Ammonia, photochemical addition

Photochemical addition of ammonia and primary amines to aryl olefins (equation 42) can be effected by irradiation in the presence of an electron acceptor such as dicyanoben-zene (DCNB)103-106. The proposed mechanism for the sensitised addition to the stilbene system is shown in Scheme 7. Electron transfer quenching of DCNB by t-S (or vice versa) yields the t-S cation radical (t-S)+ Nucleophilic addition of ammonia or the primary amine to (t-S)+ followed by proton and electron transfer steps yields the adduct and regenerates the electron transfer sensitizer. The reaction is a variation of the electron-transfer sensitized addition of nucleophiles to terminal arylolefins107,108. 

Other Addition Reactions - The photochemical addition in the gas phase of ammonia to a,P-unsaturated nitriles has been studied. The reactions are carried under conditions where all, or most, of the light is absorbed by the ammonia and this results in N-H bond fission and the production of NH2 radicals. These radicals add to the a-position of the substrate to yield 2-amino-propionitrile from acrylonitrile and analogous products are formed from crotononitrile, methacrylonitrile and 1-cyclohexenecarbonitrile. Additions also occur to but-2-yne nitrile which yields the Z, -isomers of 3-amino-crotononitrile with the E -isomer being predominant. The SET-induced amina-tion (using 1,4-dicyanobenzene as the sensitiser) of alkenylnaphthalene derivatives affords products of addition to both the alkene and the naphthalene skeleton. Suau et al. have examined the irradiation of phthalimide in the presence of low concentrations of hydroxide ion and alkenes. ° The result of this treatment is addition of the phthalimide moiety to the alkene. A SET... 

This is called the SrnI mechanism," and many other examples are known (see 13-3, 13-4,13-6,13-12). The lUPAC designation is T+Dn+An." Note that the last step of the mechanism produces ArT radical ions, so the process is a chain mechanism (see p. 895)." An electron donor is required to initiate the reaction. In the case above it was solvated electrons from KNH2 in NH3. Evidence was that the addition of potassium metal (a good producer of solvated electrons in ammonia) completely suppressed the cine substitution. Further evidence for the SrnI mechanism was that addition of radical scavengers (which would suppress a free-radical mechanism) led to 8 9 ratios much closer to 1.46 1. Numerous other observations of SrnI mechanisms that were stimulated by solvated electrons and inhibited by radical scavengers have also been recorded." Further evidence for the SrnI mechanism in the case above was that some 1,2,4-trimethylbenzene was found among the products. This could easily be formed by abstraction by Ar- of Ft from the solvent NH3. Besides initiation by solvated electrons," " SrnI reactions have been initiated photochemically," electrochemically," and even thermally." ... 

The thiocyanates are generally soluble in water, the exceptions being those of lead, silver, mercury and copper. Most of them dissolve also in alcohol and ether. Aqueous solutions of the alkali thiocyanates undergo atmospheric oxidation under the influence of sunlight with solutions of medium concentration this change takes place rapidly, with separation of a yellow, amorphous precipitate consisting of pseudocyanogen sulphide, (CNS)3 (cf. p. 236). The concentration of thiocyanate most favourable to the separation of this sulphide is about 50 per cent, in summer and 10 per cent, in winter. In addition to this substance the products of the photochemical oxidation of potassium thiocyanate include hydrocyanic acid, sulphate, carbon dioxide, ammonia and ammonium salts ... 

In contrast to the observed reactivity of phenoxide and aryl alkoxide ions, arene and heteroarene thiolate ions typically couple with aryl radical to generate C—S bonds. The only exception to this regioselective reaction is the addition of 1-naphthalene thiolate ion to p-anisyl radical to render both C- and S-substitutions in 14% and 65% yields, respectively, while with 1-naphthyl radical, 95% of C—S coupling is obtained. In general, PhS- ions react with Arl in liquid ammonia under photostimulation to afford good yields of ArSPh or heteroaryl-SAr (70-100%). Substitution of the less-reactive ArBr can be achieved under photochemical initiation in DMF, MeCN, or DM SO [1],... 

To liquid ammonia (25 mL) under argon contained in a three-necked flask fitted with a dry-ice condenser, acetone is added (4 mmol) along with one equivalent amount of t-BuOK. To the solution of the acetone enolate thus formed, 2-bromo-3,4,5-trimethoxybenzamide is added and the reaction mixture is irradiated in a photochemical reactor. The reaction is quenched by addition of NH4C1 (0.5 g) when all the substrate has been allowed to react. The ammonia is evaporated and slightly acidified water (50 mL... 

Among photochromic 1-aryloxyanthraquinones with an unsubstituted and substituted oxy group, as with a substituent in the anthraquinone nucleus, partial destruction was observed for l-phenoxy-5-oxy- and 1-phenoxy-8-acetoxyanthraqui-nones.19 In addition, 2,4-dioxy derivatives of 1-phenoxyanthraquinone also exhibited irreversible photochemical transformation. As for aminoaryloxyanthraquinones, oxy- or 9-imino compounds are produced by reaction with water or ammonia, respectively. 

Photochemically Promoted Addition of Ammonia and Amines to Phenyl-Substituted Alkenes... 

The reduction of carbon dioxide to formate in the presence of FDH represents a photochemical C02-fixation process. In addition to MV+, the enzyme recognizes other electron carriers such as 2,2 -bipyridinium radical cations [184]. Reduction of nitrate (N03 ) to nitrite (NO2 ) and subsequently the reduction of nitrite to ammonia in the presence of NitraR and NitriR, respectively, allows the sequential 8e ... 

The most general synthetic route to benzene oxides-oxepins is that initially developed by Vogel for 1. 1,4-cyclohexadienes (readily available from [2+4] cycloaddition of alkynes and butadienes, lithium-ammonia reduction of arenes, or dehydration of cyclohexenols) were converted to dibromoepoxides, the immediate precursors of benzene oxides. Modifications of this route have been used to prepare Ic and Id. Treatment of the monosubstituted arene oxide 43 (Figure 3) with (Et)4NF or thermal isomerization of 3-oxaquadricyclane provide additional synthetic routes to la. Similarly, the thermal (or photochemical) isomerization of the monoepoxide of Dewar benzene yielded la. ... 

It is also used as an electron acceptor by microorganisms. Nitrihcation of ammonia N in soil is a source of nitrate. In addition, nonpoint and point source discharges from terrestrial ecosystems can be a major source of nitrate to wetlands and aquatic systems. In the atmosphere, nitrogen oxides can react with photochemically produced free radicals and produce nitric acid, which contributes to acid rain. Nitrate is also a common fertilizer used in agricultural ecosystems. 

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