Photosensitized oxidation of alkyl phenyl sulfoxides. C-S bond cleavage in alkyl phenyl sulfoxide radical cations

The 3-cyano-N-methylquinolinium perchlorate (3-CN-NMQ(+)ClO4(-))-photosensitized oxidation of phenyl alkyl sulfoxides (PhSOCR1R2R3, 1, R1 = R2 = H, R3 = Ph; 2, R1 = H, R2 = Me, R3 = Ph; 3, R1 = R2 = Ph, R3 = H; 4, R1 = R2 = Me, R3 = Ph; 5, R1 = R2 = R3 = Me) has been investigated by steady-state irradiation and nanosecond laser flash photolysis (LFP) under nitrogen in MeCN. Steady-state photolysis showed the formation of products deriving from the heterolytic C-S bond cleavage in the sulfoxide radical cations (alcohols, R1R2R3COH, and acetamides, R1R2R3CNHCOCH3) accompanied by sulfur-containing products (phenyl benzenethiosulfinate, diphenyl disulfide, and phenyl benzenethiosulfonate). By laser irradiation, the formation of 3-CN-NMQ(*) (lambda(max) = 390 nm) and sulfoxide radical cations 1(*+) , 2(*+), and 5(*+) (lambda(max) = 550 nm) was observed within the laser pulse. The radical cations decayed by first-order kinetics with a process attributable to the heterolytic C-S bond cleavage leading to the sulfinyl radical and an alkyl carbocation. The radical cations 3(*+) and 4(*+) fragment too rapidly, decaying within the laser pulse. The absorption band of the cation Ph2CH(+) (lambda(max) = 440 nm) was observed with 3 while the absorption bands of 3-CN-NMQ(*) and PhSO(*) (lambda(max) = 460 nm) were observed just after the laser pulse in the LFP experiment with 4. No competitive beta-C-H bond cleavage has been observed in the radical cations from 1-3. The C-S bond cleavage rates were measured for 1(*+), 2(*+), and 5(*+). For 3(*+) and 4(*+), only a lower limit (ca. >3 x 10(7) s(-1)) could be given. Quantum yields (Phi) and fragmentation first-order rate constants (k) appear to depend on the structure of the alkyl group and on the bond dissociation free energy (BDFE) of the C-S bond of the radical cations determined by a thermochemical cycle using the C-S BDEs for the neutral sulfoxides 1-5 obtained by DFT calculations. Namely, Phi and k increase as the C-S BDFE becomes more negative, that is in the order 1 < 5 < 2 < 3, 4, which is also the stability order of the alkyl carbocations formed in the cleavage. An estimate of the difference in the C-S bond cleavage rate between sulfoxide and sulfide radical cations was possible by comparing the fragmentation rate of 5(*+) (1.4 x 10(6) s(-1)) with the upper limit (10(4) s(-1)) given for tert-butyl phenyl sulfide radical cation (Baciocchi, E.; Del Giacco, T.; Gerini, M. F.; Lanzalunga, O. Org. Lett. 2006, 8, 641-644). It turns out that sulfoxide radical cations undergo C-S bond breaking at a rate at least 2 orders of magnitude faster than that of corresponding sulfide radical cations.     

A metal-free protocol for direct oxidative de-alkoxycarbonylation of alkyl phenyl acetate by molecular iodine

A metal-free protocol for the direct oxidative de-alkoxycarbonylation of alkyl phenyl acetate has been carried out by molecular iodine with good yield. In the present Letter, the vital role of iodine in oxidative de-alkoxycarbonylation is described. This method has been proven to be tolerant to a broad range of functional groups.     

The mass spectra of alkyl phenyl tellurides

The mass spectra of several alkyl phenyl tellurides, C₆H₅TeR (R = CH₃, CD₃, C₂H₅, n-C₃H₇, i-C₃H₇ and n-C₄H₉) have been studied with special emphasis on the fragmentation patterns involving cleavage of the alkyl and aryl tellurium–carbon bonds. Each compound exhibited intense parent ions. The rearrangement ions [C₆H₆Te]⁺? and [C₆H₆]⁺? were found in the spectra of phenyl ethyl and higher tellurides. Two other rearrangement ions [HTe]⁺ and [C₇H₇]⁺ were observed in the spectrum of each compound. Examination of the mass spectrum of phenyl methyl-d₃ telluride demonstrated that the [HTe]⁺ ions derive hydrogen from the phenyl group.     

The fragmentation of ionized alkyl phenyl ethers

The energetics of olefin loss from ionized alkyl phenyl ethers have been determined by ionization and appearance energy measurements. It is concluded that the reaction is governed by one or more of three features: (i) the strength of the bond between the phenoxy radical and the alkyl ion; (ii) the ease of isomerization of the alkyl ions, chiefly by H-shifts therein, and (iii) the strength of the C? H bond (primary, secondary and tertiary) involved in the H transfer to oxygen which precedes the olefin loss. The possible participation in the reaction of distonic ions and proton bound radical-molecule pairs is also discussed.     

