Surendra U. Kulkarni

Bio: Surendra U. Kulkarni is an academic researcher. The author has contributed to research in topics: Boron trifluoride & Ether cleavage. The author has an hindex of 1, co-authored 1 publications receiving 305 citations.

Cleavage of Ethers

Abstract: The scope and limitations of reagents for the cleavage of ethers are discussed. The reagents are conveniently classified in the five main headings. Selectivity patterns of some of the reagents are discussed in cases where sufficient data has been given in the literature. 1. Introduction 2. Acidic Reagents 2.1. Bronsted Acids 2.2. Lewis Acids 3. Basic Reagents 3.1. Alkali Hydroxides 3.2. Alkali Alkoxides 3.3. Alkali Amides 3.4. Alkali Metals 3.5. Organo-Alkali Metal Compounds 3.6. Sodium Cyanide/Dimethyl Sulfoxide 3.7. Sodium Ethanethiolate 3.8. Sodium Thiocresolate 3.9. Lithium Iodide 3.10. Sodium Benzeneselenolate 4. Miscellaneous Reagents 4.1. Iodotrimethylsilane 4.2. Iodotrichlorosilane 4.3. Dichloroiodomethylsilane 4.4. Bromotrimethylsilane 4.5. Alkylthiotrimethylsilanes 4.6. Ethanethiol or Ethanedithiol/Boron Trifluoride Etherate 4.7. Aluminium Halide/Thiol Systems 4.8. Acetyl Iodide and Pivaloyl Iodide 4.9. Diiodomethyl Ether/Hydrogen Iodide 5. Reductive Cleavage of Ethers 5.1. Lithium Tris[t-butoxy]aluminium Hydride/Triethylborane Complex 5.2. Hydrogenolysis 6. Oxidative Cleavage of Ethers 6.1. Ceric Ammonium Nitrate 6.2. Silver Oxide 6.3. Dichlorodicyanoquinone 6.4. Tris[p-bromophenyl]ammonium Hexachloroantimonate 7. Photochemical Cleavage of Ethers 8. Selectivity in Ether Cleavage 8.1. Stereoelectronic Characteristics of the Ether-Cleaving Agent 8.2. Structural Features of the Groups Cleaved 8.3. Molecular Environment of the C-O Bond not Undergoing Cleavage 9. Addendum

New Insights Into the Molecular Architecture of Hardwood Lignins By Chemical Degradative Methods

Abstract: Lignins are composed of phenylpropane units interconnected by labile and resistant bonds. A two-step degradation, thioacidolysis, provides detailed information on these network polymers. The first step involves lignin depolymerization with ethanethiol and BF3 etherate. The determination of the recovered thioethylated monomers provides an estimation of lignin units only involved in labile ether bonds. The ligninderived dimers, representative of resistant interunit bonds, are determined after a further desulfurization step. Results obtained for native and industrial hardwood lignins underline their structural differences. Native hardwood lignins are typified by a high proportion of linear fragments linked bifunctionally by β-O-4 bonds.

New tacrine-4-oxo-4H-chromene hybrids as multifunctional agents for the treatment of Alzheimer's disease, with cholinergic, antioxidant, and β-amyloid-reducing properties.

Abstract: By using fragments endowed with interesting and complementary properties for the treatment of Alzheimer’s disease (AD), a new family of tacrine–4-oxo-4H-chromene hybrids has been designed, synthesized, and evaluated biologically. The tacrine fragment was selected for its inhibition of cholinesterases, and the flavonoid scaffold derived from 4-oxo-4H -chromene was chosen for its radical capture and β-secretase 1 (BACE-1) inhibitory activities. At nano- and picomolar concentrations, the new tacrine–4-oxo-4H-chromene hybrids inhibit human acetyl- and butyrylcholinesterase (h-AChE and h-BuChE), being more potent than the parent inhibitor, tacrine. They are also potent inhibitors of human BACE-1, better than the parent flavonoid, apigenin. They show interesting antioxidant properties and could be able to penetrate into the CNS according to the in vitro PAMPA-BBB assay. Among the hybrids investigated, 6-hydroxy-4-oxo- N-{10-[(1,2,3,4-tetrahydroacridin-9-yl)amino]decyl}-4 H-chromene-2-carboxamide (19) shows pote...

Improved Lignin Polyurethane Properties with Lewis Acid Treatment

Abstract: Chemical modification strategies to improve the mechanical properties of lignin-based polyurethanes are presented. We hypothesized that treatment of lignin with Lewis acids would increase the concentration of hydroxyl groups available to react with diisocyanate monomers. Under the conditions used, hydrogen bromide-catalyzed modification resulted in a 28% increase in hydroxyl group content. Associated increases in hydrophilicity of solvent-cast thin films were also recorded as evidenced by decreases in water contact angle. Polyurethanes were then prepared by first preparing a prepolymer based on mixtures of toluene-2,4-diisocyanate (TDI) and unmodified or modified lignin, then polymerization was completed through addition of polyethylene glycol (PEG), resulting in mass ratios of TDI:lignin:PEG of 43:17:40 in the compositions investigated here. The mixture of TDI and unmodified lignin resulted in a lignin powder at the bottom of the liquid, suggesting it did not react directly with TDI. However, a homogeneous solution resulted when TDI and the hydrogen bromide-treated lignin were mixed, suggesting demethylation indeed increased reactivity and resulted in better integration of lignin into the urethane network. Significant improvements in mechanical properties of modified lignin polyurethanes were observed, with a 6.5-fold increase in modulus, which were attributed to better integration of the modified lignin into the covalent polymer network due to the higher concentration of hydroxyl groups. This research indicates that chemical modification strategies can lead to significant improvements in the properties of lignin-based polymeric materials using a higher fraction of an inexpensive lignin monomer from renewable resources and a lower fraction an expensive, petroleum-derived isocyanate monomer to achieve the required material properties.