Cross-linking of starch with bifunctional precursors of nitroalkenes

Article abstract of DOI:10.1016/S0008-6215(98)00171-2

Granular starch was cross-linked with 1,3-di-O-acetyl-2-nitro-1,3-propanediol (1), 1,3-di-O-pivaloyl-2-nitro-1,3-propanediol (2), 2-nitro-3-O-pivaloyl-1-propene-3-ol (3), 1,3-di-O-acetyl-aci-2-nitro-1,3-propanediol (4), 1,3-di-O-pivaloyl-aci-2-nitro-1,3-propanediol (5) and 1,6-di-O-acetyl-2,5-dinitro-1,6-hexanediol (6). The bifunctional precursors for the nitro-alkenes 1, 2, 3, and 4 were readily synthesized in high yields from nitromethane, paraformaldehyde and acetic anhydride (1, 3) or pivaloyl chloride (2, 4), respectively. The reaction rate for the cross-linking was very high, and for 1 and 3, the reaction reached completion within 1 h (at room temperature). The swelling capacities of the products obtained when starch was cross-linked with precursors for the nitroalkenes 1-4 and 6 were lower in comparison to epichlorohydrin cross-linked starch. These results indicate a high reaction efficiency at low degrees of substitution. Cross-linked 2-nitroalkyl starch ethers were synthesized in a one-pot synthesis by addition of 1 or 3 and 2-nitroalkyl acetates to granular suspensions of starch. Copyright (C) 1998 Elsevier Science Ltd.

Full text of DOI:10.1016/S0008-6215(98)00171-2

Carbohydrate Research 310 (1998) 191±201
Cross-linking of starch with bifunctional
precursors of nitroalkenes
a
a,
b
c
Andre
Â
Heeres , Henk A. van Doren *, Kees F. Gotlieb , Ido P. Bleeker ,
R.M. Kelloggd
a
TNO Nutrition and Food Research Institute, Rouaanstraat 27, 9723 CC Groningen, The Netherlands
b
Wildervankstraat 12, 9648 LC Wildervank, The Netherlands
c
AVEBE B.A., Avebeweg 1, 9607 PT Foxhol, The Netherlands
d
Department of Organic and Molecular Inorganic Chemistry,University of Groningen, Nijenborgh 4,
NL-9747 AG Groningen, The Netherlands
Received 10 December 1997; accepted 20 June 1998
Abstract
Granular starch was cross-linked with 1,3-di-O-acetyl-2-nitro-1,3-propanediol (1), 1,3-di-O-
pivaloyl-2-nitro-1,3-propanediol (2), 2-nitro-3-O-pivaloyl-1-propene-3-ol (3), 1,3-di-O-acetyl-aci-
2
2
-nitro-1,3-propanediol (4), 1,3-di-O-pivaloyl-aci-2-nitro-1,3-propanediol (5) and 1,6-di-O-acetyl-
,5-dinitro-1,6-hexanediol (6). The bifunctional precursors for the nitro-alkenes 1, 2, 3, and 4 were
readily synthesized in high yields from nitromethane, paraformaldehyde and acetic anhydride (1,
) or pivaloyl chloride (2, 4), respectively. The reaction rate for the cross-linking was very high,
3
and for 1 and 3, the reaction reached completion within 1 h (at room temperature). The swelling
capacities of the products obtained when starch was cross-linked with precursors for the
nitroalkenes 1±4 and 6 were lower in comparison to epichlorohydrin cross-linked starch. These
results indicate a high reaction eciency at low degrees of substitution. Cross-linked 2-nitroalkyl
starch ethers were synthesized in a one-pot synthesis by addition of 1 or 3 and 2-nitroalkyl acetates
to granular suspensions of starch. # 1998 Elsevier Science Ltd. All rights reserved
Keywords: Starch, cross-linking; Cross-linked 2-nitroalkyl starches
1
. Introduction
The development of derivatization methods for
aggregates with di€erent rheological behaviour, or
insoluble products with a wide range of swelling
characteristics, may be synthesized. The insoluble
cross-linked polysaccharides have found several
applications, e.g., in chromatography (gel ®ltra-
tion) [1]. Well known examples of these com-
pounds are cross-linked dextrans (Sephadex) and
agaroses (Sepharose) [2].
polysaccharides with various reagents has included
reactions with bifunctional compounds that lead to
cross-linked polymers. Thus larger molecular
*
Corresponding author at current address: TNO
Nutrition and Food Research Institute, Utrechtseweg 48, P.O.
Box 360, 3700 AJ Zeist, The Netherlands; fax: +31-30-
In the starch industry the cross-linking of starch
granules with bi- or polyfunctional reagents has led
6
957224; e-mail: vandoren@voeding.tno.nl
0008-6215/98/$Ðsee front matter # 1998 Elsevier Science Ltd. All rights reserved
PII S0008-6215(98)00171-2

192
A. Heeres et al./Carbohydrate Research 310 (1998) 191±201
to a wide variety of commercial products in the
food, textile and adhesives industries [3,4]. Not
only are the cross-linked starches interesting com-
pounds themselves, but they can also be subjected
to other chemical modi®cations such as acetyla-
tion, hydroxypropylation or carboxymethylation.
In this way products with widely di€erent proper-
ties and applications have been synthesized.
Although a wide variety of cross-linking agents
for starch and other polysaccharides have been
described in the literature, only a few are of
commercial importance. Examples are adipic
anhydrides [5], phosphorus oxychloride [6],
sodium trimetaphosphate [7] and epichlorohydrin
[
8]. The cross-linking of starch with these com-
pounds can easily be achieved in aqueous starch
suspensions under alkaline reaction conditions.
Cross-linking of water soluble starches is less
favourable for industrial applications. The cross-
linked starch adipates and phosphates are used on
a large scale in the food industry. A disadvantage
of the distarch adipates and phosphates is the
instability of the ester moieties under alkaline
conditions.
