Click chemistry &its application in
Concept of Click Chemistry
“Click chemistry” is a chemical philosophy introducded by K.Barysharpless in
2001, which describes the chemistry that can generate substances quickly and
reliably by joining small units together with high thermodynamic force.
Requirements for the click reaction are ,
The reaction must be
2. Wide in scope
3. High yield of product (nearly 100%)
4. Generate only inoffensive or no byproducts
5. Stereo specific
6. High atom economy
The process must be:
7.simple reaction conditions
8.readily available starting materials and reagents
9.simple product isolation by non-chromatographic methods
Defining a “Click” Chemistry
“ A click reaction must be
modular, wide in scope, high
yielding, create only inoffensive
by-products (that can be removed
without chromatography), are
stereo specific, simple to perform
and that require benign or easily
removed solvent. ”
- Barry Sharpless
Kolb, H.C.; Finn, M.G.; Sharpless, B.K. Angew. Chem. Int. Ed. 2001, 40, 2004-2021.
Classes of “Click” Reactions
Non-Aldol type Carbonyl
of oxime ethers, hydrazones and
aromatic heterocycles )
ADDITION REACTIONS OF
ALKENES AND ALKYNES
(like epoxides, aziridines cyclic
NUCLEOPHILIC OPENING OF
HIGHLY STRAINED RINGS
Thiol-ene reaction ,Michael
(di hydroxylation of alkynes,
Historical Perspective of
1933- Dipolar nature of azide first recognized by Linus Pauling
R N N N
R N N NH2
R N N N
1960- Mechanism of 1,3-dipolar cycloaddition of azides
and alkynes pioneered by Rolf Huisgen
+ N3 R'
2001- Copper catalyzed 1,3-Dipolar cycloaddition by
L. Pauling. Proc. Natl. Acad. Sci. USA 1933, 19, 860-867; Huisgen, R. Angew. Chem. Int. Ed. 1963, 2, 633-696
Sharpless, K.B. et al. Angew. Chem. Int. Ed 2002, 41, 2596-2599; Meldal,M.J. et al. J. Org. Chem. 2002, 67, 3057-3064
Copper Catalyzed Azide/Alkynes
• Thermodynamic and kinetically
favorable (50 and 26 kcal/mol,
• 107 rate enhancement over noncatalyzed reaction
• Triazole stable to oxidation and acid
Rostovtsev et al. Angew. Chem. Int Ed. 2002, 41, 2596-2599
CuAAC Catalytic Cycle
N N N
N N N
N N N
Himo, F. et al. J. Am. Chem. Soc, 2005, 127, 210-216.
Ahlquist, M., Fokin, V.V. Organometallics 2007, 26, 4389-4391.
N N N
Click chemistry Chemistry
Applications in polymers
Some recent applications of click chemistry in material
Adhesive polymers for Cu metal
Potential Propellent binders
polymer backbone modification
Surface modification of nano particles.
In hyperbranched polymers & dendrimers
Adhesive polymes for Cu metal from
• David D. Diaz etal have recently synthesised a metal adhesive polymer
based on copper catalyzed azide-alkyne cycloaddition.
• Di or tri azide and Di or tri alkyne monomers were introduced between
copper or zinc plates,which provides necessary Cu(I) ions.
The resulting adhesive polymer was found to possess comparable or superior
adhesive strength to standard commercial glues.
• The above polymer is showing 268 24 kg load per gram adhesive.
where as commercial glue (weld-it) is showing 248 111 kg load per
Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 45, 5182–5189 (2007)
potential propellant binders
1. Propellant is the chemical mixture burned to produce thrust in rockets and
consists of a fuel and an oxidizer ,generally these are held together by polymeric
2. Polyurethanes are well known binders for propellants. But there may be a chance
of side reactions during and after the polymerization ,that degrade the
mechanical properties of the resulting propellant .e.g., loss of elasticity
3. 1,2,3-triazole polymers are recently studied as novel binders for the explosives
and high energy propellants Because of high thermal & physical stability
4. Azide and alkynes monomers react readily and form polytriazole with out any
side reaction , o these are one of the best alternative for the propellant binders
5. A typical polyurethane, elastomeric linear matrix for rocket propellants has
modulus 0.05-1.9 Mpa
6. Where as the triazole polymers having much improved modulus 0.5-3.9 MPa
7. the mixture of above cross linked polymer with 43wt% aluminum filler greatly
improve the modulus of the triazole polymers, which could reach nearly 4MPa.
Ling Wang et.al.,Journal of AppliedPolymer Science, Vol. 117, 2612–2621 (2010)
Polyurethane backbone modification by
•Du Prez et al. synthesized linear polyurethanes
(PUs) having alkyne groups
•located along the backbone
•The polyurethane was formed by reacting with two
•different alkyne-functionalized diols with a
•TGA measurements demonstrated that the
incorporated triazoles in the PU
materials strongly improves the final char yield
Surface modification of silica
Nano particles through ‘click’ chemistry
Any particle with a size from 10 nm to 100nm is generally termed as nano particle.
Nano particles have many applications.
ex:colloidal gold – useful to stain the glass with an intense red colour ,was done in ancient
Zinc nano particles are used in the sun block creams and cancer medicine.
Silica nano particles in chromatography, bio-seperation, imaging, and multifunctional
surface modification of silica nano particles by click chemistry: functionalisation of nano particles can be achieved by so many ways. But silane
coupling agents are widely used to surface modification of silica nano particles.
But it has some drawbacks such as,solvent polarity and reaction temperature. in large
scale surface capping is not uniform.
Click reaction is one of the efficient way to impart desirable funtionalities to nanoparticles
without any side reactions.
Ex:-pyrene, a fluorophore (which shows excimer emmision) is successfully attached to the
silica nano particles.
CURRENT SCIENCE, VOL. 95, NO. 9, 10 NOVEMBER 2008
Hydrogels synthesis from click
Hydrogels are Water swollen crosslinked polymers
Crosslinks may occur:
– by reaction of one or more monomers
– hydrogen bonds
– Vander Waals interactions
Hydro gels traditionally prepared by photo polymerization of water soluble
vinyl monomers, such as polyethylene glycol- diacrylates, but has some
defects like uncontrollable crosslinking
click chemistry concept is utilized In designing controlled hydro gel
With improved properties.
Another advantage of click chemistry is hydrogels can be prepared at room
Hyper branched Polymers & dendrimers from Click
1.Dendrimer = Greek words dendron (tree)+ meros
1.Made in a very easy fashion
[ Divergent and convergent process
2.Made in a very sophisticated fashion
[ Divergent and convergent process]
2.polydisperse [ Mw>Mn] and less degree of
branching ( DB >1 )
3.Perfectly built onto a core molecule
3.They are an irregular macromolecules
4.Monodisperse [ Mw =Mn] and high degree of
branching ( DB =1 )
4.These polymers structure consist of three
distinct groups : dendritic groups ;linear groups
and terminal groups.
5.They are symmetrical and layered
Examples of hyper branched polymers:
6.These polymers consist of three distinct areas :
polyfunctional central core ( center of symmetry);
radial symmetrical layers of repeating units(
generations); end standing groups (terminal
Boltorns (P( bis -MPA) hyper branched polymer),
Hybranet (poly(ester amide))
poly( phenylenes )
Dendrimers and hyper branched polymers are synthesized mainly two ways
• Divergent strategy:- Core to Surface
•Convergent strategy :-Surface to core
Click chemistry is also an efficient reaction to produce dendrimers and hyperbranched polymers with good yeilds