Acid-Catalyzed Cracking of Polyolefins: Primary Reaction Mechanisms

2006 ◽  
pp. 43-72 ◽  
Author(s):  
Robert L. White
Keyword(s):  
Reaction Mechanisms ◽  
Primary Reaction ◽  
Acid Catalyzed

scholarly journals BIS-DEACETYLATION OF TETRAACETYLGLYCOLURYL UNDER ACTION OF UREAS

2018 ◽  
Vol 61 (7) ◽  
pp. 50
Author(s):  
Ngoc Phuoc Hoang ◽  
Abdigali A. Bakibaev ◽  
Victor S. Malkov
Keyword(s):  
Reaction Mechanisms ◽  
Nucleophilic Addition ◽  
Specific Effect ◽  
Independent Effect ◽  
Similar Reaction ◽  
Urea Molecule ◽  
Acid Catalyzed ◽  
Integrated Intensities ◽  
Cis Isomer ◽  
Methyl Phenyl

It is established that tetraacetylglycoluril under the action of urea, some N-substituted ureas and benzylidenebisurea in the acid-catalyzed conditions undergoes only bis-deacetylation with the formation of syn- and anti-regio-substituted N,N-diacetylglycolurils, rather than N-acetylation as it was previously shown in a similar reaction for a number of aromatic and heterocyclic amines. In the course of individual experiments, the absence of independent effect of organic solvents during boiling for several hours (alcohols, dioxane, tetrahydrofuran, dimethylsulfoxide) on the deacetylation of tetraacetylglycoluril was revealed, since in these conditions the original substrate remained unchanged. Based on the NMR spectroscopy data, by comparison the integrated intensities of methine and acetyl protons of glycoluryl fragments, we found that the bis-deacetylation of tetraacetylglycoluril in the studied conditions occurs regioselectively with an overwhelming majority of anti-N,N-diacetylglycoluril (up to 92-94%) except for benzylidenebisurea, when the content of the trans-isomer reaches 75%. A marked increase in the cis-isomer (up to 25%) of N,N-diacetylglycoluril in the case of benzylidenebisurea seems to be dictated by the specific effect on the intermediates of reaction of phenylmethylureido carbocation from eliminating urea molecule in acid-catalyzed conditions. It is shown that N,N-diacetylglycoluril in similar conditions under the action of urea and its derivatives does not undergo further deacetylation to the progenitor of bicyclic bisureas – glycoluril, primarily related to the high hydrolytic and steric resistance of these compounds. On the basis of the above research results, the reaction mechanisms of bis-deacetylation of tetraacetylglycoluril in the acid-catalyzed conditions under the action of urea and its N-methyl (phenyl) derivatives through an intermediate process of nucleophilic addition of ureas is proposed.Forcitation:Hoang N.P., Bakibaev A.A., Malkov V.S. Bis-deacetylation of tetraacetylglycoluryl under action of ureas. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2018. V. 61. N 7. P. 49-53

N-Chlorination of secondary amides. II. Effects of substituents on rates of N-chlorination

1969 ◽  
Vol 47 (18) ◽  
pp. 3289-3297 ◽  
Author(s):  
E. W. C. W. Thomm ◽  
M. Wayman
Keyword(s):  
Hydrogen Bond ◽  
Oxygen Atom ◽  
Reaction Mechanisms ◽  
Bond Formation ◽  
Low Ph ◽  
Reverse Order ◽  
Primary Reaction ◽  
Hydrogen Bond Formation ◽  
Cl Atom ◽  
Secondary Amides

Various secondary amides have been N-chlorinated, at high and at low pH. The reactivity of the chlorinating reagents with all the amides investigated was found to have the sequence[Formula: see text]The substituent groups R1 and R2 of the amide [Formula: see text] were found to have large effects on the rate of chlorination. With the three molecular chlorinating agents, the reactivity of the amides was found to be in the order[Formula: see text]With hypochlorite ion the reverse order of reactivity was observed. These results are discussed and reaction mechanisms proposed. It is proposed that, when a hypochlorite ion is a chlorinating agent, the primary reaction is hydrogen bond formation between the amido hydrogen and the hypochlorite oxygen atom, but that the donation of electrons from the amido N to the Cl atom is the primary reaction with the molecular chlorinating agents.