Scheme 1. Synthesis of 2-nitroalkyl starch ethers (etheri®ca-
tion can also occur on O-3 and O-6).
Cross-linking of starch with epichlorohydrin
leads to distarch glycerol. Due to the toxicity of
epichlorohydrin, these cross-linked starches cannot
be applied in the food sector. Distarch glycerol is
highly resistant towards shear and owing to the
ether linkages the epichlorohydrin cross-linked
starch is stable under acidic and alkaline condi-
tions. A slight disadvantage of the reaction is the
relatively long reaction time required to achieve
satisfactory degrees of conversion.
precursors for cross-linked 2-aminoalkyl starch
ethers, is also described.
2. Results and discussion
Syntheses of the cross-linking agents.ÐThe
synthesis of 1,3-di-O-acetyl-2-nitro-1,3-propane-
diol (1), 1,3-di-O-pivaloyl-2-nitro-1,3-propanediol
(2) and 2-nitro-3-O-pivaloyl-1-propene-3-ol (3) is
described by Seebach and Knochel [12]. The
syntheses of 1 and 2 (Scheme 2) are straightfor-
ward, the yields are high and the procedure
appears to be applicable for large scale reactions.
The synthesis of 3 is achieved by adding a weak
base (NaOAc) to 2. Under these weakly alkaline
conditions one molecule of pivalic acid splits o€
and a nitroalkene is formed. However, the yield of
the selective multicoupling reagent is disappoint-
ing, the overall yield from formaldehyde, nitro-
methane and pivaloyl chloride being only about
25%.
Recently, we developed (Scheme 1) a route to 2-
nitroalkyl starch ethers by adding nitroalkenes, or
precursors thereof, to aqueous starch suspensions
[
9±11]. High reaction rates were obtained in all
cases for 2-nitroalkenes (or suitable precursors
thereof) and the eciency of the nitroalkylation
was found to be especially high when 2-nitroalkenes
were formed in situ from ꢀ-nitro-acyloxy-alkanes.
Here, we report the ecient cross-linking of
granular starch with readily available bifunctional
precursors of nitroalkenes. Similar to distarch gly-
cerol these compounds are stable under alkaline
and moderately acidic conditions owing to the
ether linkages. Due to the excellent Michael accep-
tor capacities of nitroalkenes the rate of the cross-
linking reaction is very high. The synthesis of
cross-linked 2-nitroalkyl starches, which have very
interesting application potential and are excellent
Also described in the literature is the synthesis
of an intramolecularly stabilized nitronic acid, aci-
2-nitro-1,3-propanediol [13]. High yields (73%) of
this compound are obtained by reaction of nitro-
methane and paraformaldehyde with catalytic

A. Heeres et al./Carbohydrate Research 310 (1998) 191±201
193
ꢁ
,!-dinitroalkanes with formaldehyde (Henry
reaction) followed by acetylation proceeds in good
yields for the synthesis of 1,6-di-O-acetyl-2,5-dini-
tro-1,6-hexanediol (6; Scheme 4) [15].
Unfortunately 1,3-dinitropropane is not stable
under the reaction conditions required for the
Henry reaction with formaldehyde. Due to the
alkaline conditions a reverse aldol condensation
probably takes place in which nitromethane and
nitroethene are formed. Nitroethene is known to be
very sensitive to anionic polymerisation.
Cross-linking of granular starch.ÐThe antici-
pated pathway for cross-linking of granular starch
suspensions with 1,3-di-O-acetyl-2-nitro-1,3-pro-
panediol (1) is shown in Scheme 5. Under alkaline
conditions acetic acid splits o€ and 2-nitro-3-O-
acetyl-1-propene-3-ol is formed. It is expected that
the aci-compound 4 reacts according to a similar
pathway. If the pivaloyl derivatives 2 and 5 are
used, pivalic acid splits o€, which results in the
formation of 2-nitro-3-O-pivaloyl-1-propene-3-ol
(3). After a Michael addition of the corresponding
nitroalkene with starch another molecule of acetic
acid or pivalic acid is split o€ and a 2-nitro-3-pro-
pene starch ether is formed. A second Michael
addition with starch completes the cross-link. It
should be noted that the cross-link can be intra-
molecular within the glucose monomer, intramol-
ecular within the same starch chain and
intermolecular between di€erent starch chains. The
rheology of gelatinized cross-linked starches is
predominantly in¯uenced by intermolecular cross-
links. Reaction may take place with any of the free
hydroxyl groups.
Scheme 2. Synthesis of 1,3-di-O-acetyl-2-nitro-1,3-propane-
diol (1), 1,3-di-O-pivaloyl-2-nitro-1,3-propanediol (2), and 2-
nitro-3-O-pivaloyl-1-propene-3-ol (3).
amounts of potassium ¯uoride and tetra-
butylammonium bromide. Surprisingly, the aci-
nitrocompounds
propanediol (4) and 1,3-di-O-pivaloyl-aci-2-nitro-
,3-propanediol (5) are isolated in moderate to
1,3-di-O-acetyl-aci-2-nitro-1,3-
1
good yields after acetylation with acetic anhydride
or reaction with pivaloyl chloride (Scheme 3).
Attempts to synthesize 2-nitro-3-O-pivaloyl-1-pro-
pene-3-ol (3) from 5 were not successful.
The synthesis of ꢁ,!-bis(ꢀ-nitroacetoxyalkanes),
in which the ꢀ-nitroacetoxy functionalities are
separated by a short hydrophobic chain, is com-
plicated. To our knowledge no satisfactory route
for the synthesis of ꢁ,!-dinitroalkanes has been
described in the literature. Low to moderate yields
are obtained for the reaction of ꢁ,!-di-iodoalk-
anes with silver nitrite [14]. Further reaction of the
The cross-linking of starch with ꢁ,!-bis(ꢀ-
nitroacetoxyalkanes) (Scheme 6) is comparable to
the synthesis of 2-nitroalkyl starch ethers. Forma-
tion of a (di)nitroalkene and Michael additions of
both sides of the molecule result in a cross-link
within the starch granule. In this way a (short)
hydrophobic chain is introduced into the starch
matrix.
