The Separation of Some Terpenoid Compounds by Gas–liquid Chromatography

Abstract

A study has been made of the degree of separation of mixtures of some terpene hydrocarbons, some of their oxygenated derivatives, two sesquiterpene alcohols, and three monophenols 011 a variety of colulnns. Temperature and sample size affected the degree of separation and the solid support Chromosorb \V, a calcined diatomaceous earth, was found to combine the advantages of Celite and C-22 firebrick without causing decomposition of the sample a t higher temperatures. When Craig polyesters were used as liquid phases, separations equal to those obtained on polyethylene glycol were realized with the added advantage that these produced columns which are stable a t 190 to 220' C. Consequently, sesquiterpene alcohols and ~~~o~~o p h e n o l s were also separated successfully. Another useful liquid phase for both low and high temperatures was found in a meta-linked polyphenyl ether. Squalene was found to be a n efficient liquid phase for the separation of terpene hydrocarbons a t 130' C and lower. The possible application of the present findings for preparative work is discussed. INTRODUCTIONA general method for the separation of small amounts of closely related terpene hydrocarbons, some of their oxygenated derivatives as well as some higher boiling sesquiterpene alcohols and monophenols, was required in this laboratory. Sucll mixtures often have a narrow range of boiling points and separation by fractional distillation not only requires large amounts, but frequently fails to produce pure components. Gas-liquid chrornatography (GLC) offers considerable advantages over fractional distillation when quantities of 0.01 to 0.1 g arc required, and has in several instances been extended to the gram scale. This technique was, therefore, studied in some detail to find suitable conditions for colnplete separation of such terpenoid mixtures 011 a 0.1-to 1-g scale. The experiments were can-iecl out with a Beckman GC-2 chro~natograph, using helium as carrier gas, a thermal conductivity cell as detector, and 6-foot columlls of 6-mm inner diameter.Successful separations of terpenoid co~npounds by GLC have been described in the literature. Bernhard (I) separated five monoterpene hydrocarbons on 20-foot polyethylene glycol and n-octyl phthalate columns, but obtained poor results when silicone fluid, Apiezon L , or high vacuunl grease was used as liquid phase. Bayer et al. (2) used hydrogen as carrier gas and obtained a fair degree of separation for a large variety of terpenoid compounds on columns containing silicone vacuum grease to which alkali capronates had been added. Cvrkal and Janhk (3), also using hydrogen, obtained good results for

GAS–LIQUID CHROMATOGRAPHY OF TERPENES: PART VII. THE DEHYDRATION OF p-MENTHAN-8-OL

“…I n preparative runs the detector current was reduced from 250 ma to 100 ma to prevent thermal decomposition (14). The identity of individual components was determined by comparison of infrared spectra and retention data with those of authentic samples.…”

Gas–liquid Chromatography of Terpenes: Part Iv. The Analysis of the Volatile Oil of the Leaves of Eastern White Cedar

“…The ainounts recorded for these seven coinponents in order of their retention times were about 0.3,0.1,0.3,1.1,0.4, 1.7, and 4.Oyo respectively. The separation of these con~pounds on other columns which could be operated a t 160 to 180' C was not as good (see also (26)). Sesquiterpene hydrocarbons, if present, woulcl fall into the inonoterpene alcohol range.…”

“…with the detector current off (26), and the desired fractions were isolated by timing as determined in trial runs, using the same sample size. Collection of these fractions was carried out with the Becltinan fraction collector (No.…”

Gas–liquid Chromatography of Terpenes: Part Iii. The Use of Oleic Acid Esters as Liquid Phases

“…I-Iowever, all such calculated data are obtained froin the basic equation TrR = FCtf (15) where VR is the retention volume, Fc the flow rate of carrier gas a t column temperature, and t' the time of emergence of the peali maximum. Now it was shown (4,17,18,19) that the position of the peali maximum of a given compound varies considerably with the size of the pound is preceded by a much larger quantity of another compound (20). Thus, unless all nzeasurements are carried out with identical sample sizes, considerable errors will Can.…”

“…Further examination on the rapeseed oil coluinn (2) indicated a second con~ponent, presuillably a-fenchene (3), to be present (partially resolved peak). There was no indication of this impurity on either the 6-ft adipate polyester (APEG) columil or polyphenyl ether columns (2,4). Other such unresolved or partially resolved pairs of isomeric terpeiles are frequently encountered, e.g.…”