- Self-assembled orthoester cryptands: Orthoester scope, post-functionalization, kinetic locking and tunable degradation kinetics
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Dynamic adaptability and biodegradability are key features of functional, 21st century host-guest systems. We have recently discovered a class of tripodal supramolecular hosts, in which two orthoesters act as constitutionally dynamic bridgeheads. Having previously demonstrated the adaptive nature of these hosts, we now report the synthesis and characterization-including eight solid state structures-of a diverse set of orthoester cages, which provides evidence for the broad scope of this new host class. With the same set of compounds, we demonstrated that the rates of orthoester exchange and hydrolysis can be tuned over a remarkably wide range, from rapid hydrolysis at pH 8 to nearly inert at pH 1, and that the Taft parameter of the orthoester substituent allows an adequate prediction of the reaction kinetics. Moreover, the synthesis of an alkyne-capped cryptand enabled the post-functionalization of orthoester cryptands by Sonogashira and CuAAC "click" reactions. The methylation of the resulting triazole furnished a cryptate that was kinetically inert towards orthoester exchange and hydrolysis at pH > 1, which is equivalent to the "turnoff" of constitutionally dynamic imines by means of reduction. These findings indicate that orthoester cages may be more broadly useful than anticipated, e.g. as drug delivery agents with precisely tunable biodegradability or, thanks to the kinetic locking strategy, as ion sensors.
- L?w, Henrik,Mena-Osteritz, Elena,Von Delius, Max
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p. 4785 - 4793
(2018/06/07)
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- Electrocarboxylation of CCI4 in MeCN during electrolysis with the sacrificial Zn anode
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The regularities of galvanostatic electrocarboxylation of CCl4 in Alk4NBr/MeCN in an undivided cell with sacrificial Zn anode were studied. The major product of the electrolysis is zinc trichloroacetate, which is formed as a result o
- Sigacheva,Neverov,Petrosyan
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experimental part
p. 297 - 302
(2010/07/09)
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- Fe2(SO4)3·4H 2O/concentrated H2SO4: An efficient catalyst for esterification
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The mixed catalyst system, Fe2(SO4) 3·4H2O/concentrated H2SO4 has been applied to catalyse effectively the esterification of α,β-unsaturated acids, aliphatic acids and heterocyclic aromatic acids with ethanol and methanol.
- Liang, Yong-Min,Xu, Qi-Hai,Wu, Xiao-Li,Ma, Yong-Xiang
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p. 226 - 227
(2007/10/03)
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- Alpha- haloenamine reagents
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The present invention describes immobilized haloenamine reagents, immobilized tertiary amides, methods for their preparation, and methods of use.
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- Reactions of trialkyl phosphites with mono- and diacylals of halo-substituted acetic acids
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Trialkyl phosphites react with diacylals of di- and trichloroacetic acids by the pathway of the Perkow reaction; with monoacylals of bromo- and iodoacetic acids, by the pathway of the classical Arbuzov reaction; and with monoacylals of di- and trichloroacetic acids, by the pathway of the nonclassical Arbuzov reaction.
- Gazizov,Gaisin,Khairullin,Safina,Karimova,Petrova
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p. 1738 - 1741
(2007/10/03)
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- In situ derivatization/solid-phase microextraction for the determination of haloacetic acids in water
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An in situ derivatization solid-phase microextraction method has been developed for the determination of haloacetic acids (HAAs) in water. The analytical procedure involves derivatization of HAAs to their methyl esters with dimethyl sulfate, headspace sampling using solid-phase microextraction (SPME), and gas chromatography-ion trap mass spectrometry (GC/ITMS) determination. Parameters affecting both derivatization efficiency and headspace SPME procedure, such as the selection of the SPME coating, derivatization-extraction time and temperature, and ionic strength, were optimized. The commercially available Carboxen-poly(dimethylsiloxane) (CAR-PDMS) fiber appears to be the most suitable for the determination of HAAs. Moreover, the formation of HAA methyl esters was dramatically improved (up to 90-fold) by the addition of tetrabutylammonium hydrogen sulfate (4.7 μmol) to the sample as ion-pairing agent in the derivatization step. The precision of the in situ derivatization/HS-SPME/GC/ITMS method evaluated using an internal standard gave relative standard deviations (RSDs) between 6.3 and 11.4%. The method was linear over 2 orders of magnitude, and detection limits were compound-dependent, but ranged from 10 to 450 ng/L. The method was compared with the EPA method 552.2 for the analysis of HAAs in various water samples, and good agreement was obtained. Consequently, in situ derivatization/HS-SPME/GC/ITMS is proposed for the analysis of HAAs in water.
- Sarrion,Santos,Galceran
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p. 4865 - 4873
(2007/10/03)
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- Preparation of 2,2-Dihalocarboxylic Acid Methyl Esters by Oxidation-Chlorination of 2-(1-Haloalkyl)-4-methyl-1,3-dioxolanes with Trichloroisocyanuric Acid
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Methyl 2,2-dichloro or 2-bromo-2-chloro carboxylates were obtained in excellent yields by oxidation-chlorination of 2-(1-haloalkyl)-4-methyl-1,3-dioxolanes with trichloroisocyanuric acid.
