Weygand/Hilgetag Preparative Organic Chemistry

Addition of hydrogen to C=C bonds and aromatic systems 37
Phenanthrene (40 g) is hydrogenated with copper chromite (4 g) in ethanol (100 ml) at
150° with a hydrogen pressure of 150-200 atm. The reaction lasts about 3 h. After the hydrogenation
the mixture is fractionated through a Widmer column, the fraction distilling at
176-178°/20 mm being collected. The yield amounts to 87%. When recrystallized from
methanol, the dihydrophenanthrene melts at 33.8-34.4°. Further hydrogenation of 9,10-dihydrophenanthrene
with copper chromite requires a temperature higher by 50-70°, so it
is better to use nickel catalysts for complete hydrogenation of phenanthrene.
The preparation of 4-aminocyclohexanecarboxylic acid 220 will be described
as an example of hydrogenation of aromatic compounds. The technique has the
advantage that an aqueous suspension is used, without an organic solvent.
4-Aminocyclohexanecarboxylic add: 221 /?-Aminobenzoic acid (10 g; twice recrystallized
from water) is suspended in water (800 ml) in a shaking flask, and platinum oxide (0.5 g;
freshly prepared) is added. Hydrogenation requires 14.5 h, somewhat more than the theoretical
amount of hydrogen being absorbed. The end of the hydrogenation is best recognized by
flocculation of the catalyst. On completion of the hydrogenation the mixture is filtered, the
filtrate is evaporated to dryness, and the brown crystal cake is recrystallized from a little
water with addition of charcoal. The yield amounts to 6-7 g, corresponding to 60-70% of
theory. The colorless needles of 4-aminocyclohexanecarboxylic acid contain 0.5 mole of
water of crystallization and melt at 275-280° in a closed tube. Melting points between 260°
and 330° are recorded in the literature. For separation of cis- and trans-isomcis of 4-aminocyclohexanecarboxylic
acid see reference 220).
It is possible also to start from the nitro compounds and to reduce these in aqueous
solution in one step to the corresponding amino acids.
Cyclohexanecarboxylic acid: Ipatiev and Rasuwajev 222 hydrogenated sodium benzoate
(50 g) in water (75 ml) in the presence of NiO (7 g) at an initial pressure of 92 atm of hydrogen.
At a temperature of 300° the authors obtained 40% of cyclohexanecarboxylic acid of b.p.
235-238° and 9 g of cyclohexane.
Decarboxylation usually occurs on hydrogenation of aromatic hydroxy
acids; their salts also can be only partly reduced without decarboxylation.
On hydrogenation of 65 g of methyl salicylate in 65 g of methanol containing
NiO, Ipatiev and Rasuwajev 223 obtained 40 g of cyclohexanol.
Hydrogenation of phenol also leads to cyclohexanol. It can be carried out in
the vapor phase 224 or under pressure with nickel catalysts. 225
Dihydroresorcinol is obtained in 85-95% yield from resorcinol by means of
Raney nickel or 'Universal Oil Products Ni-SiO2 catalyst' under pressure at
50° in 10-12 h. 226 Grewe, Nolte, and Rotzoll 44 used alkali-treated Raney
nickel. Stetter and Dierichs 227 simplified the process by hydrogenating with
freshly activated Raney nickel at atmospheric pressure and 50°, the duration
being 24 h and the yield of dihydroresorcinol 98%.
On hydrogenation of 3,5-dihydroxybenzoic acid with Raney nickel catalyst
W1 (see Billica and Adkins 155 ), 3,5-dioxocyclohexanecarboxylic acid is
obtained. 228 Hydrogenation of 3-ethylphenol with Raney nickel leads to
3-ethylcyclohexanol. 229
220 E. Ferber and H. Bruckner, Ber. Deut. Chem. Ges., 76, 1022 (1943).
221 R. Gabler, personal communication; see also ref. 226.
222 W. Ipatiev and G. Rasuwajev, Ber. Deut. Chem. Ges., 59, 306, 2028 (1926).
223 W. Ipatiev and G. Rasuwajev, Ber. Deut. Chem. Ges., 59, 2031 (1926).
224 P. Sabatier and J. B. Senderens, C. R. Hebd. Seances Acad. ScL, 137, 1025 (1903).
225 A. Brochet, Bull. Soc. Chim. France, [iv], 31, 1270 (1922).
226 R. B. Thompson, Org. Syn., 27, 21 (1947).
227 H. Stetter and W. Dierichs, Chem. Ber., 85, 61 (1952).
228 E. E. van Tamelen and G. T. Hildahl, /. Amer. Chem. Soc, 78, 4405 (1956).
229 C. V. Banks, D. T. Hooker, and J. J. Richard, /. Org. Chem., 21, 547 (1956).