Scheme 3. Synthesis of 1,3-diacetyl-aci-2-nitro-1,3-propane-
diol (4) and 1,3-dipivaloyl-aci-2-nitro-1,3-propanediol (5).
Scheme 4. Synthesis of ꢁ,!-bis(ꢀ-nitroacetoxyalkanes).

194
A. Heeres et al./Carbohydrate Research 310 (1998) 191±201
Scheme 5. Example of the cross-linking reaction; reaction sequence of 1,3-di-O-acetyl-2-nitro-1,3-propanediol with starch.
Viscosity pro®les of cross-linked starches.Ð
Information about the eciency of the cross-
linking can be obtained from viscosity pro®les
hydrogen bonds in starch segments. The viscosity
of the suspension rises but when shear is imposed
(by stirring) the integrity of the swollen starch
granules is lost and the viscosity of the solution
decreases. Amylose, followed by amylopectin,
leaks out of the ``ghosts'' and goes into solution.
(physical analysis). When suspensions of starch
granules are heated above a certain temperature,
water penetrates into the granules and weakens the

A. Heeres et al./Carbohydrate Research 310 (1998) 191±201
195
Fig. 1. RVA curves of starch and distarch 2-nitropropanediol
5% suspension; 1c, dsmax=0.0019; 1d, dsmax=0.00098).
(
than for gelatinized starch. At approximately 1
cross-link per 1000±1500 glucose monomers the
maximum viscosity is lower in many cases but the
end viscosity is higher than native gelatinized
starch [4]. The same trend was observed for
viscosity pro®les (Fig. 1) of distarch 2-nitroprop-
1
anediol (1c, dsmax=0.0019; 1d, dsmax=0.00098 )
cross-linked with 1,3-di-O-acetyl-2-nitro-1,3-pro-
panediol. With larger numbers of cross-links
dsmax=0.019) no increase in viscosity was
observed during the temperature programme. The
granule form remains intact but the expected loss
of crystallinity was con®rmed with polarization
microscopy.
(
Scheme 6. Synthesis of distarch ꢁ,!-bis(ꢀ-nitro)alkanediol
using (1,6-di-O-acetyl-2,5-dinitro-1,6-hexanediol (6, n=2).
After cooling down, the viscosity of the starch
paste increases again. This gelatinization behaviour
can be followed with a Rapid Visco Analyser
The RVA curves for the products of the syn-
thesis of distarch 2-nitropropanediol with com-
pounds 1±5 (1c, 2a, 4a, 5a, dsmax=0.0019; 3a,
dsmax=0.0016), distarch glycerol (epichlorohydrin
7b, dsmax=0.0022) and native potato starch (5%
solution) are shown in Fig. 2. One can readily
conclude that cross-linking of granular starch with
compounds 1 (1,3-di-O-acetyl-2-nitro-1,3-propane-
diol), 2 (1,3-di-O-pivaloyl-2-nitro-1,3-propanediol)
and 4 (1,3-di-O-acetyl-aci-2-nitro-1,3-propanediol)
leads to a lower viscosity pro®le than cross-linking
with epichlorohydrin (with the same degree of
substitution). Cross-linking with compound 5 (1,3-
di-O-pivaloyl-aci-2-nitro-1,3-propanediol) results
in products with almost similar peak and end
viscosities (after the temperature programme) as
epichlorohydrin (7b). Under the alkaline reac-
tion conditions anionic polymerization of the
(RVA), which measures the viscosity of the starch
suspension while stirring the suspension with a
revolving cup driven at constant speed [16]. The
suspension passes through a certain temperature
ꢀ
ꢀ
ꢀ
ꢀ
pro®le (1 min, 30 C; 5.4 min, 30 C!95 C;
ꢀ
ꢀ
2
.5 min, 95 C; 3.7 min, 95 C!50 C; 2.1 min,
ꢀ
5
0 C).
The gelatinization behaviour of cross-linked
starches depends on the extent of cross-linking
17±20]. If the number of cross-links is high enough
[
(
ꢁ1 cross-link per 100 glucose monomers) and the
starch granules are heated above their gelatiniza-
tion temperature, the crystallinity is lost but the
granule shape remains intact. No increase in vis-
cosity is observed. At low levels of cross-linking the
viscosity of the starch solution is altered. At
approximately 1 cross-link per 500 glucose mono-
mers the maximum and the end viscosity are lower
1
dsmax=the maximum number of cross-links per mole
glucose monomer of the cross-linked starch.

196
A. Heeres et al./Carbohydrate Research 310 (1998) 191±201
Fig. 4. Particle volume (swelling capacity) of starch cross-
linked with bifunctional precursors of nitroalkenes.
Fig. 2. RVA curves of distarch 2-nitropropanediol (5% sus-
pension; synthesized with compounds 1±5 (1c±2a, 4a±5a,
dsmax=0.0019; 3a, dsmax=0.0016), distarch glycerol (epi-
chlorohydrin. 7b, dsmax=0.0022), and native starch.
cles [21]. After centrifugation a supernatant phase,
which contains some soluble material, and a starch
gel are obtained. The volume of the starch particles
depends on the botanic source of the starch used
[22]. As suspected, the cross-linking of starch has a
drastic in¯uence on the volume of the centrifuged
starch particles. Due to the cross-links the aggre-
gates are packed tighter and the volume of the
gelatinized starch particles is reduced.
