Other reducing agents

Examples of organic molecnles [75] nsed as reducing agents inclnde ascorbic acid, which has been snccessfully employed as a radical initiator in a C—H arylation of benzene with anilines 107 to afford the biaryl componnds 108 atrt [76] (Eq. 9.21)  

The anilines 107 were transformed to the corresponding diazonium salts by terf-butyl nitrite (f-BuONO) in situ, and then ET through an inner-sphere mechanism generates N, an ascorbyl radical, and Ar, which undergoes a HAS reaction with benzene as acceptor. 

Similarly, the synthesis of 6-aiyl-phenanthridines by aryl radical addition onto 2-isocyanobiphenyls was recently reported [77], Aryl radicals were generated from diazonium salts, which were prepared in situ from anilines by diazotization. With the same approach, 3-benzyl-3-alkyloxindoles were prepared from diazotization of anilines to afford aryl radicals, which react with acrylamides, similar to compounds 85, in one-pot procedure [78], 

In sulflnatodehalogenation, a reaction is induced by dissociation of to form SO radical anions. Then, ET from SO to R X after C—X bond liagmentation gives the electrophilic R radical, SO, and the anion X (Eq. 9.22)  

According to this principle, perfluoroalkylation was performed with R X on aromatic nnclei bearing EDG [85, 86]. Eor example, aniline 109 is transformed into ortho and para perfluoroalkyl derivatives 110 and 111 using R /Na S O as the reagent system (Eq. 9.23) [87, 88]. Similar perfluoroalkylations have also been realized in aqueous DME [89]  

Finally, formic acid may be mentioned, for it was used to convert cyclic imonium compounds into saturated tertiary amines125,126 and 1,2-dihydro-quinolines into 1,2,3,4-tetrahydroquinolines 127 

A mixture of l,2-dihydro-2,2,4-trimethylquinoline (20.94 g) and 85% formic acid (50 g) was boiled under reflux for 6-8 hours. After cooling, the whole was made alkaline, the oil that separated was extracted with ether, and the extract was dried over potassium carbonate. 

The solvent was then evaporated off and the residue was distilled in a vacuum. The tetra-hydro product was thus obtained in 74% yield as a liquid of b.p. 132-138°/12-13 mm, and on recrystallization from ether melted at 39-40°. 

The use of formic acid for reduction of enamines is so characteristic that this reaction can be used for detection of the enamine group.128,129 Even enamines that are resistant to catalytic hydrogenation with Raney nickel or palladium can be reduced smoothly by formic acid.130 

Catalytic hydrogenation, which usually proceeds easily and in a clear-cut manner, is very suitable for addition of hydrogen to C=C bonds. At higher temperatures, the reverse reaction, dehydrogenation, may occur, in which case dehydrogenation products accompany the hydrogenation products in accordance with the position of the particular equilibrium involved. 

The structures of NMPs dispersed in ILs as well as the interactions between ILs and NMPs have been extensively studied using X-ray photoelectron spectroscopy (XPS), SEM, TEM, XRD, and molecular dynamics simulations, and so on. Because of the negligible vapor pressure of ILs at ambient temperature, NMPs dispersed or dissolved in ILs can be directly characterized by TEM, XPS, and so on. 

The XPS analysis of the isolated NPs (Ir, Rh, Pt, Ru, and Pd) prepared in ILs containing [PF, ] and [BF4] anions revealed the IL-metal surface interaction via M-O (metal-oxide) and M-F bonds [20]. In the case of Pt NPs prepared in [BMIm][PFg], there was also a very small contribution of phosphorus [21]. The F and P signals suggested that the isolated NMPs contained IL residues. The Pt 4f spectra revealed the presence of three chemical states of Pt, that is, Pt , Pt , and Pt , on the NPs surface, which are related to Pt-F, Pt-O, Pt-O-F, and other bonds. These results are evidence for the strong interaction of the IL with NMPs. 

It is feasible to investigate the surface properties of NMPs dispersed in I Ls by XPS [22]. After introducing lr° NPs into ILs, the binding energy of Cls of C2 position 

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SO2 absorbed from gas with Mg(OH)2 slurry, giving MgSO —MgSO sohds which are calcined with coke or other reducing agent, regenerating MgO and releasing SO2. 

Reaction of free-base porphyrin compounds with iton(II) salts in an appropriate solvent results in loss of the two N—H protons and insertion of iron into the tetradentate porphyrin dianion ligand. Five-coordinate iton(III) porphyrin complexes (hemins), which usually have the anion of the iton(II) salt for the fifth or axial ligand, ate isolated if the reaction is carried out in the presence of air. Iron(II) porphyrin complexes (hemes) can be isolated if the reaction and workup is conducted under rigorously anaerobic conditions. Typically, however, iton(II) complexes are obtained from iton(III) porphyrin complexes by reduction with dithionite, thiolate, borohydtide, chromous ion, or other reducing agents. 

The hberated iodine, as the complex triiodide ion, may be titrated with standard thiosulfate solution. A general iodometric assay method for organic peroxides has been pubUshed (253). Some peroxyesters may be determined by ferric ion-catalyzed iodometric analysis or by cupric ion catalysis. The latter has become an ASTM Standard procedure (254). Other reducing agents are ferrous, titanous, chromous, staimous, and arsenite ions triphenylphosphine diphenyl sulfide and triphenjiarsine (255,256). 

