Analysis of the positions of substitution of acetate and butyrate groups in cellulose acetate-butyrate by the reductive-cleavage method

Article abstract of DOI:10.1016/S0008-6215(98)00255-9

The degree of substitution (ds) and the distribution pattern of the two ester substituents in commercial samples of cellulose acetate-butyrate (CAB) were determined by sequential neutral methylation, direct reductive cleavage and in situ acetylation. When

Full text of DOI:10.1016/S0008-6215(98)00255-9

Carbohydrate Research 312 (1998) 225±231
Analysis of the positions of substitution of
acetate and butyrate groups in cellulose acetate±
butyrate by the reductive-cleavage method
Nanxiong Yu, Gary R. Gray *
The Department of Chemistry, University of Minnesota, Minneapolis, Minnesota 55455, USA
Received 17 July 1998; accepted 21 September 1998
Abstract
The degree of substitution (ds) and the distribution pattern of the two ester substituents in
commercial samples of cellulose acetate±butyrate (CAB) were determined by sequential neutral
methylation, direct reductive cleavage and in situ acetylation. When the reductive-cleavage reac-
tion was conducted with 35 equiv (per anhydroglucose unit) of Et SiH, 70 equiv of MeSO SiMe ,
3
3
3
.
and 14 equiv of BF OEt at room temperature for seven days, the O-acetyl groups were converted
3
2
to O-ethyl groups and the O-butyryl groups were converted to O-butyl groups concurrent with
reductive cleavage of the glycosidic linkages. Acetylation of the products gave 27 partially
methylated, ethylated, and butylated 4-O-acetyl-1,5-anhydro-d-glucitol derivatives that were
identi®ed by GLC±CIMS (NH ) and GLC±EIMS. Integration of the GLC pro®le and correction
3
for molar response gave the mole percent of each product. From these data, the fractional degree
of substitution for each ester at each position of the anhydroglucose unit was determined. The
combined fractional degree of substitution of both esters at each position and the overall ds were
also determined by sequential neutral methylation, acyl±ethyl exchange, and reductive cleavage,
and the values so obtained were in good agreement with those derived by sequential neutral
methylation and direct reductive cleavage. # 1998 Elsevier Science Ltd. All rights reserved
Keywords: Reductive-cleavage; Cellulose acetate±butyrate; Ester localization
1
. Introduction
Cellulose acetate±butyrate (CAB) has been
distribution pattern of the two ester substituent
groups on the (1!4)-ꢀ-d-glucopyranosyl residues
of the polysaccharide. The structural characteriza-
tion of cellulose acetate±butyrate samples is there-
fore of signi®cant importance, both for elucidating
structure±property relationships and for achieving
quality control in production processes. Due to the
presence of two di€erent ester substituents, there
are 27 possible monomeric anhydroglucose units
with varying substituents at the 2-, 3-, and 6-posi-
produced commercially for a wide variety of
applications, such as molding plastics, ®lm pro-
ducts, lacquer coatings, and melt coatings [1]. The
functional properties of these products depend
upon their degree of substitution (ds) as well as the
*
gray@chem.umn.edu
Corresponding author. Fax: +1-612-626-7541; e-mail:
1
tions. Although H NMR spectroscopy has been
0008-6215/98/$Ðsee front matter # 1998 Elsevier Science Ltd. All rights reserved
PII S0008-6215(98)00255-9

226
N. Yu, G.R. Gray/Carbohydrate Research 312 (1998) 225±231
employed to determine the ds of each ester sub-
Table 1
Products derived from cellulose acetate±butyrate by sequential
neutral methylation, direct reductive cleavage, and acetylation
13
stituent [2] and C NMR spectroscopy has been
used to determine the fractional degree of sub-
stitution of each ester substituent at each position
[
3], no method has yet been reported for establish-
ing the precise distribution pattern of the indivi-
dual ester substituents, namely, the mole fractions
of all 27 possible monomeric anhydroglucose
units.