Comparing the particle volume of the cen-
trifuged cross-linked starch at the same degree of
substitution gives some information about the e-
ciency of the cross-linking with di€erent cross-
linking agents. However, it should be taken into
account that topochemical aspects (distribution
across the granule, amylose/amylopectin distribu-
tion) can also in¯uence the swelling capacities of
these aggregates. The particle volumes (swelling
properties) of the cross-linked starches synthesized
are shown in Fig. 4.
nitroalkene 3 (2-nitro-3-O-pivaloyl-1-propene-3-ol)
probably leads to less ecient cross-linking for 3a.
The viscosity pro®les of granular starch cross-
linked with the ꢁ,!-bis(ꢀ-nitroacetoxyalkane) 1,6-
di-O-acetyl-2,5-dinitro-1,6-hexanediol also fall in
the range mentioned above. For relatively highly
substituted distarch 2,5-dinitro-1,6-hexanediol (6a,
dsmax=0.0065) no increase in viscosity was
observed during the temperature programme.
Lower substituted distarch 2,5-dinitro-1,6-hex-
anediol (6b, dsmax=0.0011) gave a higher end
viscosity than granular starch after gelatinization
(Fig. 3).
Swelling properties of cross-linked starches.Ð
Although gelatinized starches are often referred to
as solutions, these systems in fact consist of parti-
As expected, within one series using the same
cross-linking agent, the swelling capacity of the
cross-linked starches is decreased at higher degrees
of substitution. The swelling capacities of starch
cross-linked with bifunctional precursors for
nitroalkenes (1, 2 and 4±6) are lower than starch
cross-linked with commercially used epi-
chlorohydrin. This means not only that the reac-
tion rate of cross-linking is considerably higher
than in the case of cross-linking with epi-
chlorohydrin, but probably also that the eciency
of the cross-linking with 1, 2 and 4±6 is higher. The
results obtained are fairly consistent with the RVA
curves as shown in Figs. 1 and 2. Low end viscos-
ities and swelling capacities were obtained for 1c,
Fig. 3. RVA curves of distarch 2,5-dinitro-1,6-hexanediol (6b,
dsmax=0.0011) and starch.

A. Heeres et al./Carbohydrate Research 310 (1998) 191±201
a, 4a and 6b, moderate end viscosity and swelling
capacity was obtained for 5a, and a high end vis-
cosity and swelling capacity was obtained for 3a. It
can therefore be concluded that a novel series of
easily synthesized cross-linkers for starch (and
other polysaccharides), based on Michael additions
to (di)nitroalkenes, has been developed.
197
2
these compounds are excellent materials for the
complexation of heavy metals ions [32±35]. In
principle, primary or secondary aminoalkyl cross-
linked starches (or other polysaccharides) are
interesting materials for the immobilization of
enzymes [36]. Such compounds can be prepared
readily in a two-step (or possibly a one-step) pro-
cedure: synthesis of 2-nitroalkyl distarch 2-nitro-
propanediol followed by reduction of the nitro
functionalities.
Chemical characterization of cross-linked star-
ches.ÐChemical analysis of cross-linked starches
is often complicated due to the low degrees of
substitution [23±26]. However, the ratio between
the real cross-linking degree and mono-
functionalization and topochemical aspects are of
importance for the physical behaviour of these
compounds. For the cross-linking of starch with
2-Nitroalkyl distarch 2-nitropropanediol (Scheme
7) is synthesized by nitroalkylation of distarch 2-
nitropropanediol with 2-nitropropyl acetate (8a). The
cross-linking and nitroalkylation of granular starch
can also be accomplished in a one pot synthesis. In
this way 2-nitropropyl distarch 2-nitropropanediol
(8b, 10) and 2-nitrobutyl distarch 2-nitropropanediol
(9, 11) were synthesized by addition of 1,3-di-O-
acetyl-2-nitro-1,3-propanendiol/2-nitroalkyl acetate
(8b, 9) or 1,3-di-O-acetyl-aci-2-nitro-1,3-propane-
diol/2-nitroalkyl acetate (10, 11).
epichlorohydrin
the
amount
of
mono-
functionalization (the monoether glycerol bond)
has been established by oxidation of the modi®ed
starch with NaIO and subsequent determination
4
of formaldehyde [19]. Gel permeation chromato-
grams of gelatinized distarch glycerol (low degrees
of cross-linking) are in agreement with cross-links
between amylose and amylopectin in the amor-
phous regions of the starch granule [27].
The eciency of the reaction of starch with 1,3-
di-O-acetyl-2-nitro-1,3-propanediol (1a) can be
determined from the incorporation of nitrogen and
was found to be 85%. The infrared absorbance of
�
1
the nitrofunctionality (1552 cm ) is in agreement
with values obtained for 2-nitroalkyl starch ethers.
We have also attempted to determine the amount
of monofunctionalization, side reactions, and the
distribution over the di€erent hydroxyl groups by
synthesizing 1,3-di-O-acetyl-aci-2-nitro-1,3-propa-
13
nediol-2- C. After reaction with starch, the
labeled distarch 2-nitropropanediol-2- C (4b,
dsmax=0.020) was gelatinized and the swollen
13
`
ꢁ
3
`granules'' were treated with an enzyme cocktail of
-amylase (EC 3.2.1.1), amyloglucosidase (EC
.2.1.3) and isoamylase (EC 3.2.1.68). Normally
this procedure yields a mixture of glucose and
substituted oligomers which can subsequently be
13
separated by GPC and analyzed with C NMR
spectroscopy. Unfortunately, the cross-linked
material was not suciently accessible to the
enzymes for hydrolysis to occur.
Synthesis of 2-nitroalkyl distarch 2-nitro-
propanediol ethers.ÐCross-linking of starch is
often used in combination with another chemical
modi®cation [28±31]. It has been demonstrated
that aminoalkyl cross-linked starches have poten-
tial for application as ion-exchange resins and
Scheme 7. Structure of 2-nitroalkyl distarch 2-nitropropane-
diol ethers.