scholarly journals NEW ASPECTS ON REACTION MECHANISMS IN THE FORMALDEHYDE HISTOFLUORESCENCE METHOD FOR MONOAMINES

1973 ◽  
Vol 21 (1) ◽  
pp. 17-25 ◽  
Author(s):  
ANDERS BJÖRKLUND ◽  
BENGT FALCK ◽  
OLLE LINDVALL ◽  
LEIF-ÅKE SVENSSON
Keyword(s):  
Mass Spectrometry ◽  
Reaction Mechanisms ◽  
Equal Importance ◽  
Freeze Dried ◽  
Subsequent Step ◽  
Fluorescent Products ◽  
Acid Catalyzed ◽  
Protein Models ◽  
Layer Chromatography ◽  
Mechanisms Of Reactions

The mechanisms of reactions underlying the fluorophore formation from indolylethylamines in the Falck-Hillarp histochemical formaldehyde method were investigated with the aid of thin layer chromatography and mass spectrometry of the fluorescent products formed in protein models and freeze-dried tissue. In the reaction of formaldehyde with tryptamine and 5-hydroxytryptamine, the main fluorophores formed were 3,4-dihydro-β-carboline and the 2-methyl-3,4-dihydro-β-carbolinium compound (from tryptamine), and 6-hydroxy-3,4-dihydro-β-carboline and the 2-methyl-6-hydroxy-3,4-dihydro-β-carbolinium compound (from 5-hydroxytryptamine). From these findings, it is concluded that the fluorophore formation in the Falck-Hillarp method proceeds as follows: In the first step of the reaction, the indolylethylamines react with formaldehyde to form low fluorescent 1,2,3,4-tetrahydro-β-carbolines. In a subsequent step, these products are converted to fluorophores in either of two ways: through an autoxidation to 3,4-dihydro-β-carbolines, or through a second, acid-catalyzed reaction with formaldehyde to yield 2-methyl-3,4-dihydro-β-carbolinium compounds. Experiments with radioactive tryptamine indicated that the two alternative fluorophore-forming pathways are of fairly equal importance. The latter of these fluorophore-forming reactions was not previously known, and the interesting properties and implications of this formaldehyde-induced and acid-catalyzed reaction are discussed.

scholarly journals Noncanonical transnitrosylation network contributes to synapse loss in Alzheimer’s disease

Science ◽  
2020 ◽  
pp. eaaw0843
Author(s):  
Tomohiro Nakamura ◽  
Chang-ki Oh ◽  
Lujian Liao ◽  
Xu Zhang ◽  
Kevin M. Lopez ◽  
...  
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Reaction Mechanisms ◽  
Redox Reactions ◽  
Reproductive Period ◽  
Primary Reaction ◽  
Biochemical Pathways ◽  
Synapse Loss ◽  
Guanosine Triphosphatase ◽  
Kinase A

We describe mechanistically-distinct enzymes, i.e., a kinase, a guanosine triphosphatase and a ubiquitin protein hydrolase, which function in disparate biochemical pathways, that can also act in concert to mediate a series of redox reactions. Each enzyme manifests a second, noncanonical function – transnitrosylation – triggering a pathological biochemical cascade in Alzheimer’s disease (AD). The resulting series of transnitrosylation reactions contributes to synapse loss, the major pathological correlate to cognitive decline in AD. We conclude that enzymes with distinct primary reaction mechanisms can form a completely separate network for aberrant transnitrosylation. This network operates in the post-reproductive period, so natural selection against such abnormal activity may be decreased.

scholarly journals The acid-catalyzed hydrolysis of an <i>α</i>-pinene-derived organic nitrate: kinetics, products, reaction mechanisms, and atmospheric impact

2016 ◽  
Vol 16 (23) ◽  
pp. 15425-15432 ◽  
Author(s):  
Joel D. Rindelaub ◽  
Carlos H. Borca ◽  
Matthew A. Hostetler ◽  
Jonathan H. Slade ◽  
Mark A. Lipton ◽  
...  
Keyword(s):  
Gas Phase ◽  
Rate Constants ◽  
Reaction Mechanisms ◽  
Tropospheric Ozone ◽  
Organic Aerosol ◽  
Organic Nitrate ◽  
Organic Nitrates ◽  
Particle Phase ◽  
Fine Aerosol ◽  
Acid Catalyzed