In a previous study [4] it was shown that the
positions of substitution of O-acetyl groups in cel-
lulose acetates could be established by sequential
methylation under neutral conditions and direct
reductive cleavage under conditions that reduced
the O-acetyl groups to O-ethyl groups concurrent
with reductive cleavage of glycosidic linkages.
These results suggested that it might be possible to
establish the distribution pattern of O-acetyl and
O-butyryl groups in CAB by the same procedure.
The 27 possible products so obtained (Table 1)
should contain a single O-acetyl group (at the
Compound
number
R2 R3 R6
Parameter
S0
Molecular
weight
1
2
3
4
5
6
7
8
Me Me Me
Me Et Me
Me Me Et
Et Me Me
Me Et Et
Et Et Me
Et Me Et
Et Et Et
Me Bu Me
Me Me Bu
Bu Me Me
Me Bu Et
Me Et Bu
Et Bu Me
Bu Et Me
Bu Me Et
Et Me Bu
Et Bu Et
Et Et Bu
Bu Et Et
Me Bu Bu
Bu Bu Me
Bu Me Bu
Et Bu Bu
Bu Bu Et
Bu Et Bu
Bu Bu Bu
248
262
262
262
276
276
276
290
290
290
290
304
304
304
304
304
304
318
318
318
332
332
332
346
346
346
374
S
S
3E
6E
S2E
S
36E
S
23E
S26E
S236E
S
3B
S6B
9
10
1
1
1
1
2
3
S2B
S
3B6E
4
-position) and varying numbers of O-methyl, O-
S
6B3E
S3B2E
ethyl, and O-butyl groups. Separation and char-
acterization of these products would reveal the
fractional degree of substitution of each ester
group at the 2-, 3-, and 6-positions of the 4-linked
d-glucopyranosyl residues of the polysaccharide.
As a test of this procedure, two commercial
samples of CAB were subjected to sequential neu-
tral methylation and direct reductive cleavage, and
the products were acetylated, separated by GLC,
and characterized by mass spectrometry. In order
to validate the method, the same CAB samples
were subjected to sequential neutral methylation,
acyl±ethyl exchange, and reductive cleavage and
the eight products so obtained were separated by
GLC and characterized as previously described [4].
The latter experiment was not capable of estab-
lishing the fractional degree of substitution of each
ester at each position but could, for purposes of
comparison, establish the combined fractional
degrees of substitution of both esters at each posi-
tion as well as the overall ds.
14
1
1
1
1
5
6
7
8
S2B3E
S
S
2B6E
6B2E
S3B26E
19
S
S
6B23E
2B36E
2
2
2
0
1
2
S
36B
S23B
S26B
23
2
2
2
4
5
6
S
S
36B2E
23B6E
S26B3E
S236B
27
low acetate:butyrate ratio (0.94:1.71) and the other
(sample B; Eastman CAB 171-15S) having a high
acetate:butyrate ratio (2.08:0.78). The samples
were methylated by the method of Prehm [5], as
described by Mischnick [6], and a portion of each
was subjected to reductive cleavage at room tem-
perature for seven days in the presence of 35 equiv
(per anhydroglucose unit) of Et SiH, 70 equiv of
3
.
MeSO SiMe , and 14 equiv of BF OEt . After
3
3
3
2
quenching with anhydrous methanol, the products
were acetylated in situ by treatment with acetic
anhydride and 1-methylimidazole then analyzed by
2
. Results
Analysis of cellulose acetate±butyrate by
GLC and GLC combined with CIMS (NH ) and
3
methylation and direct reductive cleavage.ÐTwo
di€erent samples of cellulose acetate±butyrate
having similar ds values were chosen for analysis,
one (sample A; Eastman CAB 381-20) having a
EIMS. Shown in Figs. 1 and 2 are the gas±liquid
chromatograms obtained when the products
derived from samples A and B, respectively, were
chromatographed on a Restek RT -200 column.
x

N. Yu, G.R. Gray/Carbohydrate Research 312 (1998) 225±231
227
Fig. 1. Gas±liquid chromatogram of the anhydroalditol acetates derived from cellulose acetate±butyrate (Sample A) by sequential
per-O-methylation, reductive cleavage and acetylation. Chromatography was conducted on a Restek RT -200 column. The peaks
x
are numbered with the compound numbers.
