ChemInform Abstract: Synthesis of Tetrahydro-5-azaindoles and 5-Azaindoles Using Pictet-Spengler Reaction - Appreciable Difference in Products Using Different Acid Catalysts.

ChemInform ◽  
2011 ◽  
Vol 42 (29) ◽  
pp. no-no
Author(s):  
Abdullah M. A. Shumaila ◽  
Vedavati G. Puranik ◽  
Radhika S. Kusurkar
Keyword(s):  
Acid Catalysts ◽  
Appreciable Difference

Hearing Aid Gain Usage by Children

1989 ◽  
Vol 20 (2) ◽  
pp. 149-152 ◽  
Author(s):  
Kenneth W. Berger
Keyword(s):  
Hearing Aid ◽  
Appreciable Difference ◽  
Significant Difference ◽  
Clinically Significant

Hearing aid gain usage by two groups of children was examined. No appreciable difference was noted between the groups, nor was there a clinically significant difference between gain usage by these children as compared with a sample of adult hearing aid wearers.

On the Reliability of the Use of Heparin Immobilized on Agarose for the Study of the Interactions among Heparin, Thrombin and Antithrombin

1982 ◽  
Vol 48 (01) ◽  
pp. 084-086
Author(s):  
Wayne W Fish ◽  
Ingemar Björk
Keyword(s):  
Experimental Approach ◽  
Antithrombin Iii ◽  
Chromogenic Substrate ◽  
Experimental Protocol ◽  
Appreciable Difference ◽  
Thrombin Inhibition ◽  
Highly Sensitive ◽  
Inhibition Of Thrombin

SummaryThe extent of inhibition of thrombin was re-examined as a consequence of the sequence of addition of thrombin and antithrombin III to a column of heparin immobilized on agarose. With the use of pure enzyme, pure inhibitor, and a highly sensitive chromogenic substrate, no appreciable difference in the extent of thrombin inhibition was observed between the two sequences of addition. These observations, together with a demonstrated sensitivity of the method to variations in experimental protocol, challenge the conclusions reached in an earlier work (Hatton and Regoeczi, Thromb. Res. 1977; 10:645) which utilized this experimental approach but which employed larger quantities of reactants and a less sensitive substrate.

Urea-Catalyzed Functionalization of Unactivated C–H Bonds

2020 ◽  
Author(s):  
Alex L. Bagdasarian ◽  
Stasik Popov ◽  
Benjamin Wigman ◽  
Wenjing Wei ◽  
woojin lee ◽  
...  
Keyword(s):  
Hydrogen Bonding ◽  
Organic Synthesis ◽  
High Energy ◽  
Acid Catalysts ◽  
Potential Utility ◽  
New Paradigm ◽  
Lewis Acid Catalysts ◽  
Reaction Conditions ◽  
Highly Active ◽  
Acidic Nature

Herein we report the 3,5bistrifluoromethylphenyl urea-catalyzed functionalization of unactivated C–H bonds. In this system, the urea catalyst mediates the formation of high-energy vinyl carbocations that undergo facile C–H insertion and Friedel–Crafts reactions. We introduce a new paradigm for these privileged scaffolds where the combination of hydrogen bonding motifs and strong bases affords highly active Lewis acid catalysts capable of ionizing strong C–O bonds. Despite the highly Lewis acidic nature of these catalysts that enables triflate abstraction from sp<sup>2</sup> carbons, these newly found reaction conditions allow for the formation of heterocycles and tolerate highly Lewis basic heteroaromatic substrates. This strategy showcases the potential utility of dicoordinated vinyl carbocations in organic synthesis.<br>

Urea-Catalyzed Functionalization of Unactivated C–H Bonds

2020 ◽  
Author(s):  
Alex L. Bagdasarian ◽  
Stasik Popov ◽  
Benjamin Wigman ◽  
Wenjing Wei ◽  
woojin lee ◽  
...  
Keyword(s):  
Hydrogen Bonding ◽  
Organic Synthesis ◽  
High Energy ◽  
Acid Catalysts ◽  
Potential Utility ◽  
New Paradigm ◽  
Lewis Acid Catalysts ◽  
Reaction Conditions ◽  
Highly Active ◽  
Acidic Nature

