Acetalation of Starch Derivatives

Specific acetalation can be performed on starch dialdehyde. Unlike starch, acetalated by aldehydes, the aldehydo groups on starch dialdehyde lead to the formation of acetals with alcohols. Acetals are formed randomly along the macrochain, moreover, 1,4-dioxane rings (25 and 26) also formed as a result of new, hemiacetal bonds.425,426 In such a manner, an allylated derivative was prepared with the use 

It was also reported that crosslinking with urea or melamine proceeded in neutral1365 or alkaline media.1366 

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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