198
A. Heeres et al./Carbohydrate Research 310 (1998) 191±201
The eciency of the nitroalkylation is moderate
for the 2-nitrobutyl ether) to high (for the 2-
DSC7 PC Series apparatus (heating rate 5.0 K/
min).Viscosity pro®les were recorded on a Rapid
Visco Analyser RVA-3d purchased from Newport
Scienti®c. Spectrophotometric measurements were
performed with a LKB Novaspec II from Bio-
chrom. The pH-stat, a Titration Controller 1200
equipped with a Titronic T110 burette, was pur-
(
nitropropyl ether). The nitroalkyl functionality
decreases the gelatinization temperature of the
cross-linked nitroalkyl starch ethers (native starch
ꢀ
T =59.3 C). Owing to the cross-links no viscos-
gel
ity is observed for the gelatinized cross-linked 2-
nitroalkyl starch derivatives (Table 1).
È
chased from Schott Gerate. Nitrogen analyses were
The reduction of these 2-nitroalkyl cross-linked
starch ethers to the corresponding 2-aminoalkyl
cross-linked starch derivatives is currently under
investigation.
performed at the Analytical Department of
AVEBE (Foxhol, The Netherlands). Molar sub-
stitution of the 2-nitroalkyl substituent was deter-
mined according to the formula ms=1.62N/{14-
0.01N(Mwtalkyl subst-1)} (N=nitrogen content
measured in %N and Mwtalkyl subst=molecular
weight of the nitroalkyl substituent).
3
. Experimental
Synthesis
propanediol (4) .ÐA drop of conc H SO was
of
1,3-di-O-acetyl-aci-2-nitro-1,3-
2
General methods.Ð1,3-Di-O-acetyl-2-nitro-1,3-
2
4
propanediol (1) [12], 1,3-di-O-pivaloyl-2-nitro-1,3-
propanediol (2) [12], 2-nitro-3-O-pivaloyl-1-pro-
pene-3-ol (3) [12], 1,6-di-O-acetyl-2,5-dinitro-1,6-
hexanediol (6) [15], aci-2-nitro-1,3-propanediol
added to a stirred solution of aci-2-nitro-1,3-pro-
panediol (2.63 g, 21.7 mmol) and Ac O (4.45 g,
2
43.6 mmol). After 3 h, CH Cl (20 mL) was added
2
2
and the mixture was poured into sat NaHCO3
(25 mL). After separation of the organic layer, the
NaHCO3 solution was washed with CH Cl2
13
[
13], aci-2-nitro-1,3-propanediol-2- C [13], 2-
nitropropyl acetate [37] and 2-nitrobutyl acetate
36] were prepared according to literature proce-
2
[
(20 mL) and the combined CH Cl layers were
2
2
dures. Formaldehyde (37% solution), acetic anhy-
dride, 1-nitropropane (95%), NaOH pellets, KF
and tetrabutylammonium bromide were purchased
from Merck. Nitromethane (96%), nitrometha-
dried over Na SO . After ®ltration and concentra-
2 4
tion, the residue was distilled under reduced pres-
ꢀ
sure (0.1 mm Hg, 200 C) and 4 was isolated
1
(2.42 g, 55%). NMR (CDCl ): H, ꢂ 4.54 (s, 4 H,
3
13
13
ne- C (99% labeled), nitroethane (96%), salicylic
acid, AgNO , sodium methoxide (30% solution),
CH O), 2.08 (s, 6 H, CH ); C, ꢂ 169.51 (C ˆ O),
2
3
88.01 (CNO ), 60.49 (CH O), 20.43 (CH ). FT-IR
2 2 3
2
epichlorohydrin, pivaloyl chloride, and di-iodobu-
tane were purchased from Aldrich. Blue dextran
was purchased from Pharmacia Biotech. Potato
starch was a gift from AVEBE (Foxhol, The
Netherlands). H and C NMR spectra were
recorded on a 300 MHz Varian VTR-300 spectro-
meter. FT-IR spectra were recorded on a Bio-Rad
FTS 135 spectrometer. Di€erential scanning
calorimetry was performed on a Perkin±Elmer
(KBr): 2968 (w), 2905 (w), 1825 (w), 1756 (s), 1559
(s), 1465 (m), 1438 (w), 1382 (s), 1369 (s), 1224 (s),
1126 (m), 1048 (s), 1016 (m), 959 (w), 900 (w), 840
�
1
(w), 737 (w), 666 (w) cm .
1
13
Synthesis of 1,3-di-O-pivaloyl-aci-2-nitro-1,3-
propanediol (5).ÐPivaloyl chloride (10.01 g,
83 mmol) was added to a solution of aci-2-nitro-
1,3-propanediol (3.25 g, 26.9 mmol) in CH Cl2
2
(15 mL). After boiling under re¯ux for 20 h and
concentration, the residue was dissolved in CH Cl2
2
Table 1
Synthesis of 2-nitropropyl and 2-nitrobutyl distarch 2-nitro-
propanediol
(15 mL) and washed with sat NaHCO (3Â10 mL)
3
and H O (2Â10 mL). The CH Cl layer was dried
2
2
2
ms (2nps)a RE(%)b
T
c
gel dsmax(crl)d RVAe
(
crude 5 (6.02 g) was isolated. Part of the residue
Na SO ) and, after ®ltration and concentration,
2 4
Compound
8
9
1
1
b
0.062
0.046
0.057
0.043
87
65
71
61
48.4
50.3
48.6
54.7
0.0034
0.0036
0.0033
0.0032
0
0
0
0
(
(0.02 mm Hg, 150 C) and 5 (2.59 g, 60%) was iso-
3.35 g) was distilled under reduced pressure
ꢀ
0
1
1
lated. NMR (CDCl ): H, ꢂ 4.50 (s, 4 H, CH O),
3
2
1.15 (s, 18 H, CH3); 13C, ꢂ 177.8 (C ˆ O), 88.4
a
b
c
See Experimental.
Reaction eciency (ms/msmax).