Fig. 2. Gas±liquid chromatogram of the anhydroalditol acetates derived from cellulose acetate±butyrate (Sample B) by sequential
per-O-methylation, reductive cleavage and acetylation. Chromatography was conducted on a Restek RT -200 column. The peaks
are numbered with the compound numbers.
x

228
N. Yu, G.R. Gray/Carbohydrate Research 312 (1998) 225±231
The individual peaks were identi®ed based on their
molecular weights, as obtained by CIMS (NH3),
and their electron-ionization (EI) mass spectra (see
discussion below). Integration of all peaks and
correction for molar response by the e€ective
carbon response method [7,8] gave the mole per-
cent of each component in each of the samples
incomplete reduction of esters to ethers during the
reductive cleavage reaction, or from the sugar resi-
dues of non-cellulosic polysaccharides present in
the starting materials for CAB preparation. Based
on the excellent quantitative results obtained (see
Discussion), their presence in such small amounts
apparently does not a€ect the quantitative accu-
racy of the method.
(Table 2). Compounds 16 and 18 coeluted as did
compounds 23 and 26, but since the two compo-
nents in each of the coeluting peaks possessed a
di€erent molecular weight, their relative propor-
tions could be determined from the relative inten-
sities of the (M+1) peaks in the ammonia CI mass
spectra of the mixtures.
Analysis of cellulose acetate±butyrate by methyl-
ation, acyl±ethyl exchange, and reductive clea-
vage.ÐAnother portion of each fully methylated
cellulose acetate±butyrate sample was subjected to
acyl±ethyl exchange as previously described [4],
and the products were then subjected to reductive
cleavage at room temperature for 24 h in the pre-
It should also be noted that the gas±liquid chro-
matograms for the two CAB samples (Figs. 1 and
sence of 5 equiv (per equiv of acetal) of Et SiH, 5
3
.
equiv of MeSO SiMe and 1 equiv of BF OEt .
3 3 3 2
2
) contained small amounts of products that could
not be identi®ed as 4-O-acetyl-1,5-anhydro-d-glu-
citol derivatives. Although the origin of these pro-
ducts is not known, it is possible that they arise
from incomplete methylation of the CAB samples,
Analysis of the products as their acetates on an
RT -200 column revealed only eight peaks, corre-
x
sponding to the same eight products (1±8) as
derived from partially methylated cellulose acetate
by sequential neutral methylation, acetyl±ethyl
exchange, reductive cleavage and acetylation [4].
Integration of all peaks and correction for molar
response [7,8] gave the mole percent of each pro-
duct (1±8) in each sample of cellulose acetate±
butyrate analyzed (Table 3). Using these values,
the fractional degree of substitution (x , x and x )
Table 2
Mol% of products derived by reductive cleavage of O-acetyl-
O-butyryl-O-methyl cellulose
Mol%
Compound Parameter ECR Sample A b Sample B b
a
number
value
2
3
6
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
S0
S3E
0.545
0.645
0.645
0.645
0.745
0.745
0.745
0.845
0.845
0.845
0.845
0.945
0.945
0.945
0.945
0.945
0.945
1.045
1.045
1.045
1.145
1.145
1.145
1.245
1.245
1.245
1.445
0.71
0.70
0.56
0.61
0.61
2.88
0.58
3.55
1.00
1.03
1.23
0.82
1.73
3.66
2.82
0.11
1.48
5.29
7.37
6.48
1.84
8.15
2.34
9.73
10.30
8.64
15.78
±
at each of the three positions on the d-glucopyr-
anosyl residues of cellulose and the average ds
0.37
0.15
0.30
1.18
10.38
1.63
28.53
±
S
S
6E
(
ds=x +x +x ) were calculated.
