Disaccharides such as sucrose, lactose and isomaltulose belong to the least expensive yet multi-ton-scale accessible low molecular weight carbohydrates [3].
Novel Polyamides from Disaccharide-Derived Dicarboxylic Acids [1] Eckehard Cuny, Stefan Mondel, and Frieder W. Lichtenthaler Institute of Organic Chemistry, Darmstadt University of Technology, D-64287 Darmstadt, Germany
Introduction As carbohydrates represent 75% of the annually renewable biomass, they are - aside from their traditional uses for food, lumber, paper, and heat - the major bio-feedstocks from which to develop industrially and economically viable organic chemicals and materials that can replace those derived from petrochemical resources [2,3].
Carbohydrates Renewable Biomass: (~180 bill. tons/year)
20%
75%
Lignin 5% Fats, Proteins, Terpenoids, Alkaloids, Nucleic Acids
Polyamides being million-ton scale industrial products, the generation of their components - diacids and diamines - from renewables, i. e. from carbohydrates has been addressed repeatedly by substituting glucaric acid, galactaric acid [4], and fructose-derived furan-2,5dicarboxylic acid [5] for petroleum-based adipic and terephthalic acid as one of the monomer components: O
OH
OH OH
HO OH
OH
D-Glucaric acid (from D-Glucose)
O
O
OH
HO O
OH
O
OH OH
HO OH
OH
D-Galactaric
acid (from Lactose) HO
O
O HO
OH O O
Adipic acid
OH O
Terephthalic acid
Furan-2,5-dicarboxylic acid (from Fructose)
O
Disaccharides such as sucrose, lactose and isomaltulose belong to the least expensive yet multi-ton-scale accessible low molecular weight carbohydrates [3]. Thus, dicarboxylic acids derived therefrom are surmised to have even higher industrial potential as monomer building blocks since the resulting polyamides are apt to combine biocompatibility with biodegradabilitydue to the presence of a readily cleavable disaccharide linkage. These polymers are also deemed to be highly hydrophilic, hence water-soluble - a feature of relevance for medical applications.
Disaccharide Dicarboxylic Acids Thus, large-scale adaptable preparative protocols were developed for the generation of the diacids 1 - 4 from the respective disaccharides (in brackets):
HO HO
COOH
COOH O
HO
COOH O HO
3
OH
4
HO
HO 1 (sucrose)
COOH
O
HO O
HO HO
HO
O
OH
O
OH
HO
OH
HO
COOH
2 (lactose)
HO
COOH O
HO HO
OH
HO
O O
O
O
O
3 (isomaltulose)
COOH
4 (isomaltulose)
Sucrose-6,6’-dicarboxylic acid (1) Because of the persistence of an intersaccharidic water-bridge of the 2g-HO...H2O...HO-1f type in aqueous solution [6], oxidation of sucrose with air in the presence of 0.5% Pt/C at 35°C gives an approximate 1:1 mixture of the 6g- and 6f-saccharonic acids which particularly when using large amounts of the Pt catalyst and higher temperature (0-100°C), are further oxidized to the sucrose-6g,6f-dicarboxylic acid 1, isolable in up to 70% yield by continuous electrodialytic removal. 6g
6f OH
OH
O
Pt / O2
OH
H O
HO HO
water (NaHCO3)
HO O H HO
6g OH
COO
O
HO HO
6f OH
6g
OH
O
OH
O
+
HO
OH
6f
COO
COO O O
OH
HO O 1f
OH COO
6f
6g
COO
COO
Pt / O2
O
HO Pt / O2
6g
O
OH
HO O
HO O
Sucrose
HO HO
HO HO
6fCOO
HO HO
O O
OH
HO O 1
HO
OH
OH
4-O-(b-D-Galactosyl)-D-glucaric acid 6,3-lactone (2) Of the two primary OH groups in lactobionic acid, the first Pt/air oxidation product of lactose, the CH2OH of the gluconic acid part is oxidized further with high preference (access of the catalyst to the galactosyl-6-OH is obviously sterically hindered by the axial 4OH). Hence: HO
Lactose
OH
HO
COO
HO
O
Pt/air
bGalO
water, pH7 75°C
HO
OH
O
81%
HO
OH
HO
COO
O HO O
2
Lactobionic acid
5-O-(a-D-Glucuronyl)-D-arabinonic acid (3) and 5-(a-D-glucuronyloxymethyl)-furoic acid (4) The industrial production of isomaltulose from sucrose has made it a lucrative target for generating disaccharide intermediates of industrial potential. For example, air oxidation in strongly alkaline solution smoothly provides the glucosyl-a(1-5)-D-arabinonic acid in the form of its lactone (87%, [7]), subsequent Pt/air oxidation the diacid 3 (85%).