Gelatinization temperature (in C), determined with DSC
(CNO ), 60.38 (CH ), 38.90 (C-Piv), 26.64 (CH ).
2
2
3
ꢀ
(
onset).
d
2
Maximum degree of cross-linking.
In RVA units.
The synthesis of 1,3-di-O-acetyl-aci-2-nitro-1,3-propane-
13
e
diol-2- C is similar to the synthesis of 4.

A. Heeres et al./Carbohydrate Research 310 (1998) 191±201
199
FT-IR (KBr): 2976 (s), 2939 (s), 2912 (s), 2876 (s),
743 (s), 1556 (s), 1481 (s), 1466 (s), 1399 (m), 1369
Cross-linking of starch with 2-nitro-3-O-pivaloyl-
1-propene-3-ol (3a), dsmax=0.0016.ÐThe same
procedure was followed as for 1a with starch
1
(
(
(
(
m), 1352 (m), 1282 (s), 1135 (s), 1039 (m), 1014
w), 999 (w), 985 (w), 944 (w), 922 (w), 865 (m), 845
w), 813 (w), 798 (w), 784 (w), 767 (m), 665
w) cm .
Cross-linking of starch with 1,3-di-O-acetyl-2-
(100.04 g, 520 mmol), H O (100 mL) and 2-nitro-3-
2
O-pivaloyl-1-propene-3-ol (0.16 g, 0.86 mmol).
After stirring for 16 h distarch 2-nitropropanediol
(3a; 90.28 g, dry substance=91.11%) was isolated.
Cross-linking of starch with 1,3-di-O-acetyl-aci-
2-nitro-1,3-propanediol (4a), dsmax=0.0019.ÐThe
same procedure was followed as for 1a with starch
�
1
nitro-1,3-propanediol (1a), dsmax=0.096.ÐNative
starch (100.01 g, 520 mmol) was suspended in H O
2
(100 mL). The pH of the aqueous starch suspen-
sion was adjusted to 10.0 with 1 M NaOH. 1,3-
Di-O-acetyl-2-nitro-1,3-propanediol (1; 10.25 g,
(100.02 g, 520 mmol), H O (100 mL) and 1,3-di-O-
2
acetyl-aci-2-nitro-1,3-propanediol (0.20 g, 1.0 mmol).
After stirring for 16 h distarch 2-nitropropanediol
(4a; 89.60 g, dry substance=91.73%) was isolated.
Cross-linking of starch with 1,3-di-O-acetyl-aci-
5
0 mmol) was added dropwise and the pH was
controlled with a pH-stat by adding portions of
M NaOH. After 16 h the reaction was complete
no more acid formation) and the suspension was
1
(
13
2-nitro-1,3-propanediol-2- C (4b), dsmax=0.020.Ð
The same procedure was followed as for 1a
with starch (10.01 g, 52.0 mmol), H O (12 mL) and
neutralized with 0.5 M HCl. After ®ltration and
ꢀ
washing with water the product was dried at 40 C
2
1
3
and distarch 2-nitropropanediol (1a; 95.54 g, dry
substance=88.44%, %N=0.68%) was isolated.
FT-IR (KBr): 3453 (s), 2928 (m), 1658 (m), 1552
1,3-di-O-acetyl-aci-2-nitro-1,3-propanediol-2- C
(0.21 g, 1.02 mmol in 1 mL 2-propanol). After stir-
13
ring for 16 h distarch 2-nitropropanediol-2- C (4b;
9.13 g) was isolated.
(
(
m), 1164 (s), 988 (s), 857 (m), 763 (m), 573
�
1
m) cm .
Cross-linking of starch with 1,3-di-O-acetyl-2-
Cross-linking of starch with 1,3-di-O-pivaloyl-aci-
2-nitro-1,3-propanediol (5a), dsmax=0.0019.ÐThe
same procedure was followed as for 1a with starch
nitro-1,3-propanediol (1b), dsmax=0.019.ÐThe
same procedure was followed as for 1a with starch
(100.02 g, 520 mmol), H O (100 mL) and 1,3-di-O-
2
(
100.70 g, 520 mmol), H O (100 mL) and 1,3-di-O-
2
pivaloyl-aci-2-nitro-1,3-propane (0.29 g, 1.0 mmol).
After stirring for 48 h distarch 2-nitropropanediol
(5a; 90.16 g, dry substance=91.16%) was isolated.
Cross-linking of starch with 1,6-di-O-acetyl-2,5-
dinitro-1,6-hexanediol (6a), dsmax=0.0065.ÐThe
same procedure was followed as for 1a with starch
acetyl-2-nitro-1,3-propanediol (2.05 g, 10.0 mmol).
Isolated: 94.26 g distarch 2-nitropropanediol (1b;
dry substance=89.27%).
Cross-linking of starch with 1,3-di-O-acetyl-2-
nitro-1,3-propanediol (1c), dsmax=0.0019.ÐThe
same procedure was followed as for 1a with starch
(10.0 g, 52 mmol), H O (10 mL) and 1,6-di-O-ace-
2
(
250.02 g, 1.30 mol), H O (250 mL) and 1,3-di-O-
2
tyl-2,5-dinitro-1,6-hexanediol (0.10 g, 0.34 mmol).
After stirring for 20 h distarch 2,5-dinitrohex-
anediol (6a; 9.99 g, dry substance=83.78%, air
dried) was isolated.
acetyl-2-nitro-1,3-propanediol (0.51 g, 2.49 mmol).
Isolated: 222.20 g distarch 2-nitropropanediol (1c;
dry substance=91.65%).