Herein we report the 3,5bistrifluoromethylphenyl urea-catalyzed functionalization of unactivated C–H bonds. In this system, the urea catalyst mediates the formation of high-energy vinyl carbocations that undergo facile C–H insertion and Friedel–Crafts reactions. We introduce a new paradigm for these privileged scaffolds where the combination of hydrogen bonding motifs and strong bases affords highly active Lewis acid catalysts capable of ionizing strong C–O bonds. Despite the highly Lewis acidic nature of these catalysts that enables triflate abstraction from sp<sup>2</sup> carbons, these newly found reaction conditions allow for the formation of heterocycles and tolerate highly Lewis basic heteroaromatic substrates. This strategy showcases the potential utility of dicoordinated vinyl carbocations in organic synthesis.<br>

Arylboronic Acid-Catalyzed C-Allylation of Unprotected Oximes

2019 ◽  
Author(s):  
Juha Siitonen ◽  
Padmanabha V. Kattamuri ◽  
Muhammed Yousufuddin ◽  
Laszlo Kurti
Keyword(s):  
Total Synthesis ◽  
Acid Catalysts ◽  
Mechanistic Studies ◽  
Arylboronic Acid ◽  
Synthetic Utility ◽  
Acid Catalyzed

Unprotected keto- and aldoximes are readily <i>C</i>-allylated with allyl diisopropyl boronate in the presence of arylboronic acid catalysts to yield highly-substituted <i>N</i>-alpha-secondary (2°) and tertiary (3°) hydroxylamines. The method’s synthetic utility is demonstrated with the total synthesis of the trace alkaloid <i>N</i>-methyl-euphococcine. Preliminary experimental and computational mechanistic studies point toward the formation of a boroxine as the active allylating species.<br>

Role of Zeolites and Zeotypes in Green Chemistry

2020 ◽  
Vol 07 ◽  
Author(s):  
Jyotsna S. Meshram ◽  
Devendra S. Raghuvanshi
Keyword(s):  
Green Chemistry ◽  
Industrial Process ◽  
Environmental Issues ◽  
Synthetic Methods ◽  
Acid Catalysts ◽  
Chemical Waste ◽  
Specific Morphology

Abstract:: Now days, it is of utmost important to design synthetic methods; which can be utilized for the generation of substances that will minimize toxicity to health of human and the environment. The utilization of acid catalysts generates lots of corrosive and harmful wastes which has to be treated with appropriate alkalis. Hence, it generates lots of sludge and alarms environmental issues of its storage and disposal. Zeolites and Zeotypes; by virtue of their peculiar properties; such as specific morphology, porosity and residing acidity; attracting enormous attention as they replaces harmful acid catalysts efficiently and also reduces chemical waste in industrial process; Hence emerged as new plethora in the field of “Green Chemistry”.

Preparation of Strong Acid Catalysts by Sulfate Treatment of Calcined Boehmite

1992 ◽  
Vol 57 (11) ◽  
pp. 2241-2247 ◽  
Author(s):  
Tomáš Hochmann ◽  
Karel Setínek
Keyword(s):  
Catalytic Activity ◽  
Surface Area ◽  
Aluminum Sulfate ◽  
Solid Acid ◽  
Strong Acid ◽  
Acid Strength ◽  
Solid Acid Catalysts ◽  
Acid Catalysts ◽  
Preparation Methods ◽  
Indicator Method

Solid acid catalysts with acid strength of -14.52 < H0 < -8.2 were prepared by sulfate treatment of the samples of boehmite calcined at 105-800 °C. Two preparation methods were used: impregnation of the calcined boehmite with 3.5 M H2SO4 or mixing of the boehmite samples with anhydrous aluminum sulfate, in both cases followed by calcination in nitrogen at 650 °C. The catalysts were characterized by measurements of surface area, adsorption of pyridine and benzene, acid strength measurements by the indicator method and by catalytic activity tests in the isomerization of cyclohexene, p-xylene and n-hexane. Properties of the catalysts prepared by both methods were comparable.

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