Polycyclic hydrocarbons, hydrogenation

Dehydrogenation (the conversion of alicycllc or hydroaroraatic compounds into their aromatic counterparts by removal of hydrogen and also, in some cases, of other atoms or groups) finds wide appUcation in the determination of structure of natural products of complex hydroaroraatic structure. Dehydrogenation is employed also for the synthesis of polycyclic hydrocarbons and their derivatives from the readily accessible synthetic hydroaroraatic compounds. A very simple example is the formation of p-raethylnaphthalene from a-tetra-lone (which is itself prepared from benzene—see Section IV,143) ... 

Names of polycyclic hydrocarbons with less than the maximum number of noncumulative double bonds are formed from a prefix dihydro-, tetrahydro-, etc., followed by the name of the corresponding unreduced hydrocarbon. The prefix perhydro- signifies full hydrogenation. For example, 1,2-dihy-dronaphthalene is... 

Figure 7.1 Some small polycyclic hydrocarbon molecules here C Hm means n vertices (carbon atoms) including m 2-valent ones, where a hydrogen atom can be attached (double bonds are omitted for simplicity) ...

Univalent radicals derived from ortho-fused or ortho- and peri-fused polycyclic hydrocarbons with names ending in -ene by removal of a hydrogen atom from an aromatic or alicyclic ring are named in principle by changing the ending -ene of the names of the hydrocarbons to -enyl . 

Bivalent radicals derived from univalent polycyclic hydrocarbon radicals whose names end in -yl by removal of one hydrogen atom from the carbon atom with the free valence are named by adding -idene to the name of the corresponding univalent radical. 

Bivalent radicals derived from o/7/io-fused or ortho- and pen-fused polycyclic hydrocarbons by removal of a hydrogen atom from each of two different carbon atoms of the ring are named by changing the ending -yl of the univalent radical name to -ylene or -diyl . Multivalent radicals, similarly derived, are named by adding -triyl , -tetrayl , etc., to the name of the ring system. 

Polycyclic hydrocarbons.5 Perhydrogenation of 2,7-dialkyl-9,10-dihydro-phenanthrenes (1) with Pd/C as catalyst at 200° under pressures of 120-170 atm. results in the all-trans-perhydrophenanthrenes (2). A similar hydrogenation (Pd/C, HC104) converts 2,6-dialkylnaphthalenes (3) into trans-dialkyldecalins (4). 

Harris et al. (15) carried out similar hydrogenations in aqueous and 1% alkaline media over Raney nickel for 6-10 hours at 225°-250°C. and 1500-2500 p.s.i.g. hydrogen pressure the products were identical with those found in dioxane. In 1941 lignin from soda black liquors was hydrogenated over copper chromite in dioxane at 250°-300°C., and colorless saturated products were obtained (/). Cyclohexane and four alkylcyclo-hexanes were detected, but the major part of the lignin was converted to alcohols and glycols related to polycyclic hydrocarbons of 20-70 (or more) carbon atoms. 

In carbene complexes which lack /3-hydrogens, for example (48 X = H, Y = t-Bu), alkyl migration can occur to afford trisubstituted alkene complexes (66). When this involves a polycyclic hydrocarbon, the result is a strained bridgehead alkene complex (67). ... 

The mechanism of cathodic hydrogenation, which requires a proton donor, is most probably that given in Scheme 1 the reduction potentials are in the order E cathodic hydrogenation of carbonyls and polycyclic hydrocarbons , and activated... 

From the table we see that no change in the H/C ratio took place in this time. Work at Mobil (1, 2), Exxon (7, 8), and Oak Ridge National Laboratory (9) indicate that none of the following reactions takes place under the liquefaction conditions described above hydrogenation of aromatic polycyclic hydrocarbons significant aromatization of the hydroaromatic structures or destruction or formation of polycyclic saturated structures. 

The carcinogenicity of dimethylnitrosamine and 4-nitrosomorpholine was reduced by deuterium substitution for hydrogen on carbon atoms alpha to the amino nitrogen.81 82 Consistent with the hypothesis that alpha-carbon oxidation is required for reactive metabolite formation from nitrosamines, there is a substantial primary deuterium isotope effect (ku/kg = 3.8) on the rate of dimethylnitrosamine N-demethylation. 3 Specific deuteration of 3-methylcholanthrene, a potent polycyclic hydrocarbon carcinogen, showed that oxidation of the 1-carbon atom is critical in the tumor-initiating process in mouse skin. ... 

To take into account the differences in the retention of isomer polycyclic hydrocarbons and also non-planar arrangement of some groups of partly hydrogenated and phenylderivatives of polyaromatic molecules, the more number of groups should be considered as different (Fig. 16 b). 

Some values of K n and H° for aromatic saturation reactions of interest are given in Table 8.7. High values of K correspond to the hydrogenated component being favored under the conditions specified. The purpose in developing the thermodynamic terms is to provide a generalized framework within which experimental data can be compared and predictions made for similar reactions involving other polycyclic hydrocarbons. In particular, accurate thermodynamic data on a reaction allows equilibrium concentrations to be calculated. 

---