Hoffman degradation

Hoechst slurry process Hoeppler viscometer Hoffman degradation Hoffman eliminations Hofmann degradation... 

Hoffman Degradation. Polyacrylamide reacts with alkaline sodium hypochlorite [7681-52-9], NaOCl, or calcium hypochlorite [7778-54-3], Ca(OCl)2, to form a polymer with primary amine groups (58). Optimum conditions for the reaction include a slight molar excess of sodium hypochlorite, a large excess of sodium hydroxide, and low temperature (59). Cross-linking sometimes occurs if the polymer concentration is high. High temperatures can result in chain scission. 

Chemical Properties. Reactions of quaternaries can be categorized iato three types (169) Hoffman eliminations, displacements, and rearrangements. Thermal decomposition of a quaternary ammonium hydroxide to an alkene, tertiary amine, and water is known as the Hoffman elimination (eq. la) (170). This reaction has not been used extensively to prepare olefins. Some cycHc olefins, however, are best prepared this way (171). Exhaustive methylation, followed by elimination, is known as the Hoffman degradation and is important ia the stmctural determination of unknown amines, especially for alkaloids (qv) (172). 

Attempts to prepare 2,3,5,6-tetraaminopyrazine (91) by Hoffman degradation of the diamide (88) were unsuccessful. This is apparently due to both intermolecular and intramolecular urea formation from the intermediate isocyanate giving a mixture of products, which upon attempted hydrolysis to 91 undergo a significant amount of attack on the pyrazine ring (70UP1). 

Post-reactions of polyacrylamide to introduce anionic, cationic, or other functional groups are often attractive from a cost standpoint. This approach can suffer, however, from side reactions resulting in cross-linking or the introduction of unwanted functionality. Reactions include hydrolysis, sulfoiiielliylatioii, melliylol formation, reaction with other aldehydes, transamidadon, Hoffman degradation, and reaction with chlorine. 

The alpha-Si y substituted derivatives may be prepared by the Hoffman degradation reaction of the amide containing one carbon atom more than the resulting a/p/ia-allylamine derivative. 

Alternatively, a modification of the Hoffman degradation reaction may be used in which the reaction is carried out in methanol to give the intermediate methylcarbamate derivative which upon alkaline hydrolysis yields the desired alpha-d y substituted amine. 

The Hoffman degradation reaction generally is carried out by dissolving the amide in a very slight excess of cold (—5° to 5°C) aqueous hypholite solution, followed by rapid warming (30° to 70°C.) for fifteen minutes to two hours. 

The onset of neuromuscular blockade typically occurs in 3-5 min of i.v. administration and lasts for 20-35 min. Higher doses will result in a longer duration of blockade. Pancuronium is eliminated primarily in bile and vecuronium undergoes hepatic and renal excretion. The recovery from blockade produced by atracurium is a result of metabolism by non-specific plasma esterases (hydrolysis) and spontaneous Hoffman degradation (spontaneous at body temperature and physiological pH), which is independent of renal or hepatic function and, therefore, unaffected by renal or hepatic disease (Plumb 1995). Atracurium does not accumulate. 

In part c, the starting material must lose one carbon to form the desired product. Some methods of losing one carbon involve the oxidation of a terminal alkene by ozone (followed by a workup) or by hot, basic KMnO solution another method involves the Hoffman degradation of an amide (RGONH2) to an amine (RNHz). This last method is impractical... 

It has been found that Hoffman degradation of perchloroaromatic amides with sodium hypobromite is not significantly hindered by two o-chlorines, this being due, at least partly, to its well-known intramolecular character. For example, pentachlorobenzamide affords 7V//,A //-pentachloroaniline (Bandres, 1975). 

IV. Metabolism Hoffman degradation (breaks ester linkage) in bloodstream. Moderate histamine release (vasodilation, hypotension). Administer slowly to avoid massive histamine release. Refrigerate and store at low pH to prevent breakdown. 

Cjs-hydroxylation of 3,6-dihydro-2-methoxy-2H-pyran (341) afforded " a mixture of methyl 2-deoxy-a- and (3-DL-etyfAro-pentopyranosides (342). Hydrolysis of this mixture gave free 2-deoxy-DL-eo op ntos (2-deoxyribose). Compound 341 was obtained by the reductive removal of the p-toluenesul-fonyloxy group in methyl 3,4-dideoxy-2-0-p-toluenesulfonyl-a,p-DL-pent-3-eno-pyranoside (345). Mochalin °° obtained 341 in three steps starting from the Diels-Adler adduct 343 via the amide 344 and its Hoffman degradation in methanol solution. 

Picolinicacid amide undergoes oxidation to the V-oxide with the HjOj/HOAc. The latter undergoes a normal Hoffman degradation with potassium hypobromite to form 2-aminopyridine-l-oxide. The amine 7V-oxide can also... 

One of the more fundamental methods for generation of the o-xylylene intermediate is 1,4-elimination from o-xylene derivatives. o-Xylene di-, tri-, or tetrabromides undergo intramolecular 1,4-dehalogenation by means of sodium iodide [102], lithium [103], zinc [104], copper [105], iron [106], and chromium [107]. Hoffman degradation of (o-methylbenzyl)trimethylammonium hydroxides [108], as well as the more recently developed fluoride ion-induced elimination from [o-[a-(trimethylsilyl)alkyl]benzyl]trimethylammonium halides [109], have also been effectively utilized in the generation of 2. 

Selection of appropriate quaternary ammonium catalysts is limited by their stability in the reaction medium. The cellulose pretreatment requires heating in strong caustic solutions up to 120 most tetraalkyl ammonium salts undergo Hoffman degradation under these conditions. We have found two relatively stable quat salts, tetramethylammonium chloride and N,N-dimethylmorpholinium... 

Stability and performance of AEM prepared using poly(4-vinyl pyridine-costyrene), quaternized with 1-bromooctane, and deposited on fibrous woven paper was unsatisfactory [189]. Sanchez and coauthors [190] discussed problems related to the use of certain AEMs. They pointed out that the so-called Hoffman degradation that involves attack of a hydroxyl on a-hydrogen in p-position to a quaternary ammonium attached to an aliphatic chain may cause its removal, followed by release of a tertiary amine and formation of a double bond at the end of a broken chain. Attachment of DABCO on short leash prevented chain break due to Hoffman degradation, but release of DABCO and generation of a double bond attached to the chain could take place. Perhaps thermal cross-linking by DABCO of poly(vinyl benzyl chloride) may solve this problem. Sulfonated polymers prepared by polymerization or copolymerization of phosphazene, siloxans, styrene, vinylidene fluoride, and various monomers with aromatic backbones, and possibly with aliphatic spacers, have been used. Various imides as well as PPS, PEK, PEEK, PSU, PEEKK, and PPSU can also be used [190,191]. 

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