2 3 6
2E
S36E
S
S
23E
26E
Table 3
Mol% of products derived from cellulose acetate±butyrate by
sequential neutral methylation, acyl±ethyl exchange, and
acetylation and the fractional degrees of substitution of esters
at the 2-, 3-, and 6-positions
S
236E
S3B
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
S
S
6B
±
±
2B
Mol%
S
3B6E
S6B3E
0.26
0.41
1.05
3.23
0.18
0.71
8.96
13.44
12.81
0.16
1.21
1.57
3.94
4.13
3.91
1.48
Parameter a
Sample A b
Sample B b
Compound
number
S
S
3B2E
2B3E
S2B6E
S6B2E
1
2
3
4
5
6
7
8
S0
S3E
S6E
S2E
S36E
S23E
S26E
S236E
x2
0.38
1.21
1.75
1.14
4.98
14.54
5.69
70.31
0.92
0.91
0.82
2.65
±
0.51
0.50
0.47
3.52
9.97
3.71
81.32
0.96
0.95
0.89
2.80
S
3B26E
S
6B23E
S2B36E
S
S
S
36B
23B
26B
S36B2E
S
S
23B6E
x3
x6
ds
26B3E
S236B
a
a
Peak areas were divided by the indicated values in order to
correct for molar response.
A, Eastman CAB 381-20; B, Eastman CAB 171-15S.
x2=S2E+S23E+S26E+S236E; x =S3E+S23E+S36E+S236E
3
;
x =S6E+S26E+S36E+S236E; ds=x +x +x .
6
2
3
6
b
b
See footnote b, Table 2.

N. Yu, G.R. Gray/Carbohydrate Research 312 (1998) 225±231
Identi®cation of the partially methylated, ethyl- 3. Discussion
229
ated, and butylated 1,5-anhydro-d-glucitol acetates
by mass spectrometry.ÐInspection of the EI mass
spectra of compounds 1±27 revealed a fragmenta-
tion pathway (Scheme 1) identical to the one pre-
viously found for the related methyl/ethyl [9] and
methyl/methoxycarbonylmethyl [10] positional iso-
mers. The pathway begins by cleavage between C-5
Using the mole percents of products derived by
reductive cleavage of O-acetyl-O-butyryl-O-methyl
cellulose (Table 2), the fractional degree of sub-
stitution of each ester at each position of the
anhydroglucose unit in the two CAB samples was
calculated (Table 5, method 2). From these values
the fractional degree of substitution of both esters
at each position (x +x , x +x and x +x ,
and C-6 to give an A ion at (M� 45), (M� 59) and
1
(
M� 87) for the 6-O-methyl, -ethyl and -butyl deri-
2E
2B 3E
3B
6E
6B
vatives, respectively. Further elimination of acetic
acid from the A ion gives an ion (A ) at (M� 105),
where E and B represent ethyl and butyl groups
derived by reduction of acetyl and butyryl groups,
respectively), the degree of substitution of each
ester [ds (E) and ds (B)], and the overall degree of
substitution of both esters [ds (E + B)] were also
calculated (Table 5). As is evident by inspection of
the data in Table 5, the values for the fractional
degree of substitution of both esters at each posi-
tion obtained by direct reductive cleavage of fully
methylated CAB (method 2) are in excellent agree-
ment with the values obtained by sequential
methylation, acyl±ethyl exchange and reductive
cleavage (method 1). Furthermore, the values
obtained for the ds of each ester group by direct
reductive cleavage of fully methylated CAB
(method 2) were also in good agreement with those
given by the supplier. The overall ds values
obtained by sequential methylation, acyl±ethyl
exchange and reductive cleavage (method 1) and by
sequential methylation and direct reductive clea-
vage (method 2) were also in good agreement
and, moreover, these values were also in good
agreement with those given by the supplier. This is
the only procedure yet developed for establishing
the mole fractions of all 27 possible acetylated/
butyrated anhydroglucose residues in CAB samples.
