts icx- -SMe aiid -SOslle indicate clecreasetl resonance interaction between the riucleus aricl the p-substituen t as the origiual planarity of chloramphenicol with the p - X ( > ?grtmp plariar t c J the 3rOiii:ttic ring is destroyed. 'The spectra were tleterniitietl with :t Cary rerording instrument, slit schedule 20, dynode voltage -1, and 1-cin. quartz cells. The assistance oi U r s . \I. ISeclier is gratefully acknowledged. Fehnel and 1\1. C;artnark, 'I'HIJ JOI:RNAI., 71, 28b!r fl!, L!Ii. I'ehncl alii1 AI Cdrrnack. t h i o . , 71,2,'jI 1!11!11, .! I < . I I
The Ultraviolet-induced Isomerization of Tiglic Acid to Angelic Acid
coinbustion antl a lower acid dissociation constant than angelic acid. I t is also the less heat labile of the two isomers. Hecause of the unusual relationship between thc steric configurations and the physical properties of these isomers i t was of interest to investigate the possibility of converting tiglic acid (I) to angelic acid (11) by ultraviolet irradiation. It has been reported that 110 detectable isomerization occurred when an aqueous solution of tiglic acid was exposed to sunlight for 7.7 days.3 U'e have found, however, that irradiation of tiglic acid does effect a partial inversion to angelic acid. From the semi-liquid mixture which resulted from irradiating a 13-g. sample of powdered tiglic acid for 43 days there was obtained 8.2 g. of tiglic acid, 0.36 g. of angelic acid antl I .5g. of what appeared to be a mixture of tiglic and angelic acids. The angelic acid was isolated from the irradiated mixture by a fractional crystallization of the calcium salts. For this study, it was desirable to have suitable tlwivatives available for differentiating t i g k and angelic acids. Sone of those described is entirelv satisfactory either because of the difficulty of preparation (e.g., the anilide of angelic acid4j or because tlie meltiiig point tlifferencc is too small. The / I ~)he~~ylphenacyl csters were readily prepared iii good ?-iclds and found to possess suitable iiicltjiig 1)oi:its. Experimental
Irradiation of Tiglic Acid.-Samples
'J'iglic acid ( [ ) aiitl aiigelic acid (IIj are tlic f r i r ~ s xntl ris-iiic,tlific;itioris(.)i L'-iiicthyl-2-buiciioic acid.': . \ l t l i c ~ ~ gtiglic li :tc'i(l is usually considereti :IS ;L ci.si o r l ~ .u l c \ i r i r n r c [ A , , 48, :IS ( 1 9 0 4 ) ) s u p p n t t i n ~t h c ahnvr rontijiuralinns and * ~ l i r l Ihr rvidericr o f Siirllmroiicli a n d I>aries ( J . Chem Soc., 96, 976 iiwers and IVlsschncb ( R r r , 66, 723 (l023)), and Hey (.I ., 2331 (1928)), snme conlemporary textbooks of organir still assign the old and incorrrct U'isliccniis configuration3 ( A n n . . 2 5 0 , 224 (1889)) t o these acids, e.g., G. Wittig, "Stereochcmie." r\kadeniisci?e Veriagsgesellschaft, I.eipzig, 1931, pp. 134-135, and P. Rarrer, "Organic Chemistry." .Ith Euglish Edition, Elsevier Publ. Co.. CIV \-(irk, l
