Oxidation of benzylamines

A comprehensive account of the oxidation of benzylamine by both neutral and alkaline permanganate has been published recently . The neutral amine is the active reductant at all pH values and at pH 9.9 good second-order kinetics were obtained. Under these conditions the stoichiometry is... 

In the same paper the authors list the responses of a number of amines and amides towards permanganate and record the effect of freezing the medium upon the oxidation of benzylamine. 

Kinetics and mechanisms of oxidation of amines by Ru porphyrin complexes (particularly TMP species) have been reviewed [42]. rranx-Ru(0)2(TMP)/02/ CgHg/50°C/24h oxidised primary and secondary amines in the oxidation of ben-zylamine frani-Ru(NHj)jCHjPh)2(TMP) was isolated and characterised crystallo-graphically. A mechanism involving a two-electron oxidation of benzylamine to A-benzylideneamine by tra i-Ru(0)2(TMP) was proposed with concomitant reduction of the latter to Ru (0)(TMP). This disproportionates to tranx-Ru "(0)2(TMP) and Ru"(TMP) the latter regenerates Ru" (0)(TMP) with O, while the second two-electron oxidation of the imine to the aldehyde is effected by tranx-Ru(0)2(TMP) [597], (Table 5.1) [598]. 

Edmondson has carried out extensive SAR on the oxidation of benzylamine analogues with both MAO A [11] and B [30], Binding efficiency to MAO B of para-substituted benzylamines increased with increasing lipophilicity. The rate of oxidation (/Ccat) was more influenced by steric factors, p-CFs having the slowest rate in the series studied and benzylamine having the highest rate, with p-F intermediate in value. Thus, steric factors appear to be more important than electronic factors in determining the rate of MAO B oxidation of para-substituted benzylamines. In these studies, no evidence was found for radical intermediates. This and other results from this study were discussed in terms of the validity of the SET mechanism proposed by Silverman [10]. 

M.C. Walker, D.E. Edmondson, Structure-activity relationships in the oxidation of benzylamine analogues by bovine liver mitochondrial monoamine oxidase B, Biochemistry 33 (1994) 7088-7098. 

The comparison of the bands observed after benzonitrile and benzylamine transformation over vanadia-titania allows us to suggest that benzamide can also be obtained by oxidation of benzylamine. Moreover, the growth of the absorption near 1640 cm and the appearance of bands at 1330 and 1240 cm during benzylamine oxidation suggests that benzaldehyde is also formed. A likely assignment for the band at 1670 cm is to the stretching of a C=N double bond (75), so being likely indicative of the formation of benzaldimine. 

Scheme 10 Catalytic mechanism for the oxidation of benzylamine to benzylidinebenzylamine using 23...

Using structures, write the reaction for the monoamine oxidase-catalyzed oxidation of benzylamine. 

Mure, M., and Klinman, J. P., 1995a, Model studies of topaquinone-dependent amine oxidases oxidation of benzylamine by topaquinone analogues, J. Amer. Chem. Soc. 117 8698n8706. 

In the oxidation of benzylamines, apart from formation of the dealkylated amine and benzaldehyde [61-64], formation of imines [65, 66], benzonitrile [64], diazines [62] anilines [67], and iV-benzylidene benzyl amines [64, 66, 67] has also been observed. 

Silverman s studies on mechanism based MAO inactivation have provided overwhelming support for the role of electron transfer in the MAO catalyzed dealkylation of amines. It must be mentioned however that spectroscopic attempts for detecting the radical ion intermediates have hitherto been unsuccessful. Yasanobu and coworkers could not find EPR spectral evidence for radical intermediates in MAO-catalyzed oxidation of benzylamine [205]. Miller et al. failed to observe the flavin semiquinone or an amine-flavin adduct in rapid-scan-stopped flow spectroscopy [206]. The only time-dependent absorption change observed in this study was the bleaching of the oxidized flavin. Furthermore, no influence of a magnetic field up to 6500 G was observed on the rate of MAO B reduction. The reaction rates of systems with kinetically significant radical pair intermediates are known to be altered... 

Oxidations and reductions. Phase-transfer catalyst enables the oxidation of benzylamines to benzamides with KMnO in an organic solvent, whereas reduction of aldehydes can be carried out in toluene using NaBH and polyethylene glycol. ... 

