This review summarizes the different categories of topochemical polymerizations for the synthesis of fully-organic polymers and their design strategies.
Polymers are an integral part of our daily life. Hence, there are constant efforts towards synthesizing novel polymers with unique properties. As the composition and packing of polymer chains influence...
Here we report the synthesis of a trisubstituted‐1,2,3‐triazole‐linked polymer using a topochemical azide‐alkyne cycloaddition (TAAC) reaction. A cyclitol‐derived monomer having an azide and an internal alkyne group was designed. The four hydroxy groups present in this monomer dictate its crystal packing such that the monomer molecules are arranged head‐to‐tail, thereby placing the internal alkyne and the azide units of adjacent molecules proximally. Although the alignment of the reactive groups in the monomer crystal is not favourable for a topochemical reaction, a reactive orientation can be achieved by the rotation of the reactive groups. Upon heating the crystals, the monomer underwent topochemical polymerization to yield the trisubstituted‐1,2,3‐triazole‐linked‐polycyclitol. This study demonstrates a new synthetic strategy for cycloaddition reaction between non‐polarized internal alkynes and azides to yield trisubstituted triazoles.
A topochemical polymerization governed by a topotactic
polymorphic
transition is reported. A monomer functionalized with azide and an
internal alkyne crystallized as an unreactive polymorph with two molecules
in the asymmetric unit. The molecules are aligned in a head-to-head
fashion, thereby avoiding the azide–alkyne proximity for the
topochemical azide–alkyne cycloaddition (TAAC) reaction. However,
upon heating, one of the two conformers underwent a drastic 180°
rotation, leading to a single-crystal-to-single-crystal (SCSC) polymorphic
transition to a reactive form, wherein the molecules are head-to-tail
arranged, ensuring azide–alkyne proximity. The new polymorph
underwent TAAC reaction to form a trisubstituted 1,2,3-triazole-linked
polymer. These results, showing unexpected topochemical reactivity
of a crystal due to the intermediacy of an SCSC polymorphic transition
from an unreactive form to a reactive form, highlight that predicting
topochemical reactivity by relying on the static crystal structure
can be misleading.
Here we report the synthesis of a trisubstituted-1,2,3-triazole-linked polymer using a topochemical azide-alkyne cycloaddition (TAAC) reaction. A cyclitolderived monomer having an azide and an internal alkyne group was designed. The four hydroxy groups present in this monomer dictate its crystal packing such that the monomer molecules are arranged head-to-tail, thereby placing the internal alkyne and the azide units of adjacent molecules proximally. Although the alignment of the reactive groups in the monomer crystal is not favourable for a topochemical reaction, a reactive orientation can be achieved by the rotation of the reactive groups. Upon heating the crystals, the monomer underwent topochemical polymerization to yield the trisubstituted-1,2,3-triazole-linked-polycyclitol. This study demonstrates a new synthetic strategy for cycloaddition reaction between non-polarized internal alkynes and azides to yield trisubstituted triazoles.
A core–shell sorbent is developed using natural fibers for marine oil spill recovery. The core of the sorbent is made using coir fibers, which is then covered with a thin layer of shell made from cotton impregnated with a phase selective oleogelator, 12‐hydroxystearic acid. The pore volume that is available for oil uptake amounts to 85–90% of the total volume of the sorbent. When it is introduced to a crude oil–water mixture, the sorbent selectively absorbs the oil instantaneously. The gelator in the shell congeals the oil in the shell matrix, forming a rigid enclosure for the absorbed oil and this allows the collection of the oil‐absorbed sorbents without dripping. The absorbed oil can be recovered quantitatively by simple pressing. The method is general and works with all kinds of crude oils. The cheaply available natural raw materials and easy preparation make this method attractive in terms of economy, reliability, scalability, practicability, and greenness.
N-Acyl sulfonimidamides were synthesized via a Cu-catalyzed double C-H/N-H activation protocol. The imino end of sulfonimidamides was acylated using aldehyde as the acylating agent and t-butyl hydrogen peroxide (TBHP) as the oxidant in acetonitrile (MeCN) at 82 °C. The mild reaction conditions afforded low-to-moderate yields of N-acyl sulfonimidamides with high structural diversity.
Regiochemistry of topochemical reactions depends on the crystal packing and biasing the regiochemistry necessitates precise crystal engineering. The pristine crystals of monomer 1 upon topochemical azidealkyne cycloaddition (TAAC) reaction give a 1 : 1 blend of 1,4-and 1,5-triazole-linked polymers due to the presence of two self-sorted reactive conformers in the crystal. We designed a binary isomorphous cocrystal of monomer 1 and a structurally similar dummy molecule 2 to limit the number of reactive conformers of 1 to one and thus to get one type of polymer. Equimolar solution of 1 and 2 in chloroform-acetone mixture gave two 1 : 1 cocrystals Co-I and Co-II. The Co-II, a chloroform adduct, on heating undergoes desolvation and polymorphic transition to Co-I. Co-I is isomorphic to 1 and 2 and possess self-sorted arrays of 1 and 2. Heating Co-I results in the TAAC polymerization giving 1,4-triazolyllinked polymer of 1 selectively, showing the power of crystal engineering in regiocontrol.
Chemical reactions governed by the molecular arrangementin crystals-topochemical reactions-are attractive in terms of greener, catalyst-free and solvent-free reaction conditions, nonnecessity of chromatographic purification, and their ability to form unique products that are not accessible by the conventional solution-phase methods. [1][2][3][4][5][6] However unlike solution-state reactions that are well-explored, factors that influence topochemical reactions are still poorly understood. [7][8][9][10] The solution-state reactivity of molecules could be easily regulated by altering the reaction conditions such as solvent, reagents, catalyst, etc. However in the case
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