VOLATILE ALCOHOLS AND CARBONYL COMPOUNDS 1 15 



CHA RA CTERIZA TION 



Identification of isolated volatile alcohols and carbonyl compounds can be carried 

 out by standard procedures of qualitative organic analysis if enough material is available, 

 but usually it is not. 



There are many common spot tests and color reactions to indicate the presence of 

 alcohols, aldehydes, ketones, and esters. Detailed information on procedures may be 

 found in any text book of qualitative organic analysis. Primary and secondary alcohols 

 form xanthates by reaction with carbon disulfide and solid sodium hydroxide. The xan- 

 thates treated with molybdic acid give a violet color which is extractable into chloroform. 

 Aldehydes and ketones form insoluble red precipitates when treated with a dilute (0. 4%) 

 solution of 2, 4-dinitrophenylhydrazine in dilute sulfuric acid. Aldehydes give a pink color 

 with Schiff's reagent (reduced rosaniline hydrochloride), but ketones do not. Esters re- 

 act on heating with hydroxylamine in hot alkaline solution. When this solution is cooled 

 and made acidic, the hydroxamic acids which have been formed give a purple color with 

 ferric chloride solution. 



Characterization of a mixture can also be performed by chromatographic methods. 

 Most useful in this regard is probably gas chromatography since it has a high resolving 

 power, and the compounds involved are readily volatile. The fractions may be collected 

 separately as they pass from the column by bubbling into chilled carbon disulfide or by 

 using a liquid air trap, but the amounts obtainable are minute. They may be identified 

 to some extent by their rates of migration on columns of different materials, or enough 

 material may be obtained to permit identification by infrared spectroscopy or mass spec- 

 trometry. For details of such methods see references (5) and (6). 



Rather than attempt characterization of the volatile compounds as such, it is often 

 more convenient to form various derivatives which can be purified and identified. Some 

 of these derivatives are mentioned under "Isolation Methods". If derivatives of pure com- 

 pounds have been prepared, they may be identified by physical properties such as absorp- 

 tion spectra or melting points. More often mixtures of derivatives must be fractionated 

 and the compounds separately identified. Alcohol dinitrobenzoates have been separated 

 on columns of silicic acid-celite developed with petroleum ether/ethyl ether mixtures (7). 

 Dinitrobenzoates can also be chromatographed on paper using heptane/methanol as the 

 solvent (8). Partial identification can be made by Rf value. Dinitrophenylhydrazones of 

 the aldehydes and ketones can be separated on columns (silicic acid or bentonite) using 

 such solvents as hexane, ethyl ether, chloroform, and benzene, or mixtures of them (9). 

 They may also be separated on paper using heptane/methanol as the solvent (10). The 

 dinitrophenylhydrazones give a pale yellow spots on paper, but they may be intensified 

 by spraying with 10% sodium hydroxide. The absorption spectra of dinitrophenylhydra- 

 zones may be used to identify them by comparing spectra with those of known phenylhydra- 

 zones in neutral and alkaline solution (11). An ester can be hydrolyzed and the alcohols 

 and acid characterized separately by paper chromatography or other means (cf. Chapter 

 3). Another procedure is to form derivatives directly from the ester without previous 

 saponification. For example, by heating with 3, 5-dinitrobenzoyl chloride and sulfuric 

 acid, a dinitrobenzoate of the alcohol portion may be prepared and characterized. By 

 treating with alkaline hydroxylamine the acid portions can be converted to hydroxamic 

 acids and these chromatographed in butanol/acetic acid/water, 4:1:5. (12). The hydrox- 

 amic acid spots are detected by spraying with ferric chloride in water -saturated butanol. 



METABOLIC PATHWAYS 



There is no direct evidence regarding the routes of biosynthesis for the compounds 

 discussed in this chapter. It seems likely from their straight-chain, aliphatic structures 



