A more sustainable and easier applicable synthesis of aliphatic isocyanides in DMC is introduced using non-hazardous p-toluenesulfonyl chloride as dehydration reagent.
Isothiocyanates were snythesized in a more sustainable manner by sulfurization of isocyanides with elemental sulfur using catalytic amounts of DBU (down to 2 mol%).
Sequence-defined macromolecules offer applications in the field of data storage. Challenges include synthesising precise and pure sequences, reading stored information and increasing data storage capacity. Herein, the synthesis of dual sequence-defined oligomers and their application for data storage is demonstrated. While applying the well-established Passerini three-component reaction, the degree of definition of the prepared monodisperse macromolecules is improved compared to previous reports by utilising nine specifically designed isocyanide monomers to introduce backbone definition. The monomers are combined with various aldehyde components to synthesise dual-sequence defined oligomers. Thus, the side chains and the backbones of these macromolecules can be varied independently, exhibiting increased molecular diversity and hence data storage capacity per repeat unit. In case of a dual sequence-defined pentamer, 33 bits are achieved in a single molecule. The oligomers are obtained in multigram scale and excellent purity. Sequential read-out by tandem ESI-MS/MS verifies the high data storage capacity of the prepared oligomers per repeat unit in comparison to other sequence defined macromolecules.
New sustainable concepts
have to be developed to overcome the increasing
problems of resource availability. Cellulose derivatives with tunable
material properties are promising biobased alternatives to existing
petroleum-derived polymeric materials. However, the chemical modification
of cellulose is very challenging, often requiring harsh conditions
and complex solubilization or activation steps. More sustainable procedures
toward novel cellulose derivatives are therefore of great interest.
Herein, we describe a novel concept combining two approaches, (i)
tandem catalysis and (ii) cellulose derivatization, by applying a
single catalyst for three transformations in the DMSO/DBU/CO2 switchable solvent system. Cellulose was functionalized with four
different biobased isothiocyanates, which were formed in situ
via a catalytic sulfurization of isocyanides with elemental
sulfur, preventing the exposure and handling of the isothiocyanates.
The degree of substitution of the formed O-cellulose
thiocarbamates was shown to be controllable in a range of 0.52–2.16
by varying the equivalents of the reactants. All obtained products
were analyzed by ATR-IR, 1H, 13C, and 31P NMR spectroscopy as well as size exclusion chromatography, elemental
analysis, differential scanning calorimetry, and thermal gravimetric
analysis. Finally, the tandem reaction approach was shown to be beneficial
in terms of efficiency as well as sustainability compared to a stepwise
synthesis. Recycling ratios ranging from 79.1% to 95.6% were obtained
for the employed components, resulting in an E-factor
of 2.95 for the overall process.
Thioureas are frequently used in organocatalysis and typically rely on 3,5-bis(trifluoromethyl) phenyl moieties motifs to enhance their catalytic activity. In this work, these common motifs were replaced with tailorable functional groups, such as ester or sulfone aryls, applying elemental sulfur in a multicomponent reaction (MCR) strategy for the first time for thiourea catalyst synthesis. First, several thioureas bearing aryl, benzylic or aliphatic moieties were synthesized and tested for their hydrogen bonding strength by evaluating thiourea phosphine oxide complexes via 31 P NMR and their catalytic activity in an Ugi four-component reaction (U-4CR). Finally, ester and sulfone aryl thioureas were tested in the aminolysis of propylene carbonate, leading to conversions similar to those previously reported in the literature using the 3,5-bis (trifluoromethyl)phenyl moiety, proving that these groups are suitable alternatives for the trifluoromethyl group.
An easy access to
thermoplastic polythiosemicarbazones (polyTSCs)
is presented by condensation of dithiosemicarbazides and aromatic
dialdehydes, yielding eight polyTSCs and five co-polyTSCs, exhibiting M
ns up to 38 kDa in good yields (58–93%).
The polymerization proceeds at room temperature and is typically finished
after 2–3 h. The monomer scope was investigated, revealing
broad moiety tolerance (aliphatic, cyclic, benzylic, and aromatic
groups). Full characterization was performed by proton and carbon
NMR spectroscopy, IR spectroscopy, and size exclusion chromatography,
confirming the anticipated chemical structure of polyTSCs. Thermal
analysis of the polymers showed degradation starting at ∼200
°C by decomposition of the TSC function. Glass transitions were
only observed for polymers derived from rigid monomers (162–198
°C). Further versatility of the reaction was underlined by the
synthesis of five copolymers using different dithiosemicarbazide monomers.
Stereoelectronic effects in cyclohexanones, methylenecyclohexanes, spiro, and epoxy compounds of cyclohexanes and further derivatives were investigated by measuring 1JC,H coupling constants and by identification of Perlin effects, that is, of differences in the coupling constants for equatorial and axial CH bonds in the methylene groups of six‐membered rings. The Perlin effects were correlated with results from natural bond orbital analyses. NMR experiments and calculations were performed with conformationally restricted 4‐tert‐butyl‐substituted derivatives. It turned out that the coupling constants are strongly influenced not only by stereoelectronic interactions with CC, CO, and CN π bonds, or with the π‐type CC or CO bonds of the three‐membered rings, but also by the s character of the respective CH bonds' carbon orbital. Reliable correlations of measured and calculated coupling constants were achieved with B3LYP/6‐311++G(d,p) and BP86/aug‐cc‐pVTZ‐J functionals.
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