Tiichloiomethanesulfenyl chloiide can be reduced to thiophosgene by metals in the presence of acid and by various other reducing agents. The sulfur-bonded chlorine of trichloromethanesulfenyl chloride is most easily displaced by nucleophilic reagents, but under some conditions, the carbon-bound chlorines are also reactive (54). 

Impurities such as chloride ion or other reducing agents generate chlorine dioxide when the chloric acid solution is heated. Transition-metal ions do not affect the stabiUty of pure chloric acid at room temperature. Thirty-five percent solutions of HCIO have been shown to be stable for 20 days at room temperature containing up to 1000 ppm Ni ", 800 ppm Zn ", 700 ppm Fe ", or 600 ppm Cr " (2). The solubiUty of chloric acid in water is shown in Figure 1. 

The stereoselective reactions in Scheme 2.10 include one example that is completely stereoselective (entry 3), one that is highly stereoselective (entry 6), and others in which the stereoselectivity is modest to low (entries 1,2,4, 5, and 7). The addition of formic acid to norbomene (entry 3) produces only the exo ester. Reduction of 4-r-butylcyclohexanone (entry 6) is typical of the reduction of unhindered cyclohexanones in that the major diastereomer produced has an equatorial hydroxyl group. Certain other reducing agents, particularly sterically bulky ones, exhibit the opposite stereoselectivity and favor the formation of the diastereomer having an axial hydroxyl groi. The alkylation of 4-t-butylpiperidine with benzyl chloride (entry 7) provides only a slight excess of one diastereomer over the other. 

Nitro-filter cloths are composed of cellulose nitrate, which is an ester of cellulose. Any chemical compound that will saponify the ester will destroy the cloth. Caustic soda or potash in strengths of 2% at 70° C or over alkali sulfides, polysulfides and sulfohydrates or mixtures of ethyl alcohol and ether, ethyl, amyl and butyl acetates, pyridine, ferrous sulfates, and other reducing agents are detrimental to the cloth. 

This is the basis of the very sensitive Fehling s test for sugars and other reducing agents. A solution of a copper(H) salt dissolved in alkaline tartrate solution is added to the substance in question. If this is a reducing agent then a characteristic red precipitate is produced. 

Besides Fe-, other reducing agents that may be used in conjunction with H2O2 are aliphatic amines, Na2S203 thiourea, ascorbic acid, glyoxal, sulfuric acid, NaHSOs, sodium nitrite, ferric nitrate, peroxidase, AgNOs, tartaric acid, hydroxylamine, ethylene sulfate, sodium phosphite, formic acid, ferrous ammonium sulphate, acetic acid, ferrous sulphate, and HNO2, etc,... 

Metallic elements taking part in redox reactions, such as zinc in the reaction above, commonly act as reducing agents they are oxidized to cations such as Zn2+. Other reducing agents include hydrogen gas, which can be oxidized to H+ ions ... 

Other reducing agents like Ti(7y6-toluene)2 have also been used. Addition or removal of gold atoms from clusters can frequently be accomplished (Figure 4.44). 

The liberated iodine may be titrated using std thiosulfate soln, or, in trace analysis, detd by spectrophotometric methods. Other reducing agents commonly used in peroxide analysis are hydriodic acid, ferrous, titanous, stannous, and arsenious ions. Also (recently), triphenylphos-phine, which is oxidized to triphenyl phosphine oxide. The excess triphenyl phosphine may be detd gravimetric ally, tit rime trically, or spectro-photometrically... 

With other reducing agents the mechanism is not always nucleophilic... 

Sulfinic acids can be prepared by reduction of sulfonyl chlorides. Though mostly done on aromatic sulfonyl chlorides, the reaction has also been applied to alkyl compounds. Besides zinc, sodium sulfite, hydrazine, sodium sulfide, and other reducing agents have been used. For reduction of sulfonyl chlorides to thiols, see 19-57. 

Quinones are reduced to hydroquinones by LiAlH4, SnCl2—HCl, or sodium hydrosulfite (Na2S204), as well as by other reducing agents. 

It is noted that the related compounds, the isonitriles (R— N=C , also called isocyanides) have been reduced to N-methylamines with LiAlH4 as well as with other reducing agents. 

Both aldoximes and ketoximes can be reduced to primary amines with LiAlH4. The reaction is slower than with ketones, so that, for example, PhCOCH=NOH gave 34% PhCHOHCH=NOH. Among other reducing agents that give this reduc-... 

After separation of excess amalgam a solution of MXj is added. Reaction is rapid and the desired product can be separated from the Na halide or NaCN produced. If the separation of the amalgam is incomplete it is possible for Hg to be incorporated into the product (see 8.3.3.4). To avoid this, other methods of preparing carbonyl anions can be used, such as reaction with NaBH4, Na-K and other reducing agents ", or phase-transfer methods. ... 

Other reducing agents such as sodium thiosulfate or sodium metabisulfite may be used as well. 

DMS is a mild reducing agent. There are many other reducing agents that can be used in the final step of an ozonolysis, but DMS is common. 

Kasai, H. and Nishimura, S. (1984). Hydroxylation of deox-yguanosine at the C-8 position by ascorbic acid and other reducing agents. Nucleic Acids Res. 12, 2137-2145. 

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