Terpenes/terpenoids epoxidation

In a later study, the aroma constituents of a Bavarian (Pilsener) beer brewed in Hallertau, near Munich, which possessed a desirable fine hop aroma, was examined [58]. Neither the terpenes and sesquiterpenes nor the methyl esters characterized in hop oil were detected but fraction IV (Table 13.6), which contained terpenoids and sesquiterpenoids, possessed an intensive pleasant hoppy odour. Noteworthy amongst the identified constituents are the cyclic ethers (80)-(86) first found in Japanese hops, the flowery notes of which contribute to hop aroma, and the sesquiterpenoids derived from humulene such as humulene epoxide I, humulene epoxide II, humulol, and humulenol II. Similar results were found with American beers [60, 86]. Humuladienone (79)... 

The primary aromatic substances in beer are derived from raw materials (barley or hops) that confer the beer s typical odour and taste. Bitter acids of hops have a bitter taste (see Section 8.3.5.1.3), but hop cones also contain 0.3-1% m/m of terpenoids (60-80% of hop essential oil), which have a considerable influence on the smell of beer. The main components of aromatic hop oils are sesquiterpenic hydrocarbons in which a-humulene, P-caryophyllene and famesene dominate. The major monoter-penic hydrocarbon is myrcene. For example, the essential oil content of fine aromatic varieties, such as Saaz, is 0.8% m/m, of which 23% is myrcene, 20.5% a-humulene, 14% famesene 6% and P-caryophyUene. Significant components of the hop aroma in beer are mainly isomeric terpenoid monoepoxides resulting from autoxidation and diepoxides of a-humulene and fS-caryophyUene, but also other terpenoids. Important components of hops odour are also various alcohols (such as geraniol and hnalool), esters (ethyl 2-methylpropanoate, methyl 2-methylbutanoate, propyl 2-methylbutanoate and esters of terpenic alcohols, such as geranyl isobutanoate), hydrocarbons, aldehydes and ketones formed by oxidation of fatty acids, such as (3E,5Z)-undeca-l,3,5-triene, (Z)-hex-3-enal, nonanal, (Z)-octa-l,5-dien-3-one, their epoxides, such as ( )-4,5-epoxydec-2-enal and sulfur compounds. Other important components of hops are so-called polyphenols (condensed tannins) that influence the beer s taste and have antioxidant effects. Less important compounds are waxes and other hpids. Hop products, such as powder, pellets and extracts (by extraction with carbon... 

By far, the most important use of a-pinene is as a feedstock for production of other terpenoids and a wide variety of fragrance ingredients. Some of the more important conversions are shown in Fig. 8.8. a-Pinene undergoes thermal isomerization to ocimene and alloocimene, acid-catalyzed isomerization to camphene, hydration to pine oil/terpineol, and polymerization to terpene resins. Its epoxide is a useful intermediate and hydrogenation with subsequent oxidation leads on to the rose alcohols linalool, nerol, and geraniol. 

The dimers of isoprene can be transformed into a great number of terpenoids. For instance, terpene alcohols can be formed by hydrobora-tion [30, 114, 115] and epoxidation [116] reactions. Also the reaction with sulphur dioxide yielding sulfones [117, 118] has been studied. Ploner described the reaction of the 2,7-dimethyl-l,3,7-octatriene with alcohols such as methanol or ethanol [119] yielding terpene ethers which can be used as frangrancies. As catalyst, n H2O or H2lrCl6 proved to be... 

A mixture of hydrocarbons can be separated by three selective adsorbents molecular sieves which retain the n-paraffins, mercuric perchlorate which adsorbs the unsaturated compounds, and a stationary liquid phase which retains the aromatic hydrocarbons. Boric acid on a stationary phase such as Chromosorb P is used for the removal of alcohols from a mixture of organic compounds, the products are nonvolatile esters. A similar technique was used for removal of terpene alcohols from a mixture of terpenoids. Acids can be adsorbed on potassium hydroxide deposited on quartz powder. This technique was found to be suitable for the analysis of compounds having active hydrogens such as fluorene, indene, carbazole, indole, and pyrrole as well as steroids such as estrogens and ketosteroids. o-Dianisidine quantitatively subtracts aldehydes, ketones, and epoxides, and phosphoric acid subtracts epoxides. 

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