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P-hydroxyalkyl radical

Although a-hydroxyalkyl radicals such as the hydroxymethyl radical are oxidized without an adduct being noticed [reaction (14) k= 1.6 x 108 dm3 mol1 s 1], such a complex becomes apparent in the case of P-hydroxyalkyl radicals [reactions (15) and (16) k15 = 3 x 107 dm3 mol1 s k16 = 330 s Freiberg and Meyer-stein 1980], whereby the epoxide is formed (Soylemez and von Sonntag 1980). [Pg.109]

The initial reactions of alkenes and OH are the addition, and they are mostly in the high-pressure limit under atmospheric conditions including ethylene as seen in Chap. 5, Sect. 5.2.8. The addition reaction forms p-hydroxyalkyl radicals which have an OH group on the carbon adjacent to the carbon atom with an unpaired electron. [Pg.297]

Ceric ions react rapidly with 1,2-diols. There is evidence for chelation of cerium and these complexes are likely intermediates in radical generation10 106 The overall chemistry may be understood in terms of an intermediate alkoxy radical which undergoes p-scission to give a carbonyl compound and a hydroxyalkyl radical (Scheme 3.59). However, it is also possible that there is concerted electron transfer and bond-cleavage. There is little direct data on the chemical nature of the radical in termediates. [Pg.105]

Alcohols, like hydrocarbons, are oxidized by the chain mechanism. The composition of the molecular products of oxidation indicates that oxidation involves first the alcohol group and the neighboring C—H bond. This bond is broken more readily than the C—H bond of the corresponding hydrocarbon, since the unpaired electron of the formed hydroxyalkyl radical interacts with the p electrons of the oxygen atom. [Pg.288]

Schuchmann MN, von Sonntag C (1982) Flydroxyl radical induced oxidation of diethyl ether in oxygenated aqueous solution. A product and pulse radiolysis study. J Phys Chem 86 1995-2000 Schuchmann MN, Schuchmann H-P, Knolle W, von Sonntag J, Naumov S, Wang W-F, von Sonntag C (2000) Free-radical chemistry of thiourea in aqueous solution, induced by OFI radical, FI atom, a-hydroxyalkyl radicals, photoexcited maleimide, and the solvated electron. Nukleonika 45 55-62... [Pg.157]

Because of the rapid 1,2-H-shift [reaction (51)] and the ready conversion of the ensuing a-hydroxyalkyl radical into H02702 by 02 [cf. reactions (8) and (10)/(11)], primary and secondary peroxyl are often the precursor of 02 in theses systems. Furthermore, the P-fragmentation reaction (60) creates a new radical and hence a new peroxyl radical, a situation which makes the elucidation of mechanistic details often very difficult if not impossible. The peroxyl radical systems that have been investigated in detail thus far have been discussed by von Sonntag and Schuchmann (1997). [Pg.176]

The Thd C(3 ) radical is an a-hydroxyalkyl-P-alkoxyl radical that can rearrange and yields after reduction 2>4-didcoxy-pcnlos-3-ulosc, whereby Thy is released (Dizdaroglu et al. 1976) [reactions (277) and (278) for the yield, see Table 10.27]. [Pg.294]

The teduction of p-hydroxyalkyl selenides to alcohols has been achieved - - by lithium in ethylamine (Scheme 161, a Scheme 162, a Scheme 163, a Scheme 167) or triphenyl- or tributyl-tin hydride in toluene, - with or without AIBN. Most of these reactions proceed through radicals. Hie reactions involving tin hydrides can be carried out thermally around 120 C or photochemically at much lower temperature (0-20 The cleavage of the C—SePh bond is faster than that of the... [Pg.699]

As shown by J.-P. Pete the hydroxyalkyl radical formed initially can also be trapped in an intramolecular reaction, for example, by an alkyne moiety. The resulting vinyl radical abstracts another hydrogen from an external source. The starting material for this reaction sequence can be prepared by photochemical Wolff ring contraction reaction (see also Chapter 2). [Pg.13]

Reduction-addition. On reductive opening of epoxides in the presence of pyridines the radicals are intercepted, therefore 2-(P-hydroxyalkyl)pyridines such as chiral ligands 1 are readily accessible on the basis of this reaction. ... [Pg.404]