Cross-linking of starch with 1,3-di-O-acetyl-2-
nitro-1,3-propanediol (1d), dsmax=0.00098.ÐThe
same procedure was followed as for 1a with starch
Cross-linking of starch with 1,6-di-O-acetyl-2,5-
dinitro-1,6-hexanediol (6b), dsmax=0.0011.ÐThe
same procedure was followed as for 1a with starch
(250.88 g, 1.30 mol), H O (250 mL) and 1,3-di-O-
2
(10.0 g, 52 mmol), H O (10 mL) and 1,6-di-O-ace-
2
acetyl-2-nitro-1,3-propanediol (0.26 g, 12.7 mmol).
Isolated: 229.74 g distarch 2-nitropropanediol (1d,
dry substance=91.45%).
Cross-linking of starch with 1,3-di-O-pivaloyl-2-
nitro-1,3-propanediol (2a), dsmax=0.0019.ÐThe
same procedure was followed as for 1a with
tyl-2,5-dinitro-1,6-hexanediol (0.016g, 0.055 mmol).
After stirring for 20 h distarch 2,5-dinitrohex-
anediol (6b; 9.98 g, dry substance=81.19%, air
dried) was isolated.
Cross-linking of starch with epichlorohydrin (7a),
dsmax=0.019.ÐNative starch (250.02 g, 1.30 mol)
was suspended in H O (250 mL). The pH of the
starch (100.33 g, 520 mmol), H O (100 mL) and
2
2
1
1
,3-di-O-pivaloyl-2-nitro-1,3-propanediol (0.29 g,
.00 mmol). After stirring for 48 h distarch 2-nitro-
aqueous starch suspension was adjusted to 11.0
ꢀ
with 1 M NaOH and heated to 35 C. Epi-
chlorohydrin (2.28 g, 25 mmol) was added and
after 48 h the suspension was neutralized with
propanediol (2a; 91.08 g, dry substance=90.94%)
was isolated.

2
00
A. Heeres et al./Carbohydrate Research 310 (1998) 191±201
which contained Na SO (2.52 g, 17.8 mmol). The
0
.5 M HCl. After ®ltration and washing with
2
4
ꢀ
water the product was dried at 40 C, and 235.35 g
distarch glycerol (7a; dry substance=86.09%) was
isolated.
Cross-linking of starch with epichlorohydrin (7b),
dsmax=0.0022.ÐThe same procedure was fol-
lowed as for 7a with starch (150.02 g, 0.78 mol),
pH of the aqueous starch suspension was adjusted
to 10.0 with 1 M NaOH. 1,3-Di-O-acetyl-2-nitro-
1,3-propanediol (0.19 g, 0.93 mmol) and 2-nitrobu-
tyl acetate (3.00 g, 18.6 mmol) were added dropwise
and the pH was controlled with a pH-stat by add-
ing portions of 1 M NaOH. After 2 h the reaction
was complete (no more acid formation) and the
suspension was neutralized with 0.5 M HCl. After
®ltration and washing with water, the product was
H O (150mL) and epichlorohydrin (0.16g,
2
1
(
.73mmol). After stirring for 48 h distarch glycerol
7b; 134.76 g, dry substance=90.84%) was isolated.
ꢀ
Synthesis of 2-nitropropyl distarch 2-nitro-
propanediol (8a).ÐCross-linked starch (1a; 25.00 g,
45 mmol) was suspended in H O (50 mL). The pH
dried at 40 C, and 45.39 g 2-nitrobutyl distarch
2-nitropropanediol (9; dry substance=92.61%,
%N=0.39%) was isolated. FT-IR (KBr): 3451 (s),
2930 (s), 1654 (m), 1546 (m), 1464 (m), 1163 (s),
986 (s), 928 (m), 859 (m), 764 (m), 709 (m), 573
1
2
of the aqueous cross-linked starch suspension was
adjusted to 10.0 with 1 M NaOH. 2-Nitropropyl
acetate (10.27 g, 69.9 mmol) was added dropwise
and the pH was controlled with a pH-stat by add-
ing portions of 1 M NaOH. After 16 h the reaction
was complete (no more acid formation) and the
suspension was neutralized with 0.5 M HCl. After
�
1
(m) cm .
Synthesis of 2-nitropropyl distarch 2-nitroprop-
anediol (with 1,3-di-O-acetyl-aci-2-nitro-1,3-prop-
anediol, one pot synthesis) (10).ÐNative starch
(100.01 g, 520 mmol) was suspended in H O (100 mL),
2
®ltration and washing with water, the product was
which contained Na SO (5.04 g, 35.6 mmol). The
2
4
dried to air, and 26.50 g 2-nitropropyl distarch 2-
nitropropanediol (8a; %N=2.65%, dry substance
not determined due to decomposition of the mate-
rial) was isolated. FT-IR (KBr): 3448 (s), 2930 (s),
pH of the aqueous starch suspension was adjusted
to 10.0 with 1 M NaOH. 1,3-Di-O-acetyl-aci-2-
nitro-1,3-propanediol (0.35 g, 1.70 mmol) and 2-
nitropropyl acetate (5.45 g, 37.1 mmol) were added
dropwise and the pH was controlled with a pH-stat
by adding portions of 1 M NaOH. After 3 h the
reaction was complete (no more acid formation)
and the suspension was neutralized with 0.5 M
HCl. After ®ltration and washing with water, the
1
1
655 (m), 1554 (s), 1459 (m), 1364 (m), 1164 (s),
083 (s), 988 (s), 933 (m), 850 (m), 763 (m), 709
�
1
(m), 573 (m), 523 (m) cm .
