Chemical Studies on Tobacco Smoke: XI. Dibenzofurans in Cigarette Smoke

A method was developed for the isolation of dibenzofuran (DBF) and its four methyl derivatives (MDBF) from cigarette smoke. Since an excess of alkanes was found to inhibit the column chromatographic separation of dibenzofurans, distribution systems had to be developed which, in the initial step of the analysis, would lead to an enrichment of DBF and MDBF with loss of the bulk of the tobacco smoke alkanes. The three distributions which lead to a preliminary concentration of these heterocyclics were the solvent pairs methanol/water (4:1) and n-hexane; n-hexane and dimethylformamide; and water/dimethylformamide (4:1) and n-hexane. The resulting tobacco ''tar" extract was chromatographed on deactivated alumina and subsequently on Sephadex LH-20. The final concentrate of DBF was separated into individual components by gas chromatography. With the aid of this method we separated from cigarette smoke dibenzofuran and 1-, 2-, 3- and 4-methyldibenzofurans. These five dibenzofurans were identified by the retention times in two gas chromatographic systems, ultra-violet absorption spectra, and mass spectral analysis. The final DBF concentrate from cigarette smoke also contains, as major components, acenaphthylene and fluorene. For the quantitative analysis we employed dibenzofuran-1,2,3,4,4a,9b-¹⁴C6 as internal standard. This labelled compound was synthesized by the Trippett method on a microscale from phenol and 2-bromocyclohexanone. The mainstream smoke of an 85 mm U.S. nonfilter cigarette contained 106 ng of dibenzofuran, 40 ng of 1-methyldibenzofuran, 100 ng of 2- and 3-methyldibenzofurans, and 52 ng of 4-methyldibenzofuran. The identification of DBF and its four methyl derivatives in cigarette smoke represents their first isolation from a respiratory environmet