Amines, disproportionation

The acid-catalyzed amine disproportionation, R1NH2 + R2NH2 R1R2NH + NH3, always occurs in parallel with HDN. Mechanistically, it is another example of S>p nucleophilic substitution, namely, of the NH2 group... 

S tanny lphosphincs can be prepared by treating an organotin halide with a metallo-phosphine, or with a hydridophosphine in the presence of a tertiary amine, or by acidoly-sis of a stannylamine with a phosphine. Some examples of these reactions are given in equations 16-70,67 16-71,68 and 16-72.69 Stannylphosphines containing a PH group, like the corresponding amines, disproportionate unless they are stabilised by steric hindrance. 

For isolation, it must be stabilized by complexation with amines . Disproportionation of organoboron hydrides is used in the synthesis of boraheterocycles via hydroboration, as well as in the synthesis of arylboraheterocycles ... 

All metal amination catalysts are active in the disproportionation of amines, which can lead to equilibration of primary, secondary, and tertiary amines. For example, for simple primary amines the initial step is the formation of an aldimine by dehydrogenation (Scheme 2). Subsequent addition of an amine and hydrogenation lead to a mixture of primary, secondary, and tertiary amines. The same active metal sites catalyze alcohol amination and amine disproportionation, which explains why the reactant alcohol inhibits disproportionation and selectivity for the desired amine drops considerably only after consumption of alcohol [2]. It is also evident from Scheme 2 that sufficient hydrogen present on the metal surface can reduce the concentration of imine and thus suppress disproportionation. 

Higher chlorides, Si2Cle to Si6Cl,4 (highly branched - some cyclic) are formed from SiCU plus Si or a silicide or by amine catalysed disproportionations of Si2Cl,5, etc. Partial hydrolysis gives oxide chlorides, e.g. CUSiOSiCla. SiCU is used for preparation of silicones. 

The most common catalysts in order of decreasing reactivity are haUdes of aluminum, boron, zinc, and kon (76). Alkali metals and thek alcoholates, amines, nitriles, and tetraalkylureas have been used (77—80). The largest commercial processes use a resin—catalyst system (81). Trichlorosilane refluxes in a bed of anion-exchange resin containing tertiary amino or quaternary ammonium groups. Contact time can be used to control disproportionation to dichlorosilane, monochlorosilane, or silane. 

Mino and Kaizerman [12] established that certain. ceric salts such as the nitrate and sulphate form very effective redox systems in the presence of organic reducing agents such as alcohols, thiols, glycols, aldehyde, and amines. Duke and coworkers [14,15] suggested the formation of an intermediate complex between the substrate and ceric ion, which subsequently is disproportionate to a free radical species. Evidence of complex formation between Ce(IV) and cellulose has been studied by several investigators [16-19]. Using alcohol the reaction can be written as follows ... 

Purely parallel reactions are e.g. competitive reactions which are frequently carried out purposefully, with the aim of estimating relative reactivities of reactants these will be discussed elsewhere (Section IV.E). Several kinetic studies have been made of noncompetitive parallel reactions. The examples may be parallel formation of benzene and methylcyclo-pentane by simultaneous dehydrogenation and isomerization of cyclohexane on rhenium-paladium or on platinum catalysts on suitable supports (88, 89), parallel formation of mesityl oxide, acetone, and phorone from diacetone alcohol on an acidic ion exchanger (41), disproportionation of amines on alumina, accompanied by olefin-forming elimination (20), dehydrogenation of butane coupled with hydrogenation of ethylene or propylene on a chromia-alumina catalyst (24), or parallel formation of ethyl-, methylethyl-, and vinylethylbenzene from diethylbenzene on faujasite (89a). 

Hydrazino compounds can react with one or two equivalents of arenediazonium ions. In reactions of arylhydrazines without substituents at the P-nitrogen in mineral acid media the initial product, the 1,4-diaryltetraz-1-ene (6.24), disproportionates rapidly into aryl azide and amine (Scheme 6-17). As shown by 15N labeling experiments (Clusius and Craubner, 1955), equal amounts of all the products shown in Scheme 6-17 are obtained. In acetate buffer the reaction is regiospecifically different. The diazonium ion attacks the a-, not the P-nitrogen, and a 1,3-diaryltetraz-l-ene is formed (6.25). 

More recently Hand et al. (ref. 9) have studied the decomposition reaction of N-chloro-a-amino acid anions in neutral aqueous solution, where the main reaction products are carbon dioxide, chloride ion and imines (which hydrolyze rapidly to amine and carbonyl products). They found that the reaction rate constant of decarboxylation was independent of pH, so they ruled out a proton assisted decarboxylation mechanism, and the one proposed consists of a concerted decarboxylation. For N-bromoamino acids decomposition in the pH interval 9-11 a similar concerted mechanism was proposed by Antelo et al. (ref. 10), where the formation of a nitrenium ion (ref. 11) can be ruled out because it is not consistent with the experimental results. Antelo et al. have also established that when the decomposition reaction takes place at pH < 9, the disproportionation reaction of the N-Br-amino acid becomes important, and the decomposition goes through the N,N-dibromoamino acid. This reaction is also important for N-chloroamino compounds but at more acidic pH values, because the disproportionation reaction... 

When N-donor ligands, such as amines, are added to Hg(I) in H2O disproportionation occurs ... 

Aqueous HCI solutions hydrolyze the P-N bond to give the amine hydrochloride and R2P-OH, which then disproportionates and is oxidized to diphenylphosphinic acid. A free phosphinous amide anion, with the countercation complexed by a crown ether, has been shown to be hydrolyzed and oxidized to the corresponding phosphinite with unusual ease [119]. Formic acid in toluene can be utilized for converting P,P-disubstituted phosphinous amides into their respective phosphane oxides [30]. 

Apart from this mechanistic hypothesis, another scenario, with a ferrate complex as intermediate, may be possible. In 1928, Hieber discovered that Fe(CO)5 78 underwent a disproportionation in the presence of ethylenediamine 122 [97-101]. Depending on the reaction temperature, different ferrate complexes were formed that incorporated a [Fe(en)3] cation (en = ethylenediamine) and mono-, di- or trinuclear ferrate anions (Scheme 32) [102-107]. As the reaction discussed above is also performed with amines at high temperatures, these ferrates may well be involved in the catalytic cycle of the carbonylation discussed above. 

Trichloromethyl chloroformate (diphosgene) is used as a safe substitute for highly toxic phosgene gas. The latter is generated in situ by addition of catalytic amounts of tertiary amines or amides, or active carbon. Diphosgene also disproportionates to 2 equivalents of phosgene on heating above 250°C. 

Diphenyl selenide, 24, 91 Dr- -PROPYLAMINO ETHYL AMINE, 23, 24 y-Di-ra-propylaminopropylamine, 24, 46 Disproportionation, of an iodoso and an iodoxy compound, 22, 52 of iodosobenzene by steam distillation, 22, 72... 

A number of metal carbonyls undergo disproportionation reactions in the presence of other coordinating ligands. For example, in the presence of amines, Fe(CO)5 reacts as follows ... 

Even though alkali metal anions may be freely generated in solution, the isolation of solid salts containing such anions is not straightforward. Thus, the disproportionation observed when an alkali metal is dissolved in an amine or ether... 

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