Kinetics and selectivity of oxidation of saturated hydrocarbons in sulphuric acid media containing anthracene and cyclohexane oligomers

Lutsyk

2010

Theor Exp Chem

The effect of the acidity of the medium on the hydroxylation and nitration of alkanes (RH) in 90-98% H 2 SO 4 at 25°C is described quantitatively by a model taking account of the thermodynamic activity of the RH, H 2 O, and HSO 4 -particles. It was concluded that in the transition states the reagents H O HSO 3 2 4 + -and NO HSO 2 4 + -are present as HO + and NO 2 + ions without the bases H 2 O and HSO 4 -, the alkanes are present without hydrophobic shells, and the initial reaction products are ROH 2 + and RNO 2 H + . of water and bisulfate ions, electrophilic insertion.Olah and co-workers [1] observed the similarity of the products from the reactions of alkanes (RH) with hydrogen peroxide in the superacids HSO 3 F and HSO 3 F-SbF 5 -SO 2 ClF, in media HF and HF-BF 3 not forming peroxo acids, and in 96% H 2 SO 4 and concluded [1] that the reagent in these systems is the H O 3 2 + ion, which attacks the electrons of the C-H bond in the form of the generated OH + cation:The transition state (TS) contains a three-center two-electron bond (3c-2e).Olah substitution model (3c-2e), which was also proposed for nitration with NO 2 + ions [2] and other reactions of alkanes with electrophiles, was subject to criticism from Schreiner and co-workers [3]. According to their quantum calculations the scheme (1) is not general and only applies to the reactions of alkanes with protons (H/D exchange) and carbocations; in the transition state of the reaction of CH 4 + NO + in the gas the electrophilic center (N ä+ ) of the reagent interacts with the C atom but not with the C-H bond while the vacant electron pair of the oxygen atom accepts a proton. The NO + is inserted into the C-H bond with the formation of O-protonated nitrosomethane H 3 CNOH + [the first product, which then changes to the O-protonated formamide HC(NH 2 )OH + ]. [In [3] this reaction was called substitution, although in actual fact insertion occurs, while Olah process with the 3c-2e transition state or intermediate is called insertion.] Olah and co-workers [4] supported a special 20 0040-5760/10/4601-0020

Section: The Effects Of Solvation In the Kinetics Of Ion-molecular Rementioning

confidence: 63%

Section: The Mechanism Of Hydroxylationmentioning

confidence: 87%

Section: The Effects Of Solvation In the Kinetics Of Ion-molecular Rementioning

confidence: 99%

See 1 more Smart Citation

Effect of desolvation of the reactants during change in the acidity of the medium on the electrophilic hydroxylation and nitration of alkanes

Lutsyk

2010

Theor Exp Chem

“…Although many or ganic substances in concentrated sulfuric acid generate carbocations, it is difficult to find systems convenient for kinetic studies: as a rule, stable carbocations are lowly reactive, whereas unstable carbocations, such as tert butyl or cyclohexyl, rapidly undergo deep transformations with a change in the skeleton to form a complicated array of the products. [22][23][24][25][26][27] It was found that sulfuric acid solutions of anthracene and cyclohexene oligomers 28, 29 are active in the reactions with alkanes, whereas formaldehyde solu tions are active in the reactions with alkanes 30 and arenes. 31 The kinetics of these reactions was studied by the sub strate decay.…”

Section: Introductionmentioning

confidence: 99%

First steps of the reactions of alkanes and arenes with adamantyl cations in sulfuric acid in comparison with other reagents

Volkova

2008

Russ Chem Bull

Solutions of 1 adamantanol in sulfuric acid at T < 100 °С interact with alkanes (RH, [H 2 SO 4 ] > 85%) and arenes (ArH, [H 2 SO 4 ] > 59%). The data on the kinetics, kinetic isotope effect (KIE), effects of the structure of RH and ArH and acidity of the medium, and the observation of 1,4 cis dimethylcyclohexane isomerization indicate that adamanyl cations (Ad + ) serve as reactive species. In the reactions with alkanes, the Ad + cation abstracts the hydride ion from RH in the rate determining step. Compensation dependences appear between the activa tion parameters for the KIE and "effect 5/6" (ratio of the rate constants for the С-Н bond cleavage in cyclopentane and cyclohexane) in the reactions of cycloalkanes with Ad + and other electrophilic reagents, such as "anthracene" (An 2 )H + and hydroxymethyl (CH 2 OH) + cations and Hg II ions, including the points of the lower selectivity limit (k H /k D ) = 1.4, ("5/6") = 1. In the reactions with the Ad + cation, the bond selectivity 3 0 : 2 0 of alkanes is higher, while 2 0 : 2 0 is lower compared to other reagents. In the first case, the selectivity is probably deter mined predominantly by the energies of the cleaved С-Н bonds, whereas in the second case it is determined by steric hindrances. Judging by the kinetic and selectivity data in the series benzene-toluene-o xylene-m xylene and the absence of the reaction with p xylene, mesity lene, and pseudocumene, it can be concluded that the main contribution to the Ad + + ArH interaction is made by adamantylation to the para and meta positions of the benzene ring, whereas the ortho positions are inaccessible to the attack because of steric hindrances.

“…According to quantum calculations [2,3] reactions of methane with the OH + cation and other strong electrophiles D + , CH 3 + , C H 2 5 + , and F + in the gas phase also proceed via formation of 3c-2e bonds as shown in scheme (1). We have previously [4,5] studied the kinetics of the reaction of RH with hydrogen peroxide and also with ammonium peroxodisulfate in 88-95% sulfuric acid at 5 [4,5] permitted the suggestion that in both systems the basic contribution in the reactions was a non-radical mechanism involving the OH + cation. In aqueous solutions thermal, catalytic, photo-and radiolytic decomposition of S O 2 8 2− anion led to sulfate anion-radicals [5,8] which, as we discovered [5,9], removed a hydrogen atom from alkanes at 60°C.…”

mentioning

confidence: 99%

Temperature dependence of the ratios of the rate constants of hydroxylation of the cycloalkanes C6H12/C6D12 and C5H10/C6H12 in sulfuric acid

Volkova

2008

Theor Exp Chem

Key words: cycloalkanes, hydroxyl cations, sulfuric acid, kinetic isotopic effect, the 5/6 effect, temperature dependence.It was observed previously [1] that similar products of the oxidation of saturated hydrocarbons (RH) were obtained with hydrogen peroxide in the acids FSO 3 H-SbF 5 -SO 2 ClF, FSO 3 H, 96 mass % H 2 SO 4 , and also in HF and HF-BF 3 which are not capable of forming peroxoacids. It was concluded [1-3] that in these media hydroxy cations OH + were produced from protonated hydrogen peroxide, H O 3 2 + , addition of which to a C-H s-bond gave rise to a pentacoordinate hydroxycarbonium