Hydrogen sulfide nitro compounds

The Zinin reduction is also usehil for the reduction of aromatic nitro compounds to amines in the laboratory. It requires no special equipment, as is the case with catalytic hydrogenations, and is milder than reductions with iron and acid. Usually ammonium or alkah sulfides, hydrosulftdes or polysulftdes are used as the reactant with methanol or ethanol as the solvent. 

The main field of applications of hydrogen and alkali sulfides is reduction of nitrogen functions in nitro compounds [236, 240], nitroso compounds... 

Tertiary arylamines were prepared in good yields by hydrogenation of an alcoholic solution of a nitro compound and an aldehyde over Raney Ni in the presence of triethy-lamine hydrochloride or, better, over platinum oxide in the presence of acetic acid (eq. 6.22).48 Base metal and platinum metal sulfides are also effective to the reductive alkylation of nitro compounds with ketones36,37 as in an example shown in eq. 6.23. 

Iron is not a suitable reducing agent for use when only one of several nitro groups present is to be reduced, or when a nitro compound is to be reduced without altering azo groups which are present. These partial reductions are usually carried out technically with hydrogen sulfide in the form of sodium sulfide (NaaS) or sodium hydrosulfide (NaSH). This reduction method is not limited to partial reductions it frequently finds use in the anthraquinone series for reducing... 

Partial reduction of aromatic polynitro compounds leads to nitro amines. The most successful reagents are the alkali metal or ammonium sulfides in aqueous alcoholIn some instances, sodium bicarbonate combined with sodium sulfide gives better results because of the formation of sodium hydrosulfide, which is believed to be the main reducing agent. Also, aqueous methanol is preferred to aqueous ethanol. Nitro compounds that are sparingly soluble in alcohol solutions may be reduced by hydrogen sulfide in pyridine solution. ... 

The main method, both in the laboratory and in technical practice, for the introduction of an amino group into an aromatic compound, is nitration and reduction. Reduction of nitro compounds is accomplished by (1) catalytic hydrogenation, (2) iron reduction (Bechamp method), (3) sulfide reduction, or (4) zinc reduction in an alkaline medium. 

Oxidations with m-chloroperoxybenzoic acid are carried out in solutions in hexane, dichloromethane, chloroform, methanol, or tetrahydro-furan at temperatures ranging from -78 to 40 C. The applications of m-chloroperoxybenzoic acid are epoxidation [287, 314, 315, 316] the Baeyer-Villiger reaction [286, 315, 317, 378] and the oxidation of primary amines to nitro compounds [379], of tertiary amines to amine oxides [320], of sulfides to sulfoxides [327, 322, 323, 324], and of selenides to selenones [325]. Secondary alcohols are oxidized to ketones in the presence of hydrogen chloride [326], and acetals are oxidized to esters with boron trifluoride etherate as a catalyst [327]. The addition of potassium fluoride to reaction mixtures facilitates product isolation, because both m-chloroben-zoic acid and the unreacted m-chloroperoxybenzoic acid are precipitated... 

It is sometimes difficult to identily the actual cause of odor and taste problems in water. Some of common odor- and taste-causing compounds include hydrogen sulfide (H2S), methane, algae, oils, phenols, cresols, and volatile compounds. Removal of taste and odor problems is a common application for the water aeration process. The process is suitable for H2S, methane, and volatiles, but not for algae and oils, phenols, and cresols. The compounds must be volatile for aeration to be effective. Aeration is appropriate for many industrial compounds. A classic installation is at Nitro, WV, which utilizes aeration and granular activated carbon (GAC). The raw water had threshold odor numbers (T.O.N.) of 5000-6000 from industrial contamination. The process was effective for reducing the taste and odor down to levels of 10-12 T.O.N. Although taste and odor applications are most common, there are many other tastes and odors that simply cannot be removed by aeration alone, which may explain why so many early plants were abandoned (1-10). 

Manufacture of many important amino intermediates used for dyes and other purposes is usually by conversion or replacement of a substituent. For example, as already mentioned, in substituted nitro compounds, the nitro groups may be reduced with iron/hydrochloric acid, hydrogen and catalyst, or zinc in aqueous alkali. Partial reductions can be brought about with sodium sulfide. Amino groups may be introduced by replacing halogens in the aromatic ring. Another approach to amination is by attack on a substituted aromatic compound with ammonia or amines. Thus, for example, direct amination of p-chloronitrobenzene (15a) in the presence of a copper catalyst affords p-nitroaniline (15b) in almost quantitative yield l,4-dichloro-2-nitrobenzene (16) is converted in a similar way to 4-chloro-2-nitroaniline (17). Reactions of ammonia with carboxylic acids or anhydrides are carried out on an industrial scale. 

Reduction of nitro compounds. A solution of p-nitrophenylacetic acid in 6 A aqueous ammonia is cooled in ice and saturated with hydrogen sulfide.1 The solution is gently boiled until nearly all the excess hydrogen sulfide and ammonia... 

Sulfide reduction has an even broader selectivity profile than catalytic hydrogenation or the Bechamp reduction and enables the chemoselective reduction of nitro compounds in presence of C=C, azo, or other nitro groups. The method is insensitive to by-products and high levels of impurities. Depending on pH, different reduction agents with the following stoichiometries are applicable ... 

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