Reductions with Hydrogen Iodide

Hydrogen iodide (M.W. 127.93, m.p. —55°, b.p. —35.4°, density 5.56), one of the oldest reducing agents, is available as a gas but is used mainly in the form of its aqueous solution, hydriodic acid. Azeotropic hydriodic acid boils at 127°, has a density of 1.70, and contains 57% of hydrogen iodide. So-called fuming hydriodic acid is saturated at 0° and has a density of 1.93-1.99. 

Reductions with hydriodic acid are usually accomplished by refluxing organic compounds with the azeotropic (57%) acid. Acetic acid is added to increase miscibility of the acid with the organic compound. If more energetic conditions are needed the heating has to be done in sealed tubes. This 

Milder reductions with hydriodic acid can be accomplished by using more dilute hydriodic acid, or solutions of hydrogen iodide prepared from alkaline iodides and hydrochloric or acetic acid in organic solvents [22S], 

Selective reduction of a-chloro and a-bromo ketones can be achieved by treatment with sodium iodide and chlorotrimethylsilane in acetonitrile at room temperature [224], 

Hydriodic acid is a reagent of choice for reduction of alcohols [225], some phenols [225], some ketones [227, 228], quinones [222], halogen derivatives [22S, 229], sulfonyl chlorides [230], diazo ketones [231], azides [232], and even some carbon-carbon double bonds [233]. Under very drastic conditions at high temperatmes even polynuclear aromatics and carboxylic acids can be reduced to saturated hydrocarbons but such reactions are hardly ever used nowadays. 

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The carbon-chain structure of the sugar obtained from hamameli-tannin was established by the classical method of Kiliani,26 which is based on the reduction, with hydrogen iodide, of polyhydroxy acids to fatty acids. Treatment of the calcium salt of hamamelonic acid under these conditions led to inconclusive results. The reduction of the corresponding, crystalline ammonium salt, however, furnished 3.5 to 5% of 2-methylvaleric acid, which was identified by the properties of its crystalline p-iodophenacyl ester. Thus, it was proved that the sugar must have structure XIV. 

Similar waves in the cathodic polarogram were observed by Donnet and Henrich 58) using oxidized carbon black. The wave disappeared after treatment with isobutyronitrile. It was assumed that isobutyro-nitrile gives an addition reaction with quinones. No reaction with this reagent was observed after reduction with hydrogen iodide, after treatment with aniline, or after treatment with diazomethane. The latter finding confirms the assumption by Studebaker et al. 38) that diazomethane is added to the quinones in the carbon black surface. 

By reduction with hydrogen iodide, tartaric acid yields, first, malic acid, and then succinic acid,... 

Synthesis of 1,3,5-triazine cannot be achieved by catalytic hydrogenation of cyanuric chloride (2,4,6-trichloro-l,3,5-triazine), probably due to poisoning of the catalyst by 1,3,5-triazine.36,37 When one, two or all of the chlorine atoms of cyanuric chloride are replaced by amino, methoxy, methylsulfanyl or alkyl groups, reduction with hydrogen iodide and phospho-nium iodide, sodium in liquid ammonia, or catalytic hydrogenation, e.g. to give 1, can be accomplished.38-46 Reduction with zinc in acetic acid could not be achieved.44. 

The starting point for his synthesis was N,]SF-dimethylurea, the reaction of which with malonic acid gave N,N-dimethylbarbituric acid. With nitrous acid (sodium nitrite and a mineral acid) he produced dimethylvioluric acid, which gave dimethylpseudouric acid upon reduction and further reaction with potassium cyanate. Ring closure by heating with hydrochloric acid then led to 1,3-di-methyluric acid. [518] Its reaction with phosphorus pentachloride and reduction with hydrogen iodide then produced the supposed theophylline final... 

Nitric acid oxidizes the saccharinic acid to a dibasic acid which by reduction with hydrogen iodide is converted to 2-methylglutaric acid ... 

Reduction of carbonyl to methylene in aromatic ketones was also achieved by (dane prepared from lithium aluminum hydride and aluminum chloride [770], by soditim borohydride in triiluoroacetic acid [841 with triethylsilane in trifluoroacetic acid [555, 777], with sodium in refluxing ethanol [842], with zinc in hydrochloric acid [843] and with hydrogen iodide and phosphorus [227], geiibrally in good to high yields. 

Uramil has been obtained by boiling alloxantin with ammonium chloride 1 by reduction of nitrosobarbituric acid or ryjtro-barbituric acid with hydrogen iodide 2 and by reduction of alloxan phenylhydrazone with tin and hydrochloric acid.3... 

O-p-tolylsulfonyl-a-D-mannoside (39) in 37% yield. Treatment of (39) with sodium iodide in acetone gave the 6-iodo derivative (40), which underwent reduction with hydrogen in the presence of a nickel boride" catalyst" to give methyl 4-0-benzoyl-2,3-0 carbonyl-6-deoxy-o>-D-manno-side (41) in 95% yield. Reaction of (41) with hydrogen bromide in acetic acid effected replacement of the methoxyl group at C-l, affording crystalline... 