Abstract. The production of atmospheric organic nitrates (RONO2) has a large impact on air quality and climate due to their contribution to secondary organic aerosol and influence on tropospheric ozone concentrations. Since organic nitrates control the fate of gas phase NOx (NO + NO2), a byproduct of anthropogenic combustion processes, their atmospheric production and reactivity is of great interest. While the atmospheric reactivity of many relevant organic nitrates is still uncertain, one significant reactive pathway, condensed phase hydrolysis, has recently been identified as a potential sink for organic nitrate species. The partitioning of gas phase organic nitrates to aerosol particles and subsequent hydrolysis likely removes the oxidized nitrogen from further atmospheric processing, due to large organic nitrate uptake to aerosols and proposed hydrolysis lifetimes, which may impact long-range transport of NOx, a tropospheric ozone precursor. Despite the atmospheric importance, the hydrolysis rates and reaction mechanisms for atmospherically derived organic nitrates are almost completely unknown, including those derived from α-pinene, a biogenic volatile organic compound (BVOC) that is one of the most significant precursors to biogenic secondary organic aerosol (BSOA). To better understand the chemistry that governs the fate of particle phase organic nitrates, the hydrolysis mechanism and rate constants were elucidated for several organic nitrates, including an α-pinene-derived organic nitrate (APN). A positive trend in hydrolysis rate constants was observed with increasing solution acidity for all organic nitrates studied, with the tertiary APN lifetime ranging from 8.3 min at acidic pH (0.25) to 8.8 h at neutral pH (6.9). Since ambient fine aerosol pH values are observed to be acidic, the reported lifetimes, which are much shorter than that of atmospheric fine aerosol, provide important insight into the fate of particle phase organic nitrates. Along with rate constant data, product identification confirms that a unimolecular specific acid-catalyzed mechanism is responsible for organic nitrate hydrolysis under acidic conditions. The free energies and enthalpies of the isobutyl nitrate hydrolysis intermediates and products were calculated using a hybrid density functional (ωB97X-V) to support the proposed mechanisms. These findings provide valuable information regarding the organic nitrate hydrolysis mechanism and its contribution to the fate of atmospheric NOx, aerosol phase processing, and BSOA composition.

scholarly journals The Acid-Catalyzed Hydrolysis of an α-Pinene-Derived Organic Nitrate: Kinetics, Products, Reaction Mechanisms, and Atmospheric Impact

2016 ◽  
Author(s):  
Joel D. Rindelaub ◽  
Carlos H. Borca ◽  
Matthew A. Hostetler ◽  
Mark A. Lipton ◽  
Lyudmila V. Slipchenko ◽  
...  
Keyword(s):  
Gas Phase ◽  
Reaction Mechanisms ◽  
Tropospheric Ozone ◽  
Organic Aerosol ◽  
Organic Nitrate ◽  
Organic Nitrates ◽  
Particle Phase ◽  
Fine Aerosol ◽  
Acid Catalyzed ◽  
Insight Into

Abstract. The production of atmospheric organic nitrates (RONO2) has a large impact on air quality and climate, due to their contribution to secondary organic aerosol and influence on tropospheric ozone concentrations. Since organic nitrates control the fate of gas phase NOx (NO+NO2), a byproduct of anthropogenic combustion processes, their atmospheric production and reactivity is of great interest. While the atmospheric reactivity of many relevant organic nitrates is still very uncertain, one significant reactive pathway, condensed phase hydrolysis, has recently been identified as a potential sink for organic nitrate species. The partitioning of gas phase organic nitrates to aerosol particles and subsequent hydrolysis likely removes the oxidized nitrogen from further atmospheric processing, due to large organic nitrate uptake to aerosols and proposed hydrolysis lifetimes, which may impact long range transport of NOx, a tropospheric ozone precursor. Despite the atmospheric importance, the hydrolysis rates and reaction mechanisms for atmospherically-derived organic nitrates are almost completely unknown, including those derived from α-pinene, a biogenic volatile organic compound (BVOC) that is one of the most significant precursors to biogenic secondary organic aerosol (BSOA). To better understand the chemistry that governs the fate of particle phase organic nitrates, this study elucidated the hydrolysis mechanism and rate constants for several organic nitrates, including an α-pinene-derived organic nitrate (APN). A positive trend in hydrolysis rate constants was observed with increasing solution acidity for all organic nitrates studied, with the APN lifetime ranging from 8.3 minutes at acidic pH (0.25) to 8.8 hours at neutral pH (6.9). Since ambient fine aerosol pH values are observed to be acidic, the reported lifetimes, which are much shorter than that of atmospheric fine aerosol, provide important insight into the fate of particle phase organic nitrates. Along with rate constant data, the identification of the products campholenic aldehyde, pinol, and pinocamphone confirms a unimolecular specific acid-catalyzed mechanism is responsible for organic nitrate hydrolysis under acidic conditions, where carbocation rearrangement is favored for α-pinene-derived species. The free energies and enthalpies of the isobutyl nitrate hydrolysis intermediates and products were calculated using a hybrid density functional (ωB97X-V) to support the proposed mechanisms. These findings provide valuable insight into the organic nitrate hydrolysis mechanism and its contribution to the fate of atmospheric NOx, aerosol phase processing, and BSOA composition.

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