N,N,N′,N′‐Tetrasubstituted Piperazinium Salts of Perfluorinated Acids

Well crystallized diquaternary piperazinium salts of perfluorocarboxylic acids can be prepared by thermal rearrangement of a primary product obtained from the appropriate fluorinated acid chloride and N,N‐dialkylamino‐ethanol. The mechanism of the ring closure step is discussed. The synthetic strategy easily gives access to structurally different piperazinium perfluorocarboxylates. The title compounds show surface activity and can be regarded as ionic amphiphiles.     

Comparison of Benzyl Celluloses Synthesized in Aqueous NaOH and Dimethyl Sulfoxide/Tetrabutylammonium Fluoride

Cellulose was benzylated starting from the dissolved polymer in dimethyl sulfoxide (DMSO)/tetrabutylammonium fluoride trihydrate (TBAF) and heterogeneously in aqueous NaOH as reaction media. Differences in the distribution of benzyl moieties within the anhydroglucose unit in dependence on the synthesis pathway couldn't be found. However, as revealed by means of ¹H-NMR spectroscopy, significant differences in the distribution of substituents along the cellulose chains occurred. Conventionally synthesized samples (in aqueous NaOH), even in the presence of a phase transfer catalyst, possess a block-wise distribution of substituents, while a dissolution of cellulose in DMSO/TBAF prior to the reaction gives products that are uniformly substituted along the cellulose chains.     

A Novel Metal‐free Reductive Esterification of N‐Tosylhydrazones with Carboxylic Acids

A novel method for the synthesis of esters via reductive coupling of N‐tosylhydrazones with carboxylic acids under metal‐free conditions has been developed. Various functional groups were found to be tolerable under the reaction conditions to afford low to good yields.     

Efficient Homogeneous Chemical Modification of Bacterial Cellulose in the Ionic Liquid 1‐N‐Butyl‐3‐methylimidazolium Chloride

Summary: Bacterial cellulose (BC), a unique type of cellulose, with high degree of polymerization of 6 500 could be dissolved easily in the ionic liquid 1‐N‐butyl‐3‐methylimidazolium chloride. For the first time, well‐soluble BC acetates and carbanilates of high degree of substitution (up to a complete modification of all hydroxyl groups) were accessible under homogeneous and mild reaction conditions. Characterization of the new BC derivatives by NMR and FTIR spectroscopy shows an unexpected distribution of the acetyl moieties in the order O‐6 > O‐3 > O‐2.

¹³C NMR spectrum (DMSO‐d₆) of a cellulose acetate with a DS of 2.25 synthesized in 1‐N‐butyl‐3‐methylimidazolium chloride.     

Successful Application of an Ionic Liquid Carrying the Fluoride Counter‐ion in Biomacromolecular Chemistry: Microwave‐Assisted Acylation of Cellulose in the Presence of 1‐Allyl‐3‐methylimidazolium Fluoride/DMSO Mixtures

The use of ionic liquids with fluoride anion (IL‐F) is challenging because of side reactions. Neat 1‐allyl‐3‐methylimidazolium fluoride (AlMeImF) is used as a solvent in microwave‐assisted acylation of cellulose. The results are disappointing due to side reactions in the IL proper, and F^–‐mediated hydrolysis of the produced ester. A dramatic improvement is observed, when AlMeImF/DMSO mixture is employed. The results are comparable to those obtained when pure 1‐allyl‐3‐methylimidazolium chloride is employed. FTIR spectroscopy shows that dissolving a carboxylic acid anhydride in IL‐F leads to the formation of acyl fluoride. Thus ILs are far from being “spectator” solvents. The new approach (use of IL‐F/DMSO) is attractive because of its efficiency, low cost, and applicability to the derivatization of any polymer.

