Hoffmann degradation

Several other polypyridyl metal complexes have been proposed as electrocatalysts for C02 reduction.100-108 For some of them HCOO- appears as the dominant product of reduction. It has been shown for instance that the complexes [Rhin(bpy)2Cl2]+ or [Rh n(bpy)2(CF3S03)2]+ catalyze the formation of HCOO- in MeCN (at —1.55 V vs. SCE) with a current efficiency of up to 80%.100,103 The electrocatalytic process occurs via the initially electrogenerated species [RhI(bpy)2]+, formed by two-electron reduction of the metal center, which is then reduced twice more (Rlr/Rn Rh°/Rh q. The source of protons is apparently the supporting electrolyte cation, Bu4N+ via the Hoffmann degradation (Equation (34)). 

Oxidation of SeC 144 derivatives also generates AAla derivatives. Hoffmann degradation of u,p-diaminopropanoic acid, 145 Bergmann s re action11461 of condensation of amides with pyruvic acid, N-hydroxylation followed by dehydration, 147 and N-chlorination/dehydro-chlorination 122-124 have also been used for the synthesis of AAla derivatives. 

The structure of brunsvigine (583) has been established by the X-ray analysis of the corresponding 0,0 -di-p-bromobenzoate (7a). Furthermore, the H-NMR spectra of brunsvigine together with several of its derivatives have been completely assigned, and the ORD and CD spectra of these compounds have been measured. The structure of 583 was related to other 5,1 lb-methanomorphanthri-dine alkaloids by methylation and other chemical transformations including a series of Hoffmann degradations (7b). 

Ionica, Filip and Dinulescu50 studied hypohalite halogenation of A-bonded acidic hydrogens, which proceeds considerably faster than corresponding carbon-H halogena-tions. They used Hoffmann degradation of amides as a proof of their mechanism (equation 32). Based on the overall stoichiometry of the reaction they suggested that if their... 

The use of ammonium hydroxide as base furnishes 4-quinolinecarboxamides488, which when subjected to Hoffmann degradation conditions produce 4-aminoquinolines489. 4-Cyanoquinolines are produced when the corresponding acids are treated with 4-toluenesulfonamide and POCI3490. 

Chiyoda researchers later described the process in more detail, but catalyst leaching and recovery were scarcely mentioned (135). Chiyoda eventually introduced novel pyridine resins and catalysts that exhibited high activity, long catalyst life, and no significant rhodium loss (136). The pyridinium cation may be more stable than alkylammonium cations, which are prone to Hoffmann degradation. 

Hoffmann degradation is a classic way to transform aporphines into phe-nanthrene alkaloids. This transformation involves the thermolysis of the quaternary ammonium hydroxide formed by sequential treatment of an aporphine with an alkylating agent and silver oxide. This degradation was extensively used in initial degradative studies of the structure of aporphines. The alkylations are usually done with methyl iodide (20,30,45,60,85,86,88) or dimethyl sulfate... 

Two examples are known in which alkenylcyclopropanes have been prepared by the elimination of amine derivatives. Thus, Hoffmann degradation was used in the synthesis of 3a,7a-methano-l//-indene (3) in 57 yield from the quaternary ammonium hydroxide 2, which had been prepared from the corresponding amine with iodomethane and silver oxide. ... 

Perchlorination of triazines and related nitrogen compounds 346 Hoffmann degradation of perchloroaromatic amines 347 Other oxidations of 2,3,5,6-tetrachloro-p-phenylenediamine 348 An exceptional Sandmeyer-Schiemann-type reaction 350 Charge-transfer complexes 351... 

Acyltrialkylammonium salts have been prepared and were found to be very active in the alkylation of benzyl cyanide. These quats are more resistant to Hoffmann degradation than simple tetralkylammonium salts, which allows the reaction to be run at higher temperatures [46]. 

Alkyltrimethylammonium and dialkyldimethylammonium cationics are converted by Hoffmann degradation to their alk-l-enes by heating on a water bath for 30 min with potassium t-butoxide in benzene-DMSO (4 1). After extraction and clean-up, the alkenes are separated on a glass column (2m X 3mm i.d.) of 5% SE-30 on Chromosorb W AW-DMCS... 

Basically there are three major factors which must be taken into consideration in order to understand the effect of irradiation on clay nanocomposites Hoffmann degradation of organoclay modification agent, exfoliation and intercalation of organoclay and the barrier effect of organoclay. ... 

---