Halogen/hydrogen donors

Stepwise decarboxylation also occurs, particularly in reactions in which the carboxylate radical (RC02 ) is formed. This radical usually decomposes to a hydrocarbon radical (R-) and C02- The overall decarboxylation product is determined by what R- reacts with If a good hydrogen donor is present, RH is formed if a halogen donor such as Br2 is present, RBr is formed ... 

Photolysis of diaryliodonium salts take place either through homolytic or through heterolytic cleavage of the halogen-aryl bond to form species which react with a hydrogen donor compound to yield a Brpnsted acid that initiates polymerization (Scheme 11.3). 

Transfer hydrogenation of aromatic nitro compounds. Aromatic nitro compounds are reduced to anilines when refluxed in excess cyclohexene in the presence of ordinary commerical 10% Pd/C catalyst. The method is very useful for selective reduction of polynitrobenzenes. Halogen, if present, is eliminated. Cyclohexene is superior to cyclohexa-1,3-diene as hydrogen donor. The reaction is usually successful, but slower, with sulfur-containing substrates. 4-Methoxy-2,5-dinitroanisole is reduced to 2,5-dimethoxy-4-nitroaniline in 10 min. in the steam bath under these conditions. 

Compounds which contain hydrogen donor groups, e.g. halogenated compounds which contain a sufficient number of halogens to activate the hydrogens present, such as chloroform. 

The acyl radicals decayed either by decarbonylation or by radical-radical recombination. Decarbonylation reaction rates were found to decrease in more polar solvents, indicative of the more polar nature of acyl radicals relative to their decarbonylation products. Second-order rate constants for the reaction of a variety of acyl radicals with halogen atom donors, hydrogen atom donors, and oxygen were determined by monitoring the decay of the acyl radical, the growth of the product, or, when possible, both. The observed reactivity was roughly comparable with that of simple alkyl radicals. 

Recently, blocked polymeric isocyanates useful in the preparation of polyurethanes, have been prepared by direct carbonylation of a nitro-substituted polymer based on styrene with carbon monoxide in the presence of a catalyst at 60-200 "C and a pressure from atmospheric to 2000 psi in a hydrogen-donor solvent [64]. Catalysts such as PdL2X2 (X = halogen, L = heterocyclic ligand, e.g. pyridine) in the presence of [NEt4][Cl] have been used. However, from the abstract it is not clear if polynuclear ruthenium, iron, and platinum carbonyls are... 

The NARXs possess four spatially-fixed halogen-bond acceptor sites (the four anions) with deep cavities for guest binding. The resorcinarene skeleton and the strong hydrogen bond interactions from the ammonium ions shield the halide anions, so that in the presence of suitable halogen bond donors, the latter interactions can only form either parallel or perpendicular to the upper rim of the NARXs. 

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