The method of Ikeya for the determination of volatile thiols in beer by aspiration of these compounds into mercuric acetate has been examined. Cadmium acetate has been found to be unsuitable as an absorbant for removing hydrogen sulphide since it also combines with thiols. This reagent has been replaced by aqueous zinc acetate in a separate absorption trap. The proposed modification has the advantage of enabling estimations of hydrogen sulphide and of volatile thiols to be carried out on the same sample.

No abstract

By WESLEY COCKER and D. M. SAINSBURY , 4 raceinic form of 1,2,3,4-tetrahydro-'7-hydroxy-4-isopropyl-1,6-dinieth~lnaphthalene (I; R = H, R1 = I Pri) has been shown to be identical in gross structure with an optically active form derived from copaene (11).THE structure of copaene has recently been revisedOne of its derivatives was the phenol ( I ; R = H, R1 = Pri) which has now been shown to be identical in gross structure with a synthetic specimen of a compound of this structure.and shown to be (11).Condensation of methyl o-tolyl ether with isobutyryl chloride afforded 4-methosy-3rnethylisobutyrophenone (111), which on reaction with ethyl bromoacetate and zinc gave ethyl 3-hydroxy-3-(4'-methoxy-3'-methylphenyl) -4-methylpent anoate (IV) . This was dehydrated, giving ethyl 3-(4'-rnethoxy-3'-methylphenyl)-4-methylpent-2-enoate (V;It was therefore hydrolysed with methanolic potassium hydroxide giving a mixture from which the acid (V; R = H, R1 = Pri, irz = 0) and p-(4-methoxy-3-methylphenyl)-yy-dimethylbutyrolactone (VI) were isolated by acidification. The identity of the latter was confirmed by its infrared and n.m.r. spectra.

CNIDILIDE, neocnidilide, and isocnidilide, whichWe now describe a synthesis of lactones having occur in the roots of Cnidium oficinalel the gross structure of (I) and ( 11). are 3-n-butyltetrahydrophthalides with the Reaction of ethyl pentadienoate (111)3 with configurations shown1,* in (I; R = p-H), (11; acraldehyde at 90" for 9 hr. gave a 40% yield of R = a-H) and (11; R = p-H) respectively. ethyl 2-formylcyclohex-&enoate (IV), b.p. 83"/0.3

t cis and tvans are used to describe the orientation of the 4and 9-hydrogen atoms. sy" and anti refer to the orientation of the 3and 4-hydrogen atoms. Where a double bond eliminates the necessity to refer to the ring fusion, cis and trans are used t o describe the orientation of the 3and 4-hydrogen atoms,