Study of the Wallach rearrangement and related processes in the 100% sulfuric acid region

1970 ◽  
Vol 48 (2) ◽  
pp. 377-382 ◽  
Author(s):  
E. Buncel ◽  
W. M. J. Strachan
Keyword(s):  
Sulfuric Acid ◽  
Proton Transfer ◽  
Kinetic Method ◽  
Rate Data ◽  
Upper Limit ◽  
Transfer Step ◽  
Rearrangement Process ◽  
Equilibrium Process ◽  
Acid Catalyzed ◽  
Acid Region

Study of the acid-catalyzed Wallach rearrangement of azoxybenzene is extended into the 100% H2SO4 region. The rate of formation of 4-hydroxyazobenzene can be followed spectrally in a straight-forward manner until close to 99% H2SO4, but in higher acidities sulfonation of this product becomes kinetically important. The advent of second equilibrium protonations of 4-hydroxyazobenzene and of 4-hydroxyazobenzene-4′-slfonic acid further complicate the azoxybenzene rearrangement as followed spectrally. Above 100% H2SO4 a second sulfonation is also observed. A method is given for dissecting the rate data for the primary rearrangement process from the first of the sulfonation reactions.The rate of the azoxybenzene rearrangement is observed to increase continuously up to 99.99% H2SO4 (the upper limit of the present kinetic method). This suggests that the second proton transfer step to azoxybenzene is rate-determining and not an equilibrium process. These results permit a clarification of a previously proposed mechanism (1).

THE WALLACH REARRANGEMENT: PART II. KINETICS AND MECHANISM OF THE ACID-CATALYZED REARRANGEMENT OF AZOXYBENZENE

1965 ◽  
Vol 43 (4) ◽  
pp. 862-875 ◽  
Author(s):  
E. Buncel ◽  
B. T. Lawton
Keyword(s):  
Sulfuric Acid ◽  
Proton Transfer ◽  
Acid Concentration ◽  
Entire Range ◽  
Kinetics And Mechanism ◽  
The Other ◽  
Rate Data ◽  
Spectrophotometric Methods ◽  
Aqueous Sulfuric Acid ◽  
Acid Catalyzed

The rate of rearrangement of azoxybenzene to p-hydroxyazobenzene has been measured in 75.3–96.4% sulfuric acid at 25° and in 65.0–90.4% sulfuric acid at 75.5° by spectrophotometric methods. The pKa of azoxybenzene in aqueous sulfuric acid has also been determined. It is found that although azoxybesssnzene is almost completely protonated over the entire range of acid concentration studied, the rate increases by more than 1 000-fold. A two-proton process is therefore indicated and mechanisms are proposed involving a dication (II) as the key intermediate. The rate data do not allow differentiation between two proposed mechanisms, one involving two equilibrium protonations, and the other a single equilibrium protonation followed by rate-determining proton transfer. Past mechanisms of the Wallach rearrangement are discussed.

Hydrolysis mechanisms for acylhydrazines in aqueous sulfuric acid, determined using the excess acidity method

1984 ◽  
Vol 62 (8) ◽  
pp. 1613-1617 ◽  
Author(s):  
Robin A. Cox ◽  
Keith Yates
Keyword(s):  
Sulfuric Acid ◽  
Water Molecule ◽  
Proton Transfer ◽  
Medium Composition ◽  
Hydrolysis Rate ◽  
Bond Rupture ◽  
Rate Data ◽  
Dilute Acid ◽  
Aqueous Sulfuric Acid ◽  
Rate Determining Step

The excess acidity method has been applied to hydrolysis rate data for some acyl- and benzoylhydrazines, obtained as a function of medium composition in aqueous sulfuric acid mixtures. Two hydrolysis mechanisms are indicated, both involving a second proton transfer to monoprotonated substrate. In the first mechanism this transfer is to oxygen, which is the rate-determining step in dilute acid, followed by attack of a water molecule in an A-2 hydrolysis, which is rate determining in more concentrated acid. Bisulfate ion becomes the nucleophile at high acidity. The second mechanism, found at higher acid concentrations, involves rate-determining nitrogen protonation, probably concerted with C—N bond rupture, to give an acylium ion, for those substrates capable of forming one.

scholarly journals Hydrothermal Pretreatment of Wheat Straw: Effects of Temperature and Acidity on Byproduct Formation and Inhibition of Enzymatic Hydrolysis and Ethanolic Fermentation

Agronomy ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 487
Author(s):  
Dimitrios Ilanidis ◽  
Stefan Stagge ◽  
Leif J. Jönsson ◽  
Carlos Martín
Keyword(s):  
Mass Spectrometry ◽  
Sulfuric Acid ◽  
Wheat Straw ◽  
High Performance ◽  
Enzymatic Saccharification ◽  
Hydrothermal Pretreatment ◽  
Gas Chromatography Mass Spectrometry ◽  
Enzymatic Digestibility ◽  
Acid Catalyzed ◽  
Pretreatment Conditions