Bovine serum amine oxidase (BSAO) is a copper-containing amine oxidase which utilizes a covalently bound 2,4,5-trihydroxyphenylalanine quinone (TPQ) cofactor in the two-electron oxidation of a broad spectrum of primary amines [99]. The oxidation is thought to proceed via the formation of an iminium complex between the oxidized form of the cofactor and the primary amine (1 in Scheme 10.4). The substrate imine undergoes deprotonation to form product imine, which, after hydrolysis, releases aldehyde product and reduced cofactor [100]. Proton transfer is either partially or largely rate-limiting for the oxidation of benzylamines, as evidenced by a large deuterium isotope effect at the methylene adjacent to the amino group [36, 101, 102]. 

It is noteworthy that the Swain-Schaad exponents are temperature independent for both primary and secondary isotope effects at pH 6.1. Two scenarios can be considered. The first is that there is a significant commitment to catalysis which is obscuring the full value of the isotope effect on k st/Km- It is anticipated that, because the primary and secondary exponents are temperature independent, this commitment would be temperature independent. Jonsson et al. have used North-rop s expression [60] for correcting observed isotope effects based on the assumption of a temperature-independent commitment (Eq. (10.22)). A commitment of 0.6 for the oxidation of benzylamine brings the secondary exponent to about 3.3,... 

The subsequent oxidation of the hydroxymethyl group into aldehyde shows very large variations in the KIE values according to whether proton abstraction is concerted with C-O bond formation (kH/kD = 1.6) or wether the tunnelling effect contribution is great (kH/kD = 50). However oxidations with chromium derivatives have normal primary KIE (5 to 6). Similar values are observed during the oxidation of benzylamines... 

The 5-deazaflavin (203), in combination with flavin mononucleotide (FMN), provides an efficient catalytic system for the aerobic oxidation of benzylamines to benzaldehydes (Scheme 90). Alternatively, an auto-... 

The mechanism of the oxidation of primary amines to nitriles with cuprous chloride-dioxygen-pyridine mixtures has recently been investigated by measuring the hydrogen-deuterium kinetic isotope effect in the oxidation of benzylamine to benzonitrile. In earlier work , the authors reported that nitriles could be prepared from amines in almost quantitative yield and high purity using this cuprous chloride reagent. 

As04 W0(02)2 4r . Oxidation of pnmaiy alcohols to aldehydes is m general faster than the conversion of secondary alcohols to ketones. Oxidation of benzylamine by [( C, Hj3)4N]3[P04 W0(02)2)4] to a mixture of benzaldehyde and benzyloxime The... 

These oxidation states interconvert each other, allowing the construction of a catalytic system for oxidation reaction. Actually, polyanilines or polypyrroles have been demonstrated to serve as synthetic metal catalysts under oxygen atmosphere in dehydrogenative oxidation of benzylamines, 2-phenylglycine, and 2,6-di-t-butylphenol (Scheme 3.2). " A similar catalysis is also observed with the proto-nated quinonediimine or phenylenediamine derivative, a unit of polyaniline. These catalytic activities are revealed to be controlled by protonic acid doping... 

A few model systems for CAO chemistry, which are catalytic, have been reported. Suzuki, Kawamoto, and co-workers synthesized and characterized Cu(II) complex with 2,2 -bipyridine (bpy) and a tyrosine derivative, 2,4,5-trihydroxy-phenylalanine (topa) (109). The resulting complex, [Cu(DL-topa)(bpy)]+, catalyzes the aqueous aerobic oxidation of benzylamine to benzaldehyde. There is a rate improvement of up to 4 compared to topa itself (109,110). However, polymerization of the topa moiety occurred during the oxidation reaction with loss of activity of the Cu(II) catalyst (109). 

Almost at the same time, Nguyen and coworkers reported the multicomponent oxidative coupling of amines 94 with thioamides 96 catalyzed by elemental sulfur [64]. The reactions were carried out under solvent-free and harsh conditions (130°C) to afford the final thioamides 97 in good to excellent yields (62-95%). The proposed mechanism of this reaction is shown in Scheme 11.16. First, the oxidation of benzylamine 94 with sulfur affords the corresponding imine 95. Next, the oxidation of imine 95 with sulfur affords the corresponding thioamide 96 that undergoes franithioamidation to afford the final products 97. 

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