Gas-Liquid Chromatographic Hydrogenolysis of Furan Derivatives D. A. George and L. M. McDonough Entomology Research Division, Agriculture Research Service, U S D A , Yakima, Wash. 98902
IN 1960, THOMPSON et af. ( I ) reported a technique for structural analysis in which organic compounds were volatilized at temperatures of 150-350°C in a stream of hydrogen and passed over a hydrogenation catalyst. Multiple bonds were saturated and functional groups were removed so that a saturated hydrocarbon was produced with the original carbon skeleton intact except that with some functional groups, the connected carbon atom was also removed. Beroza et al. ( 2 ) then developed a catalyst tube which was connected to a gas chromatograph and allowed hydrogenolysis and detection of the product in one step. Our interest in this technique arose from our need to determine whether natural products containing a furan ring were 2-alkyl or 2,Sdialkyl substituted. Since furan derivatives suitable for testing are not commercially available, we synthesized two such compounds and determined their hydrogenolysis products. EXPERIMENTAL
Hydrogenolysis was conducted with the National Instrument Laboratories Beroza Carbon Skeleton Determinator. The catalyst was neutral 1 Pd on Gas-Chrom P and the hydrogenolysis temperature was 260 “C. 2-Hexyl-5-methylfuran was prepared from 1-bromohexane and 2-methylfuran ( 3 ) ; retention index on Apiezon-L = (1) C. J. Thompson, H. J. Coleman, R. L. Hopkins, and H. T. Rall, J. Gas Chromatogr., 5,1 (1967) and references therein. (2) M. Beroza and F. Acree, J. Ass. Offic.Agr. Chem., 41, 1 (1964) and references therein.
1175); n ~ 2 *= 1.4476. 2-(l-Heptenyl)furan was prepared by a Wittig reaction from furfural and I-bromohexane. Proof of structure was by MS and IR; retention index on SE-30 = 1270; n~~~= 1.4928. RESULTS AND DISCUSSION
2-Hexyl-S-methylfuran, upon hydrogenolysis, gave undecane and no decane; 2-(l-heptenyl)furan gave decane and no undecane. Thompson et a f . found that 2,s-dimethylfuran gave hexane and pentane. Pentane is an anomalous product in that it was produced by the removal of a carbon atom not connected to the functional group. Here Thompson et al. used a catalyst of palladium-on-alumina. Thompson et a f . also noted loss of methyl for C-methyl substituted carbazoles with a catalyst of platinum-on-glass. With the catalyst we used, our two examples indicate that alkyl substituted furans will undergo hydrogenolysis normally and a monosubstituted furan will lose a carbon atom, but a disubstituted furan will not. RECEIVED for review December 9, 1971. Accepted February 18, 1972. The mention of a proprietary product in this paper does not constitute a recommendation or an endorsement of this product by the US.Department of Agriculture. (3) Office de Recherches Industrielles de Laboratoire, French Patent No. 1,186,346;Chem. Absfr.,56, 455a (1962).
Determination of Active Hydrogen in Organic Compounds by Chemical Ionization Mass Spectrometry Donald F. Hunt,’ Charles N. McEwen, and R. A. Upham Department of Chemistry, University of Virginia, Charlottesville, Vu. 22901
STRUCTURE ELUCIDATION of a complex natural product is often aided considerably by knowledge of the number of acidic hydrogens (i.e. 0 - H , N-H, S-H and CO-OH) present in the molecule. This is particularly true if the heteroatom content has already been delineated by high resolution mass spectrometry. On a microgram scale, the qualitative determination of active hydrogen is best accomplished by equilibrating the sample with DzO or CHIOD and using mass spectrometry to measure the resulting change in molecular weight (I, 2). 1
Author to whom correspondence should be addressed.
(1) K . Biemann, “Mass Spectrometry,” McGraw-Hill, New York, N.Y., 1962, Chap. 5. (2) H. Budzikiewicz, C. Djerassi, and D. H. Williams, “Structure Elucidation of Natural Products by Mass Spectrometry,” Vol. I, Holden-Day, Inc., San Francisco, Calif., 1964, Chap. 2. 1292
ANALYTICAL CHEMISTRY, VOL. 44, NO. 7, JUNE 1972
Previously this type of analysis has been performed by adding a slurry of the sample in deuterium oxide directly to the inlet system of a mass spectrometer (3) or by allowing the sample to stand in either D20 or CH30D, evaporating the solvent, and then injecting the sample directly into the ion source of the mass spectrometer ( I , 2). When either of the above methods is employed in conjuction with a mass spectrometer operating in the conventional electron impact (EI) mode, several problems are often encountered. These include loss of deuterium due to exchange between sample and water absorbed on the walls of the ion-source and inlet system of the mass spectrometer; loss of sample during minipulations involved in the isotope exchange step; and failure of many organic compounds to form stable molecular ions when they are ionized by electron impact. (3) J. S . Shannon, A u s f .J . Chem., 15,265 (1962).
