Palustric acid

Fig. 5-5. Examples of resin acids. 1, Pimaric acid 2, sandaracopimaric acid 3, isopimaric acid 4, abietic acid 5, levopimaric acid 6, palustric acid 7, neoabietic acid 8, dehydroabietic acid.

The factors which enable the bond formation process to take precedence over the more common ring cleavage are not yet clear. For example, the photochemistry of palustric acid (14) (8-13 diene in ring C) follows a different scheme [reaction (6) ]... 

C20H23CIO2 21 -chloro-17-hydroxy-19-nor-17a-pregna-4,9-d 3124-93-4 25.00 1.1160 2 32349 C20H3002 palustric acid 1945-53-5 168.50 1.0358 2... 

Lawrence et al.1 describe a new method for the isolation of palustric acid, one of 6 isomeric acids present in rosin. The acid represents about 10% of the acidic portion of gum resin. On thermal isomerization it yields an equilibrium mixture of abietic, neoabietic, and palustric acids. 

The only method previously available for the isolation of palustric acid was by partition chromatography. The net method is based upon the precipitation of the 2,6-dimethylpiperidine salt of the resin acids from an acetone solution of pine oleoresin or rosin followed by selective crystallization of the salt from 1 1 methanol-acetone. The yield of pure palustric acid from slash gum rosin was 4%. A 10-g. portion of the amine salt was converted into the free acid by dissolving it in 350 ml. of 95% ethanol and adding, with stirring, 100 ml. of 3 Al cold H3POt Ice-water was added to the point of cloudiness and the precipitated acid was washed with water and crystallized from hot 95% ethanol. 

More than 200 diterpenes with an abietane skeleton are reported to exist naturally Numerous representatives oeeur in conifers. Selected examples include palustra-diene, also referred to as (-)-8,13-abietadiene, from the pine tree Pintds palustris, from the so-called berries of the sade tree Juniperus sabina (Cupressaceae) and other species of juniper trees, (-)-abietenol from the pine Pinus silvestris and the fir Abies sibirica, (-)-abietic aeid belonging to the resin acids of turpentine and wide-spread in conifers such as various pines Pinus), larch trees Larix) and firs Abies), as well as (+)-palustric acid from the balm and the roots of Pinus palustris, isolated from gum rosin. 

When the Diels-Alder reaction with dienophiles is used to convert these acids into novel materials, its occurrence is optimized by the concomitant isomerization process giving levopimaric acid, which is the only homologue capable of producing an adduct. The equilibrium shown in Fig. 4.7 is then displaced by the consunrqttion of levopimaric acid and the entire mixture is thus progressively consumed [5]. If, however, isomerization is minimized, this reaction can be used to isolate and quantify levopimaric acid [23]. Although the Diels-Alder reaction occurs essentially with levopimaric acid, it has been shown that in some instances it also takes place with palustric acid [24]. 

Neoabietic acid, T32.il Levopimaric acid, T32.il Palustric acid, T32.il Abietic acid, T32.il, T"33, D"4 Pimaric acid, T32.14, T"32 Isopimaric acid, T32.18 Cyathin A2, T 13.7 Isoagatholactone, T 14.2, T"39 Sandaracopimaric acid, T32.18 Trachylobanic acid, T35.6 3-Hydroxy-7-kemp-8-en-6-one, T"37.15 C20H30O3... 

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-... 

Rosin contains mainly diterpene resin acids including abietic acid (22-50%), dehydroa-bietic acid (6-30%), palustric acid (10-25%), neoabietic acid (4-20%), isopimaric acid (10-17%), and pimaric acid (4- %). Others present include dehydropimaric acid, levopi-maric acid, and sandaracopimaric acid. It also contains small amounts of diterpene alcohols and aldehydes, sterols (mainly sitosterol), and phenolic compounds. ... 

---