HO HO
OH O HO
O
6
DMSO, H 120°C O HO
Isomaltulose 80% [7]
HO HO
OH 2
OH
O
HO HO
HO O
70% [8]
O
O H
a-GMF
OH 1. KOH / O2 + 2. H 3. Pt / O 2
79% [9]
C OOH O HO
+
OH O
HO HO
Pt / O2
COOH O HO O
O HO
O
O 4
3 OH
COOH
Esters and Amides of Disaccharide Acids Diesters: Conversion of the Na salts of 1 - 4 into their respective methyl esters is smoothly and efficiently effected by stirring a suspension in dry MeOH in the presence of MeOHwashed Amberlite IR-120 (H+ form) and molecular sieve at ambient temperature for 2h; Yields: 85-90%. In similar fashion, higher alcohols (octanol, dodecanol) gave the respective diesters albeit requiring longer reaction times. Diamides: Simple aminolysis of the dimethyl esters of 1 and 4, or of the mono-methyl ester of lactone 2 (DMF, 60°C), with octyl- and dodecylamine gave the respective diamides in quant. yield, e. g. COO
COO
MeOH/Amberlite IR-120
O
HO HO
O
OH
HO HO
+
(H -form)
HO O
OH
O HO O
>85% HO
COOMe
COOMe O
OH
HO
OH
1 ROH (ion exch.)
80%
RNH2/DMF 60°C
quant.
n n
O
O
n n
O
HN HO HO
O HO HO
O O
O
O
OH
HO O
O O
NH OH
HO O
OH HO n = 4, 6
OH HO n = 4, 6
Surface-tensidometric evaluations showed all esters and amides to have s values at cmc point in the 25-40 nM/m range as compared to s = 30.4 of commercial APG (Alkyl Polyglycoside). The top value was observed for the isomaltulose-derived di-n-octylamide. H N
O
s = 25.2 at cmc
O
HO HO HO
H N
O O O
Polyhydroxypolyamides Three diamines were used for condensation polymerization with dimethyl ester 1 and 4 as well as monomethyl esters of lactones 2 and 3, namely petroleum-derived 1,6-diaminohexane, phenylenediamine, and the ‘green’, HMF-derived 2,5-bis(aminomethyl)furan. H2N
H2N
NH2
H2N
NH2
NH2
O
Condensation Polymerizations were effected apting conditions used by Kiely [3] previously (aminolysis in MeOH, or DMSO/glycol, or both consecutively), as exemplified by sucrose-
POLYAMIDES: 3 STEPS AWAY FROM SUCROSE SUCROSE 1. Pt/O2 + 2. MeOH/H
HO HO
COOMe
COOMe O O
6
OH
H2N(CH2)6NH2
HO
HO HO
O
O O
O
6'
OH
O
OH
HO
H2N
H N
O
6
HO HO
OH
OH
n
NH2
H N
O
O
6'
H N O
O O
N H
OH
HO O
HO O HO
N H
HO O
H2NC6H4NH2
6
6'
O
HO HO
HO O 5
O
O
H N
HO
OH
OH n
n
The novel disaccharide/diamine hybrid copolymers were characterized by their elemental composition (C, H, N), melting points, glass transition temperature (Tg), average molecular 1 weights (Mn) derived from H NMR end-group analysis, and their solubility in water. Results are listed in the table.
Polyhydroxypolyamides prepared from methyl esters of disaccharide dicarboxylic acids and diamines Disaccharide Educt
Polyamide
O
6
Sucrose
O
H N
6'
O
HO HO
N H
OH
O
M na
Repeating Units
mp
Water Solubility
10 400
23
180
+
8 500
19
205
-
11 600
26
190
-
6 800
15
152
+
10 000
25
145
-
8 800
21
172
-
HO O OH
HO
Sucrose
O
O
6
n
H N
6'
O
HO HO
H N
OH
O HO O HO
O
6
Sucrose
O
OH n
H N
6'
O
O
HO HO
N H
OH
O HO O HO
OH
OH
O
n
O
Lactose O
OH
OH
H N
N H
b-Gal
n
O
Isomaltulose
O
HO HO
H N
HO O
N H
O O
n
O O
HO HO
Isomaltulose
HO
H N
O O
O O
a
Derived from 1H NMR end-group analysis.
H N O
n
Literatur [1] Part 40 of the series ‘Sugar-Derived Building Blocks’. For Part 39: E. Cuny, F. W. Lichtenthaler, Tetrahedron: Asymmetry 2006, 17, 1120-1124. [2] F. W. Lichtenthaler, ‘The Key Sugars of Biomass: Non-Food Uses and Futures Development Lines’, in Biorefineries: Industrial Processes and Products, Vol. 2, Wiley-VCH 2006, pp. 3-59. [3] F. W. Lichtenthaler, S. Peters, ‘Carbohydrates as Green Raw Materials for the Chemical Industry’, Compt. Rend. Chimie 2004, 65, 65-90. [4] D. E. Kiely, ‘Carbohydrate diacids: Potential as commercial chemicals and hydrophobic polyamide precursors’, in J. J. Bozell, Ed., Chemicals and Materials from Renewable Resources, ACS Symp. Ser. 784, 2001, pp. 64-80. [5] C. Moreau, M. N. Belgacem, A. Gandini, ‘Substituted furans from carbohydrates and ensuing polymers’, Topics in Catalysis 2004, 27, 11-30. [6] S. Immel, F. W. Lichtenthaler’, Liebigs Ann. Chem. 1995, 1938-1947. [7] F. W. Lichtenthaler, R. Klimesch, V. Müller, M. Kunz, ‘Disaccharide-building blocks from isomaltulose’, Liebigs Ann. Chem. 1993, 967-974. [8] F. W. Lichtenthaler, D. Martin, T. Weber, H.Schiweck, ‘5-(a -D-Glucosyloxymethyl)-furfural: Preparation from isomaltulose and exploitation of its ensuing chemistry’, Liebigs Ann. Chem. 1993, 975-980. [9] D. Martin, F. W. Lichtenthaler, ‘Glycosylated HMFs’, Tetrahedron: Asymmetry 2006, 17, 756-762.