The valuable synthetic intermediates are benzo-2,l,3-selenadiazoles. They were used for preparation of. V-al ky I-1,2-benzenediamines, 3-nitro-1,2-benzenediamines, 3,4-diamino-2-nitrophenols, and 5-nitroqunoxalines. The key step of the reaction is their reductive deselenation with hydrogen iodide or, better, with ammonium hydrosulfide [233-238],... 

Cyclization of 152 with hydrogen iodide in acetic acid is more complicated and proceeds with concomitant reduction (of the iodo group) and acetylation, the final product being 154. With this reagent some... 

Extensive reduction of the sensitive iodide, usually encountered with hydrogen iodide, is avoided. In the conversion of 2-methyl-1-propanol, (CHj)jCHCHiOH, apparently no isomerization to the tertiary halide occurs. 

Purines are some of the most ubiquitous heterocydes. The quantity of naturally occurring purines produced on the earth is enormous, as 50% of ribo- and 2 -deoxyribonucleic acid (RNA, DNA) bases are purines. Purine is a colorless, crystalline weak base which was first prepared by E. Fischer by zinc dust reduction of 2,6-diiodopurine, which had been obtained from 2,6,8-trichloropurine by reaction with hydrogen iodide and phosphonium iodide. 

Reduction of aryl iodides has been accomplished by catalytic hydrogenation using hydrogen or hydrogen donors over palladium or Raney nickel catalysts (equation 66), by reduction with complex hydrides (equations 62-64),with metals and their compounds,with hydrogen iodide, and with organic compounds (equations 65 and 67). Table 5 shows reaction conditions for reduction of iodobenzene to benzene. 

Reduction.—(8) When hydroxy acids are treated with hydrogen iodide they are readily reduced to the unsubstituted acid. In other words, the hydroxyl group is reduced to hydrogen. In this reaction the hydroxyl group is first replaced by iodine giving the iodine substituted acid. This is then reduced because of the strong reducing... 

Corbella et a . used Iiypophosphorous acid in combination with hydrogen iodide for reduction of 2-pyrrolecarboxylic acid (I) to 3,4-dehydroproline (2). 

Two suitably placed sulphonyl chloride functions, on mild chemical reduction, form a 1,2-dithiin dioxide ring but heating the substrate (R = H) with hydrogen iodide gives the deoxygenated dibenzodithiin (R = H). 

Reduction of IFRs with hydrogen iodide. The reduction of some PTM radicals to the corresponding aH compounds takes place with HI in boiling acetic acid (Ballester et al., 1982b). Because of the steric shielding of the a-carbon, it is assumed that the initial step is a one-electron transfer, followed by an addition of a proton (163), each being an unhindered process (Ballester et al., 1970, 1982b). 

Reduction of the sulfoxide to methionine can be performed for example with hydrogen iodide and red phosphorus, or with sulfite. 

A potential two-step process to convert D-glucose to catechol (48) via D-glucose-6-phosphate (46) has been developed. This comprises a one-pot incubation of the sugar with hexokinase and recombinant 2-deoxy-scy//o-inosose synthase, followed by chemical reductive dehydration of the resulting 2-deoxy-scy/to-inosose 47 with hydrogen iodide (Scheme 10). ... 

It is apparent that substitution of fluorine for hydrogen initially causes a reduction in reactivity towards the electrophilic oxy n atom, but tetra-fluoroethylene is anomalous. A further study has indicated that substitution by trifluoromethyl has a strong deactivating effect compared with methyl, which has an activating effect. A study of the reactions of nearly thermal i F atoms, produced by F(n,2n) F and moderated by collisions with an excess of sulphur hexafluoride, with fluoro-oleflns (modes of addition were identified by scavenging the radicals produced with hydrogen iodide) has indicated that F atoms react preferentially with less-fluorinated olefins, and at the less-fluorinated end of a particular olefin. ... 

Tertiary alcohols can be reduced with mixtures of metals (such as zinc [Zn] or tin [Sn]) and aqueous hydrochloric acid (HCl) or red phosphorus (P) with hydrogen iodide (HI). The pathway by which such reductions occur is not clear. 

An interesting and unusual synthesis of racemic leucine (Leu, L) was carried out as shown in Scheme 12.34 and reported early in the twentieth century. As shown, 2-methyl-l-propanol was converted to the corresponding iodide with hydrogen iodide (HI) and the primary alkyl iodide reacted with sodium salt derived from methyl acetoacetate to yield 5-methyl-3-carboxymethyl-2-hexanone. This, treated with nitrosyl sulfate (0=N-0S03H), yields the decarbonylated methyl 5-methyl-pentanoate-2-oxime. Reduction of the latter produced racemic leucine (Leu, L). 

Scheme 12.43. A synthesis of tyrosine (Ty r, Y) via the condensation ofp-methoxybenzaldehyde with hippuric acid (A-benzoylglycine) in the presence of acetic anhydride. The reaction is presumed to involve the intermediacy of an azlactone (oxazolone), and the reduction (and ether cleavage) is accomplished with hydrogen iodide (HI) and red phosphorus (see Badshah, A. Khan, N. H. Kidwai, A. R. J. Org. Chem., 1972,37,2916 and references therein.)...

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