Palustric ester

The photochemical ring opening of palustric ester (90), an example of a [l,2]-annulated cyclohexa-diene, has been achieved wherein a -1 1 photostationaiy state mixture of diene (90) and triene (91) was obtained. Upon heating for 4 h (162 °C), the photo-mixture regenerates palustric ester (90). A related interconversion was observed for a series of photochromic cyclohexadienes of the xanttenone, dibenzo-furan and acridone types, exemplified by (92) —> (93). °... 

The four main components of wood resin from most species are the resin acids, free fatty acids, combined fatty acids (esters), and unsaponifiable sterols, alcohols, terpenes, and waxes. (The resins from tropical hardwoods (e.g., Shorea spp.) can be mainly terpenoid and steroid compounds (e.g., 88, 89, 156, 157, 184, 187) and the cause of color reversion and resin spots (156, 157) (see Sect. 9.3.7.2).) As mentioned, the composition of canal and parenchyma resins differ, and in living Picea and Pinus spp. woods, levopimaric acid predominates in the canal resin over abietic, neoabietic, and palustric acids. The resin acids are the most brittle or hardest, whereas the others range between the fluid and solid state. Consequently, variations in composition will affect the plasticity or stickiness of the resultant pitch (30). Deposits at different points in a paper mill processing ther-... 

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