Vinyl phenyl telluride from metallic tellurium,acetylene, and iodobenzene

Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, p. 200, January, 1988.     

Photo-SRN1 reactions of phenyl telluride anion with haloarenes

Phenyl telluride anion was prepared in liquid ammonia by reaction of dipheyyl ditelluride with two equivalents of sodium metal under nitrogen. This anion reacts with haloarenes under irradiation to form aryl phenyl tellurides, probably by the photo-S_RN1 mechanism of aromatic substitution.     

Indium-mediated mild and efficient one-pot synthesis of alkyl phenyl selenides

A mild and convenient one-pot process for synthesizing alkyl phenyl selenides is developed using indium metal. The reaction shows the selectivity for tert-alkyl, benzylic, and allylic halides over primary and secondary alkyl halides.     

Tandem enzyme-catalysed oxidations of alkyl phenyl sulfides and alkyl benzenes: enantiocomplementary routes to chiral phenols

Dioxygenase-catalysed trioxygenation of alkyl phenyl sulfides and alkyl benzenes yields enantiopure cis-dihydrodiol sulfoxides and triols respectively; naphthalene cis-dihydrodiol dehydrogenase-catalysed aromatisation of these diastereoisomers gives enantiopure catechols of either configuration.     

Photo-induced deep aerobic oxidation of alkyl aromatics

Oxidation is a major chemical process to produce oxygenated chemicals in both nature and the chemical industry. Presently, the industrial manufacture of benzoic acids and benzene polycarboxylic acids(BPCAs) is mainly based on the deep oxidation of polyalkyl benzene, which is somewhat suffering from environmental and economical disadvantage due to the formation of ozone-depleting Me Br and corrosion hazards of production equipment. In this report, photo-induced deep aerobic oxidation of(poly)alkyl benzene to benzene(poly)carboxylic acids was developed. CeCl_3 was proved to be an efficient HAT(hydrogen atom transfer) catalyst in the presence of alcohol as both hydrogen and electron shuttle. Dioxygen(O_2) was found as a sole terminal oxidant. In most cases, pure products were easily isolated by simple filtration, implying large-scale implementation advantages.The reaction provides an ideal protocol to produce valuable fine chemicals from naturally abundant petroleum feedstocks.     

Study of alkyl nitrites oxidation with DMSO

The oxidation of nine alkyl nitrites to the corresponding carbonyl compounds in yields of 76–96% by dimethyl sulfoxide (DMSO) is described; since oxidation with DMSO is very selective this method can be used to obtain aldehydes or ketones from alcohols which include other labile functional groups such as alkene, alkyne and aldehyde.     

Kinetics and mechanism of oxidation of substituted phenyl methyl sulphides by n-bromoacetamide

The kinetics of oxidation of several substituted phenyl methyl sulphides by N-bromoacetamide (NBA) in 80%acetonitrile-20%water (v/v) mixture are presented. The reaction is first order with respect to both sulphide and NBA and second order in Hg(II). The rate of the reaction exhibits inverse dependence on both [acetamide] and [NBA]. Electron-releasing substituents present in the phenyl ring of the sulphides accelerate the rate while electron-withdrawing ones retard it. The results are in accord with a mechanism involving the reaction between NBA-Hg(II) and sulphide-Hg(II) complexes in the slow rate-limiting step affording a sulphoniumion which hydrolyses in a subsequent fast step to the sulphoxide.     

Kinetics and mechanism of the oxidation of methyl phenyl sulfoxide by peroxodiphosphate

The kinetics of the oxidation of methyl phenyl sulfoxide (MPSO) by potassium peroxodiphosphate (PP) in 50% aqueous acetic acid obeys the rate law.-d[PP]_T/dt=k[PP] [MPSO] at constant [H⁺]. The active species in the oxidation has been found to be H₃P₂O ₈ ^– . The kinetic results have been explained by a polar mechanism.

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() () 50%- (./.) -d[]^T/dt=k·[]·[] [H^*]. H₃P₂O ₈ ^– . .

     

Water-soluble photoinitiators: Primary processes in hydroxy alkyl phenyl ketones

Photopolymerization of acrylamide in water has been investigated in the presence of watersoluble hydroxy alkyl phenyl ketones. The processes involved in the excited states (α-cleavage, electron transfer, monomer quenching) have been studied by time-resolved laserspectroscopy. Substitution at the para position of the phenyl ring changes drastically the reactivity and influences the possibility of synergistic effects when combining these photoinitiators with thioxanthone derivatives.     

A mechanism of mass spectral ketene elimination from phenyl acetates

Deuterium labelling experiments show that mass spectal ketene elimination from O-acetyl methyl salicylate involves a four-membered cyclic transition state and gives a phenolic fragment ion.