The reaction of an aromatic heterocycle with a proton is called a protonation. One of articles about this theory is 《Hydrogenation of aromatic compounds with the aid of platinum. III. Hydrogenation with platinum containing oxygen》. Authors are Willstatter, Richard; Jaquet, Daniel.The article about the compound:cis-Cyclohexane-1,2-dicarboxylic acidcas:610-09-3,SMILESS:O=C([C@H]1[C@@H](C(O)=O)CCCC1)O).Formula: C8H12O4. Through the article, more information about this compound (cas:610-09-3) is conveyed.
cf. C. A. 7, 1508. Certain reductions, like that of phthalic anhydride (a), which cannot be effected catalytically with Pt free from O, can be initiated by loading the Pt with O and brought to completion by again treating the Pt with O as the catalyst gradually loses its O by the formation of H2O. Oxygen-free Pt and that containing O behave like 2 different contact substances in reduction processes. Thus, 20.3 g. (a) in 75 cc. glacial AcOH with 5 g. Pt absorbed only 400 cc. H; if, however, the H gasometer was shut off and the reaction bulb evacuated, then allowed to fill with air, shaken 1 min. (whereupon O was rapidly absorbed -about 5 cc. per g. Pt) and the air was driven out with H, about 500 cc. of H was again absorbed after each such activation until the 20th and 21st times, when the absorption of H was 1230 and 5600 cc., rasp. The total absorption was 17040 cc. (20°, 760 mm.) or, deducting about 1150 cc. used up by the O introduced in the activations, 15890 cc. or 4.8 mols. Of the 2 rings in (a) the 5-membered one is reduced before the C6H6 ring; the first product is phthalide (b) which is partially reduced to hexahydrophthalide (c) and partially to o-MeC6H4CO2H (d) which is then reduced to the hexahydrotoluic acid (e). If the process is interrupted when only a little H has been absorbed there is obtained, besides some C6H6(CO2H)2, a mixture of (b) and (c), and while (b) is easily reduced further to (d), (c) cannot be reduced to (e). If in the process of isolation alkali is employed the (c) is in part obtained as methylolhexahydrobenzoic acid. Among the reduction products is also cis-hexahydrophthalic acid (f). In the reduction described above were obtained 7 g. (c) (partially hydrolyzed), 7 g. (e) and 4 g. (f). In a similar reduction of (b) 3.4 mols. H were absorbed and there were obtained about equal parts of (e) and (c). Phthalimide behaves quite differently from (a) on reduction, the aromatic nucleus and not the CO groups taking up the O. The activation of the Pt with O is not necessary but the reduction is successful only with the best Pt sponge preparations; many which were active towards C6H6 were inactive towards the imide. Nor can MeOH, EtOH or cyclohexane be used as a solvent; in glacial AcOH the reduction proceeds smoothly. cis-Hexahydrophthalimide seps. from H2O, alc. and AcOH in monoclinic prisms, m. 132°. Naphthalic acid purified by crystallization from alc. cannot be reduced because it always contains some anhydride (g) but the acid freshly precipitated from alk. solution can be reduced; contrary to C10H8, it takes up only 4 atoms of H; the tetrahydronaphthalic acid (h) seps. in cube-like prisms, m. 196° with loss of H2O and conversion into the anhydride, m. 119°. (g), like (a), can be reduced only with Pt activated with O; after about 4 mols. H2 have been absorbed the reaction slows up. As far as the (g) itself is reduced, the anhydride ring is attacked, but as some of the (g) is hydrolyzed by the H2O formed, some (h) is obtained. Among the reduction products are tetrahydro-1-methylnaphthalene-8-carboxylic acid (i), tetra- and decahydronaphthalides and a small amount of decahydroacenaphthene. The 2 naphthalides could not be isolated pure. The (i) seps. from Et2O-petr. ether in needles, m. 150°. o-C6H4(CO2H)2 is easily reduced in AcOH when entirely free from the anhydride, yielding exclusively the cis-hexahydro acid, m. 191-2°. The p-acid in AcOH suspension is reduced much more rapidly on gentle warming, giving about equal parts of the cis- and cis-trans-hexahydro acids, m. 162-3° and about 300°, resp. The m-acid, if pure, is likewise easily reduced in AcOH suspension, forming chiefly the cis- and some cis-trans-hexahydro acid. p-Toluylic acid very quickly gives exclusively or almost exclusively the liquid hexahydro acid whose amide m. 175-6°. Indole in AcOH smoothly absorbs 8 atoms H with formation of perhydroindole, b720 182-3°, b12 65°, a basic oil of medium consistency and unpleasant, penetrating, onion-like odor, d420 0.9947; chloroplatinate, reddish yellow monoclinic tablets from alc., m. 172-3° (not sharply); picrate, fine needles from alc., m. 137-8° (not sharply). If the reduction is interrupted before it is complete (e. g., when 2 atoms of H have been absorbed), the product contains unchanged indole, dihydroindole and perhydroindole, the last being removed by shaking the Et2O solution with 0.1 N HCl until the alk. reaction just disappears, and the first two being separated by fractional precipitation from Et2O with picric acid.
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Reference:
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