1
2
(
M� 119) and (M� 147) for the 6-O-methyl, -ethyl
and -butyl derivatives, respectively. The A ion, in
3
contrast, is formed by elimination of methanol,
ethanol or butanol from the A1 ion, and its
molecular weight establishes the identity of the
substituent at O-3. For example, 6-O-methyl deri-
vatives give A3 ions at (M� 77), (M� 91) and
(
M� 119) for 3-O-methyl, -ethyl and -butyl deriva-
tives, respectively, whereas, 6-O-ethyl derivatives
give A ions at (M� 91), (M� 105) and (M� 133) for
3
3
-O-methyl, -ethyl and -butyl derivatives, respec-
tively. In contrast, 6-O-butyl derivatives give A3
ions at (M� 119), (M� 133) and (M� 161) for 3-O-
methyl, -ethyl and -butyl derivatives, respectively.
For the bene®t of those who might use this
method, the molecular weights of these ions and
their intensities relative to the base peak (m/z 43)
are given in Table 4 for all positional isomers.
4. Experimental
Materials.ÐCellulose acetate±butyrate samples
were provided by Eastman Chemical Company,
Kingsport, TN. Triethylsilane (Et SiH), tri-
3
methylsilyl methanesulfonate (MeSO SiMe ),
3
3
.
boron tri¯uoride etherate (BF OEt ), methyl
3
2
tri¯uoromethanesulfonate (CF SO Me) and 2,6
3
3
di-tert-butylpyridine were purchased from Aldrich
Chemical Company and were used without further
Ê
puri®cation. Acetic anhydride was dried over 4 A
molecular sieves and distilled. 1-Methylimidazole
Ê
was distilled from NaOH and stored over 4 A
molecular sieves. Trimethyl phosphate was distilled
Scheme 1.

230
N. Yu, G.R. Gray/Carbohydrate Research 312 (1998) 225±231
Table 4
Characteristic fragment ions observed in the electron ionization mass spectra of compounds 1±27
Fragment ions (m/z/% of Base peak a)
Compound
Number
Parameter
Molecular weight
A1
A2
A3
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
S
S3E
S6E
0
248
262
262
262
276
276
276
290
290
290
290
304
304
304
304
304
304
318
318
318
332
332
332
346
346
346
374
203.1/13.15
217.1/8.87
203.1/19.20
217.1/8.16
217.1/13.27
231.1/6.54
217.1/6.84
217.1/2.41
245.1/7.24
203.1/19.13
245.1/7.83
245.1/4.23
217.1/16.15
259.0/6.96
259.1/6.40
245.1/3.24
217.1/7.12
259.1/8.97
231.1/11.84
259.1/9.50
245.1/14.20
287.1/6.43
245.1/5.02
259.1/14.30
287.1/8.82
259.1/9.40
287.1/8.00
143.1/25.44
157.1/31.01
143.0/35.02
157.1/20.04
157.1/26.48
171.1/25.29
157.1/8.95
171.1/22.66
185.1/36.77
143.0/15.86
185.1/21.10
185.1/11.67
157.1/24.55
199.1/34.28
199.1/31.78
185.0/25.13
157.1/15.46
199.1/27.69
171.1/30.71
199.1/27.72
185.1/31.75
227.1/35.74
185.1/2.86
171.0/25.27
171.0/19.57
171.0/35.42
185.0/12.09
171.0/28.77
185.0/12.91
185.0/13.66
185.0/18.33
171.0/27.92
171.0/52.81
213.1/8.90
171.0/16.08
171.0/49.50
185.1/15.70
213.1/10.23
213.1/2.24
185.0/12.39
185.0/25.13
185.1/26.49
213.1/14.87
171.0/58.76
213.1/23.83
213.1/17.85
185.1/33.55
213.1/20.15
213.1/17.85
213.1/19.29
S
2E
S
36E
S23E
S
26E
236E
3B
S
S
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
S6B
S
2B
S
S
3B6E
6B3E
S3B2E
S
S
2B3E
2B6E
S6B2E
S3B26E
S
S
6B23E
2B36E
S36B
S
S
23B
26B
S
36B2E
S23B6E
199.1/33.68
227.1/32.49
199.1/24.73
227.1/26.12
S
S
26B3E
236B
a
+
The base peak was at m/z 43 (CH CO ) in all spectra.
