Starch with 3.4-dihydro-27/-pyran

The reaction of polysaccharides ivith aldehydes to give cross-linked products has been known and exploited industrially for some time. Starch acetals may also be prepared by a method that does not give rise to cross-links and involves treatment of starch with a cyclic vinyl ether, 3,4-dihydro-2H-pyran, to give a tetrahydropyran-2-yl derivative (16). At low levels of substitution, the acetals are water-soluble, at... 

B. 2H-Pyran-2-one. A mixture of 9.81 g. (0.100 mole) of 5,6-dihydro-2/I-pyran-2-one, 200 mg. of benzoyl peroxide, 18.6 g. (0.105 mole) of A-bromosuccinimide [2,5-Pyrrolidinedione, 1-bromo-] (Note 7), and 800 ml. of carbon tetrachloride is prepared in a 2-1., three-necked, round-bottomed flask equipped with a reflux condenser and a mechanical stirrer. The resulting suspension is stirred and heated to reflux. After 1.5 hours at reflux, most of the solid is dissolved, and the solution gives a negative test with starch-iodide paper. The reaction mixture is then allowed to cool, dining which time succinimide [2,5-Pyrrolidine-dione] crystallizes out. The precipitate is removed by filtration, and the filtrate is concentrated under reduced pressure to leave crude 5-bromo-5,6 -dihy dro 211 -pyran-2 one [ 211 Py ran - 2-one, 5-bromo-5,6-dihydro] as an oil. 

Preparation of an acetal from 3,4-dihydro-2//-pyran and starch has been described.1367 Water was not formed in this reaction, nor did crosslinking occur. Tetrahydropyran-2-yl derivatives of starch were also prepared when samples gelatinized in dimethyl sulfoxide were treated with 4-toluenesulfonic acid followed by 3,4-dihydro-2//-pyran. When the reaction mixtures were then transferred into ethanol, materials with a low degree-of-substitution were achieved. However, when the reaction mixture was poured into water, materials with an intermediate and high degrees-of-substitution were produced.1291 This reaction proceeded with preference for the C-6 position of the glucose units.1368... 

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