Chemistry Reference
In-Depth Information
Table
8
.1
Some available supported reagents
in Fig. 8.7. Macroporous polystyrenes get a renewal
of interest through post-functionalisation: the con-
dition of copolymerisation with high contents of
DVB gives a substantial amount of free pendant
vinylic groups that survive after the reaction [27]
and are still useful for further radical grafting of func-
tional groups [31,32] (Fig. 8.8). More details on
these transformations will be given in the following
sections according to the kind of properties of each
polymer reagent.
Aminomethyl-polystyrene
Benzenesulfonic acid
Bengal Rose B
Borohydride-exchanged resin
Bromopolystyrene
Chloramine T, polymer bound
2-
t
-Butylimino-2-diethylamino-1,3-dimethyl-perhydro-1,3,2-
diazaphosphorine
2-Chlorotrityl chloride
Cyanide-exchanged resin
Dialkylaminomethyl-polystyrene (dimethyl, diisopropyl,
morpholino)
Dimethylaminopyridine on polystyrene
(Poly)ethyleneglycol, polymer bound
Hexamethylphosphotriamide
Maleimidobutyramoidomethyl-polystyrene
Methylbenzhydrylamine, polymer bound
Merrifield polymer (chloromethylated polystyrene)
Poly(methylmethacrylate)
Poly(4-vinylpyridine)
Poly(4-vinylpyridine) hydrobromide, perbromide
Pyridinium chlorochromate
Pyridinium dichromate
Pyridinium toluene-4-sulfonate
Styrene-divinylbenzene copolymer
1,5,7-Triazabicyclo[4.4.0]dec-5-ene, polystyrene bound
Tribromide-exchanged resin
Triphenylphosphine, polymer bound
2.5 Spacers
The fact that supported reagents (and catalysts) are
made essentially from gel-type polymers must be
stressed. It has been experienced that a good swelling
of the material ensures better diffusion of substrates
and products through the beads; this is an aspect of
the necessary accessibility of molecules in solution
towards the 'reactive site'.
The early functional polymers result from simple
functionalisation of polystyrene; as shown in Fig.
8.5, the reactive site is very close to the polymeric
chain (which in fact is coiled, not straight), which
induces severe steric hindrance. To improve the
freedom of the reactive site, extensions have been
(a)
(b)
Gel-type polymer : low cross-linking,
diffusion allowed by swelling
Macroporous polymer : high cross-linking,
diffusion allowed by porosity
Fig.
8
.6
Schematic structure of gel-type and macroporous polymers.