3
Table 5
Fractional degree of substitution at the 2-, 3-, and 6-positions and the average degree of substitution in cellulose acetate±butyrate
samples A and B a
Method 1 b
Sample
Method 2 b
Sample
Parameterc
Reported d
A
B
A
B
A
B
x
x
x
2E
2B
3E
0.35
0.56
0.35
0.57
0.28
0.50
0.91
0.92
0.78
0.98
1.63
2.61
0.69
0.28
0.74
0.21
0.58
0.26
0.97
0.95
0.84
2.01
0.75
2.76
x3B
x
x
x
6E
6B
2E+x2B
0.92
0.91
0.82
0.96
0.95
0.89
x3E+x3B
x
ds (E)
ds (B)
ds (E+B)
6E+x6B
0.94
1.71
2.65
2.08
0.78
2.86
2.65
2.80
a
See footnote b, Table 2.
Method 1: sequential methylation, acyl-ethyl exchange, reductive cleavage, and acetylation; Method 2: sequential methylation,
b
direct reductive cleavage, and acetylation.
c
x2E=S2E+S23E+S26E+S236E+S3B2E+S6B2E+S3B26E+S6B23E+S36B2E; x2B=S2B+S2B3E+S2B6E+S2B36E+S23B+S26B+S23B6E
+
+
+
S
S23B+S36B2E+S23B6E+S236B; x6E=S6E+S36E+S26E+S236E+S3B6E+S2B6E+S3B26E+S2B36E+S23B6E; x6B=S6B+S6B3E+S6B2E
26B3E+S236B; x3E=S3E+S36E+S23E+S236E+S6B3E+S2B3E+S6B23E+S2B36E+S26B3E; x3B=S3B+S3B6E+S3B2E+S3B26E+S36B
S
6B23E+S36B+S26B+S36B2E+S26B3E+S236B. ds (E)=x2E+x3E+x6E. ds (B)=x2B+x3B+x6B. ds (E+B)=x2E+
x
d
2B+x3E+x3B+x6E+x6B.
Values given by the supplier.

N. Yu, G.R. Gray/Carbohydrate Research 312 (1998) 225±231
231
Ê
from Na CO under vacuum and stored over 4 A
molecular sieves. Dimethyl sulfoxide (Me SO) was
2
distilled from barium oxide under vacuum and
Reductive cleavage and in situ acetylation.Ð
Fully methylated cellulose acetate±butyrate (ꢁ2
mg) was dissolved in CH Cl (250 ꢁL) in a 3-mL
2
3
2
2
Ê
stored over 4 A molecular sieves. Reagent grade
methanol was re¯uxed over magnesium methoxide,
Ê
distilled, and stored at room temperature over 4 A
molecular sieves under nitrogen. BioRad AG501-
x8(D) was used as a mixed-bed resin.
Instrumentation.ÐAnalytical GLC was per-
formed on a Hewlett±Packard model 5890A gas±
liquid chromatograph equipped with an on-column
screw-capped, conical vial, Et SiH (37 ꢁL),
.
