Hydrazine coupling

There is nothing particularly special about the product except its feed rate, which is fairly low in comparison to some of the other novel oxygen scavengers. It exhibits passivation characteristics (forming magnetite in a way similar to hydrazine), coupled with good corrosion and iron transport control. 

The success of Wolff-Kishner reductions relies on two key processes, namely the reversible reaction of hydrazine with the carbonyl compound, which must be driven toward hydrazone formation, followed by base-induced decomposition of the hydrazone to generate a diimide anion and, subsequently, the hydrocarbon as depicted in Scheme 1. As expected, generation of the required hydrazones is highly dependent on the steric environment flanking the carbonyl and, consequently, much of the efforts devoted to improvements have focused on shifting the equiliMum toward the hydrazone by removal of water and/or the use of high concentrations of hydrazine. Coupled with this is the requirement to provide sufficient rates for the hydrazone decomposition step, which has generally meant modifrcations to provide increased reaction temperatures. 

MAJOR FACTORS DETERMINING INTRINSIC REACTIVITIES OF HYDRAZINE COUPLES... 

Thirty-nine tetrasubstituted hydrazine couples were used in this work (see Table 10.1, where they are listed in order of decreasing AG (fit), i.e., increasing ET reactivity). 

The couple numbers assigned are completely arbitrary, depending principally on the order in which we studied them. Hydrazine couples span an astonishing range of intrinsic reactivity, 16.6 kcal/mol, which is 83% of the total ACj, (fit) range observed for all compounds studied. The very unreactive, high AG (fit) hydrazines are essential to study the intrinsically most reactive couples. Only by having slow couples can the cross-reaction ET rate constant be kept small relative to diffusion rates, so the... 

CHART 10.1 Examples of the abbreviations used for hydrazine couples. 

Major Factors Determining Intrinsic Reactivities of Hydrazine Couples... 

Another type of polyol often used in the manufacture of flexible polyurethane foams contains a dispersed soHd phase of organic chemical particles (234—236). The continuous phase is one of the polyols described above for either slab or molded foam as required. The dispersed phase reacts in the polyol using an addition reaction with styrene and acrylonitrile monomers in one type or a coupling reaction with an amine such as hydrazine and isocyanate in another. The soHds content ranges from about 21% with either system to nearly 40% in the styrene—acrylonitrile system. The dispersed soHds confer increased load bearing and in the case of flexible molded foams also act as a ceU opener. 

Nitrite can be deterrnined by reaction with sulfanilamide to form the diazo compound, which couples with /V-(1-naphthyl)ethylenediamine dihydrochloride to form an intensely colored red azo dye. Nitrate can be deterrnined in a similar manner after reduction to nitrite. Suitable reducing agents are cadmium filings or hydrazine. This method is useful at a nitrogen concentration of 10 -lO " M. 

Pyrazolediazonium salts (448) couple with activated aromatic molecules, like naphthols (79KGS805), and can be reduced to hydrazines (452) with tin(II) chloride (74MI40406). 

Where copper corrosion occurs, the problem usually can be traced back to an excess feed of hydrazine, DEHA, or similar product, coupled with inadequate post-boiler oxygen scavenging. 

The unsubstituted diazotetrazole (2.16 ) even couples with hydrazine in a manner not observed with benzenediazonium ions to form the hexazadiene 2.17 (Scheme 2-9, Horwitz and Grakauskas, 1957). 

P-coupling occurs in the formation of azophosphonic esters [ArN2PO(OCH3)2] from diazonium salts and dimethyl phosphite [HPO(OCH3)2] (Suckfull and Hau-brich, 1958). P-coupled intermediates are formed in the reaction between diazonium salts and tertiary phosphines, studied by Horner and Stohr (1953), and by Horner and Hoffmann (1956). The P-azo compound is hydrolyzed to triphenylphosphine oxide, but if a second equivalent of the tertiary phosphine is available, phenyl-hydrazine is finally obtained along with the phosphine oxide (Scheme 6-26 Horner and Hoffmann, 1958). It is likely that an aryldiazene (ArN = NH) is an intermediate in the hydrolysis step of the P-azo compounds. 

Nearly all (extranuclear) hydrazonoquinoxalines are made by treatment of quinoxaline aldehydes, ketones, or their acetals with hydrazine or substituted hydrazine, but a few are produced by diazo coupling. These reactions are illustrated by the following examples. 

The coupling of enals and glyoxals was realized by hydrogen-mediated reaction with the cationic Rh complex and PI13P [35]. The intermediate aldehyde enolates derived via Rh-catalyzed hydrogenation were trapped with glyoxals to form (l-hydroxy-y-kclo-aldchydes, which were treated sequentially with hydrazine to give pyridazines in a one-pot transformation to provide, for example, a 62% yield of 72 (Scheme 21). 

Hydroxamic acids are an important class of compounds targeted as potential therapeutic agents. A-Fmoc-aminooxy-2-chlorotrityl polystyrene resin 61 allowed the synthesis and subsequent cleavage under mild conditions of both peptidyl and small molecule hydroxamic acids (Fig. 14) [70]. An alternative hydroxylamine linkage 62 was prepared from trityl chloride resin and tV-hydroxyphthalimide followed by treatment with hydrazine at room temperature (Scheme 30) [71]. A series of hydroxamic acids were prepared by the addition of substituted succinic anhydrides to the resin followed by coupling with a variety of amines, and cleavage with HCOOH-THF(l 3). 

Poly(iV-substituted dithieno[3,2-3 2, 3 -rf pyrroles (PDTPs) 167a,b) <2005MM4545>, a class of soluble (chiral) conjugated polymers with a stable oxidized state, were prepared by an oxidative coupling by FeClj in chloroform under an argon atmosphere. The crude material was reduced with hydrazine to afford compound 167 (Scheme 19) <2005MM4545>. 

A one-pot process to form 1,3,4-substituted pyrazoles 25 by Suzuki coupling of arylboronic acids to chromone 24, followed by condensation with hydrazine has been reported <06JCO286>. The synthesis of 3 or 5-o-hydroxyphenol-4-benzylpyrazoles has been accomplished by treatment of 3-benzylchromones, 3-benzylflavones and their 4-thiochromone analogs with hydrazine hydrate in hot pyridine <06EJO2825>. 

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