- Boni, Monica,Ghelfi, Franco,Pagnoni, Ugo Maria,Zucchi, Claudia
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p. 1622 - 1626
(2007/10/02)
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- Oxadiazole compounds containing 4,6-bis-trichloromethyl-S-triazin-2-yl groups, process for their preparation
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Compounds of general formula I are disclosed STR1 wherein R1 denotes an unsubstituted or substituted carbocyclic or heterocyclic aryl radical, R2 and R3 are different from each other and either denote a hydrogen atom or a 4,6-bis-trichloromethyl-s-triazin-2-yl group, and n and m independently of each other, denote one of the numbers 0 and 1. The compounds are effective free-radical-forming photoinitiators and photolytically-activatable acid donors for photosensitive compositions.
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- REACTION OF 1-(ACYLCARBAMOYL)-3,5,5-TRIMETHYL-2-PYRAZOLINES WITH NUCLEOPHILIC REAGENTS
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1-(Acylcarbamoyl)-3,5,5-trimethyl-2-pyrazolines react with water and alcohols to form 3,5,5-trimethyl-4,5-dihydro-1H-pyrazole-1-carboxamide with the elimination of substituted carboxylic acids. 1-(Benzoylcarbamoyl)-3,5,5-trimethyl-2-pyrazoline and 3,5,5-trimethyl-4,5-dihydro-1H-pyrazole-1-carboxamide form 2:1 complexes with Cu(II) ions.
- Zobova, N. N.,Nazyrova, A. Z.
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p. 1906 - 1908
(2007/10/02)
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- Kinetics and mechanisms of the acid-catalysed methanolysis of halogen-substituted carboxylic esters
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The methanolysis of chloromethyl dichloroacetate in HClO4/NaClO4 solutions of aqueous methanol at cw 1.30, 2.60 and 5.56 mol/L both at variable and at the constant ionic strengths of 0.5 and 1.0 mol/L and the methanolysis of ethyl trichloroacetate in anhydrous methanol up to 0.1 mol/L hydrogen chloride solutions were studied.The acid-catalysed methanolysis of ethyl trichloroacetate and that of the esters with one or two halogen substituents is proposed to proceed by the normal AAC2 mechanism even in the case when the acid-catalysed hydrolysis in water takes place by the exceptional A-BAC3 mechanism.Under the experimental conditions, the acid catalysed methanolysis of chloromethyl dichloroacetate seems to proceed simultaneously by the AAC2 and A-BAC3 mechanisms.The involvement of the A/BAC3 mechanism in the case of chloromethyl dichloroacetate agrees with the observation that water acts as an effective general base catalyst in the rate-limiting step of the A-BAC3 reactions and that a chloro-substituent in the alkyl component retards the rate of its AAC2 reaction more than in the acyl group, at least in the case of ester hydrolysis.
- Kanerva,Liisa, T.
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p. 329 - 334
(2007/10/02)
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- ADDITION OF ESTERS OF CHLOROACETIC ACIDS TO 1,3-BUTADIENE CATALYSED BY COPPER COMPLEXES
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The addition of alkyl trichloro- and dichloroacetates to 1,3-butadiene catalysed by copper complexes has been studied.The reactivity of the chloroacetates increased with increasing number of chlorine atoms in their molecule and with decreasing number of the carbon atoms of the alkyl of their ester group.The addition of trichloroacetates gave the products (1 : 1 adducts) in around 80 per cent yields while the less reactive dichloroacetates afforded the adducts in 35percent yield.The 1 : 1 adducts were the products of both 1,4- and 1,2- addition, the relative proportion of which depended especially on the type of the ligand of copper complexes.
- Vit, Zdenek,Hajek, Milan
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p. 1280 - 1284
(2007/10/02)
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- THE SALT-FREE SYNTHESIS OF ARYL ETHERS USING METHYL TRICHLOROACETATE
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Metyl trichloroacetate is an effective reagent for salt-free synthesis of aryl ethers and anisoles from phenols.
- Renga, James M.,Wang, Pen-Chung
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- Reactions of Tributyltin Methoxide with Cloromethyl Esters
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Reactions of tributyltin methoxide with esters RCO2R' (R'=CH2Cl, CHCl2 or CCl3) have been performed to study the influence of the halogens in the alkyl component of an ester on the course of the reaction.In all reactions tributyltin chloride and methyl ester were formed whereas the subsequent reaction depended on the number of halogens in the methyl group.
- Vihanto, Jouko
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p. 699 - 702
(2007/10/02)
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- Neutral Trichloroacetylations of Alcohols by Hexachloroacetone
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The addition of simple alcohols in hexachloroacetone (HCA) in the presence of strong hydrogen bond acceptors (e.g., dimethylformamide) results in a high yield of the corresponding trichloroacetate (via a haloform reaction scheme).The trichloroacetylation reactions are carried out under neutral conditions, and the resultant ester can easily be separated from the reaction mixture via extraction/distillation procedures.Kinetic evidence demonstrates that the trichloroacetylation of alcohols by HCA is a stereoselective process, and further studies suggest that the catalytic role of the acceptors is of a hydrogen bonding nature.
- Freedlander, Richard S.,Bryson, Thomas A.,Dunlap, R. Bruce,Schulman, E. M.,Lewis, Charles A.
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p. 3519 - 3521
(2007/10/02)
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