MeSO SiMe (72 ꢁL) and BF OEt (12 ꢁL) were
3 3 3 2
3
sequentially added, the vial was capped with a
mininert valve, and the solution was stirred at
room temperature for seven days. The reaction was
quenched by the addition of methanol (30 L), and
the solution was stirred for 30 min. After cooling in
an ice bath, acetic anhydride (250 ꢁL) and 1-
methylimidazole (100 ꢁL) were added, and the
reaction mixture was stirred at room temperature
for 2 h. The reaction mixture was then extracted
injector connected to a Restek RT -200 capillary
x
column (0.25 mmÂ30 m, 0.25-ꢁm ®lm thickness), a
¯ame-ionization detector, and an HP model 3365
Series II ChemStation. The injector and detector
sequentially with saturated aqueous NaHCO , 2 N
3
ꢀ
temperatures were set at 250 and 275 C, respec-
tively, and the temperature of the column was
H SO and H O. The organic layer was dried over
2
4
2
anhydrous sodium sulfate then evaporated to dry-
ness under a stream of nitrogen. The residue was
dissolved in CH Cl and examined by GLC.
ꢀ
ꢀ
programmed from 80 to 300 C at 2 C/min with
no initial hold time. GLC±MS analyses were per-
formed using a Finnegan MAT 95 high resolution
double-focusing, reverse-geometry mass spectro-
meter equipped with a Hewlett±Packard 5890A
Series II gas±liquid chromatograph and a DEC
model 2100 workstation. Chemical ionization mass
2
2
Acknowledgements
This investigation was supported by a grant
from the Eastman Chemical Company. We thank
Dr. Edmund Larka for performing the GLC-MS
analyses.
spectra were acquired with NH as the reagent gas
3
ꢀ
at a source temperature of 180 C. Electron ioni-
zation mass spectra were obtained at an ionization
energy of 70 eV and at a source temperature of
ꢀ
2
00 C.
Methylation of cellulose acetate±butyrates.Ð
References
Methylation was performed by the method of
Prehm [5] using modi®cations of the procedure as
described by Mischnick [6]. The sample of cellulose
acetate±butyrate (ꢁ35 mg) was dissolved in tri-
methyl phosphate (3.5 mL) in a 10-mL screw-capped
vial with a Te¯on-faced septum, 2,6-di-tert-butyl-
pyridine (250 ꢁL) and CF SO Me (200 ꢁL) were
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1] R.T Bogan and R.J. Brewer, Encyclopedia of Poly-
mer Science and Technology, 2nd ed., Vol.3, Wiley,
New York, 1989, pp 158±181.
[2] S. Gedon, personal communication.
[3] Y. Tezuka, Carbohydr. Res., 241 (1993) 285±290.
[4] C.K. Lee and G.R. Gray, Carbohydr. Res., 269
(
[5] P. Prehm, Carbohydr. Res., 78 (1980) 372±374.
1995) 167±174.
3
3
ꢀ
then added, and the vial was kept at 45±50 C in a
small ultrasonic bath for 2 days. The reaction
solution typically turned brown. After cooling to
room temperature, the methylated product was
precipitated by the addition of two volumes of
water and the precipitate was collected by ®ltration
through a small fritted disc. The precipitate was
washed thoroughly with water then dissolved in
chloroform and the chloroform extract was dried
over anhydrous Na SO and evaporated to dryness.
[
[
[
[
6] P. Mischnick, J. Carbohydr. Chem., 10 (1991) 711±
22.
7
7] D.P. Sweet, R.H. Shapiro, and P. Albersheim,
Carbohydr. Res., 40 (1975) 217±225.
8] J.U. Bowie, P.V. Trescony, and G.R. Gray, Car-
bohydr. Res., 125 (1984) 301±307.
9] S.G. Zeller, A.J. D'Ambra, M.J. Rice, and
G.R. Gray, Carbohydr. Res., 182 (1988) 53±62.
[10] S.G. Zeller, G.W. Griesgraber, and G.R. Gray,
Carbohydr. Res., 211 (1991) 47±57.
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