Biochemical conversion of wheat straw was investigated using hydrothermal pretreatment, enzymatic saccharification, and microbial fermentation. Pretreatment conditions that were compared included autocatalyzed hydrothermal pretreatment at 160, 175, 190, and 205 °C and sulfuric-acid-catalyzed hydrothermal pretreatment at 160 and 190 °C. The effects of using different pretreatment conditions were investigated with regard to (i) chemical composition and enzymatic digestibility of pretreated solids, (ii) carbohydrate composition of pretreatment liquids, (iii) inhibitory byproducts in pretreatment liquids, (iv) furfural in condensates, and (v) fermentability using yeast. The methods used included two-step analytical acid hydrolysis combined with high-performance anion-exchange chromatography (HPAEC), HPLC, ultra-high performance liquid chromatography-electrospray ionization-triple quadrupole-mass spectrometry (UHPLC-ESI-QqQ-MS), and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Lignin recoveries in the range of 108–119% for autocatalyzed hydrothermal pretreatment at 205 °C and sulfuric-acid-catalyzed hydrothermal pretreatment were attributed to pseudolignin formation. Xylose concentration in the pretreatment liquid increased with temperature up to 190 °C and then decreased. Enzymatic digestibility was correlated with the removal of hemicelluloses, which was almost quantitative for the autocatalyzed hydrothermal pretreatment at 205 °C. Except for the pretreatment liquid from the autocatalyzed hydrothermal pretreatment at 205 °C, the inhibitory effects on Saccharomyces cerevisiae yeast were low. The highest combined yield of glucose and xylose was achieved for autocatalyzed hydrothermal pretreatment at 190 °C and the subsequent enzymatic saccharification that resulted in approximately 480 kg/ton (dry weight) raw wheat straw.

Antiaminic agents derived from thieno[2,3-c]-2-benzothiepin: 4-(1-Methyl-4-piperidylidene)-4,9-dihydrothieno[2,3-c]-2-benzothiepin and some related compounds

1983 ◽  
Vol 48 (2) ◽  
pp. 623-641 ◽  
Author(s):  
Zdeněk Polívka ◽  
Miroslav Rajšner ◽  
Jan Metyš ◽  
Jiří Holubek ◽  
Emil Svátek ◽  
...  
Keyword(s):  
Clinical Trials ◽  
Sulfuric Acid ◽  
Title Compound ◽  
Amino Alcohol ◽  
Hydrogen Sulfate ◽  
Geometric Isomers ◽  
Pure Alcohol ◽  
Acid Catalyzed ◽  
Anticataleptic Activity ◽  
Related Compounds

In the reaction of thieno[2,3c]-2-benzothiepin-4(9H)-one (VI) with 1-methyl-4-piperidylmagnesium chloride 7-(1-methyl-4-piperidyl)thieno[2,3-c]-2-benzothiepin-4(9H)-one (VIII) is formed in addition to the expected amino alcohol VII. The title compound I was obtained by the acid catalyzed dehydration of the pure alcohol VII. Compound I (pipethiadene) has outstanding antihistamine, antiserotonin, antireserpine and anticataleptic activity and was recommended to clinical trials as a potential antimigraine agent. For pharmacokinetic and metabolic studies there were prepared the NC2H3 analogue of pipethiadene IV and further, as potential metabolites, the demethyl analogue III, S-oxide X, demethyl S-oxide XI, N-oxide XIII and N,S-dioxide XIV. The Witting reaction of the ketone VI with 3-dimethylaminopropylidenetriphenylphosphorane resulted in a mixture of geometric isomers of 4-(3-dimethylamino-propylidene)-4,9-dihydrothieno[2,3-c]-2-benzothiepin with the strongly predominating Z-isomer XVI which was isolated from the mixture by crystallization of the hydrogen maleate. The mixture with the predominating Z-isomer XVI was converted by the treatment with 80% sulfuric acid and dilution with water to a mixture with the predominating E-isomer XV (dithiadene) which was isolated by crystallization of the hydrogen sulfate. Some further new thieno[2,3-c]-2-benzothiepin derivatives were synthesized as potential intermediates.

Jervine. V. The Sulfuric Acid-catalyzed Acetolysis of Diacetyltetrahydrojervine

1954 ◽  
Vol 76 (22) ◽  
pp. 5609-5616 ◽  
Author(s):  
O. Wintersteiner ◽  
M. Moore ◽  
B. M. Iselin
Keyword(s):  
Sulfuric Acid ◽  
Acid Catalyzed

Toward Magic Photoacids: Proton Transfer in Concentrated Sulfuric Acid

2018 ◽  
Vol 122 (46) ◽  
pp. 9025-9030 ◽  
Author(s):  
Daniel Maus ◽  
Alexander Grandjean ◽  
Gregor Jung
Keyword(s):  
Sulfuric Acid ◽  
Proton Transfer ◽  
Concentrated Sulfuric Acid
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