Tosyl starch

Abstract Pure, well soluble p-toluenesulfwiyl (tosyl) starch samples with a DSm range... 

Synthesis of /Htoluenesulfonyl (tosyl) starch, and tosyl starch acetate... 

For a typical preparation, to a stirred solution of tosyl starch (1.0 g, DStos = 1.02) in 20 ml pyridine 0.3 g A iV-dimethylaminopyridine (DMAP) and 10 ml (106.0 mmol) acetic anhydride were added. The mixture was kept at 20°C for20 h and at 80 °C for 5 h. After cooling down to room temperature, the product was isolated by precipitation in 150 ml ethanol, filtered off, washed with ethanol and dried at 50 C under vacutun. 

Reaction of tosyl starch and tosyl starch acetate viith iodine... 

The structure of the tosyl starch was confirmed by means of FITR. spectroscopy. The spectra show the characteristic absorption bands of the starch backbone as well as signals at 3064, 1597, 1495 and 816 on of the aromatics. Furthermore, two bands with a high intensity at 1360 and 1176 cm (v SO2) confirm the presence of the tosyl groups. 

Fig 1 shows a standard C-NMR spectrum of tosyl starch (DStos = 1-02) in DMSO-d< and the assignment of the signals. The peak for the C-6 atom of the AGU influenced by 0-6 tosylation appears at 6 = 68.4 ppm (C-6s), i.e. it exhibits a down field shift compared to the corresponding carbon of unmodified starch (C-6, 5 = 59,8 ppm). From the signal intensities it may be concluded that the 6 position is not or only slight tosylated. On the other hand, the signal at 8 = 93.5 ppm which is assigned to C-1 (C-1 atom... 

An important property of the tosyl starch synthesised is their solubility in common organic solvents. The derivatives with a DSjos - soluble in... 

DMSO and additionally in different dipolar j rotic solvents like DMA, N,N-dimethyl formamide (DMF) as demcmstrated in Fig 2. Samples with a slightly higher DSjos re soluble in dioxane (> 0.98), tetrahyt ftiran and acetone (> 1.15). At a DSxos of 2-02 the tosyl starch samples dissolve even in the non-polar solvraits dichloromethane and chloroform. 

Figure 2. Solubility of tosyl starch in oiganic solvents in dependoice on DSto,...

In contrast to the generally accepted idea, the determination of the extend of tosylation of primary hydroxy groups by the analysis of the corresponding iododeoxy derivatives represents a semiquantitative method. Deviations from a perfect analysis were already published , and the results should be, therefore, confirmed by alternative methods. For the determination of the partial DStos of tosyl starch at the primary position the samples were... 

Table 2. lodination of tosyl starch with Nal in acetylacetone for 2 h at 130 °C... 

Tosyl starch DStos 6-Iodo-6-deoxy tosyl starch DS,... 

Standard C-NMR spectra of the tosyl starch acetates and propionates are appropriate to gain information about the distribution of the functional groups by using the carbonyl signals. In contrast to a starch triacetate which possesses three separate signals at 170.5, 170.1 and 169.2 ppm in agreement to a C=0 moiety at position 2,6 and 3, the C-NMR spectrum of tosyl starch acetate (DStos = 1-02) shows only two carbonyl peaks at 169.9 and 169.4 ppm indicating that the position 6 and 3 are acetylated. Comparable results were obtained for tosyl starch propionates. ... 

The H-NMR spectra of tosyl starch acetate respectively tosyl starch propionate are suitable to calculate the DStos values (Eq. 1) from the protons both of the methyl groups or the aromatic rings of the tosylate moieties as well as from the methyl groups of the acetyl or propionyl ester function. 

From these results and in accordance with the above described findings of iodination of tosyl starch, it becomes obvious that the tosylation occurs faster at 0-2 compared to 0-6 and 0-3. 

It is well known that the nucleophilic displacement reactions at tosylated polysaccharides are limited or at least mainly directed towards the primary positions . Therefore, our interest was focused on 6-0-tosyl starch samples with DStos 1- One suitable synthesis path is the protection of 0-2 and the subsequent tosylation. A useful protecting group may be the acetyl ester function. It was recently found that in contrast to conventional esterification processes of starch with acetic anhydride, which leads to a statistic distribution of the ester groups, an acetylation of starch dissolved in DMSO with acetic acid vinyl ester in the presence of sodium chloride yields 2-0-acetyl starch of varying DSac from 0.1 to 1.0. The functionalisation patterns of these new starch products were unambiguously proved by means of various NMR measurements including two dimensional methods . 

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