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FUNCTIONALIZED POLY(AMIDOAMINE)
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overall activities than the homogeneous system.4 To overcome these disadvantages, soluble
polymers have been used for immobilization of catalysts.5 In this manner, the desirable
features of homogeneous catalysis, such as comparable reaction kinetics and mass transfer,
can be maintained while the macromolecular nature of the polymer provides a convenient
means of purification and, in some cases, recyclability.2
Both linear and branched polymers have been used as soluble macromolecular sup-
ports for reagents and catalysts.6 While both polymer species are, in general, readily
available, linear polymers can suffer from poor loading capacity, because only two or one
side (head and tail) of linear polymers can be grafted by reagents or catalysts. For example,
MeO-PEG5000 catalyst conjugates carry a loading of only 0.2 mmol catalyst per gram of
polymer, while branched polymers typically carry several mmol.g−1 of catalysts.7 Many
papers have described both the covalent and noncovalent grafting of reagent or catalysts into
the branched polymers.8 But as far as we are aware, there is no report about the synthesis
of a Brønsted acid functionalized PAMAM dendrimer.
Herein, we report the synthesis of PAMAM functionalized sulfamic acid. Addition to
the acidic properties of the dendrimer catalyst, the catalyst has ionic structure. The resulting
catalyst was used for the protection of aldehydes in 1,1-diacetate form. Protection of alde-
hydes as acylals is often preferred due to their ease of preparation and their stability toward
basic and neutral conditions.9 Generally, they have synthesized from acetic anhydride and
aldehydes using strong protonic acids10 and Lewis acids.11 But these methods suffer from
some drawbacks such as high catalyst loading, metal contain catalysts, and using hazardous
organic solvent.
RESULT AND DISCUSSION
Synthesis of Catalyst
We chose PAMAM dendrimer as a source of proton-affinity bases and multi-
functional polymer for the formation of the Brønsted acid catalyst. It is well-known that
PAMAM dendrimers are monodisperse, hyperbranched polymers possessing a very high
concentration of primary and tertiary amine groups, which can be readily protonated to
form cationic centers3.
The first generation of PAMAM dendrimer (G1) was prepared according to the
standard procedure.12 For sulfamic acid functionalization, chlorosulfonic acid was added
to a solution of PAMAM in dry dichloromethane. The synthetic protocol is summarized
in Scheme 1.The terminal amine groups of PAMAM react with ClSO3H to form sulfamic
acid functionalities. The tertiary inner amine groups in PAMAM structure neutralize by
ClSO3H. After washing with water, ClSO3− counterions react with H2O molecules to obtain
HSO4 as counterions.
The FT-IR spectra of PAMAM before and after functionalization are presented in
Figure S1 (Supplemental Materials). The FT-IR spectrum of PAMAM shows a strong peak
at 1663 cm−1 corresponding to the amide groups in the dendrimer. After functionalization
of PAMAM with chlorosulfonic acid, a strong peak at 1083 cm−1 and 1377, corresponding
to sulfate anions and sulfamic groups, appeared. The same carbonyl peaks can be seen
at the spectrum of functionalized PAMAM, which shows the amide groups of dendrimer
remain intact during the functionalization.
Figure S2 shows the thermal gravimetric analysis (TGA) curves of PAMAM (G1) and
PAMAM@SO3H. As seen, the decomposition of PAMAM dendrimer initiates at 190◦C,
Pourjavadi, Ali