     

Novel Biopolymer Structures Synthesized by Dendronization of 6‐Deoxy‐6‐aminopropargyl cellulose

Propargyl cellulose with regioselective functionalization pattern was synthesized by nucleophilic displacement reaction of 6‐O‐toluenesulfonyl ester of cellulose (degree of substitution, DS 0.58) with propargyl amine. The novel 6‐deoxy‐6‐aminopropargyl cellulose provides an excellent starting material for the selective dendronization of cellulose at position 6 via the copper‐catalyzed Huisgen reaction yielding 6‐deoxy‐6‐amino‐(4‐methyl‐[1,2,3‐triazolo]‐1‐propyl‐polyamido amine) cellulose derivatives of first‐ (DS 0.33) and second (DS 0.25) generation, which are soluble in polar aprotic solvents. The novel biopolymer derivatives were characterized by elemental analysis, FT‐IR spectroscopy, and one‐ and two dimensional NMR spectroscopy, showing no side reactions (cross‐linking) or impurities and no conversion at the secondary positions.

     

Solvent Effects on the Monomer/Hydrogen‐Bonded Dimer Equilibrium in Carboxylic Acids: (+)‐(S)‐Ketopinic Acid as a Case Study

The hydrogen‐bond‐assisted self‐association process of a chiral semirigid carboxylic acid, namely, (+)‐(S)‐ketopinic acid, has been studied. The multiconformational monomer/dimer equilibrium has been evaluated by means of a concentration‐dependent FTIR study that enabled the experimental equilibrium constants of the dimer formation reaction (K_dim) to be determined in two solvents of different polarity. In CDCl₃, dimeric forms predominate, even in diluted solutions ( =5.074), whereas in CD₃CN the self‐association process is hindered and monomers are always the main species, irrespective of solute concentration ( =0.194). The reliability of the dimerization constants and the derived mono‐ and dimeric experimental fractions have been proven by means of accurate matching between the experimental vibrational circular dichroism spectra of the species and the theoretical spectra generated by considering the simultaneous weighted contributions of the concomitant monomers and dimers.     

Two new thiophosphoramide structures: N,N′,N′′‐tricyclohexylphosphorothioic triamide and O,O′‐diethyl (2‐phenylhydrazin‐1‐yl)thiophosphonate

The compound N,N′,N′′‐tricyclohexylphosphorothioic triamide, C₁₈H₃₆N₃PS or P(S)[NHC₆H₁₁]₃, (I), crystallizes in the space group Pnma with the molecule lying across a mirror plane; one N atom lies on the mirror plane, whereas the bond‐angle sum at the other N atom has a deviation of some 8° from the ideal value of 360° for a planar configuration. The orientation of the atoms attached to this nonplanar N atom corresponds to an anti orientation of the corresponding lone electron pair (LEP) with respect to the P=S group. The P=S bond length of 1.9785 (6) Å is within the expected range for compounds with a P(S)[N]₃ skeleton; however, it is in the region of the longest bond lengths found for analogous structures. This may be due to the involvement of the P=S group in N—H...S=P hydrogen bonds. In O,O′‐diethyl (2‐phenylhydrazin‐1‐yl)thiophosphonate, C₁₀H₁₇N₂O₂PS or P(S)[OC₂H₅]₂[NHNHC₆H₅], (II), the bond‐angle sum at the N atom attached to the phenyl ring is 345.1°, whereas, for the N atom bonded to the P atom, a practically planar environment is observed, with a bond‐angle sum of 359.1°. A Cambridge Structural Database [CSD; Allen (2002). Acta Cryst. B 58 , 380–388] analysis shows a shift of the maximum population of P=S bond lengths in compounds with a P(S)[O]₂[N] skeleton to the shorter bond lengths relative to compounds with a P(S)[N]₃ skeleton. The influence of this difference on the collective tendencies of N...S distances in N—H...S hydrogen bonds for structures with P(S)[N]₃ and P(S)[O]₂[N] segments were studied through a CSD analysis.     

