Amine oxides decomposition

For four- or five-membered cyclic transition states, pyrolysis only leads to beta-elimination if the C -H and C -X bonds can eclipse so as to ensure the necessary proximity for reaction. The syn nature of the amine oxide decomposition has been demonstrated by elimination from the diastereoisomeric pairs of the 1,2-diphenylpropyl system. In the cyclohexyl series, an eclipsed transition state is only achieved if elimination proceeds through the boat conformer and consequently the pyrolysis of 1-methylcyclohexylamine oxide gives an almost quantitative yield of the less stable exo-olefin. This orientation contrasts markedly with that of the six-membered cyclic transition states of the corresponding esters and xanthates which yield predominantly the endo-olefin, syn-clinal stereochemistry being preferred. For all the other ring... 

We repeated Aston and Parker s preparation. The compound does indeed have the structure claimed and is quite stable, requiring hours at 180 to effect decomposition. We have also prepared di-cumyldiazene N-oxide, J., and compared it with the corresponding diazene. Decomposition of 1, like AlBN-0, is very slow. The products of decomposition are o<-methylstyrene, water, dinitrogen, and a small amount of cumyl alcohol. Nitrous oxide is not a product, and decomposition clearly is not proceeding by the process shown in eq. 4. The decomposition is most simply understood in terms of a cyclic decomposition, eq. 5, related to the Cope amine oxide decomposition (17). 

Tertiary phosphine oxides are stable. The temperatures required for thermal decomposition are approximately 300°C higher than the corresponding amine oxides (96). Trimethyl phosphine oxide is stable to 700°C. 

Decomposition. Most amine oxides undergo thermal decomposition between 90 and 200 °C. Aromatic amine oxides generally decompose at higher tempeiatuies than ahphatic amine oxides and yield the patent amine. 

In the pyrolysis of pure amine oxides, temperature has a significant effect on the ratio of products obtained (22). The principal reaction during thermal decomposition of /V,/V-dimetby11 amyl amine oxide [1643-20-5] at 80—100°C is deoxygenation to /V,/V-dimetby11 amyl amine [112-18-5] (lauryl = dodecyl). 

However, when the temperature is increased to 120°C, the principal reaction is the elimination to olefin. The thermal decomposition of dimethyl dodecyl amine oxide at 125°C in a sealed system, as opposed to a vacuum used by Cope and others, produces 2-methyl-5-decyhsoxa2ohdine, dimethyl dodecyl amine, and olefin (23). The amine oxide oxidi2es XW-diaLkylhydroxylainine to the nitrone during the pyrolysis and is reduced to a tertiary amine in the process. 

Metal Catalysis. Aqueous solutions of amine oxides are unstable in the presence of mild steel and thermal decomposition to secondary amines and aldehydes under acidic conditions occurs (24,25). The reaction proceeds by a free-radical mechanism (26). The decomposition is also cataly2ed by V(III) and Cu(I). 

Reduction. Just as aromatic amine oxides are resistant to the foregoing decomposition reactions, they are more resistant than ahphatic amine oxides to reduction. Ahphatic amine oxides are readily reduced to tertiary amines by sulfurous acid at room temperature in contrast, few aromatic amine oxides can be reduced under these conditions. The ahphatic amine oxides can also be reduced by catalytic hydrogenation (27), with 2inc in acid, or with staimous chloride (28). For the aromatic amine oxides, catalytic hydrogenation with Raney nickel is a fairly general means of deoxygenation (29). Iron in acetic acid (30), phosphoms trichloride (31), and titanium trichloride (32) are also widely used systems for deoxygenation of aromatic amine oxides. 

The mechanism is supported by findings from the decomposition reaction of the amine oxides derived from threo- and cryt/zro-2-amino-3-phenylbutane. The t/zrco-amine oxide 6 yields -2-phenylbut-2-ene 7 with a selectivity of 400 1, and the cryt/zro-derivative 8 yields the Z-olefin 9 with a selectivity of 20 1 ... 

Tertiary amines can be converted to amine oxides by oxidation. Hydrogen peroxide is often used, but peroxyacids are also important reagents for this purpose. Pyridine and its derivatives are oxidized only by peroxyacids. In the attack by hydrogen peroxide there is first formed a trialkylammonium peroxide, a hydrogen-bonded complex represented as R3N-H202, which can be isolated. The decomposition of this complex probably involves an attack by the OH moiety of the H2O2. Oxidation with Caro s acid has been shown to proceed in this manner ... 

Hence, the copper surface catalyzes the following reactions (a) decomposition of hydroperoxide to free radicals, (b) generation of free radicals by dioxygen, (c) reaction of hydroperoxide with amine, and (d) heterogeneous reaction of dioxygen with amine with free radical formation. All these reactions occur homolytically [13]. The products of amines oxidation additionally retard the oxidation of hydrocarbons after induction period. The kinetic characteristics of these reactions (T-6, T = 398 K, [13]) are presented below. 

These are the most common diazeniumdiolates, formed by the reaction of secondary amines and polyamines with nitric oxide in basic media [214, 215]. They are stable solids, capable of regenerating two equivalents of nitric oxide along with the starting amine in neutral or acidic buffers. The half-life of NO generation varies from a few seconds to many hours, depending on the amine. The decomposition to NO is a spontaneous, first-order reaction at constant pH. 

Many amines are oxidized much more rapidly than the one used in this preparation, and it is often necessary to cool such reaction mixtures in order to avoid decomposition of the amine oxide or a vigorous exothermic reaction. 

The fluoroalkylbenzylamines are characterised by their particular inertness [270], being devoid of the tendency towards oxidative decomposition that is generally characteristic of amines. In fact, oxidation of methyl will occur in preference to that of an amino group in these systems (Figure 8.107). 

The success of the Wolff-Kishner and related C==0 to CH2 transformations (see Chapter 1.14, this volume) attests to the efficiency of the diazene decomposition route applied to the reductive deamination of primary amines, this requires methods which transform RNH2 into RN=NH, which corresponds to an amination-oxidation sequence. Several one- or two-step processes have been described which carry out this transformation. Treatment of amino acids in alkaline solution with excess hydroxylamine-O-sul-fonic acid (HOS) gave moderate yields of deamination product, as exemplified by the dipeptide case shown in equation (23). 

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