In the presence of NO, the P-hydroxyalkyl peroxy radical reacts with NO to form either the P-hydroxylalkoxy radical plus N02 or the P-hydroxynitrate 8... [Pg.249]

Rate constants for the reactions of P-hydroxyalkyl peroxy radicals with NO are essentially identical to those for the reaction of NO with > C2 alkyl peroxy radicals formed from alkanes. [Pg.249]

The reactions of a-hydroxyalkyl radicals with Co P also took place via addition to the metal but, unlike the case of Fe P, the adducts were found to undergo heterolysis leading to reduction of the porphyrin to Co P. Another difference between the iron and cobalt porphyrins is in the stability of the methyl adduct CH3Co P was found to be stable even in the presence of O2. Related studies were carried out on the reactions of alkyl radicals with Co -tetrasulfophthalocyanine (tspc) and with Bi2r. Several cobalt-carbon adducts have been observed and in many cases they were found to decompose to yield the oxidized Co -complex. However, in the reaction of Co tspc with the radical derived from t-BuOH, the oxidized product was formed in neutral solutions but the reduced product, Co tspc, was formed in alkaline solutions. [Pg.470]

Carbinol ROH can be similarly eliminated [reaction (6)] (this reaction has been studied in a variety of model compounds [29, 30] cf. further [31, 32] and references therein) this reaction as well converts the exocylic glucose-derived radical 6 into a P-ketoalkyl radical. The elimination of ammonia from P-amino-a-hydroxyalkyl radicals has also been reported [33]. [Pg.485]

While a-hydroxyalkyl radicals are of a reducing nature [cf. reaction (7)] [17, 34], the resulting P-ketoalkyl radicals have oxidizing properties. The latter can effect (slow) H-abstraction from the substrate [reaction (8)] which in the case of ethylene glycol leads to a short chain reaction [35]. [Pg.485]

Reaction Scheme 7.2 summarizes the reaction mechanism for 1-butene (l-C4Hg) as an example of alkenes. The hydroxyalkyl radicals formed by the pathways (a) and (b) is a kind of alkyl radicals mentioned in the previous Sect. (7.2.2), and exclusively forms hydroxyperoxy radicals by the reaction with O2 in the atmosphere. From the hydroxyperoxy radicals, oxyradicals (hydroxybutoxy radicals) and NO2 (pathways (d), (k)), and partially hydroxybutyl nitrate (pathways (e), (1)) are produced by the reaction with NO as in the case of alkylperoxy radicals described in the previous paragraph. The yields of hydroxylalkyl nitrates are 2-6 % for C4-C6 alkenes (O Brien et al. 1998), which is about half of those for alkyl nitrates from the alkoxy radicals. Hydroxy alkoxy radicals formed in pathways (d) and (k) are known to follow the three reaction pathways, unimolecular decomposition ((g), (n)), H-atom abstraction by O2 ((h), (o)), and dihydroxyl radical formation by isomerization (p), corresponding to reactions (7.25), (7.24) and... [Pg.297]

Based on the biochemical and sequence data, we have proposed that 2-oxoacid ferredoxin oxidoreductases with different subunit compositions have an essentially similar catalytic mechanism with one TPP and at least one [4Fe-4S] cluster as the minimal set of redox centers, which will include the intermediacy of a hydroxyalkyl-TPP radical, and that the 8 subunit/domain carrying two [4Fe-4S] clusters may serve as (accessory) intramolecular electron transmitter from the [4Fe-4S] cluster in the p subunit/domain to the physiological electron acceptor... [Pg.19]


See other pages where P-hydroxyalkyl radical is mentioned: [Pg.254]    [Pg.1165]    [Pg.90]    [Pg.254]    [Pg.1165]    [Pg.90]    [Pg.386]    [Pg.104]    [Pg.312]    [Pg.232]    [Pg.675]    [Pg.257]    [Pg.249]    [Pg.470]    [Pg.616]    [Pg.5]    [Pg.482]    [Pg.79]    [Pg.1168]    [Pg.33]    [Pg.490]    [Pg.17]   
See also in sourсe #XX -- [ Pg.90 ]




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