Ring saturation

Ruthenium is excellent for hydrogenation of aliphatic carbonyl compounds (92), and it, as well as nickel, is used industrially for conversion of glucose to sorbitol (14,15,29,75,100). Nickel usually requires vigorous conditions unless large amounts of catalyst are used (11,20,27,37,60), or the catalyst is very active, such as W-6 Raney nickel (6). Copper chromite is always used at elevated temperatures and pressures and may be useful if aromatic-ring saturation is to be avoided. Rhodium has given excellent results under mild conditions when other catalysts have failed (4,5,66). It is useful in reduction of aliphatic carbonyls in molecules susceptible to hydrogenolysis. 

Rhenium oxides are also useful in reduction of carboxylic acids (170" C, 3500 psig). Aromatic acids can be reduced to alcohols without ring saturation 3,4,S,6). Strongly synergistic effects were found on substituting half of the Re207 with rulhenium-on-carbon, and excellent results can be obtained al... 

An alternative to cyclohexanones from phenols involves ring saturation to the alcohol, followed by oxidation 14). 

Heterocyclic amines are compounds that contain one or more nitrogen atoms as part of a ring. Saturated heterocyclic amines usually have the same chemistry as their open-chain analogs, but unsaturated heterocycles such as pyrrole, imidazole, pyridine, and pyrimidine are aromatic. All four are unusually stable, and all undergo aromatic substitution on reaction with electrophiles. Pyrrole is nonbasic because its nitrogen lone-pair electrons are part of the aromatic it system. Fused-ring heterocycles such as quinoline, isoquinoline, indole, and purine are also commonly found in biological molecules. 

Evans, J., Maccabee, M., Hatahet, Z., Courcelle, H., Bockrath, R., Ide, H. and Wallace, S. (1993). Thymine ring saturation and fragmentation products, lesion bypass, misinsertion and implications for mutagenesis. Mut. Res. 299, 147-156. 

Chemistry.—The chemical structures of several bacterial menaquinones (MKs) with partly saturated isoprenoid side-chains have been studied. Spectroscopic (u.v., i.r., m.s., and H n.m.r.) and chromatographic data have been recorded for the tetrahydro-MK8 and -MK9 mixture of some nocardioform and coryneform bacteria.The main component tetrahydro-MK9 has the second and third iso-prene residues from the quinone ring saturated, i.e. has structure (159), 2-... 

Cyclic ligands Square brackets designate that the ligand is cyclic and the number within the brackets is the number of atoms in the macrocyclic ring. Saturated macrocycles are designated by ane , while, for unsaturated ligands, ene is used preceded by a prefix to identify the number of double bonds (e.g. diene or tetraene). The donor atoms are then identified. Substituents attached to the macrocycle are indicated by either a prefix or suffix. 

Hydrogen sulfide At low levels, hydrogen sulfide can inhibit aromatic ring saturation. This results in higher-octane gasoline and low-smoke-point jet fuel. At high concentrations, cracking catalyst activity is adversely affected. 

Unsaturated carbon structures usually undergo addition of fluorine, but are vulnerable to fragmentation unless fluorine addition is carefully controlled. Aromatic rings saturate, but polymerization may be a serious side reaction. Many heteroaromatic molecules polymerize giving principally tars and oils. In contrast to the cobalt(III) fluoride process, benzene produces a significantly lower yield of perfluorocyclohexanc than does cyclohexane. 

Medium-ring saturated monocyclic diamines (12) have pKa values > 12 in aqueous solution (88CC1528), (12, n = m = 4) has the highest pK[ resulting from internal hydrogen bonding as suggested by NMR measurements and force-field calculations. 

Elimination of nitric oxide from 3-carbamoyl-2,2,5,5-tetramethyl-pyrroline 1-oxyl (69) was observed on photolysis in benzene, and an almost quantitative yield of the diene (70) was obtained.61 Ring-saturated nitroxides appear to be unaffected by irradiation of the same wavelength. 

E. coli Nth protein (endonuclease III) Oxidized pyrimidines Ring-saturated or fragmented Thy residues, e.g. F Thy, Tg, 5-hydroxy-5-methylhydantoine, urea, DNA damaged at Gua, some abasic sites... 

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