Synthesis of 2-nitropropyl distarch 2-nitro-
propanediol (with 1,3-di-O-acetyl-2-nitro-1,3-prop-
anediol, one pot synthesis) (8b).ÐNative starch
ꢀ
product was dried at 40 C, and 93.54 g 2-nitro-
(49.96 g, 260 mmol) was suspended in H O (50 mL),
which contained Na SO (2.53 g, 17.8 mmol). The
pH of the aqueous starch suspension was adjusted
to 10.0 with 1 M NaOH. 1,3-Di-O-acetyl-2-nitro-
propyl distarch 2-nitropropanediol (10; dry sub-
stance=91.49%, %N=0.48%) was isolated. FT-
IR (KBr): 3434 (s), 2930 (s), 1654 (m), 1548 (m),
1464 (m), 1164 (s), 986 (s), 859 (m), 764 (m), 709
2
2
4
�
1
1
,3-propanediol (0.18 g, 0.88 mmol) and 2-nitro-
(m) cm .
propyl acetate (2.72 g, 18.5 mmol) were added
dropwise and the pH was controlled with a pH-stat
by adding portions of 1 M NaOH. After 1 h the
reaction was complete (no more acid formation)
and the suspension was neutralized with 0.5 M
HCl. After ®ltration and washing with water, the
Synthesis of 2-nitrobutyl distarch 2-nitroprop-
anediol (with 1,3-di-O-acetyl-aci-2-nitro-1,3-prop-
anediol, one pot synthesis) (11).ÐNative starch
(75.03 g, 389 mmol) was suspended in H O (75 mL),
2
which contained Na SO (3.77 g, 26.6 mmol). The
2
4
pH of the aqueous starch suspension was adjusted
to 10.0 with 1 M NaOH. 1,3-Di-O-acetyl-aci-2-
nitro-1,3-propanediol (0.26 g, 1.26 mmol) and 2-
nitrobutyl acetate (4.42 g, 27.5 mmol) were added
dropwise and the pH was controlled with a pH-stat
by adding portions of 1 M NaOH. After 3 h the
reaction was complete (no more acid formation)
and the suspension was neutralized with 0.5 M
HCl. After ®ltration and washing with water, the
ꢀ
product was dried at 40 C and 45.19 g 2-nitro-
propyl distarch 2-nitropropanediol (8b; dry
substance=92.65%, %N=0.52%) was isolated.
FT-IR (KBr): 3456 (s), 2928 (s), 1658 (m), 1550
(
8
m), 1465 (m), 1164 (s), 1083 (m), 983 (s), 928 (m),
�
1
59 (m), 764 (m), 709 (m), 573 (m) cm .
Synthesis of 2-nitrobutyl distarch 2-nitro-
propanediol (with 1,3-di-O-acetyl-2-nitro-1,3-prop-
anediol, one pot synthesis) (9).ÐNative starch
ꢀ
product was dried at 40 C and 68.85 g 2-nitrobutyl
distarch 2-nitropropanediol (11; dry substance
(50.10 g, 260 mmol) was suspended in H O (50 mL),
2

A. Heeres et al./Carbohydrate Research 310 (1998) 191±201
201
=
91.08%, %N=0.36%) was isolated. FT-IR
Bleeker, and R.M. Kellogg, Synthesis and Proper-
ties of 2-Nitroalkyl Starch Ethers, in H.A. van
Doren and N. van Swaay (Eds.), Starch 96, The
Book, CRF, 1997, pp 179±183.
(
(
KBr): 3468 (s), 2929 (s), 1653 (m), 1545 (m), 1464
m), 1163 (s), 985 (s), 928 (m), 859 (m), 764 (m),
�
1
7
08 (m), 573 (m) cm .
Determination of the swelling capacity.ÐThe
[
[
[
12] P. Knochel and D. Seebach, Helv. Chim. Acta., 67
(
1984) 261±284.
swelling capacities of the cross-linked starches 1±7b
were determined by a slightly modi®ed procedure
of Evans [25]. 2.00 g Blue dextran (0.3%) was
added to a suspension of cross-linked starch (40±
13] L.W. Herman and J.W. ApSimon, Tetrahedron
Lett., 26 (1985) 1423±1224.
14] H. Feuer and G. Leston, Org. Synthesis, 34 (1954)
3
7±39.
[15] H. Feuer and R. Miller, J. Org. Chem., 26 (1961)
348±1357.
4
00 mg) in 8.00 mL H O. The closed tubes were
2
ꢀ
rotated for 45 min at 90±95 C in a ventilating fan.
After cooling down, the tubes were centrifuged
1
[16] H.J. Thiewes and P.A.M. Steeneken, Starch/
StaÈrke, 49 (1997) 85±92, 93±96.
[17] K.F. Gotlieb and P. Woldendorp, Starch/StaÈrke,
[
15 min, 3000 rpm (swing out rotor)]. The super-
natant liquid (1.5 mL) was ®ltered and the absor-
bance of the initial and the obtained supernatant
solutions were measured in a spectrophotometer at
1
9 (1967) 263±271.
[
[
18] T.J. Schoch, Starch/StaÈrke, 11 (1959) 156±162.
19] L. Kuniak and R.H. Marchessault, Starch/StaÈrke,
6
20 nm. The swelling capacity (SC) was determined
by the formula: SC=10*(A-A0/A)/w*ds mL/g
A=extinction cross-linked starch, A0=extinction
2
4 (1972) 110±116.
20] H.C. Srivaskava and M.M. Patel, Starch/StaÈrke,
5 (1973) 17±21.
21] I.D. Evans and D.R. Haisman, J. Text. Studies, 10
1979) 347±370.
22] T.J. Schoch, Methods Carbohydr. Chem. VIII,
1980) 106±108.
[
[
[
(
2
blue dextran (control), w=weight cross-linked
starch, ds=dry substance cross-linked starch).
(
(
References
[
[
23] B.M. Gough, Starch/StaÈrke, 19 (1967) 240±243.
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25] L. Holmberg, B. Lindberg, and B. Linqvist, Car-
bohydr. Res., 262 (1994) 213±221.
26] H. Koch, H.D. Bommer, and J. Koppers, Starch/
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[
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[
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[
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[
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[
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[
[
[
[
[
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[
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[
10] A. Heeres, H.A. van Doren, K.F. Gotlieb, I.P.
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[
[
35] I. Simkovic, Carbohydr. Polym., 32 (1997) 1±6.
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974, pp 5±26.
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È
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È
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[