Synthese,Strukturen, NMR‐ und EPR‐Untersuchungen der binuklearen Bis(N,N,N‴,N‴‐tetraisobutyl‐N′,N″‐isophthaloylbis(selenoureato))‐Komplexe des NiII und CuII

Synthesis, Structures, NMR and EPR Investigations of Binuclear Bis(N,N,N‴,N‴‐tetraisobutyl‐N′,N″‐isophthaloylbis(selenoureato)) Complexes of Ni^II and Cu^II The synthesis of binuclear Cu^II and Ni^II complexes of the quadridentate ligand N,N,N‴,N‴‐tetraisobutyl‐N′,N″‐isophthaloylbis(selenourea) and their crystal structures are reported. The complexes crystallize monoclinic, P2₁/c (Z = 2). In the EPR spectra of the binuclear Cu^II complex exchange‐coupled Cu^II‐Cu^II pairs were observed. In addition the signals of a mononuclear Cu^II species are observed what will be explained with the assumption of an equilibrium between the binuclear Cu^II‐complex (Cu^II‐Cu^II pairs) and oligomeric complexes with “isolated” Cu^II ions. Detailed ¹³C and ⁷⁷Se NMR investigations on the ligand and the Ni^II complex allow an exact assignment of all signals of the heteroatoms.     

Facile Synthesis and Bioactivity of Novel N,N′‐disubstituted‐1,2,3,4‐tetrahydroquinoxalines

A series of novel N ,N'‐disubstituted‐1,2,3,4‐tetrahydroquinoxalines were designed and synthesized by cyclization and acylation. The structures of all the novel compounds were confirmed by IR, ¹H NMR, ¹³C NMR, and high‐resolution mass spectrometry. The configuration of 4d was determined by X‐ray diffraction. The preliminary biological tests showed that all the products could protect maize against the injury caused by acetochlor to some extent.     

Ligand Dynamics in the Solid: Lithium‐fluorenide and Lithium‐benzo[b]fluorenide N,N,N′,N′‐Tetramethylethylenediamine (tmeda) Complexes

The dynamic behavior of the N,N,N′,N′‐tetramethylethylenediamine (tmeda) ligand has been studied in solid lithium‐fluorenide(tmeda) ( 3 ) and lithium‐benzo[b]fluorenide(tmeda) ( 4 ) using CP/MAS solid‐state ¹³C‐ and ¹⁵N‐NMR spectroscopy. It is shown that, in the ground state, the tmeda ligand is oriented parallel to the long molecular axis of the fluorenide and benzo[b]fluorenide systems. At low temperature (<250 K), the ¹³C‐NMR spectrum exhibits two MeN signals. A dynamic process, assigned to a 180° rotation of the five‐membered metallacycle (π‐flip), leads at elevated temperatures to coalescence of these signals. Line‐shape calculations yield ΔH^?=42.7 kJ mol^?1, ΔS^?=?5.3 J mol^?1 K^?1, and =44.3 kJ mol^?1 for 3 , and ΔH^?=36.8 kJ mol^?1, ΔS^?=?17.7 J mol^?1 K^?1, and =42.1 kJ mol^?1 for 4 , respectively. A second dynamic process, assigned to ring inversion of the tmeda ligand, was detected from the temperature dependence of T_1ρ, the ¹³C spin‐lattice relaxation time in the rotating frame, and led to ΔH^?=24.8 kJ mol^?1, ΔS^?=?49.2 J mol^?1 K^?1, and =39.5 kJ mol^?1 for 3 , and ΔH^?=18.2 kJ mol^?1, ΔS^?=?65.3 J mol^?1 K^?1, and =37.7 kJ mol^?1 for 4 , respectively. For (D₁₂)‐ 3 , the rotation of the CD₃ groups has also been studied, and a barrier E_a of 14.1 kJ mol^?1 was found.     

Interactions of Ionic Liquids with Polysaccharides 1. Unexpected Acetylation of Cellulose with 1‐Ethyl‐3‐methylimidazolium Acetate

The homogeneous conversion of cellulose in the ionic liquid 1‐ethyl‐3‐methylimidazolium acetate with 2‐furoyl chloride, p‐toluenesulfonyl chloride, and triphenylmethyl chloride yields surprisingly pure cellulose acetate samples in any case. From NMR spectroscopic studies, it may be concluded that during the homogeneous functionalization reactive intermediates including furane‐2‐carboxylic acid/acetic acid anhydride and acetic acid triphenylmethyl ester are formed leading to the cellulose acetates with DS values in the range from 0.55 to 1.86.