92 



SOME MISCELLANEOUS UNSAPONIFIABLE LIPIDS 



Long-chain acetylenic ketones are also found in several plants and are apparently 



less toxic than the alcohols. Two examples follow: q 



II 

 CHgC^C - C^^C - C^CCH = CH CH2CH2CCH2CH3 



artemisia ketone (Artemisia vulgaris) 



O 



II 

 CH3CH = CH - C^C - C^CCH = CHCH = CHCH2CH2 CCH2CH2CH3 



oenanthetone (Oenanthe crocata) 



Unfortunately the name "artemisia ketone" has also been given to a terpenoid from the 

 same plant (cf. Chap. 8). 



All of these long-chain compounds show physical properties similar to the fatty 

 acids but are less polar and less soluble in the common lipid solvents. The C24 alcohol 

 is soluble in benzene and chloroform at room temperature, but the longer chain alcohols 

 and ketones dissolve in these solvents only when hot and then only to a limited degree. 

 The aliphatic hydrocarbons may be dissolved in such solvents as petroleum ether or car- 

 bon disulfide. 



Isolation of these compounds is usually carried out by solvent extraction, steam 

 distillation or fractional distillation at low pressures. Heating operations should, however, 

 be avoided in isolation of the highly unsaturated, acetylenic compounds which are often 

 very unstable. The formation of urea adducts is a characteristic property of compounds 

 with long, aliphatic carbon chains and may be used to separate them from other compounds 

 (e. g. sterols) with similar solubility. To some extent this method may also be used for 

 the separation of different classes of aliphatic compounds since they differ in the ease 

 with which the adducts are formed and decompose. Completely saturated hydrocarbons 

 react most readily and form the most stable complexes whereas the conjugated acetylenic 

 compounds may show practically no tendency to complex formation. Oxygenated deriva- 

 tives react less readily than corresponding hydrocarbons. Urea inclusion methods are 

 also discussed in Chapters 5 and 8 where methods are described in more detail and refer- 

 ences given. Final purification is effectively carried out by adsorption chromatography on 

 alumina using such solvents as petroleum ether or benzene. Since these compounds are 

 not colored or fluorescent, bands of them on a column may be detected by using alumina 

 impregnated with morin and observing quenching bands in ultraviolet light (8), or fractions 

 may be collected arbitrarily and each one analyzed. 



Characterization of these long-chain aliphatic compounds is made difficult by their 

 low reactivity. Even the alcohols and ketones react only slowly with usual hydroxyl and 

 carbonyl reagents. A method which combines identification of the components with a par- 

 tial separation was developed by Chibnall et al. (9). In this procedure an unsaponifiable 

 lipid mixture is heated with phthalic anhydride in pyridine to form acid phthalates of the 

 alcohols. Esters of the primary alcohols are precipitated by pouring the reaction mixture 

 into dilute hydrochloric acid and, after removal of excess reagents, are converted to sodi- 

 um salts which are insoluble in water. The original primary alcohols may be regenerated 

 by saponification. After removal of the sodium salts, excess pyridine, and phthalic anhy- 

 dride, any residue (which would contain hydrocarbons, ketones and sodium salts of the 

 secondary hydrogen phthalates) is dissolved in ether and crystallized from boiling alcohol. 

 Ketones and hydrocarbons separate out. Sodium salts of the secondary alcohol phthalates 

 remain dissolved in alcohol but may be precipitated by adding benzene and then crystallized 

 from ethanol-benzene (4: 1). Ketones may be separated from hydrocarbons by reacting them 

 with hydroxy famine to form oximes which are more soluble than the hydrocarbons in ether - 

 acetone. 



