The decarboxylation of acetoacetic acid CH3COCH2CO2H → CH3COCH3+CO2 and its anion have been studied in aqueous solution over a range of temperature. Although the acid decomposes approximately 50 times faster than the anion at 37�, the activation energy of the acid (23.7 kcal mole-1) is comparable with that of the anion (22.9 kcal mole-1) and the large difference in reactivity is due to an entropy effect. The significance of these results is discussed and a comparison made with other β-keto acid decarboxylations.

The reaction between dicyclohexylamine and iso-alpha acids yields a crystalline product which consists of the dicyclohexylamine salts of trans-iso-cohumulone, trans-lsohumulone and trans-Iso-adhumulone.The presence of only the trans-isomers in the crystalline product was established by proton and carbon NMR. Pure trans-iso-alpha acids can be regenerated from the salt either by treatment with acid or in situ by the use of acidic buffers during HPLC analysis. The dicyclohexylamine salts of the trans-isoalpha acids are stable for extended periods at room temperature, unlike the purified trans-iso-alpha acids, and are thus suitable for use as a standard for iso-alpha acids analysis.Key Words: Iso-alpha acids, standard, HPLC, Nuclear Mag netic Resonance. IntroductionThe analysis of iso-alpha acids in isomeriscd hop extracts and beer is complicated by their instability and the several analogues and isomeric forms which exist. The most widely used method of analysis for the iso-alpha acids measures the ultra-violet (UV) absorption of the iso-alpha acids extracted by iso-octane from acidified beer or acidified hop extract solutions. This method is not specific for iso-alpha acids and contributions from other UV-absorbing components in the solution are included in the total result, expressed as Bitter ness Units (BU)12. The bitterness units are obtained by multiplying the absorption of the iso-octane solution by SO, a factor derived from the dilution factor used and the average extinction coefficients of the iso-alpha acids, assuming that 70% of the absorption of the iso-octane solution is due to iso-alpha acids. However, a multiplication factor of 70 is used for beers bittered with isomeriscd hop extracts or isomerised hop pellets. In order to accurately quantitate the isoalpha acids, it is necessary to separate them from interfering substances, and the most suitable method available is High Performance Liquid Chromatography (HPLC). HPLC sys tems have been devised that separate both isomers and ana logues of the iso-alpha acids3-4, while other systems separate only the analogues*-6-78.